Evolution of the Defect Structure of Zinc-Oxide as a Consequence of Tribophysical Activation

Zinc-oxide powder was tribophysically activated in a high-energy vibro mill in a continual regime in air for 3, 30 and 300 minutes with the purpose of modifying the powders physico-chemical properties. By analyzing of data obtained by X-ray powder diffraction, electron diffraction and transmission electron microscopy, the values of distances between corresponding crystallographic planes, average domain sizes of coherent scattering, i.e. crystallites, width of diffraction lines due to the existence of microstrains, and microstrain values, minimal dislocation densities, dislocation density due to microstrain and real dislocation density, and also average distances between dislocations were determined. The dependence of these values on the activation time was established, which enabled analysis of the evolution of the defect structure of zinc-oxide powders during tribophysical activation by grinding in the described regime.     

Evolution of real structure in Ge‐Si mosaic crystals

The structure and properties of Czochralski (Cz)‐grown Ge_1‐xSi_x mosaic crystals were investigated using optical microscopy, atomic force microscopy, X‐ray diffraction analysis, microprobe analysis, FTIR and transmission electron microscopy. The role of segregation, form of solid‐liquid interface and dislocation generation in the development of mosaic structure were analyzed and used for optimization of growth parameters such as Si concentration and growth rate. The dislocation density estimated experimentally was compared with the calculated data. Composition fluctuations caused by formation of cellular structure at the interface lead to a local lattice misorientation that is one of the reasons for crystal mosaicity. Model of mosaic structure generation in terms of dislocation density and composition variations is presented.     

AlGaN双势垒结构对高In组分InGaN/GaN MQWs太阳能电池材料晶体质量和发光性能的影响

本文利用金属有机化合物化学气相沉积(MOCVD)技术在(001)面图形化蓝宝石衬底(PSS)上生长了一种含有AlGaN-InGaN/GaN MQWs (multiple quantum wells)-AlGaN双势垒结构的高In组分太阳能电池外延材料。高分辨率X射线衍射(HRXRD)和光致发光(PL)谱分析表明,与含有AlGaN电子阻挡层的低In组分的量子阱结构太阳能电池外延材料相比,该结构材料具有较小的半峰全宽(FWHM),计算表明:此结构材料的位错密度降低了一个数量级,达到10⁷ cm^-2;同时,有源区中的应变弛豫降低了51%;此外,此结构材料的发光强度增强了35%。研究结果表明含有AlGaN双势垒结构的外延材料可以减小有源区的位错密度,降低非辐射复合中心的数目,增大有源区有效光生载流子的数目,为制备高质量太阳能电池提供实验依据。     

The features of X-ray topographic contrast formation in silicon with dislocation clusters

The features of formation of diffraction images of edge dislocation sets forming clusters (of two, three and more dislocations) as well as small-angle dislocation boundaries (walls) have been studied. A variety of diffraction effects of wave fields created in strongly distorted crystals regions along dislocation lines have been observed. Various intensity interference effects of rescattering and internal reflection of the newly formed and already existing wave fields on thickness distributions of intensity for the case of presence in the same glide plane of edge dislocations with parallel and anti-parallel Burgers vectors were discovered.     

Determination of the inhomogeneous dislocation density in a crystallographic texture

Diffraction analysis of the mixed dislocation structure of a polycrystal with an orthorhombic texture is reported. A significant difference in the dislocation densities in the texture components of cold-deformed low-carbon steel has been revealed.     

Broadening of X-ray diffraction lines of crystals containing dislocation distributions

The first part of the paper deals with a brief review over the present stage of the (kinematical) theory of the broadening of X-ray diffraction lines of crystals containing dislocation distributions. In the second part experiments of X-ray line broadening of plastically deformed Cu and NaCl single crystals are reported by which the validity of the theoretical approaches are tested. It is shown that values of the dislocation density and the elastically stored energy derived from broadened X-ray diffraction lines agree well with corresponding data obtained by other experimental techniques.     

Modification of the crystal structure of gadolinium gallium garnet by helium ion irradiation

The structure of gadolinium gallium garnet (GGG) single crystals before and after implantation by He⁺ ions has been investigated using high-resolution X-ray diffraction methods and the generalized dynamic theory of X-ray scattering. The main types of growth defects in GGG single crystals and radiation-induced defects in the ion-implanted layer have been determined. It is established that the concentration of dislocation loops in the GGG surface layer modified by ion implantation increases and their radius decreases with an increase in the implantation dose.     

Identifiability of dislocation structures of strongly distorted crystals

Diffraction analysis of polycrystals is adapted to the state of their dislocation structure. A structure with small dislocation loops (the martensite-transformation structure) is revealed clearly. For large dislocation loops (the plastic-deformation structure), distinguishability of loop sizes is restricted significantly.     

On the elements of the dislocation structure of deformed corundum

It is found by the method of transmission electron microscopy that the main elements of dislocation structure of deformed corundum are spatial triple dislocation nodes, recombination zones and dislocation network fragments. The structure of dislocation nodes is analyzed. It is shown that the nodes in corundum are the “rigid” constructions.     

On a delayed dislocation emission from hot hardness indentations

The change of the dislocation arrangements around microindentations after indentation test has been investigated by TEM and etching. The indentations were generated on {100} - surfaces of iron single crystals at temperatures between 800 K and 1000 K. The change of the dislocation structure was found to depend strongly on stress and dislocation density in the deformation field. The deformation field especially acts as a dislocation source operating over long periods. The results suggest that the propagation of emitted dislocations is controlled by dragging of Cottrell-atmospheres of carbon atoms. Conclusions regarding the hardness-temperature relation in pure iron are drawn.     

High-temperature annealing stages in irradiated imperfect crystals

The effect of neutron irradiation on the structure of crystals with different dislocation densities and types of crystal lattice and on subsequent high-temperature annealing is studied. The extent of this effect is determined by the substructure of irradiated material. The processes responsible for stage V and VI annealing of radiation-induced defects are investigated by quantitative X-ray diffraction topography and two-crystal spectrometer technique. A retarding effect of neutron irradiation on all the stages of recrystallization is established enabling the temperature range of application of hardened metal and alloys to be shifted to higher temperatures.     

The growth and dislocation characterization of Yb0.005Y0.848Lu0.147VO4 mixed laser crystal

A new mixed laser crystal, Yb_0.005Y_0.848Lu_0.147VO₄, has been successfully grown using the Czochralski method. An ICP‐OES was used to measure the concentrations of elements (Yb, Y, Lu, V) in the crystal, and the chemical formula was determined. X‐ray powder diffraction analysis shows that the crystal has ZrSiO₄ structure. A pair of edge dislocations with certain orientation was observed by the HREM, and the orientation was confirmed by the calibration of the diffraction spots. The formation mechanism of this type dislocation was given by analysis on structure and thermal expansion of crystal. The suggestion to avoid these dislocations was also given.     

Influence of Dislocations in KDP Crystals on Laser Damage Threshold

The dislocation density in KDP crystals has been determined by X-ray diffraction topography (LANG method). A method for determining the laser damage thresholds in dependence on dislocation density is described. It is found that dislocations with a density about 10³ cm⁻² reduce the laser damage threshold up to a factor of two compared with perfect regions. It is shown that experimentally measured damage results can be explained theoretically.     

A model for the growth of anomalous polytype structures in vapour grown SiC

A number of polytype structures observed in vapour grown SiC crystals have a unit-cell which is an integral multiple of the unit-cell of the basic 6H, 15R or 4H structure. The growth of such anomalous structures cannot be understood in terms of spiral growth round a single screw dislocation in a basic matrix. However many of these polytype crystals display a single growth spiral on their (0001) face indicating that they have resulted from spiral growth round a single screw dislocation. It is shown that this anomaly can be resolved if the basic matrix is assumed to contain stacking faults near the surface at the time of the origin of the screw dislocation ledge. This possibility, overlooked in the earlier deduction of polytype structures, must be taken into consideration since vapour grown SiC crystals frequently contain a high concentration of random stacking faults, producing continuous streaks on their X-ray diffraction photographs. The most probable fault configurations that can occur in 6H, 15R and 4H structures of SiC have been deduced from a calculation of their stacking fault energy. These fault configurations are then considered to lie at different distances from the surface at the time of the origin of a screw dislocation ledge. Such a faulted ledge gives rise to polytype structures during subsequent spiral growth even if the screw dislocation has an integral Burgers vector. The most probable series of polytype structures that can result from such a faulted matrix model are deduced. It is shown that nearly all the polytype structures of SiC hitherto regarded as anomalous (such as 36H, 54H, 66H, 45R, 90R etc.) are among the expected structures and there is no need to postulate a complicated configuration of cooperating dislocations to account for their growth.     

Elektronenmikroskopische Untersuchung der Verformungsmikrostruktur eines ferritischen Stahles

The relationship between dislocation structure and the plastic deformation of a low carbon steel at room temperature was investigated. The analysis of the results shows that the dislocation structure is a very important parameter for the deformation microstructure. It was found a connexion between the plastic deformation and the density of dislocation. This connexion is described with a dislocation model.     

Growth and real structure of diamond films synthesized on polycrystalline tungsten substrates

X-ray diffraction studies of diamond films obtained by chemical transport reactions at the concentrations of 2% methane and 98% hydrogen under pressures of 10.7 and 21.3 kPa showed that they are textured. The character of the texture depends on the substrate temperature. The films have {110}, {311}, or double {110} + {311} textures. It is established that the dependence of the growth rate of diamond films on the substrate temperature has maxima. The diamond films are finely dispersed and are characterized by pronounced micro-deformations and high dislocation densities. The temperature dependence of the growth rate correlates with the parameters of the real structure of the films.     

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.     

Dynamic aging of dislocations in materials with a high crystalline relief: Competition between diffusion and impurity entrainment

A model of the dynamic interaction of dislocations with the impurity subsystem of crystals that have a high lattice potential relief (Peierls barriers) has been developed. It is shown that the microscopic structure of migration barriers for impurities near a dislocation core may cause qualitatively different behavior of the impurity atmosphere on a moving dislocation. It is justified that the impurity kinetics during atmosphere formation includes two stages. The first (initial) stage is fast and significantly nonequilibrium; it is followed by the second stage, characterized by a slower approach to equilibrium. The initial stage manifests itself at a sufficiently fast dislocation motion and may lead to an anomalous increase in the driving force (or the yield strength of the material) with an increase in the temperature in some range. Blocking of the dislocation motion by impurities may cause inverse brittle-ductile transition, which is observed in some materials with an increase (rather than the usual decrease) in temperature.     

Control of the morphology of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition

Various techniques for morphological evolution of InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition have been evaluated. Atomic force microscopy, photoluminescence (PL) and X-ray diffraction measurements have been used for characterization. It is shown that inclusions, that are generated into the V-defects in the InGaN quantum wells (QW), can be removed by introducing a small amount of hydrogen during the growth of GaN barriers. This hydrogen treatment results in partial loss of indium from the QWs, but smooth surface morphology of the MQW structure and improved optical quality of InGaN wells are obtained. The density of the V-defects could be reduced by reducing the dislocation density of the underlying GaN buffer.