Phase Quantification of Heterogeneous Surfaces Using DFT-Simulated Valence Band Photoemission Spectra

Quantifying the crystallographic phases present at asurface isan important challenge in fields such as functional materials andsurface science. X-ray photoelectron spectroscopy (XPS) is routinelyemployed in surface characterization to identify and quantify chemicalspecies through core line analysis. Valence band (VB) spectra containcharacteristic but complex features that provide information on theelectronic density of states (DoS) and thus can be understood theoreticallyusing density functional theory (DFT). Here, we present a method offitting experimental photoemission spectra with DFT models for quantitativeanalysis of heterogeneous systems, specifically mapping the anataseto rutile ratio across the surface of mixed-phase TiO2 thinfilms. The results were correlated with mapped photocatalytic activitymeasured using a resazurin-based smart ink. This method allows large-scalefunctional and surface composition mapping in heterogeneous systemsand demonstrates the unique insights gained from DFT-simulated spectraon the electronic structure origins of complex VB spectral features.

Automated summary

This study presents a method for quantifying crystallographic phases on a surface by fitting experimental photoemission spectra with density functional theory (DFT) models. The method was applied to map the anatase to rutile ratio across the surface of mixed-phase TiO2 thin films, and the results were correlated with photocatalytic activity measurements. The study demonstrates the potential of this method for large-scale functional and surface composition mapping in heterogeneous systems, and the unique insights provided by DFT-simulated spectra on the electronic structure origins of complex valence band spectral features.