High thermal conductivity of a hydrogenated amorphous silicon film.

We measured the thermal conductivity kappa of an 80 microm thick hydrogenated amorphous silicon film prepared by hot-wire chemical-vapor deposition with the 3omega (80-300 K) and the time-domain thermo-reflectance (300 K) methods. The kappa is higher than any of the previous temperature dependent measurements and shows a strong phonon mean free path dependence. We also applied a Kubo based theory using a tight-binding method on three 1000 atom continuous random network models. The theory gives higher kappa for more ordered models, but not high enough to explain our results, even after extrapolating to lower frequencies with a Boltzmann approach. Our results show that this material is more ordered than any amorphous silicon previously studied.

Ab initio based tight-binding molecular dynamics simulation of the sticking and scattering of O2Pt(111).

The sticking and scattering of O(2)Pt(111) has been studied by tight-binding molecular dynamics simulations based on an ab initio potential energy surface. We focus, in particular, on the sticking probability as a function of the angle of incidence and the energy and angular distributions in scattering. Our simulations provide an explanation for the seemingly paradox experimental findings that adsorption experiments suggest that the O(2)Pt(111) interaction potential should be strongly corrugated while scattering experiments indicate a rather small corrugation. The potential energy surface is indeed strongly corrugated which leads to a pronounced dependence of the sticking probability on the angle of incidence. The scattered O(2) molecules, however, experience a rather flat surface due to the fact that they are predominantly scattered at the repulsive tail of the potential.