Solid State Phenomena Vols. 97-98

Abstract: The paper refers about problems connected with development of course on photovoltaics in the bachelor level of the study. Curricula of a course on photovoltaic systems performed at the Czech Technical University in Prague, Faculty of Electrical Engineering is presented. In the contribution is described the present state and compared with history and the project of the further development. Orientation of laboratory exercises towards applications has been supposed.

Abstract: The paper refers about a possibility to check recombination rate distribution over the area of power (large-area) solar cells from measured values of open circuit voltage V_OC using local irradiation by monochromatic light of different wavelengths (LBIV . Light Beam Initiated Voltage). The method can give information both about recombination centres distribution in large-area solar cells and surface recombination rate at the antireflection coating. From V_OC distribution, also position and extent of local defects can also be determined. The method can be used to investigate the influence of technology on characteristics of solar cells as an in-process checking with the aim of increasing efficiency and reliability of solar cells.

Abstract: Porous surface layers were studied in a series of p-type Si samples etched anodically in electrolytes based on hydrofluoric acid. The optical response of the structure consisting of substrate and surface layers was investigated by spectroscopic ellipsometry in the range 1-5 eV. The experimental results were compared with calculations, which model the optical response of a multilayer structure. The model parameters were compared to the structural data obtained by AFM and SEM studies. The experimental investigations and model calculations revealed the regularities in the dependence of the optical response on the doping degree of substrate and parameters of technological procedure.

Abstract: Thin films of ZrO₂-8mol%Y₂O₃ have been deposed by pulsed DC magnetron sputtering method. The substrates of Ni-cermet and alloy-600 for the films were used. The results of the investigation of the X-ray diffraction patterns and SEM showed that the films are nanocrystalline and belong to cubic symmetry. The relaxation process is related to the ion transport in thin films. The results of the investigation of the temperature dependencies of thin films ionic conductivity (σ) showed that the dependence σ(T) is caused by the temperature dependence of oxygen vacancy mobility, while the number of charge carriers remains constant with temperature.

Abstract: The behaviors of hydrogen in Al, Mg and MgAl thin films on stainless steel substrate were investigated in this work. The hydrogen ions extracted from plasma were used to load hydrogen into the film material. Glow discharge optical emission spectroscopy (GDOES) was applied to obtain the hydrogen depth profiles in Al films versus hydriding parameters. The MgH2, AlH3 and Mg(AlH4)2 hydrides were identified in plasma hydrided films using X-ray diffraction (XRD). It is shown that efficient supply transport of hydrogen from the surface into the bulk for Mg films takes place at temperature above 100 °C and ion irradiation intensity above 1 mAcm-2.

Abstract: Surface atoms are activated as result of replacement collisional sequences in solids by incident ions. In dependence on theirs threshold (displacement) energy and angular distribution they may be sputtered (removed) or laterally relocated on the surface. The relocation length distribution depends on the energy and angular distributions of activated atoms and interaction atom-solid potential. The process of lateral relocation of surface atoms is considered as a sequence of stochastic removal and adsorption processes. The rate equations describing processes of sputtering, relocation and thermal diffusion are built and steady state solutions are presented for multielemental solids. The mechanisms of stochastic mixing of atoms and roughening of surface is discussed.

Abstract: There are presented logic gates of molecular electronics digital computers. Maximal length of these molecular electronics digital logic gates are no more than four nanometers and maximal width 2.5 nm. The results of light induced internal molecular motions in azo-dyes molecules have been used for the design of light driven logically controlled (OR, AND) molecular machines composed from organic photoactive electron donor dithieno[3,2-b:2',3'-d]thiophene and ferrocene molecules, electron accepting tetracyano-indane molecule, and moving azo-benzene molecular fragment. Density functional theory (DFT) B3PW91/6-311G model calculations were performed for the geometry optimization of these molecular electronics logical gates. Applied DFT time dependent (DFT-TD/B3PW91) method and our visualization program give absorption spectra of designed molecular gates and show from which fragments electrons are hopping in various excited states. Quantum mechanical investigations of proton Nuclear Magnetic Resonance (NMR) values of Cu, Co, Zn, Mn and Fe biliverdin derivatives and their dimers using ab initio Hartree-Fock (HF) and DFT methods indicate that these modified derivatives should generate from one to twelve Quantum Bits (QuBits). The chemical shifts are obtained as the difference of the values of the tetramethylsilane (Si(CH₃)₄) molecule Gauge-Independent Atomic Orbital (GIAO) nuclear magnetic shielding tensor on the hydrogen atoms and that of the magnetically active molecules. There are designed several single supermolecule and supramolecular devices containing molecular electronics digital logic gates, photoactive molecular machines and elements of molecular NMR quantum computers that allowed to design several supramolecular Control NOT NMR quantum computing gates. Self-assembling simulations of these molecular quantum computing gates induced idea of self-assembled molecular quantum supercomputer and molecular quantum computing life.

Abstract: A microscopic mechanism of the self-formation of a dense pore system in the porous silicon is proposed. According to it, the process of porous silicon self-formation is dictated by the laws of dynamics for a charge carriers system. The proposed mechanism is proved by the results of computer simulation. The values of inter-pore separation distance in p-type based porous material and anodization current threshold density are evaluated; the dependence of an inter-pore separation distance on the carriers concentration, close to n^-1/2, is predicted.

Abstract: Yttria-stabilized zirconia (YSZ) coatings were synthesized using dc magnetron sputter deposition of Y/Zr layers followed by thermal treatment in the range of temperatures 600-1000 °C at atmospheric pressure in air. The characterization of YSZ coating structure was carried out by X-ray diffraction. The secondary ion mass-spectrometry analysis was used for the recording of depth profiles of the most important elements in coatings and at interface. The conducted analysis showed that processes on the surface play a dominant role in the synthesis mechanism of YSZ coatings homogeneous in structure and composition during the thermal oxidation. The excess of surface thermodynamic potentials supports an intensive intermixing across Y/Zr layers with continuous supply of oxygen through the surface. Under highly non-equilibrium conditions on the surface, the adatoms are driven into grain boundaries of crystallites and result in high compressive stress in grains. The stress relaxation initiates the plastic flow of matrix material with incorporation of oxygen atoms. Thermally activated dislocation glide is considered as the dominant plasticdeformation mechanism in these materials.

Abstract: Meso-tetra (4-sulfonatophenyl) porphine (TPPS4) is water-soluble tetrapyrrolic dye, which forms self assembled nanostructures – J-aggregates under appropriate conditions. It was shown, that such aggregates survive dried on the substrate. The spatial structure of TPPS4 Jaggregates formed in acidic aqueous solutions and dispersed on silicon substrates was analyzed by means of atomic force microscopy (AFM). The stripe-like structures were observed. The size of individual stripes ranged 4,5×40×(200-1000) nm (H×W×L). The width and height was almost the same for all stripes and independent upon the concentration of the solution, however the length was statistically distributed and the mean length increased with increasing concentration of initial TPPS4 solution. At higher concentrations such stripes stacked into thicker fibers containing 2-20 stripes. Such fibers branched and formed large bush-like structures sized up to several millimeters. According to experimental findings the model of mesostructures, formed by TPPS4 J-aggregates, was proposed.