Electron irradiation-induced changes in the surface topography of silicon dioxide

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Abstract
The irradiation of crystalline (α-SiO2) and amorphous (a-SiO2) silicon dioxide with a stationary electron beam produces characteristic changes in the surface topography. The development of these changes has been investigated using cathodoluminescence spectroscopy and microscopy, scanning probe (atomic force) microscopy, and scanning electron microscopy. Electron irradiation produces a permanent volume increase on (crystalline) α-SiO2, while in (amorphous) a-SiO2 an initial small volume increase is followed by volume loss as irradiation continues. The observed changes are consistent with electromigration of oxygen under the influence of the electric field induced by charge trapping at preexisting or irradiation-induced defects. Oxygen enrichment may produce expansion of the surface region due to the formation of peroxy linkage defects. In a-SiO2, charges trapped by defects at grain boundaries produce enhanced electric fields which may result in volume reduction at the surface, when critical field strengths are exceeded. The observed volume reductions may be attributed to electron stimulated desorption of constituents, in particular oxygen mass loss, and densification of the surface region associated with the formation of oxygen-deficient defect centers.