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

TL;DR

This study investigates how ultrathin germanium films grow on pristine and ion-irradiated silicon fractal surfaces, revealing different morphological behaviors influenced by surface roughness and fractal properties.

Contribution

It provides new insights into the influence of surface fractal properties on Ge film growth modes and morphology on silicon surfaces.

Findings

Ge grows in layer-plus-island mode on both surfaces.

Surface roughness and correlation length change significantly after Ge deposition.

Different island shapes observed on pristine versus ion-irradiated surfaces.

Abstract

We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to study the morphology of ultrathin Ge films eposited on pristine Si(100) and ion-irradiated Si(100) self-affine fractal surfaces. The pristine and the ion-irradiated Si(100) surface have roughness exponents of alpha=0.19+/-0.05 and alpha=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 (~6 A) 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 xi increases from 32 nm 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.