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.     

Birth-and-spread growth on the Kossel and a non-Kossel surface

A birth-and-spread growth model is derived for an anisotropic crystal surface and fitted to growth rate data obtained from Monte Carlo simulations of an isotropic and anisotropic Kossel (0 0 1) surface and a non-Kossel (0 0 1) surface. Only the step free energy is used as a fit parameter. All growth rate sets are nicely fitted by the new expression and the fitted values of the step free energy are in the physically relevant regime.     

The Influence of the Frequency on the Electrooptic Behaviour of Liquid Crystalline 4,4′-Bis-n-pentyl-azoxybenzene

The threshold voltage and the rise time of planar, homeotropic and twisted nematic layers were investigated in dependence of the frequency and the temperature. A strong increase of threshold voltage and rise time could be observed in the region of the dielectric relaxation frequencies between 0.1 and 1 MHz. The results were compared with those of the dielectric measurements.     

Heights of Overlapping X-ray Reflections and Phase Analysis

The influence of reflections overlapping on the heights of their maxima is investigated using the Lorentzian profile approximation. This influence should be taken into account in automatic powder diffractometer programs of phase analysis based on the peak heights.     

Polar Acetylenic Liquid Crystals with Broad Mesomorphic Ranges. The Positional Influence of Different C,C-Elements on the Transition Temperatures

Various mesogenic nitriles with inserted dimethylene, trans-vinylene and especially ethynylene units at different positions in the structures of typical nematogens have been prepared and examined with regard to their transition temperatures. The thermal stabilities of the mainly nematic phases for these new compounds were compared with those for the corresponding nitriles lacking these C, C-elements. Nematic thermal efficiency orders are given.     

CdS纳米晶的稳定化处理及介质极性对荧光光谱的影响

用硫脲、聚乙烯吡咯烷酮、L-半胱氨酸水溶液对水热法合成的硫化镉纳米晶进行稳定化处理,发现L-半胱氨酸和聚乙烯吡咯烷酮(PVP)能有效地稳定硫化镉纳米晶,荧光发射强度比处理前增强了五十倍以上.以氯仿、氧化三(正)辛基膦(TOPO)氯仿溶液以及3-巯基丙酸为萃取(或处理)剂,对水热法合成的水溶性CdS半导体纳米晶进行处理,经过荧光光谱分析,发现介质水、氯仿、氧化三(正)辛基膦(TOPO)氯仿溶液以及3-巯基丙酸会对CdS纳米晶的最大荧光激发峰与发射峰的位置产生不同影响,极性大的水分子使得荧光峰蓝移,极性小的氯仿、氧化三(正)辛基膦(TOPO)氯仿溶液以及3-巯基丙酸使得荧光峰红移,最大位移为31nm左右.     

Influence of X-ray irradiation on the optical properties of chromium-doped KliSO4 crystals

The absorption and circular-dichroism spectra of chromium-activated KLiSO₄ crystals both nonirradiated and irradiated with an X-ray beam have been studied. It was established that in nonirradiated crystals chromium ions are mainly trivalent (Cr³⁺) and have octahedral coordination. In irradiated crystals, along with the centers provided by (Cr³⁺) ions, new centers are formed associated with (^Cr4+) and (^Cr5+) ions.     

Influence of diffraction in crystals on the coherence properties of X-ray free-electron laser pulses

The spatial and temporal evolution of the field of random X-ray femtosecond pulses and their coherent properties upon pulse propagation in free space and under dynamical diffraction in perfect crystals in the Bragg and Laue geometries has been analyzed on the basis of the formalism developed in statistical optics. Particular attention is paid to the influence of large pulse propagation distances, which are characteristic of lengthy channels of X-ray free-electron lasers.     

Influence of surface roughness on the efficiency of X-ray mirrors with whispering gallery modes

Crystallography Reports - The influence of roughness on the propagation of an X-ray beam along a concave surface in the whispering gallery mode has been investigated. The transfer equation of beam...     

The Excitation Wavelength Dependence of Adenine Cation Single Crystal Luminescence

The excitation wavelength dependence of luminescence measured in adenine cation crystals at 77 K is reported. The observed variations of all the luminescence parameters exhibit a marked correlation with a changing penetration depth of the excitation light. The alterations of luminescence intensity, vibronic structure of emission spectra, emission polarization and phosphorescence decay were attributed mainly to a variable contribution of the emission from local excited states which correspond to a different trap ensembles in the crystal bulk and near the surface, respectively.     

The Behaviour of Zinc in GaP Synthesis by the SSD Technique

In this paper the principle of GaP synthesis by the SSD technique is described followed by a discussion of the results obtained in studying the transfer of an impurity such as the highly volatile zinc from the phosphorus source or gallium melt into GaP crystals. The radionuclide Zn⁶⁵ was used as a tracer to determine the concentrations of zinc in the phases involved in the process of synthesis. The results of these studies are compared with calculated values.     

The X-ray Structures of Sulfones

Abstract  

The X-rays structures of diphenyl sulfone 1, bis(3-aminophenyl) sulfone 2, bis(4-nitrophenyl) sulfone 3, 2-nitrophenylphenyl sulfone 4, benzylphenzyl sulfone 5, 4-nitrobenzylphenyl sulfone 6, 4-methylphenylbenzyl sulfone 7, dibenzyl sulfone 8, benzylisopropyl sulfone 9, and methylacetate,ethyl sulfone 10, are reported. B3PW91 DFT calculations were performed on selected sulfones for comparison. The S = O distances in these compounds range from 1.392(5) to 1.463(3) Å and S–C bond distances range from 1.743(7) to 1.790(3) Å. The C–S–C bond angles vary from 101.1(3)° to 106.80(14)° and the O–S–O bond angles vary from 116.7(2)° to 120.61(8)°. Using data obtained here and comparison with published structural data no evidence was found for para substituents on aryl groups influencing S–O bond distances, however, small changes on S–C bond distances were noted. Additionally, if the sulfur is flanked by an alkyl group the S–C distance is slightly larger than when it is flanked by an aryl group. Most of the sulfone compounds studied here display intermolecular soft hydrogen bonding interactions which influence their solid state packing. Furthermore, in dialkyl sulfone compounds these interactions appear to be strong enough to overcome conformational barriers calculated to be ca. 6 kJ mol⁻¹.     

极性晶体电气石颗粒的电极性观察

利用扫描电子显微镜(SEM)、电子探针(EPA)、浮选烘干等手段研究了黑色电气石粉体的带电性质.从电气石粉体的扫描电镜照片中发现,电气石颗粒间存在吸引与排斥;在电子探针研究中,首次直接观察到了电气石颗粒的自发极化产生的电极性.电子束轰击电气石微米颗粒后的显微照片中,轰击区域呈现半明半暗形貌,这种形貌反映了电气石颗粒自发极化的存在.并讨论了电气石颗粒表面电场.     

The Behaviour of Thin Samples of Ferroelectric Liquid Crystals

On a ferroelectric liquid crystal DOBAMBC transitions between helical and twisted structures are observed if changing the temperature. The twisted structure appears when the helical pitch becomes comparable to the sample thickness, From the switching process of the twisted DOBAMBC samples in an electric field the polarity of surface layers is determined. Low signal di- electric permittivity shows an increase below the transition to the ferroelectric phase, which is a consequence of the twisted structure deformation in the electric field.     

The Behaviour of Contact Angles of Wetting for Liquid Crystalline Drops on Glass Near the Phase Transition

The experimental values of contact angles of wetting for pazoxyanisole - glass in the nematic and isotropic phase have been obtained. At the point the phase transition, a change in the value of contact angle of wetting is observed. The values of adhesion energy, have been calculated for different orientation of molecules with respect to the glass support.

It is well-known /I/that contact angles of drops on solid supports enable an information on interfacial energy γ_SL to be obtained. A change in the structure of liquid results in alteretion of the contact angle as it a has been shown recently for polymer solutions /2/. It seem to be quite possible that orientational ordering of liquid crystals has to affect the value of contact angles of wetting. Nevertheless, this value was not found to very upon phase transition from the isotropic to liquid crystalline state /3/.

We studied the behaviour of contact angle of wetting for a drop of a classical liquid crystalline compound p-azoxyanisole (PAA) in its nematic and isotropic phases.     

He离子注入对Ge中缺陷行为的影响研究

本文采用以蒙特卡罗方法为基础的SRIM软件模拟He离子注入对Ge中缺陷行为的影响,为高质量GOI(绝缘体上Ge)材料的制备提供理论指导。本文主要模拟了He离子入射角度、能量以及注入剂量对Ge材料损伤程度和溅射产额等的影响。研究表明:入射角度较小时,拖尾效应不明显,有利于避免沟道效应,同时缺陷空位数(DPA)也处于较低水平;能量增大导致离子射程增大,溅射产额减小,离表面越近的Ge中DPA变少,可以实现低DPA GOI材料的制备;离子注入剂量增大导致损伤区域增大且集中,然而更多的He离子聚集在射程附近,能够很好地降低GOI材料的剥离温度。