Structural studies of artificial Si/Nb superlattice films

Amorphous Si/Nb superlattices with modulation wavelengths ranging from 20-200 Å have been grown on sapphire substrates at 100-150 °C by dual e-beam evaporation in an ultra-high-vacuum (UHV) system. The low-angle x-ray diffraction data can be accounted for by a symmetric trapezoidal composition profile model. The intermixing at the layer interfaces is estimated to be 6-12 Å, depending on the substrate temperatures. In the film growth direction, the coherent domain size of the polycrystalline Nb layers scales with the Nb layer thickness. High-resolution transmission electron microscopy reveals the existence of microcrystallites in the 20-Å-thick amorphous Nb layers; also resolved are the microstructure of the substrate/superlattice and superlattice/thick-Nb layer interfaces. In addition, Auger depth profiling results are also consistent with the expected composition modulation.