| AVS 60th International Symposium and Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuM |
| Session: | Developments in Electron Spectroscopies for Non-Ideal Samples |
| Presenter: | C.J. Powell, National Institute of Standards and Technology (NIST) |
| Authors: | C.J. Powell, National Institute of Standards and Technology (NIST) W.S.M. Werner, Technical University of Vienna, Austria W. Smekal, Technical University of Vienna, Austria |
| Correspondent: | Click to Email |
It has long been known that variations in sample morphology can have drastic effects on photoelectron intensities in XPS and thus on the results of quantitative analyses [1]. While detection limits for minor species in homogeneous samples have often been estimated to be between 0.1 and 1 atomic percent, no estimates are generally available for inhomogeneous samples. In general, detection limits depend on the detectability of a particular peak (which depends on the peak-detection method, the measurement statistics, peak identification, and interpretation in relation to the known or assumed sample morphology).
We have used the NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) [2,3] to estimate detection limits for buried thin films. Test simulations have been performed for thin W films of varying thicknesses buried at varying depths in a Ru matrix. For these simulations, the X-rays were incident normally on the sample and the photoelectrons were detected at an emission angle of 55° with respect to the sample normal. We initially established that the W 4d5/2 peak intensity would likely be detectable in a RuW0.001 alloy (for which the ratio of the W 4d5/2 peak intensity to the Ru 3d5/2 peak intensity was 1.25 × 10-3). Simulations were then performed with a thin W film on a Ru substrate and for thin W films at selected depths in the Ru matrix. In each case, we varied the W film thickness to obtain the same W 4d5/2 peak intensity (within 1%) as for the RuW0.001 alloy. We find that the defined detection limit in this example varies by over three orders of magnitude for a thin W surface film to a W film buried to depths up to six times the inelastic mean free path.
[1] S. Tougaard, J. Vac. Sci. Technol. A 14, 1415 (1996).
[2] NIST SRD 100, Version 1.3 (2011); http://www.nist.gov/srd/nist100.cfm.
[3] W. Smekal, W. S. M. Werner, and C. J. Powell, Surf. Interface Anal. 37, 1059 (2005).