In many cases, though, reference materials are not available or are not available in pure form or in known compositions, and in these cases spectra from advanced materials can be difficult to interpret. Consequentially, the importance of X-ray photoelectron spectroscopy (XPS), its spectra interpretation, and the quantification obtainable from it has grown dramatically.Īt NEXUS (the UK National EPSRC XPS Users' Service), we often need to make comparisons between XPS spectra from our users' samples and spectra we record from pure standard materials. Examples of the application of surface analysis are biology and bioengineering (characterization of immobilized antibodies, 1, 2 interaction between replacement joints with bones and tissues 3, 4) catalyst (characterization and behavior understanding 5, 6) coatings 7 corrosion 8, 9 defect analysis 10 fouling 11 and many others.
With the discovery of new materials and new applications for those known, the need for surface and interface analysis has notably increased. Furthermore, a series of results for molecules, containing elements of the second and the third row of the periodic table, are presented and compared with experimental results, in order to establish the quality and fitness-for-purpose of the quantum chemical-based predictions. In this work, we present a general summary of the methods for the calculation of the core electron binding energies and compare the use of 2 of these methods using the popular “GAUSSIAN” software package. In practice, though, care needs to be taken in the approximations, assumptions, and settings used in applying such software to calculate binding energies. In principle, such calculations have become much easier than in the past, due to the availability of powerful personal computers and excellent software. However, reference materials are not always available, so that it becomes necessary to estimate the binding energies of likely components through quantum chemical calculations. In many cases, reference spectra taken from pure reference samples of the chemical components can aid the peak fitting procedure. Often, these shifts are small, or an element is present in several oxidation states in the same sample, so that interpretation of the spectra is difficult without good reference data on binding energies of the likely constituents. Chemical shifts observed in high-resolution X-ray photoelectron spectroscopy (XPS) spectra are normally used to determine the chemical state of the elements of interest.
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