Proximity effect tunnelling as a probe of metallurgical processes in thin films

Abstract Electron tunnelling in a junction of the form Al-oxide-M1-M2, where M1, and M2, are metals at least one of which is a superconductor, reveals structure at the phonon frequencies of both M1 and M2. For thin films peaks in the phonon density of states from M1 appear as dips in d2 V/dI2 whereas peaks in the phonon density of states from M2 appear inverted. It is therefore possible to determine which metal is adjacent to the oxide and to monitor changes in this material as diffusion, alloying or formation of intermetallics take place in films as thin as 200 A.