Surface Analysis Using X-Ray Photoelectron Spectroscopy

Increasing demand for high-performance materials has made surface engineering crucial. The surface of a material is its interface with the environment and other materials, affecting factors such as corrosion rates, catalytic activity, adhesive properties, wettability, contact potential, and appearance. These characteristics can be tailored for desired capabilities through surface modification.

The surface layer has physical and chemical properties distinct from the bulk material, or remainder of the solid. An atom in the surface layer is not surrounded by atoms on all sides, resulting in higher reactivity and bonding potential than bulk atoms.

Surface analysis is used to quantify the surface chemistry and through that, understand the surface properties. Surface modification can alter or enhance these characteristics, with efficacy checked through surface analysis.

X-ray photoelectron spectroscopy (XPS), or electron spectroscopy for chemical analysis (ESCA), is a common surface characterization tool used for a huge range of applications, from the every day (e.g. waterproofing fabrics or non-stick cookware coatings), to advanced R&D (e.g. clean energy materials, organic thin-film electronics, and bio-active surfaces). XPS measures the elemental composition, chemical, and electronic state of atoms on a material's surface to analyze its surface chemistry.

XPS offers a significant advantage in detecting subtle changes in the position of peaks that reflect the chemical state of surface elements, such as metallic or oxidized states, and diverse bonding states in polymers. The other key advantage to XPS is that the analysis depth is limited to a few nanometers due to the strong electron-matter interactions. Electrons lose energy quickly as they interact with matter, preventing their detection as part of a peak. This limits the depth from which the signal is detected to around 10 nm, depending on the material, which makes XPS extremely surface sensitive.