T. Fonden et A. Zwartkruis, ANALYSIS OF AUGER-SPECTRA FROM A HE-SURFACE( ION NEAR A METAL), Physical review. B, Condensed matter, 48(21), 1993, pp. 15603-15612
Auger rates are computed and analyzed for a He+ ion in a wide range of
ion-metal-surface separations. For neutralization-relevant distances
close to the surface, the rate scales approximately quadratically with
the density from the electron tails. (W is-proportional-to n1.80 for
r(s) = 2.07 a0 and W is-proportional-to n1.93 for r(s) = 3.99 a0.) Fur
ther away from the surface there is a gradual transition to a more lin
ear scaling of the rate with the electron density (W is-proportional-t
o n1.16). Computed Auger spectra are analyzed as well. For all ion-sur
face distances there is excellent agreement between the spectra and a
convolution of the two hole energy distributions, left behind by the m
etal electrons neutralizing the ion and exciting to the Auger level, r
espectively. Closer to the surface the two hole spectra are almost ide
ntical. This is argued to indicate the localness of the Auger transiti
on around the ion. For larger distances the hole spectra start to diff
er, indicating that the neutralization becomes increasingly nonlocal.
The changeover in the scaling of the rate for larger ion-surface separ
ations is consistent with the spectra analysis. The self-convolutions
of the local density of states at the position of the ion do not agree
quantitatively with the spectra. Therefore, despite the local charact
er of the Auger process, the variations of the metal orbitals over the
region of the ion cannot be neglected.