High energy photoelectron diffraction: model calculations and future possibilities

TL;DR

This paper models high-energy x-ray photoelectron diffraction using dynamical electron diffraction theory, demonstrating its potential to provide bulk-sensitive structural information for complex materials at energies up to 20 keV.

Contribution

It extends dynamical diffraction modeling to high energies and compares it with cluster models, highlighting HXPD's potential for detailed bulk material analysis.

Findings

Dynamical theory predicts diffraction patterns well at energies around 1 keV.

Kikuchi bands dominate diffraction patterns above 1 keV.

Patterns are sensitive to lattice distortions and impurities.

Abstract

We discuss the theoretical modelling of x-ray photoelectron diffraction (XPD) with hard x-ray excitation at up to 20 keV, using the dynamical theory of electron diffraction to illustrate the characteristic aspects of diffraction patterns resulting from such localized emission sources in a multi-layer crystal. We show via dynamical calculations for diamond, Si, and Fe that the dynamical theory well predicts available current data for lower energies around 1 keV, and that the patterns for energies above about 1 keV are dominated by Kikuchi bands which are created by the dynamical scattering of electrons from lattice planes. The origin of the fine structure in such bands is discussed from the point of view of atomic positions in the unit cell. The profiles and positions of the element-specific photoelectron Kikuchi bands are found to be sensitive to lattice distortions (e.g. a 1% tetragonal distortion) and the position of impurities or dopants with respect to lattice sites. We also compare the dynamical calculations to results from a cluster model that is more often used to describe lower-energy XPD. We conclude that hard XPD (HXPD) should be capable of providing unique bulk-sensitive structural information for a wide variety of complex materials in future experiments.