Gallium Oxide Nanowires Research Articles

Doped gallium oxide nanowires with waveguiding behavior

Er and Cr doped β-Ga2O3 nano- and microwires have been grown by thermal treatments of Ga2O3 powder containing a fraction of Er2O3 powder or in the presence of Cr2O3 powder, respectively. Doping gives rise to the characteristic red photoluminescence (PL) of Cr3+ ions at about 700nm and to green emission of Er3+ at about 555nm. Waveguiding of the ion related PL light excited in the wires has been studied for wires with different sizes. Waveguide behavior for incident visible light of different wavelengths was demonstrated.

O2 and CO sensing of Ga2O3 multiple nanowire gas sensors

Abstract Gallium oxide nanowires were synthesized by a chemical thermal evaporation method using gallium metal as a source material. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations indicate that the obtained nanowires are well-crystallized single phase monoclinic Ga2O3. Multiple nanowire gas sensors were fabricated by dispensing the Ga2O3 nanowires on an interdigitated Pt-electrode. The Ga2O3 nanowire gas sensors show reversible response to O2 and CO gases in a working temperature range of 100–500 °C. A peak response is found at 300 °C for O2 gas and the peak response appears at 200 °C for CO gas. For both kinds of gases, the sensor response increases empirically with an increase of gas concentration. The results demonstrate the possibility of using the Ga2O3-based gas sensor at low working temperature field.

Growth of Ga2O3 and GaP nanowires synthesized from mixed Ga/GaP powder as a precursor

High-purity gallium oxide (β-Ga2O3) and/or gallium phosphide (GaP) nanowires were synthesized on the nickel or the cobalt oxide catalyzed alumina substrate by a simple chemical vapor deposition method from a mixture of gallium (Ga) and gallium phosphide powder as a source materials. The source materials were directly vaporized in the range of 750–1000°C for 60min under argon ambient. The average diameter of nanowires in the optimum synthesis temperature was around 70nm and the length was up to several hundreds of micrometer. We confirmed that β-Ga2O3 nanowires were observed in all samples, while the GaP nanowires with β-Ga2O3 nanowires were only obtained in the sample synthesized on the nickel oxide catalyst at 950°C. The β-Ga2O3 and GaP nanowires have a single-crystalline monoclinic and zinc blend structure, respectively. And the both nanowires reveal the core–shell structure, which consists of the β-Ga2O3 or GaP core and the amorphous gallium oxide outer layer.

Growth and Microstructure of Gallium Phosphide Nanowires Synthesized by the CVD Method Using Copper Oxide as a Catalyst

High purity nanowires are successfully synthesized by chemical vapor deposition. In this work, we have tried synthesis of GaP nanowires with copper oxide catalyst using chemical vapor deposition method involving a metal oxide-assisted vapor-liquid-solid (VLS) growth mechanism. The synthesis process is the same as that described in existing work except for a catalyst. The mixture of GaP and Ga powder was used as GaP source for synthesis of GaP nanowires. And the mixture powder was directly vaporized in the range of 700~1000°C under argon ambient in a furnace. The wire-like products was observed in the range of 800~950°C. The diameter of nanowires increases with increasing synthesis temperature, but reversely, the length of nanowires decreases steadily. The nanowires prepared at 850°C possess perfect wire-like shape and uniform distribution of diameter. The average diameter and length of nanowires are about 50 and 150, respectively. HRTEM and EDX analysis were carried out to obtain more detailed information of its microstructure. Nevertheless, all condition of processing was set for making the high purity GaP nanowires as existing reported method, the nanowires were identified as well-crystallized gallium oxide nanowires with an amorphous outer layer. It does not accord with existing reported results. This result means that the catalysts play a key role in the growth of nanowires.

Characteristics of Gallium Oxide Nanowires Synthesized by the Metalorganic Chemical Vapor Deposition

We have synthesized the high-density Ga2O3 nanowires on gold (Au)-coated silicon substrates using metalorganic chemical vapor deposition. The nanowires exhibited one-dimensional structures having circular cross sections with diameters in the range of 30-200 nm. The energy dispersive x-ray spectroscopy revealed that the nanowires contained elements of Ga and O, without Au-related impurities. X-ray diffraction analysis and high-resolution transmission electron microscopy showed that the Ga2O3 nanowires were crystalline.

Characterization and Electrochemical Properties of Gallium Oxide Nanowires Synthesized by CVD

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Implantation-assisted synthesis of gallium oxide nanoribbons on gallium arsenide using carbon and nitrogen

We have synthesized gallium oxide (Ga 2O 3) nanoribbons and nanowires on gallium arsenide (GaAs) substrate by using plasma immersion ion implantation (PIII) and rapid thermal annealing (RTA). Semi-insulating GaAs was treated with PIII of nitrogen, oxygen, acetylene (C 2H 2) or argon ions. For samples implanted with N 2, and C 2H 2 ions, subsequent RTA at 950 °C within 2 min produced Ga 2O 3 nanoribbons on the substrate surface. Our results suggest that each implanted species plays a different role in assisting the growth of these nanomaterials. Carbon is a key element for reduction and oxidation of Ga 2O 3, which can increase the growth rate of Ga 2O 3 nanoribbons. On the other hand, implanted nitrogen forms intermediate gallium nitride nanograins, which may in turn lead to the formation of nanograins of Ga 2O 3 upon reacting with ambient oxygen. These Ga 2O 3 nanograins then act as a growth template for nanowires or nanoribbons.

Controlled Vapor−Liquid−Solid Growth of Indium, Gallium, and Tin Oxide Nanowires via Chemical Vapor Transport

We utilized a vapor−liquid−solid growth technique to synthesize indium oxide, gallium oxide, and tin oxide nanowires using chemical vapor transport with gold nanoparticles as the catalyst. Using identical growth parameters, we were able to synthesize single crystal nanowires typically 40−100 nm diameter and more than 10−100 μm long. The products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). All the wires were grown under the same growth conditions with growth rates inversely proportional to the source metal vapor pressure. Initial experiments show that different transparent oxide nanowires can be grown simultaneously on a single substrate with potential application for multicomponent gas sensors.

Growth and structural properties of gallium oxide nanowires prepared by chemical vapour deposition

Gallium oxide nanowires have been prepared on Si(100) substrates using metallo-organic chemical vapour deposition. Growth behaviour has been investigated with various deposition times and the structural morphologies of the nanowires have been studied. The thickness and surface coverage ratio of the deposits increased with increasing deposition time. The gallium oxide nanowires were amorphous phase, having a circular cross-section with diameter of about 50–250 nm.

Direct synthesis of beta gallium oxide nanowires, nanobelts, nanosheets and nanograsses by microwave plasma

In this study, beta-gallium oxide (β-Ga 2O 3) nanowires, nanobelts, nanosheets, and nanograsses were synthesized through microwave plasma of liquid phase gallium containing H 2O in Ar atmosphere using silicon as the substrate. The nanowires with diameters of about 20–30 nm were several tens of microns long and the nanobelts with thickness of about 20–30 nm were tens to hundreds of microns long. The morphology and structure of products were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These results showed that multiple nucleation and growth of β-Ga 2O 3 nanostructures could easily occur directly out of liquid gallium exposed to appropriate H 2O and Ar in the gas phase. The growth process of β-Ga 2O 3 nanostructures may be dominated by VS (vapor–solid) mechanism.

Synthesis of β-Ga 2O 3 nanowires through microwave plasma chemical vapor deposition

In this study, we demonstrate the large-scale synthesis of beta gallium oxide (β-Ga 2O 3) nanowires through microwave plasma chemical vapor deposition (MPCVD) of a Ga droplet in the H 2O and Ar atmosphere at 600 W. Unlike the commonly used MPCVD method, the H 2O, not mixture of gas, was employed to synthesize the nanowires. The ultra-long β-Ga 2O 3 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-Ga 2O 3 nanowires was controlled by vapor–solid (VS) crystal growth mechanism.

Magnetism and luminescence evolution due to nitrogen doping in manganese–gallium oxide nanowires

We report a new method for large-scale production of GaMnN nanowires, by annealing manganese–gallium oxide nanowires in flowing ammonia at high temperature. Microstructure analysis indicates that the GaMnN nanowires have wurtzite GaN structure without Mn precipitates or Mn-related second phases. Magnetism evolution due to nitrogen doping in manganese–gallium oxide nanowires was evaluated by magnetic measurements. Magnetic measurement reveals that the magnetization increases with the increase of nitrogen concentration. Ferromagnetic ordering exists in the GaMnN nanowires, whose Curie temperature is above room temperature. Luminescence evolution was investigated by the cathodoluminesence measurement for a single nanowire and photoluminescence measurement in a temperature range between 10 and 300 K. Experimental results indicate that optical properties can be modulated by nitrogen doping in manganese–gallium oxide nanowires.

Magnetism and photoluminescence in manganese–gallium oxide nanowires with monoclinic and spinel structures

Manganese–gallium oxide nanowires were synthesized via in situ Mn doping during nanowire growth using a vapor phase evaporation method. The microstructure and composition of the products were characterized via transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The field and temperature dependence of the magnetization reveal the obvious hysteresis loop and large magnitude of Curie–Weiss temperature. The photoluminescence of the manganese–gallium oxide nanowires were studied in a temperature range between 10 and 300 K. A broad green emission band was observed which is attributed to the 4T 1– 6A 1 transition in Mn 2+(3d 5) ions.

Blueshifted Raman scattering and its correlation with the [110] growth direction in gallium oxide nanowires

The Raman spectrum of gallium oxide (β-Ga2O3) nanowires with [001] growth direction is identical to that of the bulk Ga2O3 [Y. C. Choi et al. Adv. Mater. 12, 746 (2000)] while that of β-Ga2O3 nanowires with [401¯] growth direction is redshifted by 4–23cm−1 [Y. H. Gao et al. Appl. Phys. Lett. 81, 2267 (2002)]. Here we report the Raman and Fourier transform infrared spectra of β-Ga2O3 nanowires with [110] growth direction which is blueshifted relative to the bulk spectra by ∼10–40cm−1. Based on a first principles calculation of the strain dependence of Raman mode frequencies in bulk β-Ga2O3, we correlate the observed frequency shifts to growth-direction-induced internal strains in the nanowires.

Fabrication and characterization of β-Ga 2O 3 optical nanowires

Monoclinic gallium oxide (β-Ga 2O 3) nanowires with lengths of tens of micrometers and diameters ranging from 100 to 250 nm are synthesized using simple physical evaporation based on vapor–liquid–solid (VLS) mechanism. The as-synthesized straight β-Ga 2O 3 nanowires show excellent diameter uniformity and sidewall smoothness, making them suitable for optical wave-guiding. Light from a fiber taper is launched into the nanowire by means of evanescent coupling. Measured propagation loss of the nanowire at 633 nm wavelength is on the order of 10 dB/mm. Favorable mechanical strength of these nanowires for elastic bending is also observed. Our results suggest that β-Ga 2O 3 nanowires are promising building blocks for micro- and nanophotonic circuits and devices.

Synthesis of βGa2O3 nanowires by an MOCVD approach

We have synthesized monoclinic gallium oxide (βGa2O3) nanowires on Au-coated Si substrates by a reaction of a trimethylgallium and oxygen mixture. The βGa2O3 nanowires became progressively thinner from bottom to top, with diameters ranging from 10 to 200 nm and lengths of several micrometers. We found that Au-containing nanoparticles were attached to the tips of the βGa2O3 nanowires and thus the nanowire growth could be a vapor–liquid–solid process .

Physical origin of the ferromagnetic ordering above room temperature in GaMnNnanowires

We report a new method for large-scale production of GaMnN nanowires, by annealingmanganese–gallium oxide nanowires in flowing ammonia at high temperature.Microstructure analysis indicates that the GaMnN nanowires have wurtzite GaNstructure without Mn precipitates or Mn-related second phases. Magneticmeasurements reveal that ferromagnetic ordering exists in the GaMnN nanowires,whose Curie temperature is above room temperature. A mean-field model basedon the exchange coupling of the nondegenerate carrier-localized impurity band,together with the consideration of the superexchange antiferromagnetic interaction,is used to explain the physical origin of the observed ferromagnetic ordering.Theoretical calculations indicate that the Curie temperature increases with theincrease of the hole density and reveal a small ratio of the hole to the magneticdopant density in the samples. The low ratio of hole to Mn concentration and thesuperexchange antiferromagnetic interaction lead to the very concave temperaturedependence of the magnetization curve in contrast to conventional ferromagneticM–T behaviour. The theoretical calculation is in agreement with the experimental data.

Annealing effects on the structural and optical properties of gallium oxide nanowires

We have prepared gallium oxide nanowires and investigated the effect of thermal annealing on the structural and optical properties. As-prepared and annealed nanowires, respectively, were found to be fully amorphous and amorphous with very small crystallites. Photoluminescence measurements indicated that both as-prepared and annealed nanowires under excitation at 250 nm showed two emission band at 364 and 466 nm but the relative peak intensities of UV and blue emission, respectively, increase and decrease by the thermal annealing.

Annealing effects on the structural and optical properties of gallium oxide nanowires

We have prepared gallium oxide nanowires and investigated the effect of thermal annealing on the structural and optical properties. As-prepared and annealed nanowires, respectively, were found to be fully amorphous and amorphous with very small crystallites. Photoluminescence measurements indicated that both as-prepared and annealed nanowires under excitation at 250 nm showed two emission band at 364 and 466 nm but the relative peak intensities of UV and blue emission, respectively, increase and decrease by the thermal annealing.

Synthesis and Field-Emission Properties of Ga2O3−C Nanocables

Uniform Ga2O3−C nanocables with an average core diameter of 40 nm, wall thickness of 6 nm, and lengths of up to dozens of μm were generated via co-thermal evaporation of gallium oxide and activated carbon powder. The nanocable formation is discussed based on thermodynamics and crystallography. Gallium oxide and carbon generate gaseous Ga2O and CO at a higher temperature; they then recombine to form Ga2O3 and C. The simultaneous generation of Ga2O3 and C ensures continuous uniform coatings of carbon on gallium oxide nanowires. Field-emission measurements indicated that the nanocables exhibited an unusual sharp increase in emission current density near the threshold field.