X-ray fluorescence spectra of metals excited below threshold

TL;DR

This study measures X-ray fluorescence spectra of Cu and Ni metals across a range of excitation energies, revealing how spectral shapes are modulated by energy conservation and how sub-threshold excitations relate to local density of states.

Contribution

It demonstrates that energy conservation explains spectral modulation without momentum considerations and characterizes spectral features below threshold, including Raman-type dispersion.

Findings

Spectral shape modulation explained by energy conservation.

Near-threshold spectra map local partial density of states.

Sub-threshold spectra show Raman dispersion and convolution of densities.

Abstract

X-ray scattering spectra of Cu and Ni metals have been measured using monochromatic synchrotron radiation tuned from far above to more than 10 eV below threshold. Energy conservation in the scattering process is found to be sufficient to explain the modulation of the spectral shape, neglecting momentum conservation and channel interference. At excitation energies close to and above threshold, the emission spectra map the occupied local partial density of states. For the sub-threshold excitations, the high-energy flank of the inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric low energy tail develops. For excitation far below threshold the emission spectra are proportional to a convolution of the occupied and unoccuppied local partial densities of states.