Roughening and melting of stepped aluminum surfaces

The energetics and dynamics of the vicinal (113), (115), and (117) surfaces of aluminum have been investigated using a realistic many-body potential, based upon the effective medium theory, to describe the atomic interactions. These surfaces are found to show two distinct forms of thermal disordering. Firstly, above 700 K the surfaces undergo a roughening transition, characterized by a disordering of the step edge structure, the roughening temperature decreasing with decreasing step density. Secondly, above 900 K the surfaces undergo a melting transition, characterized by a complete disordering of the surface, the melting temperature increasing with decreasing step density. From studies of the step meandering, the time dependence of fluctuations in the step position were found to show a power-law dependence, t(n), where 0.25<n less than or equal to 0.5. This is consistent with two-dimensional diffusion on the surfaces, as observed experimentally. For noninteracting steps this corresponds to a time exponent of n=0.5. The reduced time dependence is then due to the repulsion between the steps.