Ionic-Diffusion-Driven, Low-Temperature, Solid-State Reactions Observed on Copper Sulfide Nanowires

Abstract

Using vertically aligned Cu 2 S nanowires as both physical templates and chemical sources, unique heteronanostructures were synthesized by solid-state conversion reactions at low temperatures. At temperatures as low as 105 °C and in the presence of H 2 S, segmented nanowires and rod-in-a-tube (RIT) structures were produced. The different morphologies were discovered to depend on the diffusivity of the ions from various metal coatings. In the case where the inward diffusion of outer metal is faster or roughly equivalent to that of Cu + outward diffusion, incorporation and subsequent phase segregation occurred to yield segmented nanowires; in instances where Cu + diffuses outward more quickly than the metal coating inward, the RIT morphology formed via a Kirkendall-like mechanism. The nanowire–Cu substrate interface was believed to play a unique and crucial role as either a reservoir of additional Cu or as a sink for out-diffusing Cu, depending on the nature of the reaction. Full conversion of Cu 2 S nanowires to wurtzite ZnS was also demonstrated, with the complete displacement of Cu back into the Cu substrate. These low-temperature, solid-state conversion reactions show promise as a possible route for synthesizing vertically aligned nanostructures with more complicated compositions.