Investigation of optical and electronic properties in Al–Sn co-doped ZnO thin films

Al-Sn co-doped ZnO thin films were deposited onto quartz substrates by sol-gel processing. The surface morphology and electrical and optical properties were investigated at different annealing temperatures. The surface morphology showed a closely packed arrangement of crystallites in all the doped films. As prepared co-doped films show a preferred orientation along an (0 0 2) plane. This preferred orientation was enhanced by increasing the annealing temperature to between 400 °C and 500 °C, but there was a shift to the (1 0 1) plane when the annealing temperature rose above 500 °C. These samples show, on average, 91.2% optical transmittance in the visible range. In this study, the optical band gap of all the doped films was broadened compared with pure ZnO, regardless of the different annealing temperature. The carrier concentration and carrier mobility of the thin films were also investigated.     

Vibrational states in low-dimensional structures: An application to silicon quantum wires

The Raman scattering in Si nanowires is studied by means of the local bond-polarization model based on the displacement–displacement Green's function within the linear response theory. In this study, the Born potential, including central and non-central interatomic forces, and a supercell model are used. The results show a notable shift of the main Raman peak towards lower energies, in comparison with the bulk crystalline Si case. This shift is compared with the experimental data and discussed within the quantum confinement framework.     

Electronic and optical properties of ordered porous germanium

The electronic band structure and dielectric function of ordered porous Ge are studied by means of a sp³s^* tight-binding supercell model, in which periodical pores are produced by removing columns of atoms along [0 0 1] direction from a crystalline Ge structure and the pore surfaces are passivated by hydrogen atoms. The tight-binding results are compared with ab-initio calculations performed in small supercell systems. Due to the existence of periodicity in these systems, all the electron states are delocalized. However, the results of both electronic band structure and dielectric function show clear quantum confinement effects.     

铝在水－乙醇混合体系中被氨基磺酸腐蚀的腐蚀速率的研究

用分光光度法研究了铝在含２０％（体积分数）乙醇的０．２～１．２ｍｏｌ／Ｌ氨基磺酸水溶液中，在５３～６５℃温度下的腐蚀速率．根据试验数据，利用Ｍａｔｈｕｒ提出的经验公式和Ａｒｒｈｅｎｉｕｓ公式分别计算出有关的动力学参数ｋ，Ｂ，Ａ和Ｅ，并把这些动力学参数与在氨基磺酸水体系中腐蚀的动力学参数进行了比较．发现了由于加入少量乙醇导致腐蚀速率明显降低，在上述两体系中腐蚀反应速率受氨基磺酸浓度影响的结果也存在有差异．     

大型圆锥体工件外锥小径专用量具的研制

研制了一种可精确测量大型圆锥体工件外锥面与端面交线尺寸的专用量具 ,介绍了量具结构及测量原理 ,分析了量具实际回转中心偏离设计回转中心的修正原理及检定方法     

A compact separator of monoenergetic electrons

A separator of monoenergetic electrons is described, in which two kinds of assemblies of “miniorange”-type magnetic filters (six magnets in each) are used. The ²⁰⁷Bi isotope with an activity of 240 kBq (7 μCi) that emits K ₁₀₆₃ and K ₁₇₇₀ conversion electrons serves as the electron source. For different kinds of assemblies, the intensity of electrons with energies of ～970 and ～1680 keV is accompanied by an increase in the radiation intensity by factors of 3 and 4, respectively, as compared to the intensities measured without magnetic filters, the energy resolution being ～30 keV. A single cycle of chamber evacuation guarantees constancy of the instrument’s parameters for one month.     

Oxygen Absorption in Free-Standing Porous Silicon: A Structural, Optical and Kinetic Analysis

Porous silicon (PSi) is a nanostructured material possessing a huge surface area per unit volume. In consequence, the adsorption and diffusion of oxygen in PSi are particularly important phenomena and frequently cause significant changes in its properties. In this paper, we study the thermal oxidation of p ⁺-type free-standing PSi fabricated by anodic electrochemical etching. These free-standing samples were characterized by nitrogen adsorption, thermogravimetry, atomic force microscopy and powder X-ray diffraction. The results show a structural phase transition from crystalline silicon to a combination of cristobalite and quartz, passing through amorphous silicon and amorphous silicon-oxide structures, when the thermal oxidation temperature increases from 400 to 900 °C. Moreover, we observe some evidence of a sinterization at 400 °C and an optimal oxygen-absorption temperature about 700 °C. Finally, the UV/Visible spectrophotometry reveals a red and a blue shift of the optical transmittance spectra for samples with oxidation temperatures lower and higher than 700 °C, respectively.     

Theory of Raman Scattering by Phonons in Germanium Nanostructures

Within the linear response theory, a local bond-polarization model based on the displacement–displacement Green’s function and the Born potential including central and non-central interatomic forces is used to investigate the Raman response and the phonon band structure of Ge nanostructures. In particular, a supercell model is employed, in which along the [001] direction empty-column pores and nanowires are constructed preserving the crystalline Ge atomic structure. An advantage of this model is the interconnection between Ge nanocrystals in porous Ge and then, all the phonon states are delocalized. The results of both porous Ge and nanowires show a shift of the highest-energy Raman peak toward lower frequencies with respect to the Raman response of bulk crystalline Ge. This fact could be related to the confinement of phonons and is in good agreement with the experimental data. Finally, a detailed discussion of the dynamical matrix is given in the appendix section.     

发展经济型数控系统我国数控技术产业化的合理途径

本文概述了我国经济型数控系统现状及发展动向，指出发展经济型数控系统是符合我国国情的数控技术产业化合理途径．     

Vortices in Hubbard Superconductors: A Bogoliubov-de Gennes Approach

Based on the Bogoliubov-de Gennes formalism, we study vortices with quantum magnetic fluxes in two-dimensional supercells, when an external magnetic field (B) is applied to s-, d-, and anisotropic s-wave superconductors. This study is carried out by using a generalized Hubbard model including negative U and V, as well as a nearest-neighbor correlated hopping interaction (Δt). The self-consistent calculation of the superconducting gap (Δ) shows the formation of vortices in real space, whose structure depends on the electron-electron interaction. Furthermore, the supercell averaged Δ as a function of B reveals qualitatively different behaviors for the three analyzed pairing interactions. Finally, the results suggest that the d-wave superconducting states have larger second critical magnetic fields than those corresponding to isotropic and anisotropic s-wave ones.