2. Photoelectron spectroscopy

Due to the sudden changes in potential that a valence electron undergoes in the vicinity of a surface, electronic states specifically localized in this region can appear. After their theoretical prediction in the 1930s, these surface states remained essentially a theoretical concept for over thirty years, until the development of ultra-high vacuum production and surface analysis techniques paved the way for their detection by optical and electronic spectroscopy. The dominant technique for the experimental study of the electronic structure of molecules, aggregates, solids and their surfaces is electronic photoemission spectroscopy (PES – photoelectron spectroscopy ), with all its variants, which can probe both bulk and surface electronic states, whether occupied or unoccupied. Angularly resolved photoemission, whether direct (ARPES or ARUPS) or inverse (ARIPES or KRIPES), is one of the most...