X‐Ray Photoelectron Spectroscopy Investigations of the Surface Reaction Layer and its Effects on the Transformation Properties of Nanoscale Ti51Ni38Cu11 Shape Memory Thin Films

Abstract

The depth‐dependent chemical constitution of Ti51Ni38Cu11 thin films of different total film thickness from 400 to 50 nm was characterized using X‐ray photoelectron spectroscopy (XPS). It was analyzed how reaction layers, which form on the surface of the film significantly change the chemical composition of the transforming phase, which leads in turn to altered phase transformation properties. For thinner films, the deviation from the nominal chemical composition increases. For a film thickness of 50 nm, a Ti loss of ≈9 at% is observed. The Ni content is increased by ≈5 at%, whereas the Cu content stays relatively constant for films of different thickness. The results are summarized in a layer model, which supports designing nanoscale shape memory thin films.