Standard test data for x-ray photoelectron spectroscopy (XPS-STD) have been developed for determining bias and random error in peak parameters derived from curve fitting in XPS. The XPS-STD are simulated C 1s spectra from spline polynomial models of measured C 1s polymer spectra. Some have a single peak, but most are doublet spectra. The doublets were created from a factorial design with three factors: peak separation, relative intensity of the component peaks, and fractional Poisson noise. These doublet spectra simulated XPS measurements made on different two-component polymer specimens. This, the second of a three-part study, focuses on bias and random errors in determining peak intensities. We report the errors in results from 20 analysts who used a variety of programs and curve-fitting approaches. Peak intensities were analyzed as a ratio of the intensity of the larger peak in a doublet to the total intensity, or as a ratio of intensities for singlet peaks in separate but related spectra. For spectra that were correctly identified as doublets, bias and random errors in peak intensities depended on the amount of separation between the component peaks and on their relative intensities. Median biases for doublets calculated on a relative, unitless scale from -1 to 1 ranged from -0.33 to 0.17, whereas random errors for doublets calculated on the same scale ranged from 0.016 to 0.18. In most cases the magnitude of the median bias exceeded the median random error. On this scale, errors of -0.33 and 0.18 corresponded to errors of factors of 4 and 2, respectively, in determinations of the relative intensities as a ratio of the larger peak in a doublet to the smaller peak. Analysts may evaluate uncertainties in their own analyses of the XPS-STD by visiting the web site http://www.acg.nist.gov/std/.
Citation: Surface and Interface Analysis
Issue: No. 7
Pub Type: Journals
accuracy, algorithm testing, bias, curve fitting, peak intensity, precision, random error, reference data, XPS