@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{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{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{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{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{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{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{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{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{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{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{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{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{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}

}