Irradiation-induced diffusion in tracks of swift ions

Radiation-induced diffusion in tracks of swift ions caused by excitation of electrons and resulting in the formation of dilatations has been considered. The expressions for the longitudinal and radial atomic displacements are derived as well as those for the diagonal components of the strain tensor. The atomic-density distribution in the vicinity of a track is obtained in terms of the parameters of the three-dimensional energy distribution in an excited electron gas. The results obtained theoretically are compared with the known experimental data. The suggested approach provides the evaluation of the time of formation of track dilatations, the mobility of the atoms in the target irradiated with swift ions, and the energy losses for formation of wirelike dilatations in the tracks. It is shown that the ion irradiation of semiconductor crystals can be used for obtaining one-dimensional quantum objects.     

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.     

Phase equilibria of <Emphasis Type="Italic">A</Emphasis><Superscript>3</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>5</Superscript> quinary systems with an elastically strained solid phase

The contribution of the elastic component of the excess energy of mixing is determined for A³B⁵ quinary solid solutions. A relationship is derived for the activities of the components in an elastically strained solid phase of the quinary solid solutions. The correctness of the possible assumptions used in the calculation of the activity coefficients of the solid phase of a quinary solution is analyzed. The contact supercooling in the vicinity of the binary substrate isoperiods is calculated for a number of A³B⁵ quinary systems. It is shown that the negative contact supercoolings correspond to the thermodynamic instability boundaries of the quinary solid solutions.     

Plasticity of high purity iron single crystals (I) 1. work hardening

High purity iron single crystals were deformed in tension in the temperature range 4.2 to 473 K. Work-hardening characteristics were determined and the plastic behaviour in dependence on temperature, strain rate and crystal orientation isz discussed. The transition temperature between low-temperature and intermediate-temperature deformation regimes was found to be ≅ 250 K, the critical temperature estimated from the temperature dependence of the critical resolved shear stress is ≅ 380 K. A hump on the temperature dependence of the critical resolved shear stress was observed in the vicinity of 250 K. These observations are qualitatively explained by special mobilities of dislocations in b.c.c. lattice.     

Analysis of a random system of dislocations in a deformed crystal

Structure of deformed crystals is modeled by dislocation loops of random size nonuniformly randomly distributed in natural slip planes. This model is used to determine structure parameters from the harmonics of the diffraction line of a polycrystal. Practical analysis of the dislocation structure under real conditions of the diffraction experiment is performed.     

Anwendung der Protonen-Rückstreuanalyse zur Bestimmung der Zusammensetzung von AIIIBV-Mischkristallen

Spectra of 1.5 MeV protons elastically scattered from A^IIIB^V mixed crystals are analysed for the determination of the composition of the samples. A brief outline of the method of microanalysis by backscattering spectrometry is given and its application is discussed in detail by two examples. The results of the measurements show good agreement with those obtained through other analytic procedures. The appendix treats the mass and depth resolution of the backscattering technique described before.     

A simple model for cooperative and non-exponential processes in non-crystalline polymers

A quite simple Markov chain model is presented in an attempt to understand several characteristic properties of the structural relaxation in glass-former materials. A second order Markov model is proposed for a small region of the material. Only a few parameters are necessary for the definition of the material in the model equations namely the energy levels accessible to that small region and the transition probabilities between them. The later are considered dependent on the energy levels and the potential barrier heights between them, on temperature, on a reference transition rate parameter and on a cooperativity or memory parameter related to the interaction with the neighbour regions. Isothermal relaxations at different temperatures were simulated with selected values of the model parameters. As a result, non-exponentiality of energy relaxations and its temperature dependence appears directly related to the cooperativity parameter. Markov chain model shows also non-linearity and memory effects, and a transition between two different regimes in the dependence of the relaxation times with temperature.     

Stabilization of lattice period in quinary solid solutions of the <Emphasis Type="Italic">A</Emphasis><Superscript>3</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>5</Superscript> compounds

The stabilizing effect of elastic strains on the lattice period of a quinary solid solution is considered. The expression for the stabilization factor for quinary solid solutions of the A_xB_1?xC_yD_zE_1?y?z type is derived. It is shown that the stabilizing influence of the substrate sharply increases in the vicinity of the region of the chemical spinodal. The stabilization factors are calculated for the Ga_xIn_1?xP_yAs_zSb_1?y?z and A1_xGa_yIn_1?x?yP_zAs_1?z quinary solid solutions isoperiodic to InAs, GaSb, and GaAs. It is shown that in the region of thermodynamic instability the stabilization factor has negative values. The changes in the composition of the above elastically strained quinary solid solutions are analyzed with respect to the equilibrium composition. It is also shown that stabilization of the lattice period does not signify the stabilization of its composition.     

Phase states of porous sodium niobate ceramics

The effect of closed porosity p (from 1.0 to 13.6%) of sodium niobate ceramics on its phase state and structural characteristics has been investigated. It is shown that, with an increase in the porosity in the range 1.0 ≤ p ≤ 6.2%, the behavior of the structural parameters is determined by a gradual decrease in the content of the ferroelectric Q phase. At p ≥ 6.2%, their change is determined only by the porosity. The observed effects are interpreted within the model of deformed cation-anion bonds.     

Generalization of the nonstandard approach in the dynamic theory of diffraction for deformed crystals

The nonstandard theory of X-ray scattering in a deformed crystal has been generalized. The vector of atomic-plane displacement is introduced into the crystal polarizability model like in the generalized Takagi dynamic theory. The solution to the wave equation is sought for using the procedure of expanding the field amplitude and vector operators in the Fourier components of polarizability χ _H in a series according to the multiscale method. It is shown that considering lattice strain generally calls for introducing various characteristic spatial regions for the diffraction equation, which is in complete agreement with the main concept of the multiscale method. A particular case of a strain field depending on one scale is considered. If a relative change in strain occurs at a length on the order of the extinction length, one can obtain equations generalizing the Takagi equations to the case of arbitrary diffraction geometries.     

Study of the influence of the parameters of an experiment on the simulation of pole figures of polycrystalline materials using electron microscopy

A two-dimensional mathematical model of a polycrystalline sample and an experiment on electron backscattering diffraction (EBSD) is considered. The measurement parameters are taken to be the scanning step and threshold grain-boundary angle. Discrete pole figures for materials with hexagonal symmetry have been calculated based on the results of the model experiment. Discrete and smoothed (by the kernel method) pole figures of the model sample and the samples in the model experiment are compared using homogeneity criterion χ², an estimate of the pole figure maximum and its coordinate, a deviation of the pole figures of the model in the experiment from the sample in the space of L₁ measurable functions, and the RP-criterion for estimating the pole figure errors. Is is shown that the problem of calculating pole figures is ill-posed and their determination with respect to measurement parameters is not reliable.     

Model approach to solving the inverse problem of X-ray reflectometry and its application to the study of the internal structure of hafnium oxide films

The key features of the inverse problem of X-ray reflectometry (i.e., the reconstruction of the depth profile of the dielectric constant using an experimental angular dependence of reflectivity) are discussed and essential factors leading to the ambiguity of its solution are analyzed. A simple approach to studying the internal structure of HfO₂ films, which is based on the application of a physically reasonable model, is considered. The principles for constructing a film model and the criteria for choosing a minimal number of fitting parameters are discussed. It is shown that the ambiguity of the solution to the inverse problem is retained even for the simplest single-film models. Approaches allowing one to pick out the most realistic solution from several variants are discussed.     

Ultrasonic relaxation studies in the liquid crystal 80CB

The variation of the ultrasonic velocity with temperature in the liquid crystal 4′-n-octyloxy-4-cyanobiphenyl (80CB) at four different fixed ultrasonic frequencies is studied. From these studies various relaxation parameters like the adiabatic relaxation time, velocity at zero frequency, in the vicinity of isotropic-nematic phase transition and velocity at infinite frequency are estimated. From these parameters the relaxation mechanism in the vicinity of isotropic-nematic phase transition is studied and the results are discussed.     

Method of Evaluating Geometrical-Statistical Parameters of the Interaction between Dislocations and Point Obstacles from Electron Micrographs

Electron micrographs of MgO crystals deformed in the HVEM show screw dislocations of curly shape. The dislocations are pinned at localized obstacles and bow out between them. The paper describes a measuring procedure for the geometrical interaction parameters between the dislocations and the obstacles. Such are the effective stress, the obstacle distance and the force acting on the obstacles. The procedure consists in a graphical fit of loops calculated by the DE WITT-KOEHLER line tension model to the observed dislocation segments.     

A crowdion mechanism of crystal twinning

The processes of plastic deformation of crystals via mechanical twinning are considered. Models of nucleation and motion of twin boundaries leading to formation of twin interlayers are proposed. These models are based on the crowdion mechanism of deformation in crystals and are considered by an example of close-packed structures. Good agreement between the predictions of the models proposed and the experimental results for crystals deformed by a concentrated load is demonstrated.     

Defects in epitaxial layers of silicon-germanium grown on silicon substrates

Crystal defects of various kinds found in epitaxially grown Si/Ge alloy layers on Si substrate, may be either inherent to the material and originating from atomic radii misfit, or can be traced to the growth process and controlled or eliminated by varying its parameters. A network of slip lines, becoming more pronounced with increased Ge content, indicates plastic deformation resulting from partial relief of stresses during the high temperature growth process. Electron microprobe and X-ray diffraction analysis indicate some Ge segregation in the fault vicinity, and a slight anisotropy in the lattice constant expansion due to the Ge.     

Random network model for amorphous alloys

A random network model has been developed for amorphous alloys which characterizes their band structure in terms of tight binding matrix elements. This model is applied to the arsenic-selenium system as well as the germanium-sulfur system. In the latter case it predicts a local maximum in the band gap in the vicinity of the compound composition GeS₂.     

Dry Patterning of Al and Al Alloys

Plasmachemical etching of Aluminium in chlorine containing discharges is discussed from a thermochemical point of view. A model of Al etching is proposed, in which diffusion of reaction products through the carbon-rich deposite layer is considered to be rate-limiting. The model quantitatively describes the dependence of the etch reaction on different process parameters of the CCl₄-plasma.