Self-catalytic branch growth of SnO2 nanowire junctions

Chen, Y.X.; Campbell, L.J.; Zhou, Weilie

doi:10.1016/j.jcrysgro.2004.07.011

Cited by 65 publications

(43 citation statements)

References 17 publications

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“…4b inset). This spontaneous branch formation is distinct from some previous works on III-V and metal oxide NWs, where sequential catalyst seeding was applied to the NW 'trunk' to intentionally nucleate second generation branches [22,23], or rapid crystallization [24] (vapor-solid type growth) or self-catalytic growth [25,26] induced spontaneous branching. The different scenario we envision is a direct consequence of the Ga-stablized polar surface and the formation of liquid phase metal catalyst.…”

Section: Spontaneous Branch Formationmentioning

confidence: 56%

Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

2007

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Nanowires have great potential as building blocks for nanoscale electrical and optoelectronic devices. The difficulty in achieving functional and hierarchical nanowire structures poses an obstacle to realization of practical applications. While post-growth techniques such as fluidic alignment might be one solution, selfassembled structures during growth such as branches are promising for functional nanowire junction formation. In this study, we report vapor-liquid-solid (VLS) self-branching of GaN nanowires during AuPdcatalyzed chemical vapor deposition (CVD). This is distinct from branches grown by sequential catalyst seeding or vapor-solid (VS) mode. We present evidence for a VLS growth mechanism of GaN nanowires different from the well-established VLS growth of elemental wires. Here, Ga solubility in AuPd catalyst is limitless as suggested by a hypothetical pseudo-binary phase diagram, and the direct reaction between NH3 vapor and Ga in the liquid catalyst induce the nucleation and growth. The self-branching can be explained in the context of the proposed VLS scheme and migration of Ga-enriched AuPd liquid on Ga-stabilized polar surface of mother nanowires. This work is supported by DOE Grant No. DE-FG02-98ER45701. KeywordsGallium alloys, Dissolution, Electric wire, Gallium nitride, Liquids, Nanowires, Semiconducting gallium, Vapors, AuPd alloy, GaN nanowires, Growth modes, Growth morphology, Nucleation and growth, Polar surfaces, Spontaneous reactions, Vapor-liquid-solid mechanism, VLS growth ABSTRACTInvestigations of the growth morphology of AuPd-catalyzed GaN nanowires lead us to propose a vapor-liquid-solid (VLS) mechanism distinct from the well-established VLS growth of elemental wires. Here, nucleation and growth of GaN nanowires proceeds by direct spontaneous reaction between NH 3 vapor and Ga dissolved in liquid AuPd alloy, rather than by solubilitylimited supersaturation. A frequently observed self-branching growth mode can be explained by the proposed VLS scheme and the migration of Ga-enriched AuPd liquid on Ga-stabilized polar surfaces of mother nanowires. INTRODUCTIONGaN nanowires (NWs) are of interest for nanoscale optoelectronic device applications [1][2][3][4]. Synthesis can be achieved by several methods involving vapor-liquid-solid (VLS) growth, such as thermal chemical vapor deposition (CVD) [5][6][7], hydride vapor phase epitaxy (HVPE) [8], molecular beam epitaxy (MBE) [9], and metalorganic CVD (MOCVD) [10]. The low N solubility in transition metals implies that nucleation of GaN from supersaturated catalyst droplets is unlikely, in contrast to elemental structures such as Si whiskers and NWs [11]. Here we study GaN NWs grown by thermal CVD using Ga 2 O 3 , NH 3 and AuPd catalyst. The observed morphologies suggest a VLS mechanism distinct from the nucleation and growth of elemental nanostructures from supersaturated liquid. We consider a hypothetical pseudo-binary phase diagram and thermodynamics of GaN formation reaction to propose that NW nucleation and growth occur via direct ...

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Section: Spontaneous Branch Formationmentioning

confidence: 56%

Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

2007

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“…[18] The presence of a particle with a high metal content at the tip is often associated with the self-catalyst growth route. [19] However, TEM and energy dispersive X-ray (EDX) spectroscopy inspections of the particle at the tip of the Co 3 O 4 nanowires show no significant variations, either in chemical composition or in phase, compared to the main body of the nanowire. Figure 6b shows the HRTEM image of the selected region (as indicated in the inset) at the tip of the nanowire.…”

Section: Resultsmentioning

confidence: 99%

Co₃O₄ Nanostructures with Different Morphologies and their Field‐Emission Properties

Varghese

Teo

Zhu

et al. 2007

Adv Funct Materials

306

114

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We report an efficient method to synthesize vertically aligned Co3O4 nanostructures on the surface of cobalt foils. This synthesis is accomplished by simply heating the cobalt foils in the presence of oxygen gas. The resultant morphologies of the nanostructures can be tailored to be either one‐dimensional nanowires or two‐dimensional nanowalls by controlling the reactivity and the diffusion rate of the oxygen species during the growth process. A possible growth mechanism governing the formation of such nanostructures is discussed. The field‐emission properties of the as‐synthesized nanostructures are investigated in detail. The turn‐on field was determined to be 6.4 and 7.7 V μm–1 for nanowires and nanowalls, respectively. The nanowire samples show superior field‐emission characteristics with a lower turn‐on field and higher current density because of their sharp tip geometry and high aspect ratio.

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“…This is in contrast to self-catalyzed VLS growth of SnO 2 nanostructures reported in the literature, where clear evidence is seen for large Sn droplets atop SnO 2 nanostructures. 30 We thus continue to use the term VS growth to describe this growth mode in our system while noting the similarities to self-catalyzed VLS growth discussed above. In addition to VS growth, within a certain temperature range the Zn vapor may also condense on and dissolve in the Au and growth continues via the Au-catalyzed VLS mechanism, in parallel with the VS growth route described above.…”

Section: ͑1͒mentioning

confidence: 99%

Growth of ZnO nanostructures on Au-coated Si: Influence of growth temperature on growth mechanism and morphology

Kumar

McGlynn

Biswas

et al. 2008

Journal of Applied Physics

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ZnO nanostructures were grown on Au-catalyzed Si silicon substrates using vapor phase transport at growth temperatures from 800 to 1150°C. The sample location ensured a low Zn vapor supersaturation during growth. Nanostructures grown at 800 and 850°C showed a faceted rodlike morphology with mainly one-dimensional ͑1D͒ growth along the nanorod axis. Samples grown at intermediate temperatures ͑900, 950, and 1050°C͒ in all cases showed significant three dimensional ͑3D͒ growth at the base of 1D nanostructures. At higher growth temperatures ͑1100 and 1150°C͒ 3D growth tended to dominate resulting in the formation of a porous, nanostructured morphology. In all cases growth was seen only on the Au-coated region. Our results show that the majority of the nanostructures grow via a vapor-solid mechanism at low growth temperatures with no evidence of Au nanoparticles at their tip, in sharp contrast to the morphology expected for the vapor-liquid-solid ͑VLS͒ process often reported as the growth mechanism on Au-catalyzed Si. We see VLS growth only at 900 and 950°C. Transmission electron microscopy data indicate that the nanorods are single crystalline without gross structural defects. Luminescence data reveal strong ultraviolet emission in all samples and weak defect emission in the visible region. We discuss the growth mechanisms with reference to various models in the literature and suggest reasons for VLS growth only in a narrow temperature range. We also discuss the potential effects of the Zn oxidation reaction on the growth morphologies, aspects largely ignored in the general literature on this subject.

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Self-catalytic branch growth of SnO2 nanowire junctions

Cited by 65 publications

References 17 publications

Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

Co₃O₄ Nanostructures with Different Morphologies and their Field‐Emission Properties

Growth of ZnO nanostructures on Au-coated Si: Influence of growth temperature on growth mechanism and morphology

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Self-catalytic branch growth of SnO2 nanowire junctions

Cited by 65 publications

References 17 publications

Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

Co3O4 Nanostructures with Different Morphologies and their Field‐Emission Properties

Growth of ZnO nanostructures on Au-coated Si: Influence of growth temperature on growth mechanism and morphology

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Co₃O₄ Nanostructures with Different Morphologies and their Field‐Emission Properties