A study of the contrast on growth striations in silicon by X-ray double crystal topography in the Laue case

The image of growth striations in Si formed by the double crystal X-ray topography in the Laue case (DCTL) is investigated. The results of the dynamical diffraction theory for crystals with small microdefects have been compared with the contrast behaviour determined experimentally. It has been found that the theory explains qualitatively the contrast on the striations and it has been demonstrated that the DCTL method is suitable for detection of the presence of small microdefects in growth striations. Since the paper completes a series of papers on X-ray topography of growth striations, some general conclusions are formulated concerning the applicability of the X-ray topographical methods to the investigation of the structure of the growth striations     

X-ray topography characterization of the structural response of Ge(Ga) crystals to variation in gravity force vector orientation during crystallization

The influence of crystallization process disturbances connected with the variation of the crystallization front orientation relative to the gravity force vector (characteristic for crystal growth under conditions of microgravity onboard space vehicles) on the real crystal structure has been investigated by plane-wave X-ray topography. It has been found that these disturbances can result in a local disorder in the impurity distribution in the form of microsegregation growth striations. Quantitative estimations of the amplitude for the composition variation based on the analysis of contrast in growth striation images obtained by the method of plane-wave X-ray topography have been carried out.     

基于图像扩散去噪的距离特征量提取研究

距离特征量反映了目标运动过程中的距离变化率,该观测量可由目标辐射噪声LOFAR谱图的干涉条纹中提取得到。低信噪比情况下,由于噪声的影响,干涉条纹特征会变模糊,提取的距离特征量值精度会降低。为提高提取精度,提出了一种边缘定向增强型扩散方程去噪方法,对LOFAR谱图进行处理,使条纹特征更加明显。迭代次数对扩散方程去噪效果影响很大,根据相关性原理,提出了一种迭代次数选择方法。为了使条纹特征更加易于区分,提出了一种基于区域分割的图像二值化方法。数值模拟实验和海试数据处理结果表明,LOFAR谱图经过处理后,提取出的距离特征量精度明显提高。     

Reduced pore diameter fluctuations of macroporous silicon fabricated from neutron‐transmutation‐doped material

The precision of photo‐electrochemical etching of perfectly‐ordered macropores in single‐crystalline silicon is limited by pore diameter fluctuations due to doping variations of the starting wafer (striations). The doping variation originates from the rotation during crystal growth in the float‐zone or Czochralski process, respectively. Experimentally, variations of the pore diameter up to 7% can occur. These so‐called striations limit performance of possible applications of macroporous silicon. As doping inhomogeneities are the reason for the striations, uniformly doped silicon wafers by neutron transmutation doping were used for the first time. Photoelectrochemical etching of neutron transmutated silicon has been carried out and the pore diameter fluctuation has been reduced by about 40% compared to standard doped float‐zone wafers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

折射率周期变化的LiNbO3晶体的制备及其布喇格效应

提拉法生长掺有溶质的ＬｉＮｂＯ３晶体时，有意识地引入周期性生长层，制备了折射率沿生长方向周期变化的ＬｉＮｂＯ３晶体。测量和研究了晶体的双折射率和布喇格衍射。实验结果证实晶体中折射率变化周期与生长层周期相一致。     

直拉法LiNbO3单晶体中的旋转生长条纹

使晶体转轴与温场对称轴不一致,则在晶体弯月面内会产生随时间变化的正弦波式的温度分布。建立了晶体转速、温度起伏、表面生长条纹和内部生长条纹间的一一对应关系,从而在晶体中有意识地引入了其周期可以任意调节的旋转生长条纹。 关键词：     

X-ray topography study of microsegregation in crystals

Concentration microinhomogeneities in crystals were characterized using x-ray topography, digital image processing, and spectral analysis of signals. Based on the features in lattice strains in such layered inhomogeneous crystals, methods for optimizing the conditions of x-ray topography detection of growth striations were proposed to obtain quantitative information on the composition fluctuation amplitude and spatial characteristics.     

Influence of ultrasonic vibrations on the growth of semiconductor single crystals

The influence of ultrasonic vibrations on striations in InSb, GaAs and Bi-Sb alloy single crystals grown by a modified Czochralski method was investigated. Ultrasonic vibrations at frequencies of 0.15, 0.25, 0.6, 1.2, 2.5, 5 or 10 MHz were introduced into the melt parallel to the pulling axis. The introduction of ultrasonic vibrations at a frequency up to 5 MHz eliminates the striations in GaAs and Bi-Sb alloy single crystals growing with constant diameter. It was found that for Bi-Sb alloy single crystals of constant diameter growth, after ‘processing’ of the melt with ultrasonic vibrations, the striations do not reappear until after 2 h. The effectiveness of the influence of the ultrasonic vibrations on the decrease of growth striations in InSb, GaAs and Bi-Sb alloy growing crystals was estimated with the help of the calculation of the sound absorption coefficient.     

GGG单晶的助熔生长与成核温度的确定

我们研究了GGG单晶的助熔生长,实验证明在PbO-PbF₂系助熔剂中GGG结晶的组分范围相当宽,生长相当稳定,而且位错密度较低。用感生条纹技术确定了GGG晶体生长的成核温度。 关键词：     

Periodically Self-Excited Moving Striations in a Low-Temperature Gas Plasma

A new nonlinear effect in a low temperature gas plasma has been found and investigated experimentally. At a critical value of the discharge current in a special glow discharge system the positive column constricts and striations evolve spontaneously. On a large time scale the pattern seems to consist of standing striations. At higher temporal resolution the striations turn out to be moving ones which are modulated by high amplitude oscillations of the total electric current and of the voltage observed at the device. In addition phenomena like period doubling and irregular behaviour occur.     

Effect of gravitation vector orientation relative to the solidification front on the micro- and macrohomogeneity of semiconductor crystals grown under terrestrial and space conditions

The influence of gravitation vector orientation relative to the solidification front on the dopant distribution micro- and macrohomogeneity in vertical oriented crystallization of highly Ga-doped Ge crystals has been investigated using computer simulation. The deviation of the axis for crystal growth relative to the g ₀ vector, when a free surface of the melt is present, has been found to provide the formation of striations with a reduced dopant concentration. The influence of the solidification rate, convective and diffusion mass flows on the dopant distribution macrohomogeneity has been investigated.     

声矢量传感器线阵波导不变量被动测距研究

介绍一种利用水声信道的统计不变特征(波导不变量)实现被动测距的方法。对接收LOFAR(Low FrequencyAnalysis Record)图使用HOUGH变换等边缘提取技术提取条纹,得到波导不变量以及抛物线参数的估计值,进而得到目标的CPA(Closest Point of Approach)点距离。矢量水听器的振速通道数据所得LOFAR图信噪比明显高于声压LOFAR图,可以提高测距精度。仿真和试验数据结果显示本方法能以较高的精度提取CPA点距离。对比波导不变量经验值和在线估计值所得最近点距离结果,发现使用具有一定精度的在线估计波导不变量值可以显著提高测距精度。     

X-ray study of structural features of GaSb(Si) single crystals grown using a set of diffraction methods under various heat and mass transfer conditions

Structural features of GaSb(Si) single crystals grown under various heat and mass transfer conditions were studied by x-ray topography and by double- and triple-crystal diffractometry. It was shown that a decrease in the convective flow intensity during crystal growth by the vertical Bridgman method with axisymmetric upper heat supply in comparison with the Czochralski method eliminates growth striations (caused by microsegregation) and improves the uniformity of electrical parameters of materials. According to triple-crystal x-ray diffractometry data, the increased density of structural defects observed in some crystal regions causes significant lattice distortions, which makes an additional contribution to crystal inhomogeneity. Some specific features in x-ray topography images of growth striations, caused by a high silicon concentration and a dopant state deviation from an ideal substitutional solid solution, were revealed.     

Disclosure of defects in YAG crystals by the thermoluminescence method

The topograms revealing the anisotropic distribution of defects in the volume of monocrystalline YAG samples have been obtained by the thermoluminescence (TL) technique. It has also been shown that the anisotropic distribution of the lattice defects affects strongly the shape of the TL curves. The greatest changes in the TL intensity were observed in the areas of the samples distributed symmetrically every 120°. It was noted that the selective distribution of the TL intensity is caused mainly by the presence of the (211) facets as well as growth striations formed during the growth process. The groups of lines observed in the TL spectrum have been ascribed to the Tb³⁺ ions, excited owing to the radiationless energy transfer from the bound exciton states (BES).     

Some results of the growth of semiconductor crystals in microgravity conditions (to the 50th anniversary of Yuri Gagarin’s flight into space)

The history of the growth of semiconductor crystals aboard space vehicles and their subsequent investigation has been described shortly. It has been shown using Ge(Ga), GaSb(Si), and GaSb(Te) crystals as an example that the formation of segregation growth striations can be avoided during their recrystallization by the vertical Bridgman method in conditions of physical simulation of microgravity on the Earth, mainly due to the essential weakening of the thermal gravitation convection. By their structure and impurity distribution, they approach the crystals grown in space. The investigation of recrystallization of Te has made it possible to determine the role of the detachment effect characteristic of the microgravity conditions and the features of the microstructure of the samples that crystallize with a free surface. The analysis of the results obtained from experiments in space allows us to better understand the processes occurring during the crystallization of the melts and to improve the crystal growth in terrestrial conditions.     

Diagnosis of colon cancer using frequency domain fluorescence imaging technique

Early detection and treatment of colon cancer has been associated with better disease prognosis. Conventional and reported optical techniques have limitations in detecting early stages of colon cancer growth. In this paper, a homodyne signal processing assisted frequency domain (FD) fluorescence imaging methodology is proposed for the early diagnosis of colon cancer. Simulated phantom tissues representing the biopsy samples at different stages of colon cancer growth are prepared and used for the imaging study. Selective imaging of healthy and diseased sites simulated in the samples was achieved even for fluorescence emissions having close lifetimes and wavelength values. Possible extension of the methodology for in vivo investigations is also discussed.     

Liquid/solid interface profile of melt grown oxide crystals II. Crystal quality

Temperature gradients and rotation rates influence the quality of Czochralski grown oxide crystals. Decreasing the heat transfer from the melt level and increasing the rotation rate increases the optical homogeneity and structural perfection of the crystal, due to convex interface becoming flattened. Growth striations due to temperature fluctuations in the melt during growth are affected by the heat losses from the melt level but are practically unaffected by the rotation rate as long as a narrow ring of centrifugally streaming melt in the neighbourhood of the growing crystal is not formed. The parts of the crystals grown in the presence of this ring contain no striations.     

Beam intensity striations and applications

The single-element spectrogram for a continuous broadband signal, plotted as a function of range, has been shown to exhibit striated bands of intensity maxima and minima. The slope of the striations is an invariant of the modal interference and is described by a waveguide invariant parameter "beta." The striation pattern is analyzed and modeled in this paper for the beam outputs of a horizontal line array obtained by conventional beamforming. Array beamforming makes it possible to measure the waveguide invariant parameter for weak signals due to the enhancement of signal levels by the array gain over that of a single element. It is shown that the signal beam spectrogram as a function of range exhibits the same striation pattern as that (predicted) for a single element. Specifically, for a broadside signal, the beam striation is identical to that of a single-element plus a constant signal gain. For a nonbroadside target, the signal beam intensity will be modified by a frequency-bearing dependent signal gain due to the signal spread over multiple beams, nevertheless the beam spectrogram retains the same striation pattern (slope) as for a single element. The sidelobe beams (outside the canonical cones containing the signal arrivals) exhibit an entirely different striation pattern as a function of frequency and range. For array processing, it is shown that a fast range-rate, close range target and a distant, slow range-rate interference source will have a different striation pattern (slope) in the corresponding beam spectrograms as a function of time, assuming no prior knowledge of the source ranges. The difference in the striations between the beam spectrograms can be used in array processing to suppress the interference contribution. A 5-7 dB interference suppression is demonstrated using simulated data.     

直拉法生长的LiNbO3单晶体中的生长条纹和铁电畴组态间的对应关系

对应于旋转条纹和功率条纹,观测到晶体中铁电畴组态的相应变化,确定了旋转条纹与铁电畴组态间的一一对应关系,利用扫描电子显微镜中的X射线能谱分析测定了旋转条纹中的溶质浓度分布,得到了溶质浓度梯度决定了铁电畴组态的结论,自发极化与溶质浓度梯度间的耦合首次得到了实验证实。 关键词：     

三维声波测井探测特性分析与处理技术应用

三维声波测井技术是近年来测井领域的重要进展,由于其集成了井孔轴向、径向和周向的三维信息探测能力,因而在各种复杂油气藏勘探开发中具有广阔的应用前景.从井孔声波探测的基本原理入手,对三维声波测井在井孔径向和周向的探测特性进行了研究.并且在传统资料处理方法的基础上,研发了适合三维声波测井的各向异性快速反演技术、径向速度层析反...