Conductive tracks of 30-MeV C-60 clusters in doped and undoped tetrahedral amorphous carbon

Abstract

In insulating tetrahedral amorphous carbon (ta-C), the irradiation with 30-MeV C-60 cluster ions leads to the formation of well conducting tracks. While electrical currents through individual tracks produced with monoatomic projectiles (e.g. Au or U) often exhibit rather large track to track fluctuations, C-60 clusters are shown to generate highly conducting tracks with very narrow current distributions. Additionally, all recorded current-voltage curves show linear characteristics. These findings are attributed to the large specific energy loss dE/dx of the 30-MeV C-60 clusters. We also investigated C-60 tracks in ta-C films which were slightly doped with B, N or Fe during film growth. Doping apparently increases the ion track conductivity. However, at the same time the insulating characteristics of the pristine ta-C film can be reduced. The present C-60 results are compared with data from earlier experiments with monoatomic heavy ion beams. The investigations were performed by means of atomic force microscopy including temperature dependent conductivity measurements of single ion tracks. (C) 2013 Elsevier B.V. All rights reserved.