Structural change induced near surfaces of α-Al2O3 during electron irradiation

A structural change produced by electron irradiation near surfaces of 03B1-Al2O3 was observed through high resolution electron microscopy and electron diffraction. Initially smooth surfaces become rough during TEM observations at 200 and 400 kV and holes appear with a prefered orientation of growth. Planar defects are also produced near the surfaces; they appear as dark- or bright-lines parallel to the (001) plane when the specimen is observed along the [110] direction, and they are also visible along the [001] direction as a periodic modulation of bright dots. The defects give rise to streaks and extra spots in electron diffraction patterns along [110] and [001], respectively. A formation mechanism and model of the defects were proposed; the defects are induced by inelastic scattering on Al plane parallel to (001) through rearrangement of Al ions and Al-vacancies. Three quaters of the atomic sites of the Al plane are occupied by Al ions and one quater is vacant, while 2/3