ELASTIC-SCATTERING CORRECTIONS IN AES AND XPS .2. ESTIMATING ATTENUATION LENGTHS AND CONDITIONS REQUIRED FOR THEIR VALID USE IN OVERLAYER SUBSTRATE EXPERIMENTS/

We examine substrate/overlayer experiments and the equations commonly used to quantify overlayer thicknesses, Comparisons with accurate Mont e-Carlo simulations show that using attenuation lengths (rather than i nelastic mean free paths) eliminates most of the error due to elastic scattering without increasing the complexity of the quantification. We give attenutation lengths for 27 elements, calculated by the criterio n that systematic errors in such quantifications should be minimized, These are therefore the best attenuation length values to use in layer wise quantification. We show that, provided these attenuation length v alues are used, the error in estimation of the thickness of an overlay er due to elastic scattering can be limited to +/-(5% + 1 Angstrom) fo r an emission angle less than or equal to 58 degrees from the surface normal, and +/-(10% + 1 Angstrom) for an emission angle less than or e qual to 63 degrees from the surface normal, This accuracy is acceptabl e for most analytical work, Other methods (such as analytical transpor t theory) are much more complicated, and achieve ii high precision tha t is often unnecessary in view of other uncertainties typically presen t in these experiments (such as errors due to surface morphology and d iffraction effects), The results presented here, using the full theory , show that the analyst's simple straight-line approximation is in fac t of adequate accuracy, provided that the correct values of attenuatio n length are used, Simple semi-empirical equations are presented, whic h allow the analyst to estimate the attenuation length for electrons o f kinetic Energy between 50 and 2000 eV, to a standard uncertainty of 6%. (C) 1997 by John Wiley & Sons, Ltd.