Ligand-controlling synthesis and ordered assembly of ZnS nanorods and nanodots

The shape- and phase-controlled synthesis of ZnS nanocrystals (nanorods and nanodots) was realized by the selection of ligand molecules with a simple method of thermolysing single-source precursor-zinc ethylxanthate (Zn(exan)(2)) with octylamine (OA) or trioctylphosphine (TOP) as precursor solvent. The as-prepared nanocrystals were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). In hexadecylamine (HDA) + OA system, diameter- and aspect-ratio-tunable hexagonal wurtzite ZnS nanorods were attained in the temperature range of 150-250 degreesC, and the nanorods self-assembled into two-dimensional (2-D) aligned arrays. While in the HDA + TOP system, a shape change from rod to spherical particle and a phase transition from wurtzite to sphalerite simultaneously occurred with the increase of TOP content in the solution, and sphalerite nanodots were prepared in high TOP content or in TOP (or trioctylamine (TOA)) solution without HDA. The mechanism of the shape- and phase-controlled growth of ZnS nanocrystals by selecting ligand molecules was analyzed. The absorption and photoluminescence spectra of the wurtzite ZnS nanorods and the sphalerite ZnS nanodots were also measured and contrasted. In addition, the mechanism and the strategies of assembling I-D ZnS nanorods on 2-D scale were discussed, and the ordered arrays of the nanorods and nanodots were obtained on a relatively large scale.