Optical properties of Au-Hf thin films

TL;DR

This study experimentally investigates the optical properties of Au-Hf thin films, revealing their plasmonic behavior, phase composition dependence on deposition conditions, and stability issues related to oxidation, with potential implications for optical applications.

Contribution

First experimental analysis of Au-Hf thin films' optical properties, identifying phase formation conditions and stability challenges for plasmonic applications.

Findings

Au-Hf films exhibit negative permittivity and plasmonic properties.

Phase composition depends on deposition temperature, with pure Au3Hf forming above 400°C.

Oxidation resistance is limited at higher vacuum levels, affecting stability.

Abstract

The optical properties of thin films of intermetallic Au$_{3}$Hf were experimentally investigated for the first time, which display clear plasmonic properties in the optical and near infrared region with negative permittivity. In contrast to similar alloys, such as films of Au$_{3}$Zr, the films express more negative $\epsilon'$ values and lower $\epsilon''$ values across most of the wavelengths (370-1570 nm) investigated. The Au$_{3}$Hf films were fabricated by DC magnetron sputtering at a range of deposition temperatures, from room temperature to 415$^{o}$C, and annealed at different vacuum levels. The films mostly formed as a combination of Au$_{3}$Hf, Au$_{2}$Hf and Au$_{4}$Hf phases when deposited below 400$^{o}$C, and exclusively Au$_{3}$Hf phase at above 400$^{o}$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 un-encapsulated applications at elevated temperatures.