Effect of disorder on the optical properties of alloys and compounds in the Al-Au-Cu system

The effect of structural disorder on the color of Au–Cu–Al alloys was examined. Samples with a high content of lattice defects were deposited by magnetron sputtering onto glass substrates held at room temperature. After measurement of the optical properties in the poorly crystalline, as-deposited condition, the samples were annealed at 500 °C and the optical properties of the isochemical crystalline state re-measured. Upon annealing, all compositions evolved into equilibrium phases predicted by the Au–Cu–Al ternary system, exhibiting enhanced crystallinity, improved reflectivity, and reduced optical loss. Distinct color changes were observed in Al- rich films due to the formation of the AuAl2 at about 510 K.