H. Muller et al., ELECTRON-EMISSION IN LOW-ENERGY GRAZING COLLISIONS OF N+ AND N(2)+ WITH W(110) PARTIALLY COVERED BY CS ATOMS, Surface science, 303(1-2), 1994, pp. 56-66
Electron energy spectra from slow nitrogen ions N+ and N2+ (50 and 500
eV) colliding under grazing incidence with W(110) surfaces are report
ed. The surface work function was varied by the exposure to cesium ato
ms. The electron energy spectra are interpreted in terms of various in
ter- and intra-atomic Auger processes: For N+ Auger capture dominates
up to a Cs coverage of about 0.2 ML (in terms of a completed monolayer
(ML) at room temperature). For larger Cs coverages the resonant captu
re of one or two electrons from the surface leads to the formation of
core excited states of the neutralized projectile (beyond 0.3 ML) and
of the Feshbach resonance N- (2s(2)2p(2)3s2) (beyond 0.5 ML). These s
tates manifest themselves by their decay via Auger deexcitation and au
todetachment, respectively. We observe one additional rather sharp fea
ture which we tentatively attribute to the decay of the metastable neg
ative ion state N-(2s(2)2p41D). For N2+ besides Auger capture into the
N2 ground state also Auger deexcitation of excited N2 molecules (B; a
3,1PI(g)) to the ground state seems to contribute to the spectra (belo
w 0.2 ML). With increasing Cs coverage higher excited (Rydberg) states
, in particular N2 E3SIGMA(g)+, become populated manifesting themselv
es by a variety of Auger deexcitation processes. For Cs coverages larg
er than 0.6 ML the resonant capture of an electron from the surface by
the Rydberg state N2 E3SIGMA(G)+ leads to the formation of the Feshba
ch resonance N2- E2SIGMA(g)+ (parent state N2* E).