  Wolfgang S.M. Werner, Florian Simperl, Felix Bloedorn, Julian Brunner,
Johannes Kero, Alessandra Bellissimo and Olga Ridzel
  Spectroscopy of correlated electron pairs was employed to investigate the
energy dissipation process as well as the transport and the emission of low
energy electrons on a polymethylmetracylate (PMMA) surface, providing secondary
electron (SE) spectra causally related to the energy loss of the primary
electron. Two groups of electrons are identified in the cascade of slow
electrons, corresponding to different stages in the energy dissipation process.
For both groups, the characteristic lengths for attenuation due to collective
excitations and momentum relaxation are quantified and are found to be
distinctly different: l1=(12.0+/-2) Angstroem and l2=(61.5+/-11) Angstroem. The
results strongly contradict the commonly employed model of exponential
attenuation with the electron inelastic mean free path (IMFP) as characteristic
length, but essentially agree with a theory used for decades in astrophysics
and neutron transport, albeit with characteristic lengths expressed in units of
Angstroems rather than lightyears.
