Measurements of charge accumulation induced by monochromatic low-energy electrons at the surface of insulating samples

Abstract

We investigate charging of insulators with an apparatus that allows measurements of trapped charges resulting from the impact of monoenergetic electrons of 0.1–28 eV. Details are given on the construction and operation of this instrument. A high-resolution electron monochromator provides a pulsed electron beam of variable energy and current. Accumulated surface charge is monitored using a Kelvin probe and a high-sensitivity electrometer. An ultraviolet source of adjustable maximum frequency allows the sample to be discharged for multiple measurements on the same sample. We illustrate the use of the instrument with preliminary measurements for ∼100 μm thick samples cut from an industrial 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; charging near 10 eV is attributed to dissociative electron attachment to polyethylene molecules.