Charge neutralisation of insulating surfaces in the SEM by gas ionisation

A theory is presented in which the elimination of charging artefacts on uncoated insulating surfaces in the scanning electron microscope by a low-pressure ambient gas is taken to be due to ionisation of the gas. Curves of ion current against ionising field calculated from a model of gas neutralisation give good agreement with the variation of measured ion currents passing through metal specimens. This result permits a precise interpretation of the behavior occurring at the surface of insulating specimens.