Silica is SiO2, is it possible that the oxygen from the silica now just dominates everything and you don't see the O1s of your original material anymore?

Otherwise it's always helpful to post a screenshot of what you're talking about if your institute allows that.

Dear Saif Mehdi

The O1s spectra from the XPS is very complex. You can characterize several oxygen species, and after adding a layer of SiO2, you are adding amorphous oxygen content, with possible high content of hydroxil groups on the surface, which directly affects your BE values.

Another point to account is the presence of O{2-} species from the ZnO lattice, and another O{1-} that occurs in the lattice subsurface to compensate the charge difference when you add silica to the material.

You can find some good discussion about oxygen species on XPS analysis here:

Dupin, J.-C., Gonbeau, D., Vinatier, P., Levasseur, A., 2000. Systematic XPS studies of metal oxides, hydroxides and peroxides. Physical Chemistry Chemical Physics 2, 1319-1324.

Regards,

GG.

The oxygen from the silica can be source of the oxygen signal. An important thing to consider is that SiO2 is a semiconductor. Peak shifts can occur due to charge build up on your sample. It might be necessary to employ charge neutralizer while taking the XPS measurements.

Likely you will have a large O 1s sigal at ~ 533 eV characterist of the silica. What is the binding energy of the Si 2p peak, should be ~ 103.5 eV for SiO2. If you are happy that your data is calibrated OK, then focus on the shifts of metal peaks as opposed to the oxygen, but be aware the silica and the absorbant may be at different charge potentials