激光医疗仪器的新进展

该文评述了国内外近年来在激光医疗和激光医疗仪器方面的新进展。     

长延迟反射栅色散延迟线

本文报道了用于电子对抗系统的表面波反射栅色散延迟线的制作情况。器件采用离子束刻蚀沟槽栅的制作工艺,整个刻蚀过程由计算机控制,制作出的器件其主要性能参数为:展宽线中心频率80MHz,色散时间126μs,色散带宽21MHz,插入损耗37dB;压缩线中心频率28MHz,色散时间63μs,色散带宽10.5MHz,插入损耗43dB;配对压缩后,旁瓣抑制可达34—36dB。     

多孔硅的化学浸蚀制备与表征

以不同电阻率的p型单晶硅片为研究对象,通过正交实验对化学浸蚀法制备多孔硅的工艺条件进行优化,采用多种仪器对制备的多孔硅比表面积、膜厚、表面形貌、化学组成及光致发光进行表征.结果表明,p型单晶硅片经化学浸蚀后能够形成多孔硅,其膜厚达到3 μm;延长浸蚀时间,多孔硅比表面积和膜厚呈先增大后减小的趋势,但化学浸蚀时间太长将导致局部区域的多孔硅层坍塌;室温条件下,多孔硅可光致发光,由于孔洞尺寸分布范围较窄,多孔硅发光半峰宽较窄.     

Plasma chemistries for dry etching of NiFe and NiFeCo

Plasma chemistries based on chlorine, bromine, or iodine have been investigated for inductively coupled plasma etching of NiFe and NiFeCo. There is clear evidence of a chemically enhanced etch mechanism with both Cl₂- and I₂- based mixtures, with no enhancement present for Br₂ chemistries. Etch yields are typically low (≤0.25), emphasizing the need for high ion fluxes in order to achieve practical material removal rates.     

Reactive ion etching of trenches in 6H-SiC

In this paper, we report the reactive ion etching (RIE) of trenches in 6H-silicon carbide using SF₆/O₂. The plasma parameters: etchant composition, gas flow rate, chamber pressure, and radio frequency power were optimized to obtain a maximum etch rate of 360Å/min. The etch rate of SiC was found to exhibit a direct correlation with the dc self bias except when the O₂ percentage was varied. Trenches were fabricated using the optimized conditions. It was found that the trench surface was extremely rough due to the aluminum micromasking effect. To overcome this effect, a Teflon^TM sheet was used to cover the cathode during the experiment. The trenches fabricated using this modification were found to have smooth etched surfaces and sidewalls. The angle of anisotropy of these trenches was approximately 80° which is suitable for device applications.     

Characterization of surface roughness anisotropy on mismatched InAIAs/lnP heterostructures

We have studied surface roughness on mismatched In_0.65Al_0.35As epilayers of various thicknesses on (001) InP. The sample set spans the entire range from coherently strained to completely relaxed epilayers. As characterization tools, we have used atomic force microscopy (AFM), laser light scattering (LLS), and variable azimuthal angle ellipsometry (VAAE). AFM reveals that the surfaces are covered by densely packed ellipsoidal islands elongated along the [1-10] direction. The island size increases with layer thickness. Island anisotropy and the root mean square of the surface roughness increase with increasing thickness but decrease upon full lattice relaxation. LLS intensity displays a prominent azimuthal dependence that correlates well with the two-dimensional power spectrum of the surface topography, as predicted by theory. VAAE reveals a sinusoidal dependence of the ellipsometric parameter Δ on azimuthal angle. The amplitude of A correlates well with the short wavelength anisotropy of the surface power spectrum. Our work suggests that LLS and VAAE are fast, nondestructive, sensitive techniques for characterization of surface roughness in mismatched III-V heterostructures.     

Low cost surface passivation for p-type mc-Si based on pseudobinary alloys (Al2O3)x(TiO2)1−x

The conventional process for back side passivation with full face Al screen printing layer is not suitable for very thin multicrystalline (mc-Si) solar cells and approaches to new technological processes are searched for. More investigations have been concentrated on local aluminum contacts and passivation coatings with different layers on mc-Si wafers. The aim of this work is to prove that (Al₂O₃)_x(TiO₂)_1−x is one promising candidate to be applied as passivation layer on multicrystalline Si. Investigations were performed on dielectric films of pseudobinary alloy (PBA) (Al₂O₃)_x(TiO₂)_1−x, prepared by chemical solution deposition known initially as sol–gel method. It was determined that their optical, dielectric and electrophysical properties are suitable for applications of these layers as back side surface passivation for thin multicrystalline silicon cells.     

晶粒超细化方法在降低材料表面能过程中的作用

利用分子动力学的原理计算了几种超细金属晶粒的表面能。研究表明:在超细化的晶粒尺寸范围内,材料表面能随晶粒尺寸的进一步减小急剧降低,而当晶粒长大到约20 nm后,材料的表面能则很快升至一个稳定的极限值——宏观尺寸材料的表面能值。对材料表面进行晶粒的超细化处理可使材料具有极低的表面能特性,这一特性可以应用于高黏度流体的减阻输送等领域。     

Shape optimization of inclined ribs as heat transfer augmentation device

This work presents numerical optimization techniques for the design of a rectangular channel with inclined ribs toenhance turbulent heat transfer.The response surface method with Reynolds-averaged Navier-Stokes analysis isused for optimization.Shear stress transport turbulence model is used as a turbulence closure.Computational re-sults for local heat transfer rate show a reasonable agreement with the experimental data.Width-to-rib height ratioand attack angle of the rib are chosen as design variables.The objective function is defined as a linear combina-tion of heat-transfer and friction-loss related terms with the weighting factor.Full-factorial experimental designmethod is used to determine the data points.Optimum shapes of the channel have been obtained in a range of theweighting factor.