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Topography and field effects in secondary ion mass spectrometry - Part II: insulating samples.

Lee, J L S; Gilmore, I S; Seah, M P; Levick, A P; Shard, A G (2012) Topography and field effects in secondary ion mass spectrometry - Part II: insulating samples. Surf. Interface Anal., 44 (2). pp. 238-245.

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A study is conducted on the effects of sample topography on the secondary ion mass spectrometry (SIMS) analysis of insulating samples, using poly(ethylene terephthalate) (PET) fibres (diameter 100 um) as a model system and simulations of the ion extraction field using COMSOL. We focus on two significant issues: topographic field effects caused by the penetration of the extraction field into the sample, and the effect of charge compensation on the secondary ion images. Guidance is provided for setting the reflector voltage correctly for insulating fibres in reflectron SIMS instruments. The presence of the topographic sample distorts the extraction field, causing the secondary ions to be deflected laterally. This results in the severe loss of ion signals from the sides of the fibres due to the limited angular acceptance of the analyser. Strategies to reduce topographic field effects, including alternative sample mounting methods, are discussed. We also find that, in general, insulating samples are charged by the flood gun electrons resulting in a negative surface potential. This causes large variations in the SIMS images depending on the electron current, electron energy, raster mode and secondary ion polarity. Recommendations are given for analysts to obtain more reproducible images and reduce the effect of differential electron charging, for example by using a lower electron flood beam energy.

Item Type: Article
Keywords: Static SIMS, topography, imaging, field effects, charge compensation, surface potential, dielectric materials, differential charging, flood gun
Subjects: Nanoscience
Nanoscience > Surface and Nanoanalysis
Identification number/DOI: 10.1002/sia.3833
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5501

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