In XPS photons with sufficient energy are absorbed by a system causing core electrons to be ejected from the sample. XPS is based on the creation of a core hole via ionization and provides a method to study the geometric, electronic and chemical properties of a sample. The excited electron can either participate in the decay process or be passive as a spectator leading to very different types of final states as shown below. These events are called resonant processes and can involve radiant and non-radiant decays. The two steps, creation and decay, can lead to coupling and the whole process can be considered a one step event. However, an initial state with the core electron instead excited into a bound state can modify the decay process. These events only consider a core-ionized initial state prior to the decay. The radiant decay of the core holes forms the basis for XES while non-radiant decay is studied in AES, both of which provide tools for probing ocuppied electronic structure of a model system. The atom relaxes via a radiant or a non-radiant process. The creation of a core hole by ionization forms the basis for XPS while the creation of a core hole by excitation is studied in XAS.Īfter ionization the atom is in a highly excited state due to the creation of the core hole. This absoprtion causes the core electron to be excited to a bound state or to the continuum where it will become a free particle. We can create a core-hole through the absorption of incoming light with energy matched to the binding energy of a core electron. The creation of core holes forms the basis for: The different techniques can be separated into two classes, which corresponds to the creation and decay of core-holes. The resulting excitations and relaxations form the basis for the various core level x-ray spectroscopies. The core-hole decays by radiant and non-radiant processes. The ejection of a core electron is initiated by the absorption of an x-ray photon (produced by synchrotron radiation) with energy tuned to the electron's ionization as shown here.Ĭore-holes are created by core-level ionization and x-ray absorption processes. Core level spectroscopies are a group of different techniques to obtain element-specific information of the electronic structure around an absorption site and are thereby suitable tools to study the chemical state, local geometric structure, nature of chemical bonding, and dynamics in electron transfer processes centered around one atomic site.
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