Improved method for XPS and ARXPS data fitting

【Author】

A. Herrera-Gomez;J. Muoz-Flores;

【Abstract】

X-Ray Photoelectron Spectroscopy can provide chemical and, if acquired at different angles, depth-profile information. Data-fitting is employed to quantify the various peaks contributing to a core-level spectrum. In most cases, each peak corresponds to a particular chemical environment. When the binding energy difference among the peaks is equal or larger than the width of the peaks, the quantification is straightforward. For cases in which the binding energy is smaller, the accuracy on the determination of the area, width, and center of the peaks becomes much more dependent on the noise level of the data. For quantitative studies, it is fundamental to employ data analysis methods that are the least sensible to noise. Sequential-fitting is a common practice on ARXPS data analysis. It consist on first estimating the center and width of the peaks from the data acquired at one of the angles, and then using those parameters as a starting guess for fitting the data for the rest of the angles. An improvement of this method consists on averaging the centers and widths of the peaks obtained at the different angles, and then employing these values to assess the areas of the peaks for each angle. The full-use of the combined information contained in the data-set is optimized by the simultaneous fitting method. It consists of the assessment of the center and width of the peaks by fitting the data at all the angles simultaneously. Computer-generated data was employed to compare the sensitivity regarding to noise between the sequential, averaged-sequential, and simultaneous fitting methods. It will be shown that the latter is significantly more robust and could provide reliable results even for very noisy data. Among the examples of the application of the simultaneous fitting method that will be presented is 1) the analysis of the O 1s and N 1s XPS data from hafnium oxynitride grown on silicon oxynitride nanofilms and 2) the discrimination of the sp2 and sp3 contributions to the C 1s XPS data in carbon nanofilms.

【Keywords】

Simultaneous fitting; Sequential fitting, Robust method, Noise, XPS, ARXPS, Data fitting

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