基于碳纳米管模板的氮化镓纳米线束合成

通过金属有机物化学气相沉积方法在碳纳米管模板上生长氮化镓纳米线束.对所生长的纳米结构进行了扫描电镜和X射线能谱分析,结果显示氮化镓纳米晶体可以与碳纳米管形成纳米线束状复合物.纳米线束状复合物直径为100～200 nm,长度为1.5～2.5μm,纳米线的两端呈现尖角状.由于氨气很容易吸附在碳纳米管表面,可知所获得的纳米结构的初始生长机制为碳纳米管的表面氮化.该研究也证明金属有机物化学气相沉积将是用于制造化合物纳米结构材料的一项有效的技术.     

Using seed particle composition to control structural and optical properties of GaN nanowires

The morphology, structure, and optical properties of gallium nitride (GaN) nanowires grown using metal-organic chemical vapor deposition (MOCVD) on r-plane sapphire using gold and nickel seed particles were investigated. We found that different seed particles result in different growth rates and densities of structural defects in MOCVD-grown GaN nanowires. Ni-seeded GaN nanowires grow faster than Au-seeded ones, and they do not contain the basal plane stacking faults that are observed in Au-seeded GaN nanowires. We propose that stacking fault formation is related to the supersaturation and surface energies in different types of seed particles. Room temperature photoluminescence studies revealed a blue-shifted peak in Au-seeded GaN nanowires compared to the GaN near-bandgap emission. The blue-shifted peak evolves as a function of the growth time and originates from the nanowire base, likely due to strain and Al diffusion from the substrate. Our results demonstrate that seed particle composition has a direct impact on the growth, structure, and optical properties of GaN nanowires and reveal some general requirements for seed particle selection for the growth of compound semiconductor nanowires.     

Homoepitaxial n-core: p-shell gallium nitride nanowires: HVPE overgrowth on MBE nanowires

We present the homoepitaxial growth of p-type, magnesium doped gallium nitride shells by use of halide vapor phase epitaxy (HVPE) on n-type gallium nitride nanowires grown by plasma-assisted molecular beam epitaxy (MBE). Scanning electron microscopy shows clear dopant contrast between the core and shell of the nanowire. The growth of magnesium doped nanowire shells shows little or no effect on the lattice parameters of the underlying nanowires, as measured by x-ray diffraction (XRD). Photoluminescence measurements of the nanowires show the appearance of sub-bandgap features in the blue and the ultraviolet, indicating the presence of acceptors. Finally, electrical measurements confirm the presence of electrically active holes in the nanowires.     

Orientation and temperature dependence of the tensile behavior of GaN nanowires: an atomistic study

Gallium nitride (GaN) is a high-temperature semiconductor material of considerable interest. It emits brilliant light and has been considered as a key material for the next generation of high frequency and high power transistors that are capable of operating at high temperatures. Due to its anisotropic and polar nature, GaN exhibits direction-dependent properties. Growth directions along [001], [1?10] and [110] directions have all been synthesized experimentally. In this work, molecular dynamics simulations are carried out to characterize the mechanical properties of GaN nanowires with different orientations at different temperatures. The simulation results reveal that the nanowires with different growth orientations exhibit distinct deformation behavior under tensile loading. The nanowires exhibit ductility at high deformation temperatures and brittleness at lower temperature. The brittle to ductile transition (BDT) was observed in the nanowires grown along the [001] direction. The nanowires grown along the [110] direction slip in the {010} planes, whereas the nanowires grown along the [1?10] direction fracture in a cleavage manner under tensile loading.     

Single crystal GaN nanowires

Single crystal gallium nitride nanowires have been obtained by heating gallium acetylacetonate in the presence of carbon nanotubes or activated carbon in NH3 vapor at 910 degrees C. GaN nanowires also were obtained when the reaction of gallium acetylacetonate with NH3 was carried out over catalytic Fe/Ni particles dispersed over silica. The former procedure with carbon nanotubes is preferable because it avoids the presence of metal particles in the nanowire bundles.     

Internal structure of multiphase zinc-blende wurtzite gallium nitride nanowires

In this paper, the internal structure of novel multiphase gallium nitride nanowires in which multiple zinc-blende and wurtzite crystalline domains grow simultaneously along the entire length of the nanowire is investigated. Orientation relationships within the multiphase nanowires are identified using high-resolution transmission electron microscopy of nanowire cross-sections fabricated with a focused ion beam system. A coherent interface between the zinc-blende and wurtzite phases is identified. A mechanism for catalyst-free vapor-solid multiphase nanowire nucleation and growth is proposed.     

The controlled growth of GaN nanowires

This paper reports a scalable process for the growth of high-quality GaN nanowires and uniform nanowire arrays in which the position and diameter of each nanowire is precisely controlled. The approach is based on conventional metalorganic chemical vapor deposition using regular precursors and requires no additional metal catalyst. The location, orientation, and diameter of each GaN nanowire are controlled using a thin, selective growth mask that is patterned by interferometric lithography. It was found that use of a pulsed MOCVD process allowed the nanowire diameter to remain constant after the nanowires had emerged from the selective growth mask. Vertical GaN nanowire growth rates in excess of 2 mum/h were measured, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the nanowires. The paper reports transmission electron microscopy and photoluminescence data.     

Patterned procedure for template-synthesis and microstructural characterization of copper nanowires

Highly ordered circular patterns of copper nanowire arrays were successfully deposited into designed anodic aluminum oxide templates. High-resolution transmission electron microscopy was used to study the microstructure of these Cu nanostructures. The results showed that the growth orientation of the copper nanowires was along [220] direction, and the broken orientation were along [2?02?] and [02?2] directions, respectively. Regular cones were formed at the broken end of nanowires. Bent nanowires were also observed, this means that the copper nanowires have good mechanical properties when applied external force. Chemical analysis has been performed on Cu nanowires using electron energy-loss spectroscopy.     

Model of selective growth of III–V nanowires

A kinetic model of growth of nanowires of III–V semiconductor compounds (including nitride ones) in the absence of metal catalyst is proposed; these conditions correspond to the methods of selective epitaxy or self-induced growth. A stationary solution for the nanowire growth rate is obtained, which indicates that the growth can be limited by not only the kinetics of III-group element with allowance for the surface diffusion (as was suggested earlier), but also the flow of the V-group element. Different modes are characterized by radically different dependences of the growth rate on the nanowire radius. Under arsenicenriched conditions, a typical dependence with a maximum and decay at large radii (limited by the gallium adatom diffusion) is observed. Under gallium-enriched conditions, there is a transition to the growth rate that is practically independent of the radius and linearly increases with an increase in the arsenic flow.     

Synthesis of ZnO nanowire array film on Mg doped gallium nitride substrate

ZnO nanowire array films, composed of well aligned ZnO nanowires ～200?nm in diameter and 1?μm in length, were successfully synthesised on Mg doped gallium nitride by hydrothermal method. In addition, the films possess quite flatten surface. In the synthesised process, there was no catalyst that had been used. Growth conditions were comprehensively discussed in the process of aqueous solution method. It was found that the length of ZnO nanowires and the thickness of the film could be tunable by altering solution concentration and growth time. Such ZnO film assembled with vertically aligned nanowire may have potential applications as UV light emitting diodes.     

Template assisted electrochemical growth of cobalt nanowires: influence of deposition conditions on structural, optical and magnetic properties

The influence of electrodeposition potential, pH, composition and temperature of the electrolytic bath on the structure of cobalt nanowires arrays electrodeposited into anodic aluminum oxide (AAO) porous membranes is reported. XRD, SEM, and TEM analysis were employed to characterize structural (crystal phase, crystallographic texture, and grain size), and morphological nanowire properties. It was confirmed that at pH 2 the electrodeposition potential has not influence on the preferred crystallographic orientation of the electrochemically grown Co nanowires. At pH 4 the electrodeposition potential controls the growth of cobalt nanowires along some preferential crystallographic planes. The electrolytic pH bath modulates the fcc or hcp phase exhibited by the cobalt nanowires. Single crystalline nanowires with a hcp phase strongly oriented along the (2021) crystallographic plane were obtained at pH 4 and at -1.1 V (vs. Ag/AgCl), a result not previously reported. High electrolytic bath temperatures contributed to improve the single crystalline character of the cobalt nanowires. The presence of chloride anion in the electrolytic bath also influenced on the structural properties of the resulting cobalt nanowires, improving their crystallinity. The optical reflectance of the samples shows a structure in the UV-blue region that can be assigned to the two-dimensional morphology arising in the shape of the almost parallel nanowires. Magnetic measurements showed that different electrodeposition potentials and electrolytic bath pH lead to different magnetic anisotropies on the nanowire array samples.     

Bidirectional growth of indium phosphide nanowires

We present a bidirectional growth mode of InP nanowires grown by selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). We studied the effect of the supply ratio of DEZn ([DEZn]) on InP grown structure morphology and crystal structures during the SA-MOVPE. Two growth regimes were observed in the investigated range of the [DEZn] on an InP(111)B substrate. At low [DEZn], grown structures formed tripod structures featuring three nanowires branched toward the [111]A directions. At high [DEZn], we obtained hexagonal pillar-type structures vertically grown on the (111)B substrate. These results show that the growth direction changes from [111]A to [111]B as [DEZn] is increased. We propose a growth mechanism based on the correlation between the incident facet of rotational twins and the shapes of the grown structures. Our results bring us one step closer to controlling the direction of nanowires on a Si substrate that has a nonpolar nature. They can also be applied to the development of InP nanowire devices.     

ZnO nanostructures grown on epitaxial GaN

Presented is the growth of zinc oxide nanorod/nanowire arrays on gallium nitride epitaxial layers. A hierarchical zinc oxide morphology comprising of different scale zinc oxide nanostructures was observed. The first tier of the surface comprised of typical zinc oxide nanorods, with most bridging to adjacent nanorods. While the second tier comprised of smaller zinc oxide nanowires approximately 30 nm in width often growing atop the aforementioned bridges. Samples were analysed via scanning electron microscopy, as well as, cross-sectional and high resolution transmission electron microscopy to elucidate the detailed growth and structural elements of the heterostructure.     

Fabrication of single-crystalline gallium nitride nanowires by using alginate as template

Hexagonal gallium nitride nanowires were synthesized successfully by solvothermal method with alginate as template. The microstructure, morphologies and compositions of the as-prepared product were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray (EDX). Results suggested that the rod-like nanowires were hexagonal single-crystalline GaN growing along [001] direction. The photoluminescence spectra (PL) of the GaN revealed that the as-synthesized sample possesses excellent optical properties.     

Unconventional gallium oxide nanowires

Zigzag and helical beta-Ga(2)O(3) one-dimensional nanostructures were produced by thermal evaporation of gallium oxide in the presence of gallium nitride. High-resolution TEM analysis indicates that each individual zigzag nanostructure has a periodic arrangement of three distinct blocks: two structurally perfect blocks mirrored with respect to each other on the (002) plane, and one stacking-fault-rich block sandwiched between them. In a zigzag nanostructure, the growth orientation of a beta-Ga(2)O(3) crystal changes alternately in three blocks. The zigzag nanostructure as a whole has the [001] axial direction. In addition to zigzag nanostructures, single-crystalline helical nanowires were also obtained.     

Layer-structured ZnO nanowire arrays with dominant surface- and acceptor-related emissions

We report the growth of uncommon layer-structured ZnO nanowire arrays via metal-organic chemical vapor deposition (MOCVD). The morphology, microstructure, and photoluminescence (PL) of the nanowires are investigated. The nanowires grow along the [0001] direction, with periodic zig-zag edges formed by the {101?1}-type surfaces. The nanowires exhibit unique PL features. The PL spectra at low temperature are dominated by the surface exciton recombination at 3.366 eV and the controversial 3.32 eV emission. For the 3.32 eV emission, transformation from donor-acceptor pair recombination to free electron-to-acceptor transition is observed with increasing temperature. The stacking faults formed in the interface region between the layers are likely responsible for the strong emission around 3.32 eV.     

Synthesis and applications of one-dimensional semiconductors

Nanoscale inorganic materials such as quantum dots (0-dimensional) and one-dimensional (1D) structures, such as nanowires, nanobelts and nanotubes, have gained tremendous attention within the last decade. Among the huge variety of 1D nanostructures, semiconducting nanowires have gained particular interest due to their potential applications in optoelectronic and electronic devices. Despite the huge efforts to control and understand the growth mechanisms underlying the formation of these highly anisotropic structures, some fundamental phenomena are still not well understood. For example, high aspect-ratio semiconductors exhibit unexpected growth phenomena, e.g. diameter-dependent and temperature-dependent growth directions, and unusual high doping levels or compositions, which are not known for their macroscopic crystals or thin-film counterparts.This article reviews viable synthetic approaches for growing high aspect-ratio semiconductors from bottom-up techniques, such as crystal structure governed nucleation, metal-promoted vapour phase and solution growth, formation in non-metal seeded gas-phase processes, structure directing templates and electrospinning. In particular new experimental findings and theoretical models relating to the frequently applied vapour-liquid-solid (VLS) growth are highlighted. In addition, the top-down application of controlled chemical etching, using novel masking techniques, is described as a viable approach for generating certain 1D structures. The review highlights the controlled synthesis of semiconducting nanostructures and heterostructures of silicon, germanium, gallium nitride, gallium arsenide, cadmium sulphide, zinc oxide and tin oxide. The alignment of 1D nanostructures will be reviewed briefly. Whilst specific and reliable contact procedures are still a major challenge for the integration of 1D nanostructures as active building blocks, this issue will not be the focus of this paper. However, the promising applications of 1D semiconductors will be highlighted, particularly with reference to surface dependent electronic transduction (gas and biological sensors), energy generation (nanomechanical and photovoltaic) devices, energy storage (lithium storage in battery anodes) as well as nanowire photonics.     

Lateral, Ge, nanowire growth on SiO2

Vapor-liquid-solid (VLS) nanowires (NWs) typically grow in [111] directions. Previously, the authors have demonstrated guided Si NW growth, engineering the VLS NWs to grow in a [110] direction against a SiO(2) surface. In this work, the authors demonstrate guided high-quality Ge nanowire growth against a SiO(2) surface in the substrate plane to bridge between two Si mesas. The authors explore the interfaces between a Ge NW and the two Si device-layer mesas and report high-quality, epitaxial interfaces between the Ge NW and both Si mesas.     

The growth of ultralong and highly blue luminescent gallium oxide nanowires and nanobelts, and direct horizontal nanowire growth on substrates

We report the growth of ultralong β-Ga(2)O(3) nanowires and nanobelts on silicon substrates using a vapor phase transport method. The growth was carried out in a tube furnace, with gallium metal serving as the gallium source. The nanowires and nanobelts can grow to lengths of hundreds of nanometers and even millimeters. Their full lengths have been captured by both scanning electron microscope (SEM) and optical images. X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) images have been used to study the crystal structures of these nanowires and nanobelts. Strong blue emission from these ultralong nanostructures can be readily observed by irradiation with an ultraviolet (UV) lamp. Diffuse reflectance spectroscopy measurements gave a band gap of 4.56?eV for these nanostructures. The blue emission shows a band maximum at 470?nm. Interestingly, by annealing the silicon substrates in an oxygen atmosphere to form a thick SiO(2) film, and growing Ga(2)O(3) nanowires over the sputtered gold patterned regions, horizontal Ga(2)O(3) nanowire growth in the non-gold-coated regions can be observed. These horizontal nanowires can grow to as long as over 10?μm in length. Their composition has been confirmed by TEM characterization. This represents one of the first examples of direct horizontal growth of oxide nanowires on substrates.     

First principles study of electronic properties of gallium nitride nanowires grown along different crystal directions

The electronic properties of hydrogen-saturated GaN nanowires with different orientations and sizes are investigated using first principles calculations, and three types of nanowires oriented along the [0 0 1], [1 1 0] and [1 −1 0] crystal directions are considered. The electronic properties of nanowires in all three directions are extremely similar. All the hydrogen-saturated GaN nanowires show semiconducting behavior with a direct band gap larger than that of bulk wurtzite GaN. Quantum confinement leads to a decrease in the band gap of the nanowires with increasing nanowire size. The [0 0 1]-oriented nanowires with hexagonal cross sections are energetically more favorable than the [1 0 0]- and [1 −1 0]-oriented nanowires with triangular cross sections.