Energy distributions of the secondary and backscattered electrons from polymethylmethacrylate irradiated by an electron beam.
A Monte Carlo simulation
Maurizio Dapor
European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*-FBK), Trento, Italy
and
Trento Institute for Fundamental Physics and Applications (TIFPA-INFN), Trento, Italy
[email protected]
This work describes a Monte Carlo code which takes into account the
stochastic behavior of electron transport in solids and treats event-byevent all the elastic and inelastic interactions between the incident
electrons and the particles of the solid target [1].
It was recently demonstrated that the choice of the optical data model
strongly influences the result of the simulation [2]. Extended Mermin
theory [3,4] was utilized in this work, as extended Drude theory [5] is
less accurate [2].
The code is used to simulate the energy distributions of the secondary
and backscattered electrons from polymethylmethacrylate (PMMA)
irradiated by an electron beam. Several values of the initial kinetic
energy of the incident electrons are considered, and the evolution of
the shape of the spectra is investigated.
The simulation of the backscattered and secondary electron spectra
also allows calculating the secondary electron yield of PMMA as a
function of the initial energy of the incident electrons. Results of the
simulation are compared with the available experimental data.
Fig. 1.- Energy loss function (ELF) of PMMA as a
function of the transferred energy, for several
values of the momentum transfer. Symbols
correspond to the experimental optical data from
[6]. Solid (dashed) lines correspond to the
extended Mermin [3,4] (extended Drude [5])
description of the ELF. Notice that at the optical
limit (k=0) both ELF models are identical. From
Ref. [2].
Fig.2. - Mermin differential inverse inelastic mean
free path (DIIMFP) of electrons in PMMA as a
function of the energy loss W for selected values
of the incident electron kinetic energy E in the
range 10-1000 eV. From Ref. [7].
Fig 3. - Monte
Carlo simulated
spectra of the
secondary and
backscattered
electrons from
PMMA for 200
eV (green line),
400 eV (red
line), and 600
eV (black line)
primary energy.
Fig 4. - Monte Carlo simulated spectra of the backscattered electrons from PMMA for
200 eV (green line), 400 eV (red line), and 600 eV (black line) primary energy.
Plasmon-loss peaks are located at about 20 eV from the elastic peaks (zero-loss
peaks).
References
Fig 5. - Monte Carlo simulated spectra of
the secondary electrons from PMMA for
200 eV (green line), 400 eV (red line),
and 600 eV (black line) primary energy.
Fig. 6.- Monte Carlo secondary electron yield of
PMMA as a function of the primary electron
kinetic energy obtained from the Mermin model
(solid line). Symbols correspond to experimental
data [8-10]. From Ref. [2].
[1] M. Dapor, Transport of Energetic Electrons in Solids,
Springer Tracts in Modern Physics (Springer, Berlin,
2014), Vol. 257
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