Ultra-thin epitaxial Al and Cu films on CaF2/Si(1 1 1)

In this work, smooth epitaxial films of Al and Cu with thickness between 5 and 20 nm have been grown by molecular beam epitaxy (MBE). This was done in order to study the surface contribution to scattering of conduction electrons, without masking effects of grain boundary scattering. Aluminum epitaxy on CaF2/Si(1 1 1) was confirmed by reflection high energy electron diffraction (RHEED). The surface and interface rms roughness below 0.3 nm was achieved for 10 nm-thick Al films, as measured by atomic force microscopy (AFM). Threading screw dislocations but no grain boundaries were observed in these films by scanning tunneling microscopy (STM). Preliminary resistivity measurements on the films between 4 and 20 nm thick agreed qualitatively with the Fuchs–Sondheimer model of resistivity size effect due to diffuse electron scattering from surfaces. For Cu, the epitaxial growth was obtained when depositing on a 3 nm-thick Al seed layer.