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61.
Kristian Berland 《Superlattices and Microstructures》2011,50(4):411-418
A general, system-independent, formulation of the parabolic Schrödinger–Poisson equation is presented for a charged hard wall in the limit of complete screening by the ground state. It is solved numerically using iteration and asymptotic boundary conditions. The solution gives a simple relation between the band bending and sheet charge density at an interface. Approximative analytical expressions for the potential profile and wave function are developed based on properties of the exact solution. Specific tests of the validity of the assumptions leading to the general solution are made. The assumption of complete screening by the ground state is found be a limitation; however, the general solution provides a fair approximate account of the potential profile when the bulk is doped. The general solution is further used in a simple model for the potential profile of an AlN/GaN barrier structure. The result compares well with the solution of the full Schrödinger–Poisson equation. 相似文献
62.
Undoped and Cu2+ doped (0.2-0.8%) ZnS nanoparticles have been synthesized through chemical precipitation method. Tri-n-octylphosphine oxide (TOPO) and sodium hexametaphosphate (SHMP) were used as capping agents. The synthesized nanoparticles have been analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrometer, photoluminescence (PL) and thermo gravimetric-differential scanning calorimetry (TG-DTA) analysis. The size of the particles is found to be 4-6 nm range. Photoluminescence spectra were recorded for ZnS:Cu2+ under the excitation wavelength of 320 nm. The prepared Cu2+-doped sample shows efficient PL emission in 470-525 nm region. The capped ZnS:Cu emission intensity is enhanced than the uncapped particles. The doping ions were identified by electron spin resonance (ESR) spectrometer. The phase changes were observed in different temperatures. 相似文献
63.
The ab initio calculations are carried out to investigate the effect of hydrogen, oxygen and nitrogen terminations on the properties of the band edge and the values of the band-gap, as well as the oscillator strength of the silicon nanonets (SiNNs). The oxygen functional groups are found to effectively preserve the direct band-gap nature of the SiNNs, and even change the luminescence properties of the silicon nanowires (SiNWs) to the direct band-gap transition. The appreciable oscillator strength of the first direct transition is obtained for the oxygen terminated nanostructure. The study on the electronic states indicates that the variation of the band edge caused by the surface terminations is attributed to the change of the state compositions. These surface modifications are thought to be useful for silicon band-gap engineering in the area of optoelectronics. 相似文献
64.
Thin films of ZnO-SnO2 composites have been deposited on Si(1 0 0) and glass substrates at 500 °C by pulsed laser ablation using different composite targets with ZnO amount varying between 1 and 50 wt%. The effect of increasing ZnO-content on electrical, optical and structural properties of the ZnO-SnO2 films has been investigated. X-ray diffraction analysis indicates that the as-deposited ZnO-SnO2 films can be both crystalline (for ZnO <1 wt%) and amorphous (for ZnO ≥ 10 wt%) in nature. Atomic force microscopy studies of the as-prepared composite films indicate that the surfaces are fairly smooth with rms roughness varying between 3.07 and 2.04 nm. The average optical transmittance of the as-deposited films in the visible range (400-800 nm), decreases from 90% to 72% for increasing ZnO concentration in the film. The band gap energy (Eg) seems to depend on the amount of ZnO addition, with the maximum obtained at 1 wt% ZnO. Assuming that the interband electron transition is direct, the optical band gap has been found to be in the range 3.24-3.69 eV for as-deposited composite films. The lowest electrical resistivity of 7.6 × 10−3 Ω cm has been achieved with the 25 wt% ZnO composite film deposited at 500 °C. The photoluminescence spectrum of the composite films shows a decrease in PL intensity with increasing ZnO concentration. 相似文献
65.
Huanhuan KouXin Zhang Yongling DuWeichun Ye Shaoxiong LinChunming Wang 《Applied Surface Science》2011,257(10):4643-4649
Well-aligned ZnO nanoflowers and nanosheets were synthesized on porous Si (PS) at different applied potentials by electrodeposition approach. The deposits were grown using the optimized program and were characterized by means of cyclic voltammetry (CV), amperometry I-t (I-t), open-circuit potentiometry. X-ray diffraction (XRD) analysis proved a strong preferential orientation (1 0 0) on PS. Scanning electronic microscopy (SEM) observation showed the deposits consist of nanoflowers with uniform grain size of about 100 nm in diameter and nanosheets, which may have potential applications in nanodevices and nanotechnologies. Thus, ZnO grown on PS can be used as photoelectric materials due to its larger photoelectric effect compared to Si wafer according to open-circuit potential (OCP) study. Optical band gap measurements were made on samples using UV-visible spectrophotometer thus giving a band gap of 3.35 eV. 相似文献
66.
Under a large tensile strain near fracture limit, the band structures of single-wall carbon nanotubes (SWCNTs) with diameter less than 0.5 nm begin a metal to semiconductor transition and these ultra-small SWCNTs can normally maintain their metallicities. The band gap behavior of these SWCNTs intrinsically originates from the long axial direct bond lengths and the severe curvature. The gap opening comes mainly from the transfer of pπ electrons. And the localized π and σ states can result in a lower electrical conductivity. This band gap behavior suggests that it has potential to find applications in nano-electromechanical system. 相似文献
67.
S. Berkebile G. Koller A.J. Fleming P. Puschnig C. Ambrosch-Draxl K. Emtsev T. Seyller J. Riley M.G. Ramsey 《Journal of Electron Spectroscopy and Related Phenomena》2009,174(1-3):22
Recently, there have been reports of the valence band photoemission of pentacene films grown on various substrates with particular emphasis on the highest occupied molecular orbital (HOMO) and its dispersion. In various works, evidence for HOMO band dispersion as high as 0.5 eV, even for polycrystalline films, has been presented. In apparent contradiction to these results, we have previously reported a band dispersion of only 50 meV, measured on a well characterised film with a single polymorph and single crystalline orientation, 5A(0 2 2). Here, we first present the two-dimensional momentum distribution of the HOMO of a 5A(0 2 2) film. Then the development of the valence band spectra for films grown at room temperature and low temperature are compared, and we show that morphological aspects can lead to the apparent observation of high HOMO dispersion. Finally, with the aid of the two-dimensional momentum distribution of the HOMO, we show that a reasonably large dispersion (0.25 eV) does indeed exist in 5A(0 2 2). 相似文献
68.
Wei-Long Zhang Chen-Sheng Lin Ye-Yu Li Hao Zhang Wen-Dan Cheng 《Journal of solid state chemistry》2010,183(5):1108-1113
Two members of MIII2BP3O12 borophosphates, namely Fe2BP3O12 and In2BP3O12, were synthesized by the solid-state method and characterized by the X-ray single crystal diffraction, the powder diffraction and the electron microscopy. They both crystallize in the hexagonal system, space group P6(3)/m (no. 176) and feature 3D architectures, build up of the M2O9 units and B(PO4)3 groups via sharing the corners; however, they are not isomorphic for the different crystallographically distinct atomic positions. Optical property measurements of both compounds and magnetic susceptibility measurements of Fe2BP3O12 also have been performed. Moreover, in order to gain further insights into the relationship between physical properties and band structure of the MIII2BP3O12 borophosphates, theoretical calculations based on density functional theory (DFT) were performed using the total-energy code CASTEP. 相似文献
69.
S. Ben Rejeb A. Bhouri M. Debbichi J.-L. Lazzari M. Said 《Superlattices and Microstructures》2011,50(4):277-288
Reliable and precise knowledge about the strain and composition effects on the band structure properties is crucial for the optimization of InGaN based heterostructures for electronic and optoelectronic device applications. AlInGaN as quaternary barrier material permits to control the band gap and the lattice constant independently. Using the model solid theory and the multi-band k.p interaction model, we investigate the composition effects on band offsets and band structure for pseudomorphic Ga1−xInxN/AlzInyGa1−y−zN (0 0 1) heterointerfaces having zinc-blende structure. The results show that both conduction and valence band states are strongly modified while varying In and Al contents in the well and barrier materials. Furthermore, it is found that using AlInGaN as the barrier material allows the design of heterostructures including InGaN wells with tensile, zero or compressive strain. Such results give new insights for III-nitride compounds based applications and especially may guide the design of white-light emission diodes. 相似文献
70.
S. BachaA. Bechiri F. BenmakhloufH. Allouache N. Bouarissa 《Physica B: Condensed Matter》2011,406(10):2021-2024
The investigation of optoelectronic properties of zinc-blende InPxSb1−x, semiconducting alloys by pseudopotential calculations is studied. The scheme uses the local empirical pseudopotential method, which involves the disorder effect into the virtual crystal approximation by introducing an effective potential disorder. Various quantities for the alloy of interest are calculated. The obtained results show a reasonable agreement with the available experimental data. Special attention has also been given to the compositional dependence of these studied quantities. 相似文献