Ge growth on ion-irradiated Si self-affine fractal surfaces

We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to study the morphology of ultrathin Ge films deposited on pristine Si(l 0 0) and ion-irradiated Si(I 0 0) self-affine fractal surfaces. The pristine and the ion-irradiated Si(I 00) surfaces have roughness exponents of alpha = 0.19 +/- 0.05 and 0.82 +/- 0.04, respectively. These measurements were carried out on two halves of the same sample where only one half was ion-irradiated. Following deposition of a thin film of Ge (similar to6 Angstrom) the roughness exponents change to 0.11 +/- 0.04 and 0.99 +/- 0.06, respectively. Upon Ge deposition, while the roughness increases by more than an order of magnitude on the pristine surface, a smoothing is observed for the ion-irradiated surface. For the ion-irradiated surface the correlation length increases from 32 to 137 nm upon Ge deposition. Ge grows on Si surfaces in the Stranski-Krastanov or layer-plus-island mode where islands grow on a wetting layer of about three atomic layers. On the pristine surface the islands are predominantly of square or rectangular shape, while on the ion-irradiated surface the islands are nearly diamond shaped. Changes of adsorption behaviour of deposited atoms depending on the roughness exponent (or the fractal dimension) of the substrate surface are discussed. (C) 2004 Published by Elsevier B.V.