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