Alumina coating of ultrafine nanoporous gold at room temperature and their optical properties

Amorphous alumina is deposited on chemically etched nanoporous gold films using atomic layer deposition at room temperature. Nanoporous gold with ultrafine pores of 7 nm in diameter is uniformly coated with alumina film as thin as 1.4 nm. Localized surface plasmon resonance of gold skeleton exhibits a detectable red-shift in the optical transmittance spectra, the magnitude of which depends on the thickness of the alumina layer. The tunable optical properties of nanoporous gold–alumina composites provide one possibility for implementing miniaturized optical devices with high performances.