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2. EXPERIMENTAL METHODS hν = |EB| + φ + Ekin. (2.3) The equation states that an electron that has a binding energy Eb with re- spect to Fermi level, and is irradiated by a photon with energy ω, leaves the system with kinetic energy Ekin if the photon energy is high enough to be used to overcome the energy barrier Φw between the solid surface and vacuum, called the work function. This simplified picture of a single-particle system does not take into account the complexity of any solid-state system. An important role is also played by other effects that influence the energy and thus energetic distribution of electrons. They involve Auger effect, multiplet splitting, shake-up process and any other interaction of the photoelectron with electrons and ions in the system. By analysing the kinetic energy of electrons excited by a discreet wavelength - the binding energy of electrons in the investigated material is retrieved. The obtained spectrum of binding energies is unique for a given material and serves as a tool to identify chemical elements, based on the approximation that electrons in a solid are reside in orbitals. This is the most basic use of XPS method and explains the early acronym of the technique - ESCA - Electron Spectroscopy for Chemical Analysis. In samarium nickelate the basic, survey spectrum collected for Al radiation reveals (figure 2.6) several important features characteristic to XPS such as 1. main photoelectron emission lines for oxygen (O1s, O2s), nickel (Ni2s, Ni2p3/2, Ni2p1/2, Ni3s, Ni3p), samarium (Sm3d3/2, Sm3d5/2, Sm4s, Sm4p, Sm4d, Sm5s, Sm5p) 2. Auger electron peaks that arise from secondary excitation of electron due to filling of PE hole by an electron from higher level. Their energy depends only on the difference between certain electronic levels. These appear for nickel (LMM series L3M23M23, L2M23M23, L3M23M45(1P), L3M23M45(3P), L2M13M45(1P), L3M45M45), oxygen (KLL series KL1L1, KL1L23, KL23L23), samarium (MNN series M45N45N45) 3. carbon contamination line C1s and its Auger line KVV 4. background formed due to inelastically scattered photoelectrons. Because the irradiated material is a many-body system, the photoionization process causes several final state effects that in XPS cannot be disregarded. The 44PDF Image | Investigation of metal-insulator transition in magnetron sputtered samarium nickelate thin films
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