Recently, we submit a work on carbon dot-based electronic device to a journal. In the work, ultraviolet photoelectron spectroscopy (UPS) measurement was applied to determine the valence band energy of carbon dots. Before measurement,the UPS of Au standard sample was measured and the Fermi edge of Au standard sample was corrected by software. On this basis, we have corrected the UPS data of carbon dots.
However, one reviewer insist on "Measuring the Fermi edge of an electrically grounded gold standard does nothing to correct the shift in the spectrum observed for non-conductive samples. The spectrum used for charge correction must be measured from a gold layer that is electrically isolated from the sample holder or any conductive substrates by the layer of the interest (the carbon dots)."
Therefore, I would like to ask how to test the UPS of non-conductive samples?
The reviewer actually told you what (s)he expects: evaporating a gold spot on a location that is comparably insulated from the ground (or bias electrode), ideally a spot on the sample itself.
Dear all, Interesting question! I have some further questions...
When measuring on a gold sample you calibrate the analyzer energy against a reference sample. But if the sample is nonconductive the reference to the sample does not do any good due to charging.
When measuring on a non-conducting sample the sample will charge up and shift the energy scale. Once a steady state is reached the peaks will stop moving. I guess that when you evaporate a gold spot on the sample the assumption is that the gold charge up the same as your other sample such that the two spectra align in energy? Could one be sure of that?
I guess that Jürgens point that the gold spot has to be completely isolated from the ground and only in contact with the sample is important as the above assumption would not hold otherwise?
If one ads a flood gun charge compensation to the system with the gold would that increase the precision of the measurement? Or would it compensate different on the two materials and a worse result will be the outcome?
John Åhlund
You have my full agreement. My posting was explicitely referring to the reviewer request posted in the question, I personally would also consider flood gun usage absolutely valid.
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