Surface and subsurface 1 keV electron stimulated reduction of sapphire studied by electron spectroscopy

Electron irradiation may change the surface composition of solids by electron stimulated processes. In particular sapphire, α-Al2O3, is likely to be vulnerable to these processes because of the large difference in electronegativity between the cation and anion. In the present work the effect of 1 keV electron irradiation on the near surface composition of sapphire was studied. The use of the whole range of the electron spectrum produced by 1 keV primary electrons has provided a detailed picture of the variation with depth and electron dose of the surface and near surface of electron irradiated α-Al2O3(1000). Electron irradiation doses were in the range of 0.7 to 26 C/cm2. After a dose of about 1 C/cm2 sufficiently large clusters of aluminium were produced to allow the generation of the Al(LVV) 67 eV Auger peak, while after about 8 C/cm2 the collective excitations surface and bulk plasmons were generated. An equilibrium in the composition of the first nanometre depth of the surface is reached after a dose of about 6 C/cm2, with 50% of the aluminium in alumina being reduced to the metallic form. After a dose of about 13 C/cm2, the composition of the first 2 nm reaches equilibrium, while deeper alumina continues to be reduced.