H. Shi et al., DYNAMICS OF LOW-ENERGY-ELECTRON STIMULATED DESORPTION OF METASTABLE PARTICLES FROM N-2 CONDENSED ON XE AND KR FILMS, Physical review. B, Condensed matter, 53(20), 1996, pp. 13830-13838
Electron-impact desorption of metastable molecular nitrogen (N-2) fro
m N-2 condensed on Xe or Kr multilayer films is investigated as a func
tion of electron energy (0-70 eV), rare-gas film thickness, and N-2 co
verage. The different behaviors are explained with a simple mathematic
al expression which rakes into account the parameters influencing the
magnitude of the desorption yields. Two basic mechanisms are identifie
d to contribute to the observed N-2 yields: the direct excitation and
electronic energy transfer. The former mechanism proceeds via electro
nic excitation of adsorbed N-2 by the primary electron beam followed b
y exciton motion to the surface and desorption. In the energy-transfer
mechanism, primary electrons first create excitons in the rare-gas fi
lms which then transfer their energy to the adsorbed N-2 molecules. N-
2 desorption at the N-2-film-vacuum interface can proceed via intramo
lecular to molecule-surface bond vibrational energy exchange and via c
avity expulsion. When energy transfer dominates desorption, the N-2 y
ield functin clearly bears the characteristics of exciton creation in
the rare-gas film. The relative contributions of these two mechanisms
depend on the impact electron energy, and layer thickness of N-2 and r
are-gas film. The different energy-transfer efficiencies between excit
ed rare-gas atoms and N-2 molecules is found to be the major cause for
the observed difference in N-2 yield between the Xe and Kr film subs
trates.