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.     

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.     

Control synthesis of octahedral In2O3 crystals,belts, and nanowires

Octahedral In₂O₃ crystals were synthesized by evaporation of a mixture of In₂O₃ and graphite in a horizontal double-tube system. By adjusting the experimental conditions, In₂O₃ nanowires and nanobelts were also obtained. The microstructures of the resultant In₂O₃ materials were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), X-ray diffraction. In addition, the growth mechanism of the octahedral In₂O₃ crystals was discussed in detail.     

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.     

Synthesis and magnetic properties of spinel CoFe2O4 nanowire arrays

Spinel CoFe₂O₄ nanowire arrays were synthesized in nanopores of anodic aluminum oxide (AAO) template using aqueous solution of cobalt and iron nitrates as precursor. The precursor was filled into the nanopores by vacuum impregnation. After heat treatment, it transformed to spinel CoFe₂O₄ nanowires. The structure, morphology and magnetic properties of the sample were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicate that the nanowire arrays are compact. And the individual nanowires have a high aspect ratio, which are about 80 nm in diameter and 10 μm in length. The nanowires are polycrystalline spinel phase. Magnetic measurements indicate that the nanowire arrays are nearly magnetic isotropic. The reason is briefly discussed. Moreover, the temperature dependence of the coercive force of the nanowire arrays was studied.     

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.     

Infrared-to-visible upconversion in Er and Er/Yb activated Sb2O4 nanopowders prepared by sol-gel route

We prepared Er³⁺ doped and Er³⁺/Yb³⁺ codoped Sb₂O₄ nanocrystals by the sol-gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb₂O₄ nanocrystals is very low (the maximum value being 461 cm⁻¹). The upconversion (UC) red emission of the Er³⁺/Yb³⁺ codoped sample is very strong at 975 nm laser diode excitation. The Sb₂O₄ nanocrystals will be a promising luminous material.     

Synthesis of anatase TiO2 nanowires by modifying TiO2 nanoparticles using the microwave heating method

Anatase TiO₂ nanowires with a diameter of 5-10 nm and length of 500 nm to 2 μm have been successfully synthesized by modifying TiO₂ nanoparticles (P25) using the microwave heating method. The microwave power, reaction pressure, and reaction time for the synthesis of TiO₂ nanowires were 500 W, 0.5-3.0 MPa (corresponding to a temperature range of 175-260), and 40-70 min, respectively. X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and the BET techniques were used to investigate the phase structures, morphologies, and specific surface areas of the TiO₂ nanowires. The effects of reaction time, pressure, and different post-treatment processes on the microstructures of TiO₂ nanowires were discussed. It has been shown that the microwave heating method is efficient in transforming TiO₂ nanoparticles to anatase TiO₂ nanowires.     

Iron phthalocyanine oligomer/Fe3O4 hybrid microspheres and their microwave absorption property

The novel nano-scale iron phthalocyanine oligomer/Fe₃O₄ (FePc/Fe₃O₄) hybrid microspheres were synthesized from iron phthalocyanine oligomer and FeCl₃·6H₂O via a solvent-thermal crystallization route. The morphology and structure of the hybrid microspheres were characterized by Fourier transform infrared spectrophotometer, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These results showed that the hybrids were monodisperse microspheres and the morphology can be adjusted by controlling pre-polymerization time. The saturation magnetization increased with increase in the pre-polymerization time, while the coercivities decreased. The FePc/Fe₃O₄ hybrid microspheres exhibited novel microwave electromagnetic properties: the dielectric loss was enhanced when the pre-polymerization time increased and a new microwave loss peak appeared at high frequency. The microwave absorbing properties enhanced with increase in the pre-polymerization time and a maximum reflection loss of −29.7 dB was obtained at 11.7 GHz with 6 h of pre-polymerization time when the matching thickness was 3.0 mm. The novel hybrid materials are believed to have potential applications as microwave absorbing materials.     

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.     

Influence of colloidal templates on the impedance spectroscopic behaviour of Pr0.7Sr0.3Fe0.8Ni0.2O3 for solid oxide fuel cell applications

The creation of porous materials with three-dimensional periodicity has been identified as being of potential interest for increasing the overall performance of solid oxide fuel cells (SOFC). In this work, we have investigated the formation of pore systems in the nanometer scale by replicating colloidal templates. Templating methods have been used to prepare iron-nickel-based perovskite Pr_0.7Sr_0.3Fe_0.8Ni_0.2O₃ material with nanoporous microstructure. Polymethyl methacrylate (PMMA), polystyrene (PS) and polycarboxylate (PC) microspheres with different diameters were used as pore formers. These samples were synthesized and characterized by thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction, transmission electron microscopy and field emission scanning electron microscopy. The polarization resistance of the materials was studied by Electrochemical Impedance Spectroscopy. The study demonstrated that templated porosity is maintained and highly influences on the impedance spectroscopic behaviour, being the material synthesized with policarboxylate microspheres the most interesting of the three used templates for SOFC applications.     

Alumina template-assisted electrodeposition of Bi2Te2.7Se0.3 nanowire arrays

Bi₂Te_2.7Se_0.3 nanowire arrays have been fabricated by electrodeposition into the pores of an anodic aluminum oxide (AAO) template followed by annealing at 300 °C under Ar atmosphere. The as-prepared nanowires were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The nanowires are uniform single crystalline with diameter of ∼14 nm.     

Microwave-assisted synthesis of Fe3O4 nanorods and nanowires in an ionic liquid

Without using inert gas to prevent the oxidation of Fe²⁺, Fe₃O₄ nanorods and nanowires have been successfully synthesized via a microwave-assisted ionic liquid method (MAIL). Compared to the traditional methods, the whole reaction process can be carried out more easily and faster. Our result shows that temperature and time of microwave heat played important roles in the formation of Fe₃O₄ with different morphologies. These products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and FT-IR spectra.     

Large-scale synthesis of Ga2O3 nanoribbons by a two-step gas flow control

β-Ga₂O₃ nanoribbons have been prepared by a two-step gas flow control, involving adjusting the pressure inside the tube before and after the formation of the nanoribbons. In different temperature areas, separated nanoribbons and nanowires were obtained, which grew via solid–liquid–vapor–solid (SLVS) and vapor–liquid–solid (VLS) mechanisms, respectively. The samples obtained were characterized by means of scanning electron microscopy, transmission electron microscopy, micro-Raman scattering, and photoluminescence. It was found that Ga₂O₃ nanoribbons had a perfect monoclinic single-crystal structure with a [002] growth direction. The Ga₂O₃ nanoribbons give ultraviolet, cyan and green light emission at room temperature under excitation at 254 and 325 nm.     

One-step preparation of organometal/Fe3O4 hybrid microspheres and their electromagnetic properties

Novel organometal/Fe₃O₄ hybrid microspheres were prepared from bisphthalonitrile-benzoxine resin containing ferrocene (FPNBZ) and FeCl₃·6H₂O via a one-step solvent-thermal method. The phase structure, composition and morphology of as-prepared hybrid microspheres were characterized by X-ray powder diffraction, Fourier transform infrared spectrophotometer and scanning electron microscopy. The results revealed that crystallinity, dispersity and size of hybrid microspheres can be controlled by altering the reaction parameters. Density measurement showed that the density is decreased with increasing FPNBZ concentration in the hybrid materials. Electromagnetic properties of the FPNBZ/Fe₃O₄ hybrid microspheres were measured at 2-18 GHz. The electromagnetic measurement indicated that the resonance peaks of complex permittivity, complex permeability, dielectric loss and magnetic loss were shifted to the high frequencies, with the increasing amount of FPNBZ. The as-prepared hybrid materials are believed to have broad applications both in microwave absorption materials in a wide frequency range and in biomedical fields.     

Growth of single-crystal magnetite nanowires from Fe3O4 nanoparticles in a surfactant-free hydrothermal process

Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe₃O₄. A mechanism for nanowire growth is proposed.     

Electrical and structural properties of Ce0.9CoFe3Sb12 thermoelectric thin films

In this work, we show experimental results for growth conditions of thermoelectric Ce_0.9CoFe₃Sb₁₂ thin films. An rf-magnetron sputtering system has been used to grow the films on single crystal substrates of sapphire (Al₂O₃), silicon (Si), and magnesium oxide (MgO) at different substrate temperatures between 250 and 450 °C. The films were thermoelectrically characterized with resistivity and thermopower measurements as functions of temperature. The results show linear behavior of resistivity with temperature, and thermopower growth with the temperature increase. Such behavior is typical for metallic materials. The structure and surface morphology of the samples were analyzed by X-ray diffraction pattern and atomic force microscopy (AFM), respectively.     

Glass formation in the Sb2O3-ZnBr2 binary system

Glass formation has been investigated in the Sb₂O₃-ZnBr₂ binary system. Vitreous samples have been obtained for batches containing 20-90 mol% Sb₂O₃. Chemical analysis shows that bromine concentration is smaller than expected and real compositions belong to the Sb₂O₃-ZnBr₂-ZnO ternary system. However, the discrepancy between nominal and analyzed compositions is fair for Sb₂O₃ content larger than 50 mol%. Optical transmission lies between 400 nm and 7 μm and refractive index ranges from 2.0 to 2.1. Glass transition occurs around 300 °C, and crystallization exotherm does not appear in the differential scanning calorimetry scan at 10 K s⁻¹ for samples containing 50-60 mol% Sb₂O₃. Thermal expansion varies between 120 and 220×10⁻⁷ K⁻¹ as antimony content decreases. Microhardness is close to 200 kg/mm². These glasses have low phonon energy and make potential materials for infrared transmission and active fibers.     

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     

Fabrication of flower-shaped Bi2O3 superstructure by a facile template-free process

A novel flower-shaped Bi₂O₃ superstructure has been successfully synthesized by calcination of the precursor, which was prepared via a citric acid assisted hydrothermal process. The precursor and Bi₂O₃ were characterized with respect to morphology, crystal structure and elemental chemical state by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was shown that both the precursor and Bi₂O₃ flower-shaped superstructure were constructed of numerous nanosheets while the nanosheets consisted of a great deal of nanoparticles. Furthermore, key factors for the formation of the superstructures have been proposed; a mechanism for the growth of the superstructure has been presented based on the FESEM investigation of different growth stages.