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Substrate photoelectron enhancement of carbonaceous overlayer Auger emission: effect of the substrate on carbon overlayer thickness determination in XPS
Author(s) -
Brizzolara Robert A.,
Beard Bruce C.
Publication year - 1999
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/(sici)1096-9918(199908)27:8<716::aid-sia565>3.0.co;2-r
Subject(s) - overlayer , substrate (aquarium) , carbon fibers , x ray photoelectron spectroscopy , silicon , auger electron spectroscopy , materials science , auger , monolayer , titanium , analytical chemistry (journal) , chemistry , metallurgy , nanotechnology , chemical engineering , composite material , atomic physics , oceanography , physics , chromatography , composite number , nuclear physics , engineering , geology
The Ebel Model, which characterizes a sample consisting of a thin carbonaceous overlayer on a substrate of a different material, provides a relationship between the carbon 1s and Auger peak intensities and the overlayer thickness. In this paper, Ebel model predictions for six substrate materials (silicon, aluminum, titanium, copper, silver and gold) are compared with experimental data from samples prepared using self‐assembled monolayer and Langmuir–Blodgett techniques. Although the agreement between the experimentally measured carbon 1s/carbon Auger ratio and the Ebel Model was very good for silicon and aluminum and good for titanium, copper and silver, the experimentally determined ratio was consistently lower than that predicted by the Ebel Model for the gold substrate. For a 1.3 nm thick carbon layer on gold, the discrepancy between the measurement and the Ebel Model was 26%. We therefore modified the Ebel Model to include the effects of photoionization of carbon atoms in the overlayer by substrate photoelectrons. We refer to this as the Substrate Effect Model. Agreement between the Substrate Effect Model and the experimental data is very good for all six substrates examined. Because the Substrate Effect Model gives an accurate relationship between the carbon peak intensities and overlayer thickness, it can be used to determine an unknown overlayer thickness and to improve the accuracy of XPS quantitative analysis by accounting for the presence of the ubiquitous adventitious carbon layer. To this end, Substrate Effect Model results are presented for 40 substrate elements of technological interest and for overlayer thicknesses of 1,2 and 5 nm. Copyright © 1999 John Wiley & Sons, Ltd.