Growth and morphology of ultra-thin Al films on liquid substrates studied by atomic force microscopy

We study the growth process and morphology evolution of the ultra-thin Al films deposited on silicone oil surfaces by using atomic force microscopy. Initially, the deposited atoms nucleate and form compact clusters on the liquid surfaces. Then the clusters perform Brownian motion and adhere upon impact, which results in the ramified islands. Finally a continuous film forms as the nominal film thickness d increases. The mean size of the grains in the compact clusters and ramified islands is of the order of 101 nm. The ultra-thin Al films exhibit a self-affine surface morphology and therefore the dynamic scaling analysis is performed. It is found that the growth exponent β = 0.23 ± 0.05. In the range d = 0.1–1.0 nm, the roughness exponent α varies from α ≥ 1 to < 1. The physical interpretation for the crossover of the scaling behavior is presented.