Diffusion of particles over dynamically disordered lattice.

Using kinetic Monte Carlo simulations we have investigated the diffusion of particles over a lattice with moving atoms in the framework of a simple lattice-gas model of a reconstructive surface. The particle migration over the static and dynamic lattices differs considerably. The dynamic lattice reconstruction changes substantially the particle diffusion coefficient. The Arrhenius dependencies are quantitatively different. An interesting peculiarity of the particle migration is the formation of defectons--local lattice deformations around the adsorbed particles. In certain ranges of the system parameters (jump rates of the substrate atoms and adsorbed particles) the adsorbed particles cause local displacements of the nearest substrate atoms, resulting in deeper adsorption sites and lower jump rates. Such particle self-trapping produces a characteristic minimum on the Arrhenius dependencies.

Notes on the photo-induced characteristics of transition metal-doped and undoped titanium dioxide thin films.

This study reports the preparation of thin nanoparticulate films of titanium dioxide and its modified version doped with a transition metal. The behavior of prepared films was described by means of their photocatalytic and photo-induced electrochemical properties. The TiO(2) and M/TiO(2) (M=Ag, Zr, Fe) thin films were produced via a standard sol-gel method using titanium n-butoxide, acetylacetone, and transition metal acetylacetonates as precursors. Prepared films were analyzed by a series of techniques involving XRD, Raman spectroscopy, SEM, AFM, and XPS. Their photocatalytic activity was monitored with the aid of decomposition of the model compound Rhodamine B in water. All films were then tested for their photo-induced electrochemical properties based on evaluation of polarization curves (photocurrents). The highest reaction rate constant (0.0101min(-1)), which was even higher than that for pure TiO(2), was obtained for the Ag/TiO(2) sample. The highest quantum yield of the charge collection was determined for the undoped TiO(2) film.

Diffusion of particles on a dice lattice with two nonequivalent sites.

We investigated the diffusion of particles on a dice lattice with two kinds of nonequivalent sites. It is shown that the character of the particle migration depends crucially on the relative rates of the jumps from deep and shallow sites. The site inhomogeneity imposes specific pair correlation between the successive jumps. A general analytical expression for the chemical diffusion coefficient has been derived in the case of strong inhomogeneity. We have calculated coverage dependencies of the diffusion coefficients and some thermodynamic quantities for the different values of the lateral pairwise interaction between the particles. The analytical data have been compared with the numerical data obtained by the kinetic Monte Carlo simulations. Almost perfect agreement between the respective results has been found.

Atmospheric barrier-torch discharge deposited ZnO films: optical properties, doping and grain size effects.

Technology aspects, structure and characteristic properties of the atmospheric barrier torch discharge technique grown nominally pure and Al (0.1-5%) and Mn (0.05-0.5%) doped ZnO nanocrystalline thin films deposited on fused quartz substrates are reported. The set of films with various thicknesses in the range from 70 nm to 1000 nm were prepared for each composition. XRD and AFM analysis show well formed [001] preferably oriented hexagonal high quality films witch could be operatively fabricated in air atmosphere with controlled grain size. All films under study revealed n-type conductivity except some Mn doped films, which revealed p-type. Spectroscopic optical ellipsometry and luminescence spectroscopy studies evidenced luminescence properties typical for well formed ZnO and appreciable influence of Al doping and grain size on the optical absorption edge. Al doping shifts strongly absorption edge to the higher energies. The grain size decreasing (from 100 to 15 nm) leads to distinct diffusing of the absorption edge accompanied by increase of absorption in the near band edge region. For the smallest grains the pronounced Urbach-type absorption tail can be observed manifesting films inhomogeneity development.

SrTiO(3):Cr nanocrystalline powders: size effects and optical properties.

The crystal structure, optical absorption, and photoluminescence of chromium impurity centers were studied in nanocrystalline SrTiO(3):Cr (0.1 mol%) powders with average particle size within the range 13-100 nm prepared by the Pechini-type polymeric sol-gel method. Only the presence of a cubic perovskite phase of O(h)(1) symmetry was proved for the powders at room temperature, by means of x-ray diffraction. The lattice constant a = 3.910 Å, larger than that of bulk SrTiO(3) crystals (a = 3.905 Å), was found for nanoparticles with the size about 20 nm. The optical absorption edge and the zero-phonon R-line ([Formula: see text]) of luminescence of the octahedral Cr(3+) centers shifted to higher energies with decreasing nanoparticle size. These size effects were regarded as intrinsic to SrTiO(3). An unusual and large temperature shift of the R-line position very similar to the 'dielectric related' one of the bulk crystals was observed for all powders, evidencing their quantum paraelectric behavior. However, the powders with the average particle size about 13 and 20 nm did not reveal completely reproducible behavior of the R-line position at low temperatures. This instability was considered a possible manifestation of a low-temperature phase transition in small enough SrTiO(3) nanoparticles.