Umwandlung von Beryllium in Be₂C und BeO durch Elektronenbestrahlung in Anwesenheit von Kohlenwasserstoff-Polymerisaten

Abstract

The secondary electron yield from beryllium surfaces in presence of residual hydrocarbon vapour at a vacuum of 10⁻⁴ tor decreases with time fromδ=0.45 to 0.25 when the incident primary electrons hit the target with an energy of 28 keV and an incident angle of 60°. Since the yield from the hydrocarbon polymer contamination layer is 0.3, it is concluded that the beryllium surface reacts with the contamination layer.

This is confirmed by electron diffraction and electron microscopic observation of thin beryllium layers on different supporting foils, i.e. C-, Al₂O₃, polymeride from gas discharges, and self supporting Be. When a beryllium foil about 500 A. U. in thickness is first irradiated with low intensity (total beam current in the Siemens Elmiskop II<5 μA), a polymeride layer is formed. After increasing the beam current to 30 μA, the micrographs as well as the Debye-Scherrer diagrams show the formation of Be₂C and BeO. It is supposed that the carbon originates from the polymeride layer, and that the oxygen is supplied by the residual gas.