fotoemissio

Fotoemissio, commonly referred to as photoemission, is the emission of electrons from a material as a consequence of absorbing photons. The process is most often studied for solid surfaces, where electrons near the surface can escape into vacuum if the photon energy is sufficient to overcome the surface work function and any initial binding energy.

In a simple description, an electron with initial energy E_i relative to the vacuum level emits with kinetic energy E_k = hν − φ − E_i, where hν is the photon energy and φ is the work function of the surface. For electrons at the Fermi level (E_i ≈ 0), E_k ≈ hν − φ. Emission occurs when hν exceeds the work function; higher photon energies can liberate electrons from deeper states within the material. Internal photoemission can also occur in semiconductors, where photons excite electrons across barriers inside the material before emission.

Photoemission provides direct information about electronic structure. Photoemission spectroscopy (PES) measures the energy distribution of emitted electrons to determine binding energies and, in angle-resolved variants (ARPES), the momentum of electrons, revealing band structures and surface states. Time-resolved photoemission uses ultrafast light pulses to follow electron dynamics after excitation.

Historically, the photoelectric effect was explained by Albert Einstein in 1905, introducing the concept of light quanta and the photoelectric equation. Experiments by Hallwachs and others established early evidence for emission from metals, and Einstein’s work earned the Nobel Prize in Physics in 1921.

Applications of fotoemissio include vacuum photocathodes for electron sources, photoemission electron microscopy (PEEM), and extensive use in surface science, catalysis research, and condensed matter physics to study electronic structure and material properties.