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Linearity of the instrumental intensity scale in TOF-SIMS - a VAMAS interlaboratory study.

Lee, J L S; Gilmore, I S; Seah, M P (2012) Linearity of the instrumental intensity scale in TOF-SIMS - a VAMAS interlaboratory study. Surf. Interface Anal., 44 (1). pp. 1-14.

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A VAMAS interlaboratory study involving 21 time of flight secondary ion mass spectrometry (TOF SIMS) instruments from 9 countries has been conducted to evaluate the linearity of the instrumental intensity scale and procedures for intensity correction. Analysts were supplied, by NPL, with a protocol for analysis (closely aligned with ISO 23830) together with a reference material of poly(tetrafluoroethylene) (PTFE) tape. The primary ion beam current is varied to provide secondary ion intensities that span the linear to non-linear regime. The natural carbon isotope ratios 12CxFy+ / 13C12Cx 1Fy+ 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 participating instruments 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 and robust, and provides an excellent basis for the development of an ISO standard.

Item Type: Article
Keywords: Detector saturation, Dead time, Dead time correction, Secondary ion mass spectrometry, Interlaboratory comparison, VAMAS, Counting statistics, Intensity Linearity
Subjects: Nanoscience
Nanoscience > Surface and Nanoanalysis
Identification number/DOI: 10.1002/sia.3761
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5366

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