Recombination-enhanced processes in solar cell degradation

In this paper we briefly survey processes enhanced by high carrier densities and cases relevant to solar cell systems. The criteria for distinguishing between the main types of mechanism (local excitation, local heating and the Bourgoin-Corbett mechanism) are discussed. Whether or not the reaction coordinate is a normal mode proves to be of considerable importance

Weakly allowed transitions in the spin-lattice relaxation of spin pairs

Weakly allowed transitions alter the magnitude and dependence on temperature and frequency of the spin lattice relaxation rate of antiferromagnetically coupled pairs of spins. These transitions, allowed because the phonon wavelength is finite, appear to have been observed in (NH4)2PtCl6:Ir

BROADENING OF RESONANCE LINES BY CHARGED DISLOCATIONS

It is shown that the random electric fields of charge dislocations in insulators should cause appreciable broadening of sharp resonance lines such as spin-resonance signals. The degree of broadening is very sensitive to the screening of the dislocations by charged point defects. Since the shape of the inhomogeneously broadened resonance line monitors the distribution of the internal fields, the lineshape can be used to deduce properties of the charged dislocations, like their charge per unit length and the degree of screening. Quantitative calculations are presented which suggest that spectroscopic methods, notably spin resonance, should provide a convenient method of investigating charged dislocations

Elastic interactions between surface adatoms and between surface clusters

One major term is omitted in most conventional treatments of interactions between surface adatoms or groups of adatoms. This is the elastic interaction, in which adatoms interact through mutual distortion of the substrate. The indirect elastic interaction explains a range of observed surface phenomena in a consistent quantitative way. These phenomena include static and dynamic effects ranging from ordered structures to correlated motions of adatom clusters. It is likely also that substrate distortion is important in clean surface reconstruction. The elastic interaction is typically comparable with or larger than the indirect electronic interactions usually presumed. It follows that detailed calculations which ignore the substrate distortions produced will be of limited value only

Comment on 'The lattice contraction of nanometre-sized Sn and Bi particles produced by an electrohydrodynamic technique'

The contraction in lattice parameter observed in nm-sized grains of Sn and Pi appears to be dominated by the effects of surface stress, not the presence of vacancies

The challenges of nanostructures for theory

It is tempting to believe that modelling in nanotechnology is much the same as that for conventional solid-state physics. However, important areas of nanotechnology address different systems. The mechanics of DNA (for instance) resembles spaghetti more than silicon, the statistical physics needed is often not carrier statistics, and the role of viscosity (the low Reynolds number limit) is not always the familiar one. The idea of equilibrium may be irrelevant, as the kinetics of nonequilibrium (perhaps quasi-steady state) can be crucial. Even when the issues are limited to nanoscale structures (rather than functions), there is a complex range of ideas. Some features, like elasticity and electrostatic energies, have clear macroscopic analogies, but different questions emerge, such as the accuracy of self-organisation. Others concepts like epitaxy and templating are usually micro- or mesostructural. Some of the ideas, which emerge in modelling for the nanoscale, suggest parallels between molecular motors and recombination enhanced diffusion in semiconductors. (C) 2002 Elsevier Science B.V. All rights reserved

QUANTUM-THEORY OF DIFFUSION - TEMPERATURE DEPENDENCE OF DIFFUSION OF LIGHT INTERSTITIALS IN DEBYE SOLIDS

The temperature dependence of the motion of light interstitials is calculated using the quantum theory of Flynn and Stoneham (1970). The results are compared with the asymptotic expressions given previously. They show that the high temperature asymptotic is accurate over a wider range of temperature than expected, whereas the low temperature form is of very restricted application. Deviations from the asymptote depend both on the temperature and on the ratio of the activation energy to the Debye energy. Results for protons in Ta agree remarkably well with the theory for an activation energy 0.188 eV and for a hopping integral J of 29% of the Debye energy

THEORY OF ELECTRON-DIFFRACTION BY VOID LATTICE

The theory is given for the electron diffraction by the void lattice in molybdenum, recently observed by Sass and Eyre (see abstr. A52564 of 1973). The results are analysed to see if this method can give useful new information about the voids and their ordering. The predictions of the positions and intensities of the extra peaks agree with observation. However, the quantitative theory shows that void shapes cannot readily be found from the diffraction data. Nor is it easy to get accurate information about void sizes or the nature of the disorder in the void lattice, mainly because of the problems of measuring intensity profiles. The effects of the various forms of lattice disorder are discussed qualitatively

DEFECT MIGRATION IN SOLIDS - MICROSCOPIC CALCULATION OF DIFFUSION RATES

Diffusion includes some of the commonest processes on an atomic scale, in which uncorrelated atomic jumps bring about changes in solids. The many predictions of activation energies characterising the temperature dependence of diffusion have high accuracy when good interatomic potentials are known, and a continually improving accuracy from direct quantal calculations. Much more is needed to find the absolute rate at some temperatures. Recent work for both classical and quantum diffusion shows that rates too can be estimated with respectable accuracy. Such calculations highlight basic problems of solid-state defect physics. They alsow offer predictions of techonogical value for diffusion rates in cases where the timescale or physical conditions are too hard for direct experiment. This talk will discuss (a) various ways of obtaining absolute rates, (b) rates of cation diffusion in oxides and their for the so-called Compensation rule (c) issues of charge state in oxides and semiconductors or the motion of shortlived species, and (e) quantum diffusion of hydrogen in metals