High field conduction in aromatic hydrocarbons

The authors have investigated the high field conduction of aromatic liquids (toluene and benzyltoluene) in the tip-plane geometry and compared it to the conduction of n-decane under the same experimental conditions. For various tip radii they have determined the threshold field E_s for which current becomes space-charge controlled, the threshold field in the case of which current pulses are detected, the charge of each pulse and their repetition rate. Results on DC and AC voltage have been compared. It is shown that the basic prebreakdown phenomenon in aromatic liquids, i.e., electron avalanche in the liquid phase, is similar to that in aliphatic liquids. The main difference in the high field behavior of aliphatic and aromatic liquids comes from a deposit on the tip formed by polymerization of the liquid in the ionization region. Thus, after a very short period of voltage application during which the tip surface changes, current pulses are observed for about a two-fold higher electric field