Combinatorial Thin Film Sputtering AuxAl1–x Alloys: Correlating Composition and Structure with Optical Properties

The Au–Al alloy system was investigated via a combinatorial thin film sputtering method for its potential as a plasmonic material. AuxAl1–x combinatorial libraries were cosputtered from Au and Al elemental targets and the composition, phase, and dielectric function of a ∼350 nm film was determined using energy dispersive spectroscopy (EDS), grazing incidence X-ray diffraction (GIXRD), and spectroscopic ellipsometry, respectively. The phase evolution and optical properties were analyzed after annealing various compositions under a vacuum. The phases present matched the expected phases based on the published Al–Au binary phase diagram at all compositions. Interestingly, the mixed phase Al-AuAl2 region showed the most optical tunability, where a maximum in the real part of the dielectric function progressively shifted to higher energy for increasing gold concentration. For almost pure AuAl2, the imaginary component is largely reduced in the visible range and is comparable to that of pure Al in the UV region....