声速法高分子纤维模量测定的智能仪器

本文用声速法测定高分子材料的取向度与模量参数，结合微处理系统加以智能化，并具有运算、显示、打印输出结果的功能，在科研、教学实验和生产工艺过程控制中是很有实际意义的。     

A discussion on the utilization of elemental transmutation for efficient p-type doping in HgCdTe and HgCdTeSe: Approach and methodology

For p-type doping of HgCdTe, As is preferred because of its relatively low diffusion coefficient, but it suffers from being amphoteric. In this paper, two possible techniques for incorporating As into HgCdTe that should ensure its presence only on nonmetal sites are presented and discussed. These methods are primarily based on the fact that Se can be readily incorporated into group VI sites and that ⁷⁵Se naturally decays into ⁷⁵As. Because the nuclear recoils associated with this decay are too small to displace arsenic atoms, substitutional p-doping should be ensured. In addition, a methodology for accurately determining the efficiency of these doping techniques and their influence on the electrical and optical properties of the material is presented.     

Correlation of CdZnTe(211)B substrate surface morphology and HgCdTe(211)B epilayer defects

We present results on the surface morphology and recombination lifetimes of molecular-beam epitaxy (MBE)-grown HgCdTe (211)B epilayers and correlate them with the roughness of the CdZnTe substrate surfaces. The substrate surface quality was monitored by in-situ spectroscopic ellipsometry (SE) and reflection high-energy electron diffraction (RHEED). The SE roughness of the substrate was measured after oxide desorption in the growth chamber. The RHEED patterns collected show a strong correlation with the SE roughness. This proves that SE is a valuable CdZnTe prescreening tool. We also found a correlation between the substrate roughness and the epilayer morphologies. They are characterized by a high density of thin elongated defects, “needle defects,” which appear on most samples regardless of growth conditions. The HgCdTe epilayers grown on these substrates were characterized by temperature-dependent, photoconductive decay-lifetime data. Fits to the data indicate the presence of mid-gap recombination centers, which were not removed by 250°C/24-h annealing under a Hg-rich atmosphere. These centers are believed to originate from bulk defects rather than Hg vacancies. We show that Te annealing and CdTe growth on the CdZnTe substrates smooth the surface and lower substantially the density of needle defects. Additionally, a variety of interfacial layers were also introduced to reduce the defect density and improve the overall quality of the epilayer, even in the presence of less than perfect substrates. Both the perfection of the substrate surface and that of its crystalline structure are essential for the growth of high-quality material. Thus, CdZnTe surface polishing procedures and growth techniques are crucial issues.     

Performance characteristics of planar ion-implantation isolated heterojunction,near-infrared,and short-wave infrared HgCdTe devices

Two-dimensional near-infrared (NIR) and short-wave infrared (SWIR) HgCdTe arrays have been produced using planar ion-implantation isolated heterojunction (PI3H) device technology. This paper is an extension of an earlier study in which focal plane arrays (FPAs) were fabricated based on heterojunction-mesa and ion-implanted planar device structures. The PI3H device structure is pursued in order to verify whether it can encompass both the superb multilayer characteristics of heterojunction detectors as well as the planar integrity of ion-implanted devices. The PI3H devices are characterized, and R₀A measurements are carried out at different temperatures and compared to those obtained from heterojunction-mesa and ion-implanted device structures. Data shows the PI3H devices to be superior to both heterojunctionmesa and ion-implanted detectors at temperatures between 130 K and 300 K. Performance characteristics of the thermoelectric (TE) cooled SWIR FPAs with 320 × 256 format, as well as NIR FPAs with 640×512 format based on the PI3H device structure are also discussed.     

Material quality characterization of CdZnTe substrates for HgCdTe epitaxy

Cd_1−xZn_xTe (CZT) substrates were studied to investigate their bulk and surface properties. Imperfections in CZT substrates affect the quality of Hg_1−xCd_xTe (MCT) epilayers deposited on them and play a role in limiting the performance of infrared (IR) focal plane arrays. CZT wafers were studied to investigate their bulk and surface properties. Transmission and surface x-ray diffraction techniques, utilizing both a conventional closed-tube x-ray source as well as a synchrotron radiation source, and IR transmission micro-spectroscopy, were used for bulk and surface investigation. Synchrotron radiation offers the capability to combine good spatial resolution and shorter exposure times than conventional x-ray sources, which allows for high-resolution mapping of relatively large areas in an acceptable amount of time. Information on the location of grain boundaries and precipitates was also obtained. The ultimate goal of this work is to understand the defects in CZT substrates and their effects on the performance and uniformity of MCT epilayers and then to apply this understanding to produce better infrared detectors.     

An implementation and evaluation of the MPI 3.0 one‐sided communication interface

The Message Passing Interface (MPI) 3.0 standard includes a significant revision to MPI's remote memory access (RMA) interface, which provides support for one‐sided communication. MPI‐3 RMA is expected to greatly enhance the usability and performance of MPI RMA. We present the first complete implementation of MPI‐3 RMA and document implementation techniques and performance optimization opportunities enabled by the new interface. Our implementation targets messaging‐based networks and is publicly available in the latest release of the MPICH MPI implementation. Using this implementation, we explore the performance impact of new MPI‐3 functionality and semantics. Results indicate that the MPI‐3 RMA interface provides significant advantages over the MPI‐2 interface by enabling increased communication concurrency through relaxed semantics in the interface and additional routines that provide new window types, synchronization modes, and atomic operations. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of Critical Thickness for Epitaxial ZnTe Layers Grown by Molecular Beam Epitaxy on (211)B and (100) GaSb Substrates

Cross-section electron micrographs, cathodoluminescence images, and confocal photoluminescence (cPL) images have been acquired for ZnTe layers deposited to various thicknesses on GaSb substrates with (211)B and (100) orientations. The critical thickness of ZnTe on GaSb is predicted to range between 115 nm and 329 nm, depending on the theoretical approach chosen. For ZnTe layers grown on (211)B GaSb with thickness exceeding 150 nm, dark spots and lines are present in all images. We associate these with dislocations generated at the ZnTe/GaSb interface. The discrepancy between this thickness value and a critical thickness value (350 nm to 375 nm) obtained for the (211)B orientation in a previous study is related to the distinction between the onset of misfit dislocations and the onset of significant plastic deformation. The former requires a direct imaging technique, as strain-related measurements such as x-ray diffraction do not have the resolution to detect the effects of small numbers of dislocations. For ZnTe layers on (100) GaSb, x-ray diffraction measurements indicate an abrupt change characteristic of dislocation multiplication at a thickness value in the range from 250 nm to 275 nm. High-resolution electron micrographs of the ZnTe/GaSb interface indicate that deoxidation using atomic hydrogen produces GaSb surfaces suitable for ZnTe epitaxy. cPL images of a 1.2-μm-thick lattice-matched ZnTe_0.99Se _0.01 layer grown on a 150-nm-thick ZnTe buffer layer on a (211)B GaSb substrate yield a threading dislocation density of ～7 × 10⁴ cm^?2.     

Growth of Lattice-Matched ZnTeSe Alloys on (100) and (211)B GaSb

A key issue with the current HgCdTe/Si system is the high dislocation density due to the large mismatch between HgCdTe and Si. An alternative system that has superior lattice matching is HgCdSe/GaSb. A buffer layer to mitigate issues with direct nucleation of HgCdSe on GaSb is ZnTe_1?x Se _x . We have performed preliminary studies into the growth of lattice-matched ZnTe_1?x Se _x on both (100) and (211)B GaSb. The effects of substrate orientation, substrate temperature, and growth conditions on the morphology and crystallography of ZnTe_0.99Se_0.01 alloys were investigated. The lattice-matching condition yielded minimum root-mean-square (rms) roughness of 1.1?nm, x-ray rocking curve full-width at half-maximum (FWHM) value of ~29?arcsec, and density of nonradiative defects of mid-10⁵?cm^?2 as measured by imaging photoluminescence.     

Influence of gut microbiota and manipulation by probiotics and prebiotics on host tissue fat: Potential clinical implications

The gut microbiota is considered as one of the most important environmental factors impacting on host metabolism, contributing to variations in body weight, fat distribution, insulin sensitivity and lipid metabolism. Modification of the gut microbiota by dietary interventions such as probiotics and prebiotics may favourably affect host lipid metabolism. We have shown that microbial metabolism in the gut, and its manipulation by administered microbes can influence fatty acid composition of a number of organs in the host. Furthermore, a prebiotic approach was shown to alter polyunsaturated fatty acids in white adipose tissue. Although a deeper knowledge of the interactions between members of the gut microbiota and fatty acids is needed, nutritional modulation of this complex community may represent a realistic target for modification of host fatty acid composition.     

Stress enhanced TiO2 nanowire growth on Ti–6Al–4V particles by thermal oxidation

Titanium dioxide (TiO₂) nanowires were grown on Ti - 6wt% Al - 4wt% V (Ti64) particles by thermal oxidation. To investigate the effect of stress on nanowire growth, the particles were milled in a planetary ball mill prior to the thermal oxidation. Thermal oxidation of the Ti64 particles was carried out in a horizontal tube furnace in a controlled oxygen atmosphere in the temperature range of 700–900 °C. The oxygen concentration was varied from 20 ppm to 80 ppm in Ar atmosphere. Nanostructures were characterized by high resolution field emission scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. TiO₂ nanowires grew on the surface of Ti64 particles and exhibited a square/rectangular cross sectional shape with thicknesses of 20–40 nm and lengths of 2–3 μm. Residual stress was found to play a significant role in nanowire growth. This was confirmed by growing TiO₂ nanowires on Ti64 alloy sheet with an induced stress gradient along its length. An improvement in nanowire coverage was observed in regions of high residual stress. A stress-induced growth mechanism is suggested to explain the confinement of nanowire growth to one dimension during thermal oxidation.