Electron Inelastic Mean Free Path in Carbon and Polycarbonate Using Newly Developed Wide Energy Spectrum Measurement Method

Abstract

The electron Inelastic Mean Free Path (IMFP) is most commonly used in surface analysis techniques such as X-ray photoelectron spectroscopy. Though numerous studies were conducted defining the IMFP value, it is still mostly substantiated on calculations and extrapolations. Experimental methods such as elastic-peak electron spectroscopy, tends to relay on indirect measurements. Main disadvantage of the current methods is the decreasing signal to noise ratio as the layer thickness increases or with the electron energy decreases.

Newly developed Wide Energy Spectrum method (WES), previously published by our group¹, allows a direct evaluation of the IMFP for different energies. It exploits the attenuated electron multiple inelastic collisions (MIC) peak counts rather than use the signal-electron peaks and to calculate the mean electron energy loss.

Current methods traditionally focus on the signal electron in the spectrum disregarding the information encapsulated in the electrons with lower energies. By understanding how to exploit this information, “WES” enhanced the data collection using a wide energy region, starting with the signal electron energy and ending with the lower range of the “MIC Peak” energy in the spectrum.

In this work, we have widened the validity of the WES method by evaluating IMFP of a low Z polymer, and by using a different substrate to produce the photoelectrons. The experiment was performed at the Spanish beam-line (SpLine) at the ESRF and the initial results are presented. Farther more, the raw-data analysis and background reduction was improved to provide enhanced and more accurate results.

IMFP’s of Carbon and Polycarbonate were evaluated and compared with the NIST² predicted IMFP values. Although some small differences, the reported IMFP found to be well within the uncertainty boundaries.

This work presents the ability to evaluate electron IMFP in solids by directly measuring the electrons passing through matter. For the first time, there is an orderly path to evaluate experimentally electron IMFP’s using the WES method. The new method has been established to complete the gap of lack of experimental results for low energies electron IMFP’s in solid materials.

References:

[1] A. Givon , E. Tiferet, G.R Castro, J Rubio-Zuazo, E. Golan, I. Yaar, I. Orion., “Hard X-Ray Photoelectron Spectroscopy Study of Electron Spectral Structure beyond the Known Signal Electron Peak”, J. Chem. Chem. Eng., 7 (2013), 601–605.

[2] C. J. Powell and A. Jablonski, “NIST Electron Inelastic-Mean-Free-Path Database: Version 1.2”. SRD 71, (2010).