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Simple universal curve for the energy dependent electron attenuation length for all materials.

Seah, M P (2012) Simple universal curve for the energy dependent electron attenuation length for all materials. Surf. Interface Anal., 44 (10). pp. 1353-1359.

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An analysis is presented for a simple, universal equation for the computation of attenuation lengths (L) for any material, necessary for quantifying layer thicknesses in XPS. Attenuation lengths for selected materials may be computed from the inelastic mean free path (lOpt) computed, in turn, from optical data. The computation of L involves the transport mean free path and gives good L values where values of lOpt are available. However, lOpt values are not available for all materials. Instead, l may be calculated from the TPP 2M relation, but this requires the accurate estimation of a number of materials parameters that vary over a wide range. Although these procedures are all soundly based, they are impractical in many analytical situations. L is therefore simply re-expressed, here, in terms of the average Z of the layer (from XPS analysis), the average atomic size, a (varies in a small range) and the kinetic energy E of the emitted electron. A new equation, "S3", is established with an RMS deviation of 8% compared with the values of attenuation length calculated from lOpt available for elements, inorganic compounds and organic compounds. This excellent result is suitable for practical analysis. In many films, an average value of a of 0.25 nm is appropriate and then L may be expressed only in terms of the average Z and E. Then, L expressed in monolayers, equation "S4", exhibits an RMS deviation of 9% for many elements. These results are valid for the energy range 100 to 30000 eV and for angles of emission up to 65º.

Item Type: Article
Keywords: attenuation lengths, elements, IMFP, inelastic mean free path, inorganic materials, organic materials
Subjects: Nanoscience
Nanoscience > Surface and Nanoanalysis
Identification number/DOI: 10.1002/sia.5033
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5586

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