Optical properties of Au-Hf thin films

The optical properties of thin films of intermetallic Au3Hf were experimentally investigated for the first time, which display significant negative ε′ in the visible and near infrared regions, hence are clearly plasmonic materials. In contrast to similar alloys, such as films of Au3Zr, the films express more negative ε′ values and lower ε″ values across most of the wavelengths (370–1570 nm) investigated. The Au3Hf films were fabricated by DC magnetron sputtering at a range of deposition temperatures, from room temperature to 415 °C, and annealed at different vacuum levels. The films mostly formed as a combination of Au3Hf, Au2Hf and Au4Hf phases when deposited below 400 °C, and exclusively Au3Hf phase at above 400 °C, indicating key conditions for isolating this phase. The films were stable when annealed at 10−8 Torr, but when annealed again at 10−6 Torr the films oxidised and changed into a mix of Au-Hf phases, suggesting resistance to oxidization may be an issue for unencapsulated applications at elevated temperatures.