Bulk Space Charge Behavior in Polymethylmethacrylate under an Imposed Virtual Cathode Condition

Electrically stimulated acoustic wave measurements have been used to profile the space charge distribution in polymethylmethacrylate samples. Electron beam implanted samples were allowed to decay under short-circuit conditions and under a continually changing voltage which compensated the internal charge across the unirradiated bulk. The latter condition imposed a virtual cathode on the trapped charge concentration and allowed the analysis of the bulk decay process without influence from the region with radiation-enhanced conductivity. The results of this study indicate that bulk polarization is the dominant initial conduction mechanism at temperatures between 20 and 60°C. An equilibrium charge concentration only becomes established when the internal charge distribution balances the injection of electrons from the cathode.