A model dielectric function for low and very high momentum transfer

Vos, Maarten

doi:10.1016/j.nimb.2015.09.091

Cited by 14 publications

(9 citation statements)

References 33 publications

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“…It turns out that this approach improves the description of stopping of ions in metals based on the dielectric function . The dielectric function based on a sum of Mermin oscillators can describe quite well both the optical limit and the high‐momentum transfer (Compton) limit of the dielectric function …”

Section: Model Dielectric Functionssupporting

confidence: 76%

Extracting the dielectric function from high‐energy REELS measurements

Vos

Grande

2017

Surface & Interface Analysis

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A method is described for extracting the dielectric function directly from a reflection electron energy loss spectrum taken at relatively high energies (2.5 to 40 keV). It makes simplifying assumptions on separation of surface and bulk losses. The approach uses a description based on partial intensities and surface excitation parameters and fits directly the reflection electron energy loss data. Several different model dielectric functions are implemented (extended Drude, Drude Lindhard, Mermin, and the Levine-Louie dielectric functions with relaxation time), and their advantages and disadvantages are discussed. Justification of this approach is in the end based on a comparison with the dielectric function as obtained by other means, which is generally quite good, provided that the solution obtained is restrained by sum rules to the right refractive index and electron density. The fitting program, to be used in conjunction with commercial plotting software, is provided.

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Section: Model Dielectric Functionssupporting

confidence: 76%

Extracting the dielectric function from high‐energy REELS measurements

Vos

Grande

2017

Surface & Interface Analysis

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“…The Mermin method reproduces the measured Compton spectrum for high momenta (k > ∼ 20 keV) and high energy (ω > ∼ 1 keV) [61], though its validity for high k and low ω regime that is of interest for dark matter scattering is less established. In particular, the lower row of Fig.…”

Section: Calculating the Elfmentioning

confidence: 94%

DarkELF: A python package for dark matter scattering in dielectric targets

Knapen,

Kozaczuk,

Lin

2021

Preprint

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We present a python package to calculate interaction rates of light dark matter in dielectric materials, including screening effects. The full response of the material is parametrized in the terms of the energy loss function (ELF) of material, which DarkELF converts into differential scattering rates for both direct dark matter electron scattering and through the Migdal effect. In addition, DarkELF can calculate the rate to produce phonons from sub-MeV dark matter scattering via the dark photon mediator, as well as the absorption rate for dark matter comprised of dark photons. The package includes precomputed ELFs for Al, Al2O3, GaAs, GaN, Ge, Si, SiO2, and ZnS, and allows the user to easily add their own ELF extractions for arbitrary materials.

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“…The Mermin approach (Mermin, ) to a model dielectric function uses a free electron model where the width of the loss peak is dependent on q. This model has recently been explored by Vos () for a range of momentum transfer values. It should be noted that the dielectric function description of inelastic electron scattering assumes that the Born approximation holds.…”

Section: The Monte Carlo Methodsmentioning

confidence: 99%

Simulations and measurements in scanning electron microscopes at low electron energy

2016

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Summary: The advent of new imaging technologies in Scanning Electron Microscopy (SEM) using low energy (0-2 keV) electrons has brought about new ways to study materials at the nanoscale. It also brings new challenges in terms of understanding electron transport at these energies. In addition, reduction in energy has brought new contrast mechanisms producing images that are sometimes difficult to interpret. This is increasing the push for simulation tools, in particular for low impact energies of electrons. The use of Monte Carlo calculations to simulate the transport of electrons in materials has been undertaken by many authors for several decades. However, inaccuracies associated with the Monte Carlo technique start to grow as the energy is reduced. This is not simply associated with inaccuracies in the knowledge of the scattering cross-sections, but is fundamental to the Monte Carlo technique itself. This is because effects due to the wave nature of the electron and the energy band structure of the target above the vacuum energy level become important and these are properties which are difficult to handle using the Monte Carlo method. In this review we briefly describe the new techniques of scanning low energy electron microscopy and then outline the problems and challenges of trying to understand and quantify the signals that are obtained. The effects of charging and spin polarised measurement are also briefly explored. SCANNING 9999:1-17, 2016.

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A model dielectric function for low and very high momentum transfer

Cited by 14 publications

References 33 publications

Extracting the dielectric function from high‐energy REELS measurements

Extracting the dielectric function from high‐energy REELS measurements

DarkELF: A python package for dark matter scattering in dielectric targets

Simulations and measurements in scanning electron microscopes at low electron energy

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