VIBRATIONAL AND ELECTRONIC EXCITATION OF HEXATRIACONTANE THIN-FILMS BY LOW-ENERGY ELECTRON-IMPACT

Thin polycrystalline films of hexatriacontane (HTC) were irradiated with low energy (E = 0.5-15 eV) electrons, and off-specular backscattered electron spectra were measured. Below E∼7 eV, single and multiple vibrational excitations only are observed, which relax the electrons down to the bottom of the HTC conduction band. Due to the negative electron affinity of HTC, thermal electrons are emitted into vacuum. Structure in the backscattered electron current at kinetic energies about 1.5 and 4 eV are associated to conduction band density of states. Above E∼7 eV, the dominant losses correspond to electronic excitations, excitons, or above a threshold (energy of the electron inside the HTC film) at 9.2±0.2 eV, electron-hole pair generation. The latter process is very efficient and reaches a yield of the order of one at E∼11 eV. Evidence for chemical reaction above E∼4 eV is observed. © 1990 American Institute of Physics.