Is there a relationship between XPS chemical shift and crystallite size of unsupported metal oxides? if yes, is it positive or negative shift with increasing crystallite size? and why?
In going from an atom in bulk to an atom by itself, peaks can shift because ...
final state effects change
work function becomes ionization energy
This presumes that both the bulk and the atom are equally "well-grounded". In other words, differences in charging are absent in going from bulk to atom states. This also presumes that you are keeping all other factors that affect peak position constant as crystal size changes. In your case, I would for example be concerned that composition or homogeneity in composition depends on crystal size.
For further insights, look also at folks who use gas phase XPS to compare to solid state XPS. An example article is here ... http://www.sciencedirect.com/science/article/pii/036820489387006L
Also look for research on XPS results from supported pure metal particles as a function of crystal size.
Slight shifts in binding energy can be seen for changes in crystalline sizes for small nanoparticles. The reason behind this depends on a number of factors. A bulk oxide material (for example MgO) will likely see binding energy shifts due to differences in basicity/defects.
See the attached publication for more information.
In going from an atom in bulk to an atom by itself, peaks can shift because ...
final state effects change
work function becomes ionization energy
This presumes that both the bulk and the atom are equally "well-grounded". In other words, differences in charging are absent in going from bulk to atom states. This also presumes that you are keeping all other factors that affect peak position constant as crystal size changes. In your case, I would for example be concerned that composition or homogeneity in composition depends on crystal size.
For further insights, look also at folks who use gas phase XPS to compare to solid state XPS. An example article is here ... http://www.sciencedirect.com/science/article/pii/036820489387006L
Also look for research on XPS results from supported pure metal particles as a function of crystal size.