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  • 1
    Electronic Resource
    Electronic Resource
    Energy Calibration of X-ray Photoelectron Spectrometers. II. Issues in Peak Location and Comparison of Methods (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 777-787 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; x-ray photoelectron spectroscopy ; energy calibration ; peak location ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An analysis is presented of issues involved in peak location for the calibration of the binding energy (BE) scales of x-ray photoelectron spectrometers. These issues include the effects of peak asymmetry, the surface core-level shift, and the avoidance of a sloping background when fitting spectra for energy calibration purposes. Examples of uncertainty budgets for BE measurements are then presented in which illustrative values are shown for the repeatability standard deviation (for repeated BE measurements of the same calibration peak), the expanded uncertainty (at the 95% confidence level) for BE measurements following calibrations based on different numbers of peak measurements, and the tolerance for BE-scale drift and non-linearity for two chosen values (±0.1 and ±0.2 eV) of the total expanded uncertainty for a BE measurement (at the 95% confidence level). It is recommended that a user prepare an uncertainty budget of this type to show clearly the sources of random and systematic error in BE measurements following a calibration.The reference data published by the UK National Physical Laboratory for BE-scale calibration were obtained from fits with a quadratic function to a group of points comprising the top 5% of each peak. Most commercial x-ray photoelectron spectrometers have software available for spectrum synthesis, and we consider here the use of the commonly available Lorentzian, Gaussian, and asymmetric Gaussian functions for peak location. Illustrative fits with Cu 2p3/2 spectra (measured with unmonochromated Al x-rays) showed that comparable accuracy and precision could be obtained with Lorentzian and Gaussian functions as with the quadratic-equation method when different fractions of the peak were fitted. For this asymmetrical line, the asymmetric Gaussian function allowed better accuracy and precision to be obtained with a greater fraction of the line than was possible with the symmetrical functions. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Energy calibration of X-ray photoelectron spectrometers. Part III: Location of the zero point on the binding-energy scale (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 606-614 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; x-ray photoelectron spectroscopy ; calibration ; Fermi energy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Calibration of the binding energy scale in x-ray photoelectron spectroscopy (XPS) requires location of the zero point. This zero point has previously been identified with the inflection point in the Fermi-edge region of a valence-band photoemission spectrum of nickel. Comparison of photoemission spectra of nickel and silver measured with monochromated x-rays shows that the inflection points near the Fermi edge differ by 45±5 meV (where the stated uncertainty indicates the standard uncertainty) at an instrumental energy resolution of 0.30 eV. This difference is due to differences in the valence-band densities of states (DOS) of the two metals. Simulations of the Ni photoemission spectrum have been performed based on the DOS calculated by Eckhardt and Fritsche, and the simulated spectrum agrees well with the measured spectrum in the near-edge region. Additional simulations of the Ni photoemission spectrum have been carried out with both monochromated Al x-rays and unmonochromated Mg and Al characteristic x-rays to determine how the Ni near-edge inflection point varies with the energy resolution of the electron energy analyzer in XPS. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Calculations of Electron Inelastic Mean Free Paths (IMFPs) VI. Analysis of the Gries Inelastic Scattering Model and Predictive IMFP Equation (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 25-35 
    Details
    ISSN: 0142-2421
    Keywords: electron inelastic mean free path ; inelastic electron scattering ; calculated IMFP ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Gries has recently reported [Surf. Interface Anal. 24, 38 (1996)] an atomistic model for inelastic electron scattering relevant to Auger electron spectroscopy and x-ray photoelectron spectroscopy and has derived an equation (designated G1) for the estimation of inelastic mean free paths (IMFPs). We present an analysis of the Gries model and the G1 equation in terms of the similarities and differences of inelastic electron scattering by free atoms and by solids. We also compare the G1 equation with our TPP-2M equation for estimation of IMFPs. The former equation was developed from fits to our published IMFPs over the 200-2000 eV energy range, and is identical in its energy dependence to the Bethe equation for inelastic scattering cross-sections and to a simplification of our TPP-2M equation for the same energy range. Comparison of parameters indicates that the Gries fitting parameter k1 should be approximately 0.0016 and 0.0022 for non-transition and transition elements, respectively. We find that the G1 equation could be improved by allowing the Gries fitting parameter k2 to depend on density (as recommended for the equivalent parameter in TPP-2M). Although we believe that the Gries model is inconsistent with current theories for the electronic structure of metals, semiconductors and inorganic compounds, we find (from sum-rule considerations) that the G1 equation can provide an approximate guide to IMFP values. For some compounds, however, there were unexplained deviations (as found by Gries). In contrast to the G1 equation, the TPP-2M equation provides useful IMFP estimates for all materials over the parameter range that has been explored. Gries claims that the G1 equation can be extrapolated to energies lower than 200 eV on the basis of limited agreement with some experimental IMFPs over the 10-100 eV range for Be and the alkali metals, and has questioned the reliability of our IMFPs for energies below 200 eV. We consider this comparison to be inadequate, and we recommend that the G1 equation not be used in the 50-200 eV range. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Standard test data for estimating peak-parameter errors in x-ray photoelectron spectroscopy. I. Peak binding energies (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 939-956 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; reference data ; x-ray photoelectron spectroscopy ; peak fitting ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Standard test data (STD) are simulations of analytical instrument responses that help to determine the veracity of computer-based, data analysis procedures that are typically used with instruments. The STD were developed for determining errors in peak parameters obtained from data analysis algorithms used in x-ray photoelectron spectroscopy (XPS). The STD were mainly C 1s doublet spectra constructed from spline polynomial models of measured C 1s polymer spectra. Different spectra were created based on a replicated 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 specimens. Single-peak C 1s spectra for individual polymers were also simulated, to provide the null case for identification of the doublet spectra. Twenty analysts used a variety of data analysis programs and a variety of curve-fitting approaches to determine peak binding energies. Results indicate that data analysis of doublet spectra may be problematic, because up to 50% of the STD doublets were assigned incorrectly as singlets. For spectra that were correctly identified as doublets, bias and random error in peak binding energies depended on the amount of separation between the component peaks 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 the Gaussian-Lorentzian function fitted to spectra resulted in smaller biases than the use of a Gaussian function alone. As a guide to evaluating peak energy uncertainties in their own analyses, analysts may find it useful to analyze the STD themselves and then compare their results with those reported here. The spectra may be obtained at http://www.acg.nist.gov/std/main.html. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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