Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si（111） substrates

A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.     

Growth and characterization of GaAs/In_χGa_(1-χ)As/GaAs axialnanowire heterostructures with symmetrical heterointerfaces

We report on the Au-assisted vapour-liquid-solid(VLS) growth of GaAs/InxGa1-xAs/GaAs(0.2 ≤ x ≤ 1) axial double-heterostructure nanowires on GaAs(111) B substrates via the metal-organic chemical vapor deposition(MOCVD) technique.The influence of the indium(In) content in an Au particle on the morphology of nanowires is investigated systematically.A short period of pre-introduced In precursor before the growth of InxGa1-xAs segment,coupled with a group III precursor interruption,is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section.The nanowire morphology,such as kinking and tapering,are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.     

Growth of Silicon Nanowires by Heating Si substrate

Amorphous silicon nanowires were prepared by heating an Si substrate at high temperatures using an Ni (or Au) catalyst.The nanowires have a diameter of 10-40nm and a length of up to several tens of micrometres.Unlike the well-known vapour-liquid-solid mechanism,a solid-liquid-solid mechanism appeared to control the nanowire growth.The heating process had a strong influence on the growth of silicon nanowires.It was found that ambient gas was necessary to grow nanowires.This method can be used to prepare other kinds of nanowires.     

Au5Si2/Si Heterojunction Nanowires Formed by Combining SiO Evaporation with Vapour--Liquid--Solid Mechanism

Crystalline AusSi2/Si heterojunetion nanowires （AusSi2/SiNWs） are obtained by thermal evaporating SiO pow- ders on thick gold-coated silicon substrates in a low vacuum system. Structure analysis of the produced AusSh/Si heterojunetions is performed by employing a transmission electron microscope （TEM） and a selected area electric diffraetometer. The chemical compositions axe studied by a energy-dispersive x-ray spectroscope attached to the TEM. A two-step growth model is proposed to describe the formation of the AusSi2/SiNWs. During the first step, crystalline SiNWs are formed via a growth mechanism combining the oxide-assisted growth process with the vapour-liquid-solid model at relatively high temperature. In the second step, the temperature decreases and one segment of the preformed SiNWs reacts with the remnant Au to form single crystalline AusSi2 nanowires by a solid-liquid-solid process. The present work should be useful for the future synthesis and research of high-quality gold silicide nanowires and microelectronic devices based on the nanowires.     

Growth Mechanism of Vertically Aligned Ag（TCNQ） Nanowires

Highly oriented Ag(TCNQ) nanowires have been prepared on Si(111) wafer at 1O0℃ by the vapour-transport reaction between silver and TCNQ without any other catalyst. X-ray diffraction analysis shows that the composition and crystal structure of the obtained nanostructure were Ag(TCNQ) crystalline. Most Ag(TCNQ) nanowires were grown uniformly and vertically on the substrate with diameters ranging from 50 to 30Onto and the lengths measuring from 2 to 50μm by scanning electron microscopy. Ag particles were observed on the substrate from pure thin Ag film heated under the same conditions as used in synthesizing the nanowires. Nucleation and short Ag(TCNQ) nanowires were prepared by controlling the reaction time, providing direct evidence of the growth mechanism in a nanometre scale. The growth process was explained according to the vapour-liquid-solid model. The gradient of temperature and the densely distributed Ag particles may contribute to the vertically aligned growth. These results will be helpful for the controllable synthesis of Ag(TCNQ) nanowires.     

Synthesis and magnetotransport properties of Bi_2Se_3 nanowires

Bi_2Se_3, as a three-dimensional topological insulator, has attracted worldwide attention for its unique surface states which are protected by time-reversal symmetry. Here we report the synthesis and characterization of high-quality singlecrystalline Bi_2Se_3 nanowires. Bi_2Se_3 nanowires were synthesized by chemical vapor deposition(CVD) method via goldcatalyzed vapor-liquid-solid(VLS) mechanism. The structure and morphology were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), x-ray photoelectron spectroscopy(XPS), and Raman spectroscopy. In magnetotransport measurements, the Aharonov–Bohm(AB) effect was observed in a nanowire-based nanodevice, suggesting the existence of surface states in Bi_2Se_3 nanowires.     

Growth mechanism and photoluminescence of the SnO2 nanotwists on thin film and the SnO2 short nanowires on nanorods

SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders.The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),selected area electronic diffraction(SAED),high-resolution transmission electron microscopy(HRTEM),x-ray diffraction(XRD),Raman and photoluminescence(PL) spectra analysis.The new peaks at 356,450,and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed,implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects.The growth mechanism of these nanostructures belongs to the vapour-liquid-solid(VLS) mechanism.     

Synthesis and electrical characterization of tungsten oxide nanowires

Tungsten oxide nanowires of diameters ranging from 7 to 200~nm are prepared on a tungsten rod substrate by using the chemical vapour deposition (CVD) method with vapour--solid (VS) mechanism. Tin powders are used to control oxygen concentration in the furnace, thereby assisting the growth of the tungsten oxide nanowires. The grown tungsten oxide nanowires are determined to be of crystalline W₁₈O₄₉. I--V curves are measured by an \textit{in situ} transmission electron microscope (TEM) to investigate the electrical properties of the nanowires. All of the I--V curves observed are symmetric, which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I--V curves by using a metal--semiconductor--metal (MSM) model give some intrinsic parameters of the tungsten oxide nanowires, such as the carrier concentration, the carrier mobility and the conductivity.     

Refit Silver Nanostructures Using a Convergent Electron Beam

Using a superionic conductor AgI thin film and a direct current electric field, we synthesize silver nanowires in diameter of about lOOnm. In order to refit the prepared nanowires, the samples are irradiated by a convergent electron beam （200 k V） inside a transmission electron microscope to prepare new small silver nanostructures. The new nanostructures are investigated in situ by high-resolution transmission electron microscope. This electron- induced crystal growth method is useful for technical applications in fabrication of nanodevices.     

Growth and characterization of GaAs/InxGa1-xAs/GaAs axial nanowire heterostructures with symmetrical heterointerfaces

We report on the Au-assisted vapour-liquid-solid （VLS） growth of GaAs/InxGal xAs/GaAs （0.2 ≤ x ≤1） axial double-heterostructure nanowires on GaAs （ 111 ） B substrates via the metal-organic chemical vapor deposition （MOCVD） technique. The influence of the indium （In） content in an Au particle on the morphology of nanowires is investigated systematically. A short period of pre-introduced In precursor before the growth of InxGal xAs segment, coupled with a group III precursor interruption, is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section. The nanowire morphology, such as kinking and tapering, are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.     

Fabrication and Characterization of Mg-Doped GaN Nanowires

Mg-doped GaN nanowires have been synthesized by ammoniating Ga2O3 films doped with Mg under flowing ammonia atmosphere at 850℃. The Mg-doped GaN nanowires are characterized by x-ray diffraction （XRD）, scanning electron microscope （SEM）, high-resolution transmission electron microscopy （HRTEM） and photoluminescence （PL）. The results demonstrate that the nanowires are single crystalline with hexagonal wurzite structure. The diameters of the nanowires are 20-30nto and the lengths are 50-100μm. The GaN nanowires show three emission bands with well-defined PL peak at 3.45 eV, 3.26 eV, 2.95 eV, respectively. The large distinct blueshift of the bandgap emission can be attributed to the Burstein-Moss effect. The peak at 3.26 eV represents the transition from the conduction-band edge to the acceptor level AM （acceptor Mg）. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

In Situ Epitaxy of Pure Phase Ultra-Thin InAs-Al Nanowires for Quantum Devices

We demonstrate the in situ growth of ultra-thin InA s nanowires with an epitaxial Al film by molecular-beam epitaxy.Our InAs nanowire diameter(～30 nm) is much thinner than before(～100 nm).The ultra-thin InAs nanowires are pure phase crystals for various different growth directions.Transmission electron microscopy confirms an atomically abrupt and uniform interface between the Al shell and the InAs wire.Quantum transport study on these devices resolves a hard induced superconducting gap and 2 e-p...     

Formation of Co3O4 Nanotubes and the Magnetic Behaviour at Low Temperature

Tubular Co3O4 nanostructures were prepared from cobalt nanowires embedded in an anodic alumina template. The morphologies of nanowires/nanotubes were studied by transmission electron microscopy, and x-ray diffraction was used in the analysis of the nanostructures and phases. A possible formation mechanism of the process from nanowires to nanotubes is discussed. The vibrating sample magnetometer measurements show anomalous magnetic behaviour of the cobalt oxide nanotubes at low temperature.     

Novel photoluminescence properties of InAlO3（ZnO）m superlattice nanowires

One-dimension InAlO 3 (ZnO) m superlattice nanowires were successfully synthesized via chemical vapor deposition.Transmission electron microscopy measurements reveal that the nanowires have a periodic layered structure along the 0001 direction.The photoluminescence properties of InAlO 3 (ZnO) m superlattice nanowires are studied for the first time.The near-band-edge emissions exhibit an obvious red shift due to the formation of the localized tail states.The two peaks centered at 3.348 eV and 3.299 eV indicate a lever phenomenon at the low-temperature region.A new luminescence mechanism is proposed,combined with the special energy band structure of InAlO 3 (ZnO) m.     

Hydrothermal synthesis and dielectric properties of chrysanthemum-like ZnO particles

By orthogonal design theory, technological parameters of chrysanthemum-like ZnO particles prepared in a hydrothermal process are optimized. This paper reports a set of technological parameters for growing chrysanthemum-like ZnO particles on a large scale. It investigates the morphologies and crystalline structures of the as-synthesized three-dimensional ZnO particles with a scanning electron microscope, x-ray diffractometer and transmission electron microscope, and the possible growth mechanism on the three-dimensional ZnO particles. The experimental results indicate that the values of ε', ε ' and \tan δ_e gradually increase in the X band with the improvement of the developmental level of chrysanthemum-like ZnO particles, implying that the electromagnetic wave absorbing property depends on the morphologies of three-dimensional ZnO particles.     

Effects of N2 and glow discharge on growth behaviours of carbon nanotubes prepared by the hot filament chemical vapour deposition method

Carbon nanotubes (CNTs) are prepared by the hot filament chemical vapour deposition method using CH4 and H2 as reaction gases, and the growth behaviours are investigated by scanning electron microscopy and transmission electron microscopy. The results indicate that the CNTs prepared in the absence of N2 or glow discharge are bent; however, they are in an aligned state after introducing N2 into the chamber or forming glow discharge under a negative biased voltage. The results also indicate that the CNTs are of a bamboo-like structure when N2 is intruded as a reaction gas and the alignment degree of the CNTs grown under glow discharge is higher than that grown in N2. This illustrates that the nitric environment and glow discharge play important roles in the growth of CNTs. Combining with the theory related to alloy thermodynamics and collisions, we have analysed the growth mechanism of the CNTs in nitric environment and glow discharge.     

Study of nanocrystalline Fe－Al－N soft magnetic thin films

Fe－Al－N films were fabricated by reactive sputtering using a radio-frequency magnetron sputtering system. The effects of Al and N content and annealing temperature on microstructure and magnetic properties were investigated. The Fe－Al－N films, which have good soft magnetic properties, consist of nanocrystalline α-Fe grains and a small amount of other phases in the boundaries of α-Fe grains. The average α-Fe grain size is about 10－15nm. A slight amount of Fe－N and Al－N compounds precipitate in the boundaries of α-Fe grains and suppress their growth. Annealing improves the soft magnetic properties slightly by releasing the residual stress and reducing defects.     

Theoretical calculation of the triple differential cross sections of the 2p orbital of argon in a coplanar highly asymmetric（e,2e） reaction

The triple differential cross sections of the 2p electron of argon in a coplanar highly asymmetric geometry have been calculated with the modified distorted wave Born approximation (DWBA) and the target Hartree－Fock approximation methods. The damping polarization of the semi-classical short-range potentials and the M_ee factor are included in the distorting potentials of the modified DWBA. Theoretical results are compared with a recent experiment. The dynamic mechanism of inner shell ionization in a coplanar highly asymmetric geometry (e, 2e) reaction are also discussed.     

The influence of ablation products on the ablation resistance of C/C-SiC composites and the growth mechanism of SiO2 nanowires

Ablation under oxyacetylene torch with heat flux of 4186.8(10%kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration（CVI） combined with liquid silicon infiltration（LSI） process.The results indicated that C/C-SiC composites present a better ablation resistance than C/C composites without doped SiC.The doped SiC and the ablation products SiO₂ derived from it play key roles in ablation process.Bulk quantities of SiO₂ nanowires with diameter of 80 nm-150 nm and length of tens microns were observed on the surface of specimens after ablation.The growth mechanism of the SiO₂ nanowires was interpreted with a developed vapor-liquid-solid（VLS） driven by the temperature gradient.     

Nonlinear current－voltage characteristics of sintered tungsten－vanadium oxide

We have studied the densification behaviour, microstructure and electrical properties of WO_3 ceramics with V_2O_5 as the additive ranging from 0.5 to 15mol%. Scanning electron microscopic photos indicated that the grain size of WO_3－V_2O_5 specimens is smaller than that of pure WO_3. The addition of V_2O_5 to WO_3 showed a tendency to enhance the densification rate and to restrict the grain growth. Electrical properties of all specimens were measured for different electrodes at different temperatures. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I－V behaviour. The nonlinear coefficient was obtained at the current density J=0.01, 0.1 and 1mA/cm^2 for a series of WO_3－V_2O_5 samples. The V0.5mol% specimen showed an abnormal phenomenon that the nonlinear characteristics appeared at 350℃ and disappeared at lower and higher temperatures. This implies that it could be applied as a high-temperature varistor. The double Schottky barrier model was adopted to explain the phenomena for the WO_3-V_2O_5 varistors.