surfacephotoemission

Surface photoemission is the emission of electrons from a material’s surface when it is illuminated by photons with enough energy to overcome the surface work function. It is a central process in surface science and underpins photoemission spectroscopy techniques used to probe electronic structure at or near surfaces. Energy conservation in the one-step photoemission picture is often written as E_k = hν − φ − E_B, where hν is the photon energy, φ the work function, and E_B the binding energy of the initial state. The emitted electrons emerge from a shallow near-surface region, with escape depths of only a few atomic layers, making the process highly surface sensitive.

The probability and angular distribution of emitted electrons depend on photon energy, polarization, incidence angle, and the surface’s atomic arrangement and electronic states. Surface states, adsorbates, and chemical composition can imprint features on the spectra. Experimental implementations typically occur under ultra-high vacuum. Electron spectrometers measure kinetic energy, while angle-resolved variants provide momentum information parallel to the surface, enabling mapping of band structure.

Key techniques include ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and angle-resolved photoemission spectroscopy (ARPES). Two-photon photoemission (2PPE) and time-resolved PES extend capabilities to unoccupied states and ultrafast electron dynamics.

Applications span work function determination, surface composition and chemical state analysis, valence-band structure, and the study of surface states in materials such as graphene and topological insulators. Limitations arise from surface contamination, preparation requirements, and interpretive complexities related to final-state effects.