Small Angle Neutron Scattering in P+-Doped Porous Silicon

On the surface of single crystal silicon wafers, porous layers can be formed by electrochemical etching and their structural properties are determined by the doping type and concentration of the substrate. In p⁺-type doped, (1 0 0) oriented wafers the porous structure consists of tube-like voids and column-like remains of the silicon matrix, all perpendicular with respect to the wafer surface. In small angle neutron scattering experiments the micrometer long and nanometer diameter elongated scattering elements, i.e., tubes and columns can be well represented and approximated by cylindrical form factors. In an earlier experiment the diameter and scattering length distribution of the cylindrical scattering elements were measured in a p⁺-type (1 0 0) oriented porous silicon wafer [G. Kádár, G. Káli, Cs. Dücsõ, and E.B. Vázsonyi, Physica B 234–236, 1014 (1997)] and the tube diameters were seen to vary in the range from about 10 to 24 nm. In this paper the continuing small angle neutron scattering study of porous silicon layers will be presented. The evaluation conditions and method for the measured neutron intensity distributions will be discussed. The pore diameter distribution data calculated from the neutron scattering intensity curves are collected and compared in various samples of (1 0 0) oriented p⁺-doped wafers prepared with different porosity and different layer depth. The structural results and data obtained by small angle neutron scattering experiments may help in understanding the practically useful chemical, electronic and other properties of porous silicon.     

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建立了门座式起重机门座的空间力学模型，分析了由于荷载作用位置的非对称性造成门腿变形的非均匀性从而引起的门座顶平面及塔身的倾斜，并给出了此倾角的计算方法及计算公式。这将为门座式起重机的合理、精确设计，提供有益的参考。     

由一道力学摩擦题引起的思考

本文通过对一道滑动摩擦例题的分析讨论,归纳出具有多处摩擦的力学问题的多种解法,同时指出了一些力学教材中有关这类问题的值得商榷之处。     

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本文分析了异步电动机运行时的有功损耗、功率因数与入端电压的关系,阐明了异步电动机降压运行节电的机理,并导出晶闸管控制异步电动机节电的使用条件在特定延迟角触发下控制其应用的条件。     

激光照射下磁性材料的磁各向异性的研究

本文针对磁性材料经激光处理后,磁各向异性的改善,进行了细致的理论分析,根据对微观相互作用的研究,得出了磁各向异性变化的原因,是轨道猝灭程度的提高和交换相互作用减弱造成的。     

可消除鬼线或幻影的楔形分束器和楔形反射镜

对利用楔形分束器和楔形反射镜消除透射光及反射光中的鬼线或幻影进行了理论分析,给出了入射角与相应楔角的对应关系公式;并就实例进行了分析讨论。