Colors of thin films of binary and ternary gold- and platinum-based alloys

The development of precious metal alloys with new colors by casting techniques can be tedious and costly. An alternative method that allows reducing expensive material consumption is the deposition of thin layers, for example by magnetron sputter deposition. For the intermetallic phase AuAl2 it has been found that the introduction of numerous point defects during the deposition prohibits the films from displaying the expected purple color. Heat treatments are necessary to annihilate the defects and bring out the color. In this work, the melting point of intermetallic phases was identified to be the property that governs the density of point defects introduced during magnetron sputter deposition, and hence the appearance of color in AuAl2, AuIn2 and PtAl2 thin films. The production of ternary alloys of Au, Pt and Al was achieved, by means of magnetron sputter deposition, in a solid-solution-like mixing of the intermetallic phases AuAl2 and PtAl2. The Al content was kept at 66.6 at.%, while the ratio of Au to Pt was varied. The obtained ternary alloys maintained the fluorite crystal structure and their color could be tuned from purple to yellow by increasing the Pt content.