@article{Castronovo2025,

title = {Ultrafast Switching of Whispering Gallery Modes in Quantum Dot Superparticles},

author = {Pietro Castronovo and Marco Reale and Susan A. Rigter and Cherie R. Kagan and Christopher B. Murray and Salvatore Lorenzo and Erik C. Garnett and Peter Schall and Emanuele Marino and Alice Sciortino and Fabrizio Messina},

doi = {https://doi.org/10.1021/acs.nanolett.5c00643},

year  = {2025},

date = {2025-02-24},

urldate = {2025-02-24},

journal = {Nano Letters},

keywords = {nanocrystal, pump-probe, quantum dots, spectroscopy, superparticle},

pubstate = {published},

tppubtype = {article}

}

@article{Panfil2025,

title = {Room-temperature quantum emission from CuZn-VS defects in ZnS:Cu colloidal nanocrystals},

author = {Yossef E. Panfil and Sarah M. Thompson and Gary Chen and Jonah J. Ng and Cherie R. Kagan and Lee C. Bassett},

doi = {https://doi.org/10.48550/arXiv.2501.11812},

year  = {2025},

date = {2025-01-21},

journal = {arXiv},

keywords = {colloids, defects, nanocrystal, quantum information science, spectroscopy},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Shulevitz2024,

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://pubs.acs.org/doi/10.1021/acsanm.4c01699},

doi = {10.1021/acsanm.4c01699},

year  = {2024},

date = {2024-06-29},

urldate = {2023-12-04},

journal = {ACS Applied Nano Materials},

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 = {published},

tppubtype = {article}

}

@article{Xu2024,

title = {Chemically Driven Sintering of Colloidal Cu Nanocrystals for Multiscale Electronic and Optical Devices},

author = {Jun Xu and Tianshuo Zhao and Anne-Marie Zaccarin and Xingyu Du and Shengsong Yang and Yifan Ning and Qiwen Xiao and Shobhita Kramadhati and Yun Chang Choi and Christopher B. Murray and Roy H. Olsson III and Cherie R. Kagan},

url = {https://pubs-acs-org.proxy.library.upenn.edu/doi/10.1021/acsnano.4c02007},

year  = {2024},

date = {2024-06-25},

urldate = {2024-06-25},

journal = {ACS Nano},

abstract = {Emerging applications of Internet of Things (IoT) technologies in smart health, home, and city, in agriculture and environmental monitoring, and in transportation and manufacturing require materials and devices with engineered physical properties that can be manufactured by low-cost and scalable methods, support flexible forms, and are biocompatible and biodegradable. Here, we report the fabrication and device integration of low-cost and biocompatible/biodegradable colloidal Cu nanocrystal (NC) films through room temperature, solution-based deposition, and sintering, achieved via chemical exchange of NC surface ligands. Treatment of organic-ligand capped Cu NC films with solutions of shorter, environmentally benign, and noncorrosive inorganic reagents, namely, SCN– and Cl–, effectively removes the organic ligands, drives NC grain growth, and limits film oxidation. We investigate the mechanism of this chemically driven sintering by systemically varying the Cu NC size, ligand reagent, and ligand treatment time and follow the evolution of their structure and electrical and optical properties. Cl–-treated, 4.5 nm diameter Cu NC films yield the lowest DC resistivity, only 3.2 times that of bulk Cu, and metal-like dielectric functions at optical frequencies. We exploit the high conductivity of these chemically sintered Cu NC films and, in combination with photo- and nanoimprint-lithography, pattern multiscale structures to achieve high-Q radio frequency (RF) capacitive sensors and near-infrared (NIR) resonant optical metasurfaces.},

keywords = {energy devices, IOT, IoT4Ag, nanocrystal, nanocrystal electronics},

pubstate = {published},

tppubtype = {article}

}

@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{Ning2024,

title = {Dynamic Nanocrystal Superlattices with Thermally Triggerable Lubricating Ligands},

author = {Yifan Ning and Shengsong Yang and Dai-Bei Yang and Yi-Yu Cai and Jun Xu and Ruipeng Li and Yugang Zhang and Cherie R. Kagan and Jeffery G. Saven and Christopher B. Murray},

url = {https://pubs-acs-org.proxy.library.upenn.edu/doi/full/10.1021/jacs.3c10706},

doi = {10.1021/jacs.3c10706},

year  = {2024},

date = {2024-01-31},

urldate = {2024-01-31},

journal = {Journal of the American Chemical Society},

volume = {146},

number = {6},

pages = {3785-3795},

abstract = {The size-dependent and collective physical properties of nanocrystals (NCs) and their self-assembled superlattices (SLs) enable the study of mesoscale phenomena and the design of metamaterials for a broad range of applications. However, the limited mobility of NC building blocks in dried NCSLs often hampers the potential for employing postdeposition methods to produce high-quality NCSLs. In this study, we present tailored promesogenic ligands that exhibit a lubricating property akin to thermotropic liquid crystals. The lubricating ability of ligands is thermally triggerable, allowing the dry solid NC aggregates deposited on the substrates with poor ordering to be transformed into NCSLs with high crystallinity and preferred orientations. The interplay between the dynamic behavior of NCSLs and the molecular structure of the ligands is elucidated through a comprehensive analysis of their lubricating efficacy using both experimental and simulation approaches. Coarse-grained molecular dynamic modeling suggests that a shielding layer from mesogens prevents the interdigitation of ligand tails, facilitating the sliding between outer shells and consequently enhancing the mobility of NC building blocks. The dynamic organization of NCSLs can also be triggered with high spatial resolution by laser illumination. The principles, kinetics, and utility of lubricating ligands could be generalized to unlock stimuli-responsive metamaterials from NCSLs and contribute to the fabrication of NCSLs.},

keywords = {ligands, nanocrystal, superlattices},

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{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{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{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{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{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{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{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{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}

}