力学量与国际单位制(SI)

<正> 过去我国采用的基本计量单位是米制(即公制),而今后我国将逐步推行国际单位制.采用国际单位制,牵涉较多的部门主要是工业技术、生产和教学等方面,牵涉较多的学科主要是力学专业.为此,在这里介绍国际单位制和有关的力学量单位.国际单位制(Système International d'Unités,简称SI)是一九六○年第十一届国际计量大会(CGPM)通

低能离子束方法制备磁性Fe-Si合金薄膜

　利用质量分离的低能离子束技术,获得了磁性Fe Si合金薄膜。利用俄歇电子能谱法(AES)、X射线衍射法(XRD)以及交变梯度样品磁强计(AGM)测试了样品的组分、结构以及磁特性。测试结果表明在室温下制备的Fe Si合金是Fe组分渐变的非晶薄膜,具有室温铁磁性。当衬底温度为300℃时制备的非晶Fe Si薄膜中有Fe硅化物FeSi相产生,样品的铁磁性被抑制。

铁磁/半导体异质结材料MnSb/Si的物理气相沉积生长

采用一种新的生长铁磁 /半导体异质结材料的方法——物理气相沉积方法生长了一种铁磁 /半导体异质结材料 Mn Sb/Si.对所获得的样品进行特征 X射线能谱分析表明 Mn和 Sb在 Si衬底上的沉积速率相近 ,它们的原子百分数之比接近 1∶ 1.X射线衍射分析发现薄膜中形成了 Mn Sb相 ,样品在室温下测出磁滞回线也从侧面验证了存在 Mn Sb相 .用原子力显微镜对样品的表面进行观察 ,发现 Mn Sb呈有规则形状的小晶粒状 ,晶粒大小比较均匀 ,尺寸大多数在 5 0 0 nm左右 .

低能离子束方法制备Fe组分渐变的Fe-Si薄膜

利用质量分离的低能离子束技术 ,获得了Fe组分渐变的Fe Si薄膜。利用俄歇电子能谱法 (AES)、X射线衍射法 (XRD)以及X射线光电子能谱法 (XPS)测试了薄膜的组分、结构特性。测试结果表明 ,在室温下制备的Fe Si薄膜呈非晶态。非晶薄膜在 40 0℃下退火 2 0min后晶化 ,没有Fe的硅化物相形成。退火后Fe Si薄膜的Fe组分从表面向内部逐渐降低。

低能离子束方法制备重掺杂Fe的Si∶Fe固溶体

利用质量分离的低能离子束方法 ,以离子能量为 1 0 0 0 e V,剂量为 3× 1 0 1 7cm- 2 ,室温下往 p型 Si(1 1 1 )单晶衬底注入 Fe离子 ,注入的样品在 4 0 0℃真空下进行热处理 .俄歇电子能谱法 (AES)对原位注入样品深度分析表明 Fe离子浅注入到 p型 Si单晶衬底 ,注入深度约为 4 2 nm.X射线衍射法 (XRD)对热处理样品结构分析发现只有 Si衬底的衍射峰 ,没有其他新相 .X射线光电子能谱法 (XPS)对热处理样品表面分析发现 Fe2 p束缚能对应于单质 Fe的峰 ,没有形成 Fe的硅化物 .这些结果表明重掺杂 Fe的 Si∶ Fe固溶体被制备 .电化学 C- V法测量了热处理后样品载流子浓度随深度的分布 ,发现 Fe重掺杂 Si致使 Si的导电类型从 p型转为 n型 ,Si∶ Fe固溶体和 Si衬底形成 pn结 ,具有整流特性

Undercooling and Rapid Solidification of Nb-Si Eutectic Alloys Studied by Long Drop Tube

Niobium-silicide alloys have great potential for high temperature turbine applications. The two-phase Nb/Nb5Si3 in situ composites exhibit a good balance in mechanical properties. Using the 52 in drop tube, the effect of undercooling and rapid solidification on the solidification process and micro-structural characterization of Nb-Si eutectic alloy was studied. The microstructures of the Nb-Si composites were investigated by optics microscope (OM), X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with X-ray energy dispersive spectrometry (EDS). Up to 480 K, deep undercooling of the Nb-Si eutectic samples was successfully obtained, which corresponds to 25% of the liquidus temperature. Contrasting to the conventional microstructure usually found in the Nb-Si eutectic alloy, the microstructure of the undercooled sample is divided into the fine and coarse regions. The most commonly observed microstructure is Nb+Nb5Si3, and the Nb3Si phase is not be found. The change of coarseness of microstructure is due to different cooling rates during and after recalescence. The large undercooling is sufficient to completely bypass the high temperature phase field.

Electron injection by a nanowire in the bubble regime

The triggering of wave-breaking in a three-dimensional laser plasma wake (bubble) is investigated. The Coulomb potential from a nanowire is used to disturb the wake field to initialize the wave-breaking. The electron acceleration becomes more stable and the laser power needed for self-trapping is lowered. Three-dimensional particle-in-cell simulations were performed. Electrons with a charge of about 100 pC can be accelerated stably to energy about 170 MeV with a laser energy of 460 mJ. The first step towards tailoring the electron beam properties such as the energy, energy spread, and charge is discussed. (C) 2007 American Institute of Physics.

Si underlayer induced nano-ablation in AgInSbTe thin films

AgInSbTelSi thin films on glass substrates are prepared by dc magnetron sputtering at room temperature. Using Si underlayer as the thermal diffusion layer, the super-resolution nano-ablation holes with a size of 70nm in the AgInSbTe phase change films are obtained by a far-field focused laser experimental setup, with laser wavelength 405nm and objective-lens numerical aperture 0.90. The nano-ablation formation mechanism is analysed and discussed via the thermal diffusion of sample structures.

Si（111）衬底上ZnO薄膜的磁控溅射法制备及表征

采用磁控溅射法在(111)单晶硅衬底上沉积了ZnO薄膜，并研究了退火温度对ZnO薄膜晶体质量、晶粒度大小、应力和光致发光谱的影响。X射线衍射(XRD)表明薄膜为高度c轴择优取向。不同退火温度下的ZnO薄膜应力有明显变化。应力分布最为均匀的退火温度为500℃。室温下对ZnO薄膜进行了光谱分析，可观测到明显的紫光发射(波长为380nm左右)。实验结果表明，用磁控溅射法在单晶硅衬底上能获得高质量的ZnO薄膜。

退火对Si（111）衬底上ZnO薄膜的结构和发光特性的影响

采用磁控溅射法在硅（111）衬底上制备了C轴高度取向的ZnO薄膜，并研究了退火温度和氧气气氛对ZnO薄膜晶体质量、晶粒度大小和光致发光谱的影响。X射线衍射表明，所有薄膜均为高度C轴择优取向，当退火温度低于900℃时，随着退火温度的升高，薄膜的取向性和结晶度都明显提高。室温下对ZnO薄膜进行了光谱分析，退火后的样品均可观测到明显的紫光发射。在一定的退火温度范围内，还可以观测到明显的紫外双峰。空气中退火的样品，当退火温度达到或高于600℃还可观测到绿光发射。实验结果表明，发光峰强度随退火温度和氧气气氛不同而不

Intense upconversion and infrared emissions in Er3+;Yb3+ codoped Lu2 Si O5 and (Lu0.5 Gd0.5)2 Si O5 crystals

High optical quality Lu2SiO5 (LSO) and (Lu0.5Gd0.5)(2)SiO5 (LGSO) laser crystals codoped with Er3+ and Yb3+ have been fabricated by the Czochralski method. Intense upconversion (UC) and infrared emission (1543 nm) are observed under excitation of 975 nm. The luminescence processes are explained and the emission efficiencies are quantitatively obtained by measuring the UC efficiency and calculating the emission cross section. The temperature-dependent optical properties of the crystals are also investigated. Our study indicates that Er3+-Yb3+ : LSO and Er3+-Yb3+: LGSO crystals are promising gain media for developing the solid-state 1.5 mu m optical amplifiers and tunable UC lasers. (c) 2008 American Institute of Physics.

Structure and magnetic properties of CoNiP nanowire arrays embedded in AAO template

Ternary CoNiP nanowire (NW) arrays have been synthesized by electrochemical deposition inside the nanochannels of anodic aluminum oxide (AAO) template. The CoNiP NWs deposited at room temperature present soft magnetic properties, with both parallel and perpendicular coercivities less than 500 Oe. In contrast, as the electrolyte temperature (T-elc) increases from 323 to 343 K, the NWs exhibit hard magnetic properties with coercivities in the range of 1000-2500 Oe. This dramatic increase in coercivities can be attributed to the domain wall pinning that is related to the formation of Ni and Co nanocrystallites and the increase of P content. The parallel coercivity (i.e. the applied field perpendicular to the membrane surface) maximum as high as 2500 Oe with squareness ratio up to 0.8 is achieved at the electrolyte temperature of 328 K. It has been demonstrated that the parallel coercivity of CoNiP NWs can be tuned in a wide range of 200-2500 Oe by controlling the electrolyte temperature, providing an easy way to control magnetic properties and thereby for their integration with magnetic-micro-electromechanical systems (MEMS). (C) 2008 Elsevier B.V. All rights reserved.