Growth Mechanism Of Nanowires Research Articles

Silver and Copper Microstructures: The Workfunction’s Effect

To understand the growth mechanism of Ag and Cu nanowires we have studied the effect of workfunction on the metal nanowire growth by XRD, SEM and Potentiostat. Under the same potential and overpotential, the metal with a smaller workfunction has a higher current density, i.e. current density for Ag is higher than of Cu nanowires. Likewise metals, the plane with smaller workfunction grows faster than with the larger workfunction, thus the preferential growth plane is (220) for both metals. We argued that the current arises from electrons tunneling from metal surface to hydrated metal and hydrogen ions. The metal with a smaller workfunction has a thinner barrier for tunneling, thus leading to a higher current density. It is found that deposition method have no such effect on the structure of deposited nanowires.

Facile Synthesis, Characterization, Nanocrystal Growth and Photoluminescence Properties of GeS Nanowires

As a IV–VI semiconductor, GeS is winning wide attention for its excellent properties. However, few examples of GeS nanostructures, especially those with photoluminescence (PL) properties, have been reported. After the optimization of reaction conditions, including time and temperature, the GeS nanowires with PL properties are synthesized a green, facile hydrothermal route without using any toxic reagent. These materials are characterized by transmission and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), etc. With the average diameter of [Formula: see text]200[Formula: see text]nm and the length ranging from 1–25[Formula: see text][Formula: see text]m, the resulting GeS nanowires have relatively smooth surface and round top, and are oriented along [100] facet. The growth mechanism of GeS nanowires is investigated, and the understanding of their growth mechanism could provide helpful guidance for designing experimental conditions rationally to synthesize nanowires. Due to their special nanostructure, these nanowires possess very good fluorescent properties, which indicates that these nanowires have potential to apply in future optical nanodevices.

Synthesis and field-emission characteristics of SiC nanowire forest

Abstract Silicon carbide nanowire forests were successfully synthesized via a vapor–liquid–solid process. The synthesized SiC nanowires had planar stacking faults perpendicular to the nanowire axis, diameters of 70 – 180 nm and lengths of tens to hundreds of micrometers, and grew along the [111] orientation. The SiC nanowire forest was characterized in a field emitter application and exhibited excellent field emission properties. Furthermore, we carried out in-depth investigations into the growth mechanism of the SiC nanowires through adjusting the growth conditions.

Synthesis and properties of ultra-long InP nanowires on glass

We report on the synthesis of Au-catalyzed InP nanowires (NWs) on low-cost glass substrates. Ultra-dense and ultra-long (up to ∼250 μm) InP NWs, with an exceptionally high growth rate of ∼25 μm min−1, were grown directly on glass using metal organic vapor phase epitaxy (MOVPE). Structural properties of InP NWs grown on glass were similar to the ones grown typically on Si substrates showing many structural twin faults but the NWs on glass always exhibited a stronger photoluminescence (PL) intensity at room temperature. The PL measurements of NWs grown on glass reveal two additional prominent impurity related emission peaks at low temperature (10 K). In particular, the strongest unusual emission peak with an activation energy of 23.8 ± 2 meV was observed at 928 nm. Different possibilities including the role of native defects (phosphorus and/or indium vacancies) are discussed but most likely the origin of this PL peak is related to the impurity incorporation from the glass substrate. Furthermore, despite the presence of suspected impurities, the NWs on glass show outstanding light absorption in a wide spectral range (60%–95% for λ = 300–1600 nm). The optical properties and the NW growth mechanism on glass is discussed qualitatively. We attribute the exceptionally high growth rate mostly to the atmospheric pressure growth conditions of our MOVPE reactor and stronger PL intensity on glass due to the impurity doping. Overall, the III–V NWs grown on glass are similar to the ones grown on semiconductor substrates but offer additional advantages such as low-cost and light transparency.

The Mechanism of Ni-Assisted GaN Nanowire Growth.

Despite the numerous reports on the metal-catalyzed growth of GaN nanowires, the mechanism of growth is not well understood. Our study of the nickel-assisted growth of GaN nanowires using metalorganic chemical vapor deposition provides key insights into this process. From a comprehensive study of over 130 nanowires, we observe that as a function of thickness, the length of the nanowires initially increases and then decreases. We attribute this to an interplay between the Gibbs-Thomson effect dominant in very thin nanowires and a diffusion induced growth mode at larger thickness. We also investigate the alloy composition of the Ni-Ga catalyst particle for over 60 nanowires using energy dispersive X-ray spectroscopy, which along with data from electron energy loss spectroscopy and high resolution transmission electron microscopy suggests the composition to be Ni2Ga3. At the nanowire growth temperature, this alloy cannot be a liquid, even taking into account melting point depression in nanoparticles. We hence conclude that Ni-assisted GaN nanowire growth proceeds via a vapor-solid-solid mechanism instead of the conventional vapor-liquid-solid mechanism.

Studies of Silicon Nanowires with Different Parameters — By PECVD

One-dimensional nanostructures such as nanowires have a wide range of applications. Silicon is the best competitive material for the carbon nanotubes (CNTs). Carbon and silicon have some similar and peculiar properties. Silicon nanowires (SiNWs) were synthesized using plasma enhanced chemical vapor deposition (PECVD) on p-Si (111) wafer. Gold is used as a catalyst for the growth of the SiNWs. Based on our fundamental understanding of vapor–liquid–solid (VLS) nanowire growth mechanism, different levels of growth controls have been achieved. Gold catalyst deposited and annealed at different temperatures with different thicknesses (450[Formula: see text]C, 500[Formula: see text]C and 550[Formula: see text]C, 600[Formula: see text]C, 650[Formula: see text]C for 4[Formula: see text]min and 8[Formula: see text]min and 3[Formula: see text]nm, 5[Formula: see text]nm, 30[Formula: see text]nm Au thickness). SiNW grown by PECVD with different carrier gases varies with flow rate. We observed the different dimensions of Si nanowires by FESEM and optimized the growth parameters to get the vertical aligned and singular Si nanowires. Optical phonon of the Si nanowires and crystallinity nature were identified by Raman spectral studies.

Growth Mechanism of Silver Nanowires By Polyol Process and Their Application for Transparent Conductive Thin Film

One-dimensional nanowires have attracted intense interest due to their unique photo-electric, magnetic and thermal conductive characteristics. Silver nanowire (Ag NW) based thin films have been recently used as transparent conductive films because of their high optical transparency, low sheet resistance and flexibility. Previous studies have demonstrated that polyol process, one of widely used method for Ag NWs chemical synthesis, could be used to produce Ag NWs by adding Cl- ions with appropriate concentration in the process. Besides Ag NWs, Ag particles could also be formed with addition of much higher or lower Cl- ions. However, optimal reaction time and concentration of Cl-ions for Ag NWs synthesis have rarely been reported. In this study, Ethylene Glycol (EG) solution with AgNO3was prepared and added in EG solution with Polyvinylpyrrolidone (PVP) for Ag NW formation. Mechanism of Ag NW formation was investigated by adding different amount of NaCl for different reaction time. The results show that Ag nanoparticles were initially formed and gradually turned into nanowires because of PVP addition. However, Ag NWs would gradually shorten while growing at critical length in the reaction. This interesting phenomenon could be explained by the reducing of surface energy. Furthermore, the longest Ag NWs could be obtained under condition of optimal reaction time and concentration of Cl-ions. These Ag NWs were prepared as transparent conductive thin films for optical transmittance and electrical conductivity measurements. Transparent conductive thin films with long AgNWs have better conductivity than short ones, and their stability would be further increased while coating the Polymethylmethacrylate (PMMA) as protective layer.

Enhanced adhesion and field emission of CuO nanowires synthesized by simply modified thermal oxidation technique

Metal oxide nanowires (NWs) can be easily grown by the thermal oxidation method, but the low adhesion between the NWs and the substrate restricts their practical applications in functional devices. In this work, the conventional hotplate technique is simply modified by introducing one or two stainless steel plates to supply a more stable oxidation environment, which is found to be beneficial to the growth and adhesion of CuO NWs on the Cu substrate. In detail, the Cu foils were heated on the hotplate directly, on one plate over the hotplate, and between two plates over the hotplate at 400 °C in ambient condition. It is found that the NWs obtained between two plates exhibit large length and diameter with moderate density. The sufficient activated oxygen, stable temperature, and proper temperature gradient configuration caused by the two plates accelerate the formation of CuO NWs, and result in the longest NWs with enhanced adhesion. The grain-boundary diffusion and Kirkendall effect are proposed to explain the mechanism of NWs growth and the formation of cracks. The NWs obtained between two plates also showed the best field emission properties, with lowest turn-on field (5.31 V μm−1) and threshold field (9.8 V μm−1). Excellent field emission properties and enhanced NW-substrate adhesion indicate that these NW arrays could be potentially used as the cathode of field emission displays.

Contribution of droplet volume fluctuation to dispersion of nanowire length

In this work we study features of vapor-solid-liquid mechanism of nanowire growth. We consider variation of droplet volume during the growth caused by droplet depletion and refilling. Here we take into account the changes in material transport due to volume variation, which was neglected previously. We also discuss the impact of this effect on nanowire length distributions.

Optoelectronic and Electrochemical Properties of Vanadium Pentoxide Nanowires Synthesized by Vapor-Solid Process.

Substantial synthetic vanadium pentoxide (V2O5) nanowires were successfully produced by a vapor-solid (VS) method of thermal evaporation without using precursors as nucleation sites for single crystalline V2O5 nanowires with a (110) growth plane. The micromorphology and microstructure of V2O5 nanowires were analyzed by scanning electron microscope (SEM), energy-dispersive X-ray spectroscope (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD). The spiral growth mechanism of V2O5 nanowires in the VS process is proved by a TEM image. The photo-luminescence (PL) spectrum of V2O5 nanowires shows intrinsic (410 nm and 560 nm) and defect-related (710 nm) emissions, which are ascribable to the bound of inter-band transitions (V 3d conduction band to O 2p valence band). The electrical resistivity could be evaluated as 64.62 Ω·cm via four-point probe method. The potential differences between oxidation peak and reduction peak are 0.861 V and 0.470 V for the first and 10th cycle, respectively.

Topotaxial growth of α-Fe2O3 nanowires on iron substrate in thermal annealing method

A detail cross-sectional transmission electron microscopy of as-grown α-Fe2O3 nanowire sample, synthesized on iron substrate by thermal annealing method, was carried out to understand the mechanism of growth in this system. Iron undergoes sequential oxidation to form a layered structure of Fe/FeO/Fe3O4/α-Fe2O3. α-Fe2O3 nanowires grow on to the top of α-Fe2O3 layer. It was found that subsequent oxide layers grow topotaxially on the grains of iron, which results in a direct orientation relationship between the α-Fe2O3 nanowire and the parent grain of iron. The results also showed that the grains of α-Fe2O3 layer, which were uniquely oriented in [110] direction, undergo highly anisotropic growth to form the nanowire. This anisotropic growth occurs at a twin interface, given by (−11−1), in the α-Fe2O3 layer. It was concluded that the growth at twin interface could be the main driving factor for such anisotropic growth. These observations are not only helpful in understanding the growth mechanism of α-Fe2O3 nanowires, but it also demonstrates a way of patterning the nanowires by controlling the texture of iron substrate.

Study on synthesis and growth mechanism of copper nanowires via a facile oleylamine-mediated process

The uniform and well-dispersed copper nanowires (Cu NWs) with an average diameter of 70 nm and length up to 60 μm were synthesized via a facile solution-phase approach using oleylamine (OLA) as the capping agent. Polyvinypyrrolidone (PVP) was added to prevent the Cu NWs from aggregating in the synthetic process. Electron microscope and UV–visible spectroscopy were used to analyze the growth mechanism of 1-D Cu nanostructures. Our results indicate that the growth of the nanowire is along the [110] direction and the obtained Cu NWs were derived from multiply-twinned seeds. Since OLA could effectively stabilize the newly formed [100] facets rather than the [111] facets, finally leading to the 1-D elongation of Cu NWs.

Nucleation and growth mechanism of self-catalyzed InAs nanowires on silicon

We report on the nucleation and growth mechanism of self-catalyzed InAs nanowires (NWs) grown on Si (111) substrates by chemical beam epitaxy. Careful choices of the growth parameters lead to In-rich conditions such that the InAs NWs nucleate from an In droplet and grow by the vapor–liquid–solid mechanism while sustaining an In droplet at the tip. As the growth progresses, new NWs continue to nucleate on the Si (111) surface causing a spread in the NW size distribution. The observed behavior in NW nucleation and growth is described within a suitable existing theoretical model allowing us to extract relevant growth parameters. We argue that these results provide useful guidelines to rationally control the growth of self-catalyzed InAs NWs for various applications.

Growth Mechanism of TeO2 Nanowires Synthesized by Thermal Evaporation Method

Growth Mechanism of TeO2 Nanowires Synthesized by Thermal Evaporation Method

ZnSe Nanowires Synthesis and Characterization

ZnSe nanowires (NWs) were synthesized by using a thermal evaporation method in a vacuum-sealed quartz tube inside a tube furnace. NWs were used ZnSe powder as a precursor to grow. ZnSe NWs grow on silicon (100) substrates coated with different thickness 2, 5, and 10 nm Au catalysts film. The growth mechanism of NWs is vapor-liquid-solid (VLS) mechanism. It will help us to get the good crystallinity and less defect in the NWs. Moreover, we will observe the different condition of NWs by controlling the temperature of precursor, temperature of growth area, pressure, carrier gas, thickness of Au film, position of substrate and growth time of NWs. The temperature of precursor decides the amount of the ZnSe vapor. As the temperature is higher the vapor will come out more and quickly. The temperature of growth area controls the precipitate condition of NWs. Also, pressure is one of the important condition of growing NWs. It controls the growth environment, such as the magnitude of vapor pressure. In this work, the pressure is kept around 0.4 to 1 Torr to observe the variation of NWs. Carrier gas in this work mainly affects the position of the NWs growth. However, in this work different thickness of Au film cannot be observed the obviously different dimeter. Position of substrate can show the growth area of the NWs, namely the distribution of NWs. It combines above conditions such like pressure and carrier gas. NWs in different position can grow verity of configuration or distribution. At last, growth time of NWs determine the density and length of NWs. As the time is longer, NWs will become longer and more density. Combination of above conditions, the length of appropriate NWs we need is about 20-50 μm, and the dimeter is around 80 nm. Furthermore, the morphorlogy of NWs is uniform and straight. ZnSe NWs were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), and transmission electron microscope (TEM) about the morphology and crystal structure.

A Roadmap for Controlled and Efficient n‐Type Doping of Self‐Assisted GaAs Nanowires Grown by Molecular Beam Epitaxy

N‐type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n‐type GaAs nanowires with carrier density as high as 1020 electron cm−3 by self‐assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single‐wire field‐effect devices. Low‐temperature photoluminescence is used to characterize the Te‐doped nanowires over several orders of magnitude of the impurity concentration. The combined use of those techniques allows the precise definition of the growth conditions required for effective Te incorporation.

Tuning ultrafine manganese oxide nanowire synthesis seeded by Si particles and its superior Li storage behaviors

The nanostructure and the dimension of materials greatly affect their performance and function. It is important to develop synthesis strategies that enable the control of the materials’ morphology and structure and further reduce their size. In the present work, we report a novel synthesis approach that utilizes Si nanoparticles for synthesizing ultrafine MnO nanowires. The resulting nanostructure comprises MnO nanowires with a diameter of ~5–10 nm embedded in an amorphous carbon matrix. X-ray diffraction patterns and high-resolution transmission electron microscopy images clearly reveal the growth mechanism of nanowires. As an anode material for the lithium-ion battery, the nanostructure exhibits excellent charge transfer kinetics and extremely high electrochemical performance, including reversible specific capacities of 285.9 mA h g−1 at 30 A g−1 and 757.4 mA h g−1 at 1 A g−1 after 1000 cycles. X-ray absorption fine structure (XAFS) confirms that the enhanced performance is related to the increase of the ordering of the O2− ions in the MnO structure during the charge/discharge processes. This novel synthesis strategy may inspire studies of other transition-metal-oxide nanomaterials with special orientation to tune their physical chemistry properties. By using silicon nanoparticles as seeds, a team in China has made ultrafine manganese oxide (MnO) nanowires in a matrix of amorphous carbon. The properties of nanowires vary according depending on their size and shape, and hence methods are needed for controllably synthesizing nanostructures and for shrinking their dimensions. Now, Dingguo Xia and co-workers at Peking University in Beijing have used epitaxial growth to synthesize MnO nanowires with diameters in the range 5–10 nanometres embedded in a carbon matrix. They characterized the growth mechanism and properties of this nanocomposite and found that it is promising as an anode material for lithium-ion batteries. In particular, it exhibited excellent charge transfer kinetics and electrochemical performance. The scientists consider that the synthesis strategy may be applicable for making nanostructures of other transition-metal oxides. It can be found that the Mn/Si ratio is a crucial factor affecting the morphology of the as-obtained products. The pristine Si nanoparticles are sphere-like particles of ~100 nm in diameter. When the Mn/Si molar ratio is 4:1, ultrafine MnCO3 nanowires less than 10 nm in diameter are obtained. The MnO@C nanowires were synthesized via polymerization–pyrolysis steps, and the excellent high-rate performance and stability of the MnO@C nanowires used as an anode in the lithium-ion battery are attributed to the unique interconnected nanostructure.

The origin of yellow band emission and cathodoluminescence of Au-catalyzed wurtzite GaN nanowires

GaN nanowires with large yield are directly synthesized by simply ammoniating the gallium oxide powders in the presence of ammonia gas at 1000°C, under the assistance of Au nanocatalysts. The microstructure and crystallinity of as-synthesized GaN nanowires are well studied by using high-resolution transmission electron microscope (HRTEM) and some structural defects such as stacking faults are found in the GaN nano-crystal. Cathodoluminescence measurement shows that a strong near-band-edge (NBE) emission band centered at 384nm and a broad yellow band in the range of 500–800nm are observed. Finally, the growth mechanism and possible optical emission process of GaN nanowires are discussed.

Organometallically Anisotropic Growth of Ultralong Sb2Se3 Nanowires with Highly Enhanced Photothermal Response.

Ultralong orthorhombic Sb2Se3 nanowires have been successfully fabricated via an alternative facile organometallic synthetic route from the reaction of triphenylantimony(III) with dibenzyldiselenide in oleylamine at 180-240 °C without any other additives. The formation and growth mechanism of the Sb2Se3 nanowires is intensively investigated, and it is found that the anisotropic growth of the nanowires with almost constant diameters is resulted from the synergistic effects of the intrinsic property of the orthorhombic crystal structure and the weak binding assistance of oleylamine, and the length of the nanowires can be elongated easily by increasing reaction time in the synthetic route. Moreover, the photothermal response of the Sb2Se3 nanowires is first evaluated under illumination of UV light (320-390 nm), and it is especially noted that the Sb2Se3 nanowires exhibit highly enhanced photothermal responses (more than two times the intensity) as compared to the bulk Sb2Se3. In addition, the Sb2Se3 nanowires show excellent light-to-heat performance, which is superior to that of the nanostructured titanium dioxide and silicon powder under the same conditions.

Crystallographic-shear-phase-driven W18O49 nanowires growth on nanocrystalline W surfaces

The present paper reports the growth and branching mechanism of W18O49 nanowires grown on nanocrystalline tungsten (W) surfaces. Nanocrystalline W powder was prepared using high energy ball milling. The nanopowder was non-isothermally heat-treated up to 1400°C in argon atmosphere. The nanowires of 30–50nm diameter were observed on nanopowder surfaces after the heat-treatment. A model based on crystallographic shear phase formation to accommodate the oxygen deficiency during the reduction of WO3 is discussed to explain the growth and branching mechanism of these nanowires which correlates well with the observed angle for the branching.