Characterization of surface defects and determination of overlayer nucleation and growth by surface-sensitive diffraction

Abstract

The physical properties of crystalline materials are strongly influenced by disturbances of the long-range order. In thin films, the extent and nature of the defects responsible for this loss of order are governed by the interatomic forces of the constituent material and the conditions under which the film is grown. Surface-sensitive diffraction techniques (such as LEED, RHEED and small-angle X-ray diffraction) are sensitive to the degree of order over areas large enough to be statistically representative of the surface conditions. We discuss the usefulness of surface-sensitive diffraction techniques not only in establishing the existence of ordered regions on the surface but in characterizing the nature of the disorder present at the surface. Qualitative features of diffraction patterns are discussed and the applicability of quantitative diffraction techniques are illustrated in determining size distributions of stepped surfaces and in investigations of the mechanism of nucleation and growth of overlayer films. For overlayer islands growing on an ordered substrate, we relate the separation of islands to the nucleation behavior and the distribution of island sizes to the mode of growth. The intensity distribution of diffracted beams is calculated under specific assumptions for the nucleation and growth of two-dimensional overlayer islands and it is shown that such diffraction measurements can differentiate between different modes of growth.