Effect of magnetic field on diamagnetic susceptibility of two interacting electrons in a quantum dot

We have estimated the energy levels of the low‐lying states as a function of magnetic field when two electrons are introduced in a quantum dot (QD). Oscillator strength of interacting electrons for different magnetic field strengths has been calculated. There is no appreciable change in oscillator strength for stronger confinements for all the magnetic field strengths. We present the shift of diamagnetic susceptibility of a hydrogenic donor impurity in GaAs/Ga_1?xAl_xAs QD systems for the ground and low lying excited states. The effect of magnetic field on diamagnetic susceptibilities is estimated by two different methods and it has been found that values obtained from both the methods resemble each other. The diamagnetic shift is in good agreement with the other investigators. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Behavior of carriers in δ-doped quantum wells under in-plane magnetic fields

Self-consistent electronic structure calculations of δ-doped quantum wells (QW) in the presence of in-plane magnetic fields B up to 20 Tesla are carried out within the frameworks of the effective mass and the local density approximations. QWs composed of two layers of Ga_1-xA1_xAs, separated by a layer of GaAs with a donor δ-doped sheet in the center, are considered. The width of the GaAs layer was varied from 100 to 400 Å. It is shown that the diamagnetic shift increases with the increasing of the GaAs QW width. The magnetic field induces remarkable changes in the energy dispersions of electrons and holes, along an in-plane direction perpendicular to B. The most striking effect occurs in the nature of the band gap of these systems. We found that the valence band displays a double-maximum character instead of a single maximum at the center of the Brillouin zone. © 1996 John Wiley & Sons, Inc.     

Effect of pressure on spin–orbit interaction in a quantum wire with V-shaped cross section

In the present work, we have considered a GaAs/Ga_1−xAl_xAs V-shaped quantum wire with a hydrogenic donor impurity at the center. First, the Schrödinger equation is analytically solved without the impurity. Second, we have used variational approximation to obtain the ground state binding energy. Third, the spin–orbit interaction (SOI) is studied by the perturbation theory. We also have investigated the effect of pressure on the binding energy and SOI in this quantum wire. According to the obtained results, it is found that i) the binding energy increases with increasing pressure, ii) the level splitting increases by increasing pressure, iii) the splitting decreases with increasing wire size.     

Interfacial behaviour of a quantum well electrode|electrolyte: EER spectra of an SQW GaAs|AlxGa1−xAs electrode in HQ + BQ non-aqueous electrolyte

The quantum-confined Stark effect and the Franz-Keldysh oscillation of a single quantum well (SQW) GaAs|Al_xGa_1−xAs electrode were studied in non-aqueous hydroquinone + benzoquinone solution with electrolyte electroreflectance spectroscopy. By investigation of the relation of the quantum-confined Stark effect and the Franz-Keldysh oscillation with applied external bias, the interfacial behaviour of an SQW electrode was analysed.     

Laser effects in excitons in a quantum wire

We investigate the effects of laser field intensity over the ground state binding energy of light and heavy hole excitons confined in GaAs/Ga_1?xAl_x As cylindrical quantum wire. We have applied the variational method using 1s‐hydrogenic wave functions, in the framework of the single band effective mass approximation with the spatial dielectric function. The polaronic effects are included in the calculation to compute the exciton binding energy as a function of the wire radius for different field of laser intensity. The valence‐band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The dressed laser donor binding energies are calculated and compared with the results of binding energy of excitons. The results show that (i) the binding energy is found to increase with decrease with the wire radius, and decrease with increase with the value of laser field amplitude, (ii) the heavy‐hole exciton in a cylindrical quantum wire is more strongly bound than the light‐hole exciton, (iii) the values of ground state binding energy for the laser field amplitude α₀ = 10 Å resemble with the values of heavy hole exciton binding energy, and (iv) the binding energy of the impurity for the narrow well wire is more sensitive to the laser field amplitude. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Shape effect of diamagnetic susceptibility of a hydrogenic donor in a nano structured semiconductor systems

The diamagnetic susceptibility of a hydrogenic donor in GaAs/ Al_xGa_1-xAs semiconductor nanostructured systems like Quantum Well Wire and Quantum Dot has been computed for various cross-sectional geometries of these systems for various width of the confining potential in the effective mass approximation using variational method. The non parabolicity of the conduction band has also been included. This calculation may throw some light on the effect of geometries on the semiconductor–metal transition in these systems.     

花状硫化铜的合成及其光电催化性能

通过硫化介孔Cu_2O微球得到花状Cu_xS纳米催化材料,并采用丝网印刷法制备出Cu_xS/FTO对电极。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征手段对所得材料的结构和形貌进行了探究,同时系统考察了溶液浓度、硫化时间、催化剂印刷层数对Cu_xS/FTO电极的催化性能影响和所组装量子点敏化太阳电池的光电转换效率,其中基于Zn-Cu-In-Se量子点敏化的电池转换效率达8.80%,表现出花状Cu_xS优异的光电催化性能。     

基于量子点涂料的柔性光阳极及碳基对电极的制备和优化

首先制备出量子点(QDs)/TiO_2涂料,分别采用丝网印刷法与刀刮法将涂料涂覆于ITO/PET柔性基底上,结果表明刀刮法制备量子点敏化太阳电池(QDSCs)效果更佳,且具有普适性。基于铜片对电极所组装的ZnCuInSe,CdSe和CdSeTe量子点半柔性QDSCs最高效率分别达2.83%,2.46%和1.99%。另外,我们对石墨纸进行表面化学修饰以提高亲水性,再通过简单的连续离子交换吸附法(SILAR)在石墨纸上负载Cu_xS纳米粒子,制备出Cu_xS/GP柔性对电极,进一步组装成全柔性QDSCs,获得了2.13%光电转化效率。     

基于量子点涂料的柔性光阳极及碳基对电极的制备和优化

首先制备出量子点（QDs）/TiO₂涂料,分别采用丝网印刷法与刀刮法将涂料涂覆于ITO/PET柔性基底上,结果表明刀刮法制备量子点敏化太阳电池（QDSCs）效果更佳,且具有普适性。基于铜片对电极所组装的ZnCuInSe,CdSe和CdSeTe量子点半柔性QDSCs最高效率分别达2.83%,2.46%和1.99%。另外,我们对石墨纸进行表面化学修饰以提高亲水性,再通过简单的连续离子交换吸附法（SILAR）在石墨纸上负载Cu_xS纳米粒子,制备出Cu_xS/GP柔性对电极,进一步组装成全柔性QDSCs,获得了2.13%光电转化效率。     

The possibility of semiconductor–metal transition in a spherical quantum dot

We observe an abrupt change in diamagnetic susceptibility at critical donor concentration for an $\text{ Al }_\mathrm{x}\text{ Ga }_\mathrm{1-x}\text{ As/GaAs }$ Al x Ga 1 ? x As/GaAs quantum dot system in the effective mass approximation indicating a possible semiconductor metal transition. The effect of confining potential and the laser intensity on the abrupt change in diamagnetic susceptibility has also been studied. The effect of nonparabolicity of the conduction band has been included in our calculations. Results are presented and discussed.     

Photoelectrochemical behavior of a novel composite In0.15Ga0.85As/GaAs|GaAs/Al0.3Ga0.7As multiple quantum well electrode

A novel composite In_xGa_1−xAs/GaAs|GaAs/Al_xGa_1−xAs multiple quantum well material with different well widths was studied as a new kind of photoelectrode in a photoelectrochemical cell. The photocurrent spectrum and photocurrent–electrode potential curve were measured in ferrocene nonaqueous solution. Pronounced quantization effects and strong exciton absorption were observed in the photocurrent spectrum. The effects of surface states and interfacial states on the photocurrent–electrode potential curve are discussed.     

Cd1-xZnxS/ZnS core/shell quantum dot ferroelectric liquid crystal composite system: analysis of faster optical response and lower operating voltage

Cd_1?xZn_xS/ZnS core/shell-structured quantum dot (QD)-doped ferroelectric liquid crystal (FLC) Felix 17/000 has been investigated in the present study. In the SmC* phase, the effect of QD on the dielectric and electro-optical properties of FLC has been studied as a function of dopant concentration. A substantial change in the different parameters like tilt angle, spontaneous polarisation, response time and relative permittivity has been observed for the composite system. Nearly two times faster response of the composite system with lower operating voltage is one of the promising results of the present study. The faster optical response along with the decreased value of spontaneous polarisation can be utilised in low power consumption liquid crystal displays.     

Computational investigation of the adsorption and reactions of SiHx (x = 0–4) on TiO2 anatase (101) and rutile (110) surfaces

The adsorption and reactions of the SiH_x (x = 0–4) on Titanium dioxide (TiO₂) anatase (101) and rutile (110) surfaces have been studied by using periodic density functional theory in conjunction with the projected augmented wave approach. It is found that SiH_x (x = 0–4) can form the monodentate, bidentate, or tridentate adsorbates, depending on the value of x. H coadsorption is found to reduce the stability of SiH_x adsorption. Hydrogen migration on the TiO₂ surfaces is also discussed for elucidation of the SiH_x decomposition mechanism. Comparing adsorption energies, energy barriers, and potential energy profiles on the two TiO₂ surfaces, the SiH_x decomposition can occur more readily on the rutile (110) surface than on the anatase (101) surface. The results may be used for kinetic simulation of Si thin‐film deposition and quantum dot preparation on titania by chemical vapor deposition (CVD), plasma enhanced CVD, or catalytically enhanced CVD. © 2013 Wiley Periodicals, Inc.     

Transient excitation behavior of a donor–acceptor–acceptor Auger molecule in a semiconductor host

Under the particular situation of highly doped and almost compensated semiconductors, a new kind of bound state happens at high external excitation levels, which is formed of a close donor–acceptor molecule and a neighboring second donor or acceptor. The de-excitation behavior of such a bound state resembles characteristics known from Auger transitions and for this reason it is called an Auger molecule. The existence region of Auger molecules is determined in silicon-doped Ga_{1− x} Al _x As by electron-beam excited luminescence measurements at low temperature. The main peak position and the luminescence intensity of the donor–acceptor recombination channel turn out to be affected in a characteristic manner by the existence of Auger molecules at high excitation levels. An analysis of corresponding rate coefficients for the reproduction of experimental results is also presented. Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 21 June 2000     

SIMS depth profiling of semiconductor interfaces: Experimental study of depth resolution function

Reconstruction of original element distribution at semiconductor interfaces using experimental SIMS profiles encounters considerable difficulties because of the matrix effect, sputtering rate change at the interface, and also a sputtering‐induced broadening of original distributions. We performed a detailed depth profiling analysis of the Al step‐function distribution in GaAs/Al_xGa_1?xAs heterostructures by using Cs⁺ primary ion beam sputtering and CsM⁺ cluster ion monitoring (where M is the element of interest) to suppress the matrix effect. The experimental Depth Resolution Function (DRF) was obtained by differentiation of the Al step‐function profile and compared with the ‘reference’ DRF found from depth profiling of an Al delta layer. The difference between two experimental DRFs was explained by the sputtering rate change during the interface profiling. We experimentally studied the sputtering rate dependence on the Al_xGa_1?xAs layer composition and applied it for a reconstruction of the DRF found by differentiating the Al step‐function distribution: the ‘reconstructed’ and ‘reference’ DRFs were found to be in good agreement. This confirmed the correctness of the treatment elaborated. Copyright © 2010 John Wiley & Sons, Ltd.     

BAM‐L002—a new type of certified reference material for length calibration and testing of lateral resolution in the nanometre range

A new type of test sample for the determination of lateral resolution in surface analysis is presented. The certified reference material BAM‐L002 ‘Nanoscale strip pattern for length calibration and testing of lateral resolution’ is an embedded cross‐section of epitaxially grown layers of Al_xGa_1?xAs and In_xGa_1?xAs on GaAs substrate. The surface of the sample provides a flat pattern with strip widths of 0.4–500 nm. The combination of gratings, isolated narrow strips and sharp edges of wide strips offers improved possibilities for the calibration of a length scale, the determination of lateral resolution and the optimization of instrument settings. The feasibility of the reference material for an analysis of lateral resolution is demonstrated for SIMS. Copyright © 2004 John Wiley & Sons, Ltd.     

Design,synthesis, and properties of polystyrene-based through-space charge transfer polymers: Effect of triplet energy level of electron donor moiety on delayed fluorescence and electroluminescence performance

Two kinds of polystyrene-based through-space charge transfer (TSCT) polymers consisting of spatially-separated acridan donor moieties bearing phenyl or naphthyl substituents and triazine acceptor moieties are designed and synthesized. It is found that TSCT polymers containing phenyl-substituted acridan donors exhibit high-lying singlet (S₁) and triplet (T₁) states with small singlet-triplet energy splitting (∆E_ST) of 0.04–0.05 eV, resulting in thermally activated delayed fluorescence (TADF) with reverse intersystem crossing rate constants of 1.1–1.2 × 10⁶ s⁻¹. In contrast, polymers bearing naphthyl-substituted acridan donors, although still having TSCT emission, exhibit no TADF effect because of the large ∆E_ST of 0.30–0.33 eV induced by low-lying locally excited T₁ state of naphthyl donor moiety. Solution-processed organic light-emitting diodes using TSCT polymers containing phenyl-substituted acridan donors reveal sky-blue emission at 483 nm together with maximum external quantum efficiency (EQE) of 11.3%, which is about 30 times that of naphthyl-substituted counterpart with maximum EQE of 0.38%, shedding light on the importance of high triplet energy level of donor moiety on realizing TADF effect and high device efficiency for through-space charge transfer polymer.     

A Förster Resonance Energy Transfer Ratiometric Probe Based on Quantum Dot-Cresyl Violet for Imaging Hydrogen Sulfide in Living Cells

Hydrogen sulfide (H₂S) has been confirmed as a significant endogenous gaseous signaling molecule involved in various physiological processes. In order to monitor H₂S in living cells, a Forster resonance energy transfer (FRET) ratiometric probe based on quantum dot-cresyl violet was developed. In this work, the quantum dot nanospheres via a facile ultrasonication emulsion strategy, and the mixture chloroform solution containing hydrophobic quantum dots and COOH-functionalized amphiphilic polymer were successfully transferred into the oil-in-water micelle. The negatively charged quantum dot nanospheres with quantum dots embedded in the polymer matrixes were successfully fabricated after the evaporation of chloroform. And then, these quantum dot nanospheres were condensed with positively charged cresyl violet-azide (CV-N₃) via electrostatic interaction to obtain the complexes (QDS-N₃). The as-prepared QDS-N₃ complexes were monodispersed nanospheres with an average diameter of about 120 nm. These complexes were taken up by the cell through endocytosis, and they were still stable even in wide pH range. In addition, the QDS-N₃ complexes exhibited no cellular toxicity which was verified by MTT assay. In this ratiometric probe, CV-N₃ as a FRET acceptor was conjugated to quantum dot nanospheres. The quantum dots emitted at 591 nm and served as the FRET donor; once the aryl azide on the CV-N₃ was reduced by H₂S to aniline, the probe emitted at 620 nm. The ratiometric probe allowed the elimination of interference of excitation intensity, intracellular environment and other factors. Furthermore, this method also offered a general protocol for preparing nanosensors for monitoring various small molecular in living cells.     

A 200‐fold Quantum Yield Boost in the Photoluminescence of Silver‐Doped AgxAu25−x Nanoclusters: The 13 th Silver Atom Matters

The rod‐shaped Au₂₅ nanocluster possesses a low photoluminescence quantum yield (QY=0.1 %) and hence is not of practical use in bioimaging and related applications. Herein, we show that substituting silver atoms for gold in the 25‐atom matrix can drastically enhance the photoluminescence. The obtained Ag_xAu_25?x (x=1–13) nanoclusters exhibit high quantum yield (QY=40.1 %), which is in striking contrast with the normally weakly luminescent Ag_xAu_25?x species (x=1–12, QY=0.21 %). X‐ray crystallography further determines the substitution sites of Ag atoms in the Ag_xAu_25?x cluster through partial occupancy analysis, which provides further insight into the mechanism of photoluminescence enhancement.     

Thermodynamics of the Equilibrium Between a Fractional Quantum Hall liquid and a Wigner Electron Solid

Abstract

A recent paper of Wu et al., discusses thermodynamic observables in a fractional quantum Hall (FQH) liquid. In particular the de Haas-van Alphen effect is considered theoretically. Here, it is pointed out that laboratory experiments on GaAs/AlGaAs heterojunctions, plus the analogue of the Clausius-Clapeyron equation in an applied magnetic field, allow schematic analysis of the orbital magnetism of the FQH liquid. There is general agreement with the theoretical results of Wu et al.