Recycling gold nanohole arrays

Abstract

The authors report the impact of common cleaning methods on the stability of gold nanohole arrays used as extraordinary optical transmission surface plasmon resonance sensors. Their optical sensitivity, physical structure, and surface contamination levels were measured before and after multiple cycles of monolayer adsorption and removal with various wet chemicals (sulfochromic acid, piranha, or ammonium hydroxide: hydrogen peroxide) and dry oxygen plasma etchants. While these oxidative chemical and plasma etches remove organic monolayers and other contaminants, the oxidation and associated heating also damages the gold nanostructures to varying degrees. The authors observed decreases in the arrays' optical sensitivities via changes in the shapes and positions of their surface plasmon resonance peaks. The optimum recycling process was a room temperature, aqueous ammonium hydroxide: hydrogen peroxide treatment (15 min) commonly referred to as Radio Corporation of America Clean 1, followed by immersion in dilute nitric acid (0.1M, 30 min). This method was effective at removing an alkanethiol self-assembled monolayer of 11-mercaptoundecanoic acid; after six recycles, no loss in optical sensitivity was detected with minimal changes in the gold film thickness (−10%), hole area (−10%), and hole circularity (+6%).