Aca - Departamento de Física - Universidad Técnica Federico Santa ...

V Encuentro Sud Americano de Colisiones Inelásticas en la Materia
Energy-loss spectra measured for some
crystal azimuthal directions are shown in
Figs.2(a,b) and 3(a,b) for hydrogen and
fluorine incident ions. In Figs.2(a,b), the
Full-Width-at-Half-Maximum (FWHM) of
scattered beam is considerably broad and
seems to have a large energy loss tail. The
most striking difference is observed for F
ions scattering with an azimuthal angle of
70.5°, where a double peak structure is
observed in Figs. 3(a,b) for 4 keV but
disappears for 1 keV.
Intensity
relative intensity
150
100
50
0
0 200 400 600 800 1000 1200
1.1
1.0
0.9 (b)
simulation
0.8
experiment
0.7
0.6
1 keV H + -Au(110)
0.5
0.4
azimuthal angle 0 0.3
0.2
0.1
0.0
-50 0 50 100 150 200 250 300 350
Fig. 2. (a) and (b) Energy loss spectra of 4 and 1 keV H +
ions scattered off a Au (110) surface along the indicated
azimuthal direction of 0 0 respectively
intensity
200
150
100
50
(a)
(a)
energy Loss (eV)
experiment
selected total
selected on top of the surface
selected bellow the first layer
4 keV H + -Au(110)
azimuthal angle 0 0
experiment
selected on top of the surface
selected bellow the first layer
4 keV F - -Au(110)
azimuthal angle 70.5 0
electron capture again leads to F - formation.
Here we introduce neutralization
empirically, using theoretical treatments as
a guideline. Electron transfer processes
occur over the characteristic distances of
around Z F =5.0 atomic units from the image
plane for fluorine. A similar range of
distances is assumed for Auger
neutralization of hydrogen. Image charge
effects are “switched off” for neutralized
particles.
The simulated [1, 2] energy loss spectra
are also shown in Figs.2(a,b) and 3(a,b),
which are in good agreement with the
experiment. We furthermore observed a
splitting of the energy loss spectrum into
two components due to two different types
of the trajectory, as shown in Figs.2(c) and
3(c). The trajectory a results from scattering
from the most top layer of the surface and b
from subsurface has a longer effective
length.
Energy-loss spectra of hydrogen and
fluorine ions scattered off a Au (110)
single-crystal surface in grazing scattering
conditions were reported for various
orientations of the surface. We presented
simulations which take into account the
corrugation of the electron density
above the surface are in good agreement
with the experimental data.
relative intensity
1.0
0.8
0.6
0.4
0.2
0
0 50 100 150 200 250 300 350
(b)
simulation
experiment
1 keV F - -Au(110)
azimuthal angle 70.5 0
0.0
-20 0 20 40 60 80 100
energy loss (eV)
Fig. 3. (a) and (b) Energy loss spectrum of 4 and 1 keV F -
scattering along the 70.5° direction for Au(110)
respectively.
In describing H + and F - scattering on Au
one should correctly describe the effect of
the image potential. This implies a correct
description of electron transfer processesresonant
and Auger neutralization on the
incoming and outgoing path of the
trajectory. We consider H + neutralization in
the incoming path and in case of F - we
consider that at large distances (Z> Z F )
when the affinity level is above the Fermi
level electron loss occurs leading to F°
formation, while at small distances, when
the F - level lies below the Fermi level
References
[1] Valdés J E, Vargas P, Celedón C,
Sanchez E, Guillemot L and
Esaulov V A 2008 Phys. Rev. A
78 32902
[2] Valdés J E, Vargas P, Guillemot L
and Esaulov V A 2007 Nucl.
Inst. And Methods B 256 81
98 Valparaíso, Chile