XPS: X-ray Photoelectron Spectroscopy

X-ray Photoelectron Spectroscopy (XPS) is one of the most widely used surface analysis techniques. It can be applied to a broad range of materials and provides valuable quantitative and chemical state information from the surface of the material being studied.

As the demand for high performance materials increases, so does the importance of surface engineering. Many of the problems associated with modern materials can only be solved by better understanding the physical and chemical interactions that occur at the surface or at the interfaces of a material’s layers. The surface chemistry will influence such factors as corrosion rates, catalytic activity, adhesive properties, wettability, contact potential and failure mechanisms.

The material’s surface is the point of interaction with the external environment and other materials. Therefore, surface modification can be used in a wide variety of applications to alter or improve the performance and behavior of a material. XPS can be used to analyse the surface chemistry of a material after an applied treatment such as fracturing, cutting or scraping. From characterisation of nuclear waste materials to thin-film electronics and bio-active surfaces, XPS is the standard tool for surface material characterisation.

Synchrotron radiation has a variety of properties which make it an attractive source for quantitative X-ray photoelectron spectroscopy. Among the most significant are the high intensity and tunable energy it produces. This continuous source of energy means that selected wavelengths can be employed to allow depth-dependent chemical analysis (e.g. cross section and absorption edge) of a material or element being researched. In addition, the increased photon intensity of a synchrotron leads to shorter data acquisition times when compared to lab-based X-ray sources. Modern synchrotron-based ambient pressure XPS systems are also able to operate at pressures higher than 7 mbar which allows the investigations of surfaces in equilibrium with, for example, water vapour in more industrially relevant conditions.

• Surface analysis of organic and inorganic materials;
• Determining composition and chemical state information from surfaces;
• Depth profiling for thin film composition;
• Thin film oxide thickness measurement; 
• In operando studies of solid oxide electrochemical cells;
• In situ studies of surface chemical processes in catalysis.

Near Ambient Pressure XPS (NAP-XPS) is a technique to whereby XPS characterisation is carried out under realistic conditions. It is widely used in surface analysis.