These background shapes are dependent on the material under analysis and significant variation occurs in practice. Figure 2 illustrates the rapid changes to the background resulting from energy loss processing occurring as the photoelectrons are ejected from the surface material. The data in Figure 1 represents a relatively simple case, where most analysts would use a linear background approximation, however in general, the background to XPS peaks are far from simple. When peak-fitting XPS spectra a further issue is the nature of the background signal on top of which the synthetic peaks must sit. Without these inputs any model designed purely on the spectral envelope would be a cause for concern. Understanding the chemistry is important as it suggests the number of chemical states and therefore number of peaks in this example is four introducing parameter constraints to restrict the peak widths and relative intensities of the peaks force the peak model to obey the chemistry. The fit in Figure 1 is guided by the chemical formula for nylon. that a good fit is always achieved by a sufficient number of Gaussian-Lorentzian curves when optimized without constraints.
#OH RADICAL XPS PEAK SOFTWARE#
The problem is 1Ĭopyright © 2006 Casa Software Ltd. Sadly, while central to XPS, peak fitting of line-shapes to spectra is far from simple and if treated as a black-box tool will almost always yield incorrect results. The C 1s spectrum clearly contains two chemically shifted C 1s peaks however the more subtle shifts associated with the peaks labelled CH2 are the reason peak fitting is an important tool in XPS.įigure 1: C 1s region measured using a Kratos Axis 165 from a nylon sample. Consider the XPS spectrum (Figure 1) of the carbon 1s electrons measured from a nylon sample the chemical formula for nylon indicates four chemical environments for a carbon atom. These chemically shifted peaks offer information about the chemistry of the surface.
![oh radical xps peak oh radical xps peak](https://media.springernature.com/full/springer-static/image/art%3A10.1038%2Fs41467-021-27240-5/MediaObjects/41467_2021_27240_Fig1_HTML.png)
In terms of an XPS spectrum, the increase in counts as a function of kinetic energy associated with the excitation of a core level electron appears as an ensemble of peaks rather than a single peak. These variations in the initial and final state energy are due to the environment in which an atom is found and results in electrons ejected from the same element emerging with kinetic energy characteristic of the chemical state in which the element exists. Peak Fitting in XPS Small and sometimes not so small differences between the initial and final state of an atom when a core level electron is excited by an x-ray is fundamental to XPS as an analytical technique.