Photoemission spectroscopy

Regardless of the incident photon beam, however, all photoelectron spectroscopy revolves around the general theme of surface analysis by measuring the ejected electrons.

[2] X-ray photoelectron spectroscopy (XPS) was developed by Kai Siegbahn starting in 1957[3][4] and is used to study the energy levels of atomic core electrons, primarily in solids.

Later, Richard Smalley modified the technique and used a UV laser to excite the sample, in order to measure the binding energy of electrons in gaseous molecular clusters.

The technique is used to map the band structure of crystalline solids, to study quasiparticle dynamics in highly correlated materials, and to measure electron spin polarization.

Two-photon photoelectron spectroscopy (2PPE) extends the technique to optically excited electronic states through the introduction of a pump-and-probe scheme.

Photoemission is also among the most sensitive methods of detecting substances in trace concentrations, provided the sample is compatible with ultra-high vacuum and the analyte can be distinguished from background.

By adding a source monochromator and increasing the energy resolution of the electron analyzer, peaks appear with full width at half maximum (FWHM) less than 5–8 meV.