Impact of PHI XPS instruments on scientific discovery

In 2025, PHI X-ray Photoelectron Spectroscopy (XPS) instruments, including the PHI Genesis, PHI VersaProbe, PHI Quantes, and PHI Quantera, continued to play a key role in advancing research across a wide range of industrially relevant fields. Their influence is evident in over 5,150 scientific publications covering various disciplines.

The strength of PHI XPS instruments lies in their ability to analyze the chemical composition and electronic structure of materials within the top few nanometers of the surface. This surface sensitivity allows researchers to gain crucial insights into material behavior that directly impacts performance, reliability, and functionality.

This spotlight highlights three notable studies published in 2025 that leveraged PHI XPS technology to advance highly active areas of research, including next-generation materials such as battery materials, catalyst, and tribofilms.

Researchers from Stanford University studying battery materials used a PHI VersaProbe III, IV XPS to investigate the solid electrolyte interphase (SEI), a nanometer-scale and highly reactive interface that is difficult to characterize.¹ The study addresses a key challenge in battery interphase science, namely understanding the chemical nature of the SEI while accounting for its high reactivity. The authors highlight that conventional room-temperature XPS (RT-XPS) measurements performed under ultrahigh vacuum can trigger chemical reactions, causing changes in SEI thickness and composition during analysis. As a result, RT-XPS measurements may represent an interface that has changed under measurement conditions rather than the SEI in its original state. Cryogenic XPS (cryo-XPS) offers a more accurate representation of the SEI compared to traditional RT-XPS. When samples are kept at −110 °C under ultra-high vacuum (UHV), the F 1s, O 1s, and N 1s spectra remained stable during the first 60 minutes of the experiment (figure 1). In contrast, warming the same sample to room temperature causes immediate and ongoing changes in the spectra at the same analysis point.

Figure 1. Time-resolved high-resolution spectra of cryo-XPS and cryo-heated to RT-XPS for F 1s, O 1s and N 1s.

Comparisons among cryo-XPS and RT-XPS reveal that room-temperature measurements can trigger reaction-driven changes in the SEI. Notably, RT-XPS shows higher LiF intensity in the F 1s region, while other species like Li₂O decrease or change, indicating that the SEI evolves during analysis. Since LiF content is often linked to improved cycling stability, this apparent increase at room temperature which could lead to misinterpreted mechanistic conclusions. By maintaining the native SEI composition, cryo-XPS establishes stronger links between SEI chemistry and electrochemical performance, indicating that many RT-XPS studies might analyze an SEI that has changed under measurement conditions rather than the original interface.

Researchers from Zhejiang University studying thermoelectric materials used a PHI VersaProbe III XPS in a Nature Communications publication to investigate the chemical state of tin dopants in AgSbTe₂.² The study addresses a key challenge in thermoelectric materials engineering, namely improving electrical transport while maintaining phase stability. The authors suggest that introducing small amounts of Sn into the AgSbTe₂ lattice changes the material’s defect chemistry, increasing hole concentration and boosting thermoelectric performance. To confirm this mechanism, XPS was used to determine whether Sn is incorporated into the host lattice or forms separate phases (Figure 2).

Figure 2: High-resolution Ag 3d, Sn 3d, Sb 3d, and Te 3d spectra of AgSb0.94Sn0.06Te2 pellet.

High-resolution XPS measurements focus on the Sn 3d core level to determine the oxidation state of the dopant. The spectra show a single Sn 3d spin–orbit doublet with Sn 3d₅/₂ at approximately 486.1 eV, which the authors interpret as evidence that tin is mainly present as Sn²⁺ within the AgSbTe₂ matrix. The presence of a single doublet rather than multiple chemically shifted components suggests that Sn atoms are incorporated into the host lattice rather than forming metallic or oxidized secondary phases. By confirming the chemical state of the dopant, the XPS analysis supports the proposed defect-chemistry model in which Sn replaces Sb and increases hole carrier concentration. This strengthens the link between Sn incorporation, enhanced electrical transport, and improved thermoelectric performance in the engineered AgSbTe₂ system.

Researchers at TU WIEN studying hybrid MXene tribocoatings used a PHI VersaProbe III XPS to investigate chemical changes occurring during sliding wear in a Ti₃C₂Tₓ + Nb₂CTₓ coating system.³  The study focuses on a key challenge in tribology, where frictional contact can cause surface layers to react with oxygen and reorganize, forming a thin “tribolayer” whose chemistry may differ significantly from that of the original coating. To understand these changes, the authors compare the as-deposited MXene coating with the wear track after dry sliding on stainless steel, using XPS to analyze the chemical states of Ti, Nb, C, O, and F within the near-surface region. XPS analysis shows that the tribolayer formed during sliding was more oxidized than the original coating. Specifically, spectra indicate higher concentrations of TiO₂ and Nb₂O₅ within the wear track compared to the reference surface. This indicates that Nb-containing MXene phases oxidize more easily during tribological stress, whereas Ti₃C₂Tₓ retains more of its carbide-like character.

The summaries shared here highlight key results from the referenced studies. For detailed methodology and a full discussion of the findings, readers should consult the original publications. These three Nature articles represent just a small sample of the many studies in 2025 that show the significant impact of PHI XPS instruments across various scientific fields. Their use in these prominent investigations underscores PHI’s ongoing dedication to advancing both fundamental science and industrial innovation.

References

1. Shuchi, S.B., D’Acunto, G., Sayavong, P. et al. Cryogenic X-ray photoelectron spectroscopy for battery interfaces. Nature 646, 850–855 (2025). https://doi.org/10.1038/s41586-025-09618-3
2. Zhang, Y., Xing, C., Wang, D. et al. Realizing high power factor and thermoelectric performance in band engineered AgSbTe₂. Nat Commun 16, 22 (2025). https://doi.org/10.1038/s41467-024-55280-0
3. Danecker, C., Schwarz, S., Piljevic, M. et al. Hybrid MXene coatings: unlocking synergistic lubrication properties of Ti₃C₂T_x and Nb₂CT_x MXenes for improved tribological performance. Sci Rep 15, 45111 (2025). https://doi.org/10.1038/s41598-025-32533-6

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