Ulvac-PHI SFs plotted versus Scofield SFs, and Seah’s (NPL) AM-RSFs
- contributed by John Moulder (USA)
The first generation of PHI RSFs was based directly on the original work published by Wagner et al in 1981. Data collected with a Varian IEE-15 and a Physical Electronics 550 spectrometer were used to develop a set of empirically derived RSFs with the F 1s RSF set to 1. For this work a number of F based compounds were analyzed as primary standards, with Na and K based compounds being used as secondary standards. It was observed that the transmission function of the two instruments was similar and that the transmission function could be approximated by E-1. Due to the broad angular acceptance of both spectrometers angular efficiency factors were ignored. Wagner noted in the original publication that there were challenges associated with the rare earth elements and some of the transition metals. Where no empirical data was available interpolation or theoretical calculations were used to fill in the gaps. These RSFs were supplied to the users of our double pass CMA XPS instruments and the first generation of PHI SCA instruments including the PHI models: 550, 560, 570, 5100 and 5300.
The second generation of PHI RSFs was created for use with PHI SCA instruments that used the PHI Omni Lenses equipped with an aperture wheel to define the analysis area. This new RSF data set was based on the first generation of PHI RSFs with the PHI 550 Double Pass CMA transmission function removed and the transmission function for a PHI 5600 with an Omni III lens inserted to create a new set of RSFs for use with a non-monochromatic x-ray source that was located at the “magic” angle of 54.7 degrees relative to the spectrometer input lens.
A second set of RSFs was created by starting with the new 54.7 degree (magic angle) RSFs and theoretically calculating the expected transmission function with the use of a monochromatic x-ray source located at 90 degrees relative to the spectrometer input lens. These two tables of RSFs appeared in the PHI XPS handbook first published in 1992 and were supplied to users of PHI model 5400, 5500, and 5600 XPS instruments.
The third and current generation of PHI RSFs was created to enable the use of transmission function modeling and geometric (asymmetry effect) modeling to calculate instrument (measurement) specific RSFs, on demand, when requesting quantitative information from PHI XPS data. This set of RSFs is based on the original Wagner data with the instrument transmission function removed to provide a “primary” set of RSFs that can be modified by an instruments transmission function, pass energy, and instrument geometry to provide more consistent quantitative results with varying instrument conditions.
Wagner points out that there is good agreement near F and that as Z increases the gap between empirical values and Scofield’s values appears to increase. We recently plotted a comparison of the PHI “primary” RSFs, Scofield’s calculations, and NPL (Seah, Gilmore, Spencer) AM-RSF calculations for the strong peaks associated with various elements. The trends observed by Wagner are present in these plots. There are specific instances where the gap is quite large.
Plots of SFs comparing Ulvac-PHI SFs to Seah’s NPL AM-SRFs and Scofield’s SFs
(normalized to give F (1s) = 1.0)
Comparison of 1s SFs
Comparison of 2p SFs
Comparison of 3d SFs
Comparison of 4f SFs