Low energy electron bombardment of amorphous SiOi induces point defects such as oxygen vacancy by electronic excitation. The defects build a macroscopic negative charge by trapping of electrons on the localized Levels i11 the band gap; this phenomenon was previously described as the "mirror" effect. In the present paper, we investigate,by mirror effect,the behavior of the charge after an argon, nitrogen and oxygen implantation at 1 and 4 keV, and after exposure to the same gases at various Low pressures. We observe a difference of behavior between Ar Cor N2 l and o 2 , The results reinforce the outstanding role of oxygen in the defect production in Sio 2 by electronic excitation.

L23 vv Auger transition ha ~ been studied in Si, SiO 2 , Al, AlN, Al 2o 3 by electron spectroscopy excited either by electron beam or X Rays. A strong difference is observed in intensity between pure solid and oxide or nitride under electron bombardment. Auger intensity is very sensitive to changes in the backscattering coefficient or inelastic mean free path. However transient local trapping of electrons seems to be responsible for the large change observed.

Electron bombardment of thick pure SiO2 induces the buildup of a negative charge which can be observed through a ‘‘mirror’’ effect in a conventional Auger scanning microscope. A mechanism for the creation of this charge is proposed in terms of trapping of an electron in defects due to the irradiating beam. The influence of temperature is studied on amorphous and monocrystalline SiO2. The temperature dependence of the existence of high negative charge shows around 270 °C an anomalous effect which depends on the irradiation time. The role of electronic excitation to produce defects in silica is discussed.

The temperature dependence of the photoemission of amorphous silica submitted to intense laser irradiation is studied. Results obtained below and above the annealing temperature of point defectsdiffer strongly. The electron energy spectra show evidence of the important role played by point defects in the emission process and probably in laser breakdown phenomena as well.

A thin film of polyacrylonitrile, deposited by electropolymerisation onto a cathode of oxidizable metal (Ni, Fe,…) is subjected to heat treatment under vacuum (1 h, 600°C, 10−5 Pa). This procedure allows us to obtain a film of pyrolytic carbon, which retains the essential properties of a polyacrylonitrite film: homogeneity, purity, and a strong adherence to the metallic substrate.

The influence of different treatments (radiation, temperature) is studied on SiO2 which has been negatively and positively charged. Electrons, X-rays, and UV photons are able to neutralize a positive and/or a negative charge through interaction with the localized levels in the band gap of the insulator. The temperature dependence of the existence of high negative charge shows at 300°C an anomalous effect.

In order to understand the breakdown phenomena on insulators, we create in the amorphous SiO2 sample a permanent localized charge which is either negative (implanted electrons) by electron bombardment, or positive (implanted holes), by bombardment with helium metastable atoms and photons. The implanted negative charge is destroyed when another part of the sample is bombarded. This remote neutralization of the charge is tentatively explained in the frame of electronic structure of SiO2: holes and electrons could recombine through the localized levels in the forbidden band gap after a conduction mechanism in the glass. The surface breakdown could hence be explained as a band effect rather than an electron produced by an electron source on the cathode in the vacuum region.