Crystal orientation-ordered ZnS nanobelt quasi-arrays and their enhanced field-emission

Crystal orientation-ordered ZnS nanobelt quasi-arrays were fabricated using a non-catalytic and template-free thermal evaporation process; field-emission measurements show that these novel arrays are decent field emitters possessing a current density more than 20 times higher than that of randomly-oriented ZnS nanobelt ensembles at a macroscopic field of 5.5 V microm(-1).     

Electrochemical synthesis of orientation-ordered ZnO nanorod bundles

The high density and orientation-ordered ZnO nanorod bundles with wurtzite structures were prepared on Cu substrates by electrochemical deposition in solution of ZnCl₂ + tartaric acid at a temperature of 90 °C. This approach is a unique and size controlled synthetic method for the large-scale preparation of ZnO nanorod bundles. Cyclic voltammogram measured in solution of the mixture of ZnCl₂ and tartaric acid shows a restraining role of tartaric acid for the electro-reduction of Zn(II). The formation mechanism of ZnO on the surface of the cathode can be explained that the high temperature (⩾90 °C) promotes the corrosion of electrodeposited Zn via reacting with H₂O and O₂ to form the stable passive phase of ZnO. The compositions of the nanorod bundles can be entirely ZnO or Zn and ZnO composites determined by the temperature and deposition rate. The photoluminescence (PL) properties indicate that these ZnO deposits are highly crystallized and of excellent optical quality.     

Crystal orientation-ordered ZnO nanorod bundles on hexagonal heads of ZnO microcones: epitaxial growth and self-attraction

We demonstrate a preferential nucleation, epitaxial growth, and self-attraction of crystal orientation-ordered ZnO nanorod bundles on (0001) plane of single-crystal ZnO microcones.     

High-aspect-ratio aluminum borate nanowire bundles supported by sucrose

High-aspect-ratio and single-crystal aluminum borate (Al(18)B(4)O(33)) nanowire bundles with an ordered orientation were synthesized by using an innovative sucrose-assisted growth process. The process involves the dehydration and polycondensation of aluminum borate-sucrose solution to form a highly viscous precursor. The sucrose plays a crucial role in the growth of the nanowire bundles by supporting as a polymeric substrate and a type of adhesive template. Electron microscopy was used to characterize the high-aspect-ratio nanowire bundles. A possible growth mechanism for the nanowire bundles is proposed.     

Direct electrochemistry of hemoglobin immobilized in CuO nanowire bundles

It is one of main challenges to find the suitable materials to enhance the direct electron transfer between the electrode and redox protein for direct electrochemistry field. Nano-structured metal oxides have attracted considerable interest because of unique properties, well biocompatibility, and good stability. In this paper, the copper oxide nanowire bundles (CuO NWBs) were prepared via a template route, and the bioelectrochemical performances of hemoglobin (Hb) on the CuO NWBs modified glass carbon electrodes (denoted as Hb-CuO NWBs/GC) were studied. TEM and XRD were used to characterize the morphology and structure of the as synthesized CuO NWBs. Fourier transform-infrared spectroscopy (FT-IR) proved that Hb in the CuO NWBs matrix could retain its native secondary structure. A pair of well-defined and quasi-reversible redox peaks at approximately −0.325 V (vs. Ag/AgCl saturated KCl) were shown in the cyclic voltammogram curve for the Hb-CuO NWBs/GC electrode, which indicated the direct electrochemical behavior. The Hb-CuO NWBs/GC electrode also displayed a good electrocatalytic activity toward the reduction of hydrogen peroxide. These results indicate that the CuO NWBs are good substrates for immobilization of biomolecules and might be promising in the fields of (bio) electrochemical analysis.     

Hot spots in silver nanowire bundles for surface-enhanced Raman spectroscopy

We report a simple strategy for placing analyte molecules in hot spots between closely spaced nanowires leading to intense SERS enhancement. The results are highly reproducible from experiment to experiment likely because of the regularity of the SERS substrate, which consists of highly ordered and regular silver nanowires fabricated in porous aluminum oxide. Because the silver nanowires are sealed in the pores of PAO, this system is potentially immune to contamination until it is ready for use, at which point the alumina matrix is etched, thereby allowing the silver nanowires to collapse into bundles and form hot spots in the region of close contact between the nanowires, trapping the analyte in those junctions.     

Self-organized hierarchical ZnS/SiO(2) nanowire heterostructures

Novel hierarchical heterostructures formed by wrapping ZnS nanowires with highly dense SiO(2) nanowires were successfully synthesized by a vapor-liquid-solid process. The as-synthesized products were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy equipped with an energy-dispersive X-ray spectrometer. Studies indicate that a typical hierarchical ZnS/SiO(2) heterostructure consists of a single-crystalline ZnS nanowire (core) with diameter gradually decreasing from several hundred nanometers to 20 nm and adjacent amorphous SiO(2) nanowires (branches) with diameters of about 20 nm. A possible growth mechanism was also proposed for the growth of the hierarchical heterostructures.     

Microcrystalline sodium tungsten bronze nanowire bundles as efficient visible light-responsive photocatalysts

Microcrystalline sodium tungsten bronze nanowire bundles were obtained via a facile hydrothermal synthesis, and were applied in water purification as visible-light-driven photocatalysts for the first time.     

Synthesis of ordered ultrathin ZnO nanowire bundles on an indium-tin oxide substrate

Ultrathin ZnO nanowire bundles have been synthesized on an indium-tin oxide substrate without any catalyst by using a simple thermal evaporation method, where self-organized ZnO nanowire bundles were grown on the hexagonal heads of ZnO nanocolumns. The nanowires obtained typically have diameters of 8 nm, with lengths extending to 0.25 microm. The size is the same order of magnitude as the ZnO exciton Bohr radius (aB). Room-temperature photoluminescence measurement shows a prominent peak at 374 nm (3.32 eV), which is about 100 meV blue-shifted from the bulk ZnO emission.     

Hierarchical saw-like ZnO nanobelt/ZnS nanowire heterostructures induced by polar surfaces

Saw-like nanostructures composed of single-crystalline ZnO nanobelts and single-crystalline ZnS nanowires have been successfully synthesized by a vapor-solid process. Several techniques, including scanning electron microscope, transmission electron microscopy, and photoluminescence spectroscopy, were used to investigate the structures, morphology, and photoluminescence properties of the products. Due to the similar crystal habits of wurtzite ZnO and ZnS with chemically active Zn-terminated (0001) and chemically inactive O-terminated (or S-terminated) (000) polar surfaces, hierarchical saw-like nanostructures were considered to be formed by the initiation of a chemically active Zn-terminated ZnO (0001) polar surface. Photoluminescence properties of the heterostructures, different from pure ZnO nanobelts or ZnS nanowires, were also studied at room temperature.     

Crystal Growth Kinetics of Nanocrystalline ZnS under Surface Adsorption

The crystal growth mechanism,kinetics,and microstructure development play a fundamental role in tailoring the materials with controllable size and morphology. In this study,by introducing the strong surface adsorption of the concentrated NaOH,two-stage crystal growth kinetics of ZnS nanoparticles was observed. In the first stage,the primary particles grow into a size over a hundred times of the original volume and the growth is controlled by the crystal-lographically specific oriented attachment. The first stage data were fitted by the "multistep OA kinetic model" built based on the molecular collision and reaction. In the second stage,following the dispersal of nanoparticles,an abrupt transition from asymptotic to parabola growth kinetics occurs,which can be fitted by a standard Ostwald ripening volume diffusion model. The presence of surface adsorption causes the two-stage growth kinetics and permits an almost exclusive OA-based growth to dominate in the first stage.     

ZnO和ZnS本征点缺陷的理论研究

基于第一性原理和热动力学方法,通过模拟计算分析了不同温度和分压下ZnS和ZnO晶体本征点缺陷的性质.振动熵的计算结果表明,在高温条件下,振动熵对缺陷形成能的贡献不能忽略.对比分析2种晶体本征点缺陷随环境条件变化的规律,结果表明,2种晶体的主导缺陷均为空位型.氧空位(V_O)在ZnO中更易形成,富氧和低温条件有利用于ZnO的p型本征掺杂.而锌空位(V_(Zn))在ZnS中形成能最低,因此ZnS比ZnO更容易形成p型掺杂.研究还发现2种晶体的肖特基缺陷都不稳定,而弗伦克尔缺陷比较稳定.除ZnS反弗伦克尔缺陷外,有价态的缺陷对的形成能均比中性缺陷对的形成能低.     

Fabrication of Ordered Macroporous CdS and ZnS by Colloidal Crystal Template

Ordered macroporous semiconductors CdS and ZnS with regular arrays of spherical pores have been fabricated by poly (styrene-acrylic) (PSA) colloidal crystal template. It was found that the exact three-dimensional (3D) structure of the template had been imprinted in the final material.     

Formation of orientation-ordered superlattices of magnetite magnetic nanocrystals from shape-segregated self-assemblies

Magnetic magnetite (Fe3O4) nanocrystals have been synthesized by combining nonhydrolytic reaction with seed-mediated growth. The shape of these magnetite nanocrystals can be controlled either as pure spheres or a mixture of mainly faceted nanocrystals. Faceted magnetite nanocrystals consist of truncated tetrahedral platelets (TTPs), truncated octahedrons (TOs), and octahedrons (OTs). Transmission electron microscopy analysis indicates that the faceted nanocrystal mixture tends to self-segregate based upon the shape in a self-assembly process, and each shape forms its own distinct crystallographic orientation-ordered superlattice assemblies. Self-assemblies of the Fe3O4 nanocrystals in the shapes of TTP, TO, and OT show hexagonal, primitive cubic, and distorted body-centered cubic (bcc) superlattice structures, respectively. The possible mechanism for the formation of different superstructures is attributed to van der Waals interactions. Nanocrystals with different shapes provide diverse building blocks for bottom-up approaches in building nano- and mesosystems. Furthermore, the self-segregation phenomenon of different shaped nanocrystals in self-assembly processes could be very important in envisioning efficient assembly strategies for nanoscience- and nanotechnology-based devices.     

ZnO nanowire transistors

ZnO nanowire field-effect transistors (FETs) were fabricated and studied in vacuum and a variety of ambient gases from 5 to 300 K. In air, these n-type nanowire transistors have among the highest mobilities yet reported for ZnO FETs (mu(e) = 13 +/- 5 cm(2) V(-1) s(-1)), with carrier concentrations averaging 5.2 +/- 2.5 x 10(17) cm(-3) and on-off current ratios ranging from 10(5) to 10(7). Four probe measurements show that the resistivity of the Ti/Au-ZnO contacts is 0.002-0.02 Omega.cm. The performance characteristics of the nanowire transistors are intimately tied to the presence and nature of adsorbed surface species. In addition, we describe a dynamic gate effect that seems to involve mobile surface charges and causes hysteresis in the transconductance, among other effects.     

Synthesis and Crystal Structure of Compound [ZnS6 (C12H8N2)]

The title compound ZnS6(C12H8N2) was obtained by reaction of zinic powder with sulfur and 1,10-phenathtroline in DMF solvent, and its structure has been determined by single crystal X-ray diffraction analysis. The crystal data for the compound: triclinic, P-1, Z = 2, a = 8. 159(2), b = 9. 485(2), c = 11. 997(2)A , α =110. 00(3)°,β = 99.22(3)°, γ = 100.57(3)°, V = 832A3, Dc =1. 748g/cm3, μ(MoKa)=0. 2219 cm-1, F(000)=440. The structure was refined to R = 0. 0723 and Rw = 0. 0865 for 1427 independent observed reflections. The tilte crystal consists of a discrete molecules, in which the core of ZnS2N2 shows a distorted tetrahedral geometry.