Swift heavy ion induced dewetting of metal oxide thin films on silicon

Abstract

We have observed that thin oxide coatings (NiO, Fe2O3) tend to dewet their Si substrate when being bombarded with swift heavy ions (350–600MeV Au ions) even though the irradiation was carried out about 80K and hence, the films never reached their melting point. Scanning electron and atomic force microscopy reveal a surprising similarity of the dewetting morphologies with those observed for molten polymer films on Si, which have recently been reported by others [S. Herminghaus, K. Jakobs, K. Mecke, J. Bischof, A. Fery, M. Ibn-Elhaj, S. Schlagowsky, Science 282 (1998) 916; R. Seemann, S. Herminghaus, K. Jacobs, J. Phys.: Condens. Matter 13 (2001) 4925]. Like in that cases also here heterogeneous and homogeneous hole nucleation could be identified. Heterogeneous nucleation is less pronounced in Fe2O3/Si than in NiO/Si. The occurrence of spinodal-like dewetting cannot be detected unambiguously. The dewetting kinetics were determined by means of Rutherford backscattering spectroscopy and found to slightly differ for the two compounds. The dewetting kinetics as well as the final dewetting pattern strongly depend on the initial film thicknesses. No dewetting occurs for film thicknesses above about 150nm, while for very small thicknesses below about 40nm the film decays into nm-sized spherical droplets. At intermediate film thicknesses percolated networks of small oxide bridges are formed.