聚晶金刚石复合体超高压液相烧结理论研究

 在对前人有关聚晶金刚石超高压烧结机理的综合分析与评价的基础上,通过对金刚石与不同组分的钴熔体相互作用规律,及金刚石从钴熔体中的结晶热力学与动力学的理论研究,提出了石墨优先金刚石“溶解”和金刚石石墨化“溶解”的观点,阐明了钴熔体的性质对金刚石（石墨）的浸润扩散溶解过程,以及金刚石再结晶析出过程的影响,认为在金刚石-钴烧结系统中存在三种主要烧结机构：颗粒重排,溶解-析出和聚晶固架形成机构。不同温度条件下不同碳含量钴熔体在烧结过程中,对于促进金刚石表面石墨化,进一步引起颗粒重排,实现sp³结构碳原子在金刚石颗粒间的有效迁移传递以及D-D直接结合等方面起到了十分重要的作用。根据上述金刚石超高压液相烧结理论的基本观点,可较合理地解释聚晶金刚石复合体（PDC）在超高压烧结过程中观察到的一些基本现象和实验事实。     

Overlayer thickness determination by XPS using the multiline approach

An important analytical application of x‐ray photoelectron spectroscopy is the possibility of determining the overlayer thickness in the nanometer range. The relevant procedure should be based on a realistic theoretical model relating the photoelectron signal intensities, measured for the overlayer and for the substrate, to the overlayer thickness. In the most frequently used procedure, we derive the thickness from the ratio of intensity measured for the overlayer and intensity measured for the substrate. We may expect that the resulting thickness depends on the pair of intensities selected for analysis. This is due to the fact that each calculated intensity has a certain systematic error associated with accuracy of parameters used in calculations. We consider here a possibility of using more than two intensities, for a given element, in the procedure of thickness determination. In this way, we expect that the analysis is more accurate due to the fact that the systematic errors are averaged. In the past, similar approach has been successfully applied to the procedure of surface composition determination. To test the proposed multiline approach, the Au 4f, Ni 2p, and Ni 3p intensities were measured for a series of Ni overlayers deposited on the Au substrate. It has been found that the proposed approach well performs at relatively large overlayer thicknesses. It provides values that are averages of values obtained from other methods. At small overlayer thicknesses, we observe a scatter of thicknesses obtained from different methods which can be due to the discontinuity of the overlayer. Copyright © 2008 John Wiley & Sons, Ltd.     

硅烷热解多晶硅气相沉积反应模型分析与验证

在综述现有硅烷热解反应机理的基础上,针对Ho等人提出的气相和表面反应机理,采用二维边界层反应模型和CHEMKIN软件,对水平单基片CVD反应器进行模拟分析,计算结果与文献报道的实验数据拟合良好;通过改变硅烷进气浓度和进气温度,分析沉积速率的变化和各表面反应的贡献率,得到硅微粉再沉积过程随浓度和温度的变化规律;使用上述机理模型,计算了硅烷流化床对应的操作温度和硅烷浓度条件下的沉积速率,与文献报道测量结果比较,误差在合理范围,表明该机理适用于硅烷流化床化学气相沉积过程的CFD耦合模拟.     

变温退火制备铝诱导大晶粒多晶硅薄膜的机理研究

为了缩短铝诱导法制备大晶粒多晶硅薄膜的退火时间,用射频磁控溅射法在玻璃衬底上沉积了a-Si/SiO2/Al叠层膜,并用两种方法进行变温退火.分析了变温退火工艺对铝诱导晶化过程的影响,着重讨论了退火过程中温度由低温升到高温时不形成小晶粒的机理和条件.研究表明,当退火温度升高时,是否形成小晶粒取决于晶粒半径、耗尽层厚度和相邻晶粒间距三者之间的关系.     

纳米多晶La0.7Sr0.3MnO3－δ的输运性质和磁电阻效应研究

利用溶胶-凝胶法制备了纳米多晶La_0.7Sr_0.3MnO_3-δ(LSM)块体样品.详细研究了在不同烧结温度下的LSM样品电阻率随测量温度的变化关系和磁电阻效应.随着测量温度从室温降低,电阻率ρ都在250K附近存在最大值,低于该温度后,样品表现为金属导电特性,随后在50K左右存在一极小值.即随着温度从50K左右降低到4.2K,ρ反而逐渐升高,表现为绝缘体性的导电特性.研究表明,在低温下(<50K),ρ随温度降低而升高的现象与隧穿效应的理论模型(lnρ∝T^1/2)符合得很好,表明这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所致.而在50—250K的温度范围内,其电阻率与T²成正比,表现为LSM本征的金属导电特性.因此这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争.本文还详细研究了相应的隧道磁电阻效应. 关键词： 0.7Sr_0.3MnO_3-δ')" href="#">多晶La_0.7Sr_0.3MnO_3-δ 隧道效应 隧道磁电阻效应     

Catalytic Activity of Anisotropic Gold Nanoplates towards Oxygen Reduction

Glassy carbon electrode (GCE) coated with anisotropic gold nanoplates (aAuNPs) was used for the study of oxygen reduction reaction (ORR) in 0.5 M sulfuric acid instead of bulk gold electrodes. The electrode cleaning/activation procedure lead to the removal of any charged and uncharged residues on the gold nanoplates, leaving the nanostructured surface highly active towards oxygen reduction. The advantages: much lower overpotential and larger current densities of oxygen reduction are ascribed to the unique nanostructures present on the carbon electrode surface‐the gold nanoplates. They are rich in edges providing a large population of Au (100) sites with unsaturated coordination exposed to the solution, and catalytically active. Measurements performed using a rotating disc electrode, modified with the gold nanoplates, confirmed that ORR proceeds via two separate steps: oxygen is reduced to hydrogen peroxide, and the peroxide is further reduced in a two‐electron reduction to water.     

多晶硅晶体生长中固-液界面研究进展

论述了多晶硅晶体生长技术的研究现状,探讨了多晶硅在定向凝固过程中的生长机制,重点阐述了多晶硅定向生长中固-液界面的形貌、杂质分布、数学模型、数值模拟以及外场对界面调控的影响,归纳总结目前国内外多晶硅生长界面的研究现状,展望了多晶硅晶体生长过程中固-液界面调控技术的发展前景.     

新型红外非线性光学晶体LiGaTe2的多晶合成与晶体生长

采用直接合成方法无法得到纯相的碲镓锂( LiGaTe2)多晶原料,因此提出了两步合成法进行LiGaTe2多晶原料合成,即先合成二元相Ga2Te3,再以Ga2Te3、Li、Te为原料按化学计量比配料在较低温度(850℃)下合成纯相的碲镓锂多晶料,并对具体的反应机理进行了讨论.对所得碲镓锂多晶料进行了XRD分析,结果显示合成的多晶为单相高纯LiGaTe2.差示扫描量热分析(DSC)表明,LiGaTe2的熔点为674.78℃.初步开展了LiGaTe2晶体的生长研究,对晶体生长结果进行了探讨.     

衬底温度对共蒸发制备GaSb多晶薄膜性质的影响

采用共蒸发的方法在玻璃衬底上制备出GaSb多晶薄膜材料.研究了薄膜生长速率与衬底温度、Ga源温度和Sb源温度的关系.通过XRD、UV-Vis、Hall效应和AFM等测试方法,研究了衬底温度对于GaSb薄膜的结构特性、光电性质以及表面形貌的影响.GaSb多晶薄膜具有(111)择优取向,薄膜的吸收系数达到105 cm-1,晶粒尺寸随衬底温度升高逐渐增大;衬底温度为540℃时,薄膜的迁移率达到127 cm2/V·s,空穴浓度为3×1017 cm-3.GaSb薄膜的表面粗糙度随温度增加而增加.     

三氯氢硅和氢气系统中多晶硅化学气相沉积的数值模拟

本文建立了三氯氢硅和氢气系统中混合气体动量、热量和质量同时传递,并且耦合气相反应、表面反应的多晶硅气相沉积模型,利用流体力学计算软件(Computational Fluid Mechanics, CFD)Fluent6.2数值分析了气体进口速率、反应压力、表面温度和气体组成对硅化学气相沉积特性的影响,数值结果表明计算结果与相关实验数据吻合较好.分析表明在一定的条件下,硅沉积速率随温度、压力的升高而增加,在氢气浓度较高的情况下,硅沉积速率随氢气浓度增加而线性地降低.