Surface-directed spinodal decomposition in the pseudobinary alloy (HfO_2)_x(SiO_2)_{1-x}

TL;DR

This study investigates surface-directed spinodal decomposition in HfO2-SiO2 alloy films, revealing layered structures and non-uniform element distributions through advanced microscopy and spectroscopy techniques.

Contribution

It provides experimental evidence of surface-directed spinodal decomposition in the pseudobinary HfO2-SiO2 system, a phenomenon not previously characterized in this context.

Findings

Layered structures in thin films less than 8 nm thick.

Non-uniform Hf distribution within the films.

SiO2 diffusion to the surface after annealing.

Abstract

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.