d bands position and width in gold from very low temperature thermomodulation measurements

Thermomodulation measurements were made on thin semitransparent films ot Au at about 20, 70 and 340 K in the range 2 to 5 eV. Comparison of spectra taken at different temperatures allows straightforward interpretation of several structures. A model calculation is introduced to account for Δ?₂ lineshape for d bands to Fermi surface transitions. The agreement with the experimental data is very satisfactory.     

Active Micromachined Integrated Terahertz Circuits

Schottky barrier diodes have been integrated into on-chip rectangular waveguides. Two novel techniques have been developed to fabricate diodes with posts suitable for integration into waveguides. One technique produces diodes with anode diameters of the order of microns with post heights from 90 to 125 microns and the second technique produces sub-micron anodes with post heights around 20 microns. A method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.F. output in a mixer circuit. Devices have been fabricated and D.C. characterized.     

Relaxation in the photoelectric and photovoltaic responses of thin-film Pb(Zr0.25, Ti0.75)O3 ferroelectric

We study the relaxation of photoresponses in self-polarized Pb(Zr_0.25, Ti_0.75)O₃ film structures with a semitransparent NiCr top electrode under focused laser illumination with a wavelength of 0.63 μm and a power of about 40 mW. Dependences of the relaxation times of the photoresponses on the field directed both along the self-polarization vector and opposite to it are experimentally obtained. The dependences are found to be qualitatively different. We assume that in the structure under study, a screening charge occurs due to the capturing of photoinduced carriers in deep traps localized in the contact region.     

Application of the temperature distribution formula for the photoacoustic investigations of layer systems

This paper presents results of theoretical investigations of layer structures of the type: a thin semitransparent layer on the thick semitransparent substrate. Considerations presented in the paper comprise a derivation of the analytical expressions for the spatial distributions of the instantaneous temperature in the surface layer and the thermally semi infinitive substrate. These analytical expressions are of great importance as they enable computations of both frequency and spectral photoacoustic characteristics of several layer systems.     

Synthesis and PL Properties of ZnSe Nanowires with Zincblende and Wurtzite Structures

Single crystalline ZnSe nanowires with both zincblende and wurtzite structures have been synthesized via a chemical vapour deposition method under different growth conditions. The nanowires are usually 50-80nm in diameter, and several tens of microns in length. Room-temperature photoluminescence spectra from zincblende and wurtzite ZnSe nanowires show a broad luminescence band peaked at around 2. 71 e V and a deep level emission band peaked at around 2.00 eV, respectively. Effects of post-growth annealing on the photoluminescence of these nanowires have been investigated. Strong room-temperature band-edge emission could be obtained from the annealed zincblende ZnSe nanowires.     

The use of ultrasonic standing waves to enhance optical particle sizing equipment

Fluid dynamics modelling augmented with routines to simulate acoustic forces on aerosol particles has been used to investigate the potential of combining ultrasonic standing wave fields with optical particle analysis equipment. Simulations of particle dynamics in airstreams incorporating acoustic forces predict that particles in the 1-10 microns diameter range may be effectively focused to the velocity nodes of the standing wave field. Particles move to the velocity nodes within tens of milliseconds for acoustic frequencies of 10-100 kHz and at an acoustic energy density of 100 Jm-3. Larger particles are predicted to move to the velocity antinodes within similar times; however, there is a crossover region at approximately 15-20 microns particle diameter where longer times are predicted due to the competing forces driving particles to the vibration node and antinode. With sufficient transverse flow velocities the models predict that disturbances due to acoustic streaming can be overcome and a useful degree of focusing achieved for the aerosol particles. Results from a model demonstrating sampling and acoustic focusing of 3-9 microns aerosol particles to a 200 microns wide analysis area are presented.     

Quantitative Imaging by Optical Diffraction Tomography

Optical diffraction tomography (ODT) is applied to reconstruct the cross-sectional, complex refractive index distribution of cylindrical objects. Experimental reconstructions showing noticeable image contrast for refractive index variations of about 0.001, and having a spatial resolution of about 2 μm, are obtained for objects with cross-sectional diameters of about 100 μm. The results demonstrate that ODT can be used for quantitative imaging of semitransparent fibers.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994.     

基于一种新微细加工技术的亚波长光栅的研制

描述了一种新的亚波长光栅的微细加工技术，即电子束（EB）扫描曝光得到相应的亚微米级的线宽图形，再利用快速原子束刻蚀设备获得了高深宽比的立体结构。用此加工技术获得了100nm以下的刻蚀精度，并研制成功亚波长光栅。该亚微米线宽微细加工技术可用于布拉格光栅、半导体激光器、无反射表面等需要亚微米结构的器件中。     

Discontinuous finite element method for radiative heat transfer in semitransparent graded index medium

To avoid the complicated and time-consuming computation of curved ray trajectories, a discontinuous finite element method based on discrete ordinate equation is extended to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Two cases of radiative heat transfer in two-dimensional rectangular gray semitransparent graded index medium enclosed by opaque boundary are examined to verify this discontinuous finite element method. Special layered and radial graded index distributions are considered. The predicted dimensionless net radiative heat fluxes and dimensionless temperature distributions are determined by the discontinuous finite element method and compared with the results obtained by the curved Monte Carlo method in references. The results show that the discontinuous finite element method has a good accuracy in solving the multi-dimensional radiative transfer problem in a semitransparent graded index medium.     

Direct synthesis of beta gallium oxide nanowires, nanobelts, nanosheets and nanograsses by microwave plasma

In this study, beta-gallium oxide (β-Ga₂O₃) nanowires, nanobelts, nanosheets, and nanograsses were synthesized through microwave plasma of liquid phase gallium containing H₂O in Ar atmosphere using silicon as the substrate. The nanowires with diameters of about 20-30 nm were several tens of microns long and the nanobelts with thickness of about 20-30 nm were tens to hundreds of microns long. The morphology and structure of products were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These results showed that multiple nucleation and growth of β-Ga₂O₃ nanostructures could easily occur directly out of liquid gallium exposed to appropriate H₂O and Ar in the gas phase. The growth process of β-Ga₂O₃ nanostructures may be dominated by VS (vapor-solid) mechanism.     

Least-squares finite element method for radiation heat transfer in graded index medium

To avoid the complicated and time-consuming computation of curved ray trajectories, a least-squares finite element method based on discrete ordinate equation is extended to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Four cases of radiative heat transfer are examined to verify this least-squares finite element method. Linear and nonlinear graded index are considered. The predicted dimensionless net radiative heat fluxes are determined by the least-squares finite element method and compared with the results obtained by other methods. The results show that the least-squares finite element method is stable and has a good accuracy in solving the multi-dimensional radiative transfer problem in a semitransparent graded index medium, while the Galerkin finite element method sometimes suffers from nonphysical oscillations.     

锗红外干涉仪

本文叙述了一个锗制的红外干涉仪,它可供在2—11微米的红外区域内测定有机液体色散曲线之用。用此干涉仪测量了液体苯及氯仿在2—6微米区域内的色散曲线,所得结果与前人数据相比,符合良好。     

Photosensitivity and Schottky barrier height in Au-n-GaAs structures

The photosensitivity spectra of Au-n-GaAs Schottky barriers obtained by the chemical method are studied in the spectral range 0.9–2.2 eV. The barrier height is determined for the structures exposed on the side of the semitransparent Au layer and on the opposite side of GaAs at T = 300 K. It is found that, as the structures are illuminated on the side of GaAs, their photosensitivity in the Fowler spectral region, hν = 0.95–1.25 eV, is approximately one order of magnitude higher than when the barrier contact is illuminated. This circumstance may find use in studying the fundamental properties of the metal-semiconductor and metal-insulator-semiconductor interfaces, as well as in elaboration of new semiconductor devices.     

Backward Monte Carlo simulation for apparent directional emissivity of non-isothermal semitransparent slab

A backward Monte Carlo method based on radiation distribution factor is extended to compute the apparent directional emissivity of one-dimensional absorbing-emitting-scattering semitransparent slab with specular semitransparent surface and opaque diffuse substrate. A non-isothermal semitransparent slab is taken as an example to examine the efficiency of backward Monte Carlo method. The apparent directional emissivity of the semitransparent slab is determined by backward Monte Carlo simulation and compared with that determined by forward Monte Carlo simulation. The results show that the backward Monte Carlo method is very efficient in solving the apparent directional emissivity of the semitransparent slab. The backward Monte Carlo method converges more quickly than the forward Monte Carlo method.     

半透明平板边界入射辐射热流密度的反问题

对一维半透明平板内辐射、导热及边界对流耦合换热过程进行了研究。提出了一种由一侧边界出射辐射强度反演另一侧边界入射辐射热流密度的方法。通过对各向异性散射、吸收系数、散射系数、边界外侧来流温度、对流换热系数、半透明平板的导热系数和平板厚度等参数对反演精度影响的分析表明,方法是可行的。     

Discrete curved ray-tracing method for radiative transfer in an absorbing-emitting semitransparent slab with variable spatial refractive index

A discrete curved ray-tracing method is developed to analyze the radiative transfer in one-dimensional absorbing-emitting semitransparent slab with variable spatial refractive index. The curved ray trajectory is locally treated as straight line and the complicated and time-consuming computation of ray trajectory is cut down. A problem of radiative equilibrium with linear variable spatial refractive index is taken as an example to examine the accuracy of the proposed method. The temperature distributions are determined by the proposed method and compared with the data in references, which are obtained by other different methods. The results show that the discrete curved ray-tracing method has a good accuracy in solving the radiative transfer in one-dimensional semitransparent slab with variable spatial refractive index.     

半透明梯度折射率介质内辐射熵传递方程及其数值模拟

在非相干辐射条件下,基于Planck光谱辐射熵强度定义,导出半透明梯度折射率介质内光谱辐射熵传递方程,以及局部辐射熵产率理论表达式.基于离散坐标法对辐射熵传递方程进行数值求解.以一维半透明梯度介质平板为例,对辐射熵方程及其算法进行验证.平板整体无因次辐射熵产的计算结果与宏观热力学定律的结果一致.     

Erratum: transient pulsations of small gas bubbles in water [J. Acoust. Soc. Am. 84, 985-998 (1988)] [corrected and republished

Transient behavior of small gas bubbles in a liquid set into violent motion by ultrasonic pressure waves is of interest because of widespread use of microsecond pulses in diagnostic ultrasound. Such pulses contain only a few pressure cycles and the transient pulsations of bubbles set in motion by such pulses would determine the bubble-ultrasound interaction. A computer study has been made to obtain a global representation of the pulsation amplitudes R (t) of small gas bubbles (nuclei) in water during the first few cycles of a cw ultrasonic pressure. One objective was to obtain a better understanding of cavitation phenomena where many nuclei with initial radii Rn from 0.1-20 microns are set in motion at pressures ranging from 0.5-5 bars and at frequencies from 0.5-10 MHz. Results allowed construction of surfaces showing the relative bubble amplitude R/Rn as a function of Rn and of the time t/TA, where TA is the acoustic period. One finding is that, in the range of peak pressures found in diagnostic pulses, transient cavities would be generated during the first pressure cycle from nuclei with initial radii as small as a few microns (micron). Nuclei that grow into transient cavities in the first pressure cycle are here called "prompt" nuclei. At a specified pressure, the size range of radii Rn in which they occur decreases with increasing frequency. At 5 bars, the range of Rn for prompt nuclei is 0.166-11.35 microns at 0.5 MHz and vanishes at 10 MHz.     

Monte Carlo discrete curved ray-tracing method for radiative transfer in an absorbing-emitting semitransparent slab with variable spatial refractive index

A Monte Carlo discrete curved ray-tracing method is developed to analyze the radiative transfer in one-dimensional absorbing-emitting semitransparent slab with variable spatial refractive index, in which the Monte Carlo method is combined with the discrete curved ray-tracing method. A problem of radiative equilibrium with linear variable spatial refractive index is taken as an example to examine the accuracy of the proposed method. The temperature distributions and the dimensionless radiative heat flux are determined by the proposed method and compared with the data in references, which are obtained by other different methods. The results show that the Monte Carlo discrete curved ray-tracing method has a good accuracy in solving the radiative transfer in one-dimensional semitransparent slab with variable spatial refractive index.     

Finite element method for radiation heat transfer in multi-dimensional graded index medium

In graded index medium, ray goes along a curved path determined by Fermat principle, and curved ray-tracing is very difficult and complex. To avoid the complicated and time-consuming computation of curved ray trajectories, a finite element method based on discrete ordinate equation is developed to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Two particular test problems of radiative transfer are taken as examples to verify this finite element method. The predicted dimensionless net radiative heat fluxes are determined by the proposed method and compared with the results obtained by finite volume method. The results show that the finite element method presented in this paper has a good accuracy in solving the multi-dimensional radiative transfer problem in semitransparent graded index medium.