“Dynamic” charging of polymers in the LVSEM

Abstract

Recently we have been using a field emission LVSEM with an immersion-type objective lens extensively for the examination of polymers at low (<2 keV) incident beam energies. During the course of these studies it became apparent that, even though operating in the vicinity of E2 (the accelerating voltage at which no electrostatic charge builds up on the sample surface), sample charging effects of a most curious nature do, in fact, abound.In general the LVSEM has been successful in producing a wealth of exciting information. However, when nonconducting polymers are the subject of observation at E2, an unexpected and unusual charge build-up behavior is almost always encountered on the sample surface under irradiation (c.f. Figure 1). Thus for strongly insulating materials, it is not as easy to work in the realm of E2 as earlier predicted. For example, in some polymeric materials, it appears that charging is a function of magnification: at very high magnifications the sample will charge "positively", at lower magnifications (with all other parameters the same) the same sample will charge negatively, and at even lower magnifications the same sample will revert back to a positive charging situation.