QUEELS-XPS (developed by Sven Tougaard and Francisco Yubero)


Quantitative interpretation of photoelectron spectra requires models to describe the energy loss processes that are responsible for the energy distribution in the measured energy spectra of emitted  photo electrons. These are often divided into three processes: 

  • the photo-excitation process (which includes the effect of the core hole),
  • transport to the surface region (energy loss in the bulk) and
  • passage through the surface and vacuum region to the electron energy analyzer (energy loss in the surface region and while the electron travels in the vacuum).
The first is also called intrinsic- and the other two extrinsic excitations.


This software package allows to calculate the energy loss processes in a photo- and Auger electron spectrum. The calculations are done within a semi-classical dielectric response model [Phys. Rev. B 56 (1997)1612].

The model takes into account energy loss which takes place due to the sudden creation of the static core hole and as the photoelectron travels in the bulk, passes the surface region, and continues in the vacuum where it interacts with its image charge before it ends up in the electron spectrometer.

It is a one-step model which includes interference effects between these excitations.

The only input in the calculations is the dielectric function of the material. This function may be taken from published tabulations or it may be determined with the QUEELS-ε(k,ω)_REELS software package from analysis of a REELS spectrum recorded from a thin film on a substrate.

The software calculates energy loss processes caused by the static core hole, the transport of the electron to the surface region passage through the surface region and interactions of the photoelectron with its image charge as it mmoves in the vacuum to the electron energy analyser.

The remaining effects which are part of the initial photo-excitation process like life time broadening, spin-orbit coupling, and multiplet splitting are not described. The software should thus allow to isolate these effects.



The QUEELS-XPS software package is free for non-commercial use.




QUEELS-XPS software package (free)

Examples with recent applications

Surf. Interf. Anal. 36 (2004) 824

Phys Rev B71 (2005) 045414


Surf. Sci. 604 (2010) 193

Surf. Interf. Anal. (2012) in press



Within this semi-classical model, there are two origins to the energy-loss structure. The first is due to the sudden creation of an electric field from the core-hole which appears as a result of photo excitation of the core electron. This field excites valence electrons and the excitation energy is lost by the photoelectron. The second contribution is due to the time and space varying electric field from the moving photoelectron which also cause excitations and thereby energy loss and such processes occur even after the photoelectron has left the surface due to the interaction of the photoelectron with its image charge. The energy loss processes corresponding to these two contributions are usually called “intrinsic” and “extrinsic” excitations, respectively, although a strict separation is not possible because the effects interfere as mentioned above.

Although the only input in the model is the dielectric function, the theory and the corresponding equations are rather complex and this has been a hindrance for other groups to apply the model. To make the model available for practical use by other groups, we have therefore developed this user-friendly software package named QUEELS-XPS (Quantitative Analysis of Electron Energy Loss in XPS).




 User interface of the QUEELS-XPS software

Total contributions to the XPS spectrum from the core hole, the surface, the bulk, and the image charge for a thin film of Si with thickness t in the range 2.3 Å to 300 Å.This shows screedumps taken directly from the software.