TY - JOUR
T1 - How the choice of model dielectric function affects the calculated observables
AU - Vos, Maarten
AU - Grande, Pedro L.
N1 - Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2017/9/15
Y1 - 2017/9/15
N2 - It is investigated how the model used to describe a dielectric function (i.e. a Mermin, Drude, Drude–Lindhard, Levine–Louie with relaxation time dielectric function) affects the interpretation of a REELS experiment, the calculation of the electron inelastic mean free path as well proton stopping and straggling. Three dielectric functions are constructed that are based on different models describing a metal, but have identical loss functions in the optical limit. A loss function with the same shape, but half the amplitude, is used to derive four different model dielectric functions for an insulator. From these dielectric functions we calculate the differential inverse mean free path, the mean free path itself, as well as the stopping force and straggling for protons. The similarity of the underlying physics between proton stopping, straggling and the electron inelastic mean free path is stressed by describing all three in terms of the differential inverse inelastic mean free path. To further highlight the reason why observed quantities depend on the model dielectric function used we study partial differential inverse inelastic mean free paths, i.e. those obtained by integrating over only a limited range of momentum transfers. In this way it becomes quite transparent why the observable quantities depend on the choice of model dielectric function.
AB - It is investigated how the model used to describe a dielectric function (i.e. a Mermin, Drude, Drude–Lindhard, Levine–Louie with relaxation time dielectric function) affects the interpretation of a REELS experiment, the calculation of the electron inelastic mean free path as well proton stopping and straggling. Three dielectric functions are constructed that are based on different models describing a metal, but have identical loss functions in the optical limit. A loss function with the same shape, but half the amplitude, is used to derive four different model dielectric functions for an insulator. From these dielectric functions we calculate the differential inverse mean free path, the mean free path itself, as well as the stopping force and straggling for protons. The similarity of the underlying physics between proton stopping, straggling and the electron inelastic mean free path is stressed by describing all three in terms of the differential inverse inelastic mean free path. To further highlight the reason why observed quantities depend on the model dielectric function used we study partial differential inverse inelastic mean free paths, i.e. those obtained by integrating over only a limited range of momentum transfers. In this way it becomes quite transparent why the observable quantities depend on the choice of model dielectric function.
KW - Dielectric function
KW - Inelastic mean free path
KW - Ion stopping
KW - Reflection electron energy loss spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85020732569&partnerID=8YFLogxK
U2 - 10.1016/j.nimb.2017.05.064
DO - 10.1016/j.nimb.2017.05.064
M3 - Article
SN - 0168-583X
VL - 407
SP - 97
EP - 109
JO - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
JF - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
ER -