3.5
Angle and atomic number dependent energy shift in elastic scattering for free
atoms and molecules
T. Ricsóka, S. Ricz, Á. Kövér, D. Varga and Z. Berényi
bon and hydrogen. Figure 1 shows the position
of the hydrogen elastic peak relative to the carbon one as a function of the scattering angle
at 1000 eV impact energy. The experimental
data agree well with the results of the simple
model calculated by Boersch et al [2].
This is the one of the first experimental
data for the energy shift of the elastically scattered electron from free atoms and molecules.
During the past decade the elastic scattering of low-, medium- and high energy electrons from solids and liquids has been investigated experimentally and theoretically. This
phenomenon is the physical basis of the surface sensitive electron spectroscopy. Laser and
Seah [1] studied the quasielastic scattering of
electrons in the electron energy range 250–3000
eV from Cu, Ag and Au samples. They showed
that the energy losses were small and agreed
with the simple model based on the assumption of single elastic scattering on free atoms
of Boersch et al [2]. Recently Varga et al [3]
analyzed the energy shifts and energy widths
of the quasielastic peaks in the 1000–5000 eV
energy range using different samples (C, Si, Ni
and Au) and compared the results with the
single particle scattering values calculated by
Boersch et al [2]. Their experimental recoil energy shifts and broadenings were in good agreement with the formula of Boersch for Ni and
Au samples, but in the case of Si and C they
found larger energy broadening than the calculated one.
Figure 1. Comparison between the theoretical
and experimental energy shift of the elastic peak
of hydrogen relative to the carbon one for methane
target at 1000 eV impact energy. Black full circles
show the experimental data, whereas black solid
line represents the results of the model of Boersch
[2].
In order to test the validity of the simple model of Boersch [2] for free atoms and
molecules, we measured the energy shift of
the elastic peak using different targets (Ar,
He and CH4 ) in the 1000–2500 eV primary
electron energy range. Since the energy losses
are small, the scattered electrons were analyzed with the high energy resolution electronspectrometer (ESA-21). The scattered electrons are detected simultaneously by 13 channeltrons between 0◦ and 120◦ relative to the
direction of the incident electron beam.
Acknowledgements
This work was supported by the Hungarian
Scientific Research Foundation (OTKA Grant
No: T037203).
[1] D. Laser, M. P. Seah, Phys. Rev. B 47 (1993)
9836.
[2] H. Boersch, R. Wolter, H. Z. Schoenebeck, Z.
Physik 199 (1967) 124.
In the present impact energy range the
electrons scatter from the nuclei of the molecule. Due to the big mass difference of the
carbon and hydrogen nuclei in the methane we
could separate the elastic peaks from the car-
[3] D. Varga, K. Tőkési, Z. Berényi, J. Tóth, L. Kövér,
G. Gergely and A. Sulyok, Surf. Interface Anal.
31 (2001) 1019.
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