Molecular dynamics simulations have been performed that examine the microscopic mechanisms of rearrangements of atoms on the Si{ 1001 surface due to deposition of gas phase atoms. For thermal energy deposition we find that the gas atoms initially attach to dangling bonds of the surface dimer atoms. The dimer ’unreconstruction’ is due to a diffusion event on the surface, thus is temperature activated. We also find that dimers may open in regions of the surface where there are several atoms not at lattice sites, thus a low temperature amorphous structure. For 5-10 eV deposition there are direct mechanisms of dimer opening that occur on the 50-100 fs timescale. For energies greater than 15-20 eV there is implantation of the silicon atoms which leads to subsurface damage.

The interaction between F atoms and crystalline Si, which is essential for etching processes in semiconductor device fabrication, is investigated with state-of-the-art theoretical techniques. The theory is based on the pseudopotential-density-functional method in a supercell geometry. A comprehensive picture of F reactions with the Si surface, the bulk, and the near-surface region is obtained, in terms of which the etching process is elucidated. Insertion of F into Si-Si bonds becomes possible because of relaxed steric constraints in the near-surface region. Dependence of the etch rate on doping follows naturally, in agreement with observations. Similarities and differences between F-Si and H-Si reactions are discussed.

Hydrogen adsorption and diffusion on the (0001) surface of ruthenium is investigated using ab initio pseudopotentials within the local density approximation. The adsorption energies at a number of different sites and bond lengths were investigated via total energy calculations. Using these calculated values a potential surface was constructed and an estimate for the activation barrier for hydrogen diffusion was obtained. The calculated value of 4.0 kcal is in good accord with the value of ≈ 4 kcal as determined from laser-induced thermal desorption experiments.

The interaction potential between an atom and a surface is constructed using the “effective medium theory” (EMT) for the repulsive part of the interaction, and the damped dipole-dipole and dipole-quadrupole Van der Waals terms for the attractive part. This model is then applied to the following systems: He/MgO, LiF, NaCl, Ag and Cu.

Only recently have there been fully quantum-mechanical calculations of two-dimensional surface stress tensors. We have calculated total energies and stresses of semiconductor surfaces within the Local Density Approximation, using norm-conserving pseudopotentials. In order to hasten convergence of the stress with respect to basis size, it is useful to remove a fictitious tensile stress. We have calculated surface stress for the relaxed Si (111) 1×1 and 2×2-adatom surfaces, as well as for the relaxed Ge (111) 1×1 and 2×2-adatom surfaces. We have also calculated the surface stress for several chemisorbed systems, including Ga, Ge and As chemisorbed onto Si. We find a dramatic correlation between the electronic structure and chemistry of the surface, and its elastic properties.

The physical basis for electrostatic models of relaxation at metal surfaces, including the meaning of the two parameters of the modified point-ion or α model, is discussed. The empirical α parameter is shown to produce agreement with experiment and to arise from the non-uniformity of the fixed background of electronic charge around the ions. An explicit non-uniform model of the background charge is defined which is shown to be equivalent to the successful α model and provides an example of a pure electrostatic model without empirical parameters.