Growth of Vertically Aligned ZnO Nanowire Arrays Using Bilayered Metal Catalysts (original) (raw)
Related papers
Controlling the Growth Direction of ZnO Nanowires on c-Plane Sapphire
MRS Proceedings, 2004
Well oriented vertical ZnO nanowires (NWs) are grown on c-plane sapphire via a vaporphase transport process using an Au thin film as a catalyst. This new finding is unexpected due to the fact that the lattice mismatch between the zinc oxide and the underlying substrate is 18%. Xray diffraction (XRD) analysis shows that single-crystal, wurtzite NWs grow in the [0001] direction normal to the basal sapphire plane, which proves that a-plane sapphire is not essential for growth of vertical ZnO NWs, as has been previously stated.
Vertically Well-Aligned ZnO Nanowires on c-Al2O3 and GaN Substrates by Au Catalyst
ETRI Journal, 2006
Hyun-Kyu Park et al. 787 ABSTRACT⎯In this letter, we report that vertically wellaligned ZnO nanowires were grown on GaN epilayers and cplane sapphire via a vapor-liquid-solid process by introducing a 3 nm Au thin film as a catalyst. In our experiments, epitaxially grown ZnO nanowires on Au-coated GaN were vertically wellaligned, while nanowires normally tilted from the surface when grown on Au-coated c-Al 2 O 3 substrates. However, pre-growth annealing of the Au thin layer on c-Al 2 O 3 resulted in the growth of well-aligned nanowires in a normal surface direction. Highresolution transmission electron microscopy measurements showed that the grown nanowires have a hexagonal c-axis orientation with a single-crystalline structure.
Journal of Materials Research, 2008
An effective, low cost, simple, and mask-free pathway is demonstrated for achieving density control of the aligned ZnO nanowires grown for large-scale applications. By a slight variation of the thickness of the thermally evaporated gold catalyst film, a significant change in the density of aligned ZnO nanowires has been controlled. The growth processes of the nanowires on an Al 0.5 Ga 0.5 N substrate has been studied based on the wetting behavior of gold catalyst with or without source vapor, and the results classify the growth processes into three categories: separated dots initiated growth, continuous layer initiated growth, and scattered particle initiated growth. This study presents an approach for growing aligned nanowire arrays on a ceramic substrate with the simultaneous formation of a continuous conducting electrode at the roots, which is important for device applications, such as field emission.
Catalyst-free growth of uniform ZnO nanowire arrays on prepatterned substrate
Applied Physics Letters, 2006
Uniform and ordered ZnO nanowire arrays have been fabricated on the nanopatterned SiO 2 / GaN substrate without metal catalysts using hydrothermal synthesis. The nanopatterns on SiO 2 / GaN substrate with an average diameter of 65 nm are produced by inductively coupled plasma etching using anodic alumina template as a mask, which provides nucleation sites for the vertical ZnO nanowires growth. High quality of the aligned uniform ZnO nanowire arrays grown on GaN substrate was confirmed by x-ray diffraction, transmission electron microscopy, and photoluminescence. This growth technique provides a cost-effective approach to fabricate ordered nanowire arrays with controlled size, which may benefit the nanowire device applications.
High-quality ZnO nanowire arrays directly synthesized from Zn vapor deposition without catalyst
Journal of the Korean Crystal Growth and Crystal Technology
Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on GaN/sapphire and Si substrate from Zn vapor deposition without catalysts. Experimental results showed that the number density, diameter, crystallinity and degree of the alignment of ZnO NWs depended strongly on both the substrate position and kind of the substrates used for the growth. The photoluminescence (PL) characteristics of the grown ZnO NW arrays exhibit a strong and sharp ultraviolet (UV) emission at 379 nm and a broad weak emission in the visible range, indicating that the obtained ZnO NWs have a high crystal quality with excellent optical properties. The as-grown ZnO NWs were characterized by using scanning electron microscopy (SEM), high resolution transmission electronic microscopy (HR-TEM), and X-ray diffraction (XRD).
Patterned growth of aligned ZnO nanowire arrays on sapphire and GaN layers
Superlattices and Microstructures, 2004
Patterned growth of vertically aligned ZnO nanowire arrays on the micrometer and nanometer scale on sapphire and GaN epilayers is reported. In order to control the position and distribution density of the ZnO nanowires, Au seeding nanodots are defined, as regular arrays, with the assistance of deposition shadow masks. Electron micrographs reveal that the wires are single crystals having wire axes along the hexagonal c-axes. The epitaxial growth of ZnO nanowires on sapphire and GaN films on Si substrates was further verified by cross sectional electron microscopy investigations. Compared to the sapphire case, the perfect epitaxial growth on a GaN film on a Si substrate is believed to be more suitable for potential electronic device applications of ZnO nanowire arrays.
Journal of Physical Chemistry C, 2009
Recently, we showed large-scale fabrication of field-effect transistors from horizontal ZnO nanowires (NWs) on a-plane sapphire. Here, in examining the cross sections of such nanodevices, we use high-resolution transmission electron microscopy (HRTEM) and large-angle, convergent-beam electron diffraction (LACBED). We show how horizontally grown ZnO NWs influence their underlying sapphire surface and how substrate influences the growth directionality of the NWs. As a NW grows on sapphire, the substrate experiences a compressive strain of ≈7% in its [0001] sap direction (along the width of a NW) to minimize its lattice mismatch with the ZnO NW. Accordingly, ZnO expands along its width to improve its lattice match with the sapphire. The growth direction of (11 j 00) is suggested to be the direction that produces a lower lattice strain between ZnO and sapphire. Analyses of NW/sapphire interfaces show that single-crystal NWs grow epitaxially and semicoherently with many fewer misfit dislocations than theoretically expected. We attribute the formation of fewer dislocations at the interface to local relaxation of zinc oxide strain into the sapphire surface. This relaxation is in agreement with the observed deformation of the sapphire underneath the NWs. We also define a critical NW thickness beyond which the growth mode changes from horizontal to standing. Results indicate that below this thickness, gold nanodroplets partially wet both sapphire and ZnO crystals. Above the critical thickness, gold preferentially wets the ZnO nanocrystal, and formation of misfit dislocations at the interface becomes energetically favorable. Combination of these two effects is used to explain the observed change in the growth modes of the NWs.
Vertical ZnO nanowire growth on metal substrates
Nanotechnology, 2012
Vertical growth of ZnO nanowires is usually achieved on lattice-matched substrates such as ZnO or sapphire using various vapor transport techniques. Accomplishing this on silicon substrates requires thick ZnO buffer layers. Here we demonstrate growth of vertical ZnO nanowires on FeCrAl substrates. The pre-annealing prior to growth appears to preferentially segregate Al and O to the surface, thus leading to a self-forming, thin pseudo-buffer layer, which then results in vertical nanowire growth as on sapphire substrates. Metal substrates are more suitable and cheaper than others for applications in piezoelectric devices, and thin self-forming layers can also reduce interfacial resistance to electrical and thermal conduction.
physica status solidi (a), 2012
Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on Si(100) substrate without any metal catalysts by conventional thermal evaporation. The effects of the substrate positions on the structures and properties of ZnO NW arrays were primarily discussed. The orientation and morphology of the resultant NWs were analyzed by using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that the density and diameter of the ZnO NWs can be effectively controlled by changing the substrate position. The photoluminescence (PL) characteristics of the grown ZnO NW arrays show a sharp and strong ultraviolet (UV) emission at 380 nm and a very weak green emission at around 490 nm, indicating that the assynthesized NWs have outstanding optical properties with good crystalline quality and may have excellent application potential in optoelectronic devices.
Epitaxial growth of ZnO nanowires on a- and c-plane sapphire
Journal of Crystal Growth, 2005
Epitaxial ZnO nanowires were grown on a-and c-plane sapphire substrates by metalorganic chemical vapor deposition without metal catalysts or templates. Nanowires with monodisperse diameters grow in dense arrays perpendicular to a-plane sapphire and with in-plane rotational alignment due to [0 0 0 1] ZnO J[1 12 0] sapphire , ½1 12 0 ZnO ½0 0 0 1 sapphire epitaxy. On c-plane sapphire, multiple possible epitaxial relations give a mixture of nanowire orientations. The majority of the nanowires grow in one of the three directions all at an angle of 51.81 off the substrate plane with [0 0 0 1] ZnO J[1 01 4] sapphire , ½1 01 0 ZnO J[12 1 0] sapphire epitaxy. A small fraction of the nanowires grow perpendicular to the substrate with [0 0 0 1] ZnO J[0 0 0 1] sapphire .