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Electronic and atomic structures of the clean and As- and Te-covered Si(211) surface are studied using pseudopotential density-functional method. The clean surface is found to have (2 x 1) and rebonded (1 x 1) reconstructions as stable surface structures, but no π-bonded chain reconstruction. Binding energies of As and Te adatoms at a number of symmetry sites on the ideal and (2 x 1) reconstructed surfaces have been calculated because of their importance in the epitaxial growth of CdTe and other materials on the Si(211) surface. The special symmetry sites on these surfaces having the highest binding energies for isolated As and Te adatoms are identified. But more significantly, several sites are found to be nearly degenerate in binding-energy values. This has important consequences for epitaxial growth processes. Optimal structures calculated for 0.5 monolayer of As and Te coverage reveal that the As adatoms dimerize on the surface while the Te adatoms do not. However, both As- and Te-covered surfaces are found to be metallic in nature.

We perform first principles density functional calculations to investigate the adsorption of Te on the Si(0 0 1) surface from low coverage up to a monolayer coverage. At low coverage, a Te atom is adsorbed on top of the Si surface dimer bond. At higher coverages, Te atoms adsorption causes the Si-Si dimer bond to break, lifting the (2 × 1) reconstruction. We find no evidence of the Te-Te dimer bond formation as a possible source of the (2 × 1) reconstruction at a monolayer coverage. Finite temperature ab initio molecular dynamics calculations show that Te covered Si(0 0 1) surfaces do not have any definitive reconstruction. Vibrations of the bridged Te atoms in the strongly anharmonic potentials prevent the reconstruction structure from attaining any permanent, two-dimensional periodic geometry. This explains why experiments attempting to find a definite model for the reconstruction reached conflicting conclusions. © 2002 Elsevier Science B.V. All rights reserved.

Nanowires, point contacts and metallic single-wall carbon nanotubes are one-dimensional nanostructures which display important size-dependent quantum effects. Quantization due to the transverse confinement and resultant finite level spacing of electronic and phononic states are responsible for some novel effects. Many studies have revealed fundamental and technologically important properties, which are being explored for fabricating future nanodevices. Various simulation studies based on the classical molecular dynamics method and combined force and current measurements have shown the relationship between atomic structure and transport properties. The atomic, electronic and transport properties of these nanostructures have been an area of active research. This brief review presents some quantum effects in the electronic and phononic transport through nanowires.

We investigate conductance through contacts created by pressing a hard tip, as used in scanning tunneling microscopy, against substrates. Two different substrates are considered, one a normal metal (Cu) and another a semi-metal (graphite). Our study involves the molecular dynamics simulations for the atomic structure during the growth of the contact, and selfconsistent field electronic structure calculations of deformed bodies. We develop a theory predicting the conductance variations as the tip approaches the surface. We offer an explanation for a quasiperiodic variation of conductance of the contact on the graphite surface, a behavior which is dramatically different from contacts on normal metals.

This paper presents an atomic-scale study of contact, indentation, and subsequent pulling and dry sliding of a sharp and blunt metal tip on a metal surface. The evolution of atomic structure and the variation of perpendicular and lateral forces are calculated by molecular-dynamics methods using an empirical potential based on the embedded-atom model. The sharp tip experiences multiple jumps to contact in the attractive force range. The contact interface grows discontinuously mainly due to disorder-order transformation leading to disappearance of a layer and hence abrupt changes in the normal-force variation. Atom exchange occurs in the repulsive range. During the pulling off, the connective neck is reduced discontinuously; however, not all the abrupt changes of the pulling force are associated with the creation of a new layer in the neck. The sliding of the sharp tip (or single asperity) induces two consecutive structural transformations that occur periodically, but end with the wear of a layer. The situation for a blunt tip is, however, quite different.

In this paper we present an analysis of conduction through a single atom between two metal electrodes. Based on ab initio total-energy and electronic-structure calculations, and molecular-dynamics simulations using the embedded-atom model, we show that the conductance through an atom depends on the electronic structure of both the single atom and the metal electrodes, as well as the binding structure between the single atom and the surfaces of the metal electrodes. Our results enable us to interpret experimental results obtained by using a mechanical break junction on atomic-scale wires.

We present a comparative study of the pseudomorphic (Si)6/(Ge)6 and -doped (Si)3(Sb)(Si)2/(Ge)6 superlattices using the self-consistent pseudopotential method. The strained (Si)6/(Ge)6 superlattice has the lowest conduction-band states of extended character, and the difference of energy between the direct and indirect band gap is 70 meV. Upon doping by Sb in the Si sublattice, a quasi-two-dimensional band confined to the Sb layer dips into the band gap. Furthermore, the average potential in the Ge sublattice rises relative to that of the Si side, which increases the band offset, and enhances the localization of the quantum well states. These results indicate that doping provides new means for controlling the electronic properties of strained superlattices. © 1988 The American Physical Society.