Synthesis and Characterization of Glomerate GaN Nanowires

Glomerate GaN nanowires were synthesized on Si(111) substrates by annealing sputtered Ga₂O₃/Co films under flowing ammonia at temperature of 950 °C. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and Fourier transformed infrared spectra were used to characterize the morphology, crystallinity and microstructure of the as-synthesized samples. Our results show that the samples are of hexagonal wurtzite structure. For the majority of GaN nanowires, the length is up to tens of microns and the diameter is in the range of 50–200 nm. The growth process of the GaN nanowires is dominated by Co–Ga–N alloy mechanism.     

Initial Growth of Single-Crystalline Nanowires: From 3D Nucleation to 2D Growth

The initial growth stage of the single-crystalline Sb and Co nanowires with preferential orientation was studied, which were synthesized in porous anodic alumina membranes by the pulsed electrodeposition technique. It was revealed that the initial growth of the nanowires is a three-dimensional nucleation process, and then gradually transforms to two-dimensional growth via progressive nucleation mechanism, which resulting in a structure transition from polycrystalline to single crystalline. The competition among the nuclei inside the nanoscaled-confined channel and the growth kinetics is responsible for the structure transition of the initial grown nanowires.     

Electrodeposited Cu–ZnO and Mn–Cu–ZnO nanowire/tube catalysts for higher alcohols from syngas

Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO₃)₂, Cu(NO₃)₂, Mn(NO₃)₂ and NH₄NO₃ at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H₂ to produce alcohols at 270 °C, 10–20 bar, H₂/CO = 2/1, and 10,000–33,000 scc/h g_cat. In addition to methane and CO₂, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO₂ selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency.     

乙醇裂解制备碳纳米管及其生长机理研究

以乙醇作为碳源,Mo-Co/C和Mo-Fe/C作为催化剂,采用化学气相沉积法,高温裂解乙醇制备碳纳米管.利用SEM和TEM对碳纳米管形貌和结构进行表征.结果表明:乙醇在催化剂Mo-Co/C和Mo-Fe/C裂解产生的碳纳米管遵循顶部生长机理.并建立了乙醇制备碳纳米管的生长模型.     

Plasma-Assisted Synthesis of Carbon Nanotubes

The application of plasma-enhanced chemical vapour deposition (PECVD) in the production and modification of carbon nanotubes (CNTs) will be reviewed. The challenges of PECVD methods to grow CNTs include low temperature synthesis, ion bombardment effects and directional growth of CNT within the plasma sheath. New strategies have been developed for low temperature synthesis of single-walled CNTs based the understanding of plasma chemistry and modelling. The modification of CNT surface properties and synthesis of CNT hybrid materials are possible with the utilization of plasma.     

Influence of electrodeposition techniques on Ni nanostructures

Different Ni nanostructure arrays were fabricated by pulsed electrodeposition from a Watts bath inside the pores of anodic alumina membrane (AAM) templates. Under a trapezoidal waveform of potential, consisting of fast linear sweeps between 0 and −3 V (SCE) interleaved by delay times at 0 (10 s) and −3 V (0.1 s), Ni nanowires were grown. The rate of nanowires growth was constant up to 60 min of deposition. For longer times, the growth of nanowires was not uniform, and after about 180 min some nanowires reached the template surface exposed to the electrolyte. Under square potential pulses between the same potentials (pulse length 1 s), nanotubes of Ni are obtained. Morphological analysis of these nanostructures at different lengths revealed that the inner profile of nanotubes evolved from cylindrical to conical with increasing deposition time. The possibility to grow either nanowires or nanotubes in dependence of the potential waveform, as well as the growth rate of nanostructures were discussed taking into account the reaction of hydrogen evolution, occurring simultaneously with Ni electrodeposition.     

The Periodic Instability of Diameter of ZnO Nanowires via a Self-oscillatory Mechanism

ZnO nanowires with a periodic instability of diameter were successfully prepared by a thermal physical vapor deposition method. The morphology of ZnO nanowires was investigated by SEM. SEM shows ZnO possess periodic bead-like structure. The instability only appears when the diameter of ZnO nanowires is small. The kinetics and mechanism of Instability was discussed at length. The appearance of the instability is due to negative feed-back mechanism under certain experimental conditions (crystallization temperature, vapor supersaturation, etc).     

Kinetics of growth of nanowhiskers (nanowires and nanotubes)

The kinetics of nanowhiskers growth is studied theoretically taking into account the adatom diffusion from the surface to the top of needle. An exponential growth with time is expected for the initial stages of the process, when the length l of the whisker is smaller than the average diffusion length λ of adatoms. It transforms to linear growth rate for l > λ. The formation of nanotubes with a hollow core dislocation is explained by accounting for the role of the stress in the middle of screw dislocations. When the magnitude of the Burgers vector exceeds a critical value, it is energetically more favorable to remove the highly strained material around the dislocation line and to create a tube with an additional free surface. Additionally, there is an important size effect, due to the small radius R of the nanowhisker. The interplay, between the contributions from the size effects and from the diffusion, explains why for the very thin nanowhiskers the length l is proportional to the radius R while, otherwise the length is inversely proportional to it, i.e., l∼1/R.     

Controllable Synthesis of Magnesium Oxysulfate Nanowires with Different Morphologies

One-dimensional magnesium oxysulfate 5Mg(OH)₂ · MgSO₄ · 3H₂O (abbreviated as 513MOS) with high aspect ratio has attracted much attention because of its distinctive properties from those of the conventional bulk materials. 513MOS nanowires with different morphologies were formed by varying the mixing ways of MgSO₄ · 7H₂O and NH₄OH solutions at room temperature followed by hydrothermal treatment of the slurries at 150 °C for 12 h with or without EDTA. 513MOS nanowires with a length of 20–60 μm and a diameter of 60–300 nm were prepared in the case of double injection (adding MgSO₄ · 7H₂O and NH₄OH solutions simultaneously into water), compared with the 513MOS with a length of 20–30 μm and a diameter of 0.3–1.7 μm in the case of the single injection (adding MgSO₄ · 7H₂O solution into NH₄OH solution). The presence of minor amount of EDTA in the single injection method led to the formation of 513MOS nanowires with a length of 100–200 μm, a diameter of 80–200 nm, and an aspect ratio of up to 1000. The analysis of the experimental results indicated that the hydrothermal solutions with a lower supersaturation were favorable for the preferential growth of 513MOS nanowires along b axis.     

Electrocatalytic Performance of Palladium Dendrites Deposited on Titania Nanotubes for Formic Acid Oxidation

Pd catalyst with dendritic morphology was synthesized on ordered and uniformly distributed titania nanotubes (TNT/Ti), and bare Ti by a simple electrochemical deposition process. The influence of support morphology was studied in relation to Pd deposition and its electro catalytic oxidation of formic acid. The structural property of Pd dendrites was characterized by scanning electron microscopy and X‐ray diffraction. The electrochemical study showed the activity and durability of Pd/TNT/Ti catalyst for formic acid oxidation was enhanced compared to Pd/Ti electro catalyst. The synergetic contribution from TNT/Ti as support for Pd and its enhanced catalytic activity is discussed.     

Free growth of one-dimensional β-Ga2O3 nanostructures including nanowires,nanobelts and nanosheets using a thermal evaporation method

Large-scale β-Ga₂O₃ nanostructures (nanowires-NWs, nanobelts-NBs and nanosheets-NSs) were synthesized via thermal evaporation of GaN powder in an ambient argon atmosphere. The effect of the substrate type (Si, AlN-thin film/Si and ZnO-thin film/Si) on the growth of β-Ga₂O₃ nanostructures was investigated. The morphology changes from NWs to NBs or NSs when the substrate changes from Si to AlN-thin film/Si or ZnO-thin film/Si, respectively. The size and dimensionality were the most influential parameters on the structure of the as-grown β-Ga₂O₃. The as-grown nanostructures crystallize within the monoclinic crystal structure of the β-Ga₂O₃ phase. The obtained nanostructures show intense blue-red emission characterized by a broadband photoluminescence spectrum with peaks located at 430, 500–525 and 688–700 nm. These emissions originate from the defect-related donor-acceptor pair recombination mechanism and depend on the nanostructure dimensionality and morphology. A vapor-solid growth mechanism for the growth of various β-Ga₂O₃ nanostructures was also proposed.     

Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica

Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core–shell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50–200 nm and the length from tens to hundreds of micrometers. The vapor–solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core–shell interface.     

Synthesis of Tin Nitride Sn x N y Nanowires by Chemical Vapour Deposition

Tin nitride (Sn _x N _y ) nanowires have been grown for the first time by chemical vapour deposition on n-type Si(111) and in particular by nitridation of Sn containing NH₄Cl at 450 °C under a steady flow of NH₃. The Sn _x N _y nanowires have an average diameter of 200 nm and lengths ≥5 μm and were grown on Si(111) coated with a few nm’s of Au. Nitridation of Sn alone, under a flow of NH₃ is not effective and leads to the deposition of Sn droplets on the Au/Si(111) surface which impedes one-dimensional growth over a wide temperature range i.e. 300–800 °C. This was overcome by the addition of ammonium chloride (NH₄Cl) which undergoes sublimation at 338 °C thereby releasing NH₃ and HCl which act as dispersants thereby enhancing the vapour pressure of Sn and the one-dimensional growth of Sn _x N _y nanowires. In addition to the action of dispersion, Sn reacts with HCl giving SnCl₂ which in turn reacts with NH₃ leading to the formation of Sn _x N _y NWs. A first estimate of the band-gap of the Sn _x N _y nanowires grown on Si(111) was obtained from optical reflection measurements and found to be ≈2.6 eV. Finally, intricate assemblies of nanowires were also obtained at lower growth temperatures.     

PVP导向ZnO纳米线、纳米棒的可控溶剂热合成及其生长机理研究

本文采用强碱性的溶剂热法,通过调控反应温度、时间、反应物投料比、特别是添加剂等影响因素,可控合成了两种不同形貌的一维ZnO纳米材料.利用透射电镜(TEM)和扫描电镜(SEM)研究了不同影响因素对ZnO产物形貌的影响.着重分析了添加剂聚乙烯吡咯烷酮(PVP)与纳米ZnO或其生长基元的络合作用,及其对纳米ZnO形貌的控制作用,并总结出强碱性溶剂热合成中反应温度、体系压强和pH值对ZnO产物形貌的作用机理.     

一维ZnO晶须的制备与生长机理

以Zn粉为原料,采用气固反应方法制备出两种一维ZnO晶须:ZnO纳米线和ZnO短晶须。用XRD、SEM等分析手段对ZnO晶须的结构和形貌进行研究,并分析了两种ZnO晶须的生长机理。     

低温水溶液系统合成磷酸铈纳米线

在低温水相体系中,无表面活性剂或模板存在,合成磷酸铈(CePO4)纳米线。采用XRD、SEM、TEM、FT-IR和荧光分光光度计对所制样品进行表征,结果表明,控制水浴温度、陈化时间、反应物浓度可以控制CePO4纳米线的长宽比和形貌。这项研究,为磷酸铈纳米线的规模化生产提供了可能。     

Growth and formation mechanism of sea urchin-like ZnO nanostructures on Si

Sea urchin-like nanostructures of ZnO consisting of ZnO nanowires with blunt faceted ends were grown on Si (100) substrates by oxidation of metallic Zn at 600 °C. ZnO nanowires having a diameter of 30–60 nm and length of 2–4 Μm were in similar shape with uniform diameter along its entire length with well faceted blunt ends. X-ray diffraction and transmission electron microscope analysis showed that the as-grown nanostructures were highly crystalline with wurtzite hexagonal structure having lattice constants of a=b=3.25 å and c=5.21 å. Room temperature photoluminescence (PL) measurements showed a weak near band-edge emission at 380 nm, but a strong green emission at 500–530 nm. A model for vapor-solid (VS) growth mechanism of ZnO nanowires was presented, in which nucleation of ZnO is crucial for the growth of the nanostructures.     

碳纳米管的制备研究

本文介绍了国内外碳纳米管(CNTS)最新研究进展，分析了制备碳纳米管所必需的3个关键条件：碳源、催化剂、能源；并分别研究了它们对碳纳米管生长的影响。通过碳纳米管的生长机理探讨了大规模制备碳纳米管的可行性。     

Investigation of Nucleation Mechanism and Tapering Observed in ZnO Nanowire Growth by Carbothermal Reduction Technique

ZnO nanowire nucleation mechanism and initial stages of nanowire growth using the carbothermal reduction technique are studied confirming the involvement of the catalyst at the tip in the growth process. Role of the Au catalyst is further confirmed when the tapering observed in the nanowires can be explained by the change in the shape of the catalyst causing a variation of the contact area at the liquid–solid interface of the nanowires. The rate of decrease in nanowire diameter with length on the average is found to be 0.36 nm/s and this rate is larger near the base. Variation in the ZnO nanowire diameter with length is further explained on the basis of the rate at which Zn atoms are supplied as well as the droplet stability at the high flow rates and temperature. Further, saw-tooth faceting is noticed in tapered nanowires, and the formation is analyzed crystallographically.     

One-Dimensional Nanostructures and Devices of II–V Group Semiconductors

The II–V group semiconductors, with narrow band gaps, are important materials with many applications in infrared detectors, lasers, solar cells, ultrasonic multipliers, and Hall generators. Since the first report on trumpet-like Zn₃P₂ nanowires, one-dimensional (1-D) nanostructures of II–V group semiconductors have attracted great research attention recently because these special 1-D nanostructures may find applications in fabricating new electronic and optoelectronic nanoscale devices. This article covers the 1-D II–V semiconducting nanostructures that have been synthesized till now, focusing on nanotubes, nanowires, nanobelts, and special nanostructures like heterostructured nanowires. Novel electronic and optoelectronic devices built on 1-D II–V semiconducting nanostructures will also be discussed, which include metal–insulator-semiconductor field-effect transistors, metal-semiconductor field-effect transistors, and p–n heterojunction photodiode. We intent to provide the readers a brief account of these exciting research activities.