X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) is a surface sensitive analytic tool to study the surface composition and electronic state of a sample. It has proved very useful to the semiconductor fabrication industry. A sample maintained under ultra high vacuum is bombarded with X-rays . The X-rays penetrate a substantial distance into the sample (~mm) and excites electrons (referred to as photoelectrons). A small fraction of these electrons from the top ~ 5 nanometres make it outside the sample and are detected. The kinetic energy of these electrons is measured by the analyzer.

Related Topics:
X-ray - Semiconductor fabrication - Ultra high vacuum - Electrons - Kinetic energy

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When using monochromatic X-rays, the energy that one photon imparts on an electron is a known quantity. The binding energy of the ejected electron can then be determined from:

Related Topics:
Monochromatic - Photon - Electron

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:Ebinding= Ephoton - Ekinetic

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In XPS the photon is absorbed by an atom leading to ionization and the emission of a core electron (inner shell electron). This is in contrast to a complementary technique called UPS (Ultraviolet Photoelectron Spectroscopy) in which the ultraviolet photon, with much lower energy than the X-ray interacts with valence levels of the atom, leading to ionization by removal of one of the valence electrons.

Related Topics:
Photon - Atom - Ionization - Shell - X-ray - Valence electrons

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In XPS, because the energy of core electrons is very specific for the element that the atom belongs to, the spectrum gives information on the elemental composition of the shallow surface region.

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From small shifts in the binding energies additional chemical information can be derived (e.g. the oxidation state of the element).

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XPS is also often referred to as ESCA, short for Electron Spectroscopy for Chemical Analysis.

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