Borides of Ag and Au prepared by magnetron sputtering

Following the discovery of MgB2 that has a superconductive critical temperature (Tc) of ∼39 K much research was initiated in the search for materials with higher Tc. Theoretical studies predicted that diborides of metals having the AlB2 type structure, among them AgB2 and AuB2, may be superconductive at values of Tc even higher than 39 K. In our attempts to prepare AgB2 and AuB2 using films of the Ag–B and Au–B systems, no superconductivity was observed. Equilibrium phase diagrams of these systems do not support the possibility of forming AgB2 or AuB2 compounds, despite a report which indicates their existence.Films of the Ag–B and Au–B systems were obtained by magnetron cosputtering from two separate targets, that of B and Ag (or Au) on Si(1 0 0) substrates in Ar ambient. The specimens were subjected to X-ray diffraction (XRD), secondary electron microscopy (SEM), X-ray photo spectroscopy (XPS), Auger analysis and optical microscope (OM) investigations. No superconductivity was observed in the range 10–200 K on the basis of resistivity measurements. The films were not homogeneous, but rather the alloys had decomposed into two separate phases. One of the phases was in the form of dispersed particles. An XRD peak at 28° was observed which supposedly is characteristic of a noble metal boride. The possibility that the XRD peaks might belong to a boric acid phase also exists. The boric acid phase had the same diffraction peak as was observed by XRD in our films.