TIME-RESOLVED CURRENT METHOD FOR THE INVESTIGATION OF CHARGING ABILITY OF INSULATORS UNDER ELECTRON-BEAM IRRADIATION

In the present article, a convenient method for the direct measurement of the displacement current caused by electron trapping is developed to measure the trapped charge in insulators under electron beam irradi ation from a scanning electron microscope. The trapping process during electron beam irradiation can be directly observed by this method. By using the conservation of current, a macroscopic formula is derived t o describe our observation. The derived formula relates the measured c urrent to the radiated beam energy; current, radiation-induced conduct ivity, and electron penetration depth of a sample. Experiments have be en performed on polymethymethacrylate samples in which the samples are irradiated with electron beams of fixed beam energy as well as fixed beam current. The results are as predicted in theory. An agate sample is found to be unable to trap charge due to the small electron penetra tion depth and large radiation-induced conductivity of the sample. (C) 1996 American Institute of Physics.