X‐Ray Photoelectron Spectroscopy

Abstract

AbstractX‐ray photoelectron spectroscopy (XPS) uses x‐rays of a characteristic energy (wavelength) to excite electrons from orbitals in atoms. Photoelectrons are emitted from the material and collected as a function of their exiting kinetic energy. For single‐step excitation processes, the initial binding energy of the photoelectron is related through energy conservation to its kinetic energy and the x‐ray energy. A typical XPS spectrum shows intensity of electrons as number of electrons per time versus electron binding energy. Features appear in the spectrum due to photoemission from specific binding energy states (excitation from orbitals) in the material and to interactions of the escaping photoelectrons within the material. Chemical elements give rise to peaks at defined binding energies that are from their core levels. The total, integrated photoelectron emission from a core level peak is proportional to the number of orbitals in the analysis volume. This relationship is used to quantify the relative elemental composition of the material in atom percent (at%). The binding energy positions and shapes of the core level peaks and of other excitation features can also be analyzed in detail to determine chemical state information, including oxidation states, partial charges, or hybridization of the elements. The ability to provide both quantitative elemental composition and orbital bonding state information makes XPS unique and gives rise to the additional name as electron spectroscopy for chemical analysis (ESCA).