COMPARATIVE-STUDY OF K-SHELL EXCITON SERIES IN CONDENSED NEON AND NITROGEN BY ELECTRON TIME-OF-FLIGHT SPECTROSCOPY

Photon absorption and electron emission phenomena in the near-K-edge r egion are studied for condensed neon and nitrogen, employing electron time-of-flight spectroscopy in combination with high photon-energy res olution. Surface and bulk ionization thresholds and bulk exciton excit ation energies, including the 1s(-1)5p transition, are reported for ne on multilayers. For condensed nitrogen, we observe three different typ es of resonant features in the near-g-edge region. Type 1, which is ex cited by photon energies less than the surface N 1s ionization potenti al, is clearly of excitonic nature. Resonances of type two are seen fo r excitation energies which are larger than the surface K edge by more than 3 eV. They parallel maxima seen in the kinetic-energy distributi on of secondary electrons and can be well explained by transitions int o regions of the conduction band with a high density of states. Peaks of the third category appear between the surface K edge and 1.5 eV abo ve. They have no analogs either in the secondary electron distribution , or in the amplitude of the N Is photoemission signal. We explain the m as bulk excitons converging toward the bottom of the conduction band of solid nitrogen. In our study, we demonstrate that electron time-of -flight spectroscopy is a versatile analytical tool for the study of e lectronic properties of samples such as those which suffer severely un der beam induced damage and charging.