Less is More: Improved Thermal Stability and Plasmonic Response in Au Films via the Use of SubNanometer Ti Adhesion Layers

The use of a metallic adhesion layer is known to increase the thermo-mechanical stability of Au thin films against solid-state dewetting, but in turn results in damping of the plasmonic response, reducing their utility in applications such as heat-assisted magnetic recording (HAMR). In this work, 50 nm Au films with Ti adhesion layers ranging in thickness from 0 to 5 nm were fabricated, and their thermal stability, electrical resistivity, and plasmonic response were measured. Subnanometer adhesion layers are demonstrated to significantly increase the stability of the thin films against dewetting at elevated temperatures (>200 °C), compared to more commonly used adhesion layer thicknesses that are in the range of 2-5 nm. For adhesion layers thicker than 1 nm, the diffusion of excess Ti through Au grain boundaries and subsequent oxidation was determined to result in degradation of the film. This mechanism was confirmed using transmission electron microscopy and X-ray photoelectron spectroscopy on annealed 0.5 and 5 nm adhesion layer samples. The superiority of subnanometer adhesion layers was further demonstrated through measurements of the surface-plasmon polariton resonance; those with thinner adhesion layers possessed both a stronger and spectrally sharper resonance. These results have relevance beyond HAMR to all Ti/Au systems operating at elevated temperatures.