Design and construction of metal and semiconductor nanomaterials with complex multi-dimensional (MD) architectures are triggering a new tidal wave of research on selforganized growth of one-dimensional nanostructures. The realization of the hierarchical nanostructures can provide many potential opportunities for high technological applications in photonics, electronics, and magnetics as well as interface modification and advanced catalysis in engineering field. Recently, reports about branch-like metal [1] and urchin-like semiconductor complex nanostructures [2] have demonstrated a success in preparing the MD nanomaterials, but basic control mechanism and growth methods for new complex hierarchical nanostructures still remain open.Zinc oxide (ZnO), a direct wide band gap (3.37 eV) semiconductor material with a large excitation binding energy (60 meV), has become one of the most important functional materials in parallel to carbon nanotubes since the discovery of ZnO nanobelts in 2001. [3] Unlike carbon nanotubes formed by rolling graphite layers, the formation of ZnO nanobelts or nanowires is mainly dominated by the preferential growth of the material along specific crystalline orientation. From the viewpoint of crystallography, ZnO crystal has the wurtzite structure with lattice parameters of a = 0.3296 and c = 0.5206 nm. It is a hexagonal phase with space group P6 3 mc. The structure of ZnO can be depicted as a large number of alternating planes composed of tetrahedrally coordinated O 2-and Zn 2+ ions, stacked alternatively along the c-axis. The oppositely charged ions produce positively charged (0001)-Zn and negatively charged (0001)-O polar surfaces, resulting in a normal dipole moment along the c-axis. [4] The intrinsic polarity is the origination of many special properties of ZnO such as piezoelectricity and spontaneous polarization as well as an important factor in understanding growth, etching and defect generation of the material. Due to three kinds of growing directions, i.e., <0001>, <0110> and <2110>, and ± (0001) polar-surface-induced phenomena, up to date, one has found various ZnO nanostructures such as nanowires, [5,6] nanotubes, [7] nanobelts, [8] nanocombs, [9] nanosaws, [10] nanohelices [11] and nanorings [12] etc. Recently, hierarchical ZnO nanostructures have attracted much attention. Zhang et al. [13] investigated the formation of tower-like ZnO submicron-and nano-structures by simply evaporating a mixture of Zn and Ga. Mo et al. [14] employed ethylenediamine-derived Zn[en] 2 2+ as a precursor to prepare curved MD ZnO nanorod structure with the shape of hollow microhemisphere. More recently, we also have realized the size control of ZnO nanowire or nanorod unit on curved surface in alkaline solution by using hydrothermal method. The onedimensional ZnO nanounit grown on the curved surface exhibits a hexagonal cross-section profile with uniform body extending along c-axis direction. [15] In present study, we report another kind of new hierarchical ZnO micro-/nanostructure film constructed on m...
CdS quantum dots (QDs) have been synthesized on a large scale, based on the direct thermolysis of one single-source precursor, (Me(4)N)(4)[S(4)Cd(10)(SPh)(16)], in hexadecylamine (HDA). Transmission electron microscopy (TEM) observations show that the CdS QDs are well-defined, nearly spherical particles. The clear lattice fringes in high-resolution TEM (HRTEM) images confirm the crystalline nature of the QDs. The broad diffraction in the x-ray diffraction (XRD) pattern and diffuse diffraction rings of the selected-area electron diffraction (SAED) pattern are typical of nanomeric-size particles and indicative of the hexagonal phase of CdS QDs. The absorption spectra confirm quantum confinement of CdS QDs. The synthesis process for CdS QDs was investigated by ultraviolet-visible (UV-vis) absorption spectroscopy. The results demonstrate that the nucleation and growth stages were separated automatically in a homogeneous system.
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