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Al Kα XPS reference spectra of polyethylene for all instrument geometries

Shard, A G; Reed, B P (2020) Al Kα XPS reference spectra of polyethylene for all instrument geometries. Journal of Vacuum Science & Technology A, 38 (6). 063209 ISSN 0734-2101

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Abstract

This paper extends a previous description of XPS survey spectra from low density polyethylene (LDPE), which was specific for a single type of geometry, to all geometries. Instrument geometries are specified by two angles. The first angle, a, is between the sample to monochromator vector and the sample to analyser vector. The second angle, b, is the dihedral angle between the anode-monochromator-sample plane and the monochromator-sample-analyser plane. The second angle is important because of the polarisation induced by the monochromator. We show, using theory, that the XPS spectrum can be decomposed into a `magic angle' reference spectrum, I1, and an anisotropy correction spectrum, f. The `magic angle' geometry for LDPE is shown to be a function of a and b with extreme values for a of 64.6° (b = 0 or 180°) and 57.5° (b = 90°). Deviation of these `magic angles' from a = 54.7° is due to a combination of X-ray polarisation and non-dipole effects in photoemission. Two average spectra, both with b = 180°, one with a = 60° and the other with a = 45° are used to determine I1 and f and these are fitted with simple functions to allow the reproduction of LDPE reference spectra for any instrument geometry. The spectra are taken from VAMAS TWA2 (Versailles Project on Advanced Materials and Standards, Technical Working Area 2: Surface Chemical Analysis) study A27. The functions in this paper may be used in the calibration of XPS instruments with quartz-crystal-monochromated Al Kα X-rays by comparison of the calculated reference spectrum to data from clean LDPE.

Item Type: Article
Subjects: Nanoscience > Surface and Nanoanalysis
Divisions: Chemical & Biological Sciences
Identification number/DOI: 10.1116/6.0000578
Last Modified: 27 Apr 2021 12:31
URI: http://eprintspublications.npl.co.uk/id/eprint/9087

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