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

Abstract X-ray photoelectron spectroscopy (XPS) was used to investigate the binding energies and valence band of the Nb 2 SnC and Nb 2 SC compounds. The Nb 3d 5/2 , Sn 3d 5/2 , S 2p 3/2 and C 1s core levels associated with the chemical states of Nb 2 SnC and Nb 2 SC were identified. The spectra for Nb 2 SnC revealed Nb and Sn oxides on the surface of the sample, mainly Nb 2 O 5 and SnO 2 , while the Nb 2 SC only Nb 2 O 5 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 3d 5/2 and a negative chemical shift for C 1s in both samples. These results suggest that the charge transfer model can be applicable to the Nb 2 SnC and Nb 2 SC compounds. Finally, the decrease in the T c in the Nb 2 SC compound respect to Nb 2 SnC might be associated to decrease in the density of states N ( E F ).