Structural Studies Of Amorphous Ge-Au Alloys

In order to understand the structural changes associated with the occurrence of a metal-to-insulator transition in amorphous Ge-Au alloys as the proportion of Au is increased above a critical limit, we have investigated the microstructure as a function of composition. Samples, prepared in the form of thin films by r.f co-sputtering, were studied using both Ge K edge and Au L3 edge extended X-ray absorption fine structure. The results indicate that, for alloys containing less than approximately 20 at.% Au, local modification of the structure occurs; regions of a Ge-Au alloy are embedded in the amorphous Ge host network. As the proportion of Au is increased further, small clusters of Au also appear to be formed. The implications of these results for the interpretation of electrical conductivity data are discussed.