The difference between Si and Ge(001) surfaces in the initial stages of growth

The initial stages of growth of Ge and Si on the Ge(001) surface are studied and compared to growth on the Si(001) surface. Metastable rows of diluted ad-dimers exist on both surfaces as intermediate stages of epitaxial growth. Unexpectedly, for Ge(001) these rows are found exclusively in the <310> directions, whereas on Si(001) the preferred direction is <110>. This qualitative difference between Si and Ge surfaces reflects the subtle difference in the chemistry of these two elements, which has direct consequences for epitaxial growth on these surfaces.