Determination of electronic transport properties for low-speed electrons

Bo Da

The electron inelastic mean free path (IMFP) is the average distance traveled between successive inelastic collisions by an electron moving with a particular energy in a given material. It is an essential parameter for determination of surface sensitivity and quantitative analysis in electron-beam techniques such as x-ray photoelectron and Auger electron spectroscopy. Theoretical predications cannot provide very reliable IMFP results at low energies, and have large variability and also exhibit significant deviations between alternate measurement techniques at low energies below 200 eV. Despite the great importance of the appropriate description of IMFP in different theoretical approaches, it is necessary to make clear which one is most adequate.

In this work, we proposed an improved method for calculating IMFPs in solids from experimental energy-loss functions based on the Mermin dielectric function. The “extended Mermin” method employs a nonlimited number of Mermin oscillators and allows negative oscillators to take into account not only electronic transitions, as is common in the traditional approaches, but also infrared transitions and inner shell electron excitations. Excellent agreement is found between calculated IMFPs for Cu and experimental measurements from elastic peak electron spectroscopy. Notably improved fits to the IMFPs derived from analyses of x-ray absorption fine structure (XAFS) measurements for Cu and Mo illustrate the importance of the contribution of infrared transitions in IMFP calculations at low energies.