Photoelectron spectroscopy is a technique used in the field of analytical chemistry and materials science to study the electronic structure of atoms, molecules, and solid surfaces. It involves shining high-energy photons onto a material, causing the ejection of electrons from the material's surface. By measuring the kinetic energy and angle of these emitted photoelectrons, researchers can determine information about the material's chemical composition, electronic band structure, and bonding characteristics. Photoelectron spectroscopy is commonly used in the study of surfaces, thin films, and nanomaterials.