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X-Ray Photoelectron Spectroscopy. Click on the green arrow to return to the previous page
X-Ray Photoelectron Spectroscopy (XPS) is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS spectra are obtained by irradiating a material with a beam of aluminium or magnesium X-rays while simultaneously measuring the kinetic energy (KE) and number of electrons that escape from the top 1 to 10 nanometres of the material being analyzed. XPS requires ultra-high vacuum (UHV) conditions (typically greater than one ten thousandth of one millionth of atmospheric pressure).
XPS is a surface chemical analysis technique that can be used to analyze the surface chemistry of a material in its "as received" state, or after some treatment such as fracturing, or more usually after in situ ion beam etching using a directed beam of argon ions to clean off some of the surface contamination. XPS is a surface analysis technique since photoelectrons originates from only the first few atomic layers of a material. Using ion beam etching it is possible to obtain spectra as a function of etching depth. Unlike other X-ray detection techniques, such as Energy Dispersive X-Ray Analysis, performed routinely in the SEM, XPS tells you not only what elements are present and it what amounts but how they are combined chemically so you can determine oxidation states, for example. I spent a couple of years from 1998 working in Automotive research to develope better brake materials from a knowledge of chemical composition and a photograph below shows me positioning a sample inside the high vacuum chamber of the XPS using a remote drive control prior to analysis to determine how the brake material transferred to wheel rotors when brakes were applied.The spherical high vacuum chamber shown in the adjacent photograph has numerous ports around it for detectors and ion guns and a separate airlock to permit samples to be moved in and out of the chamber.