Monolayer Capping Provides Close to Optimal Resistance to Laser Dewetting of Au Films

TL;DR

This study demonstrates that monolayer capping with materials like Al or AlOx significantly enhances the thermal stability of Au films against laser-induced dewetting, which is crucial for high-temperature plasmonic applications such as HAMR.

Contribution

It introduces a simple model explaining how monolayer capping layers improve resistance to laser dewetting, guiding material selection for durable plasmonic devices.

Findings

Monolayer Al and AlOx capping layers prevent dewetting under certain laser conditions.

Thinner capping layers are more effective in resisting dewetting.

A model based on energetics explains the protective effect of thin capping layers.

Abstract

Next-generation heat-assisted magnetic recording (HAMR) relies on fast, localized heating of the magnetic medium during the write process. Au plasmonic near-field transducers are an attractive solution to this challenge, but increased thermal stability of Au films is required to improve long-term reliability. This work compares the effect of nanoscale Al, AlOx, and Ta capping films on Au thin films with Ti or Ta adhesion layers for use in HAMR and other high-temperature plasmonic applications. Thermal stability is investigated using a bespoke laser dewetting system, and SEM and AFM are extensively used to interrogate the resulting dewet areas. The most effective capping layers are found to be 0.5-1 nm of Al or AlOx, which can eliminate dewetting under certain conditions. Even one monolayer of AlOx is shown to be highly effective in reducing dewetting. In the case of thicker capping layers of Ta and AlOx, the Au film can easily dewet underneath, leaving an intact capping layer. It is concluded that thinner capping layers are most effective against dewetting as the Au cannot dewet without breaking them and pulling them apart during the dewetting process. A simple model based on energetics considerations is developed, which explains how thinner capping layers can more effectively protect the metal from pore or fissure creation. The model provides some convenient guidelines for choosing both the substrate and capping layer, for a given metal, to maximize the resistance to laser-induced damage.