Evidence of germanium segregation in gold thin films

Using X-ray Reflectometry (XRR) and X-ray Diffraction (XRD) measurements, we investigated the crystallinity of similar to 35nm-thick gold films deposited on glass substrates with 2nm-thick germanium wetting interlayer. Such wetting decreases the average grain size in the Au film and introduces gradient growth. With X-ray Photoelectron Spectroscopy (XPS) we measured the atomic concentration of Ge as a function of subsurface depth. Our results show the highest concentration of Ge atoms near the surface and the lowest at the Au/ substrate interface, which is most likely the result of segregation. Ellipsometric measurements demonstrate that although presence of Ge atoms segregated in the system introduces additional plasmonic bands in the permittivity spectrum, the intensity of these bands is low in comparison to the intensity of the Drude term, which is greater than for the pure Au film. Annealing the Ge-wetted Au films immediately after the deposition decreases the value of the Dude term, however still not to the level of the nonwetted films, which suggests that some kind of mixing still occurs.