Temperature-Controlled Fragmentation and Ripening: Synthesis of ZnSe Nanorods with Variable Dimensions and Crystal Structure Starting from Ultrathin ZnSe Nanowires

Heavy-metal-free semiconductor nanomaterials have attracted attention because of their importance in both fundamental research and commercial applications. In particular, polarized fluorescence emission in one-dimensional (1D) semiconductors makes them highly attractive as display materials. Herein, we developed a novel colloidal synthesis approach toward 1D ZnSe nanostructures with controlled size and crystal structure, which we call "temperature-controlled fragmentation and ripening". First, ultrathin ZnSe nanowires (NWs) with a length of 50-200 nm and diameter of ∼1.1 nm were synthesized. ZnSe nanorods (NRs) have been obtained through the fragmentation of these NWs in a controlled step while keeping the same diameter, and the length of the final ZnSe NRs has been tuned in the range of 10-20 nm by moderating the heating procedure. Using a higher temperature for fragmentation allowed us to break down the ZnSe NWs to shorter ZnSe NRs, whereas controlling the final growth temperature of the ZnSe NRs in a subsequent ripening stage allowed us to obtain them in either cubic zinc blende (ZB; at 220 °C) or hexagonal wurtzite (WZ; at 240 °C) crystal structures. This set of growth processes flipping from bottom-up to top-down to form ZnSe NRs with controlled length and selection of the final crystal structure (either hexagonal WZ or cubic ZB) provides a novel growth mechanism to synthesize 1D semiconductor nanostructures.