AVS 58th Annual International Symposium and Exhibition
    Applied Surface Science Division Monday Sessions
       Session AS-MoM

Paper AS-MoM5
Effect of Monochromator X-ray Bragg Reflection on Photoelectric Cross Section

Monday, October 31, 2011, 9:40 am, Room 102

Session: Quantitative Surface Chemical Analysis and Technique Development - Part I
Presenter: Alberto Herrera-Gomez, CINVESTAV-Unidad Queretaro, Mexico
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The photoelectric differential cross section plays a fundamental role for assessing the relative concentration of the various elements present within the XPS probing depth. Accounting for the different issues affecting the cross section is paramount not only for quantitative chemical studies (including angle-resolved XPS) but also for a proper comparison between the results obtained with different XPS tools, or in the same tool but with different X-ray sources. In XPS experiments employing monochromatized light, the X-ray Bragg reflection undergone by the beam at the monochromator crystal causes a partial polarization of the X-rays. The photoelectric cross section is affected since it depends on the angle between the electric field vector and the direction of the escaping electrons. An expression for the photoelectric differential cross section is presented that accounts for the effect of the monochromator and of the geometrical configuration of the XPS tool. The correction is as large as 9% for s-orbitals and reduces to up to 5% for orbitals with β ~ 1. The differences are directly related to the beta factor within the dipole approximation, which is the first order treatment of photoemission; i.e., they are not due to higher order quadruple terms.