The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Jose L. Jimenez - One of the best experts on this subject based on the ideXlab platform.
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Ultrafast Electronic structures and dynamics of CdSe nanocrystals revealed by gas phase time-resolved photoElectron spectroscopy
19th International Conference on Ultrafast Phenomena, 2014Co-Authors: Wei Xiong, Daniel D. Hickstein, Kyle J. Schnitzenbaumer, Jennifer L. Ellis, Brett B. Palm, Chengyuan Ding, Molly B. Beernink, Gordana Dukovic, Jose L. Jimenez, Margaret M. MurnaneAbstract:Using time-resolved photoElectron spectroscopy in a gas phase environment, we observed the evanescent Electron Wavefunction of quantum dot excited states, and the effect of solvent on QD charge transfer.
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photoElectron spectroscopy of cdse nanocrystals in the gas phase a direct measure of the evanescent Electron wave function of quantum dots
Nano Letters, 2013Co-Authors: Wei Xiong, Daniel D. Hickstein, Kyle J. Schnitzenbaumer, Jennifer L. Ellis, Brett B. Palm, Chengyuan Ding, Gordana Dukovic, Ellen K Keister, Luis Miajaavila, Jose L. JimenezAbstract:We present the first photoElectron spectroscopy measurements of quantum dots (semiconductor nanocrystals) in the gas phase. By coupling a nanoparticle aerosol source to a femtosecond velocity map imaging photoElectron spectrometer, we apply robust gas-phase photoElectron spectroscopy techniques to colloidal quantum dots, which typically must be studied in a liquid solvent or while bound to a surface. Working with a flowing aerosol of quantum dots offers the additional advantages of providing fresh nanoparticles for each laser shot and removing perturbations from bonding with a surface or interactions with the solvent. In this work, we perform a two-photon photoionization experiment to show that the photoElectron yield per exciton depends on the physical size of the quantum dot, increasing for smaller dots. Next, using effective mass modeling we show that the extent to which the Electron wave function of the exciton extends from the quantum dot, the so-called “evanescent Electron Wavefunction”, increases a...
Andreas Gruneis - One of the best experts on this subject based on the ideXlab platform.
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reaction energetics of hydrogen on si 100 surface a periodic many Electron theory study
Journal of Chemical Physics, 2018Co-Authors: Theodoros Tsatsoulis, Sung Sakong, Axel Gros, Andreas GruneisAbstract:We report on a many-Electron Wavefunction theory study for the reaction energetics of hydrogen dissociation on the Si(100) surface. We demonstrate that quantum chemical Wavefunction based methods using periodic boundary conditions can predict chemically accurate results for the activation barrier and the chemisorption energy in agreement with experimental findings. These highly accurate results for the reaction energetics enable a deeper understanding of the underlying physical mechanism and make it possible to benchmark widely used density functional theory methods.We report on a many-Electron Wavefunction theory study for the reaction energetics of hydrogen dissociation on the Si(100) surface. We demonstrate that quantum chemical Wavefunction based methods using periodic boundary conditions can predict chemically accurate results for the activation barrier and the chemisorption energy in agreement with experimental findings. These highly accurate results for the reaction energetics enable a deeper understanding of the underlying physical mechanism and make it possible to benchmark widely used density functional theory methods.
Yang Li - One of the best experts on this subject based on the ideXlab platform.
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effects of interface potential smoothness and Wavefunction delocalization on auger recombination in colloidal cdse based core shell quantum dots
Journal of Chemical Physics, 2019Co-Authors: Yang Li, Xiaogang PengAbstract:Auger nonradiative recombination dominates decay of multicarrier states in high quality colloidal quantum dots (QDs) and thus is critical for many of their optical and optoElectronic applications. Controlling interface-potential smoothness and Wavefunction delocalization are proposed as two main strategies for Auger engineering in core/shell QDs. Here, a series of CdSe-based core/shell QDs with nearly ideal optical quality of their single-exciton states are developed and applied for studying biexciton quantum yields and Auger nonradiative recombination rates. Comparative experiments find that the interface-potential smoothness has little influence on biexciton quantum yield and Auger rates of these core/shell QDs with the same CdS outer shells. In contrast, with a fixed total size of the series of QDs, the decreasing hole Wavefunction delocalization can increase the Auger rates of positive trions by ∼400%. A mild decrease in Electron Wavefunction delocalization among the series of QDs results in a small increase in the Auger rates of negative trions (∼50%). Smoothing the core/shell interface can indeed affect the Auger rates, but this is by the way of altering Wavefunction delocalization. These findings highlight the importance of control of Wavefunction delocalization among the strategies of Auger engineering and provide guidelines for rational design QDs for applications.Auger nonradiative recombination dominates decay of multicarrier states in high quality colloidal quantum dots (QDs) and thus is critical for many of their optical and optoElectronic applications. Controlling interface-potential smoothness and Wavefunction delocalization are proposed as two main strategies for Auger engineering in core/shell QDs. Here, a series of CdSe-based core/shell QDs with nearly ideal optical quality of their single-exciton states are developed and applied for studying biexciton quantum yields and Auger nonradiative recombination rates. Comparative experiments find that the interface-potential smoothness has little influence on biexciton quantum yield and Auger rates of these core/shell QDs with the same CdS outer shells. In contrast, with a fixed total size of the series of QDs, the decreasing hole Wavefunction delocalization can increase the Auger rates of positive trions by ∼400%. A mild decrease in Electron Wavefunction delocalization among the series of QDs results in a small i...
Wei Xiong - One of the best experts on this subject based on the ideXlab platform.
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Ultrafast Electronic structures and dynamics of CdSe nanocrystals revealed by gas phase time-resolved photoElectron spectroscopy
19th International Conference on Ultrafast Phenomena, 2014Co-Authors: Wei Xiong, Daniel D. Hickstein, Kyle J. Schnitzenbaumer, Jennifer L. Ellis, Brett B. Palm, Chengyuan Ding, Molly B. Beernink, Gordana Dukovic, Jose L. Jimenez, Margaret M. MurnaneAbstract:Using time-resolved photoElectron spectroscopy in a gas phase environment, we observed the evanescent Electron Wavefunction of quantum dot excited states, and the effect of solvent on QD charge transfer.
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photoElectron spectroscopy of cdse nanocrystals in the gas phase a direct measure of the evanescent Electron wave function of quantum dots
Nano Letters, 2013Co-Authors: Wei Xiong, Daniel D. Hickstein, Kyle J. Schnitzenbaumer, Jennifer L. Ellis, Brett B. Palm, Chengyuan Ding, Gordana Dukovic, Ellen K Keister, Luis Miajaavila, Jose L. JimenezAbstract:We present the first photoElectron spectroscopy measurements of quantum dots (semiconductor nanocrystals) in the gas phase. By coupling a nanoparticle aerosol source to a femtosecond velocity map imaging photoElectron spectrometer, we apply robust gas-phase photoElectron spectroscopy techniques to colloidal quantum dots, which typically must be studied in a liquid solvent or while bound to a surface. Working with a flowing aerosol of quantum dots offers the additional advantages of providing fresh nanoparticles for each laser shot and removing perturbations from bonding with a surface or interactions with the solvent. In this work, we perform a two-photon photoionization experiment to show that the photoElectron yield per exciton depends on the physical size of the quantum dot, increasing for smaller dots. Next, using effective mass modeling we show that the extent to which the Electron wave function of the exciton extends from the quantum dot, the so-called “evanescent Electron Wavefunction”, increases a...
Kenta Nakashima - One of the best experts on this subject based on the ideXlab platform.
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Computational study on the in-plane symmetry of Electron Wavefunctions in self-assembled InAs/GaAs quantum dots.
Journal of nanoscience and nanotechnology, 2009Co-Authors: Kohki Mukai, Keita Watanabe, Kenta NakashimaAbstract:We made a computational study of Electron Wavefunction symmetry in two types of InAs/GaAs self-assembled quantum dot (QD): one is a normal domical and pyramidal Stranski-Krastanow(SK)-type QD but embedded in InGaAs strain-reducing layer, and the other is a columnar-shaped QD fabricated via direct perpendicular stacking of SK-type QDs. Our calculations based on the three-dimensional finite element method suggested that the in-plane symmetry of the Electron Wavefunction is superior to that of the crystallographic QD structure. The presence of an InGaAs strain-reducing layer helps to improve the symmetry of SK-type QD. The higher the indium composition of the strain-reducing layer, the greater the improvement. The improvement is greater with domical QD than with pyramidal QD. We also found that the multiple wetting layers around the columnar-shaped QD structure act as a strain-reducing layer, so that the improvement of symmetry is dependent on the average indium composition of the multiple wetting/interval layers. The symmetry improvement was explained by the Wavefunction overflow outside the QDs. We found that, to achieve highly symmetric Wavefunction, the strain-reducing-layer-embedded QDs are adequate more than the columnar-shaped QDs. These results will aid in the development of an entangled-photon generator that requires symmetric in-plane QD structure.
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improvement of Electron Wavefunction symmetry in inas gaas quantum dots embedded in an ingaas strain reducing layer
International Microprocesses and Nanotechnology Conference, 2007Co-Authors: Kohki Mukai, Kenta NakashimaAbstract:Summary form only given . Semiconductor quantum dot (QD) devices for the generation of single photon and entangled photon pairs have been eagerly studied for their applications in quantum information technology. Although the single-photon generation has been progressed with vertical micro-cavity, the generation of entangled photon pairs has not yet been achieved with the devices. The well-known Stranski-Krastanov(SK)-type self-assembled QD has an in-plain asymmetric shape, and the symmetry of the Electron Wavefunction in the QD state is critical for generating entangled photon pairs using biexiton vertical emission. In this paper, we report that the InGaAs strain-reducing layer improves the in-plane symmetry of Electron Wavefunction in InAs/GaAs self-assembled QDs. The SK-type QD samples were prepared using molecular beam epitaxy. InAs/GaAs QDs were covered by a d-nm (d = 0 -10) thick InxGa1-xAs (x = 0 -0.17) strain-reducing layer and capped by a 100-nm GaAs layer. Photoluminescence (PL) perpendicular to the sample surface was measured at room temperature and its polarization dependence was investigated to evaluate structural anisotropy. We compared photoluminescence intensity in the most intense polarization direction with that in its 90deg-rotated direction. The authors show that the polarization dependence was reduced by increasing indium composition and thickness of strain reducing layer. The characteristics of the pyramidal and the domical self-assembled InAs QD structures were investigated theoretically with the three-dimensional finite element method (3D FEM). To evaluate the symmetry, they defined the major and minor axes of the QD structure and that of the Electron Wavefunction to be Lmajor, Lminor, LPhi major, and LPhi minor. Throughout the calculation, it is assumed that Lmajor has a value of 20 nm and that the QD height is 10 nm. The symmetry of the Wavefunction is improved by the strain-reducing layer. The symmetry is superior to that of the QD structure, even without the strain-reducing layer (i.e., x = 0). The higher the indium composition and the greater the thickness of strain-reducing layer, the better the resulting symmetry of the Wavefunction. They also see in there analysis that the lower the original QD symmetry, the greater the improvement, and that the Wavefunction symmetry is better in a domical dot than in a pyramidal dot. The improvement of symmetry in the calculation owes to the spread of the Wavefunction into the strain-reducing layer. The higher the indium composition of strain-reducing layer, and the lower the original QD symmetry, the larger the probability amplitude out of QD. To summarize, they report that the InGaAs strain-reducing layer improves the in-plane symmetry of Electron Wavefunction in InAs/GaAs self-assembled QDs. This is suggested experimentally by the polarization dependence of photoluminescence intensity of QD. The calculation based on the 3D FEM also supports the experiments. The results will aid in the design of an entangled photon generator that uses self-assembled QDs.
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Improvement of Electron Wavefunction symmetry in InAs/GaAs quantum dots embedded in an InGaAs strain-reducing layer
2007 Digest of papers Microprocesses and Nanotechnology, 2007Co-Authors: Kohki Mukai, Kenta NakashimaAbstract:Summary form only given . Semiconductor quantum dot (QD) devices for the generation of single photon and entangled photon pairs have been eagerly studied for their applications in quantum information technology. Although the single-photon generation has been progressed with vertical micro-cavity, the generation of entangled photon pairs has not yet been achieved with the devices. The well-known Stranski-Krastanov(SK)-type self-assembled QD has an in-plain asymmetric shape, and the symmetry of the Electron Wavefunction in the QD state is critical for generating entangled photon pairs using biexiton vertical emission. In this paper, we report that the InGaAs strain-reducing layer improves the in-plane symmetry of Electron Wavefunction in InAs/GaAs self-assembled QDs. The SK-type QD samples were prepared using molecular beam epitaxy. InAs/GaAs QDs were covered by a d-nm (d = 0 -10) thick InxGa1-xAs (x = 0 -0.17) strain-reducing layer and capped by a 100-nm GaAs layer. Photoluminescence (PL) perpendicular to the sample surface was measured at room temperature and its polarization dependence was investigated to evaluate structural anisotropy. We compared photoluminescence intensity in the most intense polarization direction with that in its 90deg-rotated direction. The authors show that the polarization dependence was reduced by increasing indium composition and thickness of strain reducing layer. The characteristics of the pyramidal and the domical self-assembled InAs QD structures were investigated theoretically with the three-dimensional finite element method (3D FEM). To evaluate the symmetry, they defined the major and minor axes of the QD structure and that of the Electron Wavefunction to be Lmajor, Lminor, LPhi major, and LPhi minor. Throughout the calculation, it is assumed that Lmajor has a value of 20 nm and that the QD height is 10 nm. The symmetry of the Wavefunction is improved by the strain-reducing layer. The symmetry is superior to that of the QD structure, even without the strain-reducing layer (i.e., x = 0). The higher the indium composition and the greater the thickness of strain-reducing layer, the better the resulting symmetry of the Wavefunction. They also see in there analysis that the lower the original QD symmetry, the greater the improvement, and that the Wavefunction symmetry is better in a domical dot than in a pyramidal dot. The improvement of symmetry in the calculation owes to the spread of the Wavefunction into the strain-reducing layer. The higher the indium composition of strain-reducing layer, and the lower the original QD symmetry, the larger the probability amplitude out of QD. To summarize, they report that the InGaAs strain-reducing layer improves the in-plane symmetry of Electron Wavefunction in InAs/GaAs self-assembled QDs. This is suggested experimentally by the polarization dependence of photoluminescence intensity of QD. The calculation based on the 3D FEM also supports the experiments. The results will aid in the design of an entangled photon generator that uses self-assembled QDs.