X-Ray Photoelectron Spectroscopy Techniques and Applications

X-Ray Photoelectron Spectroscopy (XPS) is a powerful surface-analytical technique that exploits the photoelectric effect to probe the elemental composition, chemical states and electronic environments of the outermost few nanometres of a material. Upon irradiation with monochromated X-rays, core electrons are ejected and their kinetic energies analysed to yield binding energy spectra characteristic of each element and its chemical bonding. Advances in instrumentation have extended XPS from ultra-high-vacuum measurements to ambient-pressure and hard-X-ray configurations, enabling in situ studies of catalytic interfaces, environmental processes and buried layers in multilayer devices. Depth profiling can be achieved either by varying the photoelectron escape depth through angle- or energy-resolved measurements, or by gentle sputter-etching to reveal subsurface composition. Recent developments in data modelling and spectral deconvolution have improved quantification of ultrathin oxide films, shed light on inelastic scattering phenomena in gas environments and refined methods for charge compensation and binding energy referencing. These innovations have broadened XPS applications across catalysis, energy storage, corrosion, semiconductor processing and biological surfaces, underscoring its global significance in materials and interface science.

Research from Nature Portfolio

One recent study has provided direct evidence that a single chemical state can give rise to two distinct photoelectron peaks, arising from vacuum level alignment at an organic–metal interface. The work demonstrated that adventitious carbon layers on metal foils can split the C 1s signal into two components despite identical bonding environments, thereby challenging the routine use of surface contaminants for energy calibration. It calls for the discontinuation of carbon-based referencing and an urgent revision of standard charge-referencing protocols to ensure the reliability of binding energy assignments.

X-Ray Photoelectron Spectroscopy Techniques and Applications publication trend

The graph below shows the total number of articles in x-ray photoelectron spectroscopy techniques and applications across all publications each year (not limited to Nature Index journals).

Technical terms

X-ray photoelectron spectroscopy: A surface-sensitive analytical technique that measures the kinetic energy of photoelectrons ejected by X-ray irradiation to determine elemental composition and chemical state.

Binding energy: The energy required to remove an electron from an atom or molecule, as determined by the difference between incident X-ray energy and detected electron kinetic energy.

Photoelectron: An electron emitted from a material when it absorbs a photon of sufficient energy, central to XPS analysis.

Ambient-pressure XPS (APXPS): A configuration that permits XPS measurements in the presence of gases at near-ambient pressures, enabling in situ studies of reactive interfaces.

Depth profiling: The technique of obtaining compositional or chemical state information as a function of depth below the surface, using angle-resolved measurements or controlled ion etching.

Adventitious carbon: A ubiquitous layer of hydrocarbon contamination that accumulates on surfaces, often used (but now questioned) for energy scale calibration in XPS.

References

1. When Photoelectrons Meet Gas Molecules: Determining the Role of Inelastic Scattering in Ambient Pressure X‑ray Photoelectron Spectroscopy. ACS Central Science (2024).
2. Sub‐Nanometer Depth Profiling of Native Metal Oxide Layers Within Single Fixed‐Angle X‐Ray Photoelectron Spectra. Small Methods (2023).
3. The same chemical state of carbon gives rise to two peaks in X-ray photoelectron spectroscopy. Scientific Reports (2021).
4. Binding energy referencing in X-ray photoelectron spectroscopy: Expanded data set confirms that adventitious carbon aligns to the sample vacuum level. Applied Surface Science (2024).