Reversible change between metastable crystalline phases by laser beam irradiation in sputtered Au–Ge alloy films

Abstract

Various Au–Ge alloy thin films have been prepared by the rf magnetron cosputtering method. The β (hcp) and γ (tetragonal) metastable crystalline phases were observed in as‐deposited films, depending on film composition and thickness. Films 25 nm thick with a composition of ∼50 at. % Ge, which were composed of β‐phase microcrystals, showed reversible reflectance change by laser beam irradiation. The irradiated area changed to the γ phase with oriented coarse grains. When a lower power laser beam was scanned along the previously recorded bit, i.e., the changed γ phase area, the crystals returned to the β phase with a fine microstructure. This transformation between the metastable phases accompanying microstructure change causes reversible changes in the reflectance of the film, for more than 100 cycles. Laser induced crystalline‐to‐crystalline phase transformations in Au–Ge alloy thin films are of interest for use in reversible optical data storage.