| AVS 58th Annual International Symposium and Exhibition | |
| Applied Surface Science Division | Monday Sessions |
| Session AS-MoM |
| Session: | Quantitative Surface Chemical Analysis and Technique Development - Part I |
| Presenter: | Cedric Powell, National Institute of Standards and Technology |
| Authors: | A. Jablonski, Polish Academy of Sciences, Poland C.J. Powell, National Institute of Standards and Technology |
| Correspondent: | Click to Email |
The backscattering factor (BF) has long been recognized as an important matrix-correction factor for quantitative AES. The BF definition (“fractional increase in the Auger current due to backscattered electrons” [1]) has been shown to be unsatisfactory since the “fractional increase” can be negative at low primary energies and more grazing-incidence of the primary electrons [2]. ISO/TC 201 is considering the definition of a new term, the backscattering correction factor (BCF), as a “factor equal to the ratio of the total Auger-electron current arising from ionizations in the sample caused by both the primary electrons and the backscattered electrons to the Auger-electron current arising directly from the primary electrons.” NIST recently released a new BCF Database [3] for AES. This database provides BCFs from Monte Carlo simulations for two models, a simplified model based on the previous BF definition which is relatively rapid and an advanced model based on the proposed BCF definition which is more accurate but slower. BCFs can be determined for a solid of arbitrary composition, a user-specified instrumental configuration, and primary energies up to 30 keV.
Examples will be given of the dependence of the BCF for Pd M5N45N45 Auger electrons on various instrumental conditions (primary energy, primary-beam angle of incidence (θ0), and analyzer acceptance solid angle) [4]. BCFs calculated from the advanced model of electron transport in the surface region of the Pd sample varied weakly with analyzer half-cone angle for θ0 = 0° but more strongly for θ0 = 80° where there were BCF differences varying between 19% at a primary energy of 1 keV and 6% at a primary energy of 5 keV. These BCF differences are due partly to variations of the density of inner-shell ionizations within the information depth for the detected Auger electrons. The latter variations are responsible for differences larger than 10% between BCFs from the widely used simplified BCF model and those from the more accurate advanced model for primary energies less than about 5 keV for θ0 = 80°. These and other BCF differences indicate that the simplified model can provide only approximate BCF values. In addition, the simplified model does not provide any BCF dependence on Auger-electron emission angle or analyzer acceptance angle. Comparisons will also be made with measured BCFs for elemental solids.
[1] ASTM E 673-03, “Standard Terminology Relating to Surface Analysis,” in Annual Book of ASTM Standards, Vol. 3.06, 2010, p. 655.
[2] A. Jablonski, Surf. Science 499, 219 (2002).
[3] http://www.nist.gov/srd/nist154.cfm .
[4] A. Jablonski and C. J. Powell, Surf. Science 604, 1928 (2010).