High-yield fabrication and electrochemical characterization of tetrapodal CdSe, CdTe, and CdSe_xTe_1-x nanocrystals

The high-yield fabrication of tetrapodal CdSe, CdTe, and CdSe _xTe_1-x nanocrystals is systematically studied. CdSe nanocrystals are prepared by first controlling the synthesis of high-quality wurtzite CdSe and zinc blende CdSe nanocrystals at a relatively high temperature (260°C) by selecting different ligands. Then, based on the phase control of the CdSe nanocrystals, two nanoparticle-tailoring routes (i.e., a seed-epitaxial route and ligand-dependent multi-injecting route) are used, and a high yield of CdSe tetrapods is obtained. CdTe nanocrystals are prepared by adjusting the ligand composition and the ratio of Cd to Te; CdTe tetrapods are synthesized in high yield using a mixed ligand that does not contain alkylphosphonic acids. Moreover, the nanoscale Te powder (Te nanowires/nanorods), which is highly soluble in the ligand solvent, is first used as a Te source to synthesize CdTe nanocrystals, which remarkably enhanced the output of the CdTe nanocrystals in one reaction. Furthermore, composition-tunable ternary CdSe_xTe_1-x alloyed tetrapods are synthesized on a large scale, for the first time, by thermolyzing the mixture of the organometallic Cd precursor and the mixed (Se + Te) source in a mixed-ligand solution. The CdSe, CdTe, and CdSe_xTe_1-x nanocrystals are characterized by transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, X-ray diffraction, and UV-vis and photoluminescence (PL) spectroscopy. Interesting nonlinear, composition-dependent absorption and PL spectra are observed for the ternary CdSe_xTe_1-x alloyed nanocrystals. The band-edge positions of the nanocrystals of CdSe, CdSe_xTe_1-x and CdTe are systematically studied by cyclic voltammetry.