Much Ado About Nothing? Background Anomalies Without Accompanying Primary Peaks in X-Ray Photoelectron Spectroscopy and Low Energy Ion Scattering

Much Ado About Nothing? Background Anomalies Without Accompanying Primary Peaks in X-Ray Photoelectron Spectroscopy and Low Energy Ion Scattering

WoS Article

X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS) are important methods for identifying and quantifying the elements at surfaces. XPS largely deals with zero-loss peaks produced by unattenuated photoemission, and the focus of LEIS is similarly surface peaks resulting from direct scattering from surface atoms. However, the backgrounds of these spectra also contain information. They can help reveal the structures and distributions of the atoms and layers at surfaces. Here, we show abnormalities in XPS and LEIS backgrounds that are not accompanied by zero-loss photoemission or surface peaks. These features are due to buried atoms that are far enough from the surface that they cannot produce zero loss or surface peaks but close enough to affect spectral backgrounds. This Insight Note was written to alert the reader to the existence and usefulness of these backgrounds. Spectra with background abnormalities were poorly modeled by multiple linear regression, that is, as linear combinations of the pure-material spectra. However, XPS backgrounds with anomalies can be well modeled using the QUASES software, even when zero-loss peaks are not apparent. With QUASES, it is also possible to correct the substrate spectrum for distortions caused by inelastic electron scattering. When unusual baseline features appear in XPS or LEIS spectra, it can be helpful to use a complementary technique that probes at a greater depth to confirm the presence and identity of the atoms causing the anomaly. The effects in this work were demonstrated via a lighter coating of SiO2 on a heavier stainless-steel substrate.

X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS) are important methods for identifying and quantifying the elements at surfaces. XPS largely deals with zero-loss peaks produced by unattenuated photoemission, and the focus of LEIS is similarly surface peaks resulting from direct scattering from surface atoms. However, the backgrounds of these spectra also contain information. They can help reveal the structures and distributions of the atoms and layers at surfaces. Here, we show abnormalities in XPS and LEIS backgrounds that are not accompanied by zero-loss photoemission or surface peaks. These features are due to buried atoms that are far enough from the surface that they cannot produce zero loss or surface peaks but close enough to affect spectral backgrounds. This Insight Note was written to alert the reader to the existence and usefulness of these backgrounds. Spectra with background abnormalities were poorly modeled by multiple linear regression, that is, as linear combinations of the pure-material spectra. However, XPS backgrounds with anomalies can be well modeled using the QUASES software, even when zero-loss peaks are not apparent. With QUASES, it is also possible to correct the substrate spectrum for distortions caused by inelastic electron scattering. When unusual baseline features appear in XPS or LEIS spectra, it can be helpful to use a complementary technique that probes at a greater depth to confirm the presence and identity of the atoms causing the anomaly. The effects in this work were demonstrated via a lighter coating of SiO2 on a heavier stainless-steel substrate.

background; LEIS; multiple linear regression; spectrum; XPS

background; LEIS; multiple linear regression; spectrum; XPS

PINDER, J.; MALATINOVÁ, M.; KOVAŘÍK, M.; AUSTIN, D.; ŠIKOLA, T.; TOUGAARD, S.; MORGAN, D.; ISAACS, M.; PRŮŠA, S.; LINFORD, M.

01.04.2025

SURFACE AND INTERFACE ANALYSIS

57

4

United Kingdom of Great Britain and Northern Ireland

264

274

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https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/sia.7378