Electrification and Its Evaluation of Polymers by Using the Mini-Scanning Electron Microscope

Abstract

The electron beam charging is the most suitable technique to inject the charge deeply into the dielectric material, such as polymers of high resistivity where the mean depth of the charge is easily estimated from the energy of the beam. The authors attempted to realize this electron beam injection by using the mini-scanning microscope (Akashi: Mini-SEM type S4). The beam energy values are 15, 25 and 35 ke V with beam current of a few na and the injection area is only about 1 cm2. Very low surface potential of-9KV was observed in the vacuum although the average potential profile measured in the air was only less than-KV and so on. FEP teflon sheets with thickness of 100μm and polypropylene sheets with thickness of 60μm were charged by that method and their charging characteristics were examined by the Thermally Stimulated Discharge Currents (TSDC). A homo-current peak is observed at low temperature (40-80°C) and a hetero-current peak is also recognized in most samples (teflon and polypropylene). Some new results for the polypropylene sheet were obtained that the annealed sample shows hetero-current at a little bit above 75°C where the nonannealed sample does homo-current peak at 95°C. Typical charging time was 10 minutes which was in good agreement of the estimation from the saturation of surface potential and its charging current, but longer charging caused the new hetero-current peak at less than 70°C. Metalization of one or two side of the sheet is found to be also effective to the TSDC characteristics.