@article{Marino2024,

title = {Porous Magneto-Fluorescent Superparticles by Rapid Emulsion Densification},

author = {Emanuele Marino and Thi Vo and Cristian Gonzalez and Daniel J. Rosen and Steven J. Neuhaus and Alice Sciortino and Harshit Bharti and Austin W. Keller and Cherie R. Kagan and Marco Cannas and Fabrizio Messina and Sharon C. Glotzer and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/acs.chemmater.3c03209},

doi = {10.1021/acs.chemmater.3c03209},

year  = {2024},

date = {2024-04-01},

urldate = {2024-04-01},

journal = {Chemistry of Materials},

abstract = {Porous superstructures are characterized by a large surface area and efficient molecular transport. Although methods aimed at generating porous superstructures from nanocrystals exist, current state-of-the-art strategies are limited to single-component nanocrystal dispersions. More importantly, such processes afford little control over the size and shape of the pores. Here, we present a new strategy for the nanofabrication of porous magneto-fluorescent nanocrystal superparticles that are well controlled in size and shape. We synthesize these composite superparticles by confining semiconductor and superparamagnetic nanocrystals within oil-in-water droplets generated using microfluidics. The rapid densification of these droplets yields spherical, monodisperse, and porous nanocrystal superparticles. Molecular simulations reveal that the formation of pores throughout the superparticles is linked to repulsion between nanocrystals of different compositions, leading to phase separation during self-assembly. We confirm the presence of nanocrystal phase separation at the single superparticle level by analyzing the changes in the optical and photonic properties of the superstructures as a function of nanocrystal composition. This excellent agreement between experiments and simulations allows us to develop a theory that predicts superparticle porosity from experimentally tunable physical parameters, such as nanocrystal size ratio, stoichiometry, and droplet densification rate. Our combined theoretical, computational, and experimental findings provide a blueprint for designing porous, multifunctional superparticles with immediate applications in catalytic, electrochemical, sensing, and cargo delivery applications.},

keywords = {emulsions, lasers, magnetic nanocrystals, magnetic properties, nanocrystal, superlattices, superparticle},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {One-pot heat-up synthesis of short-wavelength infrared, colloidal InAs quantum dots},

author = {J Lee and T Zhao and S Yang and M Muduli and CB Murray and CR Kagan},

url = {https://pubs.aip.org/aip/jcp/article/160/7/071103/3266823},

doi = {10.1063/5.0187162},

year  = {2024},

date = {2024-02-21},

urldate = {2024-02-21},

journal = {The Journal of Chemical Physics},

volume = {160},

pages = {071103},

abstract = {III–V colloidal quantum dots (QDs) promise Pb and Hg-free QD compositions with which to build short-wavelength infrared (SWIR) optoelectronic devices. However, their synthesis is limited by the availability of group-V precursors with controllable reactivities to prepare monodisperse, SWIR-absorbing III–V QDs. Here, we report a one-pot heat-up method to synthesize ∼8 nm edge length (∼6.5 nm in height) tetrahedral, SWIR-absorbing InAs QDs by increasing the [In3+]:[As3+] ratio introduced using commercially available InCl3 and AsCl3 precursors and by decreasing the concentration and optimizing the volume of the reducing reagent superhydride to control the concentration of In(0) and As(0) intermediates through QD nucleation and growth. InAs QDs are treated with NOBF4, and their deposited films are exchanged with Na2S to yield n-type InAs QD films. We realize the only colloidal InAs QD photoconductors with responsivity at the technologically important wavelength of 1.55 μm.},

keywords = {colloids, nanocrystal, nanocrystal electronics, optical properties, quantum dots, semiconductors, spectroscopy, surface modification, synthesis, TEM, thin films, transport},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Nanodiamond emulsions for enhanced quantum sensing and click-chemistry conjugation},

author = {Henry J. Shulevitz and Ahmad Amirshaghaghi and Mathieu Ouellet and Caroline Brustoloni and Shengsong Yang and Jonah J. Ng and Tzu-Yung Huang and Davit Jishkariani and Christopher B. Murray and Andrew Tsourkas and Cherie R. Kagan and Lee C. Bassett},

url = {https://arxiv.org/abs/2311.16530},

doi = {10.48550/arXiv.2311.16530},

year  = {2023},

date = {2023-12-04},

urldate = {2023-12-04},

abstract = {Nanodiamonds containing nitrogen-vacancy (NV) centers can serve as colloidal quantum sensors of local fields in biological and chemical environments. However, nanodiamond surfaces are challenging to modify without degrading their colloidal stability or the NV center's optical and spin properties. Here, we report a simple and general method to coat nanodiamonds with a thin emulsion layer that preserves their quantum features, enhances their colloidal stability, and provides functional groups for subsequent crosslinking and click-chemistry conjugation reactions. To demonstrate this technique, we decorate the nanodiamonds with combinations of carboxyl- and azide-terminated amphiphiles that enable conjugation using two different strategies. We study the effect of the emulsion layer on the NV center's spin lifetime, and we quantify the nanodiamonds' chemical sensitivity to paramagnetic ions using T1 relaxometry. This general approach to nanodiamond surface functionalization will enable advances in quantum nanomedicine and biological sensing.},

keywords = {colloids, nanocrystal, quantum information science, surface modification},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Choi2023b,

title = {Thermally Reconfigurable, 3D Chiral Optical Metamaterials: Building with Colloidal Nanoparticle Assemblies},

author = {Yun Chang Choi and Shengsong Yang and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.3c06757},

doi = {10.1021/acsnano.3c06757},

year  = {2023},

date = {2023-11-13},

journal = {ACS Nano},

volume = {17},

issue = {22},

pages = {22611–22619},

abstract = {The three-dimensional, geometric handedness of chiral optical metamaterials allows for the rotation of linearly polarized light and creates a differential interaction with right and left circularly polarized light, known as circular dichroism. These three-dimensional metamaterials enable polarization control of optical and spin excitation and detection, and their stimuli-responsive, dynamic switching widens applications in chiral molecular sensing and imaging and spintronics; however, there are few reconfigurable solid-state implementations. Here, we report all-solid-state, thermally reconfigurable chiroptical metamaterials composed of arrays of three-dimensional nanoparticle/metal bilayer heterostructures fabricated from coassemblies of phase change VO2 and metallic Au colloidal nanoparticles and thin films of Ni. These metamaterials show dynamic switching in the mid-infrared as VO2 is thermally cycled through an insulator–metal phase transition. The spectral range of operation is tailored in breadth by controlling the periodicity of the arrays and thus the hybridization of optical modes and in position through the mixing of VO2 and Au nanoparticles.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marino2023,

title = {Crystallization of binary nanocrystal superlattices and the relevance of short-range attraction},

author = {Emanuele Marino and R. Allen LaCour and Timothy C. Moore and Sjoerd W. van Dongen and Austin W. Keller and Di An and Shengsong Yang and Daniel J. Rosen and Guillaume Gouget and Esther H. R. Tsai and Cherie R. Kagan and Thomas E. Kodger and Sharon C. Glotzer and Christopher B. Murray },

url = {https://doi.org/10.1038/s44160-023-00407-2},

doi = {10.1038/s44160-023-00407-2},

year  = {2023},

date = {2023-10-12},

journal = {Nature Synthesis},

abstract = {The synthesis of binary nanocrystal superlattices (BNSLs) enables the targeted integration of orthogonal physical properties, such as photoluminescence and magnetism, into a single superstructure, unlocking a vast design space for multifunctional materials. However, the formation mechanism of BNSLs remains poorly understood, restricting the prediction of the structure and properties of superlattices. Here we use a combination of in situ scattering and molecular simulation to elucidate the self-assembly of two common BNSLs (AlB2 and NaZn13) through emulsion templating. Our self-assembly experiments reveal that no intermediate structures precede the formation of the final binary phases, indicating that their formation proceeds through classical nucleation. Using simulations, we find that, despite the formation of AlB2 and NaZn13 typically being attributed to entropy, their self-assembly is most consistent with the nanocrystals possessing short-range interparticle attraction, which we find can accelerate nucleation kinetics in BNSLs. We also find homogeneous, classical nucleation in simulations, corroborating our experiments. These results establish a robust correspondence between experiment and theory, paving the way towards prediction of BNSLs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mallavarapu2023,

title = {TiO2 Metasurfaces with Visible Quasi-Guided Mode Resonances via Direct Imprinting of Aqueous Nanocrystal Dispersions},

author = {Akhila Mallavarapu and Chavez FK Lawrence and Brian Huang and Bryan O Torres Maldonado and Paulo Arratia and Cherie R Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsanm.3c03507},

doi = {10.1021/acsanm.3c03507},

year  = {2023},

date = {2023-09-07},

journal = {ACS Applied Nano Materials},

abstract = {We report a room temperature, environmentally benign, water-based, single-step direct nanoimprint process to pattern dielectric metasurfaces using aqueous titanium dioxide (TiO2) nanocrystal (NC) inks, which are free of polymer additives or nonaqueous solvents typically used in nanofabrication. The metasurfaces are composed of TiO2 NC structures with a high refractive index of 1.94 ± 0.02 at 543 nm. TiO2 NC metasurfaces are designed to resonate at visible wavelengths and are fabricated as two-dimensional nanopillar gratings atop waveguides. Guided mode resonances within the waveguide couple to the overlaying gratings and scatter into free space, forming high quality (Q) factor quasi-guided mode (QGM) resonances. Electric and magnetic QGM resonances are observed, and their environmental refractive index sensitivities (S) are measured to be 69.1 and 70.4 nm/RIU, respectively, with a figure of merit (FOM) = Q × S > 3000. The use of water-based inks and the room temperature processing allow integration of TiO2 NC metasurfaces on rigid and flexible, polymeric substrates.},

keywords = {dielectric metasurfaces, ink-lithography, lithography, metasurfaces, nanocrystal, nanoimprinting, optical metamaterials, optical properties, quasi-guided modes, sensors, sustainable manufacturing, TiO2 nanocrystals},

pubstate = {published},

tppubtype = {article}

}

@article{Lynch2023,

title = {Gate-Tunable Optical Anisotropy in Wafer-Scale, Aligned Carbon Nanotube Films},

author = {Jason Lynch and Evan Smith and Adam Alfieri and Baokun Song and Cindy Yueli Chen and Chavez Lawrence and Cherie Kagan and Honggang Gu and Shiyuan Liu and Lian-Mao Peng and Shivashankar Vangala and Joshua R. Hendrickson and Deep Jariwala},

url = {https://arxiv.org/abs/2304.08337},

year  = {2023},

date = {2023-08-03},

abstract = {Telecommunications and polarimetry both require the active control of the polarization of light, Currently, this is done by combining intrinsically anisotropic materials with tunable isotropic materials into heterostructures using complicated fabrication techniques due to the lack of scalable materials that possess both properties. Tunable birefringent and dichromic materials are scarce and rarely available in high-quality thin films over wafer scales. In this paper, we report semiconducting, highly aligned, single-walled carbon nanotubes (SWCNTs) over 4" wafers with normalized birefringence and dichroism values 0.09 and 0.58, respectively. The real and imaginary parts of the refractive index of the SWCNT films are tuned by up to 5.9% and 14.3% in the infrared at 2200 nm and 1660 nm, respectively, using electrostatic doping. Our results suggest that aligned SWCNTs are among the most anisotropic and tunable optical materials known and opens new avenues for their application in integrated photonics and telecommunications.},

keywords = {carbon nanotubes, gate-tunable refractive index, in-plane anisotropy, nanowires, optical properties, thin films},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Choi2023,

title = {Surface Engineering of Metal and Semiconductor Nanocrystal Assemblies and Their Optical and Electronic Devices},

author = {Yun Chang Choi and Jaeyoung Lee and Jonah J. Ng and Cherie R. Kagan},

url = {https://doi.org/10.1021/acs.accounts.3c00147},

doi = {10.1021/acs.accounts.3c00147},

year  = {2023},

date = {2023-06-21},

urldate = {2023-06-21},

journal = {Accounts of Chemical Research},

volume = {56},

number = {13},

pages = {1791–1802},

abstract = {Colloidal nanocrystals (NCs) are composed of inorganic cores and organic or inorganic ligand shells and serve as building blocks of NC assemblies. Metal and semiconductor NCs are well known for the size-dependent physical properties of their cores. The large NC surface-to-volume ratio and the space between NCs in assemblies places significant importance on the composition of the NC surface and ligand shell. Nonaqueous colloidal NC syntheses use relatively long organic ligands to control NC size and uniformity during growth and to prepare stable NC dispersions. However, these ligands create large interparticle distances that dilute the metal and semiconductor NC properties of their assemblies. In this Account, we describe postsynthesis chemical treatments to engineer the NC surface and design the optical and electronic properties of NC assemblies. In metal NC assemblies, compact ligand exchange reduces the interparticle distance and drives an insulator-to-metal transition tuning the dc resistivity over a 1010 range and the real part of the optical dielectric function from positive to negative across the visible-to-IR region. Juxtaposing NC and bulk metal thin films in bilayers allows the differential chemical and thermal addressability of the NC surface to be exploited in device fabrication. Ligand exchange and thermal annealing densifies the NC layer, creating interfacial misfit strain that triggers folding of the bilayers and is used to fabricate, with only one lithography step, large-area 3D chiral metamaterials. In semiconductor NC assemblies, chemical treatments such as ligand exchange, doping, and cation exchange control the interparticle distance and composition to add impurities, tailor stoichiometry, or make entirely new compounds. These treatments are employed in longer studied II–VI and IV–VI materials and are being developed as interest in III–V and I–III–VI2 NC materials grows. NC surface engineering is used to design NC assemblies with tailored carrier energy, type, concentration, mobility, and lifetime. Compact ligand exchange increases the coupling between NCs but can introduce intragap states that scatter and reduce the lifetime of carriers. Hybrid ligand exchange with two different chemistries can enhance the mobility-lifetime product. Doping increases carrier concentration, shifts the Fermi energy, and increases carrier mobility, creating n- and p-type building blocks for optoelectronic and electronic devices and circuits. Surface engineering of semiconductor NC assemblies is also important to modify device interfaces to allow the stacking and patterning of NC layers and to realize excellent device performance. It is used to construct NC-integrated circuits, exploiting the library of metal, semiconductor, and insulator NCs, to achieve all-NC, solution-fabricated transistors.},

keywords = {gold, ligand exchange, ligands, nanocrystal, nanoparticle assembly, Noble metal nanoparticles, optical metamaterials, optical properties, quantum dots, semiconductors, surface modification},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2023,

title = {Open- and Close-Packed, Shape-engineered Polygonal Nanoparticle Metamolecules with Tailorable Fano Resonances},

author = {Yi-Yu Cai and Asma Fallah and Shengsong Yang and Yun Chang Choi and Jun Xu and Aaron Stein and James M. Kikkawa and Christopher B. Murray and Nader Engheta and Cherie R. Kagan},

url = { https://doi.org/10.1002/adma.202301323},

doi = {10.1002/adma.202301323},

year  = {2023},

date = {2023-05-11},

urldate = {2023-05-11},

journal = {Advanced Materials},

abstract = {A top-down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well-defined sizes, shapes, and compositions that are often not accessible by wet-chemical synthetic methods. These NPs are ligated and harvested from the substrate surface to prepare colloidal NP dispersions. Using a template-assisted assembly technique, fabricated NPs are driven by capillary forces to assemble into size- and shape-engineered templates and organize into open or close-packed multi-NP structures or NP metamolecules. The sizes and shapes of the NPs and of the templates control the NP number, coordination, interparticle gap size, disorder, and location of defects such as voids in the NP metamolecules. The plasmonic resonances of polygonal-shaped Au NPs are exploited to correlate the structure and optical properties of assembled NP metamolecules. Comparing open- and close-packed architectures highlights that introduction of a center NP to form closed-packed assemblies supports collective interactions, altering magnetic optical modes and multipolar interactions in Fano resonances. Decreasing the distance between NPs strengthens the plasmonic coupling, and the structural symmetries of the NP metamolecules determine the orientation-dependent scattering response.},

keywords = {nanoparticle assembly, optical properties, plasmonic, templated assembly},

pubstate = {published},

tppubtype = {article}

}

@article{McNeill2023,

title = {Three-Dimensionally Complex Phase Behavior and Collective Phenomena in Mixtures of Acoustically Powered Chiral Microspinners},

author = {Jeffrey M. McNeill and Yun Chang Choi and Yi-Yu Cai and Jiacen Guo and François Nadal and Cherie R. Kagan and Thomas E. Mallouk},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.3c01966},

doi = {10.1021/acsnano.3c01966},

year  = {2023},

date = {2023-04-06},

journal = {ACS Nano},

volume = {17},

issue = {8},

pages = {7911–7919},

abstract = {The process of dynamic self-organization of small building blocks is fundamental to the emergent function of living systems and is characteristic of their out-of-equilibrium homeostasis. The ability to control the interactions of synthetic particles in large groups could lead to the realization of analogous macroscopic robotic systems with microscopic complexity. Rotationally induced self-organization has been observed in biological systems and modeled theoretically, but studies of fast, autonomously moving synthetic rotors remain rare. Here, we report switchable, out-of-equilibrium hydrodynamic assembly and phase separation in suspensions of acoustically powered chiral microspinners. Semiquantitative modeling suggests that three-dimensionally (3D) complex spinners interact through viscous and weakly inertial (streaming) flows. The interactions between spinners were studied over a range of densities to construct a phase diagram, which included gaseous dimer pairing at low density, collective rotation and multiphase separation at intermediate densities, and ultimately jamming at high density. The 3D chirality of the spinners leads to self-organization in parallel planes, forming a three-dimensionally hierarchical system that goes beyond the 2D systems that have so far been modeled computationally. Dense mixtures of spinners and passive tracer particles also show active–passive phase separation. These observations are consistent with recent theoretical predictions of the hydrodynamic coupling between rotlets generated by autonomous spinners and provide an exciting experimental window to the study of colloidal active matter and microrobotic systems.},

keywords = {chiral, nanocrystal, phase separation, plasmonic},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2023,

title = {Self-Assembly of Atomically Aligned Nanoparticle Superlattices from Pt–Fe3O4 Heterodimer Nanoparticles},

author = {Shengsong Yang and R. Allen LaCour and Yi-Yu Cai and Jun Xu and Daniel J. Rosen and Yugang Zhang and Cherie R. Kagan and Sharon C. Glotzer and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/jacs.2c12993},

doi = {10.1021/jacs.2c12993},

year  = {2023},

date = {2023-03-13},

urldate = {2023-03-13},

journal = {Journal of the American Chemical Society},

volume = {145},

issue = {11},

pages = {6280–6288},

abstract = {Multicomponent nanoparticle superlattices (SLs) promise the integration of nanoparticles (NPs) with remarkable electronic, magnetic, and optical properties into a single structure. Here, we demonstrate that heterodimers consisting of two conjoined NPs can self-assemble into novel multicomponent SLs with a high degree of alignment between the atomic lattices of individual NPs, which has been theorized to lead to a wide variety of remarkable properties. Specifically, by using simulations and experiments, we show that heterodimers composed of larger Fe3O4 domains decorated with a Pt domain at one vertex can self-assemble into an SL with long-range atomic alignment between the Fe3O4 domains of different NPs across the SL. The SLs show an unanticipated decreased coercivity relative to nonassembled NPs. In situ scattering of the self-assembly reveals a two-stage mechanism of self-assembly: translational ordering between NPs develops before atomic alignment. Our experiments and simulation indicate that atomic alignment requires selective epitaxial growth of the smaller domain during heterodimer synthesis and specific size ratios of the heterodimer domains as opposed to specific chemical composition. This composition independence makes the self-assembly principles elucidated here applicable to the future preparation of multicomponent materials with fine structural control.},

keywords = {nanocrystal, nanoparticle assembly, self-assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Thompson2023,

title = {Red Emission from Copper-Vacancy Color Centers in Zinc Sulfide Colloidal Nanocrystals},

author = {Sarah M. Thompson and Cüneyt Şahin and Shengsong Yang and Michael E. Flatté and Christopher B. Murray and Lee C. Bassett and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.3c00191

https://arxiv.org/abs/2301.04223},

doi = {10.1021/acsnano.3c00191},

year  = {2023},

date = {2023-03-09},

urldate = {2023-03-09},

journal = {ACS Nano},

volume = {17},

number = {6},

pages = {5963-5973},

abstract = {Copper-doped zinc sulfide (ZnS:Cu) exhibits down-conversion luminescence in the UV, visible, and IR regions of the electromagnetic spectrum; the visible red, green, and blue emission is referred to as R-Cu, G-Cu, and B-Cu, respectively. The sub-bandgap emission arises from optical transitions between localized electronic states created by point defects, making ZnS:Cu a prolific phosphor material and an intriguing candidate material for quantum information science, where point defects excel as single-photon sources and spin qubits. Colloidal nanocrystals (NCs) of ZnS:Cu are particularly interesting as hosts for the creation, isolation, and measurement of quantum defects, since their size, composition, and surface chemistry can be precisely tailored for bio-sensing and opto-electronic applications. Here, we present a method for synthesizing colloidal ZnS:Cu NCs that emit primarily R-Cu, which has been proposed to arise from the Cu_{Zn}-V_{S} complex, an impurity-vacancy point defect structure analogous to well-known quantum defects in other materials that produce favorable optical and spin dynamics. First principles calculations confirm the thermodynamic stability and electronic structure of Cu_{Zn}-V_{S}. Temperature- and time-dependent optical properties of ZnS:Cu NCs show blueshifting luminescence and an anomalous plateau in the intensity dependence as temperature is increased from 19 K to 290 K, for which we propose an empirical dynamical model based on thermally-activated coupling between two manifolds of states inside the ZnS bandgap. Understanding of R-Cu emission dynamics, combined with a controlled synthesis method for obtaining R-Cu centers in colloidal NC hosts, will greatly facilitate the development of Cu_{Zn}-V_{S} and related complexes as quantum point defects in ZnS.},

keywords = {color centers, doping, impurities, nanocrystal, optical properties, quantum information science, time-resolved photoluminescence, transition metals, zinc sulfide},

pubstate = {published},

tppubtype = {article}

}

@article{Neuhaus2023,

title = {Frequency Stabilization and Optically Tunable Lasing in Colloidal Quantum Dot Superparticles},

author = {Steven J. Neuhaus and Emanuele Marino and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acs.nanolett.2c04498},

doi = {10.1021/acs.nanolett.2c04498},

year  = {2023},

date = {2023-01-05},

urldate = {2023-01-05},

journal = {Nano Letters},

volume = {23},

issue = {2},

pages = {645–651},

abstract = {Self-assembled superparticles composed of colloidal quantum dots establish microsphere cavities that support optically pumped lasing from whispering gallery modes. Here, we report on the time- and excitation fluence-dependent lasing properties of CdSe/CdS quantum dot superparticles. Spectra collected under constant photoexcitation reveal that the lasing modes are not temporally stable but instead blue-shift by more than 30 meV over 15 min. To counter this effect, we establish a high-fluence light-soaking protocol that reduces this blue-shift by more than an order of magnitude to 1.7 ± 0.5 meV, with champion superparticles displaying mode blue-shifts of <0.5 meV. Increasing the pump fluence allows for optically controlled, reversible, color-tunable red-to-green lasing. Combining these two paradigms suggests that quantum dot superparticles could serve in applications as low-cost, robust, solution-processable, tunable microlasers.},

keywords = {lasers, lasing, nanocrystal, optical properties, optical stability, quantum dots, superparticle, supraparticle, tunable laser},

pubstate = {published},

tppubtype = {article}

}

@article{Parra2022,

title = {Large Exciton Polaron Formation in 2D Hybrid Perovskites via Time-Resolved Photoluminescence},

author = {Sebastian Hurtado Parra and Daniel B. Straus and Bryan T. Fichera and Natasha Iotov and Cherie R. Kagan and James M. Kikkawa},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.2c09256},

doi = {10.1021/acsnano.2c09256},

year  = {2022},

date = {2022-12-15},

journal = {ACS Nano},

volume = {16},

issue = {12},

pages = {21259–21265},

abstract = {We find evidence for the formation and relaxation of large exciton polarons in 2D organic–inorganic hybrid perovskites. Using ps-scale time-resolved photoluminescence within the phenethylammonium lead iodide family of compounds, we identify a red shifting of emission that we associate with exciton polaron formation time scales of 3–10 ps. Atomic substitutions of the phenethylammonium cation allow local control over the structure of the inorganic lattice, and we show that the structural differences among materials strongly influence the exciton polaron relaxation process, revealing a polaron binding energy that grows larger (up to 15 meV) in more strongly distorted compounds.},

keywords = {2D-materials, exciton-polarons, octahedral distortions, perovskites, time-resolved photoluminescence, transient absorption, transient PL},

pubstate = {published},

tppubtype = {article}

}

@article{Nguyen2022,

title = {Deterministic Quantum Light Arrays from Giant Silica-Shelled Quantum Dots},

author = {Hao A. Nguyen and David Sharp and Johannes E. Fröch, and Yi-Yu Cai and Shenwei Wu and Madison Monahan and Christopher Munley and Arnab Manna and Arka Majumdar and Cherie R. Kagan and Brandi M. Cossairt*},

url = {https://pubs.acs.org/doi/full/10.1021/acsami.2c18475},

doi = {10.1021/acsami.2c18475},

year  = {2022},

date = {2022-12-12},

urldate = {2022-12-12},

journal = {ACS Applied Materials & Interfaces},

volume = {15},

issue = {3},

pages = {4294–4302},

abstract = {Colloidal quantum dots (QDs) are promising candidates for single-photon sources with applications in photonic quantum information technologies. Developing practical photonic quantum devices with colloidal materials, however, requires scalable deterministic placement of stable single QD emitters. In this work, we describe a method to exploit QD size to facilitate deterministic positioning of single QDs into large arrays while maintaining their photostability and single-photon emission properties. CdSe/CdS core/shell QDs were encapsulated in silica to both increase their physical size without perturbing their quantum-confined emission and enhance their photostability. These giant QDs were then precisely positioned into ordered arrays using template-assisted self-assembly with a 75% yield for single QDs. We show that the QDs before and after assembly exhibit antibunching behavior at room temperature and their optical properties are retained after an extended period of time. Together, this bottom-up synthetic approach via silica shelling and the robust template-assisted self-assembly offer a unique strategy to produce scalable quantum photonics platforms using colloidal QDs as single-photon emitters.},

keywords = {colloids, nanoparticle assembly, organic compounds, quantum dots, silica},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2022,

title = {Engineering the Surface Chemistry of Colloidal InP Quantum Dots for Charge Transport},

author = {Tianshuo Zhao and Qinghua Zhao and Jaeyoung Lee and Shengsong Yang and Han Wang and Ming-Yuan Chuang and Yulian He and Sarah M. Thompson and Guannan Liu and Nuri Oh and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acs.chemmater.2c01840},

doi = {10.1021/acs.chemmater.2c01840},

year  = {2022},

date = {2022-09-07},

urldate = {2022-09-07},

journal = {Chemistry of Materials},

volume = {34},

issue = {18},

pages = {8306–8315},

abstract = {Colloidal InP quantum dots (QDs) have emerged as potential candidates for constructing nontoxic QD-based optoelectronic devices. However, charge transport in InP QD thin-film assemblies has been limitedly explored. Herein, we report the synthesis of ∼8 nm edge length (∼6.5 nm in height), tetrahedral InP QDs and study charge transport in thin films using the platform of the field-effect transistor (FET). We design a hybrid ligand-exchange strategy that combines solution-based exchange with S2– and solid-state exchange with N3– to enhance interdot coupling and control the n-doping of InP QD films. Further modifying the QD surface with thin, thermally evaporated Se overlayers yields FETs with an average electron mobility of 0.45 cm2 V–1 s–1, ∼10 times that of previously reported devices, and a higher on–off current ratio of 103–104. Analytical measurements suggest lower trap-state densities and longer carrier lifetimes in the Se-modified InP QD films, giving rise to a four-time longer carrier diffusion length.},

keywords = {ligand exchange, ligands, mobility, quantum dots, thin films, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Gabinet2022,

title = {Magnetic Field Alignment and Optical Anisotropy of MoS2 Nanosheets Dispersed in a Liquid Crystal Polymer},

author = {Uri R. Gabinet and Changyeon Lee and Na Kyung Kim and Martin Hulman and Sarah M. Thompson and Cherie R. Kagan and Chinedum O. Osuji},

url = {https://pubs.acs.org/doi/full/10.1021/acs.jpclett.2c01819},

doi = {10.1021/acs.jpclett.2c01819},

year  = {2022},

date = {2022-08-19},

urldate = {2022-08-19},

journal = {The Journal of Physical Chemistry Letters},

volume = {13},

issue = {34},

pages = {7994–8001},

abstract = {Molybdenum disulfide (MoS2) nanosheets exhibit anisotropic optical and electronic properties, stemming from their shape and electronic structure. Unveiling this anisotropy for study and usage in materials and devices requires the ability to control the orientation of dispersed nanosheets, but to date this has proved a challenging proposition. Here, we demonstrate magnetic field driven alignment of MoS2 nanosheets in a liquid crystal (LC) polymer and unveil the optical properties of the resulting anisotropic assembly. Nanosheet optical anisotropy is observed spectroscopically by Raman and direction-dependent photoluminescence (PL) measurements. Resulting data indicate significantly lower PL emission due to optical excitation with electric field oscillation out of plane, parallel to the MoS2c-axis, than that associated with perpendicular excitation, with the dichroic ratio Iperp/Ipar = 3. The approach developed here provides a useful route to elucidate anisotropic optical properties of MoS2 nanosheets and to utilize such properties in new materials and devices.},

keywords = {2D-materials, liquid chromatography, magnetic properties, optical properties, scattering},

pubstate = {published},

tppubtype = {article}

}

@article{Marino2022,

title = {Nanocrystal Superparticles with Whispering-Gallery Modes Tunable through Chemical and Optical Triggers},

author = {Emanuele Marino and Harshit Bharti and Jun Xu and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/acs.nanolett.2c01011},

doi = {10.1021/acs.nanolett.2c01011},

year  = {2022},

date = {2022-06-01},

journal = {Nano Letters},

volume = {22},

issue = {12},

pages = {4765–4773},

abstract = {Whispering-gallery microresonators have the potential to become the building blocks for optical circuits. However, encoding information in an optical signal requires on-demand tuning of optical resonances. Tuning is achieved by modifying the cavity length or the refractive index of the microresonator. Due to their solid, nondeformable structure, conventional microresonators based on bulk materials are inherently difficult to tune. In this work, we fabricate irreversibly tunable optical microresonators by using semiconductor nanocrystals. These nanocrystals are first assembled into colloidal spherical superparticles featuring whispering-gallery modes. Exposing the superparticles to shorter ligands changes the nanocrystal surface chemistry, decreasing the cavity length of the microresonator by 20% and increasing the refractive index by 8.2%. Illuminating the superparticles with ultraviolet light initiates nanocrystal photo-oxidation, providing an orthogonal channel to decrease the refractive index of the microresonator in a continuous fashion. Through these approaches, we demonstrate optical microresonators tunable by several times their free spectral range.},

keywords = {cavities, CdSe, emulsions, ligands, optical properties},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Electrochemically deposited molybdenum disulfide surfaces enable polymer adsorption studies using quartz crystal microbalance with dissipation monitoring (QCM-D)},

author = {Christopher S. O'Bryan and Joseph Rosenfeld and Aria Zhang and Austin W. Keller and Denis Bendejacq and Cherie R. Kagan and Christopher B. Murray and Daeyeon Lee and Russell J. Composto},

url = {https://www.sciencedirect.com/science/article/pii/S0021979722001114},

doi = {10.1016/j.jcis.2022.01.098},

year  = {2022},

date = {2022-05-15},

urldate = {2022-05-15},

journal = {Journal of Colloid and Interface Science},

volume = {614},

pages = {522-531},

abstract = {Polymer and small molecules are often used to modify the wettability of mineral surfaces which facilitates the separation of valuable minerals such as molybdenum disulfide (MoS2) from gangue material through the process of froth flotation. By design, traditional methods used in the field for evaluating the separation efficacy of these additives fail to give proper access to adsorption kinetics and molecule conformation, crucial aspects of flotation where contact times may not allow for full thermodynamic equilibrium. Thus, there is a need for alternative methods for evaluating additives that accurately capture these features during the adsorption of additives at the solid/liquid interface. Here, we present a novel method for preparing MoS2 films on quartz crystals used for Quartz Crystal Microbalance with Dissipation (QCM-D) measurements through an electrochemical deposition process. The resulting films exhibit well-controlled structure, composition, and thickness and therefore are ideal for quantifying polymer adsorption. After deposition, the sensors can be annealed without damaging the quartz crystal, resulting in a phase transition of the MoS2 from the as-deposited, amorphous phase to the 2H semiconducting phase. Furthermore, we demonstrate the application of these sensors to study the interactions of additives at the solid/liquid interface by investigating the adsorption of a model polymer, dextran, onto both the amorphous and crystalline MoS2 surfaces. We find that the adsorption rate of dextran onto the amorphous surface is approximately twice as fast as the adsorption onto the annealed surface. These studies demonstrate the ability to gain insight into the short-term kinetics of interaction between molecules and mineral surface, behavior that is key to designing additives with superior separation efficiency.},

keywords = {dextran adsorption, electrochemical deposition, molybdenum disulfide, polymer adsorption},

pubstate = {published},

tppubtype = {article}

}

@article{Kim2022,

title = {Dynamic magnetic field alignment and polarized emission of semiconductor nanoplatelets in a liquid crystal polymer},

author = {Dahin Kim and Dennis Ndaya and Reuben Bosire and Francis K. Masese and Weixingyue Li and Sarah M. Thompson and Cherie R. Kagan and Christopher B. Murray and Rajeswari M. Kasi and Chinedum O. Osuji},

url = {https://www.nature.com/articles/s41467-022-30200-2},

doi = {10.1038/s41467-022-30200-2},

year  = {2022},

date = {2022-05-06},

urldate = {2022-05-06},

journal = {Nature Communications},

volume = {13},

number = {2507 },

abstract = {Reconfigurable arrays of 2D nanomaterials are essential for the realization of switchable and intelligent material systems. Using liquid crystals (LCs) as a medium represents a promising approach, in principle, to enable such control. In practice, however, this approach is hampered by the difficulty of achieving stable dispersions of nanomaterials. Here, we report on good dispersions of pristine CdSe nanoplatelets (NPLs) in LCs, and reversible, rapid control of their alignment and associated anisotropic photoluminescence, using a magnetic field. We reveal that dispersion stability is greatly enhanced using polymeric, rather than small molecule, LCs and is considerably greater in the smectic phases of the resulting systems relative to the nematic phases. Aligned composites exhibit highly polarized emission that is readily manipulated by field-realignment. Such dynamic alignment of optically-active 2D nanomaterials may enable the development of programmable materials for photonic applications and the methodology can guide designs for anisotropic nanomaterial composites for a broad set of related nanomaterials.},

keywords = {2D-materials, CdSe, liquid crystals},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2022,

title = {Special report: The Internet of Things for Precision Agriculture (IoT4Ag)},

author = {Cherie R. Kagan and David P. Arnold and David J. Cappelleri and Catherine M. Keske and Kevin T. Turner},

url = {https://doi.org/10.1016/j.compag.2022.106742},

doi = {10.1016/j.compag.2022.106742},

year  = {2022},

date = {2022-05-01},

journal = {Computers and Electronics in Agriculture},

volume = {196},

pages = {106742},

abstract = {The National Science Foundation (NSF) Engineering Research Center (ERC) for the Internet of Things for Precision Agriculture (IoT4Ag) was established on September 1, 2020 and launched its collaborative programs across the four NSF ERC pillars of convergent research, engineering workforce development, diversity and culture of inclusion, and innovation ecosystem. IoT4Ag unites an interdisciplinary cadre of faculty and students from the University of Pennsylvania, Purdue University, the University of California-Merced, and the University of Florida, with partners in education, government, industry, and the end-user farming community. The IoT4Ag mission is to create and translate to practice Internet of Things (IoT) technologies for precision agriculture and to train an educated and diverse workforce that will address the societal grand challenge of food, energy, and water security for decades to come.},

keywords = {communications, decision controls, energy devices, IOT, IoT4Ag, machine learning, robotics, sensors},

pubstate = {published},

tppubtype = {article}

}

@article{Kotov2022,

title = {Tanks and Truth},

author = {Nicholas A. Kotov and Deji Akinwande and C. Jeffrey Brinker and Jillian M. Buriak and Warren C. W. Chan and Xiaodong Chen and Manish Chhowalla and William Chueh and Sharon C. Glotzer and Yury Gogotsi and Mark C. Hersam and Dean Ho and Tony Hu and Ali Javey and Cherie R. Kagan and Kazunori Kataoka and Il-Doo Kim and Shuit-Tong Lee and Young Hee Lee and Luis M. Liz-Marzán and Jill E. Millstone and Paul Mulvaney and Andre E. Nel and Peter Nordlander and Wolfgang J. Parak and Reginald M. Penner and Andrey L. Rogach and Mathieu Salanne and Raymond E. Schaak and Ajay K. Sood and Molly Stevens and Vladimir Tsukruk and Andrew T. S. Wee and Ilja Voets and Tanja Weil and Paul S. Weiss},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.2c02602},

doi = {10.1021/acsnano.2c02602},

year  = {2022},

date = {2022-03-22},

urldate = {2022-03-22},

journal = {ACS Nano},

volume = {16},

issue = {4},

pages = {4975–4976},

abstract = {The core value of science is the truth. When scientists see that an equation on the blackboard is wrong, they call it out. Facts form the foundation of our professional world as the stewards of truth, so to see falsities about the war atrocities in Ukraine deliberately multiplied over and over again by Putin’s propaganda machine and other actors on the international scene is devastating. In our very recent past, the possibility of Russian tanks rolling into Ukraine seemed remote, like a scene from a surrealistic dystopian movie, but the devastating reality is now upon us. This result is the shocking consequence of untruths and half-truths that have been overlooked for far too long. Tragic faults are playing out in front of us, demonstrating once again the power of political lies that we far too often dismiss as “obvious”. It is our duty as scientists and human beings to ensure that the truth of this wrong turn of history is delivered openly and honestly, regardless of international borders.



As a global community, we must make our voices heard, louder now than ever, because if we do not, such atrocities may multiply. We must do it for the sake of our colleagues in Ukraine whose scientific endeavors have been brutally interrupted. We must do it for the citizens of Ukraine whose lives are being uprooted and whose families are suffering. We must do it for both our colleagues in and the citizens of Russia who have the courage to adhere to the core scientific and human values condemning the war, regardless of their own safety.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Monodisperse Nanocrystal Superparticles through a Source–Sink Emulsion System},

author = {Emanuele Marino and Sjoerd W. van Dongen and Steven J. Neuhaus and Weixingyue Li and Austin W. Keller and Cherie R. Kagan and Thomas E. Kodger and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/acs.chemmater.2c00039},

doi = {10.1021/acs.chemmater.2c00039},

year  = {2022},

date = {2022-03-09},

urldate = {2022-03-09},

journal = {Chemistry of Materials},

volume = {34},

number = {6},

issue = {6},

pages = {2779–2789},

abstract = {Superparticles made from colloidal nanocrystals have recently shown great promise in bridging the nanoscale and mesoscale, building artificial materials with properties designed from the bottom-up. As these properties depend on the dimension of the superparticle, there is a need for a general method to produce monodisperse nanocrystal superparticles. Here, we demonstrate an approach that readily yields spherical nanocrystal superparticles with a polydispersity as low as 2%. This method relies on the controlled densification of the nanocrystal-containing “source” emulsion by the swelling of a secondary “sink” emulsion. We show that this strategy is general and rapid, yielding monodisperse superparticles with controllable sizes and morphologies, including core/shell structures, within a few minutes. The superparticles show a high optical quality that results in lasing through the whispering-gallery modes of the spherical structure, with an average quality factor of 1600. Assembling superparticles into small clusters selects the wavelength of the lasing modes, demonstrating an example of collective photonic behavior of these artificial solids.},

keywords = {aromatic compounds, emulsions, hydrocarbons, lasers, liquids},

pubstate = {published},

tppubtype = {article}

}

@article{Keller2022,

title = {Sub-5 nm Anisotropic Pattern Transfer via Colloidal Lithography of a Self-Assembled GdF3 Nanocrystal Monolayer},

author = {Austin W. Keller and Emanuele Marino and Di An and Steven J. Neuhaus and Katherine C. Elbert and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.1c04761},

doi = {10.1021/acs.nanolett.1c04761},

year  = {2022},

date = {2022-02-28},

urldate = {2022-02-28},

journal = {Nano Letters},

volume = {22},

issue = {5},

pages = {1992–2000},

abstract = {Patterning materials with nanoscale features opens many research opportunities ranging from fundamental science to technological applications. However, current nanofabrication methods are ill-suited for sub-5 nm patterning and pattern transfer. We demonstrate the use of colloidal lithography to transfer an anisotropic pattern of discrete features into substrates with a critical dimension below 5 nm. The assembly of monodisperse, anisotropic nanocrystals (NCs) with a rhombic-plate morphology spaced by dendrimer ligands results in a well-ordered monolayer that serves as a 2D anisotropic hard mask pattern. This pattern is transferred into the underlying substrate using dry etching followed by removal of the NC mask. We exemplify this approach by fabricating an array of pillars with a rhombic cross-section and edge-to-edge spacing of 4.4 ± 1.1 nm. The fabrication approach enables broader access to patterning materials at the deep nanoscale by implementing innovative processes into well-established fabrication methods while minimizing process complexity.},

keywords = {lithography, manufacturing, nanocrystal, nanoparticle assembly, nanoscience, nanotechnology, patterning, self-assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Straus2021,

title = {Photophysics of Two-Dimensional Semiconducting Organic-Inorganic Metal-Halide Perovskites},

author = {Daniel B. Straus and Cherie R. Kagan},

url = {https://www.annualreviews.org/doi/10.1146/annurev-physchem-082820-015402

https://arxiv.org/abs/2108.13501},

doi = {10.1146/annurev-physchem-082820-015402},

year  = {2022},

date = {2022-02-04},

urldate = {2022-02-04},

journal = {Annual Review of Physical Chemistry},

volume = {73},

issue = {1},

abstract = {2D organic-inorganic hybrid perovskites (2DHPs) consist of alternating anionic metal-halide and cationic organic layers. They have widely tunable structural and optical properties. We review the role of the organic cation in defining the structural and optical properties of 2DHPs through example lead iodide 2DHPs. Even though excitons reside in the metal halide layers, the organic and inorganic frameworks cannot be separated-they must be considered as a single unit to fully understand the photophysics of 2DHPs. We correlate cation-induced distortion and disorder in the inorganic lattice with the resulting optical properties. We also discuss the role of the cation in creating and altering the discrete excitonic structure that appears at cryogenic temperatures in some 2DHPs, including the cation-dependent presence of hot exciton photoluminescence. We conclude our review with an outlook for 2DHPs, highlighting existing gaps in fundamental knowledge as well as potential future applications.},

keywords = {2D-materials, hybrid perovskite, perovskites},

pubstate = {published},

tppubtype = {article}

}

@article{Shulevitz2021,

title = {Template-Assisted Self Assembly of Fluorescent Nanodiamonds for Scalable Quantum Technologies},

author = {Henry J. Shulevitz and Tzu-Yung Huang and Jun Xu and Steven Neuhaus and Raj N. Patel and Lee C. Bassett, Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acsnano.1c09839

https://arxiv.org/abs/2111.14921},

year  = {2022},

date = {2022-01-13},

urldate = {2022-01-13},

journal = {ACS Nano},

volume = {16},

issue = {2},

pages = {1847–1856},

abstract = {Milled nanodiamonds containing nitrogen-vacancy (NV) centers provide an excellent platform for sensing applications as they are optically robust, have nanoscale quantum sensitivity, and form colloidal dispersions which enable bottom-up assembly techniques for device integration. However, variations in their size, shape, and surface chemistry limit the ability to position individual nanodiamonds and statistically study properties that affect their optical and quantum characteristics. Here, we present a scalable strategy to form ordered arrays of nanodiamonds using capillary-driven, template-assisted self assembly. This method enables the precise spatial arrangement of isolated nanodiamonds with diameters below 50 nm across millimeter-scale areas. Measurements of over 200 assembled nanodiamonds yield a statistical understanding of their structural, optical, and quantum properties. The NV centers' spin and charge properties are uncorrelated with nanodiamond size, but rather are consistent with heterogeneity in their nanoscale environment. This flexible assembly method, together with improved understanding of the material, will enable the integration of nanodiamonds into future quantum photonic and electronic devices.},

keywords = {nanoparticle assembly, nanotechnology, quantum information science, self-assembly, TEM, templated assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2021,

title = {Chemical and Physical Properties of Photonic Noble-metal Nanomaterials},

author = {Yi-Yu Cai and Yun Chang Choi and Cherie R. Kagan},

url = {https://onlinelibrary.wiley.com/doi/10.1002/adma.202108104},

doi = {10.1002/adma.202108104},

year  = {2021},

date = {2021-12-12},

urldate = {2021-12-12},

journal = {Advanced Materials},

pages = {2108104},

abstract = {Colloidal noble metal nanoparticles are composed of metal cores and organic or inorganic ligand shells. These nanoparticles support size- and shape-dependent plasmonic resonances. They can be assembled from dispersions into artificial metamolecules which have collective plasmonic resonances originating from coupled bright and dark optical electric and magnetic modes that form depending on the size and shape of the constituent nanoparticles and their number, arrangement, and interparticle distance. Nanoparticles can also be assembled into extended two- and three-dimensional metamaterials that are glassy thin films or ordered thin films or crystals, also known as superlattices and supercrystals. The metamaterials have tunable optical properties that depend on the size, shape, and composition of the nanoparticles, and on the number of nanoparticle layers and their interparticle distance. Interestingly, strong light-matter interactions in superlattices form plasmon polaritons. Tunable interparticle distances allow designer materials with dielectric functions tailorable from that characteristic of an insulator to that of a metal, and serve as strong optical absorbers or scatterers, respectively. In combination with lithography techniques, these extended assemblies can be patterned to create subwavelength nanoparticle superstructures and form large-area 2D and 3D metamaterials that manipulate the amplitude, phase, and polarization of transmitted or reflected light.},

keywords = {chiral, metamolecule, nanoparticle assembly, Noble metal nanoparticles, optical metamaterials, plasmonic},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2021c,

title = {Heavy-Metal-Free Quantum Dot-Based Flexible Electronics},

author = {Tianshuo Zhao and Amrita Basu and Karthik Ramasamy and Nikolay S. Makarov and Hunter McDaniel and Cherie R. Kagan},

url = {https://sid.onlinelibrary.wiley.com/doi/full/10.1002/msid.1258},

year  = {2021},

date = {2021-11-29},

journal = {Information Display},

volume = {37},

number = {6},

pages = {24-32},

abstract = {Applications of flexible electronics typically depend less on high computational power, instead exploiting the advantages of devices with a high degree of deformation that are lightweight, disposable or degradable, and low-cost.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ahn2021,

title = {Ink-Lithography for Property Engineering and Patterning of Nanocrystal Thin Films},

author = {Junhyuk Ahn and Sanghyun Jeon and Ho Kun Woo and Junsung Bang and Yong Min Lee and Steven J. Neuhaus and Woo Seok Lee and Taesung Park and Sang Yeop Lee and Byung Ku Jung and Hyungmok Joh and Mingi Seong and Ji-hyuk Choi and Ho Gyu Yoon and Cherie R. Kagan and Soong Ju Oh},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.1c04772},

doi = {10.1021/acsnano.1c04772},

year  = {2021},

date = {2021-09-08},

urldate = {2021-09-08},

journal = {ACS Nano},

volume = {15},

issue = {10},

pages = {15667–15675},

abstract = {Next-generation devices and systems require the development and integration of advanced materials, the realization of which inevitably requires two separate processes: property engineering and patterning. Here, we report a one-step, ink-lithography technique to pattern and engineer the properties of thin films of colloidal nanocrystals that exploits their chemically addressable surface. Colloidal nanocrystals are deposited by solution-based methods to form thin films and a local chemical treatment is applied using an ink-printing technique to simultaneously modify (i) the chemical nature of the nanocrystal surface to allow thin-film patterning and (ii) the physical electronic, optical, thermal, and mechanical properties of the nanocrystal thin films. The ink-lithography technique is applied to the library of colloidal nanocrystals to engineer thin films of metals, semiconductors, and insulators on both rigid and flexible substrates and demonstrate their application in high-resolution image replications, anticounterfeit devices, multicolor filters, thin-film transistors and circuits, photoconductors, and wearable multisensors.},

keywords = {ink-lithography, ligand exchange, nanocrystal, nanocrystal ink-lithography ligand exchange surface modification patterning property engineering, patterning, property engineering, surface modification},

pubstate = {published},

tppubtype = {article}

}

@article{Maguire2021,

title = {Grafted Nanoparticle Surface Wetting during Phase Separation in Polymer Nanocomposite Films},

author = {Shawn M. Maguire and Michael J. Boyle and Connor R. Bilchak and John Derek Demaree and Austin W. Keller and Nadia M. Krook and Kohji Ohno and Cherie R. Kagan and Christopher B. Murray and Patrice Rannou and Russell J. Composto},

url = {https://pubs.acs.org/doi/abs/10.1021/acsami.1c09233},

doi = {10.1021/acsami.1c09233},

year  = {2021},

date = {2021-07-29},

journal = {ACS Applied Materials & Interfaces},

volume = {13},

number = {31},

pages = {37628–37637},

abstract = {Wetting of polymer-grafted nanoparticles (NPs) in a polymer nanocomposite (PNC) film is driven by a difference in surface energy between components as well as bulk thermodynamics, namely, the value of the interaction parameter, χ. The interplay between these contributions is investigated in a PNC containing 25 wt % polymethyl methacrylate (PMMA)-grafted silica NPs (PMMA-NPs) in poly(styrene-ran-acrylonitrile) (SAN) upon annealing above the lower critical solution temperature (LCST, 160 °C). Atomic force microscopy (AFM) studies show that the areal density of particles increases rapidly and then approaches 80% of that expected for random close-packed hard spheres. A slightly greater areal density is observed at 190 °C compared to 170 °C. The PMMA-NPs are also shown to prevent dewetting of PNC films under conditions where the analogous polymer blend is unstable. Transmission electron microscopy (TEM) imaging shows that PMMA-NPs symmetrically wet both interfaces and form columns that span the free surface and substrate interface. Using grazing-incidence Rutherford backscattering spectrometry (GI-RBS), the PMMA-NP surface excess (Z*) initially increases rapidly with time and then approaches a constant value at longer times. Consistent with the areal density, Z* is slightly greater at deeper quench depths, which is attributed to the more unfavorable interactions between the PMMA brush and SAN segments. The Z* values at early times are used to determine the PMMA-NP diffusion coefficients, which are significantly larger than theoretical predictions. These studies provide insights into the interplay between wetting and phase separation in PNCs and can be utilized in nanotechnology applications where surface-dependent properties, such as wettability, durability, and friction, are important.},

keywords = {diffusion, grafted nanoparticles, polymer nanocomposites, polymer surfaces, surface segregation, wetting},

pubstate = {published},

tppubtype = {article}

}

@article{Yoon2021,

title = {Entrepreneurial Talent Building for 21st Century Agricultural Innovation},

author = {Bo Kyeong Yoon and Hyunhyuk Tae and Joshua A. Jackman and Supratik Guha and Cherie R. Kagan and Andrew J. Margenot and Diane L. Rowland and Paul S. Weiss and Nam-Joon Cho},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.1c05980},

doi = {10.1021/acsnano.1c05980},

year  = {2021},

date = {2021-07-16},

urldate = {2021-07-16},

journal = {ACS Nano},

volume = {15},

number = {7},

pages = {10748–10758},

abstract = {Agricultural innovation is a key component of the global economy and enhances food security, health, and nutrition. Current innovation efforts focus mainly on supporting the transition to sustainable food systems, which is expected to harness technological advances across a range of fields. In this Nano Focus, we discuss how such efforts would benefit from not only supporting farmer participation in deciding transition pathways but also in fostering the interdisciplinary training and development of entrepreneurial-minded farmers, whom we term “AgTech Pioneers”, to participate in cross-sector agricultural innovation ecosystems as cocreators and informed users of developing and future technologies. Toward this goal, we discuss possible strategies based on talent development, cross-disciplinary educational and training programs, and innovation clusters to build an AgTech Pioneer ecosystem, which can help to reinvigorate interest in farming careers and to identify and address challenges and opportunities in agriculture by accelerating and applying advances in nanoscience, nanotechnology, and related fields.},

keywords = {agriculture, food, nanoscience, plant-derived food, students},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2021b,

title = {Impurities in Nanocrystal Thin-Film Transistors Fabricated by Cation Exchange},

author = {Qinghua Zhao and Shengsong Yang and Jonah J. Ng and Jun Xu and Yun Chang Choi and Christopher B. Murray and Cherie R. Kagan},

url = {https://doi.org/10.1021/acs.jpclett.1c01551},

doi = {10.1021/acs.jpclett.1c01551},

year  = {2021},

date = {2021-07-09},

urldate = {2021-07-09},

journal = {The Journal of Physical Chemistry Letters},

volume = {12},

number = {28},

pages = {6514–6518},

abstract = {Cation exchange is a versatile tool used to alter the composition of nanostructures and thus to design next-generation catalysts and photonic and electronic devices. However, chemical impurities inherited from the starting materials can degrade device performance. Here, we use a sequential cation-exchange process to convert PbSe into CdSe nanocrystal thin films and study their temperature-dependent electrical properties in the platform of the thin-film transistor. We show that residual Pb impurities have detrimental effects on the device turn-on, hysteresis, and electrical stability, and as the amount increases from 2% to 7%, the activation energy for carrier transport increases from 38(3) to 62(2) meV. Selection and surface functionalization of the transistor’s gate oxide layer and low-temperature atomic-layer deposition encapsulation of the thin-film channel suppress these detrimental effects. By conversion of the nanocrystal thin films layer upon layer, impurities are driven away from the gate–oxide interface and mobilities improve from 3(1) to 32(3) cm2 V–1 s–1.},

keywords = {CdSe, impurities, interfaces, nanocrystal electronics, thin films, transistors, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Gabinet2021,

title = {Nanocomposites of 2D-MoS2 Exfoliated in Thermotropic Liquid Crystals},

author = {Uri R. Gabinet and Changyeon Lee and Ryan Poling-Skutvik and Daniel Keane and Na Kyung Kim and Ruiqi Dong and Zachariah Vicars and Yusheng Cai and Aniket U. Thosar and Alexander Grun and Sarah M. Thompson and Amish J. Patel and Cherie R. Kagan and Russell J. Composto and Chinedum O. Osuji},

url = {https://pubs.acs.org/doi/abs/10.1021/acsmaterialslett.1c00222},

doi = {10.1021/acsmaterialslett.1c00222},

year  = {2021},

date = {2021-05-05},

urldate = {2021-05-05},

journal = {ACS Materials Letters},

volume = {3},

number = {6},

pages = {704–712},

abstract = {Atomically thin MoS2 nanosheets are of interest due to unique electronic, optical, and catalytic properties that are absent in the bulk material. Methods to prepare nanosheets from bulk material that facilitate studies of 2D-MoS2 and the fabrication of useful devices have consequently assumed considerable importance. Here, we report the simultaneous exfoliation and stable dispersion of MoS2 nanosheets in a liquid crystal. Exfoliation of bulk MoS2 in mesogen-containing solutions produced stable dispersions of 2D-MoS2 that retained suspension stability for several weeks. Solvent removal in cast films yielded nanocomposites of 2D-MoS2. Preservation of single- and few-sheet MoS2 was confirmed utilizing UV–vis and Raman spectroscopy in the nematic and isotropic fluid states of the system and, remarkably, in the solid crystal as well. Importantly, the MoS2 nanosheets remained well-dispersed upon polymerization of the reactive mesogen to form a liquid crystal polymer. The ability to stably disperse 2D-MoS2 in a structured fluid opens up new possibilities for studying anisotropic properties of MoS2 and for exploiting such properties in responsive materials.},

keywords = {2D-materials, colloids, exfoliation, polymerization, surface interactions},

pubstate = {published},

tppubtype = {article}

}

@article{Guo2021,

title = {Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays},

author = {Jiacen Guo and Ji-Young Kim and Shengsong Yang and Jun Xu and Yun Chang Choi and Aaron Stein and Christopher B. Murray and Nicholas A. Kotov and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsphotonics.1c00310},

doi = {10.1021/acsphotonics.1c00310},

year  = {2021},

date = {2021-04-13},

urldate = {2021-04-13},

journal = {ACS Photonics},

volume = {8},

issue = {5},

pages = {1286–1292},

abstract = {We report broadband circular polarizers achieved by engineering the electromagnetic coupling between 3D meta-atoms in large-area arrays. The 3D meta-atoms are composed of bulk Au/Au nanocrystal (NC) bilayer helical arms, tailored in their number, length, and curvature through a one-step patterning process and postfabrication chemical and thermal treatments. By tuning the meta-atom array periodicity, hybridization originating from dipole–dipole and quadrupole–quadrupole interactions broadens the chiral response. We demonstrate circular polarizers operating at wavelengths spanning 2.5 to 5 μm, with a maximal transmission difference between left- and right-hand circularly polarized light of 43%.},

keywords = {chiral, optical metamaterials, plasmonic},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2021,

title = {Enhanced Carrier Transport in Strongly Coupled, Epitaxially Fused CdSe Nanocrystal Solids},

author = {Qinghua Zhao and Guillaume Gouget and Jiacen Guo and Shengsong Yang and Tianshuo Zhao and Daniel B. Straus and Chengyang Qian and Nuri Oh and Han Wang and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.1c00860},

doi = {10.1021/acs.nanolett.1c00860},

year  = {2021},

date = {2021-04-01},

journal = {Nano Letters},

volume = {21},

number = {7},

pages = {3318–3324},

abstract = {Strongly coupled, epitaxially fused colloidal nanocrystal (NC) solids are promising solution-processable semiconductors to realize optoelectronic devices with high carrier mobilities. Here, we demonstrate sequential, solid-state cation exchange reactions to transform epitaxially connected PbSe NC thin films into Cu2Se nanostructured thin-film intermediates and then successfully to achieve zinc-blende, CdSe NC solids with wide epitaxial necking along {100} facets. Transient photoconductivity measurements probe carrier transport at nanometer length scales and show a photoconductance of 0.28(1) cm2 V–1 s–1, the highest among CdSe NC solids reported. Atomic-layer deposition of a thin Al2O3 layer infiltrates and protects the structure from fusing into a polycrystalline thin film during annealing and further improves the photoconductance to 1.71(5) cm2 V–1 s–1 and the diffusion length to 760 nm. We fabricate field-effect transistors to study carrier transport at micron length scales and realize high electron mobilities of 35(3) cm2 V–1 s–1 with on–off ratios of 106 after doping.},

keywords = {nanocrystal electronics, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2020,

title = {Colloidal Quantum Dots as Platforms for Quantum Information Science},

author = {Cherie R. Kagan and Lee C. Bassett and Christopher B. Murray and Sarah M. Thompson},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.chemrev.0c00831},

doi = {10.1021/acs.chemrev.0c00831},

year  = {2020},

date = {2020-12-29},

journal = {Chemical Reviews},

volume = {121},

number = {5},

pages = {3186–3233},

abstract = {Colloidal quantum dots (QDs) are nanoscale semiconductor crystals with surface ligands that enable their dispersion in solvents. Quantum confinement effects facilitate wave function engineering to sculpt the spatial distribution of charge and spin states and thus the energy and dynamics of QD optical transitions. Colloidal QDs can be integrated in devices using solution-based assembly methods to position single QDs and to create ordered QD arrays. Here, we describe the synthesis, assembly, and photophysical properties of colloidal QDs that have captured scientific imagination and have been harnessed in optical applications. We focus especially on the current understanding of their quantum coherent effects and opportunities to exploit QDs as platforms for quantum information science. Freedom in QD design to isolate and control the quantum mechanical properties of charge, spin, and light presents various approaches to create systems with robust, addressable quantum states. We consider the attributes of QDs for optically addressable qubits in emerging quantum computation, sensing, simulation, and communication technologies, e.g., as robust sources of indistinguishable, single photons that can be integrated into photonic structures to amplify, direct, and tune their emission or as hosts for isolated, coherent spin states that can be coupled to light or to other spins in QD arrays.},

keywords = {nanoparticle assembly, quantum dots, quantum information science, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2020b,

title = {Self-assembly for electronics},

author = {Cherie R. Kagan and Taeghwan Hyeon and Dae-Hyeong Kim and Ricardo Ruiz and Maryann C. Tung and H.-S. Philip Wong },

url = {https://link.springer.com/article/10.1557/mrs.2020.248},

doi = {10.1557/mrs.2020.248},

year  = {2020},

date = {2020-12-24},

journal = {MRS Bulletin},

volume = {45},

pages = {807–814},

abstract = {Self-assembly, a process in which molecules, polymers, and particles are driven by local interactions to organize into patterns and functional structures, is being exploited in advancing silicon electronics and in emerging, unconventional electronics. Silicon electronics has relied on lithographic patterning of polymer resists at progressively smaller lengths to scale down device dimensions. Yet, this has become increasingly difficult and costly. Assembly of block copolymers and colloidal nanoparticles allows resolution enhancement and the definition of essential shapes to pattern circuits and memory devices. As we look to a future in which electronics are integrated at large numbers and in new forms for the Internet of Things and wearable and implantable technologies, we also explore a broader material set. Semiconductor nanoparticles and biomolecules are prized for their size-, shape-, and composition-dependent properties and for their solution-based assembly and integration into devices that are enabling unconventional manufacturing and new device functions.},

keywords = {nanocrystal electronics, nanoparticle assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Marino2020,

title = {Favoring the Growth of High-Quality, Three-Dimensional Supercrystals of Nanocrystals},

author = {Emanuele Marino and Austin W. Keller and Di An, Sjoerd van Dongen and Thomas E. Kodger and Katherine E. MacArthur and Marc Heggen and Cherie R. Kagan and Christopher B. Murray and Peter Schall},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.0c02805},

doi = {abs/10.1021/acs.jpcc.0c02805},

year  = {2020},

date = {2020-04-28},

journal = {The Journal of Physical Chemistry C},

volume = {124},

number = {20},

pages = {11256–11264},

abstract = {A recently developed emulsion-templated assembly method promises the scalable, low-cost, and reproducible fabrication of hierarchical nanocrystal (NC) superstructures. These superstructures derive properties from the unique combination of choices of NC building blocks and superstructure morphology and therefore realize the concept of “artificial solids”. To control the final properties of these superstructures, it is essential to control the assembly conditions that yield distinct architectural morphologies. Here, we explore the phase-space of experimental parameters describing the emulsion-templated assembly including temperature, interfacial tension, and NC polydispersity and demonstrate which conditions lead to the growth of the most crystalline NC superstructures or supercrystals. By using a combination of electron microscopy and small-angle X-ray scattering, we show that slower assembly kinetics, softer interfaces, and lower NC polydispersity contribute to the formation of supercrystals with grain sizes up to 600 nm, while reversing these trends yields glassy solids. These results provide a clear path to the realization of higher-quality supercrystals, necessary to many applications.},

keywords = {multifunctional nanomaterials, nanoparticle assembly, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Straus2020,

title = {Tailoring Hot Exciton Dynamics in 2D Hybrid Perovskites through Cation Modification},

author = {Daniel B Straus and Sebastian Hurtado Parra and Natasha Iotov and Qinghua Zhao and Michael R. Gau and Patrick J. Carroll and James M. Kikkawa and and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acsnano.0c00037},

doi = {10.1021/acsnano.0c00037},

year  = {2020},

date = {2020-03-02},

journal = {ACS Nano},

volume = {14},

number = {3},

pages = {3621–3629},

abstract = {We report a family of two-dimensional hybrid perovskites (2DHPs) based on phenethylammonium lead iodide ((PEA)2PbI4) that show complex structure in their low-temperature excitonic absorption and photoluminescence (PL) spectra as well as hot exciton PL. We replace the 2-position (ortho) H on the phenyl group of the PEA cation with F, Cl, or Br to systematically increase the cation’s cross-sectional area and mass and study changes in the excitonic structure. These single atom substitutions substantially change the observable number of and spacing between discrete resonances in the excitonic absorption and PL spectra and drastically increase the amount of hot exciton PL that violates Kasha’s rule by over an order of magnitude. To fit the progressively larger cations, the inorganic framework distorts and is strained, reducing the Pb–I–Pb bond angles and increasing the 2DHP band gap. Correlation between the 2DHP structure and steady-state and time-resolved spectra suggests the complex structure of resonances arises from one or two manifolds of states, depending on the 2DHP Pb–I–Pb bond angle (as)symmetry, and the resonances within a manifold are regularly spaced with an energy separation that decreases as the mass of the cation increases. The uniform separation between resonances and the dynamics that show excitons can only relax to the next-lowest state are consistent with a vibronic progression caused by a vibrational mode on the cation. These results demonstrate that simple changes to the cation can be used to tailor the properties and dynamics of the confined excitons without directly modifying the inorganic framework.},

keywords = {broadening, exciton−phonon coupling, hybrid perovskite, lifetime, phonons, spectroscopy, strain},

pubstate = {published},

tppubtype = {article}

}

@article{Guo2019,

title = {Chemo- and Thermomechanically Configurable 3D Optical Metamaterials Constructed from Colloidal Nanocrystal Assemblies},

author = {Jiacen Guo and Ji-Young Kim and Mingliang Zhang and Haonan Wang and Aaron Stein and Christopher B. Murray and Nicholas A. Kotov and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acsnano.9b08452},

doi = {10.1021/acsnano.9b08452},

year  = {2019},

date = {2019-12-26},

journal = {ACS Nano},

volume = {14},

number = {2},

pages = {1427-1435},

abstract = {Nanofabrication has limited most optical metamaterials to 2D or, often with multiple patterning steps, simple 3D meta-atoms that typically have limited built-in tunability. Here, with a one-step scalable patterning process, we exploit the chemical addressability and structural adaptability of colloidal Au nanocrystal assemblies to transform 2D nanocrystal/Ti bilayers into complex, 3D-structured meta-atoms and to thermally direct their shape morphing and alter their optical properties. By tailoring the length, number, and curvature of 3D helical structures in each meta-atom, we create large-area metamaterials with chiroptical responses of as high as ∼40% transmission difference between left-hand (LCP) and right-hand (RCP) circularly polarized light (ΔT = TRCP – TLCP) that are suitable for broadband circular polarizers and, upon thermally configuring their shape, switch the polarity of polarization rotation. These 3D optical metamaterials provide prototypes for low-cost, large-scale fabrication of optical metamaterials for ultrathin lenses, polarizers, and waveplates.},

keywords = {chiral, plasmonic, templated assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2019,

title = {General Synthetic Route to High-Quality Colloidal III–V Semiconductor Quantum Dots Based on Pnictogen Chlorides},

author = {Tianshuo Zhao and Nuri Oh and Davit Jishkariani and Mingliang Zhang and Han Wang and Na Li and Jennifer D. Lee and Chenjie Zeng and Manisha Muduli and Hak-Jong Choi and Dong Su and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/jacs.9b06652},

doi = {10.1021/jacs.9b06652},

year  = {2019},

date = {2019-09-07},

journal = {Journal of the American Chemical Society},

volume = {141},

number = {38},

pages = {15145-15152},

abstract = {The synthesis of colloidal III–V quantum dots (QDs), particularly of the arsenides and antimonides, has been limited by the lack of stable and available group V precursors. In this work, we exploit accessible InCl3- and pnictogen chloride-oleylamine as precursors to synthesize III–V QDs. Through coreduction reactions of the precursors, we achieve size- and stoichiometry-tunable binary InAs and InSb as well as ternary alloy InAs1–xSbx QDs. On the basis of structural, analytical, optical, and electrical characterization of the QDs and their thin-film assemblies, we study the effects of alloying on their particle formation and optoelectronic properties. We introduce a hydrazine-free hybrid ligand-exchange process to improve carrier transport in III–V QD thin films and realize InAs QD field-effect transistors with electron mobility > 5 cm2/(V s). We demonstrate that III–V QD thin films are promising candidate materials for infrared devices and show InAs1–xSbx QD photoconductors with superior short-wavelength infrared (SWIR) photoresponse than those of the binary QD devices.},

keywords = {quantum dots, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Chen2019,

title = {Designing Strong Optical Absorbers via Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies},

author = {Wenxiang Chen and Jiacen Guo and Qinghua Zhao and Prashanth Gopalan and Aaron T. Fafarman and Austin Keller and Mingliang Zhang and Yaoting Wu and Christopher B. Murray and Cherie R. Kagan},

doi = {10.1021/acsnano.9b02818},

year  = {2019},

date = {2019-05-28},

journal = {ACS Nano},

volume = {13},

number = {7},

pages = {7493-7501},

abstract = {We program the optical properties of colloidal Au nanocrystal (NC) assemblies via an unconventional ligand hybridization (LH) strategy to precisely engineer interparticle interactions and design materials with optical properties difficult or impossible to achieve in bulk form. Long-chain hydrocarbon ligands used in NC synthesis are partially exchanged, from 0% to 100%, with compact thiocyanate ligands by controlling the reaction time for exchange. The resulting NC assemblies show transmittance, reflectance, optical permittivity, and direct-current (DC) resistivity that continuously traverse a dielectric-metal transition, providing analog tuning of their physical properties, unlike the digital control realized by complete exchange with ligands of varying length. Exploiting this LH strategy, we create Au NC assemblies that are strong, ultrathin film optical absorbers, as seen by a 6× increase in the extinction of infrared light compared to that in bulk Au thin films and by a temperature rise of 20 °C upon illumination with 808 nm light. Our LH strategy may be applied to the design of materials constructed from NCs of different size, shape, and composition for specific applications.},

keywords = {nanoparticle assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Straus2019,

title = {Longer Cations Increase Energetic Disorder in Excitonic 2D Hybrid Perovskites},

author = {Daniel B. Straus and Natasha Iotov and Michael R. Gau and Qinghua Zhao and Patrick J. Carroll and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acs.jpclett.9b00247},

doi = {10.1021/acs.jpclett.9b00247},

year  = {2019},

date = {2019-02-26},

journal = {Journal of Physical Chemistry Letters},

volume = {10},

number = {6},

pages = {1198–1205},

abstract = {We synthesize and characterize derivatives of the two-dimensional hybrid perovskite (2DHP) phenethylammonium lead iodide ((PEA)2PbI4) in which the para H on the cation is replaced with F, Cl, CH3, or Br. These substitutions increase the length of the cation but leave the cross-sectional area unchanged, resulting in structurally similar PbI42– frameworks with increasing interlayer spacing. Longer cations result in broader, blue-shifted excitonic absorption spectra with reduced or eliminated structure, indicating greater energetic disorder. Photoluminescence spectra are largely invariant and insensitive to cation length, suggesting polaron formation stabilizes a structural and electronic minimum. Temperature-dependent line width analysis reveals excitons couple to a vibration on the organic framework that is weakly sensitive to these cation substitutions, and Raman spectra and electronic structure calculations support the presence of such a cationic mode. Despite carriers being confined to the inorganic framework, the length of the organic cation alters the optical and electronic properties of 2DHPs.},

keywords = {2D-materials, perovskites},

pubstate = {published},

tppubtype = {article}

}

@article{Wang2019,

title = {Air-Stable CuInSe2 Nanocrystal Transistors and Circuits via Post-Deposition Cation Exchange},

author = {Han Wang and Derrick J. Butler and Daniel B. Straus and Nuri Oh and Fengkai Wu and Jiacen Guo and Kun Xue and Jennifer D. Lee and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.8b09055},

doi = {10.1021/acsnano.8b09055},

year  = {2019},

date = {2019-02-01},

journal = {ACS Nano},

volume = {13},

number = {2},

pages = {2324–2333},

abstract = {Colloidal semiconductor nanocrystals (NCs) are a promising materials class for solution-processable, next-generation electronic devices. However, most high-performance devices and circuits have been achieved using NCs containing toxic elements, which may limit their further device development. We fabricate high mobility CuInSe2 NC field-effect transistors (FETs) using a solution-based, post-deposition, sequential cation exchange process that starts with electronically coupled, thiocyanate (SCN)-capped CdSe NC thin films. First Cu+ is substituted for Cd2+ transforming CdSe NCs to Cu-rich Cu2Se NC films. Next, Cu2Se NC films are dipped into a Na2Se solution to Se-enrich the NCs, thus compensating the Cu-rich surface, promoting fusion of the Cu2Se NCs, and providing sites for subsequent In-dopants. The liquid-coordination-complex trioctylphosphine–indium chloride (TOP–InCl3) is used as a source of In3+ to partially exchange and n-dope CuInSe2 NC films. We demonstrate Al2O3-encapsulated, air-stable CuInSe2 NC FETs with linear (saturation) electron mobilities of 8.2 ± 1.8 cm2/(V s) (10.5 ± 2.4 cm2/(V s)) and with current modulation of 105, comparable to that for high-performance Cd-, Pb-, and As-based NC FETs. The CuInSe2 NC FETs are used as building blocks of integrated inverters to demonstrate their promise for low-cost, low-toxicity NC circuits.},

keywords = {nanocrystal electronics, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Greybush2019,

title = {Plasmonic Optical and Chiroptical Response of Self-Assembled Au Nanorod Equilateral Trimers},

author = {Nicholas J. Greybush and Victor Pacheco-Peña and Nader Engheta and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acsnano.8b07619},

doi = {10.1021/acsnano.8b07619},

year  = {2019},

date = {2019-01-10},

journal = {ACS Nano},

volume = {13},

number = {2},

pages = {1617–1624},

abstract = {Assembling metamolecules from anisotropic, shape-engineered nanocrystals provides the opportunity to orchestrate distinct optical responses one nanocrystal at a time. The Au nanorod has long been a structural archetype in plasmonics, but nanorod assemblies have largely been limited to end-to-end or side-to-side arrangements, accessing only a subset of potential metamolecule structures. Here, we employ triangular templates to direct the assembly of Au nanorods along the edges of an equilateral triangle. Using spatially resolved, dark-field scattering spectroscopy in concert with numerical simulation of individual metamolecules, we map the evolution in surface plasmon resonances as we add one, two, and three nanorods to construct triangular nanorod assemblies. The assemblies exhibit rotation- and polarization-dependent hybridized plasmon modes, which are sensitive to variations in nanorod size, position, and orientation that lead to geometrical symmetry breaking. The triangular arrangement of nanorods supports magnetic plasmon modes where electric fields are directed along the perimeter of the triangle, and the magnetic field intensity within the triangle’s open interior is enhanced. Circumferential displacements of the nanorods within the templates impart either a left- or right-handed sense of rotation to the structure, which generates a chiroptical response under unidirectional oblique illumination. Our results represent an important step in realizing and characterizing metamaterial assemblies with “open” structures utilizing anisotropic plasmonic building blocks, with implications for optical magnetic field enhancement and chiral plasmonics.},

keywords = {plasmonic, templated assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2018,

title = {Nanoimprinted Chiral Plasmonic Substrates with Three-Dimensional Nanostructures},

author = {Mingliang Zhang and Victor Pacheco-Peña and Yao Yu and Wenxiang Chen and Nicholas J. Greybush and Aaron Stein and Nader Engheta and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acs.nanolett.8b03785},

doi = {10.1021/acs.nanolett.8b03785},

year  = {2018},

date = {2018-09-26},

journal = {Nano Letters},

volume = {18},

number = {11},

pages = {7389–7394},

abstract = {We report a large-area fabrication method to prepare chiral substrates patterned with arrays of multilayer, three-dimensional nanostructures using a combination of nanoimprint lithography and glancing angle deposition. Several structures are successfully fabricated using this method, including L-shaped, twisted arc and trilayer twisted Au nanorod structures, demonstrating its generality. As one typical example, arrays of L-shaped nanostructures, consisting of two layers of orthogonally oriented Au nanorods separated by a Ge dielectric layer in the thickness direction, exhibit giant optical chirality in the infrared region with an experimentally achieved g-factor as high as 0.38. Electromagnetic simulations show that the optical chirality results from plasmon hybridization between the two orthogonal Au segments. To demonstrate scalability, a 1 cm2 chiral substrate is fabricated with uniform chiral optical property. This method combines both high throughput and precise geometrical control and is therefore promising for applications of chiral metamaterials.},

keywords = {chiral, optical metamaterials},

pubstate = {published},

tppubtype = {article}

}

@article{Chen2018,

title = {Ultrasensitive, Mechanically Responsive Optical Metasurfaces via Strain Amplification},

author = {Wenxiang Chen and Wenjing Liu and Yijie Jiang and Mingliang Zhang and Naixin Song and Nicholas J. Greybush and Jiacen Guo and Anna K. Estep and Kevin T. Turner and Ritesh Agarwal and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acsnano.8b04889},

doi = {doi/10.1021/acsnano.8b04889},

year  = {2018},

date = {2018-09-24},

journal = {ACS Nano},

volume = {12},

number = {11},

pages = {10683–10692},

abstract = {Optical metasurfaces promise ultrathin, lightweight, miniaturized optical components with outstanding capabilities to manipulate the amplitude, phase, and polarization of light compared to conventional, bulk optics. The emergence of reconfigurable metasurfaces further integrates dynamic tunability with optical functionalities. Here, we report a structurally reconfigurable, optical metasurface constructed by integrating a plasmonic lattice array in the gap between a pair of symmetric microrods that serve to locally amplify the strain created on an elastomeric substrate by an external mechanical stimulus. The strain on the metasurface is amplified by a factor of 1.5–15.9 relative to the external strain by tailoring the microrod geometry. For the highest strain amplification geometry, the mechano-sensitivity of the optical responses of the plasmonic lattice array is a factor of 10 greater than that of state-of-the-art stretchable plasmonic resonator arrays. The spatial arrangement and therefore the optical response of the plasmonic lattice array are reversible, showing little hysteresis.},

keywords = {optical metamaterials, strain},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2018,

title = {Flexible colloidal nanocrystal electronics},

author = {Cherie R. Kagan},

url = {https://pubs.rsc.org/en/content/articlelanding/2018/cs/c8cs00629f#!divAbstract},

doi = {doi.org/10.1039/C8CS00629F},

year  = {2018},

date = {2018-09-12},

journal = {Chemical Society Reviews},

volume = {48},

number = {6},

pages = {1626-1641},

abstract = {Nanometer-scale crystals of bulk group IV, III–V, II–VI, IV–VI, I–III–VI2, and metal–halide perovskite semiconductors, dispersed in solvents, are known as colloidal nanocrystals and form an excellent, solution-processable materials class for thin film and flexible electronics. This review surveys the size, composition, and surface chemistry-dependent properties of semiconductor NCs and thin films derived therefrom and provides physico-chemical insight into the recent leaps forward in the performance of NC field-effect transistors. Device design and fabrication methods are described that have enabled the demonstration and scaling up in complexity and area and scaling down in device size of flexible, colloidal nanocrystal integrated circuits. Finally, taking stock of the advances made in the science and engineering of NC systems, challenges and opportunities are presented to develop next-generation, colloidal NC electronic materials and devices, important to their potential in future computational and in Internet of Things applications.



},

keywords = {nanocrystal electronics},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2018,

title = {Charge Transport Modulation in PbSe Nanocrystal Solids by AuxAg1–x Nanoparticle Doping},

author = {Haoran Yang and Eric Wong and Tianshuo Zhao and Jennifer D. Lee and Huolin L. Xin and Miaofang Chi and Blaise Fleury and Han-Yu Tang and E. Ashley Gaulding and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/10.1021/acsnano.8b03112},

doi = {10.1021/acsnano.8b03112},

year  = {2018},

date = {2018-08-27},

journal = {ACS Nano},

volume = {12},

number = {9},

pages = {9091–9100},

abstract = {Nanocrystal (NC) solids are an exciting class of materials, whose physical properties are tunable by choice of the NCs as well as the strength of the interparticle coupling. One can consider these NCs as “artificial atoms” in analogy to the formation of condensed matter from atoms. Akin to atomic doping, the doping of a semiconducting NC solid with impurity NCs can drastically alter its electronic properties. A high degree of complexity is possible in these artificial structures by adjusting the size, shape, and composition of the building blocks, which enables “designer” materials with targeted properties. Here, we present the doping of the PbSe NC solids with a series of AuxAg1–x alloy nanoparticles (NPs). A combination of temperature-dependent electrical conductance and Seebeck coefficient measurements and room-temperature Hall effect measurements demonstrates that the incorporation of metal NPs both modifies the charge carrier density of the NC solids and introduces energy barriers for charge transport. These studies point to charge carrier injection from the metal NPs into the PbSe NC matrix. The charge carrier density and charge transport dynamics in the doped NC solids are adjustable in a wide range by employing the AuxAg1–x NP with different Au:Ag ratio as dopants. This doping strategy could be of great interest for thermoelectric applications taking advantage of the energy filtering effect introduced by the metal NPs.},

keywords = {doping, nanocrystal electronics, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Paik2018,

title = {Photocatalytic Hydrogen Evolution from Substoichiometric Colloidal WO3–x Nanowires},

author = {Taejong Paik and Matteo Cargnello and Thomas R. Gordon and Sen Zhang and Hongseok Yun and Jennifer D. Lee and Ho Young Woo and Soong Ju Oh and Cherie R. Kagan and Paolo Fornasiero and Christopher B. Murray},

url = {https://pubs.acs.org/doi/10.1021/acsenergylett.8b00925},

doi = {10.1021/acsenergylett.8b00925},

year  = {2018},

date = {2018-06-29},

journal = {ACS Energy Letters},

volume = {3},

number = {8},

pages = {1904–1910},

abstract = {We report direct photocatalytic hydrogen evolution from substoichiometric highly reduced tungsten oxide (WOx) nanowires (NWs) using sacrificial alcohol. WOx NWs are synthesized via nonaqueous colloidal synthesis with a diameter of about 4 nm and an average length of about 250 nm. As-synthesized WOx NWs exhibit a broad absorption across the visible to infrared regions attributed to the presence of oxygen vacancies. The optical band gap is increased in these WOx NWs compared to stoichiometric bulk tungsten oxide (WO3) powders as a result of the Burstein–Moss shift. As a consequence of this increase, we demonstrate direct photocatalytic hydrogen production from WOx NWs through alcohol photoreforming. The stable H2 evolution on platinized WOx NWs is observed under conditions in which platinized bulk WO3 and bulk WO2.9 powders either do not show activity or show very low rates, suggesting that increased surface area and specific exposed facets are key for the improved performance of WOx NWs. This work demonstrates that control of size and composition can lead to unexpected and beneficial changes in the photocatalytic properties of semiconductor materials.},

keywords = {nanowires, thermodynamic modeling, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Najmr2018,

title = {Preparation of silica coated and 90Y-radiolabeled β-NaYF4 upconverting nanophosphors for multimodal tracing},

author = {Stan Najmr and Tianfeng Lu and Austin W Keller and Mingyue Zhang and Jennifer D Lee and Mehran Makvandi and Daniel A Pryma and Cherie R Kagan and Christopher B Murray},

url = {https://iopscience.iop.org/article/10.1088/2399-1984/aab947/meta},

year  = {2018},

date = {2018-04-18},

journal = {Nano Futures},

volume = {2},

number = {2},

pages = {025002},

abstract = {Rare-earth (RE) compounds have been actively pursued for therapeutic and diagnostic applications due to their ability to upconvert near infrared light into the UV–vis range. Through nanoengineering and bottom-up synthesis, additional functionality can be added to these upconverting systems. Herein, we report the synthesis of 90Y-doped β-NaYF4:Er, Yb upconverting nanophosphors (UCNPs) to enable β-particle emission and upconversion by the same UCNP. To homogenously incorporate the radionuclides, we employ a hydroxide metathesis method to produce the RE precursor required for the solvothermal synthesis of monodisperse UCNPs. Once incorporated, we find that the β-emitting 90Y dopants do not influence the energy pathways required for upconversion, enabling simultaneous radio- and optical-tracing. The resulting large (>100 nm in height and width), anisotropic, 90Y-radiolabeled β-NaYF4 UCNPs are then coated with silica using a modified, micelle-driven Stöber process to enable their dispersion in polar solvents. Doing so highlights the importance of surfactant (Igepal CO-520) and silica source (tetraethyl orthosilicate) interactions to the continuity of the silica shell and makes the vast library of silica surface chemistry and functionality accessible to upconverting radiotracers.},

keywords = {multifunctional nanomaterials, synthesis, upconverting nanophosphors},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2018b,

title = {3D Nanofabrication via Chemo‐Mechanical Transformation of Nanocrystal/Bulk Heterostructures},

author = {Mingliang Zhang and Jiacen Guo and Yao Yu and Yaoting Wu and Hongseok Yun and Davit Jishkariani and Wenxiang Chen and Nicholas J. Greybush and Christian Kübel and Aaron Stein and Christopher B. Murray and Cherie R. Kagan},

url = {https://onlinelibrary.wiley.com/doi/10.1002/adma.201800233},

doi = {10.1002/adma.201800233},

year  = {2018},

date = {2018-04-15},

journal = {Advanced Materials},

volume = {30},

number = {22},

pages = {1800233},

abstract = {Planar nanocrystal/bulk heterostructures are transformed into 3D architectures by taking advantage of the different chemical and mechanical properties of nanocrystal and bulk thin films. Nanocrystal/bulk heterostructures are fabricated via bottom‐up assembly and top‐down fabrication. The nanocrystals are capped by long ligands introduced in their synthesis, and therefore their surfaces are chemically addressable, and their assemblies are mechanically “soft,” in contrast to the bulk films. Chemical modification of the nanocrystal surface, exchanging the long ligands for more compact chemistries, triggers large volume shrinkage of the nanocrystal layer and drives bending of the nanocrystal/bulk heterostructures. Exploiting the differential chemo‐mechanical properties of nanocrystal and bulk materials, the scalable fabrication of designed 3D, cell‐sized nanocrystal/bulk superstructures is demonstrated, which possess unique functions derived from nanocrystal building blocks.},

keywords = {chiral, multifunctional nanomaterials, optical metamaterials, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Chen2018b,

title = {Angle-Independent Optical Moisture Sensors Based on Hydrogel-Coated Plasmonic Lattice Arrays},

author = {Wenxiang Chen and Gaoxiang Wu and Mingliang Zhang and Nicholas J. Greybush and Jordan P. Howard-Jennings and Naixin Song and F. Scott Stinner and Shu Yang and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsanm.8b00268},

doi = {abs/10.1021/acsanm.8b00268},

year  = {2018},

date = {2018-03-06},

journal = {ACS Applied Nano Materials},

volume = {1},

number = {3},

pages = {1430–1437},

keywords = {IOT, optical metamaterials, plasmonic},

pubstate = {published},

tppubtype = {article}

}

@article{Straus2018,

title = {Electrons, Excitons, and Phonons in Two-Dimensional Hybrid Perovskites: Connecting Structural, Optical, and Electronic Properties},

author = {Daniel B. Straus and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acs.jpclett.8b00201},

doi = {10.1021/acs.jpclett.8b00201},

year  = {2018},

date = {2018-02-26},

journal = {The Journal of Physical Chemistry Letters},

volume = {9},

number = {6},

pages = {1434–1447},

abstract = {Two-dimensional (2D) hybrid perovskites are stoichiometric compounds consisting of alternating inorganic metal-halide sheets and organoammonium cationic layers. This materials class is widely tailorable in composition, structure, and dimensionality and is providing an intriguing playground for the solid-state chemistry and physics communities to uncover structure–property relationships. In this Perspective, we describe semiconducting 2D perovskites containing lead and tin halide inorganic frameworks. In these 2D perovskites, charges are typically confined to the inorganic framework because of strong quantum and dielectric confinement effects, and exciton binding energies are many times greater than kT at room temperature. We describe the role of the heavy atoms in the inorganic framework; the geometry and chemistry of organic cations; and the “softness” of the organic–inorganic lattice on the electronic structure and dynamics of electrons, excitons, and phonons that govern the physical properties of these materials.},

keywords = {2D-materials, exciton−phonon coupling, hybrid perovskite, perovskites},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2018,

title = {The Effect of Dielectric Environment on Doping Efficiency in Colloidal PbSe Nanostructures},

author = {Qinghua Zhao and Tianshuo Zhao and Jiacen Guo and Wenxiang Chen and Mingliang Zhang and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acsnano.7b07602},

doi = {10.1021/acsnano.7b07602},

year  = {2018},

date = {2018-01-18},

journal = {ACS Nano},

volume = {12},

number = {2},

pages = {1313–1320},

abstract = {Doping, as a central strategy to control free carrier type and concentration in semiconductor materials, suffers from low efficiency at the nanoscale, especially in systems having high permittivity (ϵ) and large Bohr radii, such as lead chalcogenide nanocrystals (NCs) and nanowires (NWs). Here, we study dielectric confinement effects on the doping efficiency of lead chalcogenides nanostructures by integrating PbSe NWs in the platform of field effect transistors (FETs). Elemental Pb or In or elemental Se is deposited by thermal evaporation to remotely n- or p-dope the NWs. Polymeric and oxide materials of varying ϵ are subsequently deposited to control the dielectric environment surrounding the NWs. Analyzing the device characteristics, we extract the change of carrier concentration introduced by tailoring the dielectric environment. The calculated doping efficiency for n-type (Pb/In) and p-type (Se) dopants increases as the ϵ of the surrounding medium increases. Using a high-ϵ material, such as HfO2 for encapsulation, the doping efficiency can be enhanced by >10-fold. A theoretical model is built to describe the doping efficiency in PbSe NWs embedded in different dielectric environments, which agrees with our experimental data for both NW array and single NW devices. As dielectric confinement affects all low-dimensional materials, engineering the dielectric environment is a promising general approach to enhance doping concentrations, without introducing excess impurities that may scatter carriers, and is suitable for various device applications.},

keywords = {doping, nanocrystal electronics},

pubstate = {published},

tppubtype = {article}

}

@article{Jishkariani2017,

title = {The dendritic effect and magnetic permeability in dendron coated nickel and manganese zinc ferrite nanoparticles},

author = {Davit Jishkariani and Jennifer D. Lee and Hongseok Yun and Taejong Paik and James M. Kikkawa and Cherie R. Kagan and Bertrand Donnioand Christopher B. Murray},

url = {https://pubs.rsc.org/en/content/articlelanding/2017/nr/c7nr05769e#!divAbstract},

doi = {10.1039/C7NR05769E},

year  = {2017},

date = {2017-08-21},

journal = {Nanoscale},

volume = {9},

number = {37},

pages = {13922-13928},

abstract = {The collective magnetic properties of nanoparticle (NP) solid films are greatly affected by inter-particle dipole–dipole interactions and therefore the proximity of the neighboring particles. In this study, a series of dendritic ligands (generations 0 to 3, G0–G3) have been designed and used to cover the surface of magnetic NPs to control the spacings between the NP components in single lattices. The dendrons of different generations introduced here were based on the 2,2-bis(hydroxymethyl)propionic acid (Bis-MPA) scaffold and equipped with an appropriate surface binding group at one end and several fatty acid segments at the other extremity. The surface of the NPs was then modified by partial ligand exchange between the primary stabilizing surfactants and the new dendritic wedges. It was shown that this strategy permitted very precise tuning of inter-particle spacings in the range of 2.9–5.0 nm. As expected, the increase in the inter-particle spacings reduced the dipole–dipole interactions between magnetic NPs and therefore allowed changes in their magnetic permeability. The dendron size and inter-particle distance dependence was studied to reveal the dendritic effect and identify the optimal geometry and generation.},

keywords = {nanoparticle assembly, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Ashkar2017,

title = {Rapid Large-Scale Assembly and Pattern Transfer of One-Dimensional Gold Nanorod Superstructures},

author = {Rana Ashkar and Michael J. A. Hore and Xingchen Ye and Bharath Natarajan and Nicholas J. Greybush and Thomas and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/abs/10.1021/acsami.7b06273},

doi = {abs/10.1021/acsami.7b06273},

year  = {2017},

date = {2017-07-07},

journal = {ACS Applied Materials & Interfaces},

volume = {9},

number = {30},

pages = {25513–25521},

abstract = {The utility of gold nanorods for plasmonic applications largely depends on the relative orientation and proximity of the nanorods. Though side-by-side or chainlike nanorod morphologies have been previously demonstrated, a simple reliable method to obtain high-yield oriented gold nanorod assemblies remains a significant challenge. We present a facile, scalable approach which exploits meniscus drag, evaporative self-assembly, and van der Waals interactions to precisely position and orient gold nanorods over macroscopic areas of 1D nanostructured substrates. By adjusting the ratio of the nanorod diameter to the width of the nanochannels, we demonstrate the formation of two highly desired translationally ordered nanorod patterns. We further demonstrate a method to transfer the aligned nanorods into a polymer matrix which exhibits anisotropic optical properties, allowing for rapid fabrication and deployment of flexible optical and electronic materials in future nanoscale devices.},

keywords = {nanoparticle assembly, plasmonic, templated assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Elbaz2017,

title = {Unbalanced Hole and Electron Diffusion in Lead Bromide Perovskites},

author = {Giselle A. Elbaz and Daniel B. Straus and Octavi E. Semonin and Trevor D. Hull and Daniel W. Paley and Philip Kim and Jonathan S. Owen and Cherie R. Kagan and Xavier Roy},

url = {https://pubs.acs.org/doi/10.1021/acs.nanolett.6b05022},

doi = {10.1021/acs.nanolett.6b05022},

year  = {2017},

date = {2017-02-27},

journal = {Nano Letters},

volume = {17},

number = {3},

pages = {1727–1732},

abstract = {We use scanning photocurrent microscopy and time-resolved microwave conductivity to measure the diffusion of holes and electrons in a series of lead bromide perovskite single crystals, APbBr3, with A = methylammonium (MA), formamidinium (FA), and Cs. We find that the diffusion length of holes (LDh+ ∼ 10–50 μm) is on average an order of magnitude longer than that of electrons (LDe– ∼ 1–5 μm), regardless of the A-type cation or applied bias. Furthermore, we observe a weak dependence of LD across the A-cation series MA > FA > Cs. When considering the role of the halide, we find that the diffusion of holes in MAPbBr3 is comparable to that in MAPbI3, but the electron diffusion length is up to five times shorter. This study shows that the disparity between hole and electron diffusion is a ubiquitous feature of lead halide perovskites. As with organic photovoltaics, this imbalance will likely become an important consideration in the optimization of lead halide perovskite solar cells.},

keywords = {perovskites, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Greybush2017,

title = {Plasmon Resonances in Self-Assembled Two-Dimensional Au Nanocrystal Metamolecules},

author = {Nicholas J. Greybush and Iñigo Libera and Ludivine Malassis and James M. Kikkawa and Nader Engheta and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.6b08189},

doi = {10.1021/acsnano.6b08189},

year  = {2017},

date = {2017-02-12},

journal = {ACS Nano},

volume = {11},

number = {3},

pages = {2917–2927},

abstract = {We explore the evolution of plasmonic modes in two-dimensional nanocrystal oligomer “metamolecules” as the number of nanocrystals is systematically varied. Precise, hexagonally ordered Au nanocrystal oligomers with 1–31 members are assembled via capillary forces into polygonal topographic templates defined using electron-beam lithography. The visible and near-infrared scattering response of individual oligomers is measured by spatially resolved, polarized darkfield scattering spectroscopy. The response is highly sensitive to in-plane versus out-of-plane incident polarization, and we observe an exponentially saturating red shift in plasmon resonance wavelength as the number of nanocrystals per oligomer increases, in agreement with theoretical predictions. Simulations further elucidate the modes supported by the oligomers, including electric dipole and magnetic dipole resonances and their Fano interference. The single-oligomer sensitivity of our measurements also reveals the role of positional disorder in determining the wavelength and character of the plasmonic response. The progression of oligomer metamolecule structures studied here advances our understanding of fundamental plasmonic interactions in the transition regime between few-member plasmonic clusters and extended two-dimensional arrays.},

keywords = {nanoparticle assembly, optical metamaterials, plasmonic, templated assembly},

pubstate = {published},

tppubtype = {article}

}

@article{Wu2017,

title = {Directional Carrier Transfer in Strongly Coupled Binary Nanocrystal Superlattice Films Formed by Assembly and in Situ Ligand Exchange at a Liquid–Air Interface},

author = {Yaoting Wu and Siming and Natalie Gogotsi and Tianshuo Zhao and Blaise Fleury and Cherie R. Kagan and Christopher B. Murray and Jason B. Baxter},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b12327},

doi = {abs/10.1021/acs.jpcc.6b12327},

year  = {2017},

date = {2017-02-05},

journal = {The Journal of Physical Chemistry C},

volume = {121},

number = {8},

pages = {4146–4157},

abstract = {Two species of monodisperse nanocrystals (NCs) can self-assemble into a variety of complex 2D and 3D periodic structures, or binary NC superlattice (BNSL) films, based on the relative number and size of the NCs. BNSL films offer great promise for both fundamental scientific studies and optoelectronic applications; however, the utility of as-assembled structures has been limited by the insulating ligands that originate from the synthesis of NCs. Here we report the application of an in situ ligand exchange strategy at a liquid–air interface to replace the long synthesis ligands with short ligands while preserving the long-range order of BNSL films. This approach is demonstrated for BNSL structures consisting of PbSe NCs of different size combinations and ligands of interest for photovoltaic devices, infrared detectors, and light-emitting diodes. To confirm enhanced coupling introduced by ligand exchange, we show ultrafast (∼1 ps) directional carrier transfer across the type-I heterojunction formed by NCs of different sizes within ligand-exchanged BNSL films. This approach shows the potential promise of functional BNSL films, where the local and long-range energy landscape and electronic coupling can be adjusted by tuning NC composition, size, and interparticle spacing.},

keywords = {nanoparticle assembly, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Paik2017,

title = {Hierarchical Materials Design by Pattern Transfer Printing of Self-Assembled Binary Nanocrystal Superlattices},

author = {Taejong Paik and Hongseok and Blaise Fleury and Sung-Hoon Hong and Pil Sung Jo and Yaoting Wu and Soong-Ju Oh and Matteo Cargnello and Haoran Yang and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b04279},

doi = {abs/10.1021/acs.nanolett.6b04279},

year  = {2017},

date = {2017-02-01},

journal = {Nano Letters},

volume = {17},

number = {3},

pages = {1387–1394},

abstract = {We demonstrate the fabrication of hierarchical materials by controlling the structure of highly ordered binary nanocrystal superlattices (BNSLs) on multiple length scales. Combinations of magnetic, plasmonic, semiconducting, and insulating colloidal nanocrystal (NC) building blocks are self-assembled into BNSL membranes via the liquid–interfacial assembly technique. Free-standing BNSL membranes are transferred onto topographically structured poly(dimethylsiloxane) molds via the Langmuir–Schaefer technique and then deposited in patterns onto substrates via transfer printing. BNSLs with different structural motifs are successfully patterned into various meso- and microstructures such as lines, circles, and even three-dimensional grids across large-area substrates. A combination of electron microscopy and grazing incidence small-angle X-ray scattering (GISAXS) measurements confirm the ordering of NC building blocks in meso- and micropatterned BNSLs. This technique demonstrates structural diversity in the design of hierarchical materials by assembling BNSLs from NC building blocks of different composition and size by patterning BNSLs into various size and shape superstructures of interest for a broad range of applications.},

keywords = {multifunctional nanomaterials, nanoparticle assembly, self-assembly, TEM},

pubstate = {published},

tppubtype = {article}

}

@article{Oh2016,

title = {Engineering the surface chemistry of lead chalcogenide nanocrystal solids to enhance carrier mobility and lifetime in optoelectronic devices},

author = {S. J. Oh and D. B. Straus and T. Zhao and J.-H. Choi and S.-W. Lee and A. Gaulding and C. B. Murray and C. R. Kagan},

url = {https://pubs.rsc.org/en/content/articlelanding/2016/cc/c6cc07916d#!divAbstract},

year  = {2016},

date = {2016-12-12},

journal = {Chemical Communications},

volume = {53},

number = {4},

pages = {728-731},

abstract = {We introduce a stepwise, hybrid ligand-exchange method for lead chalcogenide nanocrystal (NC) thin films using the compact-inorganic ligand thiocyanate and the short organic ligand benzenediothiolate. Spectroscopic and device measurements show that hybrid exchange enhances both carrier mobility and lifetime in NC thin films. The increased mobility-lifetime product achieved by this method enables demonstration of optoelectronic devices with enhanced power conversion and quantum efficiency.},

keywords = {nanocrystal electronics, synthesis, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2016,

title = {High-strength magnetically switchable plasmonic nanorods assembled from a binary nanocrystal mixture},

author = {Mingliang Zhang and Daniel J. Magagnosc and Iñigo Liberal and Yao Yu and Hongseok Yun and Haoran Yang and Yaoting Wu and Jiacen Guo and Wenxiang Chen and Young Jae Shin and Aaron Stein and James M. Kikkawa and Nader Engheta and Daniel S. Gianola and Christopher B. Murray and Cherie R. Kagan},

url = {https://www.nature.com/articles/nnano.2016.235},

doi = {10.1038/nnano.2016.235},

year  = {2016},

date = {2016-11-07},

journal = {Nature Nanotechnology},

volume = {12},

pages = {228–232},

abstract = {Next-generation ‘smart’ nanoparticle systems should be precisely engineered in size, shape and composition to introduce multiple functionalities, unattainable from a single material1,2,3. Bottom-up chemical methods are prized for the synthesis of crystalline nanoparticles, that is, nanocrystals, with size- and shape-dependent physical properties4,5,6, but they are less successful in achieving multifunctionality7,8,9. Top-down lithographic methods can produce multifunctional nanoparticles with precise size and shape control2,3,10,11, yet this becomes increasingly difficult at sizes of ∼10 nm. Here, we report the fabrication of multifunctional, smart nanoparticle systems by combining top-down fabrication and bottom-up self-assembly methods. Particularly, we template nanorods from a mixture of superparamagnetic Zn0.2Fe2.8O4 and plasmonic Au nanocrystals. The superparamagnetism of Zn0.2Fe2.8O4 prevents these nanorods from spontaneous magnetic-dipole-induced aggregation, while their magnetic anisotropy makes them responsive to an external field. Ligand exchange drives Au nanocrystal fusion and forms a porous network, imparting the nanorods with high mechanical strength and polarization-dependent infrared surface plasmon resonances. The combined superparamagnetic and plasmonic functions enable switching of the infrared transmission of a hybrid nanorod suspension using an external magnetic field.},

keywords = {nanoparticle assembly, optical metamaterials},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2016,

title = {Nano Day: Celebrating the Next Decade of Nanoscience and Nanotechnology},

author = {Cherie R. Kagan and Laura E. Fernandez and Yury Gogotsi and Paula T. Hammond and Mark C. Hersam and André E. Nel and Reginald M. Penner and C. Grant Willson and Paul S. Weiss},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.6b06655},

doi = {10.1021/acsnano.6b06655},

year  = {2016},

date = {2016-10-07},

journal = {ACS Nano},

volume = {10},

number = {10},

pages = {9093–9103},

abstract = {Nanoscience and nanotechnology are poised to contribute to a wide range of fields, from health and medicine to electronics, energy, security, and more. These contributions come both directly in the form of new materials, interfaces, tools, and even properties as well as indirectly by connecting fields together. We celebrate how far we have come, and here, we look at what is to come over the next decade that will leverage the strong and growing base that we have built in nanoscience and nanotechnology.},

keywords = {nanoscience, nanotechnology},

pubstate = {published},

tppubtype = {article}

}

@article{Straus2016,

title = {Direct Observation of Electron–Phonon Coupling and Slow Vibrational Relaxation in Organic–Inorganic Hybrid Perovskites},

author = {Daniel B. Straus and Sebastian Hurtado Parra and Natasha Iotov and Julian Gebhardt and Andrew M. Rappe and Joseph E. Subotnik and James M. Kikkawa and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/jacs.6b08175},

doi = {10.1021/jacs.6b08175},

year  = {2016},

date = {2016-10-05},

journal = {Journal of the American Chemical Society},

volume = {138},

number = {42},

pages = {13798–13801},

abstract = {Quantum and dielectric confinement effects in Ruddlesden-Popper 2D hybrid perovskites create excitons with a binding energy exceeding 150 meV. We exploit the large exciton binding energy to study exciton and carrier dynamics as well as electron–phonon coupling (EPC) in hybrid perovskites using absorption and photoluminescence (PL) spectroscopies. At temperatures <75 K, we resolve splitting of the excitonic absorption and PL into multiple regularly spaced resonances every 40–46 meV, consistent with EPC to phonons located on the organic cation. We also resolve resonances with a 14 meV spacing, in accord with coupling to phonons with mixed organic and inorganic character. These assignments are supported by density-functional theory calculations. Hot exciton PL and time-resolved PL measurements show that vibrational relaxation occurs on a picosecond time scale competitive with that for PL. At temperatures >75 K, excitonic absorption and PL exhibit homogeneous broadening. While absorption remains homogeneous, PL becomes inhomogeneous at temperatures <75K, which we speculate is caused by the formation and subsequent dynamics of a polaronic exciton.},

keywords = {hybrid perovskite, molecular dynamics, perovskites, phonons},

pubstate = {published},

tppubtype = {article}

}

@article{Oh2016b,

title = {Mapping the Competition between Exciton Dissociation and Charge Transport in Organic Solar Cells},

author = {Soong Ju Oh and Jongbok Kim and Jeffrey M. Mativetsky and Yueh-Lin Loo and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsami.6b07810},

doi = {10.1021/acsami.6b07810},

year  = {2016},

date = {2016-10-03},

journal = {ACS Applied Materials & Interfaces},

volume = {8},

number = {42},

pages = {28743–28749},

abstract = {The competition between exciton dissociation and charge transport in organic solar cells comprising poly(3-hexylthiophene) [P3HT] and phenyl-C61-butyric acid methyl ester [PCBM] is investigated by correlated scanning confocal photoluminescence and photocurrent microscopies. Contrary to the general expectation that higher photoluminescence quenching is indicative of higher photocurrent, microscale mapping of bulk-heterojunction solar-cell devices shows that photoluminescence quenching and photocurrent can be inversely proportional to one another. To understand this phenomenon, we construct a model system by selectively laminating a PCBM layer onto a P3HT film to form a PCBM/P3HT planar junction on half of the device and a P3HT single junction on the other half. Upon thermal annealing to allow for interdiffusion of PCBM into P3HT, an inverse relationship between photoluminescence quenching and photocurrent is observed at the boundary between the PCBM/P3HT junction and P3HT layer. Incorporation of PCBM in P3HT works to increase photoluminescence quenching, consistent with efficient charge separation, but conductive atomic force microscopy measurements reveal that PCBM acts to decrease P3HT hole mobility, limiting the efficiency of charge transport. This suggests that photoluminescence-quenching measurements should be used with caution in evaluating new organic materials for organic solar cells.},

keywords = {organic solar cells, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2016,

title = {Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer},

author = {Tianshuo Zhao and Earl D. Goodwin and Jiacen Guo and Han Wang and Benjamin T. Diroll and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.6b03175},

doi = {10.1021/acsnano.6b03175},

year  = {2016},

date = {2016-09-20},

journal = {ACS Nano},

volume = {10},

number = {10},

pages = {9267–9273},

abstract = {Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI2-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency.},

keywords = {nanocrystal electronics, solar cells},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2016b,

title = {Building devices from colloidal quantum dots},

author = {Cherie R. Kagan and Efrat Lifshitz and Edward H. Sargent and Dmitri V. Talapin},

url = {https://science.sciencemag.org/content/353/6302/aac5523.full.pdf+html},

doi = {10.1126/science.aac5523},

year  = {2016},

date = {2016-08-26},

journal = {Science},

volume = {353},

number = {6302},

pages = {aac5523},

abstract = {Semiconductors, which are at the heart of electronics and optoelectronics, come with high demands on chemical purity and structural perfection. Alternatives to silicon technology are expected to combine the electronic and optical properties of inorganic semiconductors (high charge carrier mobility, precise n- and p-type doping, and the ability to engineer the band gap energy) with the benefits of additive device manufacturing: low cost, large area, and the use of solution-based fabrication techniques. Along these lines, colloidal semiconductor quantum dots (QDs), which are nanoscale crystals of analogous bulk semiconductor crystals, offer a powerful platform for device engineers. Colloidal QDs may be tailored in size, shape, and composition and their surfaces functionalized with molecular ligands of diverse chemistry. At the nanoscale (typically 2 to 20 nm), quantum and dielectric confinement effects give rise to the prized size-, shape-, and composition-tunable electronic and optical properties of QDs. Surface ligands enable the stabilization of QDs in the form of colloids, allowing their bottom-up assembly into QD solids. The physical properties of QD solids can be designed by selecting the characteristics of the individual QD building

blocks and by controlling the electronic communication between the QDs in the solid state. These

QD solids can be engineered with application-specific electronic and optoelectronic properties for the large-area, solution-based assembly

of devices.},

keywords = {nanocrystal electronics},

pubstate = {published},

tppubtype = {article}

}

@article{Semonin2016,

title = {Limits of Carrier Diffusion in n-Type and p-Type CH3NH3PbI3 Perovskite Single Crystals},

author = {Octavi E. Semonin and Giselle A. Elbaz and Daniel B. Straus and Trevor D. Hull and Daniel W. Paley and Arend M. van der Zande and James C. Hone and Ioannis Kymissis and Cherie R. Kagan and Xavier Roy and Jonathan S. Owen},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.6b01308},

doi = {10.1021/acs.jpclett.6b01308},

year  = {2016},

date = {2016-08-15},

journal = {The Journal of Physical Chemistry Letters},

volume = {7},

number = {17},

pages = {3510–3518},

abstract = {Using a combination of scanning photocurrent microscopy (SPCM) and time-resolved microwave conductivity (TRMC) measurements, we monitor the diffusion and recombination of photoexcited charges in CH3NH3PbI3 perovskite single crystals. The majority carrier type was controlled by growing crystals in the presence or absence of air, allowing the diffusion lengths of electrons (LDe–) and holes (LDh+) to be directly imaged with SPCM (LDe– = 10–28 μm, LDh+ = 27–65 μm). TRMC measurements reveal a photogenerated carrier mobility (μh + μe) of 115 ± 15 cm2 V–1 s–1 and recombination that depends on the excitation intensity. From the intensity dependence of the recombination kinetics and by accounting for carrier diffusion away from the point of photogeneration, we extract a second-order recombination rate constant (krad = 5 ± 3 × 10–10 cm3/s) that is consistent with the predicted radiative rate. First-order recombination at low photoexcited carrier density (knrp-type = 1.0 ± 0.3 × 105 s–1, knrn-type = 1.5 ± 0.3 × 105 s–1) is slower than that observed in CH3NH3PbI3 thin films or in GaAs single crystals with AlGaAs passivation layers. By accounting for the dilution of photogenerated carriers upon diffusion, and by combining SPCM and TRMC measurements, we resolve disagreement between previous reports of carrier diffusion length.},

keywords = {perovskites, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Urbas2016,

title = {Roadmap on optical metamaterials},

author = {Augustine M Urbas and Zubin Jacob and Luca Dal Negro and Nader Engheta and A D Boardman and P Egan and Alexander B Khanikaev and Vinod Menon and Marcello Ferrera and Nathaniel Kinsey and Clayton DeVault and Jongbum Kim and Vladimir Shalaev and Alexandra Boltasseva and Jason Valentine and Carl Pfeiffer and Anthony Grbic and Evgenii Narimanov and Linxiao Zhu and Shanhui Fan and Andrea Alù and Ekaterina Poutrina and Natalia M Litchinitser and Mikhail A Noginov and Kevin F MacDonald and Eric Plum and Xiaoying Liu and Paul F Nealey and Cherie R Kagan and Christopher B Murray and Dorota A Pawlak and Igor I Smolyaninov and Vera N Smolyaninova and Debashis Chanda},

url = {https://iopscience.iop.org/article/10.1088/2040-8978/18/9/093005},

doi = {10.1088/2040-8978/18/9/093005},

year  = {2016},

date = {2016-08-09},

journal = {Journal of Optics},

volume = {18},

number = {9},

pages = {093005},

abstract = {Optical metamaterials have redefined how we understand light in notable ways: from strong response to optical magnetic fields, negative refraction, fast and slow light propagation in zero index and trapping structures, to flat, thin and perfect lenses. Many rules of thumb regarding optics, such as μ = 1, now have an exception, and basic formulas, such as the Fresnel equations, have been expanded. The field of metamaterials has developed strongly over the past two decades. Leveraging structured materials systems to generate tailored response to a stimulus, it has grown to encompass research in optics, electromagnetics, acoustics and, increasingly, novel hybrid material responses. This roadmap is an effort to present emerging fronts in areas of optical metamaterials that could contribute and apply to other research communities. By anchoring each contribution in current work and prospectively discussing future potential and directions, the authors are translating the work of the field in selected areas to a wider community and offering an incentive for outside researchers to engage our community where solid links do not already exist.},

keywords = {optical metamaterials},

pubstate = {published},

tppubtype = {article}

}

@article{Goodwin2016,

title = {The effects of inorganic surface treatments on photogenerated carrier mobility and lifetime in PbSe quantum dot thin films},

author = {E.D. Goodwin and Daniel B. Straus and E. Ashley Gaulding and Christopher B. Murray and Cherie R. Kagan},

url = {https://www.sciencedirect.com/science/article/abs/pii/S0301010415002220},

doi = {10.1016/j.chemphys.2015.07.031},

year  = {2016},

date = {2016-06-01},

journal = {Chemical Physics },

volume = {471},

pages = {81-88},

abstract = {We used flash-photolysis, time-resolved microwave conductivity (TRMC) to probe the carrier mobility and lifetime in PbSe quantum dot (QD) thin films treated with solutions of the metal salts of Na2Se and PbCl2. The metal salt treatments tuned the Pb:Se stoichiometry and swept the Fermi energy throughout the QD thin film bandgap. A stoichiometric imbalance favoring excess Se heavily p-doped the QD thin film, shifted the Fermi energy toward the valence band, and yielded the highest TRMC mobility and lifetime. Introducing Pb first compensated the p-doping and shifted the Fermi level through mid-gap, decreasing the TRMC mobility. Further Pb addition created an excess of Pb, n-doped the QD thin film, moved the Fermi level to near the conduction band, and again increased the TRMC mobility. The increase in TRMC mobility as the Fermi energy was shifted toward the band edges by non-stoichiometry is consistent with the QD thin film density of states.},

keywords = {mobility, PbSe, quantum dots, surface modification, thin films, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Choi2016,

title = {Exploiting the colloidal nanocrystal library to construct electronic devices},

author = {Ji-Hyuk Choi and Han Wang and Soong Ju Oh and Taejong Paik and Pil Sung, Jo and Jinwoo Sung and Xingchen Ye and Tianshuo Zhao and Benjamin T. Diroll and Christopher B. Murray and Cherie R. Kagan},

url = {https://science.sciencemag.org/content/352/6282/205},

doi = {10.1126/science.aad0371},

year  = {2016},

date = {2016-04-08},

journal = {Science},

volume = {352},

number = {6282},

pages = {205-208},

abstract = {Synthetic methods produce libraries of colloidal nanocrystals with tunable physical properties by tailoring the nanocrystal size, shape, and composition. Here, we exploit colloidal nanocrystal diversity and design the materials, interfaces, and processes to construct all-nanocrystal electronic devices using solution-based processes. Metallic silver and semiconducting cadmium selenide nanocrystals are deposited to form high-conductivity and high-mobility thin-film electrodes and channel layers of field-effect transistors. Insulating aluminum oxide nanocrystals are assembled layer by layer with polyelectrolytes to form high–dielectric constant gate insulator layers for low-voltage device operation. Metallic indium nanocrystals are codispersed with silver nanocrystals to integrate an indium supply in the deposited electrodes that serves to passivate and dope the cadmium selenide nanocrystal channel layer. We fabricate all-nanocrystal field-effect transistors on flexible plastics with electron mobilities of 21.7 square centimeters per volt-second.},

keywords = {nanocrystal electronics},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2016c,

title = {At the Nexus of Food Security and Safety: Opportunities for Nanoscience and Nanotechnology},

author = {Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acsnano.6b01483},

doi = {10.1021/acsnano.6b01483},

year  = {2016},

date = {2016-03-22},

urldate = {2016-03-22},

volume = {10},

number = {3},

pages = {2985–2986},

abstract = {In a 2009 report, the United Nations Food and Agriculture Organization (UNFAO) presented the grand challenge “How to Feed the World in 2050”, as the number of people worldwide is estimated to grow to 9.1 billion.(1) This increase in population is largely centered in the developing world, and ensuring its food security is projected to require a 70% increase in food production. The needed increase in food production faces pressures from increasing urbanization and biofuel production and from climate change, which limit available land, water, biodiversity, and agriculture yield. In 2013, the UNFAO highlighted a “missed opportunity” in the quest for food security. One third of food produced (1.3 billion metric tons per year) is wasted in the supply chain; in the developing world, this is mostly due to poor quality, spoilage, and contamination, and in the developed world, this waste is largely due to package expiration and aesthetics.(2, 3) Food waste, in turn, impacts our environment, adding to the stress on the amount of available land and water for food production and creating greenhouse gases that affect world climate.},

keywords = {nanoscience, nanotechnology, sensors},

pubstate = {published},

tppubtype = {article}

}

@article{Yun2016,

title = {Alternate current magnetic property characterization of nonstoichiometric zinc ferrite nanocrystals for inductor fabrication via a solution based process},

author = {Hongseok Yun and Jungkwun Kim and Taejong Paik and Lingyao Meng and Pil Sung Jo and James M. Kikkawa and Cherie R. Kagan and Mark G. Allen and Christopher B. Murray},

url = {https://aip.scitation.org/doi/full/10.1063/1.4942865},

doi = {10.1063/1.4942865},

year  = {2016},

date = {2016-03-17},

journal = {Journal of Applied Physics},

volume = {119},

pages = {113901 },

abstract = {We investigate the ac magnetic behavior of solution processable, non-stoichiometric zinc ferrite nanocrystals with a series of sizes and zinc concentrations. Nearly monodisperse ZnxFe3−xO4 nanocrystals (x = 0–0.25) with an average size ranging from 7.4 nm to 13.8 nm are synthesized by using a solvothermal method. All the nanocrystals are in a superparamagnetic state at 300 K, which is confirmed by Superconductive Quantum Interference Device magnetometry. Due to the doping of non-magnetic Zn2+ into A site of ferrite, the saturation magnetization of nanocrystals increases as the size and Zn concentration increases. The ac magnetic permeability measurements at radio frequencies reveal that the real part of the magnetic permeability of similarly sized ferrite nanocrystals can be enhanced by almost twofold as the Zn2+ doping level increases from 0 to 0.25. The integration of 12.3 nm Zn0.25Fe2.75O4 nanocrystals into a toroidal inductor and a solenoid inductor prepared via a simple solution cast process yields a higher quality factors than air core inductors with the same geometries up to 5 MHz and 9 MHz, respectively, which is in the regime of the switching frequencies for the advanced integrated power converters.},

keywords = {magnetic nanocrystals, synthesis},

pubstate = {published},

tppubtype = {article}

}

@article{Kagan2015,

title = {Charge transport in strongly coupled quantum dot solids},

author = {Cherie R. Kagan and Christopher B. Murray },

url = {https://www.nature.com/articles/nnano.2015.247},

doi = {nnano.2015.247},

issn = {1748-3395},

year  = {2015},

date = {2015-11-09},

journal = {Nature Nanotechnology},

volume = {10},

pages = {1013–1026},

abstract = {The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Straus2015,

title = {Increased Carrier Mobility and Lifetime in CdSe Quantum Dot Thin Films through Surface Trap Passivation and Doping},

author = {Daniel B. Straus and E. D. Goodwin and E. Ashley Gaulding and Shin Muramoto and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/10.1021/acs.jpclett.5b02251},

doi = {10.1021/acs.jpclett.5b02251},

year  = {2015},

date = {2015-11-04},

journal = {The Journal of Physical Chemistry Letters},

volume = {6},

issue = {22},

pages = {4605–4609},

abstract = {Passivating surface defects and controlling the carrier concentration and mobility in quantum dot (QD) thin films is prerequisite to designing electronic and optoelectronic devices. We investigate the effect of introducing indium in CdSe QD thin films on the dark mobility and the photogenerated carrier mobility and lifetime using field-effect transistor (FET) and time-resolved microwave conductivity (TRMC) measurements. We evaporate indium films ranging from 1 to 11 nm in thickness on top of approximately 40 nm thick thiocyanate-capped CdSe QD thin films and anneal the QD films at 300 °C to densify and drive diffusion of indium through the films. As the amount of indium increases, the FET and TRMC mobilities and the TRMC lifetime increase. The increase in mobility and lifetime is consistent with increased indium passivating midgap and band-tail trap states and doping the films, shifting the Fermi energy closer to and into the conduction band.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Stinner2015,

title = {Flexible, High-Speed CdSe Nanocrystal Integrated Circuits},

author = {F. Scott Stinner and Yuming Lai and Daniel B. Straus and Benjamin T. Diroll and David K. Kim and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/acs.nanolett.5b03363},

doi = {10.1021/acs.nanolett.5b03363},

year  = {2015},

date = {2015-09-25},

journal = {Nano Letters},

volume = {15},

issue = {10},

pages = {7155–7160},

abstract = {We report large-area, flexible, high-speed analog and digital colloidal CdSe nanocrystal integrated circuits operating at low voltages. Using photolithography and a newly developed process to fabricate vertical interconnect access holes, we scale down device dimensions, reducing parasitic capacitances and increasing the frequency of circuit operation, and scale up device fabrication over 4 in. flexible substrates. We demonstrate amplifiers with ∼7 kHz bandwidth, ring oscillators with <10 μs stage delays, and NAND and NOR logic gates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Spectrally-Resolved Dielectric Functions of Solution-Cast Quantum Dot Thin Films},

author = {Benjamin T. Diroll and E. Ashley Gaulding and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/acs.chemmater.5b02953},

doi = {10.1021/acs.chemmater.5b02953},

year  = {2015},

date = {2015-08-28},

journal = {Chemistry of Materials},

volume = {27},

issue = {18},

pages = {6463–6469},

abstract = {Quantum confinement is the divergence, at small crystallite size, of the electronic structure of semiconductor nanocrystals, or quantum dots, from the properties of larger crystals of the same materials. Although the extinction properties of quantum dots in the dispersed state have been extensively studied, many applications for quantum dots require the formation of a solid material which nonetheless retains a size-dependent electronic structure. The complex index of refraction (or complex dielectric function), including the extinction coefficient, is critical information for interpretation of optoelectronic measurements and use of quantum dot solids in optoelectronic devices. Here, spectroscopic ellipsometry is used to provide an all-optical method to determine the thickness, complex index, and extinction coefficient of thin films made of quantum-confined materials through the visible and near-infrared spectral ranges. The characteristic, size-dependent spectral features in the absorption of monodisperse quantum dots are readily translated into spectral variations of the index of refraction. The complex indices of refraction of CdSe and PbS quantum dot solids depend strongly on quantum dot size and the processing conditions of the thin film, including ligand exchange and annealing. The dielectric functions of quantum dot solids are dominated by the fill fraction of quantum dots, with only secondary influence from interparticle interaction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cargnello2015,

title = {Substitutional doping in nanocrystal superlattices},

author = {Matteo Cargnello and Aaron C. Johnston-Peck and Benjamin T. Diroll and Eric Wong and Bianca Datta and Divij Damodhar and Vicky V. T. Doan-Nguyen and Andrew A. Herzing and Cherie R. Kagan and Christopher B. Murray },

url = {https://www.nature.com/articles/nature14872},

doi = {nature14872},

year  = {2015},

date = {2015-08-26},

journal = {Nature},

volume = {524},

pages = {450–453},

abstract = {Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic1,2, magnetic3,4, luminescent5,6, and catalytic7 properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Chen2015,

title = {Large-Area Nanoimprinted Colloidal Au Nanocrystal-Based Nanoantennas for Ultrathin Polarizing Plasmonic Metasurfaces},

author = {Wenxiang Chen and Mykhailo Tymchenko∥ and Prashanth Gopalan and Xingchen Ye and Yaoting Wu and Mingliang Zhang and Christopher B. Murray and Andrea Alu and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b02647},

doi = {10.1021/acs.nanolett.5b02647},

year  = {2015},

date = {2015-07-10},

urldate = {2015-07-10},

journal = {Nano Letters},

volume = {15},

number = {8},

issue = {8},

pages = {5254–5260},

abstract = {We report a low-cost, large-area fabrication process using solution-based nanoimprinting and compact ligand exchange of colloidal Au nanocrystals to define anisotropic, subwavelength, plasmonic nanoinclusions for optical metasurfaces. Rod-shaped, Au nanocrystal-based nanoantennas possess strong, localized, plasmonic resonances able to control polarization. We fabricate metasurfaces from rod-shaped nanoantennas tailored in size and spacing to demonstrate Au nanocrystal-based quarter-wave plates that operate with extreme bandwidths and provide high polarization conversion efficiencies in the near-to-mid infrared.},

keywords = {gold, nanocrystal, nanoimprinting, optical metamaterials, optical properties, plasmonic},

pubstate = {published},

tppubtype = {article}

}

@article{Oh2015,

title = {Selective p- and n-Doping of Colloidal PbSe Nanowires To Construct Electronic and Optoelectronic Devices},

author = {Soong Ju Oh and Chawit Uswachoke and Tianshuo Zhao and Ji-Hyuk Choi and Benjamin T. Diroll and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.5b02734},

doi = {10.1021/acsnano.5b02734},

year  = {2015},

date = {2015-06-12},

urldate = {2015-06-12},

journal = {ACS Nano},

volume = {9},

issue = {7},

pages = {7536–7544},

abstract = {We report the controlled and selective doping of colloidal PbSe nanowire arrays to define pn junctions for electronic and optoelectronic applications. The nanowires are remotely doped through their surface, p-type by exposure to oxygen and n-type by introducing a stoichiometric imbalance in favor of excess lead. By employing a patternable poly(methyl)methacrylate blocking layer, we define pn junctions in the nanowires along their length. We demonstrate integrated complementary metal-oxide semiconductor inverters in axially doped nanowires that have gains of 15 and a near full signal swing. We also show that these pn junction PbSe nanowire arrays form fast switching photodiodes with photocurrents that can be optimized in a gated-diode structure. Doping of the colloidal nanowires is compatible with device fabrication on flexible plastic substrates, promising a low-cost, solution-based route to high-performance nanowire devices.},

keywords = {doping, nanocrystal electronics, nanowires, PbSe},

pubstate = {published},

tppubtype = {article}

}

@article{Paik2015,

title = {Binary and Ternary Superlattices Self-Assembled from Colloidal Nanodisks and Nanorods},

author = {Taejong Paik and Benjamin T. Diroll and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/abs/10.1021/jacs.5b03234},

doi = {10.1021/jacs.5b03234},

year  = {2015},

date = {2015-04-30},

journal = {Journal of the American Chemical Society},

volume = {137},

number = {20},

pages = {6662–6669},

abstract = {Self-assembly of multicomponent anisotropic nanocrystals with controlled orientation and spatial distribution allows the design of novel metamaterials with unique shape- and orientation-dependent collective properties. Although many phases of binary structures are theoretically proposed, the examples of multicomponent assemblies, which are experimentally realized with colloidal anisotropic nanocrystals, are still limited. In this report, we demonstrate the formation of binary and ternary superlattices from colloidal two-dimensional LaF3 nanodisks and one-dimensional CdSe/CdS nanorods via liquid interfacial assembly. The colloidal nanodisks and nanorods are coassembled into AB-, AB2-, and AB6-type binary arrays determined by their relative size ratio and concentration to maximize their packing density. The position and orientation of anisotropic nanocrystal building blocks are tightly controlled in the self-assembled binary and ternary lattices. The macroscopic orientation of the superlattices is further tuned by changing the liquid subphase used for self-assembly, resulting in the formation of lamellar-type binary liquid crystalline superlattices. In addition, we demonstrate a novel ternary superlattice self-assembled from two different sizes of nanodisks and a nanorod, which offers the unique opportunity to design multifunctional metamaterials.},

keywords = {colloids, liquid crystals, nanodisks, nanorods, self-assembly, superlattices},

pubstate = {published},

tppubtype = {article}

}

@article{Gaulding2015,

title = {Deposition of Wafer-Scale Single-Component and Binary Nanocrystal Superlattice Thin Films Via Dip-Coating},

author = {E. Ashley Gaulding and Benjamin T. Diroll and E. D. Goodwin and Zachary J. Vrtis and Cherie R. Kagan and Christopher B. Murray},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201405575},

doi = {10.1002/adma.201405575},

year  = {2015},

date = {2015-03-27},

journal = {Advanced Materials},

volume = {27},

issue = {18},

pages = {2846-2851},

abstract = {Single-component and binary nanocrystal superlattices are assembled over wafer-scale areas using the dip-coating method. A series of measurements are performed to confirm superlattice assembly. This study demonstrates the versatility of dip-coating in depositing a diverse set of nanocrystal materials and superlattice structures, while combining large-area deposition with nanoscale control.},

keywords = {nanocrystal, superlattices, thin films},

pubstate = {published},

tppubtype = {article}

}

@article{Diroll2015,

title = {Smectic Nanorod Superlattices Assembled on Liquid Subphases: Structure, Orientation, Defects, and Optical Polarization},

author = {Benjamin T. Diroll and Nicholas J. Greybush and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.chemmater.5b00355},

doi = {10.1021/acs.chemmater.5b00355},

year  = {2015},

date = {2015-03-10},

urldate = {2015-03-10},

journal = {Chemistry of Materials},

volume = {27},

issue = {8},

pages = {2998–3008},

abstract = {Directing the orientation of anisotropic nanocrystal assemblies is important for harnessing the shape-dependent properties of nanocrystal solids in devices. We control the orientation of smectic B superlattices of CdSe/CdS dot-in-rod nanocrystals through assembly on different polar interfaces and quantify the superlattice orientation through correlated small- and wide-angle grazing-incidence diffraction. Small-angle scattering is used to determine the phase of the nanorod superlattices and their preferential growth directions from the subphase. Wide-angle diffraction is used to quantify the orientations of nanorods within the superlattices and with respect to the substrate. Not only are the nanorod long axes aligned within the structures, but truncation of the short axes also coaligns the crystal axes of the nanorods with the zone axes in assembled smectic B crystals. Three dimensional orientational alignment of nanocrystals in superlattices is highly desirable in device applications. Depending on the subphase used for self-assembly, the films range from nearly quantitative vertical to horizontal alignment. Controlling for other variables, we find that the surface tension of the subphase is strongly correlated with the orientational ordering of the nanorod superlattices. The microstructure of nanorod superlattices shows many classic defects of atomic and liquid crystalline systems. The nature of defect structures supports a mechanism of nuclei formation on the subphase–solvent interface rather than in solution. Last, we demonstrate the relationship between optical absorption polarization and superlattice structure using correlated optical spectroscopy and electron microscopy.},

keywords = {defects, liquid crystals, nanorods, optical properties, self-assembly, superlattices},

pubstate = {published},

tppubtype = {article}

}

@article{Turk2015,

title = {Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies},

author = {Michael E. Turk and Patrick M. Vora and Aaron T. Fafarman and Benjamin T. Diroll and Christopher B. Murray and Cherie R. Kagan and James M. Kikkawa},

url = {https://pubs.acs.org/doi/full/10.1021/nn505862g},

doi = {10.1021/nn505862g},

year  = {2015},

date = {2015-01-30},

urldate = {2015-01-30},

journal = {ACS Nano},

volume = {9},

number = {2},

pages = {1440-1447},

abstract = {We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature optical properties of CdSe quantum dot solids after exchanging native aliphatic ligands for thiocyanate and subsequent thermal annealing. In contrast to trends established at room temperature, our data show that at low temperature the band-edge absorptive bleach is dominated by 1S3/2h hole occupation in the quantum dot interior. We find that our ligand treatments, which bring enhanced interparticle coupling, lead to faster surface state electron trapping, a greater proportion of surface-related photoluminescence, and decreased band-edge photoluminescence lifetimes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kovalenko2015,

title = {Prospects of Nanoscience with Nanocrystals},

author = {Maksym V. Kovalenko and Liberato Manna and Andreu Cabo and Zeger Hens and Dmitri V. Talapin and Cherie R. Kagan and Victor I. Klimov and Andrey L. Rogach and Peter Reiss and Delia J. Milliron and Philippe Guyot-Sionnnest and Gerasimos Konstantatos and Wolfgang J. Parak and Taeghwan Hyeon and Brian A. Korgel and Christopher B. Murray and Wolfgang Heiss},

url = {https://pubs.acs.org/doi/full/10.1021/nn506223h},

doi = {10.1021/nn506223h},

year  = {2015},

date = {2015-01-22},

journal = {ACS Nano},

volume = {9},

number = {2},

pages = {1012–1057},

abstract = {Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.},

keywords = {colloids, nanocrystal, nanocrystal electronics},

pubstate = {published},

tppubtype = {article}

}

@article{Saudari2015,

title = {Electron and hole transport in ambipolar, thin film pentacene transistors },

author = {Sangameshwar R. Saudari and Cherie R. Kagan},

url = {https://pubs.aip.org/aip/jap/article/117/3/035501/167833/Electron-and-hole-transport-in-ambipolar-thin-film},

doi = {10.1063/1.4906145},

year  = {2015},

date = {2015-01-21},

journal = {Journal of Applied Physics},

volume = {117},

pages = {035501 },

abstract = {Solution-processed, ambipolar, thin-film pentacene field-effect transistors were employed to study both electron and hole transport simultaneously in a single, organic solid-state device. Electron and hole mobilities were extracted from the respective unipolar saturation regimes and show thermally activated behavior and gate voltage dependence. We fit the gate voltage dependent saturation mobility to a power law to extract the characteristic Meyer-Neldel (MN) energy, a measure of the width of the exponential distribution of localized states extending into the energy gap of the organic semiconductor. The MN energy is ∼78 and ∼28 meV for electrons and holes, respectively, which reflects a greater density of localized tail states for electrons than holes. This is consistent with the lower measured electron than hole mobility. For holes, the well-behaved linear regime allows for four-point probe measurement of the contact resistance independent mobility and separate characterization of the width of the localized density of states, yielding a consistent MN energy of 28 meV.},

keywords = {organic compounds, transistors, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Cativo2014,

title = {Air–Liquid Interfacial Self-Assembly of Conjugated Block Copolymers into Ordered Nanowire Arrays},

author = {Ma. Helen M. Cativo and David K. Kim and Robert A. Riggleman and Kevin G. Yager and Stephen S. Nonnenmann and Huikuan Chao and Dawn A. BonnellvCharles T. Black and Cherie R. Kagan and So-Jung Park},

url = {https://pubs.acs.org/doi/full/10.1021/nn505871b},

doi = {10.1021/nn505871b},

year  = {2014},

date = {2014-12-08},

urldate = {2014-12-08},

journal = {ACS Nano},

volume = {8},

number = {12},

pages = {12755–12762},

abstract = {The ability to control the molecular packing and nanoscale morphology of conjugated polymers is important for many of their applications. Here, we report the fabrication of well-ordered nanoarrays of conjugated polymers, based on the self-assembly of conjugated block copolymers at the air–liquid interface. We demonstrate that the self-assembly of poly(3-hexylthiophene)-block-poly(ethylene glycol) (P3HT-b-PEG) at the air–water interface leads to large-area free-standing films of well-aligned P3HT nanowires. Block copolymers with high P3HT contents (82–91%) formed well-ordered nanoarrays at the interface. The fluidic nature of the interface, block copolymer architecture, and rigid nature of P3HT were necessary for the formation of well-ordered nanostructures. The free-standing films formed at the interface can be readily transferred to arbitrary solid substrates. The P3HT-b-PEG films are integrated in field-effect transistors and show orders of magnitude higher charge carrier mobility than spin-cast films, demonstrating that the air–liquid interfacial self-assembly is an effective thin film fabrication tool for conjugated block copolymers.},

keywords = {copolymers, interfaces, organic compounds, self-assembly, self-organization, thin films},

pubstate = {published},

tppubtype = {article}

}

@article{Diroll2014,

title = {X-ray Mapping of Nanoparticle Superlattice Thin Films},

author = {Benjamin T. Diroll and Vicky V. T. Doan-Nguyen and Matteo Cargnello and E. Ashley Gaulding and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/nn5062832},

doi = {10.1021/nn5062832},

year  = {2014},

date = {2014-12-05},

urldate = {2014-12-05},

journal = {ACS Nano},

volume = {8},

number = {12},

pages = {12843–12850},

abstract = {We combine grazing-incidence and transmission small-angle X-ray diffraction with electron microscopy studies to characterize the structure of nanoparticle films with long-range order. Transmission diffraction is used to collect in-plane diffraction data from single grains and locally aligned nanoparticle superlattice films. Systematic mapping of samples can be achieved by translating the sample in front of the X-ray beam with a spot size selected to be on the order of superlattice grain features. This allows a statistical determination of superlattice grain size and size distribution over much larger areas than typically accessible with electron microscopy. Transmission X-ray measurements enables spatial mapping of the grain size, orientation, uniformity, strain, or crystal projections and polymorphs. We expand this methodology to binary nanoparticle superlattice and nanorod superlattice films. This study provides a framework for characterization of nanoparticle superlattices over large areas which complements or expands microstructure information from real-space imaging.},

keywords = {nanocrystal, nanoparticle assembly, superlattices, thin films},

pubstate = {published},

tppubtype = {article}

}

@article{Goodwin2014,

title = {Effects of Post-Synthesis Processing on CdSe Nanocrystals and Their Solids: Correlation between Surface Chemistry and Optoelectronic Properties},

author = {E. D. Goodwin and Benjamin T. Diroll and Soong Ju Oh and Taejong Paik and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/jp5076912},

doi = {10.1021/jp5076912},

year  = {2014},

date = {2014-10-21},

urldate = {2014-10-21},

journal = {The Journal of Physical Chemistry C},

volume = {118},

number = {46},

pages = {27097–27105},

abstract = {In this work, we report the effects on CdSe nanocrystal (NC) surface chemistry of acetone and methanol when used as the antisolvents for NC washing and as the solvents for ligand exchange of NC solids with ammonium thiocyanate (NH4SCN). We find that NCs washed with methanol have significantly fewer remaining organic ligands and lower photoluminescence quantum yield than those washed with acetone. When used as the ligand exchange solvent, methanol leaves more organic ligands and introduces fewer bound thiocyanates on the NC surface than when acetone is used. We demonstrate the effect of these different surface chemistries on NC solid optoelectronic properties through photoconductivity measurements, showing a greater photocurrent in NC solids with greater organic ligand coverage. We also show that NC washing with methanol or ligand exchange with NH4SCN in methanol removes a significant number of surface Cd atoms from the NCs, creating Cd vacancies that act as traps for recombination. Independent of the wash and exchange process, the NC surface may be repaired by introducing CdCl2 to the NC surface, enhancing the measured photocurrent.},

keywords = {CdSe, nanocrystal, nanocrystal electronics, optical properties, optical stability, semiconductors, surface modification, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Oh2014,

title = {Engineering Charge Injection and Charge Transport for High Performance PbSe Nanocrystal Thin Film Devices and Circuits},

author = {Soong Ju Oh and Zhuqing Wang and Nathaniel E. Berry and Ji-Hyuk Choi and Tianshuo Zhao and E. Ashley Gaulding and Taejong Paik and Yuming Lai and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/nl502491d},

doi = {10.1021/nl502491d},

year  = {2014},

date = {2014-10-09},

journal = {Nano Letters},

volume = {14},

number = {11},

pages = {6210–6216},

abstract = {We study charge injection and transport in PbSe nanocrystal thin films. By engineering the contact metallurgy and nanocrystal ligand exchange chemistry and surface passivation, we demonstrate partial Fermi-level pinning at the metal–nanocrystal interface and an insulator-to-metal transition with increased coupling and doping, allowing us to design high conductivity and mobility PbSe nanocrystal films. We construct complementary nanocrystal circuits from n-type and p-type transistors realized from a single nanocrystal material by selecting the contact metallurgy.},

keywords = {doping, interfaces, ligand exchange, mobility, nanocrystal, nanocrystal electronics, PbSe, surface interactions, surface modification, thin films, transistors, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Lai2014,

title = {Low-Frequency (1/f) Noise in Nanocrystal Field-Effect Transistors},

author = {Yuming Lai and Haipeng Li and David K. Kim and Benjamin T. Diroll and Christopher B. Murray and Cherie R. Kagan},

url = {https://pubs.acs.org/doi/full/10.1021/nn504303b},

doi = {10.1021/nn504303b},

year  = {2014},

date = {2014-09-07},

journal = {ACS NAno},

volume = {8},

number = {9},

pages = {9664–9672},

abstract = {We investigate the origins and magnitude of low-frequency noise in high-mobility nanocrystal field-effect transistors and show the noise is of 1/f-type. Sub-band gap states, in particular, those introduced by nanocrystal surfaces, have a significant influence on the 1/f noise. By engineering the device geometry and passivating nanocrystal surfaces, we show that in the linear and saturation regimes the 1/f noise obeys Hooge’s model of mobility fluctuations, consistent with transport of a high density of accumulated carriers in extended electronic states of the NC thin films. In the subthreshold regime, the Fermi energy moves deeper into the mobility gap and sub-band gap trap states give rise to a transition to noise dominated by carrier number fluctuations as described in McWhorter’s model. CdSe nanocrystal field-effect transistors have a Hooge parameter of 3 × 10–2, comparable to other solution-deposited, thin-film devices, promising high-performance, low-cost, low-noise integrated circuitry.},

keywords = {CdSe, defects, mobility, nanocrystal, nanocrystal electronics, surface interactions, surface modification, transistors},

pubstate = {published},

tppubtype = {article}

}

@article{Turk2014,

title = {Gate-Induced Carrier Delocalization in Quantum Dot Field Effect Transistors},

author = {Michael E. Turk and Ji-Hyuk Choi and Soong Ju Oh and Aaron T. Fafarman and Benjamin T. Diroll and Christopher B. Murray and Cherie R. Kagan and James M. Kikkawa},

url = {https://pubs.acs.org/doi/full/10.1021/nl5029655},

doi = {10.1021/nl5029655},

year  = {2014},

date = {2014-08-29},

journal = {Nano Letters},

volume = {14},

number = {10},

pages = {5948–5952},

abstract = {We study gate-controlled, low-temperature resistance and magnetotransport in indium-doped CdSe quantum dot field effect transistors. We show that using the gate to accumulate electrons in the quantum dot channel increases the “localization product” (localization length times dielectric constant) describing transport at the Fermi level, as expected for Fermi level changes near a mobility edge. Our measurements suggest that the localization length increases to significantly greater than the quantum dot diameter.},

keywords = {CdSe, magnetotransport, nanocrystal, nanocrystal electronics, quantum dots, transistors, transport},

pubstate = {published},

tppubtype = {article}

}

@article{Diroll2014b,

title = {Synthesis of N-Type Plasmonic Oxide Nanocrystals and the Optical and Electrical Characterization of their Transparent Conducting Films},

author = {Benjamin T. Diroll and Thomas R. Gordon and E. Ashley Gaulding and Dahlia R. Klein and Taejong Paik and Hyeong Jin Yun and E.D. Goodwin and Divij Damodhar and Cherie R. Kagan and Christopher B. Murray},

url = {https://pubs.acs.org/doi/full/10.1021/cm5018823},

doi = {10.1021/cm5018823},

year  = {2014},

date = {2014-07-18},

journal = {Chemistry of Materials},

volume = {26},

number = {15},

pages = {4579–4588},

abstract = {We present a general synthesis for a family of n-type transparent conducting oxide nanocrystals through doping with aliovalent cations. These monodisperse nanocrystals exhibit localized surface plasmon resonances tunable in the mid- and near-infrared with increasing dopant concentration. We employ a battery of electrical measurements to demonstrate that the plasmonic resonance in isolated particles is consistent with the electronic properties of oxide nanocrystal thin films. Hall and Seebeck measurements show that the particles form degenerately doped n-type solids with free electron concentrations in the range of 1019 to 1021 cm–3. These heavily doped oxide nanocrystals are used as the building blocks of conductive, n-type thin films with high visible light transparency.},

keywords = {doping, nanocrystal, nanocrystal electronics, optical properties, plasmonic, thin films},

pubstate = {published},

tppubtype = {article}

}