X-ray Photoelectron Spectrometry
The SPECS NAP-XPS system is a technique that allows for XPS characterisation under realistic conditions. XPS is a spectroscopic technique that allows for the chemical composition of the surface of a sample to be determined, with soft X-rays fired at the sample and photoelectrons ejected.
These photoelectrons carry information about the elements present in the sample and their bonding environment. Critically, only electrons from the very surface of the sample escape and reach the detector – making XPS a surface-sensitive technique. The sample and the detector are kept under high vacuum conditions during measurement (otherwise the photoelectrons would be absorbed by air molecules before reaching the detector).
XPS has been employed for many years to study surfaces and is routinely used in fields such as catalysis, corrosion and electrochemistry, where the chemical nature of the surface is critical. However, it has a major drawback – it is a post mortem technique. As the sample must be in high vacuum during the measurement, one can only observe the state of the sample before and after a chemical reaction has occurred; it’s not possible to look at the surface during a chemical reaction, which is the most interesting part.
NAP-XPS represents a revolution in the field, allowing for XPS characterisation of a sample in a gaseous environment. This is achieved by containing the sample in a high pressure cell that is only open to the analyser via a small aperture. A series of pumping stages after this aperture quickly reduce the pressure back down to high vacuum and limits the distance the electrons have to travel through a high pressure of gas. By placing the surface of the sample very close to this aperture, the area under analysis can be in a high pressure of gas while also allowing a usable fraction of the emitted photoelectrons to escape and reach the detector.