Scanning Microscopy


The approach to thermodynamic equilibrium is the driving force for kinetic processes in adsorbate and thin film structure formation. Macroscopic thermodynamic concepts may be used to predict the rates of nucleation, cluster formation and cluster growth. They involve mass transport concepts usually limited by surface concentration gradients. Time and temperature dependence of nucleation and cluster growth, described in terms of cluster ripening mechanism, therefore reveal information on the microscopic surface diffusion processes, including surface structure and surface energies. Examples of structures studied include, Ga, Sn, and Ge on Si, As terminated Si and GaAs surfaces where the activation energies for clustering are obtained without using laterally resolved techniques requiring μm-patch deposition. The results are in agreement with activation energies found in nucleation experiments of Ag on Si.

The concentration dependence of the surface diffusion coefficient in clustering systems is connected to the difference between the intrinsic diffusion coefficient and the chemical or mass transport diffusion coefficient. The difference results from the analysis of an extended Einstein relation for diffusion in these systems. The intrinsic diffusion coefficient of Sn and Ga on Si is concentration independent in cluster growth experiments. Literature data for surface diffusion of Ag/Ge(111) and O/W(110) show a concentration dependence which is in good agreement with the dependence predicted for the chemical diffusion coefficient by this model.

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