Secondary anti-stokes emission from the bulk of gallium phosphide at 4.2 K

Secondary radiation (photoluminescence and Raman scattering) emitted by gallium phosphide single crystals at helium temperatures is investigated. It is established for the first time that, in the case when the secondary emission spectra are excited by a cw low-power He-Ne laser, whose linewidth lies in the transparency region of GaP, anti-Stokes photoluminescence from the bulk of the sample occurs due to interband and impurity recombination. The results obtained make it possible to carry out a qualitative and quantitative analysis of impurities which are present in the bulk of a semiconductor by recording the bulk anti-Stokes photoluminescence spectra at low temperatures.     

Cherenkov and transition radiation generated in 200 kV electron microscope

Abstract

Cherenkov radiation emitted from electron irradiated dielectrics such as mica, quartz and BaTiO₃ was detected in a transmission electron microscope with the accelerating voltages of 80 kV to 200 kV. Transition radiation was also observed from metals (Al, Ag, Au) and semiconductors (GaAs, Si). Dependence of their intensities and spectra on accelerating voltage and crystal thickness was investigated.     

Computer simulation of the photoluminescence of nanostructured aluminum oxide excited with pulsed synchrotron radiation

An algorithm and a program are developed to calculate the photoluminescence (PL) parameters for bulk single-crystal and nanoscale dielectrics excited with pulsed synchrotron radiation. The luminescence spectra of F and F ⁺ centers and the PL decay kinetics in single-crystal and nanoscale aluminum-oxide samples containing oxygen anion vacancies are calculated for various nanoparticle sizes. It is shown that a noticeable broadening of the bands and a decrease in the afterglow time is observed for nanoparticle sizes that are less than 20 nm.     

a-Si:H/a-SiNx:H超晶格薄膜光致发光性质的研究

本文报道了a-Si:H/a-SiNx:H超晶格薄膜光致发光某些性质的研究。实验发现,这种超晶格薄膜光致发光的强度和峰值能量随交替层a-Si:H厚度,测量温度及光照时间等而变化。同时还发现,在阴、阳两极上,利用GD法沉积的样品,发光强度和峰值能量也有所不同。文中对这些实验结果作了初步解释。     

In_(0.2)Ga_(0.8)As/GaAs单量子阱PL谱温度特性及其机制

测量了不同阱宽In0.2Ga0.8As/GaAs单量子阱的PL谱的峰值波长和荧光谱线半峰全宽随温度的变化。利用Varshni公式对实验峰值波长进行拟合,得到了新的参数。结果表明,无位错应变量子阱带隙仍具有其体材料的特性:荧光谱线半峰全宽随温度升高迅速展宽,这主要归因于声子关联作用增强和激子热离化为自由载流子所致;阱宽越窄荧光峰值能量越高,将其与量子尺寸效应的理论计算结果进行了比较。文中还考察了谱线半峰全宽和阱宽的关系,利用合金无序对这一现象进行了解释。     

A Novel Approach for the Evaluation of Band Gap Energy in Semiconductors

On the basis of absorption nature of semiconductors, we present a novel and simple method to determine the band gap energies of semiconductors directly from their absorption spectra at any temperatures, without any fitting processes and restrictions of sample thickness. The key point of the approach is the different dependence of the absorption coefficient derivative on the photon energy at different absorption regions in semiconductors. We first demonstrate and verify the approach by detailed temperature-dependent absorption measurements, combined with photoluminescence measurements and empirical band gap equations for the direct band gap of uniform InAs films, and then extend successfully to the indirect band gap of elemental Ge and to the ternary HgCdTe alloys with composition gradient. Furthermore, we have also shown that our approach can not only evaluate the average band gap energy for ternary semiconductor alloys, but also estimate their composition uniformity to monitor the material quality.     

Er离子注入GaP,GaAs, InP的二次离子质谱(SIMS)的研究

近年来掺稀土元素的Ⅲ—Ⅴ族化合物研究在基础物理和器件应用方面都越来越引起人们的关注,[1,2]其中又由于Er3+的4I13/2—4I15/2的特征发光波长为1.54μm,恰好对应于石英光纤的低损耗区,且离子注入技术简单易行,因而倍受重视.国际上已报道了不少有关Er注入Ⅲ—Ⅴ族化合物的研究,大多选用较低的注入剂量(约1012～1014Er/cm2),而对较高剂量的注入有待于进一步研究.     

Photoluminescence identification of surface contaminants on zinc oxide from their phase transitions

The spectra of photoluminescence (PL) from a zinc oxide (ZnO) crystal included an unusual feature of an ultraviolet (UV) emission at a higher energy than the ZnO interband transitions. The energy of this UV emission varied with temperature and included two discontinuous energy steps in the temperature range from 78 to 700?K. The temperature values of the steps match phase transition temperatures of ethanol. Ethanol was used during sample cleaning and can be trapped in the form of nanoparticles inclusions. Both the intrinsic and defect site, PL signals have different temperature dependencies from those of bulk crystals, as seen during radioluminescence. The origins of the changes are discussed.     

Vibronic relaxation processes of the FA center in RbCl:Li

The vibronic relaxation process of F_A centers in RbCl:Li, which have Type I emission at low temperatures and Type II emission at high temperatures, has been studied at 10 and 77 K by measuring the resonant secondary radiation (RSR) spectrum from optically excited F_A centers with pico-second time-resolved spectroscopy. This study has been prompted by the quest to improve our knowledge on the de-excitation process in the F_A centers. The adiabatic potential energy curves are deduced from a theoretical analysis of the measured RSR spectra and compared with those already known. It is shown that Type II relaxation observed at 77 K occurs after Type I relaxation, supporting in turn a model proposed by Baldacchini et al. based on photoluminescence measurements.     

溶胶凝胶法制备以HfO2为绝缘层和ZITO为有源层的高迁移率薄膜晶体管

采用溶胶凝胶法制备了h-k氧化铪HfO₂薄膜, 经500℃退火后, 获得了高透过率、表面光滑、低漏电流和相对高介电常数的HfO₂薄膜. 并采用氧化铪作为绝缘层和锌铟锡氧化物作为有源层成功地制备了底栅顶接触结构薄膜晶体管器件. 获得的薄膜晶体管器件的饱和迁移率大于100 cm²·V^-1·s^-1, 阈值电压为-0.5 V, 开关比为5×10⁶, 亚阈值摆幅为105 mV/decade. 表明采用溶胶凝胶制备的薄膜晶体管具备高的迁移率, 其迁移率接近低温多晶硅薄膜晶体管的迁移率.     

(110)取向的调制掺杂GaAs-AIGaAs单异质结的光致荧光谱

测量了含碳量高低不同的(110)取向的调制掺杂GaAs-Al_0.3Ga_0.7As单异质结在4.2K下的光致荧光谱。在含碳量高的样品中,出现了强的沟道二维电子到受主的复合荧光峰;而在含碳量很低的样品的光致荧光中则只出现体GaAs的荧光峰。     

Orientation-selective excitation and dissociation in multilayer benzene

A newly constructed rotatable detector for desorption ion is described. The high resolution total yield spectra of desorbing ions from condensed benzene, along with the corresponding photoabsorption spectra, have been measured with various polarization angles of incident synchrotron radiation (SR) in the C 1s region. Polarization analysis of photoabsorption measurement showed that molecular planes of the adsorbed benzene molecules were randomly oriented. However, enhanced ion yields were observed at some resonances corresponding to in-plane transition, i.e. σ-symmetry, when the electric field vector (E) of SR became close to parallel to the surface normal. The results suggest that the probability of C–D dissociation and ion-desorption sequence becomes higher value in the molecular orientation perpendicular to the surface. The result also shows considerably high desorption probabilities in grazing incidence angles of less than 10°. This suggests that the contribution of a secondary effect resulting from bulk electrons is suppressed because the penetration depth of soft X-rays becomes small.     

Many-body effects in the radiative emission spectrum of semiconductors

We consider the effect of the interaction among photoinjected electrons, on the radiative emission spectra of semiconductors. The observed shift of the photoluminescence spectra, at high excitation levels, towards lower energies is accounted for by the present calculation.     

Generation of intense directional radiation during the fast motion of a liquid jet through a narrow dielectric channel

The results of theoretical and experimental studies of the cavitation phenomena in the volume of a moving liquid jet after its passing through thin and long oriented channels in dielectrics are considered. It is shown that the stationary generation of intense directional radiation in the optical range occurs in the moving jet volume as a threshold pressure is reached in the liquid (pure spindle oil). The parameters of radiation are close to those of laser radiation. The effective temperature of the generation region was estimated as corresponding to 50–100 eV. In some cases, optical radiation is accompanied by the pulsed generation of directional gamma radiation. These processes are accompanied by a sequence of high-voltage electric discharges of a great length in the liquid bulk and at the surface, corresponding to potential differences of 50–100 kV. One of the causes of the observed phenomena can be energetically favorable nuclear fusion reactions involving light nuclei in the liquid jet volume. It was shown that such processes can be efficiently stimulated by multibubble cavitation.     

纳米锗颗粒镶嵌薄膜的荧光特性研究

研究了不同颗粒尺寸的纳米Ge-SiO₂镶嵌薄膜的室温荧光光谱以及不同激发光能量对荧光峰的影响．实验结果表明，沉积态Ge-SiO₂薄膜样品在可见光区域不发光．退火后的样品（平均锗颗粒尺寸为3.2—6.0nm）在380—520nm波长范围内有明显的蓝光发射现象．当用λ=300nm的光激发，观测到中心波长为420nm（2.95eV）的光致荧光峰；而用633nm波长的光激发，谱图上出现中心波长分别为420和470nm的两个荧光峰．随着纳米锗颗粒尺寸的增加，光致荧光峰的相 关键词：     

A study of the orientation dependence of the electron energy loss spectra for single crystal films of copper and silver

Apart from two peaks caused by bulk and surface plasmons, four or five peaks (depending on the crystal type) of electron energy losses due to inter- and intraband electron transitions are observed in the investigation of the electron energy loss spectra for metals (Cu, Ag). A comparative analysis of the spectra for Cu or Ag films reveals a shift of bulk plasmon loss peaks to higher values for polycrystals, as in the case of transition metals and semiconductors. In a study concerning the orientation dependence of the energy loss spectra (ELS) for electrons scattered from the copper and silver surface, the anisotropy of the bulk plasmon peak is found when the incident beam’s polar angle or the sample’s azimuthal angle are altered. The anisotropy of the primary electron energy loss for plasmon excitation is also observed, depending on the sample orientation relative to the direction incident electrons. The energy losses are found to increase with an increasing atomic packing density of planes and crystal transparency relative to the incident beam.     

Effect of dopant concentration on the properties of HCl-doped PANI thin films prepared at different temperatures

Polyaniline thin film doped with hydrochloric acid (PANI-HCl) has been prepared by chemical oxidative polymerization at three different temperatures (4 °C, 13 °C and 31 °C) with two different dopant concentrations (1 M, 2 M). Fourier transform infrared spectroscopy indicated the presence of dopant and increase in degree of polymerization with decrease in temperature. X-ray diffraction revealed that all the films are of amorphous nature. Scanning electron microscopy showed fiber morphology with high dense inter-fiber fusion. Hall-effect analysis showed that appreciable increase in conductivity of the PANI-HCl films with 2 M-dopant concentration prepared at low temperatures (4 °C, 13 °C) occurs due to increase in carrier concentration. It also indicates the films as P-type semiconductors. UV–vis absorption spectra and photoluminescence spectra revealed that the role of dopant concentration is highly effective in the films prepared at low temperatures. High intense absorption cum emission peaks observed for the films with 2 M dopant concentration prepared at low temperatures is due to the decreased fiber diameter which increased the surface to volume ratio of the fibers and increased localized defect states. Photoluminescence spectra of the films excited using 300 nm show high intense emission peaks at 360 nm, 494 nm and a weak peak at 409 nm confirming the semiconductor nature.