Thin Films Of Ptal2 And Aual2 By Solid-State Reactive Synthesis

The intermetallic compounds AuAl2 and PtAl2 are colored purple and yellow respectively. In the past they have been prepared by bulk melting techniques or by co-deposition in a magnetron sputterer. Here, however, we investigate films of AuAl2, PtAl2 and (Au,Pt)Al-2 prepared by sequential physical vapor deposition of the elements, followed by in situ solid-state reaction. The microstructure, dielectric functions, optical properties and thermal stability of the resulting films are characterized and compared to those prepared by bulk melting or co-deposition. The (Au, Pt)Al-2 films show a color gamut that stretches from purple to brassy yellow depending on composition and microstructure. High temperature synchrotron X-ray diffraction experiments show that the (Au, Pt)Al-2 phase is metastable, decomposing when heated above 420 degrees C. In contrast, the pure AuAl2 or PtAl2 phases are stable to about 580 degrees C before they oxidize or decompose. The alternative possibility of producing the purple-to-yellow color gamut by depositing optical stacks of very thin films of AuAl2 and PtAl2 is also assessed. Either scheme will provide a range of colors lying between those of the binary compound endpoints. Calculations predict that deposition of AuAl2 onto PtAl2 will produce more intense colors than vice versa, an unexpected finding that is worth further investigation. (C) 2015 Elsevier B.V. All rights reserved.