QUEELS-ε(k,ω)-REELS (developed by Sven Tougaard and Francisco Yubero)
What the software will do
With this software it is possible to determine the dielectric function and optical properties of a material by analysis of a measured reflected electron energy loss spectrum (REELS).
It determines the electronic properties in terms of the real and imaginary parts of the dielectric function ε(k,ω) and the optical properties as e.g. the extinction coefficient and index of refraction.
In general, there is very limited data available on the dielectric function and optical constants in the high energy range because these are not easily obtained with other methods.
The analysis with QUEELS-ε(k,ω)-REELS is fast and easy and the method also works for nano-meter thin materials on top of a substrate.
The REELS experiment requires an electron gun and an electron energy analyzer which is available in most surface analysis machines.
The REELS experiment is quite easy from an experimental and practical point of view, because the sample can be grown, prepared, cleaned and handled with ease. The method applied by this software package is valid even for energies of ~ 200 eV, for which the IMFP is < 1 nm.
Therefore it can be applied even for films of ~ 2 nm thickness. The properties of a few nano-meter thick film can also easily be studied because they can be formed on a supporting substrate.
In contrast to this, the transmission electron energy loss (TEELS) experiment, which has also in the past been applied to get similar information, is much more complicated because it relies on analysis of the energy distribution of monoenergetic electrons that have passed through a thin film of the material. TEELS therefore require clean, thin and self supporting films with uniform thickness. Such films are virtually impossible to make in practice when the film thickness is in the nano-meter range.
Examples with recent applications
Electronic and optical properties of Al2O3/SiO2 thin films on Si.
Electronic and Optical properties of GIZO thin films on SiO2/Si substrates.
Electronic and Optical properties of hafnium indium zinc oxide thin film
The basic theory
Test of validity
Example of a recent application: Denny et al. J. El. Spectr. 185 (2012) 18
Electronic and Optical properties of HfInZnO thin films on Si
Schematic of the REELS experiment.Thin or thick films
|Experimental inelastic cross section from REELS data and the theoretical inelastic cross section. This is done with the software and determined the energy loss function for GIZO, HIZO and IZO thin films.||The determined complex dielectric function of GIZO, HIZO and IZO thin films.||With a focused electron beam, the properties of nano-structures can be studied.
|Determined Energy loss functions (ELFs) and surface energy loss function (SELF) for GIZO, HIZO and IZO||Determined transmission spectra as a function of wavelength for GIZO, HIZO and IZO thin films.|