Kateryna Artyushkova

This paper presents the characteristics and operating modes of the PHI VersaProbe family of scanning x-ray photoelectron spectroscopy (XPS) microprobe instruments in detail to support accurate referencing in scientific publications and to provide readers with instrumental context often missing in research articles. The PHI VersaProbe is a commercial laboratory-based, multitechnique XPS system designed for spatially resolved surface analysis of a wide range of materials under ultrahigh vacuum conditions. An overview of the instrument's architecture, component geometries, and tables of key geometry as well as operator-selected parameters are provided. The paper details hardware and software configurations across multiple instrument generations and various data acquisition modes. Raw data from PHI VersaProbe instruments, collected from sputter-cleaned silver and polyethylene terephthalate samples, are included in the Surface Science Spectra submission. Figures throughout the paper compare performance characteristics across multiple instrument generations—PHI VersaProbe 4, PHI VersaProbe III, PHI VersaProbe II, and PHI VersaProbe I—that highlight how analyst-controlled variables such as analyzer pass energy influence analyzer energy resolution. Information that needs to be reported on experiments performed using the PHI VersaProbe is also discussed.

X-ray sources with a photon energy higher than 2140 eV are increasingly being used for routine x-ray photoelectron spectroscopy (XPS) on laboratory-based instruments. This analytical approach is termed “HAXPES” (hard x-ray photoelectron spectroscopy). This article provides an overview of the current and potential future uses of laboratory-based HAXPES in comparison to routine XPS performed using Al Kα and Mg Kα x-ray sources. The standardization of XPS has occurred over 30 years and many of the procedures and reference works are specific to the use of Al Kα and Mg Kα x-ray sources. In this article, we discuss the translation of standard XPS practices to HAXPES, indicate useful resources for HAXPES users, and highlight areas where there is a need for improved information and guidance.

X-ray photoelectron spectroscopy (XPS) is one of the most common techniques used to analyze the surface composition of catalysts and support materials used in polymer electrolyte membrane (PEM) fuel cells and electrolyzers, providing important insights for further improvement of their properties. Characterization of catalyst layers (CLs) is more challenging, which can be at least partially attributed to the instability of ionomer materials such as Nafion during measurements. This work explores the stability of Nafion during XPS measurements, illuminating and addressing Nafion degradation concerns. The extent of Nafion damage as a function of XPS instrumentation, measurement conditions, and sample properties was evaluated across multiple instruments. Results revealed that significant Nafion damage to the ion-conducting sulfonic acid species (>50% loss in sulfur signal) may occur in a relatively short time frame (tens of minutes) depending on the exact nature of the sample and XPS instrument. This motivated the development and validation of a multipoint XPS data acquisition protocol that minimizes Nafion damage, resulting in reliable data acquisition by avoiding significant artifacts from Nafion instability. The developed protocol was then used to analyze both thin film ionomer samples and Pt/C-based CLs. Comparison of PEM fuel cell CLs to Nafion thin films revealed several changes in Nafion spectral features attributed to charge transfer due to interaction with conductive catalyst and support species. This study provides a method to reliably characterize ionomer-containing samples, facilitating fundamental studies of the catalyst-ionomer interface and more applied investigations of structure-processing-performance correlations in PEM fuel cell and electrolyzer CLs.

Monochromatic Cr Kα radiation (5414.8 eV) was used to acquire high-energy photoelectron spectroscopy (HAXPES) data on pure Mo and bulk MoSe2 compound with special attention paid to binding energy scale correction and quantification. The reported spectra include a survey scan and high-resolution Mo 2s, Mo 2p1/2, Mo 2p3/2, Mo 3d, Mo 3p1/2, Mo 3p3/2, Mo 3s, Mo 4s, Mo4p, Se2s, Se 2p1/2, Se 2p3/2, Se 3s, Se 3p1/2, Se 3p3/2, and Se 3d core-levels. The data will be useful as reference core-level spectra for HAXPES studies on molybdenum and its compounds.

Energy storage (batteries, capacitors) and conversion (solar cells) systems are increasing demand for vehicles, mobile electronics, and other areas as alternatives to fossil fuels.These systems are complex and multi-component with many materials and interfaces that are difficult to handle and characterize. To optimize materials properties and improve battery lifetimes, there is a pressing need for physicochemical characterization approaches with air-free handling capabilities, high spatial resolution, the ability to analyze buried interfaces without damaging the chemistry, and the need to bridge the gap by in situ and operando surface analysis. Developments in X-ray Photoelectron Spectrometers (XPS) open up new capabilities to address these challenges. In this talk, I will discuss how we can overcome obstacles in analyzing battery materials using: Inert environment transfer vessel: This allows for handling battery materials in an air-free environment, which is essential for preventing oxidation and other degradation reactions. Microprobe X-ray source with <5 µm spatial resolution: This provides high spatial resolution for analyzing small areas of interest, such as SEI, dendrites and other features. Hard X-ray source and cluster ion gun source: These allow for the analysis of buried interfaces not accessible by conventional soft X-ray XPS. In situ energy gap measurements: These allow for the study of the changes in the electronic structure of battery materials as they are cycled, which can provide insights into the mechanisms of charge storage and discharge. Operando XPS experiments: These allow for the study of the changes in the surface structure of battery materials as they are operating, which can provide insights into the factors that affect their performance. Figure 1

Bulk germanium was analyzed using high-resolution high-energy x-ray photoelectron spectroscopy (HAXPES). The HAXPES spectra of germanium obtained using monochromatic Cr Kα radiation at 5414.8 eV include survey scan and high-resolution spectra of Ge 2s, Ge 2p3/2, Ge 3s, Ge 3p, and Ge 3d.

Indium was analyzed using high-resolution high energy x-ray photoelectron spectroscopy (HAXPES). The HAXPES spectra of indium obtained using monochromatic Cr Kα radiation at 5414.8 eV include survey scan and high-resolution spectra of In 2s, In 2p3/2, In 3s, In 3p3/2, In 3d, In 4s, and In 4d.

Gadolinium was analyzed using high-resolution high energy x-ray photoelectron spectroscopy (HAXPES). The HAXPES spectra of gadolinium obtained using monochromatic Cr Kα radiation at 5414.8 eV include survey scan and high-resolution spectra of Gd 3s, Gd 3p, Gd 3d, Gd 4s, Gd 4p, and Gd 4d.

Hafnium was analyzed using high-resolution high energy x-ray photoelectron spectroscopy (HAXPES). The HAXPES spectra of Hafnium obtained using monochromatic Cr Kα radiation at 5414.8 eV include survey scan and high-resolution spectra of Hf 3s, Hf 3p3/2, Hf 3d5/2, Hf 4p3/2, Hf 4d, and Hf 4f.

Monochromatic Cr Kα radiation (5414.8 eV) was used to acquire high-energy photoelectron spectroscopy data on pure W and bulk WSe2 compound. The reported spectra include a survey scan and high-resolution W 3p1/2, W 3p3/2, W 3d3/2, W 3d5/2, W 4s, W 4p1/2, W 4p3/2, W 4d, W 4f, Se 2s, Se 2p1/2, Se 2p3/2, Se 3s, and Se 3p core-levels. The data will be useful as reference core-level spectra for HAXPES studies on tungsten and its compounds.