Absolute Determination of Optical Constants by a Direct Physical Modeling of Reflection Electron Energy Loss Spectra

TL;DR

This paper introduces a novel method to accurately determine optical constants of metals by directly modeling reflection electron energy loss spectra using reverse Monte Carlo techniques, validated through sum rules and comparison with existing data.

Contribution

It presents a new absolute extraction technique for optical constants from REELS spectra using physical modeling and optimization, improving accuracy over previous methods.

Findings

Optical constants of Fe were successfully extracted at multiple energies.

The method's validity was confirmed via sum rules and comparison with prior data.

The approach accurately describes electron scattering near surfaces.

Abstract

We present an absolute extraction method of optical constants of metal from the measured reflection electron energy loss (REELS) spectra by using the recently developed reverse Monte Carlo (RMC) technique. The method is based on a direct physical modeling of electron elastic and electron inelastic scattering near the surface region where the surface excitation becomes important to fully describe the spectrum loss feature intensity in relative to the elastic peak intensity. An optimization procedure of oscillator parameters appeared in the energy loss function (ELF) for describing electron inelastic scattering due to the bulk- and surface-excitations was performed with the simulated annealing method by a successive comparison between the measured and Monte Carlo simulated REELS spectra. The ELF and corresponding optical constants of Fe were obtained from the REELS spectra measured at incident energies of 1000, 2000 and 3000 eV. The validity of the present optical data has been verified with the f- and ps-sum rules showing the accuracy and applicability of the present approach. Our data are also compared with previous optical data from other sources.