Calculated core-level sensitivity factors for quantitative XPS using an HP5950B spectrometer (original) (raw)
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The alignment of spectrometers and quantitative measurements in X-ray photoelectron spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 1997
The alignment of the sample in X-ray photoelectron spectrometers is usually made to optimize the spectral intensities. There are two important classes of spectrometer: (i) those in which the analyser acceptance area is independent of the analysed electron kinetic energy; and (ii) those in which this area varies. Model experiments show how an example of a VG ESCALAB II conforms to class (i) whereas an example of an SSI X-probe is of class (ii) and shows an analyser acceptance area which depends approximately inversely on the emitted electron kinetic energy. This latter result means that the SSI X-probe spectrometer must be aligned for the electrons of the highest kinetic energy (smallest analyser acceptance area). A misalignment of 0.1 mm in the sample height can cause a 10% change in the relative intensities between 0 and 1000 eV binding energies. This dependence of the analyser acceptance area with energy is an effect likely to be common in the advanced electron optical systems of modern electron spectrometers and should be understood in order to use such spectrometers effectively. Such dependencies should be determined by analysts for their own instruments in the operating mode that is used for conducting work in which the repeatability of intensity measurements is important.
Enhancing the interpretation of x-ray photoelectron spectra using numerical methods
Surface and Interface Analysis, 1992
X-ray photoelectron spectroscopy (XPS) has long been used as a surface analytical method for the determination of elemental composition and chemistry of a material. Small-area analysis allows the comparison of different areas of a sample surface, while sputter depth profiling makes it possible to follow the specific chemistry as a function of depth. Often in XPS, peak overlap or subtle changes in chemistry may sometimes make the chemical-state analysis of the elements in a material difficult. By using a variety of numerical methods, it is possible to enhance the analysis and interpretation of surface analytical data. Such numerical methods would include linear least-squares fitting and target factor analysis. By using these methods it is possible to enhance the chemical-state interpretation and in many cases significantly increase the detection limits of specific elements. Several examples of the application of numerical methods are used to illustrate the enhancement of data interpretation of XPS data, with special emphasis on linescans and sputter depth profiles.
On the relation between X-ray Photoelectron Spectroscopy and XAFS
Journal of Physics: Conference Series, 2013
XAFS and X-ray Photoelectron Spectroscopy (XPS) are element specific techniques used in a great variety of research fields. The near edge regime of XAFS provides information on the unoccupied electronic states of a system. For the detailed interpretation of the XAFS results, input from XPS is crucial. The combination of the two techniques is also the basis for the so called core-hole clock technique. One of the important aspects of photoelectron spectroscopy is its chemical sensitivity and that one can obtain detailed information about the composition of a sample. We have for a series of carbon based model molecules carefully investigated the relationship between core level photoelectron intensities and stoichiometry. We find strong EXAFS-like modulations of the core ionization cross sections as function of photon energy and that the intensities at high photon energies converge towards values that do not correspond to the stoichiometric ratios. The photoelectron intensities are dependent on the local molecular structure around the ionized atoms. These effects are well described by molecular calculations using multiple scattering theory and by considering the effects due to monopole shake-up and shake-off as well as to intramolecular inelastic scattering processes.
Surface and Interface Analysis, 2000
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/.
Journal of Electron Spectroscopy and Related Phenomena, 2014
In order to achieve the most accurate quantification results in an X-ray photoelectron spectroscopy (XPS) experiment, a fine calibration of the analyzer response is required. In this work an experimental characterization of a modern angle-resolved analyzer, carried out with a unfocused and a highly collimated synchrotron source, is shown. The transmission function is extrapolated from the discrepancy between experimental and theoretically predicted XPS peak areas; the influence of different sensitivity factors and of the escape depth correction on the expected values is also discussed. The analyzer response and the theoretical approach are then tested against energy dispersive XPS measurements (EDXPS). These results are finally compared with TF calculated on the basis of an high accuracy electron ray tracing code, also described in this work.
Recent developments in instrumentation for x-ray photoelectron spectroscopy
Analytical Chemistry, 1989
X-ray photoelectron spectroscopy (XPS or ESCA) is one of the many electron spectroscopies particularly useful for the chemical analysis of surfaces. The technique, based on the photoemission of electrons induced by soft X-rays, is widely used for detailed surface analytical problem solving hecause it allows multiple-element detection, provides chemical bonding and state information from chemical shifts, and provides quantitative information.
Modeling of X-ray photoelectron spectra: surface and core hole effects
Surface and Interface Analysis, 2014
The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and by intrinsic excitations induced by the sudden creation of the static core hole. Besides, elastic electron scattering may also be important. These effects should be included in the theoretical description of the emitted photoelectron peaks. To investigate the importance of surface and core hole effects relative to elastic scattering effect, we have calculated full XPS spectra for the Cu 2p emissions of Cu and CuO with the simulation of electron spectra for surface analysis (SESSA) software and with a convolution procedure using the differential inelastic electron scattering cross-section obtained with the quantitative analysis of electron energy loss in XPS (QUEELS-XPS) software. Surface and core hole effects are included in QUEELS-XPS but absent in SESSA while elastic electron scattering effects are included in SESSA but absent in QUEELS-XPS. Our results show that the shape of the XPS spectra are strongly modified because of surface and core hole effects, especially for energy losses smaller than about 20 eV.