Cu₂ZnSnS₄ Nanorods Doped with Tetrahedral, High Spin Transition Metal Ions: Mn²⁺, Co²⁺, and Ni²⁺

Because of its useful optoelectronic properties and the relative abundance of its elements, the quaternary semiconductor Cu 2 ZnSnS 4 (CZTS) has garnered considerable interest in recent years. In this work, we dope divalent, high spin transition metal ions (M 2+ = Mn 2+, Co 2+, Ni 2+ ) into the tetrahedral Zn 2+ sites of wurtzite CZTS nanorods. The resulting Cu 2 M x Zn 1– x SnS 4 (CMTS) nanocrystals retain the hexagonal crystalline structure, elongated morphology, and broad visible light absorption profile of the undoped CZTS nanorods. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and infrared (IR) spectroscopy help corroborate the composition and local ion environment of the doped nanocrystals. EPR shows that, similarly to Mn x Cd 1– x Se, washing Cu 2 Mn x Zn 1– x SnS 4 nanocrystals with trioctylphosphine oxide (TOPO) is an efficient way to remove excess Mn 2+ ions from the particle surface. XPS and IR of as-isolated and thiol-washed samples show that, in contrast to binary chalcogenides, Cu 2 Mn x Zn 1– x SnS 4 nanocrystals aggregate not through dichalcogenide bonds, but through excess metal ions cross-linking the sulfur-rich surfaces of neighboring particles. Our results may help in expanding the synthetic applicability of CZTS and CMTS materials beyond photovoltaics and into the fields of spintronics and magnetic data storage.