Am. Arrale et al., MODEL OF THE CONTAMINATION EFFECT IN ION-INDUCED ELECTRON-EMISSION, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 89(1-4), 1994, pp. 437-442
Ion-induced electron emission yields from contaminated surfaces are we
ll known to be enhanced relative to the yields from atomically clean s
urfaces. Under the bombardment of energetic ions, the surfaces become
sputter-cleaned with time and the yields from the samples are reduced
accordingly. The time dependent reduction of yields observed are shown
to be due to various effects such as desorption of contaminant atoms
and molecules by incident ions and adsorption of residual gas onto pre
viously clean sites. Experimental results obtained in the present work
show the lower, saturated yield (gamma(s)) to be a function of residu
al gas pressure (P) and the fluence (phi(i)) of the ion. We present a
dynamic equilibrium model which explains the increase in yields for su
rface gas contamination, the decrease in yields for contaminant desorp
tion, and the pressure/fluence dependence in the time required to reac
h gamma(s). The predictions of the model agree well with the observati
ons of gamma(s) as a function of the ratio of gas flux to ion flux, an
d the electron yields of clean and gas covered surfaces.