Secondary Electron Emission of Crystalline MgO

Secondary emission is measured from single crystals of MgO cleaved along the (100) plane. The maximum ratio of secondary to primary current, ${\ensuremath{\delta}}_{max}$, is about 7 at about 1 000 volts and room temperature. The cross-overs are at 33 volts and far above 5 000 volts. Most probable energy of emission is 1 ev or less. A definite effect of temperature is established, $\ensuremath{\delta}$ decreasing with increasing temperature, in accord with expectations for an insulator.