Photoemission spectroscopy (PES) is an analytical technique used to investigate the electronic properties of materials. It involves the absorption of photons (light) by a sample, which results in the emission of electrons. The primary goal of PES is to study the energy and distribution of these emitted electrons, providing valuable insights into the material's electronic structure. ### Basic Principles: - **Excitation:** A sample is irradiated with high-energy photons, typically from ultraviolet or X-ray sources.
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Photoelectron spectroscopy measures the kinetic energies of photoelectrons produced by illuminating matter with photons of known energy. The photoelectric effect supplies the emission mechanism; spectroscopy turns the distribution of emitted electron energies into information about occupied energy levels and chemical bonds. A broad survey helps identify chemical elements, while small shifts within one element's lines can distinguish different chemical surroundings. These are different questions: finding carbon does not establish which chemical bonds its chemical atoms form.
The useful inversion is an energy balance. A known incoming photon energy pays for removal of an electron and for its outgoing kinetic energy. To apply that balance to a solid, specify the zero of energy and the work function of the instrument. Photoelectron binding energy reference derives the conversion for a conducting sample in electrical contact with its analyzer. A free molecule instead has an ionization energy referenced to an electron at rest in vacuum; it need not share a Fermi level with the analyzer.