Hello Sammera,

normally the energies are plotted against a reference standard, which defines the energy zero. Often silver is used (fresh evaporated in vacuum). The energy zero is defined by the position of the quasi Fremi level. The Fermi level (better chemical potential) separates occupied from unoccuoied states. If you measure a metal like silver, the highest occupied state defines the position of the fermi level. This reference energy is used to separate occupied from unoccupied states. You measure the reference sample parallel to your investigated material. Then you compare your spectra and define the energy zero.

It is important to ground all samples. Floating potentials must be avoided.

Yours

R. Mitdank

The negative binding energies are just a different way to depict your data. If you do a theoretical calculation, bound states will of course be below the Fermi energy so their energy IS negative.

However, in most of the community it has been established to use the absolute value below the Fermi energy as the binding energy.

So in most cases a theoretician's negative binding energy is the experimentator's positive binding energy.

In gas phase PES you can actually investigate highly charged anions whose charge state is metastable, then you may get "actual negative binding energies" but I don't think you should be concerned about that since that's not what you're doing, apparently.

Jürgen Weippert and Rüdiger Mitdank Thank you so much for sharing your knowledge.

-ray photoelectron spectroscopy (XPS) is by far the most commonly used ... priori, there are no straightforward means to compensate for this effect