Differential Charging in XPS. Part I: Demonstration of Lateral Charging in a Bulk Insulator Using Imaging XPS

Abstract

Recent literature has drawn a distinction between charging across the surface (lateral differential charging) and charging with depth (vertical differential charging) for insulating samples. In this study, differential charging in a bulk insulator was investigated using imaging and small-area spectra acquired with a monochromatic x-ray source. With no charge neutralization, reproducible photoelectron images and spectra could be acquired from a glass sample after ∽90 min of x-ray exposure. The charge shifts and photoelectron peak shapes vary as a function of x-ray flux on the sample, indicating that lateral charging is the dominant mechanism on a bulk insulator. Uniform binding energies, photoelectron peak shapes and images are acquired with the charge neutralizer on.