Diffusion properties of plastically deformed silicon crystals

The effect of dislocations generated by electroplastic strain on the electric-field-driven transport of impurity atoms of indium in single crystals of P-silicon is investigated experimentally. It is shown that when electrodiffusion of indium and strain are induced simultaneously, the impurity ions are preferentially dragged towards the anode. Fiz. Tverd. Tela (St. Petersburg) 41, 1028–1029 (June 1999)     

Numerical calculations of the radiation-induced strain rate of interstitial solid solutions. II Allowance for the main channels for the influence of impurities on radiationinduced creep

A previously developed numerical method for calculating the radiation-induced creep rate [Yu. S. Pyatiletov and A. D. Lopuga, Tech. Phys. 45 (1999)] is used to study the influence of impurity atmospheres around dislocations and pores, impurity traps, and mobile impurity-vacancy and impurity-interstitial complexes on the radiation-induced strain rate of interstitial alloys. Quantitative data are obtained on the creep rate as a function of impurity concentration, and a physical interpretation allowing for the recombination of interstitial atoms and vacancies directly with one another, on impurity traps, and on mobile complexes is put forward. Zh. Tekh. Fiz. 69, 19–23 (March 1999)     

Effect of electric current on the migration of hydrogen interstitial atoms in the region of a crack tip in a crystal

The effect of a constant electric current on the migration of interstitial atoms dissolved in a crystal in the region of a tensile crack tip is estimated. The calculation takes into account plastic deformation that is produced in the vicinity of the crack tip in the loaded sample by dislocation motion in active slip planes of the crystal under the action of mechanically and electrically induced shear stresses, Joule heat release, the Thomson effect, and ponderomotive forces and allows for the effect of gas exchange near the crack edges on the evolution of the distribution of interstitial impurity atoms. The time dependence of the stress intensity factor is found for both the cases of the presence and absence of a constant electric current near the crack tip. Numerical calculations are performed for an α-Fe crystal.     

Analysis of the plasticizing effect of hydrogen dissolved in a crystal on the evolution of plastic deformation at the tip of a crack

The effect of interstitial hydrogen atoms on the evolution of plastic deformation in a crystal at the tip of a tensile crack is estimated taking into account gas exchange at the crack banks. It is found that, for an initial concentration of not less than 10^?4, the plasticizing effect of dissolved hydrogen causing a dislocation expulsion is significant and can be responsible (at least, partially) for plasticization. As regards the evolution of the distribution of hydrogen atoms, a monotonic drain of dissolved hydrogen atoms into the hollow of the crack is observed for concentrations below 5×10^?4, while at higher concentrations the impurity concentration at the banks of the crack varies periodically: complete drain is replaced by the accumulation of hydrogen corresponding to a “blocking” of the drain by the gas pressure. Numerical calculations are made for an α-Fe crystal.     

Point Defect Production Under High Internal Stress Without Dislocations in Ni and Cu

Kiritani et al. have observed a large number of small vacancy clusters without dislocations at the tip of torn portions of fcc metals such as Au, Ag, Cu and Ni. Small vacancy clusters, rather than dislocation cell structures, have also been observed after high-speed compressive deformation, suggesting the possibility of plastic deformation without dislocations. In this paper, in order to investigate the mechanism of deformation without dislocations, change in formation energy of point defects under high internal stress was estimated by computer simulation. Elastic deformation up to - 20% strain was found to provide a remarkable lowering of formation energy of point defects. For example, when Ni is subjected to elastic strain, the formation energy of an interstitial atom decreases to 40% that without strain and the formation energy of a vacancy decreases to 51% that without strain. The number of point defects formed under thermal equilibrium during deformation was evaluated. The number was judged to be insufficient for explaining the formation of vacancy clusters as observed in experiments.     

The stress-driven migration of point defects to a slowly moving crack

The migration kinetics of point defects near a slowly moving brittle crack are studied under the condition of pure drift. In the pure-drift approximation it is assumed that the point-defect flow in the vicinity of a crack tip is dominated by the elastic interaction between the stress field of the crack and a point defect and that concentration gradient effects can be neglected. While such a pure-drift approach has been shown to be useful to calculate the short-time diffusion kinetics of impurity-induced subcritical crack growth, previous applications are based on the drift solutions for a stationary crack. In the present paper, the first-order drift diffusion equation for a slowly moving crack at uniform velocity is solved. This yields the flow lines of the point defects and the impurity segregation rate directly in terms of the crack growth rate. The flow line patterns reveal important insights with respect to the point-defect migration kinetics near a steadily advancing crack. Although the calculation is entirely elastic, it is shown that the present drift model maintains some relevance also in the presence of a plastic zone ahead of the crack tip.     

Magnetoplastic effect in silicon: A search for new methods of controlling structure-sensitive properties of elemental semiconductors

The effect of static magnetic fields up to 1 T on the state of impurity point defects and the mobility of surface dislocation segments in doped (0.01–1.00 Ω cm) silicon has been considered. Long-lived (∼100 h) changes in the state of point defects have been revealed from the mobility of dislocations introduced after the magnetic-field treatment. The concentration dependence of the magnetoplastic effect in p-type silicon has been studied. A threshold impurity concentration of 10¹⁵ cm⁻³ has been found, below which the magneto-plastic effect has not been observed. The influence of magnetic-field pretreatment on the expectation times and activation barriers for dislocation depinning from stoppers and the effect of thermal preannealing on the magnetoplasticity in Si have been considered.     

Formation mechanism for nanodefects on surfaces of loaded metals

Tunneling profilometry is used to investigate the shape and orientation of defects that form at the surfaces of Cu, Au, Mo and Pd under loading. The defects have the shape of an indented prism. The value of the angles at the tip of the defects coincide with the angles between glide planes, while the orientation of the walls coincide with the orientation of these planes. At the edges of the defects there exist “swellings” caused by expulsion of material at the surface. Based on these results, the creation of these defects is explained by the exit of dislocations as they burst through barriers formed at intersecting glide planes. Fiz. Tverd. Tela (St. Petersburg) 40, 668–671 (April 1998)     

Evolution of vacancy defects in the surface layers of a metal irradiated with a pulsed electron beam

The distribution of vacancy defects in the surface layers of α-Fe after irradiation with a high-current pulsed electron beam is studied experimentally by unique nuclear-physical methods — low-energy positron annihilation, Rutherford backscattering (RBS), and proton-induced x-ray emission (PIXE). Regions with low local density, which are sources of crater formation on the surface of the irradiated sample, are observed by scanning a proton microbeam. Positron lifetime measurements reveal that as the electron beam power increases, nonequilibrium vacancies tend to be captured by carbon impurity atoms. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 618–622 (25 April 1997)     

Effect of the fermi level position in silicon on ion-induced displacement of impurities

Abstract

With the channeling technique the lattice location of both As and B is studied in single As-or B-doped and in doubly As-and B-doped silicon single crystals. The influence of the position of the Fermi-level on the displacement of impurity atoms off substitutional lattice sites is investigated by changing the crystals from n- to p?type or vice versa by choosing implant conditions and annealing termperatures for the doubly doped crystals in an appropriate way. Big changes were found in displacement cross sections for As and B after conversion of the crystals from n- to p-type. The results can be explained by assuming that the interaction between primary defects and impurity atoms causing the displacement of the impurity atom is controlled by Coulomb attraction between charged point defects and the impurity atoms.     

Modeling of surfaces of constant force above a lattice of close-packed atoms in the repulsive mode

Surfaces of constant force (force contours) are calculated for the scanning of an AFM tip over a lattice of close-packed atoms in the repulsive mode. It is shown that discontinuities are observed on the force contours in the regions between the atoms of the surface lattice for sufficiently small initial scanning heights of a tip with a single atom at its end. A cluster model of the tip end, which ensures continuity of the scanning at arbitrary initial heights, is constructed. The dependence of the AFM images on the orientation of the cluster on the tip end relative to the crystallographic axes of the surface is investigated for both an unperturbed lattice of close-packed atoms and a lattice containing point defects. The diagnostic possibilities of the findings are discussed. Zh. Tekh. Fiz. 67, 77–85 (June 1997)     

Theorem on the kinetic energy in an elastic continuum with defects

An expression of the theorem on the kinetic energy for an elastic continuum with dislocations is derived on the basis of the dynamical equations of a gauge model of the medium. This relation shows that the work performed by internal surface stresses in the volume is redistributed between the work performed by the effective stresses at the rates of the effective elastic distortions and plastic distortions. In phenomenological theories of plasticity the latter quantity, representing the rate of energy dissipation, governs the dissipative processes. An expression is obtained which relates the rate of energy dissipation with the self-energy density of the field of the defects and the energy flux of the defects. Zh. Tekh. Fiz. 68, 82–83 (March 1998)     

Reversible and irreversible magnetic-field-induced changes in the plastic properties of NaCl crystals

It is established that a weak magnetic field with induction B∼1 T gives rise to irreversible changes in NaCl crystals without freshly introduced dislocations, while a strong magnetic field with induction 16<B<35 T gives rise predominantly to reversible changes. It is inferred that there exist two different channels whereby a magnetic field influences the state of point defects. Fiz. Tverd. Tela (St. Petersburg) 40, 2065–2068 (November 1998)     

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.     

Effect of vacancies and interstitials on the dynamic properties of the La2−x SrxCuO4 superconductor

The effect of vacancies and interstitials in the CuO₂ layer on the vibrational spectrum in the La_2−x Sr_xCuO₄ system has been calculated by molecular dynamics. It is shown that the excitation probability for local ∼0.4-eV high-frequency vibrations of nonphonon origin in the vicinity of Sr impurity atoms decreases if copper vacancies are introduced at a concentration x=0.17, which corresponds to the maximum superconducting transition temperature, this decrease being still more effective (by about ten times) if interstitial atoms are present. The appearance of interstitials makes a considerable region around them (five to six nearest neighbors) quasi-amorphous. A comparison with available experimental data is made. It is concluded that the behavior of the system under irradiation is accounted for primarily by interstitials, which bring about strong perturbation in the lattice (∼1 nm) up to making it completely amorphous. Fiz. Tverd. Tela (St. Petersburg) 40, 984–988 (June 1998)     

Effect of a weak magnetic field on the state of structural defects and the plasticity of ionic crystals

The aim of this work is to examine the influence of a weak (on the energy scale) magnetic field on the state of dislocations and point defects in ionic crystals. It is found that complex point defects existing in a metastable state are sensitive to a magnetic field B∼1 T. The contributions are identified, and the kinetics of various types of reactions within the structural defects and between them leading to plastification of the crystals in a magnetic field are determined. The effect of light on the sensitivity of the point defects to a magnetic field is described, and the spectral characteristics of this effect are determined. A resonant effect of the combined action of a weak constant magnetic field and a high-frequency magnetic field on the dislocation mobility is found to occur when these fields satisfy the conditions of electron paramagnetic resonance. Zh. éksp. Teor. Fiz. 115, 605–623 (February 1999)     

Kinetics of accumulation of vacancy complexes in dislocated silicon under 60Co γ-ray irradiation

Abstract

Radiation defect accumulation in ⁶⁰Co γ-ray-irradiated n-type Si single crystals (ρ=150ωcm) with various densities of dislocations (N_D = 1 × 10⁴ to 1 × 10⁷ cm ^?2) introduced at plastic deformation was studied. The temperature dependences of the Hall coefficient were measured. The probabilities of interaction of vacancies with oxygen, phosphorus atoms, and dislocation line elements were determined. It has been established that with the increase of N_D they can increase at the expense of complication of dislocation structure, decrease during formation of impurity atmosphere near dislocations and compensation of deformation fields, and they do not change if complex formation of vacancies with impurities occurs far from dislocations. Kinetics of A- and E-centre accumulation in the crystals containing dislocations with different impurity atmosphere was described.     

Nanometer-resolution scanning optical microscope with resonance excitation of the fluorescence of the samples from a single-atom excited center

A scanning optical microscope whose active element (the tip) consists of a crystal containing impurity ions or color centers, which are excited by laser radiation, is proposed. The excitation energy from a single impurity center located at the point of the tip is transferred to the fluorescence centers of the experimental sample by the mechanism of resonant dipole-dipole exchange. It is shown that this approach can give nanometer spatial resolution with high sensitivity, which in many cases is much higher than the sensitivity of the “standard” near-field fluorescence microscopy. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 311–315 (10 March 1996)     

Study of the influence of vacancies and vacancy complexes on the yield limit of Al subjected to strain aging

Mechanical properties of metals are most sensitive to the presence of point defects. The influence of point defects on the kinetics of plastic deformation is highly diversified: the point defects can be the main carriers of plastic deformation (diffusion creep, crowdion plasticity, etc.), can imitate the velocity of nonconservative motion of dislocations, and can serve as centers of pinning of dislocations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 18–20, March, 2008.     

Analytical estimation of dislocation distribution at the tip of arrested cracks

Computer simulation technique is used for studying the plastic flow at the tip of an arrested crack in lithium fluoride crystals. Two stages of the dislocation structure formation at the tip of a crack are analyzed: the formation of slip lines at the instant of crack arresting, and their evolution after sample unloading and partial healing of the crack. The size and the number of dislocations in a slip line are determined as functions of the loading force at the instant of crack arresting and on frictional stresses. It is shown that, during sample unloading and healing, some dislocations emerge at the plane of the crack under the action of mutual repulsion and image forces, so that the dislocation density attains its maximum value at a distance from the crack tip. A finite region free of dislocations exists in the immediate vicinity of the crack tip.