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-d efined 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 ste ps during high temperature annealing. Most of our results correspond to tem peratures below surface roughening; in this regime atomic steps are not cre ated spontaneously (except on extremely large terraces) and the morphologic al development is controlled by the motion of pre-existing steps. Results o n the rate of shrinkage of atomic islands and holes on 2-dimensional gratin g structures indicate that mass transport is controlled by attachment and d etachment of atoms from atomic steps. Interesting correlations in the motio n of neighbouring steps are described. The motion of atomic steps due to su blimation processes is also demonstrated. On 1-dimensional gratings the vel ocity of atomic steps at extrema has been measured; the motion is mainly du e to sublimation but with differences between maxima and minima due to surf ace diffusion. Our studies of morphology development on biperiodic surfaces has led to a method for making atomically flat surfaces over regularly arr ayed areas of 25x25 microns and greater. Differences in the behaviour of th e Si(001) and (111) surfaces are noted.