Yaohua Zhang

Symmetric and asymmetric growth of ZnO hierarchical nanostructures: nanocombs and their optical properties

One-dimensional nanostructure growth behaves very differently on the ±(0001) polar surfaces of wurtzite ZnO, resulting in asymmetric growth in these two directions. In this report we show that by tuning the degree of supersaturation, the growth asymmetry can either be rationally utilized or broken to obtain single- or double-sided ZnO nanocombs, respectively. The nanowires grown on the two polar surfaces of the double-sided nanocombs are of comparable length, suggesting some kind of symmetric growth, but they are distributed on the two sides in an asymmetric manner. More interestingly, the two sides of the double-sided nanocomb exhibit distinct optical properties. Possible mechanisms are proposed to explain the growth and optical properties of the double-sided nanocombs.

Lithium Storage Performance of Zinc Ferrite Nanoparticle Synthesized with the Assistance of Triblock Copolymer P123

The ZnFe2O4 samples with the triblock copolymer P123 (P123) additive quantity of 0 wt.%, 2 wt.%, 5 wt.%, 8 wt.% and 10 wt.% were prepared by a very facile homogeneous precipitation method followed by high temperature sintering. The microstructures of the prepared samples were analyzed by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM). The results revealed that the five prepared samples are all normal spinel zinc ferrite (ZnFe2O4); the sample with the P123 additive quantity of 8 wt.% has the smallest particle size among the five samples. The lithium storage performances of the prepared samples are characterized by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge tests. The results demonstrated that adding proper amount of P123 can obviously improve the lithium storage performances of zinc ferrite spinel powder. But excessive P123 can induce the particle agglomerates so that the lithium storage performance of sample decays significantly. The ZnFe2O4 sample with the P123 additive quantity of 8 wt.% exhibited the highest electrochemical activity, the best rate performance, and superior cycling stability. For example, after 50 charge/discharge cycles under a current density of 120 mA g-1, the ZnFe2O4 sample with the P123 additive quantity of 8 wt.% can retain a specific discharge capacity of 468 mAh g-1, much higher than that of for the ZnFe2O4 sample with the P123 additive quantity of 0 wt.% (224 mAh g-1).

Synthesis and Magnetic Properties of FeCo Alloy Nanoparticles by Hydrogen Plasma Metal Reaction

Fe61Co39 nanoparticles were prepared by hydrogen plasma metal reaction. The as-synthesized nanoparticles were characterized by x-ray differaction (XRD), transimition electron microscope (TEM) and superconducting quantum interference device (SQUID). The nanoparticles are spherical in shape, have bcc structure with the mean particle diameter of 41 nm, and are basically ferromagnetic with a slight amount of superparamagnetic part. The saturation magnetization and coercivity of the nanoparticles at 4.2 K are 190.15 emu/g and 1280 Oe, respectively. The blocking temperature is 250 K in 100 Oe and decreases with increasing the magnetic field.

LOW-TEMPERATURE SYNTHESIS OF NOVEL ZINC OXIDE SINGLE-SIDED COMB-LIKE STRUCTURE

Single-sided ZnO nanocombs have been synthesized by thermal evaporation of Zn powders at 440°C through a vapor–solid (VS) process. The stem ribbon of the as-synthesized nanocomb takes a growth direction of , and its top/bottom surfaces are . The nanoteeth grow epitaxially out of the stem ribbon along [0001]. Such a low temperature process may be useful in future device fabrication.