I was measured the XPS of my FeF2 coated by carbon and got the XPS results of 288.5 eV and 292eV in C1s which were correspond to the C-F and C-F2, also in my F1s contain that peak of C-F and C-F2 peak. Actually, what kind of bond from that two? is that two bond different?
because I just know that the C-F bond is sp2 carbon make ionic bond with F,and have no idea of C-F2 even C-F3, CMIW.
Just some thoughts:
-careful with the assignment of C-C-sigma bonds; sp2 carbon often exhibits a non-Gaussian asymmetry, the so-called Doniach-Sunjic lineshape; that unluckily overlaps with the sp3 region.
-are you sure about ionic C-F-bonds? That would be pretty rare.
-8eV (from C=C to C-F2) is a big shift, can you exclude charging islands on the surface? Those would also be observed at higher binding energies. On the other hand, such a shift has been observed for triple halogenated carbon (https://srdata.nist.gov/xps/EngElmSrchQuery.aspx?EType=PE&CSOpt=Retri_ex_dat&Elm=C , entry ClF2CCFCl2) so it would be more likel you have a CF3 group.
Difference is that number of fluorine atoms (bonded to carbon) increases, availability of electrons (belonged to carbon atom) decreases because of highly electromotive fluorine which draws electrons toward itself from C-F bond. So, binding energy of C atom in XPS shifted to higher energy. That means C atom in (F-CH2-F) has higher binding energy than that of (F-CH2-H).
Thanks for your respond Mr. Jürgen Weippert,
In the first I just thought because of my C=C sp2 more dominant than C-C sp3, so the fluorine will be making more bond with that sp2 than sp3.
However, when I studied more about this, I think that would be become semi ionic C-F bond between C-C and fluorine, because I also think that very hard to make bond with C=C.
Moreover, I'm not making polymer so it more rarely I got triple halogenated carbon bonds.
Thanks for your help Mr. Md Aslam Uddin,
now I'm understand what the difference of that C-F, C-F2, C-F3.
Actually, C-F bond is very common. C-F is a covalent bond (sometime C-F is a polarized covalent bond depending on the nature of compounds).
Okey.. but some papers said of C-F semi ionic bond. how it can be C-F semi ionic and covalent? how to distinguish that?
Well, it is a strongly polarized bond but usually it is classified as covalent. Strictly spoken, electrons don't know what kind of bond they are forming, that is more like an "afterwards assignment" building on their distribution. The electrons only "know" their wavefunction. In some cases (salts) the distribution is so polar that it is cleary assignable as ionic while in some cases (C-H bonds) it is almost completely unpolar.
XPS only sees that either valence band atoms have been drained (=binding energy increases due to positive surrounding) or pushed in (binding energy decreases due to negative surrounding) to a certain extent.
Of course, that is unsatisfying to work with and it is simpler to explain a bond as semi-ionic if it has a strong polarization in it.
wow.. thanks for your explanation Mr. Jürgen Weippert, it help me to understand more about binding energy in XPS.
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