AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA3
Low-Symmetry DFT Diffusion Barriers and Dimer Dynamics in Homoepitaxial Growth of Al(111)

Tuesday, November 3, 1998, 2:40 pm, Room 309

Session: Morton M. Traum Student Award Session
Presenter: A. Bogicevic, Chalmers Univ. of Tech. and Göteborg Univ., Sweden
Authors: A. Bogicevic, Chalmers Univ. of Tech. and Göteborg Univ., Sweden
J. Strömquist, Chalmers Univ. of Tech. and Göteborg Univ., Sweden
P. Hyldgaard, Chalmers Univ. of Tech. and Göteborg Univ., Sweden
G. Wahnström, Chalmers Univ. of Tech. and Göteborg Univ., Sweden
B.I. Lundqvist, Chalmers Univ. of Tech. and Göteborg Univ., Sweden
Correspondent: Click to Email
From fractals to compact islands, epitaxial growth offers an exotic variety of surface morphologies that emanate from a handful of elementary atomic diffusion processes. Adsorption calculations have hitherto been limited to high-symmetry configurations, or to semi-quantitative methods. Using extensive density-functional calculations on parallel computers, we map out barriers for self-diffusion at steps, kinks, and corners on Al(111). The results include an unexpected exchange mechanism at kinks and a large barrier anisotropy at corners. Using transition state theory we are able to transform the barriers into a set of activation temperatures and hereby predict various growth modes as a function of temperature. New STM experiments confirm four of our main results in great detail, including the fractal-compact island transition and the transition to equilibrium shaped islands. The central role dimer stability and mobility plays during nucleation and in later stages of growth has motivated us to study Al dimer diffusion at 0 and 5% compressive strain. The smooth potential energy surface enables a long-ranged attraction between the dimer atoms, leading to a substantial temperature window in which dissociation is frozen and fascinating dimer dynamics takes place. Surface relaxations play a prominent role in the uncovering of unexpected ground states, which should be easy to verify with, e.g., STM measurements of dimer height or dimer direction. A new diffusion mechanism is found, where dimers migrate by concerted sliding. The effect of elastic strain on dimer diffusivity is addressed, and its impact on the epitaxial growth mode is discussed.