Efficiency of automated peak identification with daily used commercial software for X‐ray photoelectron spectra ‐ report from VAMAS/TWA 2/A 9 project

In the first step of X‐ray photoelectron spectroscopy (XPS) analysis, photoelectron peaks in a survey spectrum for the specimen of interest are generally identified as arising from particular elements and electron energy levels. This peak identification is performed using sophisticated software on commercial XPS instruments. For the Versailles Project on Advanced Materials and Standards (VAMAS)/Technical Working Area (TWA) 2/A 9 project, automated peak‐identification efficiency using commercial software utilities has been investigated with simulated test XPS spectra. This efficiency has been investigated with reference peaks that were detected by eye in our previous work [SIA, 2008, 40, 1337]. We found (i) one software that identified the binding energy (BE) at the peak maximum for a fitted curve in the peak region, a second that reported the BE stored in its database, and a third that reported the BE as the local maximum, (ii) software does not identify some weak peaks even though they were obviously detected by analysts, (iii) only one major peak of a doublet appeared to be in software database when the energy separation is less than about 4 eV such as 3.6 eV for Au 4f, and (iv) the identification efficiency is larger than 90% when the ratio between peak height and noise amplitude is greater than 10. We suggest several things for improving software design to assist non‐expert analysts. Copyright © 2013 John Wiley & Sons, Ltd.     

Final report on VAMAS round‐robin study to evaluate a correction method for saturation effects in DSIMS

A Versailles Project on Advanced Materials and Standards round robin test (RRT) has been conducted to evaluate the linearity of the instrumental intensity scale and correction method using an approximation intermediate extended dead time model with parameters derived from two different isotope depth profiles. Nine organizations in five countries participated. An arsenic‐implanted silicon wafer and a film of BN diffused into a Si wafer were supplied by the National Institute of Advanced Industrial Science and Technology along with instructions for the RRT. The instruments used to analyze ¹⁰³(AsSi)^? and ¹⁰⁵(AsSi)^? from arsenic‐implanted samples were five quadrupole‐type SIMS and four magnetic‐sector type SIMS. The instruments used to analyze ¹⁰B⁺ and ¹¹B⁺ from the BN‐diffused samples were three quadrupole‐type SIMS, four magnetic‐sector type SIMS, and one time‐of‐flight type SIMS. We validated the usefulness of the approximation intermediate extended dead time model to correct saturated intensities for all SIMS in this RRT. The optimum extension parameter ρ tends to be affected by the ratio of the maximum reliable intensity to the maximum intensity in raw profiles. From the ratio, ρ may be predicted when the intensity reaches full saturation. On the other hand, ρ is also affected by lateral non‐uniformity of intensity. In practice, because the maximum intensity does not reach full saturation and the intensity is not laterally uniform, ρ is likely to be smaller than its predicted value. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficiency of visual peak detection in X‐ray photoelectron spectra

We report initial results of a VAMAS/TWA2 project to evaluate procedures for automated peak detection in X‐ray photoelectron spectra. As a reference for investigations of the efficiency of automated peak‐detection software, we report the efficiency of visual peak detection in three test spectra. It was found that (i) characteristics of analysts are grouped into four categories using principal component analysis (PCA); the first participant group to detect large numbers of peaks for the three test spectra, the second one to detect small numbers of peaks for them, the third one to detect similar numbers of peaks, and the fourth one to detect a relatively large number of peaks for one of them and small numbers for two of them, (ii) scattering of detected peak numbers seems to depend on detection of medium‐intensity peaks because of participants' subjectivity or ambivalence for judgment of intensity, and (iii) the peaks that are detected by the analysts with a detectability more than 75% almost correspond to the peak signal‐to‐noise(S/N) ratio of more than 10 in logarithmic expression. Copyright © 2008 John Wiley & Sons, Ltd.     

Linearity of the instrumental intensity scale in TOF‐SIMS—a VAMAS interlaboratory study

A VAMAS interlaboratory study involving 21 time‐of‐flight SIMS instruments from nine countries has been conducted to evaluate the linearity of the instrumental intensity scale and procedures for intensity correction. Analysts were supplied, by National Physical Laboratory (NPL), with a protocol for analysis (closely aligned with ISO 23830) together with a reference material of polytetrafluoroethylene (PTFE) tape. The primary ion beam current is varied to provide secondary ion intensities that span the linear to nonlinear regime. The natural carbon isotope ratios ¹²C_xF_y⁺/¹³C¹²C_x?1F_y⁺ for five peaks are used to evaluate the linearity, without a need to measure the ion beam current. A method is given for determining the linearity as a function of secondary ion intensity, with and without dead time correction. It is found that single ion counting statistics is closely obeyed, and the linearity achievable is generally excellent with careful application of dead time correction. Three quarters of instruments in the study achieved better than 95% linearity at a count rate of 0.8 measured counts per pulse, equivalent to 1.6 secondary ions impinging the detector per primary ion pulse. We discuss factors affecting linearity and the precise application of dead time correction and give guidance for practical analysis. This includes suboptimal detector efficiency, inhomogeneous intensities across the rastered area, inadequate charge compensation, and the choice of peak integration limits. The interlaboratory study shows that the method to determine linearity is generally applicable, robust and provides an excellent basis for the development of an ISO standard. © Crown copyright 2011. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.