Chemical composition of superconducting SmFeAs doped with fluorine

Bulk samples of SmFeAsO with and without F doping were prepared by thermal synthesis of the powders. Some samples of obtained oxy-pnictides were further pressed and sintered at 1300 degrees C. The crystalline structure of the samples was investigated by X-ray powder diffraction. The samples were also characterized by resistivity measurements and SEM-Energy Dispersive Spectroscopy (EDS) analysis. The chemical composition (atomic concentration and chemical states of constituent elements) of the samples' surface was analyzed by means of XPS before and after the sample cleaning by Ar ion sputtering. For the analysis of the bulk composition, the samples were scraped by using superfine diamond file and immediately transferred into XPS apparatus. In this way, the in-depth distribution of fluorine and the contribution of surface oxides were revealed.