IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM5
Temperature-Dependent Surface Diffusion Parameters on Amorphous Materials

Wednesday, October 31, 2001, 9:40 am, Room 120

Session: Surface Diffusion
Presenter: E.G. Seebauer, University of Illinois, Urbana
Authors: E.G. Seebauer, University of Illinois, Urbana
D. Llera-Hurlburt, University of Illinois, Urbana
A. Dalton, University of Illinois, Urbana
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Diffusion on amorphous surfaces represents a little-studied physical phenomenon that controls several important kinds of material processing. To elucidate some general features of this phenomenon, we have determined Arrhenius parameters for the surface self-diffusion of amorphous silicon (a-Si) by measuring the formation kinetics of hemispherical grained silicon. The results exhibit significant temperature dependence in the activation energy for total mass transport. We develop a physical model and associated mathematical formalism to show that this behavior should characterize diffusion on amorphous surfaces in general. Adatom formation on amorphous surface can arise from a near-continuum of structures and energy states. The formation energy for mobile atoms is therefore described by a continuous distribution function f(E). The breadth of f(E) on a-Si and related surfaces contrasts sharply with the sum of delta functions corresponding to kinks, steps and terraces on crystalline surfaces. Thus as T increases on amorphous surfaces, the average formation energy for mobile adatoms increases continuously, and the Arrhenius plot for total mass transport bends upward. The sharpness of the curvature depends upon the breadth of f(E); a broader distribution yields more gentle curvature.