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.     

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.     

Synthesis and characterization of GaN nanowires by ammoniating Ga2O3/Cr thin films deposited on Si(1 1 1) substrates

GaN nanowires have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Cr thin films at 950 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrophotometer, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high-quality crystalline, have the size of 30-80 nm in diameter and several tens of microns in length with good emission properties. The growth direction of GaN nanowires is perpendicular to the fringe of (1 0 1) plane. The growth mechanism of GaN nanowires is also discussed in detail.     

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     

Growth and characterization of high-quality GaN nanowires by ammonification technique

GaN nanowires were successfully synthesized at high quality and large yield on Si (1 1 1) substrate through ammoniating Ga₂O₃/BN films deposited by radio frequency (RF) magnetron sputtering system. X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and selected-area electron diffraction (SAED) confirm that the as-synthesized nanowires are of a hexagonal GaN with wurtzite structure. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) reveal that the nanowires have a straight and smooth curved structure with extremely uniform diameter of about 60 nm, which is helpful to the application of GaN nanowires. The present results demonstrate that the BN is a very important intermedium in the growth of GaN nanowires by this method.     

Fabrication and characterization of GaN/amorphous Ga2O3 nanocables through thermal oxidation

In an effort to obtain one-dimensional core/shell nanostructures, thermal oxidation behavior of GaN nanowires in O₂ with N₂ ambients was investigated by x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. Crystallinity and chemical bonding states of the oxidized surface in the GaN nanowires were strongly dependent on the oxidation temperature. Chemical oxidation reaction occurred upon increasing the temperature, accompanied by the formation of an amorphous Ga₂O₃ layer at the GaN nanowire surface at 900 ^°C. The XPS analyses provided further evidence supporting the change in the chemical bonding states with increasing oxidation temperature.     

Two-step synthesis of one-dimensional single crystalline GaN nanowires

Straight and smooth GaN nanowires were synthesized on quartz substrates through the direct reaction of Ga₂O₃ thin films with flowing ammonia in a horizontal oven without using a template or catalyst. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM) and photoluminescence (PL) were used to characterize the samples. The straight and smooth cylindrical nanostructures are high quality single crystalline hexagonal wurtzite GaN nanowires with diameters ranging from 5 to 30 nm and lengths up to 20 μm. The near-band-edge emission peak located at 367 nm was observed at room temperature.     

Synthesis and characterization of GaN nanowires by a catalyst assisted chemical vapor deposition

GaN nanowires have been fabricated on Si(1 1 1) substrates by chemical vapor deposition (CVD) method with NiCl₂ as catalyst and their compositions, microstructures, morphologies and light emitting properties were characterized by X-ray diffraction (XRD), FT-IR spectrophotometer (FTIR), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), Raman spectroscopy and photoluminescence (PL). The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high crystalline quality, having the size of 20-50 nm in diameter and several tens of microns in length with some nano-droplets on their tips, which reveals that the growth mechanism of GaN nanowires agrees with vapor-liquid-solid (VLS) process. Five first-order Raman active phonon bands move to low shift and A₁(TO), E₁(TO), and E₂ (high) bands are overlapped and broaden, which is caused by uncertainty in the phonon wave vector. Five non-first-order active Raman phonons also appear, which is caused by the small dimension and high surface disorder degree. A blue-shift of the band-gap emission occurs due to quantum confinement effect.     

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.     

Synthesis of GaN nanowires on gold-coated SiC substrates by novel pulsed electron deposition technique

A two-step approach for macro-synthesis of GaN nanowires was developed in this study. GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent dicyandiamide (C₂N₄H₄) and Ga₂O₃ as precursors. Subsequently, single-crystalline wurtzite GaN nanowires were grown on gold-coated 6H-SiC substrates via novel pulsed electron deposition (PED) technique using the as-prepared GaN nanoparticles as target, which provides a new route employing nanoparticles as precursors to fabricate GaN nanowires. It is found that pulsed electron ablation induced Ga and N plasma directly towards the gold-coated substrate to initialize the vapor-liquid-solid (VLS) growth processes. The morphological and structural properties were investigated in detail and Raman scattering spectrum of these nanowires presented some new features.     

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.     

Synthesis of β-Ga2O3 nanowires through microwave plasma chemical vapor deposition

In this study, we demonstrate the large-scale synthesis of beta gallium oxide (β-Ga₂O₃) nanowires through microwave plasma chemical vapor deposition (MPCVD) of a Ga droplet in the H₂O and Ar atmosphere at 600 W. Unlike the commonly used MPCVD method, the H₂O, not mixture of gas, was employed to synthesize the nanowires. The ultra-long β-Ga₂O₃ nanowires with diameters of about 20-30 nm were several tens of micrometers long. The morphology and structure of products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM). The growth of β-Ga₂O₃ nanowires was controlled by vapor-solid (VS) crystal growth mechanism.     

The effect of the aminating temperature on the synthesis of gallium nitride nanowires doped with magnesium

GaN nanowires doped with Mg have been synthesized at different temperature through ammoniating the magnetron-sputtered Ga₂O₃/Au layered films deposited on Si substrates. X-ray diffraction (XRD), Scanning electron microscope (SEM), high-resolution TEM (HRTEM) equipped with an energy-dispersive X-ray (EDX) spectrometer and photoluminescence (PL) were used to analyze the structure, morphology, composition and optical properties of the as-synthesized sample. The results show that the ammoniating temperature has a great impact on the properties of GaN. The optimally ammoniating temperature of Ga₂O₃/Au layer is 900 C for the growth of GaN nanowires(NWs). The band gap emission (358 nm) relative to that (370 nm) of undoped GaN NWs has an apparent blueshift, which can be ascribed to the doping of Mg. Finally, the growth mechanism is also briefly discussed.     

Synthesis and photoluminescence of single-crystal GaN nanorods prepared by sol-gel method

A new method was applied to prepare GaN nanorods. In this method, gallium oxide (Ga₂O₃) gel was firstly formed by a sol-gel processing using gallium ethanol, Ga(OC₂H₅)₃, as a new precursor. GaN nanorods were successfully synthesized after annealing of the Ga₂O₃ gel at 1000 °C for 20 min in flowing ammonia. The as-prepared nanorods were confirmed as single crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Transmission electron microscopy (TEM) displayed that the GaN nanorods were straight and smooth, with diameters ranging from 200 nm to 1.8 μm and lengths typically up to several tens of microns. When excited by 280 nm light at room temperature, the GaN nanorods had a strong ultraviolet luminescence peak located at 369 nm and a blue luminescence peak located at 462 nm, attributed to GaN band-edge emission and the existence of the defects or surface states, respectively.     

Size and density control of silicon oxide nanowires by rapid thermal annealing and their growth mechanism

In this work, we demonstrate a fast approach to grow SiO₂ nanowires by rapid thermal annealing (RTA). The material characteristics of SiO₂ nanowires are investigated by field emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field (HAADF) imaging, electron energy loss spectroscopy (EELS), and energy-filtered TEM (EFTEM). The HAADF images show that the wire tip is predominantly composed of Pt with brighter contrast, while the elemental mappings in EFTEM and EELS spectra reveal that the wire consists of Si and O elements. The SiO₂ nanowires are amorphous with featureless contrast in HRTEM images after RTA at 900°C. Furthermore, the nanowire length and diameter are found to be dependent on the initial Pt film thickness. It is suggested that a high SiO₂ growth rate of >1 μm/min can be achieved by RTA, showing a promising way to enable large-area fabrication of nanowires.     

Synthesis of quasi-1D cuprous oxide nanostructure and its structural characterizations

A wealth of superfine polycrystalline cuprous oxide (Cu₂O) nanowires have been synthesized with hydrazine hydrated (N₂H₄·H₂O), act as the reducing agent, and Cu(OH)₂ nanowires, act as a soft template and surfactant, at room temperature. Two methods were employed for the synthesis of these nanowires, i.e. with and without capping agent (polyethylene glycol Mw 8000). Techniques of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern, electron diffraction X-ray (EDX) spectroscopy, and UV-visible (UV-vis) spectroscopy have been used to characterize the morphology, structure, crystallinity, purity, and composition of nanowires. The average diameters of Cu₂O nanowires, prepared with and without capping agent, were observed to be 8-10 and 12-15 nm and lengths of several microns, respectively. It is found that capping agent (PEG) confines the dimensions of synthesized nanowires. In addition, the observed optical band gap of products show blue-shift effect compared to the bulk Cu₂O (E_g=2.17 eV), which ascribe it as a promising material for the conversion between solar energy and electrical or chemical energy.     

Synthesis of In-doped Ga2O3 zigzag-shaped nanowires and optical properties

In-doped Ga₂O₃ zigzag-shaped nanowires and undoped Ga₂O₃ nanowires have been synthesized on Si substrate by thermal evaporation of mixed powders of Ga, In₂O₃ and graphite at 1000 °C without using any catalyst via a vapor-solid growth mechanism. The morphologies and microstructures of the products were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The nanowires range from 100 nm to several hundreds of nanometers in diameter and several tens of micrometers in length. A broad emission band from 400 to 700 nm is obtained in the PL spectrum of these nanowires at room temperature. There are two blue-emission peaks centering at 450 and 500 nm, which originate from the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.     

GaN-nanowire-based dye-sensitized solar cells

GaN nanowires typically exhibit high electron mobility and excellent chemical stability. However, stability of GaN is detrimental for successful attachment of dye molecules and its application in dye-sensitized solar cells (DSSCs). Here we demonstrate DSSCs based on GaN/gallium oxide and GaN/TiO _x core–shell structures, and we show that coating of GaN nanowires with a TiO _x shell significantly increases dye adsorption and consequently photovoltaic performance. The best cells exhibited short circuit current density of 1.83 mA/cm² and power conversion efficiency of 0.44% under AM 1.5 simulated solar illumination.     

Mesoporous TiO2-B nanowires synthesized from tetrabutyl titanate

Ultralong mesoporous TiO₂-B nanowires were synthesized via a hybrid hydrothermal-ion exchanging-thermal treatment using tetrabutyl titanate (TBOT) as a raw material. The phase transformations and porous structures of TiO₂-B nanowires were characterized and studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption-desorption measurement. Mesoporous TiO₂-B nanowires showed a length of several micrometers and diameter of about 25 nm. The porous structures of obtained TiO₂-B nanowires were demonstrated by BJH pore distribution measurement. The wirelike morphologies and porous structures of monodisperse nanowires calcined at 600 °C showed little change, which indicated that such nanowires possessed high thermal stability. The formation mechanism of TiO₂-B nanowires with mesoporous structures were also discussed based on our experimental results.     

Large-scale synthesis of In2O3 nanowires

In₂O₃ nanowires have been successfully fabricated on a large scale from indium particles by thermal evaporation at 1030 °C. The as-synthesized products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM images show that these nanowires are uniform with diameters of about 60–120 nm and lengths of about 15–25 μm. XRD and selected-area electron diffraction analysis together indicate that these In₂O₃ nanowires crystallize in a cubic structure of the bixbyite Mn₂O₃ (I) type (also called the C-type rare-earth oxide structure). The growth mechanism of these nanowires is also discussed. Received: 29 June 2001 / Accepted: 28 September 2001 / Published online: 20 December 2001