Center for Functional Nanomaterials Seminar

Nanostructures play an important role in proposed materials for scientific and technical purposes. Their synthesis and properties largely depend on fundamental behavior related to the kinetics and energetics of surface thermal defects. Kinetics on surfaces are largely determined by the surface mass diffusion coefficient. Important information about the surface mass diffusion coefficient is contained in the near-equilibrium configurations of the surface structures, and in the amplitudes and decay rates of their fluctuations. This information can be accessed by various microscopies such as low-energy electron microscopy (LEEM). The first focus of the presentation is on discussion of the systematic application of LEEM to investigations of surface kinetics and energetics on clean close-packed surfaces.

Low-energy ion irradiation has proven to be an important component of the processing of nanostructured materials, offering the unique capability of stimulating surface diffusion processes even while bulk diffusion is decreased by operating at reduced temperatures. For research interests such as e.g. hyperthermal growth, surface erosion, the operation of driven surface sinks during irradiation, and structural patterning caused by self- and foreign ion beams, ion beams provide an opportunity to probe the equilibrium behavior of the surface system of thermal point defects (i.e. adatoms, advacancies, surface mass diffusion, etc.) and also to observe its response when driven by ion beam irradiation. Our LEEM instrument has been modified to incorporate a variable-energy ion beam source such that the behavior of surface structures like step edges can be observed at video rates in real time during actual ion irradiation, and down to very low ion impact energies that are needed if surface damage is to be minimized. Initial results will illustrate the second focus of the presentation.