X-ray photoemission spectroscopy analysis

J. Stumper, H. J. Lewerenz, and C. Pettenkofer, X-ray photoemission spectroscopy analysis of Si(lll) under photocurrent-doubling conditions, Phys. Rev. B 41(3), 1592, 1990. 

Niwa H, Kobayashi M, Horiba K, Harada Y, Oshima M, Terakura K, Ikeda T, Koshigoe Y, Ozaki JI, Miyata S, Ueda S, Yamashita Y, Yoshikawa H, Kobayashi K (2011) X-ray photoemission spectroscopy analysis of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells. J Power Sources 196 1006-1011... 

X-Ray Photoelearon Spectroscopy X-Ray Photoemission Spectroscopy Electron Spectroscopy for Chemical Analysis X-Ray Photoelectron Diffraction Photoelectron Diffraction Kinetic Energy... 

In the mid-50 s it was observed that the energy of a photoelectron, ejected from the core of an atom by an X-ray photon, is a rather sensitive probe of the chemical environment of the atom. From this observation has evolved a major research technique named electron spectroscopy for chemical analysis (ESCA) by the Uppsala group 1,2) which pioneered the subject and called X-ray photoemission spectroscopy (XPS) by many others. The field has developed rapidly a third generation of spectrometers is in use at many laboratories and the understanding of the spectra observed is improving apace. A view of the current status of X-ray photoelectron spectroscopy in application to metals and alloys is presented in this article. We have not been encyclopedic in describing what has been done we have instead attempted to cover the classes of results obtained and the kinds of problems encountered in interpretation of these results. 

Photoemission spectroscopy applied to chemistry and electronic properties studies is a fairly recent development. The x-ray photoemission spectroscopy (XPS) technique was developed, primarily to be a chemical analysis tool (1). In particular it was observed that the absolute binding energies of the atomic-like electron core levels are dependent on the chemical state of the atom under study. This observation led to the widespread use of XPS for basic and applied chemistry studies. Many studies were also undertaken to better understand the physics of the various excitation processes involved. Consequently, XPS has become a powerful tool for studying electronic structure of the outer electron states in solids. 

During the last 5 to 10 years there has been much interest in electron spectroscopies (Hiifner and Steiner 1982), since it was realized that these also suggest a very different picture of mixed valence Ce compounds. Valence photoemission spectroscopy (PES) studies showed that the f-spectrum of Ce has weight at (8p ) — 2eV below Ep (Platau and Karlsson 1978, Johansson et al. 1978). It was further found that core level X-ray photoemission spectroscopy (XPS) measurements were hard to understand unless A (Fuggle et al. 1980b) is much larger than previously assumed. This discrepancy between the interpretations of spectroscopic and thermodynamic data showed the need for a theoretical analysis, based on a microscopic model, of what kind of information can be extracted from different experiments. This was further emphasized when PES studies showed f-character in the spectrum both at —2eV and close to 8p = 0 (Martensson et al. 1982). This observation created a lively debate about how to interpret the PES spectra. 

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

Four UHV spectroscopies used for the compositional and chemical analysis of surfaces are discussed. These are X-ray Photoemission, Auger Spectroscopy, Secondary Ion Mass Spectroscopy, and Ion Scattering (both low and high energy). Descriptions of the basic processes and information contents are given, followed by a comparative discussion of the surface sensitivities, advantages and disadvantages of each spectroscopy. 

The elemental composition of the surface can be obtained with ESCA (Electron Spectroscopy for Chemical Analysis or X-ray Photoemission), Auger (24) or X-ray fluorescence. In addition, the information on the chemical bonds can be recovered from the energy shifts in ESCA studies. 

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