Photoelectron

Photoelectron refers to an electron ejected from an atom, molecule, or solid as a result of absorbing photons with energies exceeding the binding energy of the electron. The photoelectric effect, which describes this process, is fundamental to the study of light–matter interactions and underpins techniques and devices such as photoelectron spectroscopy and solar cells.

The kinetic energy of a photoelectron is described by KE = hν − φ, where h is Planck’s constant, ν is the photon frequency, and φ is the work function—the energy needed to remove an electron from a surface or the ionization energy in a gas. If hν is less than φ, emission does not occur. In solids, the work function depends on the material and surface condition and ranges from a few tenths to several electron volts.

In metals, emitted photoelectrons exhibit a spectrum of kinetic energies reflecting the initial electronic states and the photon energy. The angular distribution of emission depends on light polarization and the orbital origin of the electron. Photoelectrons are typically detected with electron spectrometers; analysis of kinetic energy and stopping potential yields information about binding energies and electronic structure.

Applications of photoelectrons include photoelectron spectroscopy, such as X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), used to determine elemental composition and chemical states. Photoemission also plays a role in solid-state devices and imaging techniques like photoelectron microscopy, where emitted electrons reveal surface and near-surface properties.

The concept was explained by Albert Einstein in 1905, introducing light quanta (photons) and linking photon energy to material work functions and emitted electron energy.