Electron tunneling in (SN)x and conducting organic salts

We have made tunnel junctions on (SN)x and several tetracyanoquinodimethane (TCNQ) compounds by evaporation of Pb, Sn, and In and by application of a Hg-In amalgam. Junctions formed with (SN)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 (SN)x down to 60 mK. A broad zero-bias anomaly suggests that the surface of (SN)x consists of small particles which are not superconducting and hence are similar to (SNx) films. © 1978 The American Physical Society.