MEASUREMENTS OF CHARGE ACCUMULATION INDUCED BY MONOCHROMATIC LOW-ENERGY ELECTRONS AT THE SURFACE OF INSULATING SAMPLES

We investigate charging of insulators with an apparatus that allows me asurements of trapped charges resulting from the impact of monoenerget ic electrons of 0.1-28 eV. Details are given on the construction and o peration of this instrument. A high-resolution electron monochromator provides a pulsed electron beam of variable energy and current. Accumu lated surface charge is monitored using a Kelvin probe and a high-sens itivity electrometer. An ultraviolet source of adjustable maximum freq uency allows the sample to be discharged for multiple measurements on the same sample. We illustrate the use of the instrument with prelimin ary measurements for similar to 100 mu m thick samples cut from an ind ustrial polyethylene cable. The incident electron-energy dependence of the trapping probability exhibits large variation and indicates that electrons with energies <5 eV are the most efficiently trapped; chargi ng near 10 eV is attributed to dissociative electron attachment to pol yethylene molecules. (C) 1998 American Institute of Physics. [S0021-89 79(98)04817-8]