@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{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{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{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{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{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{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{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{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}

}