J. Ling et al./ Journal of Solid State Chemistry 178(2005)819-824 2. Experimental Zno micro- and nanocrystals were synthesized using chemical vapor transport and condensation system developed in our lab. In a typical synthesis processes, 5 of pure metal Zn(99.99%)or Cu-Zn(99.99%)mixed powders at certain weight ratio( Cu/Zn=2/8, 4/ 6, 5/5, 6/4, 7/3, and 9/1, respectively) were put in a small alumina boat to serve as the source material. The alumina boat was then pushed to the central of the A BA B alumina tube in air atmosphere at 1250C and held for several minutes. After the reaction, a large amount of white powder could also be collected at the alumina boat and the downstream area of this alumina tube. a Fig. I. XRD pattern of the as-synthesized dendrite Zno nanocrystals representative yield for the reactions of Cu/zn=6/4 (Cu/Zn=4/6 weight ratio). Indices of the peaks are specified above was~7.0%. the peaks(A) peaks of purity of zinc, (B)peaks of purity of zinc Zno nanowires were synthesized in the same manner nitride) by oxidizing a block of brass (41.51 wt% of Zn)with the weight of 46 g. The furnace was first heated to 1250C and held for 30 minutes under the protection of an argon flow of 80 standard cubic centimeters per minute. Cu/Zn= 4 6, Fig. 2d Cu/Zn= 5/5, and Fig. 2e Cu/ Followed let the melted brass exposed to the air Zn= 6/4). The diameter of the arms in the tetrapod atmosphere and reacted for several minutes. After the structure decreases with increasing Cu content. The thin reaction, the alumina tube was clogged up with a cotton- tetrapods generally have the needle-shaped arms(Fig like Zno product. The collected product in the tube 2d), while the thick ones have two kinds of uniform weighted 4.0 g and the yield was x8.7%. Small brass structures: special edge -like arms(Fig. 2c) and hexago- bean remained in the alumina boat nal cylinder arms(Fig. 2e and the inset), which are Morphology, structure and chemical composition of unique morphologies of Zno nanocrystals compared to the samples were examined using an X-ray diffraction that reported previously [6]. Furthermore, while a (XRD, D/max-rB, CuKo radiation), a scanning electron her Cu proportion was used, microwires microscopy (SEM, Hitachi X-650) equipped with an with a radiation flower (Fig. 2f, Cu/Zn= 7/3)and EDS, and transmission electron microscopy (TEM, chrysanthemum petal-like microcrystals (Fig. 2g, JEM-100C Cu/Zn= 9 High yield of ZnO nanowires can be produced by oxidation of melted brass with a commercial purity 3. Results and discussion (41.51 wt of Zn)using the same COva method Fig 3 shows the typical SEM and TEM images of these ZnO Fig. 1 shows a typical XRD pattern of the as- nanowires Determined from TEM images(Fig. 3b), the synthesized white powder sample(Cu/Zn= 4/6, weight diameter of the ZnO nanowires varied from 10 to ratio). The diffraction peaks can be indexed to 150nm. The observed variation in diameter may be hexagonal structure of Zno with cell constants of a related to the inhomogeneous sizes of the nuclei of th 3. 24 and c=5.19A. No diffraction peaks produced oxide nanowires [7]. The lengths of these nanowires from Cu and Cuo could be found from the pattern, distributed from 3 to 10 um. The nanosheets and though there are some weak peaks from small amount nanoscale tripods, as by-products, often appear in the of A: zinc that has not been oxidized and B: zinc nitride products(Fig 3a). XRD pattern confirms a hexagonal from the reaction of zinc and nitrogen in the air structure of ZnO(Fig 3c). Some weak peaks from small Further structural characterization of the products amount of zinc and zinc nitride are also detected, same was performed using TEM and SEM. Fig. 2 shows as those in Fig. I typical SEM images of the Zno micro- and nanocrys- Understanding the growth mechanism will be im tals. When pure Zn was used as reactant, uniform portant in order to control and design nanostruc sprout-like ZnO tetrapod microstructures were obtained tures. All experiments in this study were carried out in (Fig 2a). When Cu was added to the Zn with the weight air atmosphere. It is apparent that the synthesis ratio 2/8, bullet-like product with hexagonal cylinder of Zno nanostructures discussed here is based on microstructures was achieved (Fig 2b). However, when the oxidation of thermal evaporation of Zn powder more proportion of Cu was added, the ZnO w under the controlled conditions. The crystal growth may tetrapod micro- and nanostructure appeared(Fig. 2c be dominated mainly by the following two growth2. Experimental ZnO micro- and nanocrystals were synthesized using a chemical vapor transport and condensation system developed in our lab. In a typical synthesis processes, 5 g of pure metal Zn (99.99%) or Cu–Zn (99.99%) mixed powders at certain weight ratio (Cu/Zn ¼ 2/8, 4/6, 5/5, 6/4, 7/3, and 9/1, respectively) were put in a small alumina boat to serve as the source material. The alumina boat was then pushed to the central of the alumina tube in air atmosphere at 1250 1C and held for several minutes. After the reaction, a large amount of white powder could also be collected at the alumina boat and the downstream area of this alumina tube. A representative yield for the reactions of Cu/Zn ¼ 6/4 was 7.0%. ZnO nanowires were synthesized in the same manner by oxidizing a block of brass (41.51 wt% of Zn) with the weight of 46 g. The furnace was first heated to 1250 1C and held for 30 minutes under the protection of an argon flowof 80 standard cubic centimeters per minute. Followed let the melted brass exposed to the air atmosphere and reacted for several minutes. After the reaction, the alumina tube was clogged up with a cotton￾like ZnO product. The collected product in the tube weighted 4.0 g and the yield was 8.7%. Small brass bean remained in the alumina boat. Morphology, structure and chemical composition of the samples were examined using an X-ray diffraction (XRD, D/max-rB, CuKa radiation), a scanning electron microscopy (SEM, Hitachi X-650) equipped with an EDS, and transmission electron microscopy (TEM, JEM-100C). 3. Results and discussion Fig. 1 shows a typical XRD pattern of the as￾synthesized white powder sample (Cu/Zn ¼ 4/6, weight ratio). The diffraction peaks can be indexed to a hexagonal structure of ZnO with cell constants of a ¼ 3:24 and c ¼ 5:19 A( : No diffraction peaks produced from Cu and CuO could be found from the pattern, though there are some weak peaks from small amount of A: zinc that has not been oxidized and B: zinc nitride from the reaction of zinc and nitrogen in the air. Further structural characterization of the products was performed using TEM and SEM. Fig. 2 shows typical SEM images of the ZnO micro- and nanocrys￾tals. When pure Zn was used as reactant, uniform sprout-like ZnO tetrapod microstructures were obtained (Fig. 2a). When Cu was added to the Zn with the weight ratio 2/8, bullet-like product with hexagonal cylinder microstructures was achieved (Fig. 2b). However, when more proportion of Cu was added, the ZnO with tetrapod micro- and nanostructure appeared (Fig. 2c Cu/Zn ¼ 4/6, Fig. 2d Cu/Zn ¼ 5/5, and Fig. 2e Cu/ Zn ¼ 6/4). The diameter of the arms in the tetrapod structure decreases with increasing Cu content. The thin tetrapods generally have the needle-shaped arms (Fig. 2d), while the thick ones have two kinds of uniform structures: special edge-like arms (Fig. 2c) and hexago￾nal cylinder arms (Fig. 2e and the inset), which are unique morphologies of ZnO nanocrystals compared to that reported previously [6]. Furthermore, while a further higher Cu proportion was used, microwires with a radiation flower (Fig. 2f, Cu/Zn ¼ 7/3) and chrysanthemum petal-like microcrystals (Fig. 2g, Cu/Zn ¼ 9/1) were obtained. High yield of ZnO nanowires can be produced by oxidation of melted brass with a commercial purity (41.51 wt% of Zn) using the same CGVA method. Fig. 3 shows the typical SEM and TEM images of these ZnO nanowires. Determined from TEM images (Fig. 3b), the diameter of the ZnO nanowires varied from 10 to 150 nm. The observed variation in diameter may be related to the inhomogeneous sizes of the nuclei of the oxide nanowires [7]. The lengths of these nanowires distributed from 3 to 10 um. The nanosheets and nanoscale tripods, as by-products, often appear in the products (Fig. 3a). XRD pattern confirms a hexagonal structure of ZnO (Fig. 3c). Some weak peaks from small amount of zinc and zinc nitride are also detected, same as those in Fig. 1. Understanding the growth mechanism will be im￾portant in order to control and design nanostruc￾tures. All experiments in this study were carried out in air atmosphere. It is apparent that the synthesis of ZnO nanostructures discussed here is based on the oxidation of thermal evaporation of Zn powder under the controlled conditions. The crystal growth may be dominated mainly by the following two growth ARTICLE IN PRESS Fig. 1. XRD pattern of the as-synthesized dendrite ZnO nanocrystals (Cu/Zn ¼ 4/6 weight ratio). Indices of the peaks are specified above the peaks ((A) peaks of purity of zinc, (B) peaks of purity of zinc nitride). 820 J. Ling et al. / Journal of Solid State Chemistry 178 (2005) 819–824