晶体位错处理对X射线衍射性能的影响

为提高晶体对波长为0.1~20 nm的X射线的衍射效率,通过特殊工艺对特定晶体表面进行位错处理。将云母、α-石英和LiF晶体劈成80 mm×10 mm的晶体薄片,其中LiF晶体厚度研磨到1 mm,其余三种晶体厚度为0.2 mm。将LiF晶体加热到400 ℃,然后用椭圆型折弯机进行多次弯曲,自然冷却降到室温,使晶格发生位错现象。在波长为0.154 nm的Cu靶X射线衍射仪上进行衍射试验,经晶体后利用成像板或X射线CCD获得衍射谱线,其中Mica球弯晶获得多级衍射谱线,经过表面处理的LiF晶体获取的X射线光子数比未处理的高2倍。结果表明晶体表面经过位错处理后提高了衍射效率,更适合X射线诊断研究。     

半导体异质结构材料的X射线晶体衍射测试分析

本文介绍Ｘ射线晶体衍射的测试原理，讨论了半导体薄片异质结构材料Ｘ射线晶体衍射测量中正、负失配，晶片微弯曲，摇摆曲线的对称性，复杂曲线的分解、干涉带等问题。指出了晶体衍射测试结果对ＭＯＣＶＤ、ＬＰＥ工艺调整的重要性。     

Li2B4O7晶体的X射线衍射分析

本文用X射线衍射法对Li_2B_4C_7晶体进行了分析,得到了它的点阵参数、晶面指数、重要晶带中的晶面夹角值和主要面族间的夹角值.利用以上数据绘制了三种标准极图.这些结果可用于Li_2B_4C_7单晶生长研究、晶片加工以及以它为基片的SAW器件设计.     

X射线衍射形貌术在碲锌镉晶体中的应用

碲锌镉晶体中存在着各种典型晶体缺陷,X射线衍射形貌术是一种非破坏性地整体研究晶体材料结构完整性、均匀性的有效方法。本文将反射式X射线衍射形貌术应用于碲锌镉晶体质量的评价,研究了入射线狭缝宽度、积分时间、扫描步长等测试参数以及样品表面加工状态对X射线衍射形貌的影响。结果表明入射线狭缝宽度对碲锌镉晶体的X射线衍射成像及晶体质量筛选应用影响很大,积分时间、样品扫描步长等测试参数的选择与入射线狭缝宽度密切相关。     

半绝缘GaAs单晶化学配比的X射线双晶衍射Bond方法测量

本文利用Ｘ射线双晶衍射Ｂｏｎｄ方法，精确测量了各种条件下生长的半绝缘ＧａＡｓ的晶格参数．建立了过量Ａｓ在晶体中存在的间隙原子对模型，在理论上找到了影响半绝缘ＧａＡｓ晶格参数的根本原因．并建立了半绝缘ＧａＡｓ晶格参数与化学配比的关系，实现了化学配比的无损测量．这对于ＧａＡｓ单晶的制备和相关光电子器件的研究具有重要意义．     

碲锌镉晶体的X射线衍射形貌与腐蚀形貌

碲锌镉晶体中存在着各种典型晶体缺陷,其缺陷研究一直倍受关注,X射线衍射形貌术是一种非破坏性地研究晶体材料结构完整性、均匀性的有效方法.采用反射式X射线衍射形貌术对碲锌镉衬底的质量进行了研究,并将衬底的X射线衍射形貌与Everson腐蚀形貌进行了对比分析,碲锌镉衬底的X射线衍射形貌主要有六种特征类型,分别对应不同的晶体结构或缺陷,包括均匀结构、镶嵌结构、孪晶、小角晶界、夹杂、表面划伤,对上述特征类型进行了详细的分析.目前,衬底的X射线衍射形貌主要以均匀结构类型为主,划伤和镶嵌结构缺陷基本已消除,存在的晶体缺陷主要以小角晶界为主.通过对比分析碲锌镉衬底和液相外延碲镉汞薄膜的X射线衍射形貌,发现小角晶界等晶体结构缺陷会延伸到外延层上,碲锌镉衬底质量会直接影响碲镉汞外延层的质量,晶体结构完整的衬底是制备高质量碲镉汞外延材料的基础.     

基于谐衍射元件的新型光子晶体光纤熔接机校准系统设计

通过分析光子晶体光纤特殊的单芯、多气孔结构及在熔接中传统校准方法的局限性,研究了光纤熔接机中校准系统结构的关键技术.利用谐衍射透镜体积小,衍射效率、精度高等特点,设计了基于谐衍射透镜的离轴光学校准系统.在可见光单波段成像,不仅有效地消除了系统的色差、彗差,大大提高了衍射效率,而且很好地完成了系统像差校正,通过该系统,准确地得到了清晰的PCF截面图像.比较两端面的PCF图像,再对光纤进行空间坐标的调整,即可实现光子晶体光纤熔接中光纤的精确对准.     

Corner diffraction coefficients for the quarter plane

The current near a right-angled corner on a perfectly conducting flat scatterer illuminated by a plane wave is expressed as a sum of three currents. The first is the physical optics current, which describes the surface effect. The second is the fringe wave current, which is found from the half-plane solution and accounts for the distortion of the current caused by the edges. The third is the corner current, which is found from the numerical solution to the electric-field integral equation applied to the square plate, and accounts for the distortion of the current caused by the corner. It is found that the corner current for the right-angled corner, illuminated from a forward direction, consists mainly of two edge waves propagating along the edges forming the corner. Analytical expressions for these edge wave currents are constructed from the numerical results. A corner diffracted field is calculated by evaluating the asymptotic corner contributions to the radiation integral over the sum of the three currents. It is found that the corner contribution from the edge wave currents in some cases is of the same size as the corner contributions from the physical optics current and the fringe wave current     

An alternative diffraction coefficient for the wedge

A geometrical theory of diffraction (GTD) interpretation of a uniform solution for the wedge given by Mohsen is given. The diffraction coefficients are equal to those given by Kouyoumjian and Pathak except that the Fresnel argument in the two solutions are different. This uniform geometrical theory of diffraction (UTD) result is compared with exact series expansions for a plane wave incident on a90degwedge.     

An FEM-based numerical diffraction coefficient for irregular wedgeconfigurations

A hybrid numerical technique based on the finite-element method (FEM) is exploited to define a numerical diffraction coefficient for irregular wedge configurations as, for instance, a perfectly conducting wedge with an inhomogeneously filled cavity-backed aperture in one of its faces, or a wedge with a rounded edge. The hybrid technique combines the FEM with the uniform geometrical theory of diffraction (UTD), and is used to develop a numerical diffraction coefficient to account for contributions to the scattered field due to localized inhomogeneities in an otherwise canonical perfectly conducting wedge     

Fringe wave diffraction coefficients for higher order discontinuities

We consider the diffraction of waves by objects with higher order discontinuities. The geometric theory of diffraction (gtd) diffracted field for this type of discontinuities have strong divergence near normal incidence. We substract from this diffracted field, the field radiated by the Luneberg-Kline currents to get the fringe diffracted field; and show that this field is finite. The formulae can be used to improve the accuracy of physical theory of diffraction (ptd) for smooth objects without edges. Explicit formulas are given for the discontinuity up to order 5. We present a numerical application for the discontinuity in the curvature. All computations are done by using Maple symbolic computation system.     

A heuristic UTD slope diffraction coefficient for rough lossywedges

Heuristic wedge diffraction coefficients for computing propagation path loss over finitely conducting earth are extended to include slope diffraction, with the assumption that propagation of energy through the wedge is negligible. The slope diffraction terms for the lossy wedge are obtained in an analogous manner as for the perfectly conducting case, except that special care must be taken with the factor multiplying the incident field for grazing incidence. Results given show that the slope diffraction term produces continuous results that behave reasonably when compared with results for perfectly conducting wedges     

A diffraction coefficient for a cylindrically truncated planar surface

A numerically derived solution of the diffraction coefficient for a source mounted on a perfectly conducting planar surface which is smoothly terminated by a circular cylinder is obtained using the hybrid approach which combines the moment method (MM) with the geometrical theory of diffraction (GTD). This solution is valid not only in the region away from, but also in the region near, the shadow boundary. The accuracy and usefulness of this solution is demonstrated as various structures are treated using it.     

电小尺寸凹槽的远区数值绕射系数

应用时域有限差分（FDTD）方法和时域加窗技术从物体的时域散射场中分离出劈和凹槽一类散射中心的贡献,计算其远区数值绕射系数。对于电小尺寸凹槽的远区数值绕射系数,结合微扰法给出了其计算结果。     

A new heuristic UTD diffraction coefficient for nonperfectly conducting wedges

A new heuristic UTD diffraction coefficient for non-perfectly conducting wedges is proposed. The coefficient is an extension of the heuristic one given by Luebbers (1984) and as simple as that to compute. In the case of forward-scattering and neglecting the surface wave effects, the new coefficient gives a result close to Maliuzhinets's (1958) solution, also deep in the shadow region where the previous one fails. Moreover, it makes the special care used by Luebbers to deal with grazing incidence unnecessary.