Resonant soft x-ray scattering from stepped surfaces of SrTiO3

TL;DR

This study demonstrates the high sensitivity of resonant soft x-ray diffraction to surface steps on SrTiO3, revealing detailed surface structure and optical parameters through comparison with XAS and reflectivity data.

Contribution

It introduces the use of stepped SrTiO3 surfaces as a model system for resonant soft x-ray diffraction and analyzes the differences between diffraction, XAS, and reflectivity spectra.

Findings

Resonant diffraction peaks are detectable even at low step densities.

Diffraction spectra resemble reflectivity at larger angles but differ from XAS.

Surface steps cause energy shifts in spectra at grazing incidence.

Abstract

We studied the resonant diffraction signal from stepped surfaces of SrTiO3 at the Ti 2p -> 3d (L2,3) resonance in comparison with x-ray absorption (XAS) and specular reflectivity data. The steps on the surface form an artificial superstructure suited as a model system for resonant soft x-ray diffraction. A small step density on the surface is sufficient to produce a well defined diffraction peak, showing the high sensitivity of the method. At larger incidence angles, the resonant diffraction spectrum from the steps on the surface resembles the spectrum for specular reflectivity. Both deviate from the XAS data in the relative peak intensities and positions of the peak maxima. We determined the optical parameters of the sample across the resonance and found that the differences between the XAS and scattering spectra reflect the different quantities probed in the different signals. When recorded at low incidence or detection angles, XAS and specular reflectivity spectra are distorted by the changes of the angle of total reflection with energy. Also the step peak spectra, though less affected, show an energy shift of the peak maxima in grazing incidence geometry.