Determination of the epitaxial growth of zinc oxide nanowires on sapphire by grazing incidence synchrotron x-ray diffraction (original) (raw)
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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 .
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.
Journal of Crystal Growth, 2012
We report on the epitaxial growth of ZnO nanosheets and nanowires on a-and c-plane sapphire substrates by Au-assisted pulsed laser deposition. The epitaxial relationship of the nanostructures was determined by x-ray diffraction (XRD) pole figure measurements. On c-plane sapphire, the ZnO nanowires grew along the ZnO c-axis and were inclined to the substrate surface normal with an angle of about 371. The ZnO(0001) plane of the wires aligned with Al 2 O 3 ð1014Þ of the sapphire substrate via two degenerate in-plane configurations, promoted by low lattice mismatch (0.05%). ZnO nanosheets grown on c-plane sapphire exhibited no preferential orientation on the substrate and no epitaxial relationship could be unambiguously identified. On a-plane sapphire, ZnO nanowires grew vertically along the ZnO c-axis with a single epitaxial configuration, whereas ZnO nanosheets seemed to grow along ZnO½1010 in two preferred in-plane orientations, 721-741 apart. These configurations could be explained by two distinct alignments of the ZnOð1011Þ plane on the a-plane sapphire substrate surface, promoted by low lattice mismatches.
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.
Buffer-Facilitated Epitaxial Growth of ZnO Nanowire
Crystal Growth & Design, 2005
This study introduces a new train of thought regarding the growth of well-arrayed nanowires. To reduce how defects such as grain boundary affect subsequent growth of the nanowires, the epitaxial buffer layer should be carefully chosen. The titanium nitride (TiN) buffer layer facilitates the growth not only of the arrays but also the epitaxy of zinc oxide (ZnO) nanowires, even given a lattice mismatch of up to 8.35% and the entirely different crystal structures between them. [12 h10] ZnO || [01 h1] TiN || [01 h1] Si plus (0001) ZnO || (111) TiN || (111) Si
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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.
Growth habits and defects in ZnO nanowires grown on GaN/sapphire substrates
Applied Physics Letters, 2005
Growth habits and defects in epitaxial ZnO nanowires grown from Au catalyst on ͑00.1͒ GaN/ sapphire substrate using the vapor-liquid-solid ͑VLS͒ technique were studied using electron microscopy and x-ray diffraction. The results revealed presence of both horizontal ͑crawling-like͒ and vertical nanowires having similar orientation relationship to the substrate ͑00.1͒ ZnO ʈ ͑00.1͒ GaN , ͓11.0͔ ZnO ʈ ͓11.0͔ GaN . The crawling-like growth precedes the vertical growth, and the coalescence and overgrowth of the crawling nanowires produce a highly defective layer which separates the substrate and vertical nanorods. Transmission electron microscopy revealed a high density of planar defects in this interfacial layer. A significant density of stacking faults residing on the ͑0001͒ planes was also observed in the shorter vertical nanorods. The crawling nanowires are under residual compressive strain, whereas the vertical nanorods grow strain-free.
Study of the Substrate Influence in ZnO Nanowires Oriented Growth
Procedia Materials Science, 2015
A solution growth approach for zinc oxide (ZnO) nanowires is highly appealing because of the low growth temperature and possibility for large area synthesis. In our work, ZnO nanowires were obtained from thin films prepared on silica glass, Si (100) and Si (111) from a single and five layers spin-coating deposition of a sol-gel prepared with dehydrate zinc acetate, monoethanolamine and isopropanol. Crystallization annealing was performed at 450 °C. These films were used as seed layer to prepare ZnO nanowires/nanorods from a zinc nitrate and hexamethylenetetramine solution. X-ray diffraction analysis showed that nanowires/nanorods grown on Si (111) were preferentially orientated along the [002] direction.
Epitaxial growth of self-arranged periodic ZnO nanostructures on sapphire substrates grown by MOCVD
Journal of Alloys and Compounds, 2010
This article reports an investigation on the growth behaviour of ZnO epitaxial nanostructures and thin films grown by metalorganic chemical vapour deposition (MOCVD). Self-arranged periodic ZnO nanostructures consisting of a large number of ZnO nano-columns can be directly grown on bare sapphire surface without any lithography or other pre-patterning processes. The spacing of periodic nanostructures was ∼117 nm. The measurements of XRD 2Â/ω and ϕ scans indicated that epitaxial and non-epitaxial ZnO grains coexisted on the same substrate. According to cross-sectional transmission electron microscopy observation, these periodic ZnO nanostructures were epitaxially grown on sapphire substrates and separated by non-epitaxial ZnO grains. However, the in-plane periodic arrangement of ZnO nanostructures disappeared while increasing the growth temperature. Initial sapphire surface structure and CVD growth kinetics closely relate to the growth of self-arranged periodic ZnO nanostructures.
Mechanistic investigation of ZnO nanowire growth
Applied Physics Letters, 2009
ZnO nanowire ͑NW͒ growth mechanism was investigated in a nonvapor and noncatalytic approach for the controlled NW synthesis in a second time scale. The experimental results showed what ZnO NW growth was determined by migration of zinc interstitials and vacancies in a ZnO layer, which should be also considered in other synthesis techniques and mechanisms. The mechanism of the ZnO NW growth was explained as due to the advantageous diffusion through grain boundaries in ZnO layer and crystal defects in NWs. Additionally, on the basis of photoluminescence measurements, a feasible application of as-produced wires for optoelectronic devices was demonstrated.