Secondary-electron emission mechanism of LiF film by (e,2e) spectroscopy

Secondary-electron emission (SEE) from LiF films deposited on Si(0 0 1) surface was studied using time-of-flight two-electron coincidence spectroscopy. A set of energy-distribution curves (EDCs) of secondary electrons excited from a LiF film by electrons with energies in the range of 20–50 eV exhibits emission features at about 7 and 11 eV. The energy positions of these maxima do not depend on the incident energy. To reveal the origin of these features, each of the EDCs was spanned in the second dimension E2 using two-electron coincidence spectroscopy. Two-dimensional mapping of the energy sharing between correlated electrons shows that above 25 eV incident energy, one electron of the pair is preferentially emitted with E1=7.2±0.3 eV energy and the second one with energy E2=(Ep−23.3)±0.5 eV, where Ep is the incident electron energy. At about 30 eV incident energy, a second favoured emission energy of 10.9 ± 0.3 eV is observed. The unique capability of (e,2e) spectroscopy established the links between electron energy loss process and emission features in the EDCs. suggested that the mechanism of SEE from LiF film includes the excitation of two collective excitations with subsequent decay via electron ejection. It was shown that the mechanism of secondary emission from LiF film depends on the film thickness and its structure.