Shape-controlled synthesis of nanopyramids and nanoprisms of nickel sulfide (Ni3S4).

Two different nickel precursors (NiCl2 or Ni(CH3COCH2COCH3)2) in the presence of 1-dodecanethiol and a mixture of oleylamine and oleic acid were used for a one-pot colloidal synthesis to produce high purity Ni3S4 nanoparticles with controlled shapes in high yields and narrow size distributions. By simply changing the nickel precursors, the shape of Ni3S4 nanocrystals can be readily tuned from triangular nanoprisms to tetrahedra (nanopyramids). The produced nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction, selected area electron diffraction, ultraviolet-visible spectroscopy and superconducting quantum interference device (SQUID). TEM tomography (3D-TEM) was employed to determine details of the particle shapes. SQUID measurements confirmed that particle shape and domain size could dramatically impact their magnetic properties, where tetrahedral nanopyramids of Ni3S4 nanoparticles showed ferromagnetic properties while the Ni3S4 nanoprisms showed random antiferromagnetic interactions between magnetic centers.