Fotoelektrons

Fotoelektrons, or photoelectrons, are electrons ejected from a material, typically a solid surface, after absorption of light. The phenomenon lies at the core of the photoelectric effect and underpins a range of surface analysis and imaging techniques. When photons strike a material, electrons can be emitted if the photon energy hν exceeds the work function φ, the minimum energy needed to remove an electron from the surface. The maximum kinetic energy of emitted electrons is Kmax = hν − φ (for electrons starting near the Fermi level). The emission probability, or quantum yield, depends on photon flux, photon energy, and the surface condition and material.

Historically, the photoelectric effect provided crucial evidence for the quantum nature of light. Albert Einstein explained it in 1905, introducing the concept of photons and thereby supporting the quantum theory of light; he received the Nobel Prize in Physics in 1921 for this work.

Applications include photoelectron spectroscopy, such as X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), which reveal elemental composition and electronic structure by measuring the kinetic energies and binding energies of photoelectrons. Angle-resolved variants (ARPES) map momentum-resolved electronic bands in solids. Photoelectrons are also utilized in detectors and imaging devices, including photoemission electron microscopy (PEEM) and certain vacuum-tube technologies, where light-induced electron emission is used for signaling or imaging. Surface properties—work function, cleanliness, and adsorbates—strongly influence emission.

Work functions vary widely, from about 2 eV for low-work-function materials to around 5 eV for many noble metals, typically requiring ultraviolet or higher-energy photons to trigger emission. The energy and angular distributions of photoelectrons encode information about a material’s surface electronic structure.