XPS - X-ray Photoelectron Spectroscopy
X-ray Photoelectron Spectroscopy is a valuable tool for surface science and chemical analysis of a wide variety of materials. XPS allows for a wide variety of elements to not only be identified and quantified, but for chemical state information regarding these elements in the sample to be determined. XPS bombards a vacuum stable sample with a concentrated beam of x-rays, allowing the interaction of the x-ray beam and the sample to liberate electrons from the sample. By correlating the energy of liberated electrons with known binding energies, the spectrum of electron energies gives quantitative and oxidation state information about the elements on the sample surface.
Because of the detailed oxidation state information XPS allows for very detailed information about the relative chemical environment in a sample. Because the electrons liberated from the sample need to migrate to the detector, this chemical information is only obtained from a very small volume of material at the surface of a sample. This allows for analysis that is very surface specific, leading to nm scale interaction with the surface, with a thin film sample orientation profile of 2nm easily achievable. Due to the extreme surface sensitivity, small amounts of contaminants can often interfere with the desired material, and so the instrument is equipped with an ion sputter gun for surface cleaning. With the proper alignment, samples can also be successively sputtered to perform analysis at varying depth, creating a depth resolved profile of composition. Analysis of depth profile, surface film analysis, work-function measurements, and surface mapping by composition are all possible with this technique.
XPS is a preferred technique for thin film electronics. Examination of thin contaminants or surface poisoning is possible using the extreme sensitivity of the instrument, allowing for fine auto-oxidation layers or staining to be identified. Semi-conductors, organo-metallic polymers, composite materials, and all manner of metals and ceramic materials can be examined using XPS to both guide process and materials research, as well as determine root cause of material contamination or disruption.