Energy dispersive X-ray spectrometry of uncoated insulators performed at low beam energy (incident energy ≤ 5 keV) and in the variable pressure scanning electron microscope and the environmental scanning electron microscope is subject to spectral artifacts. Charging decelerates the incident beam electrons and reduces the impact energy, lowering the available overvoltage to excite characteristic X-ray peaks. The Duane–Hunt limit of the X-ray bremsstrahlung continuum is commonly used as a diagnostic of charging. Dynamic charging effects can hide the true impact of charging on the X-ray spectrum. Careful examination of the behavior of the X-ray spectrum with time and other variables is needed to avoid spectral artifacts, particularly on relative X-ray intensities.

In variable pressure scanning electron microscopy (VPSEM) the current data suggests that considerable caution is required in the interpretation of X-ray data from nonconductive samples, depending on the operating conditions. This article reviews some of the documented approaches and presents data that illustrate the nature and magnitude of the effects of charge above, on, and in the sample on the detected X-ray emissions from the sample and from elsewhere within the VPSEM specimen chamber. The collection of reliable and reproducible X-ray data has been found to require relatively high specimen chamber gas pressures, at the upper end of or beyond the available pressures for most VPSEMs. It is also shown that sample characteristics, including composition, strongly influence local charge effects, which can significantly affect the primary electron landing energy and consequently the resultant emitted X-ray signal under low pressure environments.