Effective attenuation lengths for different X-ray photoelectron spectroscopy applications

For X-ray photoelectron spectroscopy (XPS), the effective attenuation length (EAL) is a useful parameter that replaces the inelastic mean free path in expressions to correct for elastic scattering of the photoelectrons. However, EAL values can differ depending on the XPS application, the instrumental configuration, and whether unpolarized or linearly polarized X-rays are employed.

Aleksander Jablonski and Cedric Powell present EALs for applications including determining the thickness of an overlayer film on a planar substrate, the surface composition of a sample, and the shell thickness of a core-shell nanoparticle. The review provided an overview of EAL predictive equations for different XPS applications and experimental conditions, and included data for the predictive equations.

“While EALs have been measured, there have often been large scatters in the results due to the difficulty of preparing uniform thin films with known thicknesses on the nanometer or sub-nanometer scale. We therefore calculated EALs for many applications and made comparisons with illustrative experimental results,” said Powell.

Also included are tabulations of albedo values – measures of the strength of elastic-scattering effects in a material – for 41 elemental solids and 42 inorganic compounds for photoelectron energies between 0.05-30 keV. This parameter is needed for calculating EALs from predictive EAL formulae.

They hope that their review will stimulate future experiments to improve the accuracy of EAL measurements for different applications. In the example case of gold, differences between calculated and measured EALs for energies less than 9 keV can be explained by growth of thin evaporated films as islands that later coalesce for thicker films.

Source: “Effective attenuation lengths for different quantitative applications of X-ray photoelectron spectroscopy,” by Aleksander Jablonski and Cedric J. Powell, Journal of Physical and Chemical Reference Data (2020). The article can be accessed at https://doi.org/10.1063/5.0008576 .