Investigations of Local Electrical Characteristics of a Pentacene Thin Film by Point-Contact Current Imaging Atomic Force Microscopy

We performed local electrical property measurements on a pentacene semiconducting thin film, which was connected to a Pt electrode, using point-contact current imaging atomic force microscopy (PCI-AFM). The measurements were conducted not only under ambient conditions, but also in a vacuum on the same film by employing the Q-control method to reduce the settling time of the cantilever oscillation amplitude. In both environments, the obtained current images showed that the current in the film gradually decreased with the increasing distance from the electrode. We also found differences in the threshold voltage among the grains and discontinuities in the apparent resistance at the grain boundaries, which suggest that the conductance of the thin film is limited by the grain boundaries. Moreover, by comparison of the measurement results on the same grains in air and in a vacuum, an increase in the current and a shift in the threshold voltage to a positive value in air were observed, which can be attributed to the exposure of the film to atmospheric oxygen. (C) 2012 The Japan Society of Applied Physics