The second image shows the In 3d doublet. In(OH) 3 and In(OH) 3*nH 2O can only be differentiated by a shift in the M 4N 45N 45 Auger line.Ī heavily oxidized In foil was sputtered while performing XPS. Also phases with little difference in the XPS 3d 5/2 binding energy, such as In 2O 3 and In(OH) 3, have a much more significant chemical shift in the Auger M 4N 45N 45 kinetic energy. What is immediately evident is that chemical states that might be difficult to identify through small chemical shifts in the XPS 3d 5/2 binding energy- might be easy to identify through huge changes in the Auger M 4N 45N 45 kinetic energy, as in the case of In and In 2O 3. Each chemical state is indicated with horizontal and vertical lines indicating the range of the available data- not the uncertainty in the available data. The diagonal lines are lines of constant modified Auger parameter- the sum of the XPS binding energy and Auger kinetic energy. The Wagner plot shows the binding energy of the XPS In 3d 5/2 peak on the X-axis and the kinetic energy of the Auger In M 4N 45N 45 peak on the Y-axis. The Wagner plot for In, In 2O 3, In(OH) 3 and In(OH) 3*nH 2O is shown. Metallic indium can be differentiated from the indium oxide and hydroxide phases, but the oxide and hydroxide chemical states can't be differentiated using the XPS BE chemical shift alone. The corresponding In 3d 5/2 BE's for In 2O 3 are 444.8 ± 0.2 eV. In the case of indium metal, the In 3d 5/2 XPS BE is 443.8 ± 0.1 eV based on the entries in the NIST XPS database. In some cases the shift of XPS lines is insufficient to identify chemical states. This has been demonstrated in the case of AuO x surface oxidation elsewhere in this blog.
![xps peak identification xps peak identification](https://kartyush.files.wordpress.com/2012/05/sp1.png)
The high energy resolution of XPS, < 1 eV, allows one to identify chemical states through chemical shifts- shifts of the core level XPS binding energies due to the charge transfer that occurs in the binding of different chemical states.