Abstract :
In electron spectroscopy, charging of insulating specimens is characterised by a normally steady surface potential,VS, which results from the equilibrium between the electron emission into the vacuum, I (out), and various compensation mechanisms contributing to I (in). Continuing from a recent paper (J. Cazaux, J. Electr. Spectrosc. Rel. Phen. 105, 1999, 155), this emission and these compensation mechanisms (including the role of flood guns) are analysed here in more detail for a situation mainly restricted to conventional XPS. In particular, a new graphical representation can be used to explain why the irradiation conditions and the environment of the specimen play a role on the charging shift, VS, and on differential charging, delta VS, that is more important than its exact chemical composition. A critical analysis of the negative (and positive) biasing of the specimen is also performed. Various practical consequences are deduced from an approach based on I(in)=I(out) at the steady state. Additional electrostatic considerations are given, extending the investigation to small spot XPS and some consequences may also be easily transposed to SEM (scanning electron microscopy) and to AES (Auger electron spectroscopy).
