The structure of vapor-quenched Ag–Ge films

Abstract

Ag–Ge films of thickness 1 to 3 microns were prepared by co-evaporation of Ag and Ge onto 0.005′′ thick vitreous silica plates held at liquid nitrogen temperature. The pressure during evaporation was 3 × 10−7 Torr or less. The X-ray scattering of the films and substrates was measured at room temperature with monochromatic Mo Kα and Cu Kα radiation. After correction for substrate scattering, the interference function I(K) was evaluated for each alloy as a function of K = 4π sin θ/λ. The Fourier transform of K[I(K)−1] yielded the reduced distribution function G(r) = 4πrV(r)[ρ(r)−ρ0], where ρ(r) is the weighted atomic density at a distance r from a reference atom, ρ0 is the average atomic density and V(r) is the size factor of the coherently diffracting domains in the sample. Both I(K) and G(r) indicate that the alloy films consist of the Ag solid solution and Ge. The Ag phase cannot be characterized as amorphous, but is micropolycrystalline. The sizes of the coherently diffracting domains or the correlation distances determined from G(r) increased from 12 Å in Ge to 30 Å in Ag-40 at. %Ge. Fourier analyses of the (111) peak profiles of Ge and Ag yielded particle sizes of 13 Å for Ge and 16 Å for the Ag phase in the Ag-83 at. %Ge alloy. The Ag phase particles increased with increasing Ag concentration, reaching a value of 45 Å in the Ag-28 at. %Ge alloy.