Electron tunneling in(SN)xand conducting organic salts

We have made tunnel junctions on ${\left(\mathrm{SN}\right)}_x$ and several tetracyanoquinodimethane (TCNQ) compounds by evaporation of Pb, Sn, and In and by application of a Hg-In amalgam. Junctions formed with ${\left(\mathrm{SN}\right)}_x$ and HMTSeF-TCNQ show the usual gap structure of the superconducting counterelectrode when cooled to liquid-helium temperatures. Although good tunnel junctions are formed, we are not able to detect a superconducting gap in the ${\left(\mathrm{SN}\right)}_x$ down to 60 mK. A broad zero-bias anomaly suggests that the surface of ${\left(\mathrm{SN}\right)}_x$ consists of small particles which are not superconducting and hence are similar to ($\mathrm{S}{\mathrm{N}}_x$) films.