X-ray Photoelectron Spectroscopy (XPS, ESCA)
X-ray photoelectron spectroscopy (XPS, also called electron spectroscopy for chemical analysis, ESCA) is a electron spectroscopic method that uses x-rays to knock electrons out of inner-shell orbitals. The kinetic energy (Ek) of these photoelectrons is determined by the energy of the x-ray radiation h(nu) and the electron binding energy (Eb) as given by:
EK = h(nu) - Eb
The electron binding energies are dependent on the chemical environment of the atom. XPS is therefore useful to identify the oxidation state and ligands of an atom.
The detection of photoelectrons requires that the sample be placed in a high vacuum chamber. Since the photoelectron energy depends on x-ray energy, the excitation source must be monochromatic. The energy of the photoelectrons is analyzed by an electrostatic analyzer and the photoelectrons are detected by an electron multiplier tube or a multichannel detector such as a microchannel plate.
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