Untitled - IAP/TU Wien - Technische Universität Wien

71st IUVSTA Workshop
Quantification of XPS Analysis of Stratified Samples
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*Email: ajablonski@ichf.edu.pl
An analysis of inhomogeneous samples with a complicated morphology is a frequent application of
X-ray photoelectron spectroscopy. The stratified samples, with uniform lateral compositions of layers parallel
to the surface, are the idealized examples of inhomogeneities. Devices with surface region consisting of planar
structures of different materials exhibit properties that are of current technological interest.
Theoretical models describing the photoelectron transport in multilayer samples are compared and
discussed. These models are applied to different multilayer systems with layers of varying thicknesses. An
extension of the definition of the emission depth distribution function (EMDDF) is discussed, and exemplary
calculations of this function are shown. The EMDDF for a layer deposited at a surface turns out to be identical
as for the bulk of the layer material, however it may differ considerably when the layer is buried at a certain
depth [1]. The EMDDFs for buried layers are found to be considerably affected by elastic photoelectron
scattering, however in a different way as the EMDDF for the bulk material. The XPS depth profiles calculated
for multilayer materials are noticeably affected by elastic photoelectron collisions.
Photoelectron signal intensities calculated for a thin overlayer on a uniform substrate from theoretical
models taking elastic photoelectron collisions into account are shown to be very weakly dependent on the
substrate material. This result has been obtained for photoelectrons analyzed in XPS spectrometers equipped
with typical X-ray sources, i.e. sources of Mg K and Al K radiation. Consequently, an analytical model
that can accurately describe the photoelectron intensity from an overlayer deposited on any material (e.g. on a
substrate of the same material as the overlayer) can be a useful basis for a universal and convenient method for
determination of the overlayer thickness [2]. An example of such analytical formalism based on the dipole
approximation is discussed. It is also shown that the postulated method for overlayer-thickness measurements
does not need time-consuming Monte Carlo simulations of photoelectron transport, and does not require
knowledge of the effective attenuation lengths. Unfortunately, due to small information depth, this method is
applicable to layers of small thicknesses. This limitation can be circumvented by the use of high-energy
photoelectrons. An extension of formalism to Zr L and Ti K radiation sources, involving the multipole
photoemission cross section, is briefly discussed.
References
[1] A. Jablonski, J. Phys. D: Appl. Phys. 45 (2012) 315302.
[2] A. Jablonski, J. Electron Spectrosc. Relat. Phenom. 185 (2012) 498
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