Al2O3衬底无催化剂生长GaN纳米线及其光学性能

采用一种绿色的等离子增强化学气相沉积法,以Al2O3为衬底, Ga金属为镓源, N2为氮源,在不采用催化剂的情况下,成功制备获得了结晶质量良好的GaN纳米线.研究表明,生长温度可显著调控GaN纳米线的形貌,当反应温度为950℃时,生长出的GaN微米片为六边形;当反应温度为1000℃时,生长出了长度为10-20μm的超长GaN纳米线.随着反应时间增加, GaN纳米线的长度增加. GaN纳米线内部存在着压应力,应力大小为0.84 GPa.同时,也进一步讨论了GaN纳米线无催化剂生长机制. GaN纳米线光致发光结果显示, GaN纳米线缺陷较少,结晶质量良好,在360 nm处有一个较为尖锐的本征发光峰,可应用于紫外激光器等光电子器件.本研究结果将为新型光电器件低成本绿色制备提供一个可行的技术方案.     

Synthesis and Raman scattering of GaN nanorings, nanoribbons and nanowires

Low-dimensional GaN materials, including nanorings, nanoribbons and smooth nanowires have been synthesized by reacting gallium and ammonia using Ag particles as a catalyst on the substrate of MgO single crystals. They were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). EDX, XRD indicated that the low-dimensional nanomaterials were wurtzite GaN. New features are found in Raman scatterings for these low-dimensional GaN materials, which are different from the previous observations of GaN materials. Received: 16 November 2000 / Accepted: 17 November 2000 / Published online: 21 March 2001     

High-quality GaN nanowires synthesized using a CVD approach

High-quality GaN nanowires were synthesized on a large-area Si substrate by direct reaction of gallium with ammonia using InCl₃ as a catalyst. The morphology and microstructure of the resulting products were characterized using a field-emission scanning electron microscope (SEM), a high-resolution transmission electron microscope, and X-ray diffraction (XRD). XRD and electron diffraction revealed that the nanowires are of a hexagonal GaN phase with the wurtzite structure. The SEM study showed that the nanowires are straight and have a smooth morphology with lengths up to 500 μm. The present results reveal that InCl₃ is an optimal catalyst in GaN nanowire production. Received: 2 April 2002 / Accepted: 12 April 2002 / Published online: 19 July 2002     

Carbon nanotubes filled with long continuous cobalt nanowires

In this paper, we report the catalytic synthesis of carbon nanotubes filled with long continuous cobalt nanowires by a simple chemical process. The average diameter of the multi-walled nanotubes is about 40 nm. The nanowires are a few micrometers long with a diameter of 20 nm. X-ray diffraction analysis reveals that the as-prepared material, following treatment with HCl, shows the cobalt nanowires, encapsulated in the carbon nanotubes, as having an fcc and not the table hexagonal structure. The filled nanotubes can be seperated by using a permanent magnet. TEM, XPS and Raman spectroscopy were also used to analyze the products.     

Catalytic synthesis of single-crystalline gallium nitride nanobelts

Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed.     

Synthesis of aligned gallium nitride nanowire quasi-arrays

Self-aligned GaN nanowire quasi-arrays were synthesized on MgO crystal through a simple gas reaction method. They were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy and high-resolution transmission electron microscopy (HRTEM). FE-SEMimages showed that the product consisted of quasi-arrays of nanowires. XRD, EDX and HRTEM indicated that the nanowires were wurtzite GaN single crystals. Received: 19 June 2000 / Accepted: 21 June 2000 / Published online: 9 August 2000     

Structural,electronic and magnetic properties of hcp Fe,Co and Ni nanowires encapsulated in zigzag carbon nanotubes

The structural, electronic and magnetic properties of hcp transition metal (TM = Fe, Co or Ni) nanowires TM₄ encapsulated inside zigzag nanotubes C(m, 0) (m = 7, 8, 9, 10, 11 or 12), along with TM _n (n = 4, 10 or 13) encapsulated inside C(12, 0), have been systematically investigated using the first-principle calculations. The results show that the TM nanowires can be inserted inside a variety of zigzag carbon nanotubes (CNTs) exothermically, except from the systems TM₄@(7, 0) and TM₁₃@(12, 0) which are endothermic. The charge is transferred from TM nanowires to CNTs, and the transferred charge increases with decreasing CNT diameter or increasing nanowire thickness. The magnetic moments of hybrid systems are smaller than those of the freestanding TM nanowires, especially for the atoms on the outermost shell of the nanowires. The magnetic moment per TM atom of TM/CNT system increases with increasing CNT diameter or decreasing nanowire thickness. Both the density of states and spin charge density analysis show that the spin polarization and the magnetic moments of all hybrid systems mainly originate from the TM nanowires, implying these systems can be applied in magnetic data storage devices.     

碳纳米管包裹的硅纳米线复合结构的热稳定性研究

采用经典分子动力学方法模拟一定直径[111]晶向的硅纳米线填充不同扶手椅型单壁碳纳米管复合结构的加热过程, 通过可视化和能量分析的方法判断复合结构中硅纳米线和碳纳米管的热稳定性. 通过讨论碳纳米管的空间限制作用和分子间相互作用力的关系, 对碳纳米管和硅纳米线的热稳定性变化进行初步解释. 研究发现碳纳米管中硅纳米线的热稳定性和碳纳米管的直径关系密切: 当管径较小时, 硅纳米线的热稳定性有所提高, 当管径增大到一定大小时, 硅纳米线的热稳定性会突然显著地下降, 直到硅纳米线与管壁不存在分子间相互作用力, 硅纳米线的热稳定性才会恢复. 而硅纳米线填充到碳纳米管中对碳纳米管的热稳定性有着明显的降低作用.     

Vacancies in GaN bulk and nanowires: effect of self-interaction corrections

We investigate gallium and nitrogen vacancies in gallium nitride (GaN) bulk and nanowires using self-interaction corrected pseudopotentials (SIC). In particular, we examine the band structures to compare and contrast differences between the SIC results and standard density functional theory (DFT) results using a generalized gradient approximation (GGA) (Perdew et al 1996 Phys. Rev. Lett. 77 3865) functional. For pure nanowires, we observed similar trends in the bandgap behaviour, with the gap decreasing for increasing nanowire diameters (with larger bandgaps using SIC pseudopotentials). For gallium vacancies in bulk GaN and GaN nanowires, SIC results are similar to DFT-GGA results, albeit with larger bandgaps. Nitrogen vacancies in bulk GaN show similar defect-induced states near the conduction band, whilst a lower lying defect state is observed below the valence band for the DFT-GGA calculations and above the valence band for the SIC results. For nitrogen vacancies in GaN nanowires, similar defect states are observed near the conduction band, however, while the SIC calculations also show a defect state/s above the valence band, we were unable to locate this state for the DFT-GGA calculations (possibly because it is hybridized with edge states and buried below the valence band).     

碳纳米管中α-Ga和β-Ga纳米线相对稳定性的理论研究

采用密度泛函理论研究了碳纳米管中填充的金属镓纳米线的稳定性.结果表明,无论是在碳纳米管内的受限空间,还是在自由空间,较大尺寸的β-Ga纳米线都要比α-Ga纳米线稳定.通过对镓纳米线的平均能量和镓纳米线与碳纳米管间的结合能的分析,揭示了实验中观测到碳纳米管中金属镓会存在β-Ga相而无α-Ga相的物理原因. 关键词： 碳纳米管 纳米线 密度泛函理论     

Surface analysis, TEM, dynamic and controlled rate thermal analysis, and infrared emission spectroscopy of gallium doped boehmite nanofibres and nanosheets

Ga doped boehmite nanofibres with varying Ga content have been prepared at low temperatures using hydrothermal treatment in the presence of poly (ethylene oxide) surfactant. The resulting nanofibres were characterized by X-ray diffraction (XRD), dynamic and controlled rate thermal analysis and infrared emission spectroscopy (IES), transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDX), N₂ adsorption/desorption. TEM results show that nanotubes are dominant when the doped gallium percentage is no more than 5%; nanosheets and an amorphous phase are observed in 10% and 20% gallium doped samples. N₂ adsorption/desorption analysis reveals a large amount of micropores and mesopores are present in the resultant samples. Similar to iron and yttrium doped boehmite nanomaterials, remarkable larger BET specific area was achieved compared to pure boehmite nanomaterials. Both dynamic and controlled thermal analyses show that the gallium doped boehmite nanomaterials dehydrate at higher temperature than that of pure boehmite. Interestingly, the higher the crystallinity of the resultant nanotubes is, the higher the dehydration temperature. The IES spectra show that dehydroxylation of the resultant gallium doped boehmite nanomaterials starts at 250 °C and is complete by 450 °C, in harmony with the dynamic and controlled rate thermal analysis results.     

Comparison of modification of electronic properties of single-walled carbon nanotubes filled with metal halogenide, chalcogenide, and pure metal

In present work, thulium chloride, gallium selenide, bismuth telluride, and silver were encapsulated into the channels of single-walled carbon nanotubes (SWCNTs). The structural properties of obtained nanostructures were studied by high-resolution transmission electron microscopy, and the modification of electronic properties of nanotubes as result of filling their channels with chosen substances was investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. It was shown that the electronic properties of filled SWCNTs depend on the chemical nature of incorporated materials. The encapsulation of TmCl₃ and GaSe into the carbon nanotube channels leads to acceptor doping of the SWCNTs, and this effect is more prominent for thulium chloride. The incorporation of bismuth telluride into the nanotube cavities does not result in any modification of their electronic properties. The filling of the nanotube channels with silver leads to donor doping of the single-walled carbon nanotubes.     

Unusual freezing and melting of gallium encapsulated in carbon nanotubes

The freezing and melting behavior of gallium (Ga) encapsulated in carbon nanotubes was investigated through in situ observation in a transmission electron microscope. It is shown that Ga remains liquid up to -80 degrees C when encapsulated in carbon nanotubes. Results of detailed electron diffraction analysis show that the encapsulated Ga can crystallize in either beta phase or gamma phase rather than the common alpha phase upon freezing. Both beta-Ga and gamma-Ga melt at around -20 degrees C. While this is very close to the melting point of bulk beta-Ga (-16 degrees C), it is considerably higher than that of bulk gamma-Ga (-35.6 degrees C). It was observed that upon solidification, Ga has its unique crystallographic orientation relative to the host carbon nanotube.     

Synthesis and field emission properties of GaN nanowires

Gallium nitride (GaN) nanowires grown on nickel-coated n-type Si (1 0 0) substrates have been synthesized using chemical vapor deposition (CVD), and the field emission properties of GaN nanowires have been studied. The results show that (1) the grown GaN nanowires, which have diameters in the range of 50-100 nm and lengths of several micrometers, are uniformly distributed on Si substrates. The characteristics of the grown GaN nanowires have been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and through these investigations it was found that the GaN nanowires are of a good crystalline quality (2) When the emission current density is 100 μA/cm², the necessary electric field is an open electric field of around 9.1 V/μm (at room temperature). The field enhancement factor is ∼730. The field emission properties of GaN nanowires films are related both to the surface roughness and the density of the nanowires in the film.     

Fabrication, morphology, and photoluminescence properties of GaN nanowires and nanorods by ammoniating Ga2O3/V films on Si(1 1 1)

GaN nanowires and nanorods have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/V films at 900 °C in a quartz tube. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectrum were carried out to characterize the structure, morphology, and photoluminescence properties of GaN sample. The results show that the GaN nanowires and nanorods with pure hexagonal wurtzite structure have good emission properties. The growth direction of nanostructures is perpendicular to the fringes of (1 0 1) plane. The growth mechanism is also briefly discussed.     

Large-scale and catalyst-free synthesis of zinc nanotubes and nanowires

Metallic zinc one-dimensional materials including nanotubes and nanowires were synthesized on a large scale by a simple method. The process was both catalyst and template free. The resulting Zn nanotubes and Zn nanowires were characterized and confirmed by means of X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. The growth of Zn nanotubes was reported for the first time.     

Synthesis of high nitrogen doping of carbon nanotubes and modeling the stabilization of filled DAATO@CNTs (10,10) for nanoenergetic materials

In this work, we have performed synthesis of nitrogen-doped carbon nanotubes using chemical vapor deposition method. Morphology, structure and composition of the carbon nanotubes (CNTs), as well as concentration and distribution of nitrogen inside CNTs are characterized by scanning electron microscopy, transmission electron microscopy, X-ray dispersive spectroscopy and X-ray photoelectron spectroscopy techniques. A bamboo-like structure of the nitrogen-doped CNTs has been observed. Temperature dependency on the synthesis of nitrogen-doped carbon nanotubes has been investigated and discussed. Diameter and growth rate of these hybrid materials are obviously temperature dependent. Nitrogen concentration inside the CNTs increases with declining synthesis temperature. Nitrogen-doped CNTs with nitrogen content up to 10.4 at% can be achieved at a low temperature of 800 ^oC. Synthesis of the high nitrogen CNTs proposes a feasible way to develop novel nanoenergetic materials. Besides the experimental study, we have carried out Density Functional Theory calculations on five energetic molecules named n-oxides of 3,3′-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO), where n=1-5 refer to oxygen atoms, encapsulated in CNTs (10,10), in order to investigate the chemical stabilization of filled DAATO_n inside CNTs (10,10). In fact, the predicted adsorption energy values confirmed the chemical stability of the hybrid systems DAATO_n@CNTs (10,10) under normal conditions.     

First-principles study on structural and electronic properties of copper nanowire encapsulated into GaN nanotube

We present a systemic study of the structural and electronic properties of Cu_n nanowires (n=5, 9 and 13) encapsulated in armchair (8,8) gallium nitride nanotubes (GaNNTs) using the first-principles calculations. We find that the formation processes of these systems are all exothermic. The initial shapes are preserved without any visible changes for the Cu₅@(8,8) and Cu₉@(8,8) combined systems, but a quadratic-like cross-section shape is formed for the outer nanotube of the Cu₁₃@(8,8) combined system due to the stronger attraction between nanowire and nanotube. The electrons of Ga and N atoms in outer GaN sheath affect the electron conductance of the encapsulated metallic nanowire in the Cu₁₃@(8,8) combined system. But in the Cu₅@(8,8) and Cu₉@(8,8) combined systems, the conduction electrons are distributed only on the copper atoms, so charge transport will occur only in the inner copper nanowire, which is effectively insulated by the outer GaN nanotube. Considering the maximal metal filling ratio in nanotube, we know that the Cu₉@(8,8) combined system is top-priority in the ultra-large-scale integration (ULSI) circuits and micro-electromechanical systems (MEMS) devices that demand steady transport of electrons.     

Synthesis of GaN nanowires by Tb catalysis

Rare earth metal seed Tb was employed as catalyst for the growth of GaN wires. GaN nanowires were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. The samples characterization by X-ray diffraction and Fourier transform infrared indicated that the nanowires are constituted of hexagonal wurtzite GaN. Scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy showed that the samples are single-crystal GaN nanowire structures. The growth mechanism of the GaN nanowires is discussed.     

Confocal Raman spectromicroscopy for tin-core/carbon-shell nanowire heterostructure

High density heterostructures of carbon nanotubes encapsulated single crystalline tin nanowires have been characterized by Raman spectromicroscopy. The morphology, composition and structure of the synthesized nanoheterostructures were examined by using scanning electron microscopy, transmission electron microscopy. The Raman spectra obviously manifest the crystalline nano-graphite within amorphous carbon walls in the heterostructures. The Raman image reproduces the pristine heterostructures of the CNTs as seen in SEM image, which illustrate the single nanowires oriented uniformly grown on micro-graphitic fibers. It was found that the resultant heterostructures are luminescent which was attributed to crystalline nano-graphite embedded in the amorphous carbon matrix, which is a consequence of excitons localization within an increasing number of sp² rich clusters. The contrast in the Raman image reflects nonuniform distribution of the graphite cluster size which acts as the radiative centers. The luminescent property was reviewed. The enhanced Raman spectra and luminescent property by the well-defined tin nanowires inside the heterostructures was revealed.