Untitled - IAP/TU Wien - Technische Universität Wien

71st IUVSTA Workshop
Model studies of the validity of trajectory methods for calculating very low
energy (< 100 eV) electron transport in condensed media
David Liljequist
Department of Physics, Stockholm University, SE-106 91 Stockholm, Sweden
cemd@fysik.su.se
Trajectory methods, for example conventional detailed Monte Carlo trajectory simulation, are often
used to calculate plural or multiple scattering of electrons in matter. However, due to the neglect of coherent
scattering they cannot be generally valid, but must be regarded as a fortunately useful approximation of
quantum scattering. In particular, one may suspect that coherence effect should be more strong with a larger
wavelength, causing trajectory methods to fail at low electron energies.
In order to study the limits of validity of trajectory methods, one may, if possible, compare them to
a corresponding quantum calculation. Such calculations, which involve multiple wave scattering within
clusters of atoms, are in general too complex to permit a comparison of scattering in, for example,
amorphous matter, within reasonable computer time. There is however one case which permits a both rapid
and exact quantum calculation, and that is the multiple elastic scattering of an electron in a cluster of point
scatterers. It has recently been shown that this case can be extended to include a model of plural inelastic
scattering.
Using this method of comparison, the object in which the electron scattering occurs is a cluster with
a size of a few nm, containing about 10 3 more or less randomly distributed point scatterers, each scatterer
modelling an atom. This may seem a poor model for a real scattering medium, such as bulk amorphous solid
or bulk liquid. However, the point scatterer is not a physically unreasonable model at very low electron
energies, and simple phase considerations suggest that the validity limits obtained with the point scatterer
model should be similar to those obtained for electrons in real amorphous solids or liquids.
The presentation aims to give 1) a brief look at the theory of quantum scattering in a cluster of
point scatterers, 2) the most recent procedure used for comparison with a corresponding trajectory simulation,
and 3) the most important results so far.
References
D.Liljequist, Nucl.Instr.Meth.B 251 (2006) 27.
D.Liljequist, Rad.Phys.Chem. 77 (2008) 835
D.Liljequist, Rad.Phys.Chem. 80 (2011) 291
D.Liljequist, Nucl.Instr.Meth.B 275 (2012) 69
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