Showing papers by "Adrian P. Sutton published in 1992"

Atomic and Electronic Structures of the 90° Partial Dislocation in Silicon.

Abstract: Two reconstructions of the 90\ifmmode^\circ\else\textdegree\fi{} partial dislocation core in silicon have been investigated using ab initio total-energy pseudopotential calculations. The asymmetric fourfold-coordinated configuration is shown to be stable and to be associated with only shallow states in the band gap. The symmetric quasi-fivefold-coordinated configuration is found to be metastable and to be associated with states that span the band gap. These results are reproduced with tight-binding Hamiltonians if the range of hopping integrals is restricted to include no more than four nearest neighbors.

First principles calculation of the structure and energy of Si(113).

Abstract: Results of an ab initio pseudopotential total energy calculation of the atomic structure and surface energy of the 3×2 reconstruction of the (113) surface of Si are presented Despite many reports in the literature that (113) is a particularly low energy surface of Si, the calculated surface energy of 0138 eV A -2 is not small in comparison with similar calculations of the surface energy of Si(111) and Si(100) This discrepancy is discussed with reference to the role of carbon contamination in stabilizing the (113) surface

Static junction growth during frictional sliding of metals

Abstract: We report a molecular dynamics simulation of junction growth during frictional sliding of a nanometre scale copper tip on a copper substrate under compressive loading. Much less junction growth is seen under tensile loading. In contrast to the usual form of junction growth discussed by Tabor [Proc. R. Soc. A251, 378 (1959)] the junction growth we see does not lead to an increase in the frictional force. Under both compressive and tensile loading we see material transfer from the tip to the substrate.

Direct free energy minimization methods: application to grain boundaries

Abstract: A critical review is given of recently developed methods for determining the atomic structures and solute concentration profiles at defects in elemental solids and substitutional alloys as a function of temperature. Exact results are given for the effective force on an atom arising from the vibrational entropy in the quasiharmonic approximation and for the occupancy of a site in the pair potential approximation. An improved, approximate formula is given for the effective force arising from the vibrational entropy. The mean field approximation that is used in the alloy problem is compared with the auto-correlation approximation. It is shown that the better statistical averaging of the auto-correlation approximation leads to effective pair interactions that are temperature and concentration dependent.

Direct Free Energy Minimization Methods: Application to Grain Boundaries: Discussion

Abstract: A critical review is given of recently developed methods for determining the atomic structures and solute concentration profiles at defects in elemental solids and substitutional alloys as a function of temperature. Exact results are given for the effective force on an atom arising from the vibrational entropy in the quasiharmonic approximation and for the occupancy of a site in the pair potential approximation. An improved, approximate formula is given for the effective force arising from the vibrational entropy. The mean field approximation that is used in the alloy problem is compared with the auto-correlation approximation. It is shown that the better statistical averaging of the auto-correlation approximation leads to effective pair interactions that are temperature and concentration dependent.

Mechanism of lubrication by a thin solid film on a metal surface

Abstract: Molecular dynamics simulations of frictional sliding of a tip over a flat substrate in the presence of a lubricating solid film of one or two atomic layers thickness are presented. The role of adhesion in promoting wear is discussed by reference to earlier simulations of frictional sliding in the absence of a lubricating layer. Two conditions for lubrication are identified. First, the shear strength of the interface between the tip and the film must be lower than the shear strength of the tip or the underlying substrate. Secondly, the film must have a sufficient strength in compression to prevent penetration of the film by the tip. The importance of lubrication in obtaining images from the frictional force microscope is also discussed.