Synthesis, characterization, and electrical properties of nickel sulfide nanowires filled carbon nanotubes

Filled carbon nanotubes (CNTs) exhibit unique physical properties arising from the synergistic effects between the carbon shells and the filling material making them attractive towards numerous applications. Although many inorganic and organic materials have been successfully encapsulated inside CNTs until now, there is still a lack of a reliable, efficient, upscaled, and economic method to achieve a complete filling of CNT cores with transition metal sulfide nanowires. We have developed a simple in situ method for the first time to synthesize CNTs filled with nickel sulfide nanowire (Ni₃S₂@CNTs) on various substrates using a chemical vapor deposition technique. Electron microscopy measurements reveal that CNTs are completely and continuously filled with single crystalline nanowires up to several micrometers in length. Raman spectroscopy suggests that the Ni₃S₂@CNTs are exceptionally well graphitized and of ultra-high quality. The I-V characteristics of individual Ni₃S₂@CNTs were studied using both two probe and four-point probe methods which reveal the metallic properties of Ni₃S₂@CNTs.