Electronic depth profiles with atomic layer resolution from resonant soft x-ray reflectivity

TL;DR

This paper introduces a novel method for analyzing resonant soft x-ray reflectivity data that accounts for atomic-scale variations in optical properties, enabling atomic-resolution depth profiling of heterostructures.

Contribution

The authors develop a slicing scheme that models heterostructures at atomic layer resolution, improving the analysis of resonant soft x-ray reflectivity data.

Findings

Allows determination of atomic-scale interface structures

Enables depth-resolved spectroscopic analysis with atomic resolution

Enhances understanding of surface and interface phenomena

Abstract

The analysis of x-ray reflectivity data from artificial heterostructures usually relies on the homogeneity of optical properties of the constituent materials. However, when the x-ray energy is tuned to an absorption edge, this homogeneity no longer exists. Within the same material, spatial regions containing elements at resonance will have optical properties very different from regions without resonating sites. In this situation, models assuming homogeneous optical properties throughout the material can fail to describe the reflectivity adequately. As we show here, resonant soft x-ray reflectivity is sensitive to these variations, even though the wavelength is typically large as compared to the atomic distances over which the optical properties vary. We have therefore developed a scheme for analyzing resonant soft x-ray reflectivity data, which takes the atomic structure of a material into account by "slicing" it into atomic planes with characteristic optical properties. Using LaSrMnO4 as an example, we discuss both the theoretical and experimental implications of this approach. Our analysis not only allows to determine important structural information such as interface terminations and stacking of atomic layers, but also enables to extract depth-resolved spectroscopic information with atomic resolution, thus enhancing the capability of the technique to study emergent phenomena at surfaces and interfaces.