Growth and characterization of superconducting beta-FeSe type iron chalcogenide nanowires

We have grown highly crystalline beta-FeSe type iron chalcogenide nanowires (NWs) by annealing thin film that is prepared by a pulsed laser deposition method. Three kinds of NWs with compositions of Fe0.8Se, Fe0.88Se0.32Te0.68 and Fe0.88Te0.91S0.09 have been prepared and carefully characterized by a high-resolution transmission electron microscope (HRTEM). The NWs reveal ideal tetragonal structure with crystal growth along the [100] direction. Energy dispersive spectroscopy (EDS) studies and HRTEM images show the NWs to have good compositional uniformity, except for the existence of a thin layer of oxide on the surface. No superconducting transition was observed in the FeSex NWs, which is possibly caused by Fe deficiency. The other two types of NWs show relatively higher and sharper superconducting transitions than their bulk counterparts. Interestingly, a resistive transition tail is observed in the NWs with diameter smaller than 100 nm, which might originate from a phase slip process in the quasi-one-dimensional system. The success in producing these high quality NWs provides a new avenue for better understanding the origin of superconductivity in beta-FeSe type iron chalcogenides.