Exceptional reduction of the diffusion constant in partially disordered photonic crystals

In real photonic crystals light is scattered by the imperfections of the periodic potential. We study experimentally the propagation of diffused light in silicon inverse opals and report an exceptionally reduced diffusion constant of 3.0+/-0.7 m(2)/s, in samples which are only partially disordered. Waves scattered both by the lattice planes and by their imperfections interfere and light is efficiently trapped in this hybrid scattering regime. Not only higher quality crystals, but also random materials present an order of magnitude bigger diffusion constant and hence weaker scattering.     

Anomalous elastic response of silicon to uniaxial shock compression on nanosecond time scales

We have used x-ray diffraction with subnanosecond temporal resolution to measure the lattice parameters of orthogonal planes in shock compressed single crystals of silicon (Si) and copper (Cu). Despite uniaxial compression along the (400) direction of Si reducing the lattice spacing by nearly 11%, no observable changes occur in planes with normals orthogonal to the shock propagation direction. In contrast, shocked Cu shows prompt hydrostaticlike compression. These results are consistent with simple estimates of plastic strain rates based on dislocation velocity data.     

Solution-grown crystals of poly(vinyl alcohol)

The growth mechanism and crystalline texture of solution-grown crystals of poly(vinyl alcohol) have been studied by electron microscopy. From morphological data it is shown that single crystals of poly(vinyl alcohol) (PVA) have two growth faces, i.e., the (100) and (101) fold planes. It is suggested that the parallelogrammic single crystals grow from the center by molecular folds. The rate of addition on the (100) plane is about three times larger than that on the (101) plane. Twinning of the PVA crystals takes place at the (100), (001), (101), and (101) planes at the time of the nucleation or during the growth. The single crystal and twins of PVA are corrugated lamellae. Granulated structure is observed on the surface in a figure similar to the external form of the crystals. Dark-field micrographs show that the PVA single crystals possess a mosaic structure with the arrangement of the blocks deviating slightly from parallel alignment in the lamella. The reactivities of single crystals to various aldehydes indicate that the single crystals contain crystal lattice defects.     

Calculation of interplanar distances near the faces of ionic crystals with lattices of NaCl type and face-centered molecular crystals

Conclusions Interplanar distances near faces have been calculated for ideal ionic crystals of NaCl type and face-centered molecular crystals by successive approximation [4]. The repulsive forces for the ionic crystals were taken as br^–n, while the attractive and repulsive forces for the molecular crystals were taken asar^–m and br^–n, respectively. The numerical values fora and b were derived from the equilibrium conditions for an infinite crystal.We found that the difference between the interplanar distance and the lattice constant increased as n decreased for ionic crystals, the distance between the second and third planes being the largest.The above difference is positive for molecular crystals and decreases inwards; it is 5% of the lattice constant for the first and second planes but only 0.1% for the fifth and sixth.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 148–150, February, 1972.     

Polarization anisotropy of optical transmission in opals and Langmuir-Blodgett crystals

The transmission spectra of thin-film colloidal photonic crystals with three-dimensional and one-dimensional-two-dimensional photonic energy band structures, i.e., opals and Langmuir-Blodgett crystals with a refractive index contrast of ∼1.5: 1.0, have been measured in linearly polarized light. It has been demonstrated that the polarization anisotropy in the light transmitted through the crystal is uniquely related to the diffraction resonance and that the degree of polarization can exceed 90%. A higher degree of polarization is provided by lattices that are characterized by a smaller attenuation of light polarized in the plane of incidence. It has been revealed that the diffraction resonances from the crystal planes for which the dispersions are in anticrossing with the dispersion of the growth planes acquire the same anisotropy. The general character of the results obtained has been confirmed by the fact that the polarization anisotropy identically manifests itself in colloidal crystals that have different symmetries and lattice orderings.     

Symmetry Groups of the Austenite Lattice and Construction of Self-Accommodation Complexes of Martensite Crystals in Alloys with the Shape-Memory Effect

The internal structure of experimentally observed self-accommodation complexes of martensite crystals, which is determined by the system of twinning planes, is studied in this work. The direct correlation of the construction type of the complexes with the subgroups of the austenite lattice symmetry group is shown.     

Half analytical method with application to the high order Laue zone effects in monoclinic and triclinic crystals

The simulation of the high order Laue zone (HOLZ) diffractions of monoclinic and triclinic crystals is a very complicated problem. The conventional multislice (MS) method suffers from the problem of infinity of the phase grating size. To avoid the difficulty of the infinity, Chen et al. arranged the phase grating plane along the ab plane of the crystal lattice. In this paper we introduce a new method which allows the incident and exit wavefunction planes perpendicular to the zone axis without the difficulty of infinity. We name the method half analytical method. The results calculated by half analytical method are in good agreement with those calculated by the conventional MS method.     

Directional anisotropy in the cleavage fracture of silicon

Total-energy pseudopotential calculations are used to study the cleavage anisotropy in silicon. It is shown that cracks propagate easily on 111 and 110 planes provided crack propagation proceeds in the <1;10> direction. In contrast, if the crack is driven in a <001> direction on a 110 plane the bond breaking process is discontinuous and associated with pronounced relaxations of the surrounding atoms, which results in a large lattice trapping. The different lattice trapping for different crack propagation directions can explain the experimentally observed cleavage anisotropy in silicon single crystals.     

Zur Untersuchung des reziproken Gitters von Einkristallen mit Hilfe von Kikuchi-Diagrammen

A new method has been developed for the examination of the reciprocal lattice of single crystals by means of Kikuchi patterns. The Kikuchi bands belonging to a zone axis may be used to locate the lattice points lying within the reciprocal lattice plane, which is orthogonal to this axis and passes through the origin. For the investigation of the whole reciprocal lattice, a series of reflection patterns is taken at different orientations of the specimen. Each group of Kikuchi bands belonging to a zone axis is used to locate the reciprocal lattice points in a section orthogonal to the respective zone axis. The angles between the section planes are obtained by recording the angle of rotation between successive exposures and by considering the inclinations of the zone axes relative to the primary beam. In a perspective drawing the reciprocal lattice region near the origin is then composed of these sections.     

Structure and stability of a homologous series of tin oxides

The structures and stabilities of a series of nonstoichiometric SnO2-x compounds, which are yet unknown experimentally, are predicted using the cluster expansion technique combined with first-principles calculations. A homologous series of Sn(n+1)O(2n) in which oxygen vacancies are layered on (101) planes of the rutile lattice is discovered. The homologous crystals are composed of divalent and quadrivalent Sn atoms. No trivalent Sn atoms are formed.     

带电胶体粒子结晶过程的实验研究

利用带电单分散聚苯乙烯胶体粒子，通过自组装机理，制备了体积百分比为4.8%的具有多晶结构的胶体晶体，并用Kossel衍射技术和紫外可见分光光度计分别对晶体的生长过程进行了监测.通过对Kossel的图像分析检测不同阶段相应的晶格结构，发现胶体结晶过程晶体结构演变顺序为由液态—随机层结构—堆无序结构—面心立方孪晶结构到面心立方结构.定量地确定了结晶过程中晶体不同晶面的晶面间距和晶体的晶格常数，通过紫外可见分光光度计测量的晶体透射谱图，计算得到111晶面的晶面间距和晶体的晶格常数，与用Kossel衍射技术得到的结果相一致，还发现随样品放置时间的延长，衰减峰变窄和加深，并向短波方向移动，对应着晶体的晶格常数减小的现象. 关键词： 胶体晶体 自组织 Kossel环 聚苯乙烯粒子     

Growth, structural, spectral, mechanical and dielectric characterization of RbCl-doped l-alanine hydrogen chloride monohydrate single crystals

Pure (undoped) and RbCl-doped LAHC single crystals were grown successfully by the solution method with the slow evaporation technique at room temperature. The grown crystals were colourless and transparent. The solubility of the grown samples were found out at various temperatures. The lattice parameters of the grown crystals were determined by the single crystal X-ray diffraction technique and the diffracting planes were indentified by recording the powder X-ray diffraction pattern. UV-visible transmittance studies were carried out for the grown samples. Chemical analysis and atomic absorption studies indicate the presence of rubidium in the doped LAHC crystals. Nonlinear optical studies reveal that the SHG efficiency increases when the LAHC crystal is doped with rubidium chloride (RbCl). From microhardness studies, it is observed that the RbCl-doped LAHC crystal is harder than the pure sample. It is observed that the dielectric properties of the LAHC crystal are altered when it is doped with rubidium chloride.     

Surface morphologies of anthracene single crystals grown from vapor phase

The morphologies and lattice structures of anthracene single crystals grown from the vapor phase were investigated using optical microscopy, phase contrast microscopy, atomic force microscopy (AFM), and X-ray diffraction analysis. Common morphologies with hexagonal large planes were observed irrespective of crystal size. The observation of certain surface morphologies with a phase contrast microscopy revealed that the spiral steps originated from screw dislocations present on the (0 0 1) planes. Moreover, the center and edge of the (0 0 1) planes had large curvatures, similar to hills. Resultantly, quarter-monolayer (ML) steps were observed on the large and flat planes between both hills.     

Elastic strain and coloration pattern in natural quartz crystals

Very small elastic strains (tilts of the order of 0.25 sec of arc and dilationsΔd/d?10^?6, whered is the spacing of net planes) have been observed in natural quartz crystals. According to their rocking curves which are of almost theoretical width, these crystals were commonly expected to be practically perfect crystals. On double crystal X-ray topographs a pattern was revealed of uniformly strained layers parallel to the rhombohedron faces (10¯11) and with thickness ranging between 20 and 200 microns. This fine structure strain pattern was correlated to the pattern of the optical coloration which could be produced by irradiating the originally transparent crystals with X-rays. A localincrease of coloration matched with a localcontraction of the lattice. Tilts occurred in transition zones between adjacent layers with slightly different lattice spacings. Strain and coloration patterns probably have as a common cause the deposition of layers with different impurity concentrations during the growth process of the crystals. Although no change of the strain as a result of the X irradiation could be detected in the colored layers in particular, experimental evidence has been found for anoverall expansion of the lattice of the order ofΔd/d?5×10^?7 due to X irradiation. This expansion seems to saturate at this low value and is probably caused by electronic processes connected with the coloration. Some aspects concerning the nature of the color centers have been discussed. It seems likely from the results of the strain measurements that both sets of layers, colored and transparent ones, play a combined role in coloration.     

Propagation of polarized light in opals: Amplitude and phase anisotropy

The interaction of linearly polarized light with photonic crystals based on bulk and thin-film synthetic opals is studied. Experimental transmission spectra and spectra showing the polarization state of light transmitted through opals are discussed. A change in polarization is found for waves experiencing Bragg diffraction from systems of crystallographic planes of the opal lattice. It is shown that the polarization plane of the incident linearly polarized wave at the exit from photonic crystals can be considerably rotated. In addition, incident linearly polarized light can be transformed to elliptically polarized light with the turned major axis of the polarization ellipse. Analysis of polarization states of transmitted light by using the transfer-matrix theory and homogenization theory revealed good agreement between calculated and experimental spectra.     

Proton channeling in ionic and semiconducting single crystals

Measurements have been made of the energy distributions of protons passing through NaCl, KCl, Si, and Ge single crystals at various angles with respect to the {100} and {110} planes. The fraction of protons passing through lattice channels has been evaluated, and its dependences on the angle of incidence, the chemical composition of the sample, and the proton energy have been found.     

Quasichanneling of ions in crystals. I. Elastic scattering of ions on atomic “chains” and planes

The scattering of quasichanneled particles on atomic chains and planes is studied by computer simulation for the crystals of chemical compounds. It is shown that quasichanneling is the specific regime of ion motion in the lattice. Its main features are: (1) a sharp increase of the backscattering probability; (2) transition of the ions from the quasichanneled component into a random one; (3) high sensitivity to the structure and the composition of the atomic “chain”; (4) dependence on the value and the direction of the atomic displacements.     

平板电极间胶体晶体在电场作用下的各向同性压缩

用直径 300 nm的聚苯乙烯微球配制不同浓度的胶体晶体溶液, 将其快速注入内表面镀有导电薄膜的玻璃样品池中, 形成 (111) 晶面平行于玻璃表面的面心立方单晶结构. 通过激光衍射Kossel线方法, 研究了不同体积分数的胶体晶体样品 及它们在均匀电场作用下晶体结构的变化. 实验发现, 随着电场强度的增加, 胶体晶体表现为各向同性的压缩. 胶体晶体在恒定电场下始终保持面心立方结构, 晶格常数随着电场强度的增加逐渐减小. 实验结果可用电场力、电流体力学作用力及颗粒间静电斥力共同解释: 电场力使带电微球克服静电斥力并沿电场反方向运动导致晶体压缩, 而由电场力作用引起的电流体力学液流产生的持续推力使垂直于电场平面上的胶体微球相互靠近. 本实验为天宫一号搭载科学实验的地基实验. 关键词： 胶体晶体 Kossel衍射 结构变化     

非晶Ni-P合金晶化过程中生成的六角亚稳相

本文利用透射电镜中的双倾台绕c^{*轴旋转晶体,唯一地确定了Ni-P非晶膜晶化后生成成分约为Ni_2.2P的针状亚稳相具有六角点阵,a=6.73?,c=9.42?。堆垛类型为AA…。(001)平面的高分辨点阵象以及衍射斑点沿c*方向拉长成条纹均表明晶体存在一维无序错排。 关键词：}