INVESTIGATION OF INSULATOR CHARGING PROPERTIES

WITH A SCANNING ELECTRON MICROSCOPE :

DOSE AND CURRENT DENSITY EFFECTS

G. Blaise, D. Braga*

Laboratoire de Physique des Solides, Université Paris-Sud,Bât. 510, 91405 Orsay, France

* Corresponding author. E-mail : braga@lps.u-psud.fr

Received : 30 April 2002; revised version accepted : 28 August 2002

Abstract

Fundamental aspect of the charging properties of insulators is investigated with a Scanning Electron Microscope, by meaning the amount of trapped charges and the Secondary Electron Emission yield as a function of dose and current densities, in a wide energy range (~ 200 eV to 40 keV).

Three charging regimes are observed, depending on the current density. At low current densities J (J d 2.104 pA/cm2) a self-regulated regime is obtained, characterised by the formation of a static space charge build up which prevents any further charge accumulation. At intermediate current densities (2.104 d  J d  7.106 pA/cm2) a small fraction (a few %) of incoming electrons is continuously absorbed in proportion to the injected dose. The consequence of this invasion is an internal stress which affects the life time of the material; this is the ageing regime. At high current densities strong relaxations occur, producing an irreversible damaging of the material; this is the degradation regime. These relaxations are probably at the origin of the partial discharges observed in insulators at a pC level.

Keywords: Insulators; Charging regime; SEM.

 
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