Bicrystalline gallium oxide nanobelts

We have synthesized gallium oxide (Ga₂O₃) nanobelts by heating GaN powders in the conventional furnace. The nanobelts exhibited a unique bicrystalline structure that consisted of two single-crystalline monoclinic Ga₂O₃ nanobelts, which split along the twin boundary that exists at the centerline. Energy dispersive X-ray spectroscopy and electron energy loss spectroscopy spectra coincidentally indicated the presence of nitrogen in the Ga₂O₃ nanobelts. Photoluminescence spectra exhibited the visible light emission. We discussed the possible emission mechanisms, including the effect of the nitrogen dopant.     

Synthesis of ultra-long single crystalline CuV2O6 nanobelts

Ultra-long single crystalline CuV₂O₆ nanobelts have been successfully synthesized via a facile homogeneous reaction between peroxovanadic acid and cupric acetate. The reaction parameters, such as reaction time, and with or without H₂O₂, have profound influences on the crystal structures and morphologies of the resulting products. The time-dependent experiments reveal that the formation of ultra-long CuV₂O₆ nanobelts is related to the disassembly of urchin-like Cu₃(OH)₂V₂O₇·2H₂O nanostructures composed of radially aligned nanobelts, and the growth of CuV₂O₆ along the direction of [010]. Without the addition of H₂O₂ aqueous solution, wide and short CuV₂O₆ nanobelts coexist with some irregular particles and microrods in the products.     

Conversion of V2O5·xH2O into orthorhombic V2O5 single-crystalline nanobelts

Orthorhombic V₂O₅ single-crystalline nanobelts have been synthesized by hydrothermal treating V₂O₅·xH₂O precipitate derived from aqueous solution of V₂O₅ and H₂O₂. The synthetic method is facile, fast, environmental friendly, and easy to scale up. The V₂O₅ single-crystalline nanobelts are 30-80 nm in width, 30-40 nm in thickness, and lengths up to several tens of micrometers. The V₂O₅·xH₂O precursor is crucial for the formation of orthorhombic V₂O₅ single-crystalline nanobelts. The influences of synthetic parameters, such as reaction time and reaction temperature, on the crystal structures and morphologies of the resulting products have been investigated. Time-dependent experiments show that V₂O₅·xH₂O are dehydrated gradually and converted into orthorhombic V₂O₅ single-crystalline nanobelts. High reaction temperature also favors the formation of orthorhombic V₂O₅ nanobelts.     

Self-propagating high temperature synthesis of high purity single-crystalline SnO2 nanobelts

A new application of conventional self-propagating high temperature synthesis technology was developed to synthesise high purity single-crystalline SnO₂ nanobelts through a simple, convenient and efficient method. The outcome of the research, for which an experimental setup was designed and manufactured, turned out to be successful and propagable. High purity SnO₂ nanobelts could be obtained within minutes. The growth mechanism of these SnO₂ nanobelts is discussed in this article.     

Preparation and characterization of bio-functionalized iron oxide nanoparticles for biomedical application

Amine modified iron oxide (Fe₃O₄) nanoparticles were synthesized by thermal decomposition method and were further used to bio-functionalize by grafting of N-hydroxysuccinimide (NHS) ester of folate and ethylenediaminetetraacetate (EDTA). Fe₃O₄ nanoparticles of ~ 22 nm were confirmed from X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. FT-IR studies indicated two bands at 1515 cm^− 1and 1646 cm^− 1, which can be attributed to carboxylic group and the amide linkage respectively, revealing the conjugation of folate with Fe₃O₄. The conjugation of the chelating agent showed strong C=O stretch and Fe-O vibrations at 1647 and 588 cm^− 1 respectively. The value of saturation magnetization for Fe₃O₄ nanoparticles was found to be 88 emu/g, which further reduced to 18 and 32% upon functionalization with EDTA and NHS ester folate, respectively. These amine modified Fe₃O₄ nanoparticles can also be functionalized with other bifunctional chelators, such as amino acids based diethylene triamine pentaacetic acid (DTPA), and thus find potential applications in radio-labeling, biosensors and cancer detection, etc.     

Preparation of mesoporous tantalum oxide and its enhanced photocatalytic activity

Mesoporous Ta₂O₅ was synthesized by a surfactant-assisted sol-gel method under mild condition. Based on XRD pattern, the products, obtained by calcination at 600 and 700 °C, were found to be in the amorphous and the orthorhombic phases, respectively. The morphology and pore structure of the products were characterized by SEM, TEM and nitrogen adsorption-desorption measurements. The photocatalytic activity was evaluated by measuring the degradation of methylene blue under UV irradiation. Mesoporous orthorhombic Ta₂O₅ showed higher photocatalytic activity than that of the mesoporous sample in the amorphous state, although orthorhombic Ta₂O₅ had a lower surface area. The reason of this enhanced photocatalytic property is discussed.     

Preparation and characterization of Nb2O5-Al2O3 composite oxide formed by cathodic electroplating and anodizing

Al foil was coated with niobium oxide by cathodic electroplating and anodized in a neutral boric acid solution to achieve high capacitance in a thin film capacitor. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed the niobium oxide layer on Al to be a hydroxide-rich amorphous phase. The film was crystalline and had stoichiometric stability after annealing at temperatures up to 600 °C followed by anodizing at 500 V, and the specific capacitance of the Nb₂O₅-Al₂O₃ composite oxide was approximately 27% higher than that of Al₂O₃ without a Nb₂O₅ layer. The capacitance was quite stable to the resonance frequency. Overall, the Nb₂O₅-Al₂O₃ composite oxide film is a suitable material for thin film capacitors.     

In2O3-ZnO transparent conductive oxide film deposition on polycarbonate substrates

Amorphous transparent conductive oxide films in the In-Zn-O system were deposited on polycarbonate (PC) substrates by simultaneous DC sputtering of an In₂O₃ target and a ZnO target with either 4 wt% Al₂O₃ or 7.5 wt% Ga₂O₃ impurities. Although the resistivity of the amorphous, non-doped In-Zn-O film on PC was about one order of magnitude higher than that on the glass substrate, the resistivity of the In-Zn-O films with Ga₂O₃ impurities on PC substrates was reduced to the level of the non-doped In-Zn-O films on glass substrates. The addition of Al₂O₃ or Ga₂O₃ to the In-Zn-O films also induced the widening of the optical band gap, which would improve transparency at blue wavelengths.     

Synthesis and characterization of crystalline β-Bi2O3 nanobelts

We synthesized β-Bi₂O₃ nanobelts on silicon substrates without using a metal catalyst. Trimethylbismuth and O₂ were taken as the source of bismuth and oxygen, respectively. X-ray diffraction and transmission electron microscopy studies confirmed the formation of tetragonal Bi₂O₃ phase. The typical width of the β-Bi₂O₃ nanobelts was in the range of 40-400 nm. We suggested that the growth of β-Bi₂O₃ nanobelts was mainly controlled by a vapor-solid mechanism. Photoluminescence measurements at room temperature exhibited a visible light emission band peaking at around 2.81 eV.     

Preparation and characterization of magnetic nanofibrous composite membranes with catalytic activity

Magnetic nanofibrous composite membranes were electrospun from the mixtures of poly(acrylonitrile-co-acrylic acid) (PANCAA) and Fe₃O₄ nanoparticles. Field emission scanning electron microscopy (FESEM) and thermal gravimetric analysis (TGA) were used to characterize the composite membranes. TGA results indicate that the addition of Fe₃O₄ nanoparticles catalyzes the carbonization of PANCAA as well as dramatically increases the carbonization temperature. The intrinsic peroxidase-like activity of Fe₃O₄ nanoparticles was measured by the color reaction of phenol/4-amino antipyrine in the presence of H₂O₂. Under optimal conditions, the electrospun composite membranes show high peroxidase-like catalytic activity and reusability. Taking into account of the potentiality for separation, these as-prepared magnetic nanofibrous composite membranes will be applied in phenolic wastewater treatment.     

Preparation and laser performance of Nd-doped yttrium lanthanum oxide transparent ceramic

1.5 at.% Nd:Y_1.8La_0.2O₃ transparent ceramic was fabricated by a solid-state reaction method and sintered at 1650-1700 °C for 40-50 h under H₂ atmosphere. The spectroscopic properties were investigated at room temperature. The transparent ceramic has excellent spectroscopic properties, with the absorption cross section of 1.50 × 10⁻²⁰ cm² and broad full width at half maximum (FWHM) of about 8 nm at LD wavelength 806 nm, the emission cross section of 2.03 × 10⁻²⁰ cm² at 1079 nm, and the decay lifetime of 200 μs. Laser performance was carried out using an uncoated Nd:Y_1.8La_0.2O₃ ceramic plate under laser diode end-pumping without any water cooling device. The room temperature thermal conductivity of this ceramic is 6.20 W/mK. For Nd:Y_1.8La_0.2O₃ ceramic laser, a maximum output power of 62 mW was obtained at 1079 nm under a 808 nm diode pump.     

Characterization of oxidized gallium droplets on silicon surface: An ellipsoidal droplet shape model for angle resolved X-ray photoelectron spectroscopy analysis

Deposition and oxidation of metallic gallium droplets on Si(111) were studied by angle resolved X-ray photoelectron spectroscopy. Two gallium peaks - Ga 3d and Ga 2p - were simultaneously measured in order to get an advantage of different inelastic mean free paths of photoelectrons from these two energy levels differing in binding energy by 1100 eV. Together with the angular dependent data it enhances the precision of the size characterization of Ga droplets and oxide thickness determination. A model for the calculation of theoretical intensities based on an ellipsoidal shape of droplets is presented and a simple procedure for estimation of droplet height and actual surface coverage based on measurement on a single emission angle is suggested.     

Use of oxygen isotope to study the transport mechanism during high temperature oxide scale growth

Abstract

The examination of high temperature (HT) oxide scale growth mechanisms was performed using secondary ion mass spectrometry (SIMS) and secondary neutral mass spectrometry (SNMS), in conjunction with ¹⁶O₂/¹⁸O₂ HT oxidation experiments. Cr₂O₃, NiO, ZrO₂ and Al₂O₃ were studied because they constitute excellent representative thermally grown oxide scales: they grow by cationic diffusion (Cr₂O₃, NiO), anionic diffusion (ZrO₂) or mixed anionic-cationic diffusion (Al₂O₃). The oxidation tests were performed first in ¹⁶O₂ and subsequently in ¹⁸O₂ at several temperatures (600–1000°C for NiO, 600°C for ZrO₂, 1000°C for Cr₂O₃ and 1100°C for Al₂O₃). The oxygen isotope distribution observed by SIMS and SNMS profiles are discussed and related with the HT oxidation mechanisms proposed in the literature.     

Preparation and characterization of hollow glass microspheres-cobalt ferrite core-shell particles based on homogeneous coprecipitation

Hollow glass microspheres-CoFe₂O₄ (HGMs-CF) core-shell particles were successfully synthesized directly by using the homogeneous coprecipitation method at 90 °C without calcination. The morphology, composition, microstructure and the magnetic property of the samples were characterized by SEM, XRD, EDX and VSM, respectively. The results showed that the HGMs-CF core-shell particles exhibited smooth, compact and continuous CoFe₂O₄ coating on the surface of the HGMs. The Fe/Co atom ratio of the CoFe₂O₄ coating was 2.2, saturation magnetization (M_s) and coercivity (H_c) of the samples were 46 emu/g and 612 Oe, respectively. It was suggested that this method could be applied to the scale industry production for high purity products.     

Controlled hydrothermal synthesis of VO2(B) nanobelts

Large-scale VO₂(B) nanobelts have been synthesized by hydrothermal strategy via one-step method using V₂O₅ as vanadium source and C₆H₅-(CH₂)_n-NH₂ with n = 2 and 4 (2-phenylethylamine and 4-phenylbutylamine) as structure-directing templates. The composition and morphology of the nanobelts were established by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The as-obtained VO₂(B) nanobelts have a length of 3-10 μm, a wideness of 100-375 nm and a thickness of 30-66 nm.     

Synthesis of MoO3 nanobelts by medium energy nitrogen ion implantation

Ion implantation has been revealed as a potential technique to modify the surface of materials. In this work, MoO₃ nanobelts were synthesized on MoO₃ whisker surfaces by means of ion implantation with 60 keV nitrogen ions at a dose of 1 × 10¹⁶ atom/cm² and characterized by scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. The result showed that the nanostructures of MoO₃ occurred over the whisker surfaces and had belt-like shapes. The size of the synthesized MoO₃ nanobelts mostly ranged from 20 to 60 nm in width and 300 to 800 nm in length. The nanobelts were found to have an orthorhombic crystal structure with growth preferential in the [001] direction. The growth process of the nanobelts based on the common vapor-solid mechanism is discussed.     

Luminescence properties of Ce-Dy codoped aluminium oxide films

Photoluminescence properties of CeCl₃ and DyCl₃ codoped aluminium oxide films deposited by the ultrasonic spray pyrolysis technique were characterized by excitation, emission and decay time spectroscopy. When excited by ultraviolet radiation the films emit a combination of blue and yellow wavelengths through an efficient energy transfer from Ce³⁺ to Dy³⁺ ions (up to around 77%). From spectroscopic data it is inferred that such energy transfer is nonradiative in nature taking place between Ce³⁺ and Dy³⁺ clusters through a short-range interaction mechanism. In the Ce³⁺ doped single film the chromaticity coordinates are in the purplish blue region, whereas that in the cerium and dysprosium codoped films the coordinates move toward the white light emission region.     

Nanostructural and chemical characterization of supported metal oxide catalysts by aberration corrected analytical electron microscopy

The performance of catalyst materials are usually governed by the precise atomic structure and composition of very specific catalytically active sites. Therefore, structural and chemical characterization at the atomic scale becomes a vital requirement in order to identify any structure-performance relationships existing in heterogeneous catalyst systems. Aberration-corrected scanning transmission electron microscopy (STEM) represents an ideal means to probe the atomic scale structural and chemical information via a combination of various imaging and spectroscopy techniques. In particular, high-angle annular dark-field (HAADF) imaging provides directly interpretable atomic number (Z) contrast information; while X-ray energy dispersive spectroscopy (XEDS) and electron energy-loss spectroscopy (EELS) spectrum imaging can be used to identify the chemical composition and oxidation state. Here we review some applications of aberration-corrected STEM to catalyst research, firstly in the context of supported metal catalysts, which serve as ideal material systems to illustrate the power of these techniques. Then we focus our attention on more recent progress relating to the characterization of supported metal oxide catalysts using aberration-corrected STEM. We demonstrate that it is now possible to directly image supported surface oxide species, study oxide wetting characteristics, identify the catalytic active sites and develop new insights into the structure-activity relationships for complex double supported oxide catalysts. Future possibilities for in situ and gentle low voltage electron microscopy studies of oxide-on-oxide materials are also discussed.     

Solid phase growth of tin oxide nanostructures

For the first time, single-crystalline SnO₂ nanostructures comprising of nanobelts, nanowires and nanosheets have been synthesised by solid phase crystal growth from tin oxide single crystals. The product was characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, and Raman spectroscopy. The procedure consisted of two stages. In the first stage, a mixture of SnO₂ polyhedral single crystals attached with graphite particles were produced by heating a mixture of SnCl₂ and graphite. Then, the SnO₂ single crystals were grown into nanobelts, nanowires and nanosheets by further heating. The role of graphite in the process is also discussed to be the surface reduction of SnO₂ into oxides with lower oxygen content which provide a driving force for surface diffusion and subsequent crystal growth of tin oxide into the one and two dimensional nanostructures. The results provide insights for both fundamental research as well as technological production of SnO₂ nanostructures.