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Copyright © 2008 Casa Software Ltd. www.casaxps.com exponent of -0.2, numerically equivalent RSF values are Quantification of JEOL XPS Spectra reproduced in CasaXPS. Table 1 is a quantification table from SpecSurf calculated in CasaXPS for the same data for which the JEOL system reports RSFs shown in Figure 1. The small differences The quantification procedure used by the JEOL SpecSurf between the total RSFs reported by CasaXPS and those in software involves modifying the Scofield cross-sections to Figure 1 are due to different peak positions between the two account for both an energy dependency and also angular systems, probably due to slight differences in the background distribution corrections. However, to reproduce the definition. quantification tables in CasaXPS produced by the JEOL Library Total Raw %At SpecSurf software, it is sufficient to use an energy exponent of Name Position RSF RSF Area Conc -0.2, entered on the Regions Property Page, and the unaltered C 1s 284.7 1.01548 4.19415 6367.69 58.1 Scofield cross-sections for the RSF values. While the reported N 1s 401.2 1.82786 7.39709 78.6979 0.4 RSFs will not match in absolute terms, the relative RSFs are O 1s 532.4 2.97535 11.7345 2740.05 8.9 the same between the two systems and therefore the F 1s 688.6 4.49857 17.1189 3212.83 7.2 quantification tables will be identical (assuming the same Si 2p 100.4 0.829645 3.5258 2337.71 25.4 calculated peak areas and positions for the peaks). Table 1: Quantification table generated in CasaXPS While the infrastructure for adjusting the RSFs for angular distribution is in place for the JEOL software, the current JEOL system sets the asymmetry β parameter to unity and therefore the angular distribution function returns the same value for all transitions, hence the Scofield cross-sections are all scaled by the same factor. The only significant adjustment to the quantification values derive from the energy dependency. The Figure 1: JEOL RSF values for the transitions in Table 1. actual modifications to the Scofield cross-sections applied by the JEOL system can be fully reproduced in CasaXPS version 2.3.15, where a set of configuration parameters defined in the In order to obtain the quantification table in Table 1, it is ParameterFile.txt file in the CasaXPS.DEF directory control necessary to add lines to the ParameterFile.txt file in the the calculated RSFs. When initialised using an angle of 56º CasaXPS.DEF directory as shown in Figure 2. between the x-ray source and the analyser, and an energy 1 Copyright © 2008 Casa Software Ltd. www.casaxps.com The default CasaXPS library is populated with Scofield cross- sections. These Scofield cross-sections are computed from Hartree-Slater wave-functions and therefore are appropriate for an XPS instrument designed with the, so called, magic angle between the x-ray source and the analyser axis. Given the angle between the x-ray source and the analyser, a correction can be made to these magic angle RSFs appropriate for the given instrument. The configuration file in Figure 2 shows the method for specifying the require angle for the JEOL instrument, which is 56º. Each time one or more files are opened in CasaXPS for which the angle has yet to be set, a dialog window prompts the user for the missing angle and offers the configured angle as the default. Once a file is updated with an entry in the VAMAS file Figure 2: ParameterFile.txt file in the CasaXPS.DEF directory used in comment of the form “SourceAnalyserAngle: 56.000000 d”, version 2.3.15 of CasaXPS. the source to analyser angle is defined for that file. When coupled with the configuration entry, “jeol angular The JEOL element library includes the asymmetry parameters distribution”, the magic angle Scofield cross-sections from the and therefore, should these be implemented in future releases element library will be adjusted each time an RSF is extracted of the JEOL software the line in the ParameterFile.txt file “jeol from the element library for use with a Region or Component. angular distribution” would need to be changed to “correct for The column in Table 1 headed Total RSF is calculated from angular distribution”. With this adjustment, CasaXPS would the RSF in the Region or Component multiplied by the energy extract RSFs from a Scofield library to include the full angular dependence defined by the value in the text-field on the distribution correction. Regions property page. The theory behind the use of angular distribution correction is discussed in detail elsewhere in the CasaXPS manual. An outline of the procedure will be given below. 2 Copyright © 2008 Casa Software Ltd. www.casaxps.com Quantification Examples The follow examples illustrate how to quantify data from the JEOL JPS-9200 instruments at University of Wageningen, The Netherlands. 3 Copyright © 2008 Casa Software Ltd. www.casaxps.com spectrum displaying element marks for oxygen, carbon and silicon in preparation for creating regions using the Create Quantification of a Survey Spectrum Region button. Survey spectra are typically used to measure elemental concentrations and therefore quantification regions are usually the tool of choice to measure the peak areas. A low resolution acquisition mode enhances the signal-to-noise in a survey spectrum, but broadens the peaks in the data making these peaks less appropriate for chemical state analysis by peak modelling, hence the use of regions only. The first example describes how to quantify a survey spectrum using quantification regions. The Quantification Parameters dialog window is available from the Options menu on the CasaXPS main window or via the top toolbar button . Quantification Regions are edited on the Regions property page on the Quantification Parameters dialog window, where the limits of integration, background type and RSF parameters are set. For successful quantification of a sample using a survey spectrum, a set of Regions must be created with the appropriate RSFs for the transitions identified. To ensure the correct RSF is extracted from the element library, the best means of creating regions for survey spectra is to use the Element Library dialog window to create the regions. Buttons labelled Create Regions are on both the Element Table property page (Figure 3) and the Periodic Table property page. These Create Regions buttons use the set of Figure 3: Element Library Dialog Window element marks currently defined on the survey spectrum to initialise a set of regions on the data. Figure 4 shows a survey 4
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