The photocatalytic activity of GaN nanowires was investigated for the use of GaN nanowires as photocatalysts in harsh environments. GaN nanowires with diameters of 20-50 nm and lengths of 4-6 microm were prepared by Ni catalyst-assisted metal-organic chemical vapor deposition. Comparisons of GaN nanowires with GaN submicron dot arrays and thin films showed that GaN nanowires exhibit much better photocatalytic activity, resulting from a high surface-to-volume ratio. In addition, GaN nanowires exhibited good ability to photodegrade organic dye at various pHs, even under strong acidity and alkalinity. The photocatalytic activity of GaN nanowires was also compared with that of ZnO and TiO(2) nanowires.
A novel method for shaping and positioning ZnO nanoarchitectures using conventional lithography and catalyst‐free metal organic vapor‐phase epitaxy is demonstrated. Nanowalls and nanotubes of desired shapes and arrangements can be grown heteroepitaxially on Si substrates, and their electron‐emission characteristics were optimized by changing their diameter and spacing. This method can be readily expanded to create many artificial 1D and 2D structures, as required for various device applications.
There has been an increasing demand for fabrications of optoelectronic components which can be integrated with conventional silicon devices. [1][2][3] For the Si-based optoelectronic device fabrications, a tremendous effort has been made on heteroepitaxial growth of compound semiconductor films on Si substrates [4] and nanometer-scale lithography. Although the top-down method controls the position of nanostructures accurately on specific positions, a strain effect between Si and a heteroepitaxial film is involved due to lattice misfits of the materials and many etching techniques also result in surface damage as well as contamination. The problems associated with the top-down method may be solved using the bottomup approach, i.e., selective growth of one-dimensional (1D) nanostructures on Si substrates. [5,6] In particular, position-controlled vertical arrays of 1D nanostructures on Si substrates offer the ideal geometry for their use as functional components in Si-based electronic and photonic nanodevices. Although a few well-controlled semiconductor nanowires have recently been prepared by either metal catalyst-assisted [7][8][9][10][11][12] or catalyst-free methods, [13,14] only limited semiconductor nanomaterials and substrates were employed. In particular, the catalyst-free methods have not demonstrated positioncontrolled heteroepitaxial growth of oxide semiconductor nanorods on Si substrates. In this communication, we report on position-controlled selective growth of vertically aligned ZnO nanorods on Si substrates by catalyst-free metal-organic vapor-phase epitaxy (MOVPE). The catalyst-free MOVPE has recently been employed for growth of vertically well-aligned ZnO nanorods with high crystallinity and purity on many substrates including Si substrates. [15][16][17] Various ZnO-based nanorod heterostructures with abrupt interfaces were also obtained. [18,19] Furthermore, catalyst-free grown ZnO nanorods demonstrated feasibility for many nanodevice applications including nanorod field-effect transistors [20] and logic gates. [21] In contrast to the catalyst-assisted vapor-liquid-solid methods, however, the random nucleation process during catalyst-free growth makes it difficult to control the nucleation sites on many substrates. Meanwhile, for catalyst-free ZnO nanorod growth, GaN micropatterns with different surface planes offer growth-selectivity for position-controlled ZnO nanorods since anisotropic surface energies of ZnO have a critical role in forming nanorods. In addition, GaN micropatterns can be easily prepared on Si substrates which are very cheap and have widely been used for electronic and optoelectronic device applications. Here, we employed position-and facet-controlled GaN micropatterns with highly anisotropic surface energies for selective growth of ZnO nanorods on Si substrates. Prior to ZnO nanorod growth, facet-controlled GaN micropattern arrays were prepared on Si(111) substrates for catalyst-free, selective growth of ZnO nanorods. As illustrated in Figure 1a, a 1-lm-thick GaN seed layer wi...
High temperature carrier controlled ferromagnetism in alkali doped ZnO nanorods
The position‐controlled growth and structural and optical characteristics of ZnO nanotubes and their coaxial heterostructures are reported. To control both the shape and position of ZnO nanotubes, hole‐patterned SiO2 growth‐mask layers on Si(111) substrates with GaN/AlN intermediate layers using conventional lithography are prepared. ZnO nanotubes are grown only on the hole patterns at 600 °C by catalyst‐free metal–organic vapor‐phase epitaxy. Furthermore, the position‐controlled nanotube growth method allows the fabrication of artificial arrays of ZnO‐based coaxial nanotube single‐quantum‐well structures (SQWs) on Si substrates. In situ heteroepitaxial growth of ZnO and Zn0.8Mg0.2O layers along the circumference of the ZnO nanotube enable an artificial formation of quantum‐well arrays in a designed fashion. The structural and optical characteristics of the ZnO nanotubes and SQW arrays are also investigated using synchrotron radiation X‐ray diffractometry and photoluminescence and cathodoluminescence spectroscopy.
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