Coulomb effects in granular materials at not very low temperatures

We consider effects of Coulomb interaction in a granular normal metal at not very low temperatures suppressing weak localization effects. In this limit calculations with the initial electron Hamiltonian are reduced to integrations over a phase variable with an effective action, which can be considered as a bosonization for the granular metal. Conditions of the applicability of the effective action are considered in detail and importance of winding numbers for the phase variables is emphasized. Explicit calculations are carried out for the conductivity and the tunneling density of states in the limits of large $g\gg 1$ and small $g\ll 1$ tunnelling conductances. It is demonstrated for any dimension of the array of the grains that at small $g$ the conductivity and the tunnelling density of states decay with temperature exponentially. At large $g$ the conductivity also decays with decreasing the temparature and its temperature dependence is logarithmic independent of dimensionality and presence of a magnetic field. The tunnelling density of states for $g\gg 1$ is anomalous in any dimension but the anomaly is stronger than logarithmic in low dimensions and is similar to that for disordered systems. The formulae derived are compared with existing experiments. The logarithmic behavior of the conductivity at large $g$ obtained in our model can explain numerous experiments on systems with a granular structure including some high $T_{c}$ materials.Comment: 30 page

Design and characterization of a thermal hydrogen atom source

The hydrogen atom source considered here incorporates a hot capillary fed by hydrogen gas. Our earlier measurements on a source heated by electron bombardment are interpreted in terms of a simple model which encourages us to design a source heated by the radiation from a filament. The radiatively heated source is much simpler, more reliable, and easier to run than the electronically heated source. Furthermore, the radiatively heated source is free of any energetic particles. In order to obtain quantitative data on the intensity, an apparatus is constructed revealing the angular distribution of the hydrogen atoms and molecules by means of a quadrupole mass analyzer. The intensity of the source is controlled by the mass flow rate of the feed gas and the electric power to the filament. The flux density of hydrogen atoms at a substrate 6 cm away from the source is variable over two orders of magnitude and extends up to some 10(15) atoms/cm(2) s. (C) 2008 American Institute of Physics

Adjustable hydrogen atom incorporation into sputter desposited a-SiC

Thin films of a-Si0.8C0.2:H are deposited by ion beam sputtering combined with the simultaneous irradiation of hydrogen atoms delivered by a thermal hydrogen atom source. Elemental composition and bonding structure of the films are analysed by XPS, RBS, ERD, and FTIR. The hydrogen concentration can be varied in a controlled manner. Up to concentrations of 5%, the hydrogen is exclusively incorporated in single Si-H bonds. (c) 2005 Elsevier B.V. All rights reserved

How to use oxygen and atomic hydrogen to prepare atomically flat fcc Co(110) films

It is shown that atomic hydrogen from a specially designed atomic beam source is well suited for removing chemisorbed oxygen from an fcc Co(110) film that has been grown on a Cu(110) substrate using oxygen as a surfactant. Exposing the oxygen-terminated Co surface to atomic hydrogen leads to a surface reaction which destroys the (3×1) ordered-O induced surface reconstruction of the Co film. Upon annealing at 380 K, the hydrogen remaining on the O-free Co surface can be completely desorbed. With this technique, it is possible for the first time to prepare about 15 monolayers thick, atomically-flat fcc Co(110) films