You can find the work function by looking at the secondary-electron cut-off. What is a valence band potential?
The short answer is that the valance band is not sufficient to determine the work function. Just like Thorsten Schultz said, you need to measure when the spectra ends. By comparing the end of the spectra to the photon energy you will find the work function
hv=BE+KE+work function
At the end of the spectra this becomes:
hv=BE+0+Work function
If lowest KE you can measure is only 3 eV that means it takes 3eV for electrons to leave the surface, the definition of the work function.
There a few technical details:
Some XPS can not measure up to the Al k-alpha edge and you need to apply a bias, in this case you need to use a spectral feature to validate the potential applied.
Finally fitting the low energy electrons at the end of the spectrometer can be challenging ensure you use a low pass energy these spectra can take a long time to gather. Much longer than even the valance band.
Just one comment, due to the spectral width of non-monochromatic x-ray tubes typically used for XPS, the determination of both ends of the spectrum might be tricky. And, for the Low energy end of the spectrum, application of a sufficient bias voltage (say 20 V or so) is mandatory. I would in any case prefer UV excitation ... Good luck, Dirk
Hi, A similar quesiton was asked under this headline on researchgate. This might help you as well.
How can I read the UPS spectrum when it goes to zero at energies larger than zero eV? | ResearchGate
John Åhlund That sounds like the normal thing to happen, if you significantly had electrons above the Fermi level, it wouldn't be the Fermi level.
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