As an important II-VI semiconductor, ZnO has attracted increasing interests owing to its unique properties such as wide band-gap (3.37 eV) and large exciton binding energy (60 meV).[1] ZnO has shown great potential in optoelectronic devices such as light emitting diodes (LED) and laser diodes (LDs) operating in the short-wavelength or UV region.[2]Compared to their thin-film counterparts, [3][4] nanoscale devices assembled on free-standing nanowires [5][6][7][8][9][10] could enable new functions, high efficiency, enhanced performance, and diverse applications. [11][12][13][14][15][16][17][18][19][20] As in thin-film devices, the success of nanodevices similarly relies on the capability of controlling the transport and electrical properties of the selected materials. Doping via introducing electron donor or acceptor elements into the host crystal is a successful approach in thin-film or planar electronic/optoelectronic devices. However, such doping approach remains a challenge for nanostructured materials. To date, while n-and p-type dopings have been achieved in Si, [11][12] InP, [13] CdS, [14] and GaN [15] nanowires/ nanoribbons, many issues of doping, such as control of doping type and conductivity, remain largely untapped or unresolved. For ZnO nanostructures, group III elements (Al, Ga, or In) are commonly used to substitute Zn to induce n-type conductivity. The success of doping is often accompanied and characterized by changes in optical, electrical, and/or structural properties of ZnO nanostructures. For example, Al-doped ZnO nanowires exhibited a blue shift from 3.29 to 3.34 eV in the cathodoluminescent (CL) spectra.[21] Ga 2 O 3 was also employed to dope n-type ZnO nanofibers grown in a vaporphase transport process. [22] however switched to n-type after two months storage in an ambient environment. Despite the considerable efforts, rational synthesis of ZnO nanostructures with tunable n-type conductivity is not available. The as-synthesized ZnO nanostructures are often randomly oriented, and thus have limited applications in optoelectronic devices. Therefore, it is necessary to have a better understanding of the doping efficiency and transport properties of ZnO nanostructures. Herein, we report a controlled growth and doping process of well-aligned ZnO nanowire (NW) arrays via thermal evaporation. The growth direction of ZnO NWs was found to depend on the dopant content, and NW conductivity could be varied over two orders of magnitude. The electrical properties of ZnO NWs were characterized using single-nanowire field-effect transistors (FETs). Figure 1 shows the electron microscopy images of ZnO NW arrays synthesized on a-plane sapphire substrates. The content of Ga 2 O 3 in the source mixtures was varied from 0 to 1 at %. The representative NWs synthesized with 0, 0.2, and 1 at % of Ga 2 O 3 are denoted as samples A, B, and C, respectively. Both the undoped (Fig. 1a and b) and Ga-doped (Fig. 1c) ZnO NWs are aligned vertically on the substrates, and uniform over a large area. The NWs have a uniform dia...

Arrays of well-aligned one-dimensional ZnO nanostructures (nanowires, nanorods, nanoribbons, nanobuds, and flocky nanorods) with high aspect ratios have been grown on zinc substrates by a solution-phase method using a mixture of ethylenediamine, ethanol, and water. The morphology of the ZnO nanostructures has been modulated by controlling the concentration of ethylenediamine and ethanol and regulating the reaction temperature. Chemical and structural analyses and emission spectra show that the arrays of ZnO nanorods favor nearly stoichiometric composition and good crystallization quality, whereas the arrays of ZnO nanowires, nanoribbons, nanobuds, and flocky nanorods confine a considerable amount of oxygen vacancies. The photocatalytic effect investigated at decomposition of methyl red correlates with the defect-related emission properties of these nanoarrays. Particularly ZnO nanobuds and flocky nanorods arrays have been found to be effective photocatalysts.

Many facets: A controlled synthesis results in high‐symmetry small‐molecular organic microcrystals with shapes that range from cubes through truncated cubes to rhombic dodecahedra (see picture). Morphological control was achieved by changes in solubility, which substantially alters the growth rate in the 〈100〉 direction relative to that in the 〈110〉 direction. Changes in morphology also lead to different optical properties of the crystals.

Nanostructures have attracted wide attention for their potential applications as building blocks for nanoscale devices. Various types of single-crystal nanostructures have been synthesized and extensive efforts have been devoted to the development of more complex functional nanostructures. Component-modulated materials, such as superlattices, heterojunctions, and core/shell nanostructures, are special kinds of nanomaterials, [1][2][3][4][5][6][7][8][9][10][11][12] which not only offer the benefit of designing and fabricating nanodevices without further assembling, but can also provide unique desirable properties. [13][14][15] In general, it is difficult to fabricate heterojunctions of high single-crystal quality from two different materials with a large lattice mismatch, since dislocations are readily formed at the interface region. However, at the nanoscale, small-size interface and surface effects can assert considerable influence on the formation of nanostructures [16][17][18] to enable the formation of high-quality heterojunctions free of dislocations in nanosized domains.ZnS (band-gap %3.68 eV at 300 K) and ZnO (band-gap %3.37 eV at 300 K) are important II-VI group semiconductors, and attract intense interest owing to their wide applications in optoelectronics. Extensive effort has focused on the synthesis of ZnS and ZnO nanocrystals of various morphologies and properties. [19,20] Here, we report for the first time the fabrication of a novel heterojunction nanoribbon composed of two side-byside ribbons of ZnS and ZnO with a unique crystallographic structure and high-quality crystallinity. Figure 1a is the X-ray diffraction (XRD) spectrum of the sample, in which all the peaks can be well assigned to those of wurtzite (hexagonal) ZnS with lattice constants of a ¼ 0.382 nm and c ¼ 0.626 nm (JCPDS: 36-1450), and wurtzite (hexagonal) ZnO with lattice constants of a ¼ 0.325 nm and c ¼ 0.521 nm (JCPDS: 36-1451). No characteristic peaks from impurities, such as Zn and S, can be detected in the XRD spectrum, suggesting that the sample has high phase purity. Figure 1b is a low-magnification scanning electron microscopy (SEM) image showing a precipitate to consist of nanoribbons with lengths up to several hundreds of micrometers. Figure 1c

Facettenreich: Die gezielte Synthese hochsymmetrischer niedermolekularer organischer Mikrokristalle mit Formen von Würfeln über angeschnittene Würfel zu rhombischen Dodekaedern (siehe Bild) gelang durch Änderungen in der Löslichkeit, die die Wachstumsgeschwindigkeit in 〈100〉‐Richtung relativ zu der in 〈110〉‐Richtung erheblich beeinflusst. Unterschiedliche Morphologien haben auch unterschiedliche optische Eigenschaften der Kristalle zur Folge.