Growth of MgO films with high secondary electron emission on Al-Mg alloys

Abstract

We have identified the processes which take place during the formation of MgO layers on the surface of Al-1% Mg alloys by measuring surface composition, electron multiplication, and Mg evaporation. An initial layer of Al 2O 3 on the alloy plays a vital role in this process: it acts as a sink for Mg, and prevents the inward diffusion of O 2 during the heating, thereby localizing the MgO formation on the outer surface. The Mg concentration in the Al 2O 3 layer increases about 20-fold over its original value, and the Al 2O 3 is partially reduced. For a given temperature and pressure of oxygen, the MgO growth rate depends on the thickness and crystallinity of the Al 2O 3. Electron multiplication factors 5 of 10 to 15 are obtained; part of the secondary electrons originate in the underlying Al 2O 3 layer.