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Topography and field effects in secondary ion mass spectrometry - Part I: conducting samples.

Lee, J L S; Gilmore, I S; Seah, M P; Fletcher, I W* (2011) Topography and field effects in secondary ion mass spectrometry - Part I: conducting samples. J. Am. Soc. Mass Spectrom., 22 (10). pp. 1718-1728.

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Quantitative chemical characterisation of surfaces with topography by Secondary Ion Mass Spectrometry (SIMS) remains a significant challenge due to the lack of systematic and validated measurement methods. In this study we combine an experimental approach using a simple model system, with computer simulation using SIMION, to understand and quantify the key factors that give rise to unwanted topographical artefacts in SIMS images of conducting samples. Experimental data are acquired for gold wires (diameters 33 to 125 um) mounted onto silicon wafers. Significant loss of ion intensities and shadowing arise from the distortion of the extraction field, and the chemical analysis over the whole of the sample surface is difficult. For large primary ion incidence angles of > 55° to the surface normal, a fraction of the primary ions are scattered from the target and impact the substrate, emitting secondary ions which may be mistaken as originating from the wire. For conducting samples, topographic field effects may be reduced by the use of a lower extraction voltage and an extraction delay. The effects of an extraction delay on ion intensities, mass resolution and time-of-flight are studied, and its application is demonstrated on an anisotropically etched silicon sample. The use of a simple sample holder with a V-shaped groove to reduce topographic field effects for wires is also presented. Using these results, we provide clear guidance to analysts for the diagnosis and identification of topography effects in SIMS, and present key recommendations to minimise them in practical analysis.

Item Type: Article
Keywords: Static SIMS, topography, imaging, extraction delay, extraction voltage, ion scattering, field effects, extraction field
Subjects: Nanoscience
Nanoscience > Surface and Nanoanalysis
Identification number/DOI: 10.1007/s13361-011-0201-1
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5273

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