Low-Temperature Growth of Rock Salt MnS Nanocrystals with Facet-Dependent Behaviors

Rock salt-phase MnS nanocubes with tunable sizes of 35 to 110 and 65 to 154 nm octahedra have been synthesized at 60-90 degrees C in aqueous solutions. At 110 degrees C, 323 nm MnS cubes, 370 nm cuboctahedra, and 630 nm octahedra can also be prepared. Crystal unit cells show a dependence on particle size and shape. High-resolution electron microscopy analysis indicates the presence of a thick surface region with notably different lattice features for the {100} and {111} faces. This gives rise to the observations of facet-dependent optical and electrical conductivity behaviors of these crystals. Their band gaps also change continuously with the particle sizes. The antiferromagnetic MnS cubes show a clear transition between different magnetic states at 36 K, but this transition is less obvious for octahedra. Cubes are more magnetized at 5 K and present a hysteresis response, yet this is not observed in octahedra. Clearly, the surface lattices significantly affect various properties of the MnS crystals, including magnetic properties.