钼晶体中存在有柏格斯矢量为〈100〉的位错的实验证据

实验结果表明:以乙二酸水溶液为电解浸蚀液,可以在钼单晶体表面上显示位错的浸蚀斑。选{100}面为观察面,沿三叉亚晶界定出了浸蚀斑密度。观测结果证实了不对称倾侧晶界的Read-shockley公式,由此确定了沿亚晶界排列的浸蚀斑与柏格斯矢量为<100>的刃型位错间的一一对应关系。 关键词：     

Design principles for broad-spectrum protein-crystal nucleants with nanoscale pits

Growing high-quality crystals is a bottleneck in the determination of protein structures by x-ray diffraction. Experiments find that materials with a disordered pitted surface seed the growth of protein crystals. Here we report computer simulations of rapid crystal nucleation in nanoscale pits. Nucleation is rapid, as the crystal forms in pits that have filled with liquid via capillary condensation. Surprisingly, we find that pits whose surfaces are rough are better than pits with crystalline surfaces; the roughness prevents the growing crystal from trying to conform to the pit surface and becoming strained.     

Dislocations and their spatial configuration in amethyst crystals

Etch patterns produced on habit rhombohedral faces and rhombohedral cleavages of amethyst crystals are described and illustrated. Fidelity of etchants used is assessed. Also described are paired pits produced on match cleavages etched with the same or different etchants. By prolonged etching experiments it is established that the dislocations penetrate into the body of the crystal. Spatial distribution of dislocation in the body of the crystal is worked out. Uniformly spaced etch pits in an array observed on match cleavages (etched with different etchants) are attributed to low-angle tilt boundaries.     

硅中位错与蚀斑的对应关系

通过实验肯定了硅单晶的化学侵蚀定向方法,找出抛光液的最佳配比及抛光时间。确定了所选定的位错侵蚀剂的侵蚀规范;此侵蚀剂对晶面无选择性,能显示出刃型和螺型位错,以及“新”、“旧”位错。通过长时间侵蚀、逐层侵蚀、劈裂面蚀斑的对应、小角晶界上蚀斑的观察、形变硅单晶中蚀斑排列以及弯曲形变样品中蚀斑密度与曲率半径间的关系的研究等方法,证明了用此侵蚀剂所得的蚀斑确实与位错一一对应。     

KDP晶体中位错的研究

本文用化学腐蚀方法揭示了KDP晶体中(001)和(100)晶面上的位错蚀坑,观察测量了不同质量的晶体中位错的形态、类型、分布和密度,并简要讨论了位错的成因。 关键词：     

晶体表面微观结构的反射电子显微术观察

本文用反射电子显微术观察了球状铂单晶表面的微观结构,分析了单晶形成中内部缺陷的变化。当球状液滴凝固时,晶体中存在位错、小角晶界等缺陷。在其后的退火过程中,晶粒内部的位错向亚晶界运动,降低了晶粒内部的位错密度,而亚晶界中的位错向晶体表面的运动,导致亚晶界的消失,形成单晶。 关键词：     

Etch pits on fresh and grown-in dislocations and etching of antiphase domain boundaries in Fe-Si alloys

The etching of fresh and grown-in dislocations on the chemically polished (100) surface of Fe-3% Si alloy single crystals and fresh dislocations on the same surface of Fe-7% Si alloy single crystals in a 1–2% nital is described. Antiphase domain boundaries are revealed by the same etching on the surfaces of Fe-7% Si alloy single crystals with different crystallographic orientation.     

Surface modification of highly oriented pyrolytic graphite by reaction with atomic nitrogen at high temperatures

Dry etching of {0 0 0 1} basal planes of highly oriented pyrolytic graphite (HOPG) using active nitridation by nitrogen atoms was investigated at low pressures and high temperatures. The etching process produces channels at grain boundaries and pits whose shapes depend on the reaction temperature. For temperatures below 600 °C, the majority of pits are nearly circular, with a small fraction of hexagonal pits with rounded edges. For temperatures above 600 °C, the pits are almost exclusively hexagonal with straight edges. The Raman spectra of samples etched at 1000 °C show the D mode near 1360 cm⁻¹, which is absent in pristine HOPG. For deep hexagonal pits that penetrate many graphene layers, neither the surface number density of pits nor the width of pit size distribution changes substantially with the nitridation time, suggesting that these pits are initiated at a fixed number of extended defects intersecting {0 0 0 1} planes. Shallow pits that penetrate 1-2 graphene layers have a wide size distribution, which suggests that these pits are initiated on pristine graphene surfaces from lattice vacancies continually formed by N atoms. A similar wide size distribution of shallow hexagonal pits is observed in an n-layer graphene sample after N-atom etching.     

Investigation of etch pits on KDP crystals with porous sol–gel coatings

We have investigated etch-pit formation on potassium dihydrogen phosphate (KDP) crystals with porous anti-reflective coatings. Etch pits develop beneath the sol–gel coatings after exposure to ambient humidity. The etch pits are homogeneously distributed with a density and an average size governed by the relative humidity and the coating thickness. Furthermore, the etch pits are self-similar in shape and possess facets corresponding to low-energy planes of KDP. Results from optical microscopy, light scattering, and atomic force microscopy support the following model for etch-pit formation in this system. Water adsorbed from the environment into the porous sol–gel coating contacts the crystal surface, causing etch-pit nucleation at high undersaturation. The plume of KDP rising from an etch pit slowly diffuses laterally, reducing the undersaturation and shutting off nucleation in the surrounding area. Because surface kinetics are rapid compared to mass transport through the sol–gel, etch pits continually undergo equilibration to maintain a low-energy geometry and generate an average spacing. Growth continues until the reservoir of water in the sol–gel is saturated with KDP. Coarsening is only observed in high relative humidity environments. Received: 13 Juni 2001 / Accepted: 30 July 2001 / Published online: 30 October 2001     

Synthesis and characterization of p-type boron-doped IIb diamond large single crystals

High-quality p-type boron-doped IIb diamond large single crystals are successfully synthesized by the temperature gradient method in a china-type cubic anvil high-pressure apparatus at about 5.5 GPa and 1600 K.The morphologies and surface textures of the synthetic diamond crystals with different boron additive quantities are characterized by using an optical microscope and a scanning electron microscope respectively.The impurities of nitrogen and boron in diamonds are detected by micro Fourier transform infrared technique.The electrical properties including resistivities,Hall coefficients,Hall mobilities and carrier densities of the synthesized samples are measured by a four-point probe and the Hall effect method.The results show that large p-type boron-doped diamond single crystals with few nitrogen impurities have been synthesized.With the increase of quantity of additive boron,some high-index crystal faces such as {113} gradually disappear,and some stripes and triangle pits occur on the crystal surface.This work is helpful for the further research and application of boron-doped semiconductor diamond.     

Dispersionless surface polaritons at twist boundaries of crystals and in a transition layer between the crystals

Dispersionless surface polaritons at twist boundaries of transparent uniaxial crystals are investigated. Exact analytical expressions for the central angles of the sectors of propagation of the surface polaritons are derived for arbitrary degrees of crystalline anisotropy η = ε_‖/ε_⊥ ? 1. The character of the change in the propagation sectors is determined with due regard for the isotropic transition layer between the crystals.     

The precipitation of BaCl2 in NaCl single crystals

The precipitation of BaCl₂ in NaCl single crystals has been investigated by means of decorating the crystal surface. Stickshaped formations have been observed on the decoration replicas but it has not been possible to determine whether they are pits or hills. X-ray diffraction analysis and the method of oblique shadows were used to solve this problem. The existence of BaCl₂ in doped crystals was proved by means of these methods. The amount of precipitates increases with increasing dose of BaCl₂ and therefore the stick-shaped formations are believed to be BaCl₂ precipitates.     

Growth, structural, optical and electrical behavior of glycine potassium nitrate (GPN) crystal with non-linear optical response

New trapezoidal, non-linear optical crystals of glycine potassium nitrate (GPN) have been grown by slow cooling from solutions with an initial pH of 4.3. Chemical composition, phase formation and functional groups have been verified by CHN, EDAX, XRF, NMR, XRD, FTIR and Raman studies. UV studies show a much lower cut off wavelength (195 nm) compared to the much investigated glycine sodium nitrate (GSN). The powder SHG efficiency of GPN is found to be 0.6 times compared to that of potassium dihydrogen phosphate (KDP). Cut and polished crystals exposed to light indicate positive photoconductivity. Electrical conductivity studies show an activation energy of 0.16 eV and the dielectric loss is found to decay drastically at higher frequencies (1 MHz) which is desirable in electronic applications. Vickers microhardness studies indicate a Mayer's index value of 2.78. Well resolved, elongated and oriented etch pits have been observed on the side habit face (220) treated in glacial acetic acid for 5 s. Typical circular features resisting the formation of etch pits representing impurity elements have been observed on the cleavage faces. Moisture has been traced on the surface of the crystals subjected to heat treatment.     

PbFe12O19单晶体中的位错蚀斑研究

应用50％HCl作为浸蚀剂,对助熔法生长的PbFe₁₂O₁₉单晶体的(0001)解理面进行了浸蚀,以显示位错蚀斑。根据蚀斑所具有的形态,将其进行了分类,并确定了各自对应的位错类型。应用Mathews等人提出的机制,解释了在(0001)基面上所观察到的位错蚀斑阵列。 关键词：     

Atomic structure of alkali halide surfaces

The atomic structure of surfaces of alkali halide crystals has been revealed by means of high-resolution dynamic force microscopy. True atomic resolution is demonstrated both on steps surrounding islands or pits, and on a chemically mixed crystal. We have directly observed the enhanced interaction at low-coordinated sites by force microscopy. The growth of NaCl films on metal surfaces and radiation damage in a KBr surface is discussed based on force microscopy results. The damping of the tip oscillation in dynamic force microscopy might provide insight into dissipation processes on the atomic scale. Finally, we present atomically resolved images of wear debris found after scratching a KBr surface. PACS 68.37.-d; 68.37.Ps; 75.55.Fv     

Morphology and fluorescence spectra of rubrene single crystals grown by physical vapor transport

Rubrene single crystals with pentagon, hexagon, lath-like, and needle-like shape were grown by physical vapor transport. The morphology of surface and transect of rubrene crystals was characterized by optical microscope, atomic force microscope and scanning electron microscope. Monolayers and layer-like structures were observed on the rubrene crystal surface and in the interior of single crystals, respectively. Size and quality of rubrene crystals could be controlled by tuning growth parameters including source temperature, deposition temperature, and growth time. Compared with the emission peak at 555 nm of rubrene solution with the concentration of 10⁻⁵ M, the emission peak of rubrene single crystals is at 649 nm with a shift of 94 nm. Hexagon etching pits with typical ladder-like structure were also observed on the (1 0 0) crystal plane and the density of dislocation lines is about 10³ cm⁻².     

Determination of the orientation parameters of grains from the contrast of an image of a multisilicon polished surface using backscattered electrons

The grain structure of multisilicon crystals are investigated by scanning electron microscopy and electron backscatter diffraction. It is found that the contrast of an image obtained by scanning polished multisilicon surfaces in the mode of backscattered electrons by electron-probe microanalysis is caused by the fact that the contrasting grains on the test site of the surface belong to different crystallographic orientations. It is revealed that high-angle grain boundaries are areas where the contrast varies, whereas small-angle boundaries are not observed on the polished surfaces. Consequently, the degree of contrast of the image obtained in this scan mode can be used to qualitatively assess the degree of misorientation of neighboring grains.     

On the nature and mechanism of surface polygonization of NaCl and KCl single crystals produced by electron bombardment and illumination

Abstract

The polygonization phenomenon observed on alkali halide surfaces, irradiated with electrons and subsequently illuminated, was studied by optical and electron microscopy. For the explanation of the nature and mechanism of this process, we have investigated the influence of light (containing the F?centre absorption band) on the development and annihilation in time of some polygonization lines, as well as the correlation of the polygonization patterns with dislocation etch pits and subgrain boundaries revealed by a selective chemical etching.

Preceded by an optical bleaching effect which locally induces surface potential changes, the polygonization process is explained taking into account the mobility of unpinned charged dislocations and the surface atom migration. The disappearance of some polygonization lines may be produced by a vacancy-interstitial annihilation process.

No identification was found between the polygonization patterns and the subgrain boundaries.     

Optical,etching, and interferometric studies on ferroelectric PbNb2O6

Optical, interferometric and etching studies of (001) surfaces of ferroelectric PbNb₂O₆ are presented. It is found that crystal growth takes place mainly by layer formation. The layer boundaries can be distinguished from the domain lines by interferometric studies. Thermal etch pits are found near 90° domain walls and the layer boundaries. The etching studies show that these pits are at the sites of dislocations, and it is deduced that no extensive motion of dislocation takes place at the Curie-temperature in the process of domain formation.     

Sputtering induced topography development on f.c.c. metals

The generation and development of surface features by ion bombardment induced sputtering erosion of f.c.c. metals is reviewed. Studies with polycrystalline substrates reveal the plethora of individual features, both etch pits and cones and the repetitive features, such as ripple trains, which form differently on different crystallite surfaces. Studies with well defined single crystals clarify the origins of such features and the relative independence of their habit on ion species and substrate material.