Energy Distribution of Ion-Induced Secondary Electrons from MgO Surface

Energy distributions of ion-induced secondary electrons (IISEs) from a MgO thin-film surface were investigated. An abnormal IISE emission was observed in addition to the normal one and it continued after ion irradiation was cut off, and thus was a so-called self-sustained electron emission. The energies of the abnormal secondary electrons (SEs) are lower than the vacuum level at the MgO surface. In addition, the energy distribution of the abnormal SEs is very close to the profile of the density of states of the valence band (VB). The results strongly suggest that the abnormal SEs are emitted from the VB of MgO by the field emission.