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

Next-generation heat-assistedmagnetic recording (HAMR) relieson fast, localized heating of the magnetic medium during the writeprocess. Au plasmonic near-field transducers are an attractive solutionto this challenge, but increased thermal stability of Au films isrequired to improve long-term reliability. This work compares theeffect of nanoscale Al, AlO x , and Ta cappingfilms on Au thin films with Ti or Ta adhesion layers for use in HAMRand other high-temperature plasmonic applications. Thermal stabilityis investigated using a bespoke laser dewetting system, and SEM andAFM are extensively used to interrogate the resulting dewet areas.The most effective capping layers are found to be 0.5-1 nmof Al or AlO x , which can eliminate dewettingunder certain conditions. Even one monolayer of AlO x is shown to be highly effective in reducing dewetting. Inthe case of thicker capping layers of Ta and AlO x , the Au film can easily dewet underneath, leaving an intactcapping layer. It is concluded that thinner capping layers are mosteffective against dewetting as the Au cannot dewet without breakingthem and pulling them apart during the dewetting process. A simplemodel based on energetics considerations is developed, which explainshow thinner capping layers can more effectively protect the metalfrom pore or fissure creation. The model provides some convenientguidelines for choosing both the substrate and capping layer, fora given metal, to maximize the resistance to laser-induced damage.

Automated summary

This study compares the thermal stability of Au thin films with different thicknesses of Al and AlOx capping films. It is found that 0.5-1 nm of Al or AlOx capping films are most effective in reducing the dewetting of Au thin films, while thicker Ta and AlOx capping films fail to completely prevent dewetting. A simple model is developed to explain how thinner capping layers can better protect the metal from laser-induced damage.