Semiconductor Nanocrystal

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Min Xiao - One of the best experts on this subject based on the ideXlab platform.

  • energy transfer of biexcitons in a single Semiconductor Nanocrystal
    Nano Letters, 2016
    Co-Authors: Xiangnan Huang, Chunfeng Zhang, Xiaoyong Wang, Min Xiao
    Abstract:

    Photoluminescence (PL) decay dynamics of multiexcitons in Semiconductor Nanocrystals (NCs) are dominated by the nonradiative Auger effect, making it difficult to explore their basic optical processes such as radiative recombination and energy transfer (ET). Here we constructed a single-particle ET system by attaching several acceptor dyes to the surface of a donor NC to study the ET of biexcitons at a single-NC level. By comparing the single-exciton and biexciton PL lifetimes of the same donor NC before and after the acceptor dyes were bleached, their respective ET lifetimes could be reliably extracted without the Auger influence. From statistical measurements on a large number of single ET particles, the average ET rate ratio between biexcitons and single excitons was estimated to be larger than four, and the same scaling rule could be naturally extended to their radiative rates.

  • carrier multiplication in a single Semiconductor Nanocrystal
    Physical Review Letters, 2016
    Co-Authors: Chunyang Yin, Chunfeng Zhang, Xiaoyong Wang, Brahim Lounis, Min Xiao
    Abstract:

    To confirm the existence of the carrier multiplication (CM) effect and estimate its generation efficiency of multiple excitons in Semiconductor Nanocrystals (NCs), it is imperative to completely exclude the false contribution of charged excitons from the measured CM signal. Here we place single CdSe NCs above an aluminum film and successfully resolve their UV-excited photoluminescence (PL) time trajectories where the true and false CM signals are contained in the blinking "on" and "off" levels, respectively. By analyzing the PL dynamics of the on-level photons, an average CM efficiency of ∼20.2% can be reliably estimated when the UV photon energy is ∼2.46 times the NC energy gap.

  • charged two exciton emission from a single Semiconductor Nanocrystal
    Applied Physics Letters, 2015
    Co-Authors: Qiang Zhang, Chunfeng Zhang, Xiaoyong Wang, Min Xiao
    Abstract:

    Here, we study the photoluminescence (PL) time trajectories of single CdSe/ZnS Nanocrystals (NCs) as a function of the laser excitation power. At the low laser power, the PL intensity of a single NC switches between the “on” and “off” levels arising from the neutral and positively charged single excitons, respectively. With the increasing laser power, an intermediate “grey” level is formed due to the optical emission from a charged multiexciton state composed of two excitons and an extra electron. Both the inter-photon correlation and the PL decay measurements demonstrate that lifetime-indistinguishable photon pairs are emitted from this negatively charged two-exciton state.

Paul A Alivisatos - One of the best experts on this subject based on the ideXlab platform.

  • enhanced Semiconductor Nanocrystal conductance via solution grown contacts
    Nano Letters, 2009
    Co-Authors: Matthew T Sheldon, Taleb Mokari, Lin-wang Wang, Paulemile Trudeau, Paul A Alivisatos
    Abstract:

    We report a 100,000-fold increase in the conductance of individual CdSe nanorods when they are electrically contacted via direct solution phase growth of Au tips on the nanorod ends. Ensemble UV-Vis and X-Ray photoelectron spectroscopy indicate this enhancement does not result from alloying of the nanorod. Rather, low temperature tunneling and high temperature (250-400 K) thermionic emission across the junction at the Au contact reveal a 75percent lower interface barrier to conduction compared to a control sample. We correlate this barrier lowering with the electronic structure at the Au-CdSe interface. Our results emphasize the importance of Nanocrystal surface structure for robust device performance and the advantage of this contact method.

  • mechanistic study of precursor evolution in colloidal group ii vi Semiconductor Nanocrystal synthesis
    Journal of the American Chemical Society, 2007
    Co-Authors: Haitao Liu, And Jonathan S Owen, Paul A Alivisatos
    Abstract:

    The molecular mechanism of precursor evolution in the synthesis of colloidal group II−VI Semiconductor Nanocrystals was studied using 1H, 13C, and 31P NMR spectroscopy and mass spectrometry. Tri-n-butylphosphine chalcogenides (TBPE; E = S, Se, Te) react with an oleic acid complex of cadmium or zinc (M−OA; M = Zn, Cd) in a noncoordinating solvent (octadecene (ODE), n-nonane-d20, or n-decane-d22), affording ME Nanocrystals, tri-n-butylphosphine oxide (TBPO), and oleic acid anhydride ((OA)2O). Likewise, the reaction between trialkylphosphine selenide and cadmium n-octadecylphosphonic acid complex (Cd−ODPA) in tri-n-octylphosphine oxide (TOPO) produces CdSe Nanocrystals, trialkylphosphine oxide, and anhydrides of n-octadecylphosphonic acid. The disappearance of tri-n-octylphosphine selenide in the presence of Cd−OA and Cd−ODPA can be fit to a single-exponential decay (kobs = (1.30 ± 0.08) × 10-3 s-1, Cd−ODPA, 260 °C, and kobs = (1.51 ± 0.04) × 10-3 s-1, Cd−OA, 117 °C). The reaction approaches completion at 70...

  • mechanistic study of precursor evolution in colloidal group ii vi Semiconductor Nanocrystal synthesis
    Journal of the American Chemical Society, 2007
    Co-Authors: Haitao Liu, And Jonathan S Owen, Paul A Alivisatos
    Abstract:

    The molecular mechanism of precursor evolution in the synthesis of colloidal group II−VI Semiconductor Nanocrystals was studied using 1H, 13C, and 31P NMR spectroscopy and mass spectrometry. Tri-n-butylphosphine chalcogenides (TBPE; E = S, Se, Te) react with an oleic acid complex of cadmium or zinc (M−OA; M = Zn, Cd) in a noncoordinating solvent (octadecene (ODE), n-nonane-d20, or n-decane-d22), affording ME Nanocrystals, tri-n-butylphosphine oxide (TBPO), and oleic acid anhydride ((OA)2O). Likewise, the reaction between trialkylphosphine selenide and cadmium n-octadecylphosphonic acid complex (Cd−ODPA) in tri-n-octylphosphine oxide (TOPO) produces CdSe Nanocrystals, trialkylphosphine oxide, and anhydrides of n-octadecylphosphonic acid. The disappearance of tri-n-octylphosphine selenide in the presence of Cd−OA and Cd−ODPA can be fit to a single-exponential decay (kobs = (1.30 ± 0.08) × 10-3 s-1, Cd−ODPA, 260 °C, and kobs = (1.51 ± 0.04) × 10-3 s-1, Cd−OA, 117 °C). The reaction approaches completion at 70...

  • Semiconductor Nanocrystal quantum dots on single crystal Semiconductor substrates high resolution transmission electron microscopy
    Nano Letters, 2005
    Co-Authors: A Konkar, A Madhukar, Steven M Hughes, Paul A Alivisatos
    Abstract:

    We report on high-resolution transmission electron microscope structural studies of InAs colloidal Semiconductor Nanocrystal quantum dots (NCQDs) on ultrathin GaAs (001) Semiconductor single-crystal substrates. We employ a benign method for preparing electron transparent specimens that is suitable for the study of such fragile samples. The image contrast comprises contributions from electron scattering from both the NCs and the GaAs substrate. Long-term electron exposure studies reveal different damage mechanisms operative in the Nanocrystals and the substrate.

  • integrated Semiconductor Nanocrystal and epitaxical nanostructure systems structural and optical behavior
    Nano Letters, 2005
    Co-Authors: A Madhukar, A Konkar, Steven M Hughes, Yi Zhang, Paul A Alivisatos
    Abstract:

    Integration of Semiconductor epitaxical nanostructures and Nanocrystals into two classes of quantum structures, uncovered adsorbed Nanocrystals or buried via epitaxical overgrowth, is successfully demonstrated through structural and optical studies. The combination InGaAs/GaAs epitaxical structures and InAs Nanocrystals is employed as a vehicle with the functional aim of exploiting the well developed optoelectronic communication technology based on the former with the biochemical and biomedical applications for which the latter are well suited.

Andrey L Rogach - One of the best experts on this subject based on the ideXlab platform.

  • Materials aspects of Semiconductor Nanocrystals for optoelectronic applications
    Materials Horizons, 2017
    Co-Authors: Stephen V Kershaw, Lihong Jing, Xiaodan Huang, Mingyuan Gao, Andrey L Rogach
    Abstract:

    Semiconductor Nanocrystal quantum dots are at last starting to emerge in commercial applications such as flat panel displays. Meanwhile, they are also showing seriously attractive performance levels in other types of optoelectronic devices. This maturing has been driven to a large degree by a deep level of understanding of materials related aspects of Semiconductor Nanocrystals themselves and in combination with other materials in the form of composite films to build optoelectronic components. We examine the synthetic and post synthetic chemical strategies that have led to Semiconductor quantum dot structures with robust and strong device performance, and review the current work-in-progress as well as longer term developments in the areas of photovoltaics and photoelectrochemical cells, photodetectors, solid state lighting, photocatalysts, and sensing applications.

  • Semiconductor Nanocrystal quantum dots as solar cell components and photosensitizers material charge transfer and separation aspects of some device topologies
    Journal of Physical Chemistry Letters, 2011
    Co-Authors: Frederik Hetsch, Xueqing Xu, Hongkang Wang, Stephen V Kershaw, Andrey L Rogach
    Abstract:

    Nanocrystalline wide band gap Semiconductors photosensitized with Semiconductor Nanocrystal quantum dots have recently attracted increasing attention as promising photovoltaic devices. This Perspective addresses several issues related to the choice of Nanocrystal materials for quantum dot sensitized solar cells, the methods of quantum dot deposition on mesoporous wide band gap Semiconductor layers, and combinations of quantum dots and classical ruthenium dyes as panchromatic sensitizers. It further discusses charge transfer kinetics and electron recombination in quantum dot sensitized solar cells. An alternate emerging concept, a structure combining the latter with a quantum dot based Schottky junction solar cell, is also briefly reviewed. Together these areas offer ample scope for improvements making use of the specific advantages of Semiconductor Nanocrystals.

  • energetic disorder limits energy transfer in Semiconductor Nanocrystal dna dye conjugates
    Applied Physics Letters, 2009
    Co-Authors: K D Becker, Andrey L Rogach, Jochen Feldmann, Dmitri V Talapin, John M Lupton
    Abstract:

    We demonstrate the influence of spectral linewidths of individual donor-acceptor couples on energy transfer efficiency in Semiconductor Nanocrystal–DNA–organic dye conjugates. Temperature-dependent single molecule and ensemble spectroscopy data are analyzed using the Forster theory within the macroscopic and microscopic approaches. The results obtained evidence on the importance of the spectral overlap between emission of a single donor and absorption of a single acceptor in its close vicinity, which determines the microscopic resonance and transfer efficiency between individual neighbors. This realization poses important implications on the applicability of ensemble spectral overlap for the analysis of distance dependencies of nanoscopic objects.

  • Anti-Stokes cooling in Semiconductor Nanocrystal quantum dots: A feasibility study
    physica status solidi (a), 2009
    Co-Authors: Yury P. Rakovich, John F. Donegan, Mikhail Vasilevskiy, Andrey L Rogach
    Abstract:

    In this review, we discuss the feasibility of laser cooling of Semiconductor Nanocrystal quantum dots by phonon-assisted anti-Stokes photoluminescence. Taking into account recent experimental advances, in particular, the development of Semiconductor Nanocrystals with very high quantum yield, we analyze in detail how the various physical processes in Nanocrystals might help or hinder the cooling process. Possible experimental approaches to achieve efficient optical cooling are also discussed.

  • Light‐Emitting Diodes with Semiconductor Nanocrystals
    Angewandte Chemie International Edition, 2008
    Co-Authors: Andrey L Rogach, John M Lupton, Diego E Gallardo, Cristina Bertoni, Steve Dunn, Nikolai Gaponik, Nello Li Pira, Marzia Paderi, Piermario Repetto, Sergei G. Romanov
    Abstract:

    Colloidal Semiconductor Nanocrystals are promising luminophores for creating a new generation of electroluminescence devices. Research on Semiconductor Nanocrystal based light-emitting diodes (LEDs) has made remarkable advances in just one decade: the external quantum efficiency has improved by over two orders of magnitude and highly saturated color emission is now the norm. Although the device efficiencies are still more than an order of magnitude lower than those of the purely organic LEDs there are potential advantages associated with Nanocrystal-based devices, such as a spectrally pure emission color, which will certainly merit future research. Further developments of Nanocrystal-based LEDs will be improving material stability, understanding and controlling chemical and physical phenomena at the interfaces, and optimizing charge injection and charge transport.

Chunfeng Zhang - One of the best experts on this subject based on the ideXlab platform.

  • energy transfer of biexcitons in a single Semiconductor Nanocrystal
    Nano Letters, 2016
    Co-Authors: Xiangnan Huang, Chunfeng Zhang, Xiaoyong Wang, Min Xiao
    Abstract:

    Photoluminescence (PL) decay dynamics of multiexcitons in Semiconductor Nanocrystals (NCs) are dominated by the nonradiative Auger effect, making it difficult to explore their basic optical processes such as radiative recombination and energy transfer (ET). Here we constructed a single-particle ET system by attaching several acceptor dyes to the surface of a donor NC to study the ET of biexcitons at a single-NC level. By comparing the single-exciton and biexciton PL lifetimes of the same donor NC before and after the acceptor dyes were bleached, their respective ET lifetimes could be reliably extracted without the Auger influence. From statistical measurements on a large number of single ET particles, the average ET rate ratio between biexcitons and single excitons was estimated to be larger than four, and the same scaling rule could be naturally extended to their radiative rates.

  • two photon pumped perovskite Semiconductor Nanocrystal lasers
    Journal of the American Chemical Society, 2016
    Co-Authors: Yanqing Xu, Qi Chen, Chunfeng Zhang, Rui Wang, Hua Wu, Xiaoyu Zhang, Guichuan Xing, William W Yu, Xiaoyong Wang, Yu Zhang
    Abstract:

    Two-photon-pumped lasers have been regarded as a promising strategy to achieve frequency up-conversion for situations where the condition of phase matching required by conventional approaches cannot be fulfilled. However, their practical applications have been hindered by the lack of materials holding both efficient two-photon absorption and ease of achieving population inversion. Here, we show that this challenge can be tackled by employing colloidal Nanocrystals of perovskite Semiconductors. We observe highly efficient two-photon absorption (with a cross section of 2.7 × 106 GM) in toluene solutions of CsPbBr3 Nanocrystals that can excite large optical gain (>500 cm–1) in thin films. We have succeeded in demonstrating stable two-photon-pumped lasing at a remarkable low threshold by coupling CsPbBr3 Nanocrystals with microtubule resonators. Our findings suggest perovskite Nanocrystals can be used as excellent gain medium for high-performance frequency-up-conversion lasers toward practical applications.

  • carrier multiplication in a single Semiconductor Nanocrystal
    Physical Review Letters, 2016
    Co-Authors: Chunyang Yin, Chunfeng Zhang, Xiaoyong Wang, Brahim Lounis, Min Xiao
    Abstract:

    To confirm the existence of the carrier multiplication (CM) effect and estimate its generation efficiency of multiple excitons in Semiconductor Nanocrystals (NCs), it is imperative to completely exclude the false contribution of charged excitons from the measured CM signal. Here we place single CdSe NCs above an aluminum film and successfully resolve their UV-excited photoluminescence (PL) time trajectories where the true and false CM signals are contained in the blinking "on" and "off" levels, respectively. By analyzing the PL dynamics of the on-level photons, an average CM efficiency of ∼20.2% can be reliably estimated when the UV photon energy is ∼2.46 times the NC energy gap.

  • charged two exciton emission from a single Semiconductor Nanocrystal
    Applied Physics Letters, 2015
    Co-Authors: Qiang Zhang, Chunfeng Zhang, Xiaoyong Wang, Min Xiao
    Abstract:

    Here, we study the photoluminescence (PL) time trajectories of single CdSe/ZnS Nanocrystals (NCs) as a function of the laser excitation power. At the low laser power, the PL intensity of a single NC switches between the “on” and “off” levels arising from the neutral and positively charged single excitons, respectively. With the increasing laser power, an intermediate “grey” level is formed due to the optical emission from a charged multiexciton state composed of two excitons and an extra electron. Both the inter-photon correlation and the PL decay measurements demonstrate that lifetime-indistinguishable photon pairs are emitted from this negatively charged two-exciton state.

  • quantum efficiency of stimulated emission in colloidal Semiconductor Nanocrystal quantum dots
    Physical Review B, 2009
    Co-Authors: Chunfeng Zhang, Ting Zhu, Fan Zhang, Zhanao Tan, Steven J Schiff, Shuai Gao, Andrew Y Wang
    Abstract:

    External differential quantum efficiencies were studied for the stimulated emission of thin films of colloidal CdSe/CdS/ZnS Nanocrystal quantum dots (NQDs) using the integrating sphere technique. A maximum efficiency of 34% was measured for the stimulated emission in NQDs which far exceeds that for spontaneous emission (9%). The competition between the radiative exciton/biexciton recombination and the carrier density-dependent nonradiative relaxation processes in NQDs was modeled to account for the observed difference in efficiency.

Moungi G Bawendi - One of the best experts on this subject based on the ideXlab platform.

  • evolution of the single Nanocrystal photoluminescence linewidth with size and shell implications for exciton phonon coupling and the optimization of spectral linewidths
    Nano Letters, 2016
    Co-Authors: Andrew P Beyler, Liam Cleary, Thomas R Avila, Jose M Cordero, Leigh S Heathcote, Ou Chen, Igor Coropceanu, Daniel K. Harris, Yue Chen, Moungi G Bawendi
    Abstract:

    The optimization of photoluminescence spectral linewidths in Semiconductor Nanocrystal preparations involves minimizing both the homogeneous and inhomogeneous contributions to the ensemble spectrum. Although the inhomogeneous contribution can be controlled by eliminating interparticle inhomogeneities, far less is known about how to synthetically control the homogeneous, or single-Nanocrystal, spectral linewidth. Here, we use solution photon-correlation Fourier spectroscopy (S-PCFS) to measure how the sample-averaged single-Nanocrystal emission linewidth of CdSe core and core/shell Nanocrystals change with systematic changes in the size of the cores and the thickness and composition of the shells. We find that the single-Nanocrystal linewidth at room temperature is heavily influenced by the nature of the CdSe surface and the epitaxial shell, which have a profound impact on the internal electric fields that affect exciton–phonon coupling. Our results explain the wide variations, both experimental and theore...

  • Nanopatterned Electrically Conductive Films of Semiconductor Nanocrystals
    Nano Letters, 2012
    Co-Authors: Tamar Mentzel, Moungi G Bawendi, Darcy D. Wanger, Nirat Ray, Brian J. Walker, David B. Strasfeld, Marc Kastner
    Abstract:

    We present the first Semiconductor Nanocrystal films of nanoscale dimensions that are electrically conductive and crack-free. These films make it possible to study the electrical properties intrinsic to the Nanocrystals unimpeded by defects such as cracking and clustering that typically exist in larger-scale films. We find that the electrical conductivity of the nanoscale films is 180 times higher than that of drop-cast, microscopic films made of the same type of Nanocrystal. Our technique for forming the nanoscale films is based on electron-beam lithography and a lift-off process. The patterns have dimensions as small as 30 nm and are positioned on a surface with 30 nm precision. The method is flexible in the choice of Nanocrystal core–shell materials and ligands. We demonstrate patterns with PbS, PbSe, and CdSe cores and Zn0.5Cd0.5Se–Zn0.5Cd0.5S core–shell Nanocrystals with a variety of ligands. We achieve unprecedented versatility in integrating Semiconductor Nanocrystal films into device structures bo...

  • Insights into the Kinetics of Semiconductor Nanocrystal Nucleation and Growth
    Journal of the American Chemical Society, 2009
    Co-Authors: Jane Y. Rempel, Moungi G Bawendi, Klavs F. Jensen
    Abstract:

    A model is presented for the colloidal synthesis of Semiconductor Nanocrystals capturing the reactions underlying nucleation and growth processes. The model combines an activation mechanism for precursor conversion to monomers, discrete rate equations for formation of small-sized clusters, and continuous Fokker−Planck equation for growth of large-sized clusters. The model allows us to track the temporal evolution of the entire cluster size distribution and compute several experimental observables including mean size and size distribution. The model predicts five distinct regions: generation of monomers, small cluster formation, size distribution focusing due to precursor depletion, pseudo steady state region, and size distribution broadening, with the latter three explicitly reproducing available experimental data at larger cluster sizes. Furthermore, we identify two nondimensional parameter combinations and discuss how these can be used to guide experiments to yield a more rational approach to synthesis ...

  • blue Semiconductor Nanocrystal laser
    Applied Physics Letters, 2005
    Co-Authors: Yinthai Chan, Jonathan S Steckel, Preston T Snee, Michel J Caruge, Justin M Hodgkiss, Daniel G Nocera, Moungi G Bawendi
    Abstract:

    We demonstrate tunable room-temperature amplified spontaneous emission and lasing from blue-emitting core-shell CdS∕ZnS Nanocrystals (NCs) stabilized in a sol-gel derived silica matrix. Variable stripe length measurements show that these NC-silica composites have a modal gain of ∼100cm−1 at room temperature. Coating microspheres with a NC-silica composite film via a facile process resulted in uniform resonators that exhibit room-temperature lasing over long periods of continuous excitation. This work opens up a spectral window for emission tunable, microscale NC-based lasers.

  • color selective Semiconductor Nanocrystal laser
    Applied Physics Letters, 2002
    Co-Authors: Hansjurgen Eisler, Moungi G Bawendi, Vikram C Sundar, Michael Walsh, Henry I Smith, Victor I Klimov
    Abstract:

    Theoretical predictions of the benefits of three-dimensional quantum confinement have provided motivation for the development of quantum-dot lasers. Such lasers, developed in the case of self-assembled quantum dots, have not been successfully demonstrated with quantum-confined colloidal Nanocrystals (NCs). Here, using recently developed NC-titania chemistry, we report the successful development of an optically pumped, NC-based distributed feedback laser, in which the narrow gain profiles of these nanoparticles have been matched with the feedback of a second-order distributed feedback laser. This laser, whose output color can be selected by choosing appropriately sized Nanocrystals, operates at 80 K and at room temperature.

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