Enhancement of several Kikuchi lines in the vicinity of spot reflections

Kikuchi electron diffraction patterns of silicon have been obtained which demonstrate the simultaneous enhancement of several excess Kikuchi lines near different point reflections. This enhancement is explained within the elementary mechanism of the formation of Kikuchi patterns while taking into account the Kikuchi electron double diffraction.     

Mechanism of formation of curved Kikuchi lines

The mechanism of formation of curved Kikuchi lines, observed at displacement of point reflections from their normal positions, is proposed. Curving of Kikuchi lines is explained taking into account the participation of diffracted electron beams in the formation of Kikuchi electron diffraction patterns.     

Electron differaction patterns with curved Kikuchi lines

Curved Kikuchi lines have been observed in electron diffraction patterns obtained for silicon by transmission electron microscopy. It is found that the curvature of Kikuchi lines is related to the shift of point reflections from their normal positions. The formation of curved Kikuchi lines stems from the local structural defects in the crystals under study.     

Electron diffraction patterns with thermal diffuse scattering maxima around Kikuchi lines

Transmission electron diffraction patterns of silicon with thermal diffuse maxima around Kikuchi lines, which are analogs of the maxima of thermal diffuse electron scattering around point reflections, have been recorded. Diffuse maxima are observed only around Kikuchi lines with indices that are forbidden for the silicon structure. The diffraction conditions for forming these maxima are discussed.     

Study of X-ray diffraction from a surface acoustic wave in the grazing geometry with allowance for the curvature of the unperturbed crystal surface

Fresnel X-ray diffraction from a concave crystal surface in the presence of a surface acoustic wave (SAW) has been considered for grazing angles of incidence in noncoplanar symmetric Laue geometry. It is shown that the main peak and diffraction satellites are focused at different distances from a crystal. The effect of deviation from the Bragg angle, the spectral line width, and the SAW amplitude on the X-ray diffraction pattern has been analyzed. It is established that the contrast of an X-ray diffraction pattern of an SAW in Bragg-Laue grazing geometry is related to the character of irregularities of the crystal surface, and the pattern details depend on the measurement mode. The sensitivity of the method is about a nanometer. The focal image of the SAW serves as a scale landmark for determining the crystal surface characteristics.     

电子背散衍射花样的数学特征

电子背散衍射(EBSD)花样揭示了材料的物相成分、晶体结构、晶粒取向、晶粒大小和晶界的信息。EBSD花样非常复杂,通常需要借助专门的计算软件才能解析。本文系统地研究了EBSD花样的数学特征,建立了任意晶体取向与EBSD花样之间的数理关系,推导了面心立方、体心立方和六方晶体的基本晶带轴的理论EBSD花样的数学特征,以及面心立方晶体的(001)<110>取向和(001)<100>取向的理论菊池(Kikuchi)花样特征。在实测EBSD花样的分析中与各晶系各点阵的基本晶带轴的理论EBSD花样特征比较,即通过图像特征对比,就可以直接确定实测EBSD花样所属的晶系、点阵和Kikuchi线交点对应的晶带轴[uvw],再由基本晶带轴的坐标计算出晶体取向,还能提供基本晶面信息,如原子密排晶面在样品中的空间分布,这有利于晶体的变形或生长机理研究。EBSD为单晶芯片质量检验提供了新方法。     

On the Intensity of Kossel Reflections

The line intensity of Kossel reflections of various single crystals (A1, A2, B3, B4 and C16 type of structure) has been studied experimentally as well as theoretically. In contrast to earlier results high excess intensity of experimental Kossel lines can be explained solely by dynamical diffraction effects without an additional consideration of real structure effects. It has been shown that the different maxima of intensities of Kossel lines found above all result from the different line width. depending strongly on the X-ray wavelength used (λ = 0.47−8.34 Å): Sole convolution of the theoretical profiles partly transforms the differences in the line width into variation of height.     

Formation and oxidation of porous silicon by anodic reaction

Porous silicon film (PSF) was formed by anodic reaction in aqueous hydrofluoric acid (HF) in the range 2 ? n < 4, n being the average number of electrons flowing through the external circuit per atom of silicon dissolved. Electron diffraction pattern of as-grown PSF changes to a very broad Kikuchi pattern from a sharp Kikuchi pattern for smaller values of n. The disproportionation reactions occur at a local point of the silicon surface for n between 2 and 4. When n is nearly equal to 2, the PSF structure changes to be amorphous and the reactions occur over the entire area of the silicon surface. The oxidation of PSF proceeds with the increase of the absorption intensities of three Si-O bands at 1070, 455, and 800 cm^-1 below 600°C, and two Si-O bands which are 455 and 800 cm^-1 above 600°C. Activation energies of Si-O bands at 1070, 455, and 800 cm^-1 at oxidation below 600°C are 0.1, 0.3, and 0.6 eV respectively. The activation energy changes remarkably below and above 600°C. The oxygen distributions in oxidized porous silicon of p-type and n-type PSF are uniform and nonuniform respectively in the thickness direction.     

Die Präparation von GaAs-Substraten,untersucht mit Reflexionselektroneninterferenzen

The RHEED-method is used for the examination and characterization of gallium arsenide substrates. It is shown the use of both beam focussing at the object and at the photoplate in studying this subject. It was found that the samples after abrasive cutting and machine lapping give interference patterns of mechanical damaged surfaces with characteristical features. Lap polished surfaces give Kikuchi pattern and a rel-rod pattern of perfect single crystal which is nearly smooth in the atomic level. Critical remarks are given on the Kikuchi pattern as a feature of perfection of the crystal. Results on the penetration depth of rough defects due to machine lapping are in good agreement with data from literature.     

Helldunkel-Struktur der Kossel-Interferenzlinien und Kristallstruktur-Analyse (II). Theoretische Linienprofil-Ausläufer und Vergleich mit experimentellen Ergebnissen

As shown in part I of this paper, from a Kossel-line profile the tails are best suited for crystal structure analysis. In this part a general theoretical expression has been derived for the tails of line profile in case of different examples often observed. The theoretical results have been compared with experimental ones. As a consequence two possibilities of application in crystal structure analysis can be recommended: at first the proof of proposals of structure by the use of tails of the profiles including phase information, and secondly the direct evaluation of structure amplitudes in favourable cases. – The dark and bright fields in Kossel patterns can be explained by taking into consideration the long ranging tails of profiles. The physical similarities and differences between Kossel interferences, divergent beam interferences, Kikuchi lines and channelling patterns are considered.     

Structure and chemical composition of LiB3O5 surfaces

The electronic and structural properties of LiB₃O₅ (LBO) surfaces have been studied by X‐ray photoemission spectroscopy (XPS) and reflectance high‐energy electron diffraction (RHEED). The as‐grown (110) crystal face and mechanically polished (001) surfaces have been investigated comparatively. Electronic structure of LBO has been determined on as‐grown (110) crystal face previously cleaned by chemical etching with RHEED control. The correlation of valence band structure and measured binding energies with earlier reported results has been discussed. Core‐level spectroscopy reveals strong enriching of mechanically polished LBO surface with carbon, when nanodiamond powder is used as an abrasive. So high carbon level as C:B = 0.7 has been observed at the surface while the ratio Li:B:O remains according to LBO chemical composition. The association of LBO Kikuchi‐lines with strong background has been shown by RHEED analysis of the surface. Thus, the polished LBO surface constitutes a high structure quality LBO with the inclusions of some amorphous carbon compound. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of purification on the polytypism in solution-grown cadmium iodide crystals

The effect of purification on the polytypism in cadmium iodide crystals has been studied by X-ray diffraction in three hundred and sixty polytypes. Formation of small period polytype 2H is governed by both temperature and impurities contained in the starting material. 4H is the most stable polytype and higher occurrence of unidentified polytypes in crystals of purified material has been attributed to free movement of edge dislocations during growth. The results have been examined against empirical conclusions of earlier investigations.     

Measurement of Microcrystal Size by Means of Diffraction of X-Rays

The diffraction function expressing the dependence of the intensity of the diffracted X-rays on the angle of diffraction ϱ is derived. On the basis of this equation two methods of measuring the microcrystal size in the direction of the normal line onto the beam of coherently diffracting atom planes are elaborated. Further, the methods for measuring the diffraction line enlargement owing to the experimental conditions are given here.     

Studies on the Smectic Phase of Some Schiff's Bases With a Terminal Trifluoromethyl Group

Some terminally substituted trifluoromethylbenzylideneanilines have been synthesized with a view to investigate an unidentified smectic phase which exhibits an unusual texture as observed under the polarizing microscope. This phase was first reported by Griffin et al.² for the compound N-(4-n-decyloxybenzylidene)-4'-trifluoromethylaniline. In a comparable compound but with reversed imine linkage the nature of this smectic phase remains unchanged. Also if the terminal n-decyloxy group is replaced by an n-decyl group the nature of the smectic phase remains the same except that it is observed at a considerably lower temperature. We observe that this smectic phase has uniaxial symmetry when studied with a polarizing microscope as well as with NMR techniques; the latter showing an order parameter S = 0.8 for this phase. X-ray diffraction patterns show this phase to be crystal smectic B.     

Kontrastsimulationen für die Transmissionselektronenmikroskopie und -beugung mit elektronischen Rechenmaschinen

The paper summarily reports on the computer simulations of diffraction effects caused by fast electrons at multidimensional lattice defects as well as on the output of the results in the form of contrast maps of contrast profiles. Important phenomena of transmission electron diffraction, also accessible to this procedure, are treated likewise. The image structures derived from the theory of electron diffraction in this way are comparable to those, which are observable in thin crystals by transmission electron microscopy and transmission electron diffraction. Introductorily the mathematical and physical starting situation respectively is shortly treated.     

Nontrivial role of the resolution function in the formation of double-crystal X-ray rocking curves

A theoretical analysis of the shape of the resolution function of an X-ray diffractometer in the double-crystal nondispersive scheme for measuring rocking curves has been performed. It is shown that this function, along with the strong narrow central line (corresponding to the characteristic line to which the collimator crystal and slits in the experimental scheme are tuned) always contains an additional weak satellite, corresponding to the neighboring characteristic line. This feature manifests itself in experimental curves as an additional pseudopeak, whose intensity is comparable with the corresponding diffraction scattering intensity from a sample in the fundamental characteristic line, and whose shape and exact position are set by the resolution function in a specific experimental scheme. It is shown that the exact allowance for the angular and spectral distribution of incident radiation in the double-crystal scheme makes it possible to precisely determine the parameters of the structures studied.     

X‐ray diffraction studies of bone apatite under acid demineralization

The analysis of the X‐ray diffraction line broadening used to determine bone apatite crystallite size and lattice microstrain can provide information about the substructure of the bone mineral under differing real or simulated conditions. The paper discusses modifications in the bioapatite crystals observed in the bone subjected to demineralization in a 0.1 N HCl solution. Planar oriented specimens of mature bone with the analyzed surface normal to the longer bone axis were treated for varied immersion times. The crystallite size and the lattice microstrain were determined simultaneously by Fourier analysis of the X‐ray diffraction line profiles. Both were observed to decrease during the acid demineralization. These findings support the idea that the distribution of lattice imperfections in the bulk of bioapatite crystals is highly nonuniform, with crystallite surface regions richer in imperfections dissolving more readily. In addition, an approach is proposed suitable for rough estimation of the reaction front advancement by demineralization‐induced variations in the integrated intensity or shift in the position of the (002) and (004) diffraction lines. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of a random system of dislocations in a deformed crystal

Structure of deformed crystals is modeled by dislocation loops of random size nonuniformly randomly distributed in natural slip planes. This model is used to determine structure parameters from the harmonics of the diffraction line of a polycrystal. Practical analysis of the dislocation structure under real conditions of the diffraction experiment is performed.     

Untersuchung gestörter Oberflächenschichten an Siliziumeinkristallen

It has been proved that by densitometric measurements of reflections of Kikuchi photograms a numeric value can be found for the quality of polished surfaces of Si single crystals. This value is given by the proportion ΔS₁/ΔS₀, characterizing the relation of the initial state of surface and the state of deeper layers, not being affected by mechanical working. This method enables to estimate the quality of crystal surfaces.