Defect and Diffusion Forum Vols. 237-240

Abstract: In this paper we discuss possible mechanisms of PV annealing in Si. Our approach includes a combination of density functional theory and lattice kinetic Monte-Carlo (LKMC) simulations. The density functional theory is used to find the binding energies and jump barriers for P-V pair at different separations (from one to three interatomic bonds between complex constituents) and in different charge states. The mobility of the complex is simulated by LKMC with event probabilities calculated based on the energies from ab-initio calculations. .

Abstract: A systematic investigation of the segregation of Bi at both free surfaces and grain boundaries in Cu, under identical conditions, is reported. The problem of Bi evaporation upon Bi segregation at free surfaces was overcome using a special method for sample preparation. Cu bicrystals containing deliberately made internal cavities at the grain boundary were doped with Bi, annealed at temperatures between 1073 and 1223 K, and broken along the grain boundary in an ultrahigh vacuum chamber for Auger electron spectroscopy. For the first time, the equilibrium surface segregation of Bi in Cu has been measured. The segregation at the free surface was found to be stronger than the segregation at the grain boundary.

Abstract: ε/γ'-iron nitride (ε-Fe3N1+x, γ'-Fe4N) compound layers with thicknesses of about 10 µm were grown on pure α-Fe by gas nitriding at 823 K followed by quenching and were annealed at different temperatures in the range of 613 K – 693 K for different periods of time. These heat treatments led to a redistribution of nitrogen within the compound layer as well as between the compound layer and the adjacent ferrite, inducing thickness changes of the ε- and γ'-layers. The changes were analysed by light microscopy, electron probe microanalysis and X-ray diffraction. Models to describe and interpret the phase transformations in the ε/γ'-iron nitride compound layers as a function of time and temperature are discussed.

Abstract: Results of microstructural investigations of aluminide coatings modified by Si are presented in this work. Protective coating (TiAlSi type) was deposited by Arc-PVD. Thickness of the outside layer of deposited coating was 35µm and it contained TiAl3 phase modified by Si as a main component. The second layer was found as a transition area between the TiAl3 outside layer and the surface of TiAlCrNb substrate. Thickness of the inside sublayer was 5 µm. The diffusion treatment caused the progress of coating homogenisation from the point of view of phase and chemical composition. It was found that the coating consisted of the dominant TiAl3 phase and Ti5Si3 in thick outer sublayer and only TiAl2 phase in transition thin sublayer. Below the transition area, on the surface of TiAlCrNb substrate alloy, the layer of g−TiAl was found. The amount of silicides was increased in comparison with the coating only after the Arc-PVD process and the area of its presence had been removed in the outside direction of the coating.

Abstract: When oxygen dissolves from atmosphere and diffuses into an alloy during oxidation, the less noble alloy components may react to form oxide particles within the metal. This process is termed internal oxidation. Classical approaches to describe this phenomenon were derived under many strong simplifications such as constant diffusion coefficients, certain boundary conditions and semi-infinite sample. The presented general approach is based on the finite difference solution of the general diffusion equations coupled through the stoichiometry of reaction between oxygen and the considered element. The main enhancement is the consideration of concentration dependent diffusion coefficients, concentration dependent source terms and arbitrary time-dependent boundary conditions formulated as a concentration, a flux or mixed conditions. Furthermore, finite dimension of the specimen is incorporated. This general treatment also allows for the incorporation of the energy balance.

Abstract: A new concept of generation and annihilation of vacancies at uniform sinks and sources for vacancies is incorporated into the standard Monte Carlo model for vacancy mediated diffusion. This model enables to treat the vacancy wind as well as the deformation of the specimen and the shift of the Kirkendall plane. The Monte Carlo model is used for the testing of the recent phenomenological theories of diffusion by Darken, Manning and Moleko. The agreement with the self-consistent Moleko theory is excellent. On the other hand the agreement with the classical Darken theory used very often for the explanation of the Kirkendall effect is rather poor.

Abstract: Molecular machines described in this paper are meant to be such molecular systems that make use of conformational mobility (i.e. hindered rotation around chemical bonds and molecular construction deformations with formation and breakage of nonvalent bonds). Components of molecular machines move mainly by means of restricted diffusion. As an example of molecular machines of a nonbiological nature catenanes (compounds with two interlocked molecular rings) can be proposed. Thus, for example, model catenane ((2)-(cyclo-bi (paraquat-p-phenylene))- (1(2,6)-tetrathiafulvalena-16(1,5)naphtalena-3, 6, 9, 12, 15, 17, 20, 23, 26, 29- decaoxatnacontaphane)-catenane) changes its redox status when an electric field is applied, and rotation of the rings takes place. It occurs with fixation at certain moments of the influence. To find out characteristic properties of rings movements under various external conditions molecular dynamics simulation was carried out. Three cationic forms of the catenane were first subjected to geometrical optimization and quantum chemical calculation.

Abstract: Multiple-time spin-alignment echo (SAE) NMR spectroscopy of spin- 3 2 nuclei is used to study ultraslow diffusion in the hexagonal layered Li ion conductor LixTiS2 (x  1). Two-time correlation functions were monitored by recording (Jeener-Broekaert) echo amplitudes for constant evolution and variable mixing times. Echo decay rates t