My work is related to the induced defect in zinc oxide. To study its valence band, I did the XPS. However, I don't know how to analyze this? What should I keep in mind when I am analyzing?
A starting point is to read about XPS from basic books. Then, search for valence band spectra with XPS in a citation database.
Valence band spectra (VBS) can be calculated from first principles for comparison. Alternatively, they can be compared as a function of treatment methods. They give information about the density and occupancy of electronic states in the valence band of the material. Generally, the better tool than a general purpose laboratory XPS for high-quality VBS is ultra-violet photoemission (UPS) or synchrotron radiation, although I have seen a reference for high-resolution VBS from XPS.
In XPS, especially monochromatized for high resolution, you see basically the DOS and a little more deeper into the material as for UPS. In addition you have here the joined density of states (JDOS). For ZnO you can detect a partial coverage of the surface by- OH as to be seen as a different peak pattern in the O2p region.
I have a question about the valence band spectra for normal polymer, especially for polymer brushes. All the peaks could be fitted by the Gaussian method or just calculated by the first principle? Why all the literature just analyze this region as C2s and C2p, not as the SP orbitals. If all the bond types could be found in the valence band region , why not fitting it?
@M Saxena: I would just do a GoogleScholar search to start ...
https://scholar.google.com/scholar?q=high+resolution+xps+of+valence+band&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwjWvPf8pM7QAhXmhlQKHaa7AAgQgQMIGzAA
@W Haigang: The VB spectra of materials are convolutions of different factors as others have noted. The peaks are not as simple to define with just one shape function (i.e. Gaussian).
XPS is also ok a more convenient is to take UV-Vis spectra from where you can easily get band gap. And using following relations you can find valence band and conduction band
The potentials of the conduction band (CB) and valence band (VB) of a semiconductor can be calculated using Mulliken electronegativity theory :
ECB = X- Ec - 0.5 Eg (Eq.1)
EVB = ECB + Eg (Eq.2)
Where Ec is the energy of free electrons vs. hydrogen (4.5 eV) and χ is Mulliken electronegativity of the semiconductor. X was calculated by the following equation:
χ = [x(A)^ax(B)^bx(C)^c ] ^(1/(a+b+c) ) (Eq.3)
a, b, and c are the number of atoms in the compounds.
χ calculation for CuAl2O4
Cu:
EIE (Molar ionization energies) = 7.73 eV
EEA (Electron affinity) = 1.23 eV
XCu = (7.73+1.23)1/2 = 4.48
Al:
EIE = 5.98 eV
EEA = 0.43 eV
XAl= (5.98+0.43)1/2 = 3.20
O:
EIE = 13.61 eV
EEA = 1.46 eV
XO = (13.61+1.46)1/2 = 7.54
XCuAl2O4 = (4.48×3.20×3.20×7.54×7.54×7.54×7.54)1/7 = 5.48
ECB = 5.48 – 4.5 – 0.5Eg
EVB= 1.48+ 0.5Eg
Conduction band (CB) and valence band (VB) potentials of semiconductors are calculated using the following empirical equations:
ECB = χ – Ee – 0.5Eg (1)
EVB = ECB + Eg (2)
Where EVB and ECB are the VB and CB potentials, respectively. Moreover, Ee is the energy of free electrons vs. hydrogen (4.5 eV). Finally, χ is the electronegativity of semiconductor and it was calculated by the following equation:
χ = [x(A)ax(B)bx(C)c]1/(a+b+c) (3)
In which a, b, and c are the number of atoms in the compounds. For example, in the case of Cu2CoS4, the calculation procedure is as follows:
χ calculation for Cu2CoS4
For Cu: EIE = 745.5 kj/mol ÷ 96.48 = 7.73 eV
EEA = 119.2 kj/mol ÷ 96.48 = 1.23 eV
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