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

V Encuentro Sud Americano de Colisiones Inelásticas en la Materia
The role of electronic excitations in the energy loss of hydrogen clusters in
dielectric and metallic materials
S. M. Shubeita 1 , R. C. Fadanelli 1 , J. F. Dias 1 , P. L. Grande 1 , C. D. Denton 2 , I. Abril 2 ,
R. Garcia-Molina 3 and N. R. Arista 4
1 Instituto de Física da Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
2 Departamento de Física Aplicada, Universidad d’Alicante, Alicante, Spain
3 Departamento de Física – CIOyN, Universidad de Murcia, Murcia, Spain
4 Centro Atômico Bariloche, Instituto Balseiro, San Carlos de Bariloche, Rio Negro, Argentina
e-mail address corresponding author: samir.shubeita@ufrgs.br
The aim of this work is to study the
signature of plasmon excitations induced by
H + 2 and H + 3 ionic clusters when interacting
with thin (10-50 Å) layers of dielectric
(SiO 2 , LaScO 3 , HfO 2 ) and metallic (Au)
materials. For this purpose, high energy
resolution backscattering experiments were
carried out as a function of the incoming
projectile energy, covering an energy range
between 40 and 200 keV/nucleon. The ratio
R n between the energy loss of the cluster and
the sum of the energy loss of its constituents
provides the information about the plasmon
excitation threshold, which is characteristic
for each material. The results obtained for
the high-k dielectrics (LaScO 3 and HfO 2 )
and Au do not show any clear evidence of
plasmon excitations induced by H +
2 ionic
clusters (see fig. 1 for HfO 2 ). These results
are supported by calculations based on the
dielectric formalism. However, for the SiO 2
thin film (fig. 2), the plasmon excitation
threshold is observed at about 70
keV/nucleon for both cluster ions (H + 2 and
H + 3 ) [1]. In fact, unlike SiO 2 where a dominant
long-range electronic excitation is present,
the HfO 2 , LaScO 3 and Au have several
and equally important excitation energies
(mix of plasmon excitations, excitons and
interband transitions). They lead to different
onset projectile-energies, which explains the
smoothly increase of stopping ratio [2].
Also, the results obtained for Au are compared
with previous results [3].
Figure 1. The experimental energy loss ratio R 2
(squares) for HfO 2 as a function of the incident cluster
energy, in comparison with different theoretical
approaches.
Figure 2. The experimental stopping ratio R 2 (full
squares) as a function of the incident H +
2 cluster
energy. The thick lines represent the dielectric formalism
calculations including plasmon excitations
(full line) and without plasmon excitations (dotted
lines) after averaging over charge-state fractions of
H + and H 0 .
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