Phase-Selective Synthesis of CuInS2 Nanocrystals

Abstract

Single-source precursor, [(Ph3P)CuIn(SC{O}Ph)4] (1), and dual-source precursors, [Cu(SC{O}Ph)] (2) and [In(bipy)(SC{O}Ph)3] (3), have been used to obtain the monodispersed wurtzite (hexagonal) and zincblende (also called sphalerite, cubic) phases of copper indium sulfide nanocrystals (CIS NCs). The NCs have been characterized by X-ray powder diffraction patterns, transmission electron microscopy, selected area electron diffraction, and energy-dispersive X-ray analysis. It is shown that the relative ratios of surfactants have influence on the formation of the wurtzite or zincblende phase of CIS. Moreover, the reaction temperature plays a role in stabilizing the high-temperature metastable zincblende cubic phase at room temperature. In the presence of trioctylphosphine oxide (TOPO) and dodecanethiol (DT), 1 generates the wurtzite phase of CIS when the reaction temperature is below 275 °C, but above this temperature the obtained product belongs to zincblende (cubic). The morphology of the CIS also changes from nanoplates to nanoparticles when it undergoes phase transformation. In the wurtzite phase, monodispersed nanoplates are formed at 175 °C and nanorods (NRs) produced at 250 °C along with the plates. Wurtzite and zincblende CIS nanocrystals exhibit intense emission in the ultraviolet region and weak emission in the visible region. The nonlinear optical (NLO) properties of the CIS NCs have also been characterized with femtosecond laser pulses at a wavelength of 780 nm.