Shard, A G; Miisho, A; Vorng, J L; Havelund, R; Gilmore, I S; Aoyagi, S (2021) A two-point calibration method for quantifying organic binary mixtures using secondary ion mass spectrometry in the presence of matrix effects. Surface and Interface Analysis, 54 (4). pp. 363-373.

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Abstract

Quantification of the composition of binary mixtures in secondary ion mass spectrometry is required in the analyses of technological materials from organic electronics to drug delivery systems. In some instances, it is found that there is a linear dependence between the composition, expressed as a ratio of component volumes, and the secondary ion intensities, expressed as a ratio of intensities of ions from each component. However, this ideal relationship fails in the presence of matrix effects and linearity is observed only over small compositional ranges, particularly in the dilute limits. In this paper we assess an empirical method which introduces a power law dependence between the intensity ratio and the volume fraction ratio. A previously published model of the organic matrix effect is employed to test the limits of the method and a mixed system of 3,3’-bis(9-carbazolyl) biphenyl and tris(2-phenylpyridinato)iridium(III) is used to demonstrate the method. Previous work had shown that quantification of this mixture with SIMS using an assumption of linearity was possible for volume fractions of the iridium coordination compound up to 0.055. In these mixtures there are pronounced matrix effects which invalidated traditional quantification procedures except in the dilute limit. This paper introduces a two-point calibration, which determines the exponent in the power law and the sensitivity factor for the conversion of ion intensity ratio into volume fraction ratio. We demonstrate that this provides significantly improved accuracy over a wide compositional range in SIMS quantification and a weak dependence on matrix effects. For the material system studied here and using the molecular secondary ions, which display the strongest matrix effects, we find that an accuracy of better than 0.005 in fractional volume can be achieved with volume fractions of the iridium coordination compound ranging from zero to 0.42, the highest concentration analysed. Since the method enables the use of clearly identifiable secondary ions for quantitative purposes and mitigates many common matrix effects, the two-point calibration method could be of significant benefit to SIMS analysts.

Item Type:	Article
Keywords:	secondary ion mass spectrometry; organic electronics; matrix effects; calibration; quantitation; metrology; surface analysis; molecular; ions enhancement suppression
Subjects:	Nanoscience > Surface and Nanoanalysis
Divisions:	Chemical & Biological Sciences
Identification number/DOI:	10.1002/sia.7042
Last Modified:	04 Jul 2024 13:57
URI:	https://eprintspublications.npl.co.uk/id/eprint/9497