Surface morphology of thin Cu films grown on magnesium oxide (100)

Copper films were epitaxially grown on MgO(001) with a thickness of 50 nm employing molecular beam epitaxy. Depending on the growth temperature and growth rate different sizes of Cu islands can be achieved. The island size increases with substrate temperature from about 30 nm at 320 K up to about 100 nm at 420 K; at higher temperatures, the size does not change significantly. At a substrate temperature of 420 K, a higher growth rate resulted in smaller island sizes due to the enhanced nucleation density. The island size is closely related to the in-plane correlation length derived through a scaling analysis from scanning probe microscopy images of the surface. The roughness exponent α for a sample is calculated as the slope of the rms roughness as a function of the scanning probe microscopy image scan size. Values of α between 0.7 and 0.95 were found for scan sizes smaller than the island size. At larger scan sizes, the rms value saturates and does not depend significantly on the scan size.