Dielectric constant of gold, copper, and gold-copper alloys between 18 and 35 eV

The complex dielectric constant of Au, Cu, and Au-Cu alloys has been determined between 18 and 35 eV from multiangle reflection measurements performed with the ACO synchrotron radiation source. The different techniques as well as the reliability and accuracy of the results are discussed in detail. The optical properties of pure Au and pure Cu are compared, and their modifications upon alloying are investigated by both static and differential experiments. Special attention is paid to pure Au, where fine structure in the main absorption peak is related to the presence of two critical points, the location of which is discussed. The Au spectrum is found to be rather insensitive to alloying with Cu, while on the Cu-rich side the behavior is completely different; different interpretations are proposed.