ABSTRACT
This chapter summarizes the theoretical facts concerning these tunnel junctions. It reports the connection with the development of proximity electron spectroscopy, which is concerned with extracting detailed information on the electron-phonon interaction in the N and S layers of an N'INS junction. Of primary interest in that research was the energy dependence of the gap functions arising from this interaction, which produces the so-called phonon structure in the tunneling density of states. The chapter focuses instead on those aspects of NS bilayers which affect the gap region in the tunneling density of states, the region most important for Josephson tunneling. It assumes that there is negligible elastic scattering in the N metal. The chapter discusses the effects of elastic scattering in the N metal. When an aluminum overlayer was evaporated onto the niobium and that layer was oxidized before evaporating the counter-electrode, however, the tunneling characteristics were markedly improved.
