X-ray photoelectron spectroscopy studies of the electronic structure of superconducting Nb2SnC and Nb2SC

X-ray photoelectron spectroscopy (XPS) was used to investigate the binding energies and valence band of the Nb2SnC and Nb2SC compounds. The Nb 3d5/2, Sn 3d5/2, S 2p3/2 and C 1s core levels associated with the chemical states of Nb2SnC and Nb2SC were identified. The spectra for Nb2SnC revealed Nb and Sn oxides on the surface of the sample, mainly Nb2O5 and SnO2, while the Nb2SC only Nb2O5 oxide. After Ar+ ion etching the intensity of the oxides decreased in both samples. Comparing the Nb 3d, Sn 3d, S 2p and C 1s core levels with metallic Nb, Sn, S and C reference materials, we observed a positive chemical shift for Nb 3d5/2 and a negative chemical shift for C 1s in both samples. These results suggest that the charge transfer model can be applicable to the Nb2SnC and Nb2SC compounds. Finally, the decrease in the Tc in the Nb2SC compound respect to Nb2SnC might be associated to decrease in the density of states N(EF).