刃型位错形成对面心立方金属Cu体积的影响

使用分子动力学方法,采用嵌入原子势（EAM）,在0K下模拟了面心立方金属Cu单晶的刃型位错,研究了刃型位错产生对晶体体积的影响．模拟结果表明,无论使用推入还是抽出原子层的方法获得刃型位错,平衡状态时刃型位错的存在使晶体体积增大．     

The photodamping of dislocations in KCl single crystals

The effect of F-light (λ = 550 nm) on the dislocation amplitude-dependent internal friction (dislocation photodamping) and dislocation charge in KCl crystals of different purity containing F-centers has been investigated. The photodamping process in all the crystals under study has been found to be due to the optical generation of new pinning points. The conditions of photopinner formation are found to depend on the magnitude of dislocation charge, the manner of the F-center introduction (γ-irradiation, additive coloration), and crystal purity. A model of photopinner formation has been proposed. The results obtained are used to analyse the binary systems in which the effect of dislocation photodamping is likely to occur.     

Shrinking stacking fault through glide of the Shockley partial dislocation in hard-sphere crystal under gravity

Disappearance of a stacking fault in the hard-sphere crystal under gravity, such as reported by Zhuet al. [Nature 387, 883 (1997)], has successfully been demonstrated by Monte Carlo simulations. We previously found that a less ordered (or defective) crystal formed above a bottom ordered crystal under stepwise controlled gravity [Moriet al. J. Chem. Phys. 124, 174507 (2006)]. A defect in the upper defective region has been identified with a stacking fault for the (001) growth. We have looked at the shrinking of a stacking fault mediated by the motion of the Shockley partial dislocation; the Shockley partial dislocation terminating the lower end of the stacking fault glides. In addition, the presence of crystal strain, which cooperates with gravity to reduce stacking faults, has been observed.     

Effect of crystallographic orientation on the dislocation structure development in ion implanted Si

Transmission electron microscopy (TEM) has been employed to study the damage structure of P⁺-implanted (001) and (111) Si annealed in inert and oxidizing atmospheres. Both the dislocation structure composition and the density of misfit dislocations have been found to be strongly dependent upon the crystal orientation. Role of the crystal orientation in the dislocation structure development has been discussed.     

Size effects under plastic deformation of microcrystals and nanocrystals

A theoretical analysis of size effects in plastically deformed crystals with transverse sizes in micro and nanometer ranges has been performed in the framework of the dislocation-kinetic approach. The analysis is based on the evolution equation of the dislocation density in these crystals and takes into account the generation of dislocations from surface dislocation sources and the escape of dislocations from the crystal through the crystal surface. It has been established that the generation of dislocations from the sources leads to a strong strain hardening of the crystal and that the escape of dislocations through the crystal surface results in a fast equilibration of these two kinetic processes. As a result, there occurs a strong “exhaustion” of strain hardening of thin crystals at the early stage of their plastic deformation in accordance with experiments. According to the theory, the flow stresses σ and transverse sizes D of microcrystals and nanocrystals are related by the expressions σ ∼ D ⁻ⁿ (n = 0.625–1.0), which are in agreement with the experiment.     

Dynamic interaction of edge dislocations with point defects and prismatic dislocation loops at high-strain-rate deformation of crystals

The motion of an ensemble of edge dislocations at high-strain-rate deformation of a crystal with a high concentration of prismatic dislocation loops and point defects has been analyzed. It has been shown that, under certain conditions, the drag of an edge dislocation by prismatic dislocation loops has the character of dry friction, and the magnitude of the drag force of the dislocation is determined by the relationship between the concentration of prismatic dislocation loops and the density of mobile dislocations. An increase in the density of mobile dislocations leads to an enhancement of their collective interaction, thus facilitating the overcoming of prismatic dislocation loops by edge dislocations. The total drag force of an edge dislocation is a nonmonotonic function of the concentration of point defects, which, under certain conditions, has a minimum.     

KDP晶体台阶生长动力学的激光干涉实验研究

采用迈克尔逊干涉技术 ,通过测量KDP晶体生长的法向速率和台阶斜率来研究其台阶生长的动力学系数、台阶自由能、溶质在边界层内的扩散特征以及激发晶体生长台阶的位错活性 .实验表明 ,KDP中不同活性位错的台阶动力学系数差异较大 ,例如高活性和低活性台阶动力学系数分别为 10 .3× 10 -2 和 5 .2 1× 10 -2 cm/s,位错源在晶体表面的形状、面积的变化 ,以及Burgers矢量的变化是造成晶体生长动力学测量数据重复性差的主要原因     

XRD法计算4H-SiC外延单晶中的位错密度

对用X射线衍射法计算4H-SiC外延中的位错密度方法进行了理论和实验研究。材料中的位错密度大于106 cm-2会给材料位错密度的测试会带来一定的困难。首先从理论上分析了位错密度对X射线衍射结果的影响,得出位错密度和峰宽FWHM展宽的关系。然后对4H-SiC样品进行了X射线三轴晶ω-2θ测试,采用不同晶面衍射峰,计算出样品的位错密度。分析了外延中位错产生的原因,并提出了相应的解决办法。     

A study of structural properties of bulk double-doped InP by laser scattering tomography and photoetching

In this work the structural properties of bulk InP:(CdS) have been investigated. The characterization has particularly been focused on detection of microdefects. Microdefects have been found in all the samples which were studied, but their distribution as well as their size have been observed to vary according to the growth conditions and the crystal zone from which the samples were cut. Generally, the (100) wafers cut from 111-pulled crystals are more homogeneous than those from 100 ingots. Very often the micro-precipitates are associated with dislocation lines but sometimes they appear as isolated spots inside the crystal matrix.     

二维声子晶体同质位错结缺陷态特性

利用平面波展开法结合超原胞的方法研究了二维声子晶体同质位错结的缺陷态.分别研究了横向位错和纵向位错两种情况，研究结果表明：横向位错效应与线缺陷相似，它可以使处于禁带频率范围内的声波沿位错通道进行传播，形成声波导；纵向位错效应则类似于点缺陷，位错线两边三个最接近的散射子形成腔，因而能够产生局域模.另外，横向位错距离和纵向位错距离的大小将影响缺陷带的位置和数量，因此，可以通过调节横向位错距离或纵向位错距离来人为的控制同质位错结中的缺陷带. 关键词： 声子晶体 同质位错结 缺陷态     

Experimental and theoretical investigation of formation of the oxygen-containing precipitate-dislocation loop system in silicon

A model of coherent and incoherent oxygen-containing precipitates formed in an anisotropic silicon crystal due to the decomposition of a supersaturated oxygen solid solution has been considered. The stresses acting inside and outside the precipitate have been determined in the framework of the classical Eshelby’s approach. A criterion has been proposed for the generation of the misfit dislocation and the onset of motion of the perfect interstitial dislocation loop lying in the precipitate plane. The proposed precipitate model and criterion have been used for determining the dependence of the precipitate radius that corresponds to the formation of the misfit dislocation and the onset of motion of the perfect interstitial dislocation loop when an external load is applied to the sample. The results obtained are compared with the available experimental data.     

Influence of extended defects on gold diffusion in plastically deformed silicon

The effect of defects formed in dislocation trails behind dislocations on the gold diffusion has been investigated by the deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC) methods. It is found that the gold concentration in the deformed samples is two orders of magnitude higher than that in the defect-free crystal. Estimations show that the concentration of electrically active gold obtained from the DLTS data is at least ten times higher than the value, which might be expected for the dislocations themselves. A strong increase in the recombination activity of dislocation trails after gold diffusion is found from EBIC measurements, which probably is related with gettering properties of defects formed in the dislocation trails.     

An improvement of the lattice theory of dislocation for a two-dimensional triangular crystal

The structure of dislocation in a two-dimensional triangular crystal has been studied theoretically on the basis of atomic interaction and lattice statics. The theory presented in this paper is an improvement to that published previously.Within a reasonable interaction approximation, a new dislocation equation is obtained, which remedies a fault existing in the lattice theory of dislocation. A better simplification of non-diagonal terms of the kernel is given. The solution of the new dislocation equation asymptotically becomes the same as that obtained in the elastic theory, and agrees with experimental data. It is found that the solution is formally identical with that proposed phenomenologically by Foreman et al, where the parameter can be chosen freely, but cannot uniquely determined from theory. Indeed, if the parameter in the expression of the solution is selected suitably, the expression can be well applied to describe the fine structure of the dislocation.     

α-Fe裂纹的分子动力学研究

通过分子动力学方法，模拟了α-Fe裂纹的单轴拉伸实验中的形变过程.研究了不同晶体取向裂纹的形变特点和断裂机理，观察到各种形变现象，如位错形核和发射，位错运动，堆垛层错或孪晶的形成，纳米空洞的形成与连接等.计算结果表明，裂纹扩展是塑性过程和弹性过程相结合的过程，其中塑性过程表现为由裂尖发射的位错导致的原子切变行为，而弹性过程的发生则是由无位错区中的原子断键所导致.同时还研究了α-Fe裂纹的形变特点和断裂机理与温度场和应力场的依赖关系.     

Ultrasonic investigation of sandwich single crystals designed for studies of dislocation resonance damping

A novel sandwich single crystal (SSC) technique has been designed for improved MHz-pulse-echo investigations of dislocation damping. In the present SSC the high purity Cu crystal to be investigated is epitaxially overgrown by a buffer crystal doped with 200 ppm Mn. The buffer avoids interference between ultrasonic transducer and sample by shielding the investigated dislocation structure against stresses caused e.g., by different thermal expansion of the quartz transducer. The frequency dependence of dislocation resonance damping measured on the SSC has been analyzed and compared with measurements on normal single crystalline samples of high purity Cu and Cu doped with 200 ppm Mn.     

Ultrasonic detection of the pinning of dislocations by point defects in lead-I determination of migration energies

The ultrasonic attenuation of a γ-irradiated, deformed, single-crystal of lead has been measured between 77 and 270 K. Constant heating rate and isothermal anneals after low temperature irradiation yielded two dislocation pinning stages centered at 140 and 200 K and two dislocation depinning stages centered about 170 and 250 K. For an unirradiated sample one pinning stage centered at 170 and one depinning stage centered at 250 K were observed. Activation energies were calculated from isothermal anneals using an eigenfunction expansion model to be 0·16±0·04 and 0·36±0·05 eV for the pinning stages in the irradiated crystal and 0·28±0·05 eV for the pinning stage in the unirradiated crystal. The activation energy calculated from the same isothermal anneals using a Cottrell-Bilby analysis was 0·23±0·03 eV for the low temperature pinning stage in the irradiated crystal. The other activation energies were not changed. The discrepancy is discussed in Part II.     

Influence of collective effects on the dynamic behavior of a single edge dislocation in a crystal with point defects

The glide of a single edge dislocation in an elastic field of point defects randomly distributed over a crystal is investigated taking into account the influence of the phonon subsystem of the crystal. The force of retardation of the dislocation motion is calculated, and the velocities at which this force has a local maximum and a local minimum are determined. A comparative analysis of the glide of a single dislocation and the glide of a pair of edge dislocations is performed.     

Structure,impurity composition,and photoluminescence of mechanically polished layers of single-crystal silicon

The introduction of optically active defects (such as atomic clusters, dislocations, precipitates) into a silicon single crystal using irradiation, plastic deformation, or heat treatment has been considered a possible approach to the design of silicon-based light-emitting structures in the near infrared region. Defects were introduced into silicon plates by traditional mechanical polishing. The changes in the defect structure and the impurity composition of damaged silicon layers during thermal annealing (TA) of a crystal were examined using transmission electronic microscopy and x-ray fluorescence. Optical properties of the defects were studied at 77 K using photoluminescence (PL) in the near infrared region. It has been shown that the defects generated by mechanical polishing transform into dislocations and dislocation loops and that SiO₂ precipitates also form as a result of annealing at temperatures of 850 to 1000°C. Depending on the annealing temperature, either oxide precipitates or dislocations decorated by copper atoms, which are gettered from the crystal bulk, make the predominant contribution to PL spectra.     

Fine structure of the diffraction image of an edge dislocation in high-resolution section topography

The propagation of an x-ray wave field in an elastic field of an edge dislocation crossing a scattering triangle exactly along the bisector of the scattering angle has been considered. The scattering of the x-ray wave field by a complex elastic field of the edge dislocation has been analyzed using the methods of geometrical optics. It has been established that the fine structure of a diffraction image of defects in thick crystals is determined by the differences in scattering of the normal and anomalous modes of the x-ray wave field in the vicinity of the Bragg reflection. In the case of thick crystals, the x-ray diffraction image of defects can have a symmetry different from the symmetry of the function of local misorientations of the crystal lattice. X-ray wave scattering by local distortions of the crystal lattice can occur according to two different mechanisms depending on the gradient of space changes in the deformation field. In the crystal regions where the elastic field varies slowly with a change in the distance, the x-ray wave field has had time to adjust itself to follow the course of deviations of the crystal lattice from the exact Bragg condition. In the crystal region where the elastic field changes significantly at distances of the order of the extinction length, this region leaves the reflecting position and interference scattering occurs at the interface of the region. It is important that the form of the deformation field in this case is of no significance.     

Acoustic emission caused by large alternating strains

By vibrating specimens at very high strains, acoustic emission has been observed under controlled conditions. Continuous emission, in the form of strong harmonic generation, has been observed for polycrystalline copper and brass. In single crystal copper, a non-harmonic, burst type, response has also been observed. For brass the internal friction and the the third harmonic were analysed in terms of the dislocation models of Granato-Lücke and Peguin et al. A dynamic dislocation multiplication mechanism is suggested for the burst type emissions.