Auger electron spectroscopy (AES) is an analytical technique used to determine the composition of surface layers of a sample. It involves three steps: (1) removing a core electron from an atom via ionization, typically using a 2-10 keV electron beam; (2) an electron dropping to fill the vacancy, releasing energy; (3) this energy causes the emission of an Auger electron. AES collects these low-energy (20-2000 eV) Auger electrons that escape from within 50 angstroms of the surface, allowing it to provide compositional information about just the sample's surface.