Structural characteristics and phase separation of superconducting Fe_1+ySe_1-xTe_x nanowires

Superconducting Fe_1+ySe_1-xTe_x nanowires with considerable differences in the diameter and aspect ratio were synthesized via annealing thin films with particular composition prepared by pulsed laser deposition. Using transmission electron microscopy and related techniques, we found they were all crystallized in a PbO-type tetragonal structure with a growth direction of [010] (equivalent to [100]). All the nanowires were covered by a thin amorphous oxide layer (~5 nm) determined by electron energy loss spectroscopy. Chemical analysis and the calculated lattice constants reveal the fact that these nanowires are different from chemical compositions. High-resolution electron microscopy images show that the two thick nanowires (with diameters ~80 nm) are composed of multiple phases, while the thin nanowires (with diameters of 14 and 22 nm) are single phase. Digital moiré analysis reveals that the thin nanowires contain surface defects, as well as dislocations, inside the nanowires.