ICMCTF2008 Session TS1: The Atomistics of Thin Film Growth: Computational and Experimental Studies

Thursday, May 1, 2008 11:20 AM in Room Royal Palm 4-6

Thursday Morning

Start	Invited?	Item
11:20 AM		TS1-11 Elastic Properties of Amorphous Boron Suboxide Based Solids Studied by ab Initio Molecular Dynamics D. Music, J.M. Schneider (RWTH Aachen University, Germany) We have studied the correlation between chemical composition, structure, chemical bonding, and elastic properties of amorphous B₆O based solids using ab initio molecular dynamics. The calculated elastic modulus data appear independent of the chemical composition, which is in agreement with previous experimental observations. As the density increases by a factor of 1.5, the elastic modulus increases by a factor of 3.4. This may be understood by analyzing the chemical bonding of these configurations. Based on the electron density distributions, Mulliken analysis, and radial distribution functions, icosahedral bonding is the most dominating bonding type and is independent of density. We propose that the conservation of icosahderal bonding is responsible for the observed elastic modulus - density dependence.
11:40 AM		TS1-12 Intra- and Interlayer Mass Transport Rates During Layer-by-Layer Homoepitaxial Pt(111) Growth from Hyperthermal Beams (5-50 eV) V. Chirita, D. Adamovic, E.P. Münger, L. Hultman (Linköping University, Sweden); J.E. Greene (University of Illinois, Urbana) We employ multi-billion time step embedded-atom method molecular dynamics simulations to study homoepitaxial growth of Pt(111) using low-energy (0.2 - 50 eV) hyperthermal Pt fluxes. We deposit 5 monolayers at 1000K and with deposition rates approaching experimental conditions. The results reveal a transition from a three-dimensional (3D) multilayer growth mode to layer-by-layer growth at ~ 20 eV which is maintained for energies of up to 50 eV. In order to determine the mechanisms responsible for the observed change in the growth mode, we resolve, with picosecond resolution, both irradiation-induced and thermally activated processes. This allows us to determine, with unprecedented accuracy, the energy dependence of the net intra- and interlayer migration rates during the deposition process. Results show, that for all energies, irradiation events are completed within 10 ps following energetic impacts and that these processes dictate the growth mode. As expected, thermal migration is not affected by the deposition energy. For Pt deposition energies above 20 eV, the net interlayer migration induced by irradiation is towards the surface. This type of mass transport occurs via exchange mechanisms between surface and sub-surface atoms. On the growing layers, we observe primarily the descent of adatoms at step-edges and the recombination of adatoms with surface vacancies, i.e. mainly thermally activated processes. However, thermally activated net downward migration is an order of magnitude less than irradiation-induced upward migration. Intralayer migration is shown to depend strongly on adatom surface coverage. Results show that adatoms are the primary source of in-layer mass transport, which is observed to peak at a coverage of ~ 0.05 ML. Sputtering is observed to occur for energies higher than 25 eV. However, the yield is too small, less than 1% at 50 eV, to have a significant effect on island nucleation and coalescence kinetics.