Brief description of the QUEELS-ε(k,ω)-REELS analysis procedure:

The first step in the analysis is to apply an algorithm [1] to remove the multiple scattered electrons from the REELS spectrum and determine an effective singlescattering cross section. The next step is to interpret this experimental effective cross section in terms of the dielectric function. At energies below ~ 1500 eV, there is a strong interference between surface and bulk excitations, and it is necessary to use a detailed model for comparison with experiment. Thus, it is not possible to interpret the spectra as a linear combination of surface and bulk loss terms because of the interference between the surface and bulk excitations.

These effects are included in the semi-classical dielectric response model [2-4] which is the basis for the QUEELS ε(k,ω)-REELS software package. This model includes interference effects between surface and bulk excitations and excitations that take place after the electron has left the solid and travels in the vacuum towards the electron energy analyzer. The dielectric function is determined by an interactive fitting procedure of the model calculations to the experimental effective inelastic scattering cross section. The validity and consistency of this method was extensively tested [5,6] and it has previously been successfully used to obtain the electronic and optical properties of metals, oxides and ultrathin dielectric, semiconductor, and transparent oxide films.

There is only limited data available from other techniques on optical constants in the high energy range because these are not easily obtained with alternative experiments.

1. S. Tougaard and I. Chorkendorff, Phys. Rev. B35, 6570 (1987)

2. F. Yubero and S. Tougaard, Phys. Rev.B46, 2486 (1992).

3. F. Yubero, J. M. Sanz, B. Ramskov and S. Tougaard, Phys. Rev. B53, 9719 (1996).

4. S. Tougaard and F. Yubero, 2004 Surf. Interf. Anal. 36, 824

5. F. Yubero, D. Fujita, B. Ramskov and S. Tougaard, 1996 Phys. Rev. B53, 9278.

6. S. Hajati, O. Romanyuk, J. Zemek, and S. Tougaard, Phys. Rev. B77, 155403 (2008).