FIM PHENOMENA OBSERVED WITH BENZENE AS IMAGE GAS

Properties of benzene as the image gas in field ion microscopy (FIM) a nd its ionization behavior have been investigated. In FIM of Pt/Ir tip s prepared by field evaporation large bright spots and dynamic phenome na with the appearance of ring structures are observed. These phenomen a, which are not observed with cyclohexane as the image gas, are attri buted to field ionization of molecules at the end of charged polymer c hains grown by field induced cationic polymerization of benzene on the anode surface. Thermochemistry reveals that the cationic polymerizati on of benzene is only exothermic in a high electric field and depends on the formation of carbocations on the tip surface.