  Hf silicate films (HfO_2)_{0.25}(SiO_2)_{0.75} with thicknesses in the range
4-20 nm were grown on silicon substrate by atomic layer deposition at 350
deg.C.The Hf distributions in as-grown and 800 deg.C annealed films were
investigated by high resolution transmission electron microscopy (HRTEM),
angle-resolved x-ray photoelectron spectroscopy (ARXPS) and medium energy ion
scattering (MEIS). HRTEM images show a layered structure in films thinner than
8 nm. The ARXPS data also reveal a non-uniform distribution of Hf throughout
the film depth. Diffusion of SiO_2 to the film surface after a longer time
anneal was observed by MEIS. All these observations provide evidence for
surface-directed spinodal decomposition in the pseudobinary
(HfO_2)_x(SiO_2)_{1-x} alloy system.
