STANDARD TEST DATA FOR ESTIMATING PEAK-PARAMETER ERRORS IN X-RAY PHOTOELECTRON-SPECTROSCOPY - I - PEAK BINDING-ENERGIES

Standard test data (STD) are simulations of analytical instrument resp onses that help to determine the veracity of computer-based, data anal ysis procedures that are typically used with instruments. The STD were developed for determining errors in peak parameters obtained from dat a analysis algorithms used in x-ray photoelectron spectroscopy (XPS). The STD were mainly C 1s doublet spectra constructed from spline polyn omial models of measured C 1s polymer spectra. Different spectra were created based on a replicated factorial design with three factors: pea k separation; relative intensity of the component peaks; and fractiona l Poisson noise. These doublet spectra simulated XPS measurements made on different two-component specimens. Single-peak C 1s spectra for in dividual polymers were also simulated, to provide the null case for id entification of the doublet spectra. Twenty analysts used a variety of data analysis programs and a variety of curve-fitting approaches to d etermine peak binding energies. Results indicate that data analysis of doublet spectra may be problematic, because up to 50% of the STD doub lets were assigned incorrectly as singlets. For spectra that were corr ectly identified as doublets, bias and random error in peak binding en ergies depended on the amount of separation between the component peak s and on their relative intensities. Biases ranged from -0.055 eV to 0 .34 eV, while random errors ranged from 0.012 eV to 0.13 eV. Use of th e Gaussian-Lorentzian function fitted to spectra resulted in smaller b iases than the use of a Gaussian function alone. As a guide to evaluat ing peak energy uncertainties in their own analyses, analysts may find it useful to analyze the STD themselves and then compare their result s with those reported here. The spectra may be obtained at http://www. acg.nist.gov/std/main.html. (C) 1998 John Wiley & Sons, Ltd.