Atomic step dynamics on periodic semiconductor surface structures

A series of experiments using periodically patterned morphologies have been carried out on Si surfaces. Both 1- and 2-dimensional periodic structures have been studied. These experiments allow us to study properties of well-defined atomic step arrays and in some cases to control the distribution of atomic steps on surfaces. We describe results from atomic force microscopy (AFM) and low energy electron microscopy (LEEM) on the motion of atomic steps during high temperature annealing. Most of our results correspond to temperatures below surface roughening; in this regime atomic steps are not created spontaneously (except on extremely large terraces) and the morphological development is controlled by the motion of pre-existing steps. Results on the rate of shrinkage of atomic islands and holes on 2-dimensional grating structures indicate that mass transport is controlled by attachment and detachment of atoms from atomic steps. Interesting correlations in the motion of neighbouring steps are described. The motion of atomic steps due to sublimation processes is also demonstrated. On 1-dimensional gratings the velocity of atomic steps at extrema has been measured; the motion is mainly due to sublimation but with differences between maxima and minima due to surface diffusion. Our studies of morphology development on biperiodic surfaces has led to a method for making atomically flat surfaces over regularly arrayed areas of 25x25 microns and greater. Differences in the behaviour of the Si(001) and (111) surfaces are noted.