Structure and optical spectrum of GaN nanorods produced on Si(111) substrates

A novel method is applied to prepare nanorods. In this method, nanorods have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Nb films under flowing ammonia at 950 °C in a quartz tube. The as-synthesized nanorods are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The results show that the nanorod is single-crystalline GaN. It has a diameter of about 200 nm and lengths typically up to several micrometers. Photoluminescence spectrum under excitation at 325 nm only exhibits a UV light emission peak is located at about 368.5 nm. Finally, the growth mechanism of nanorods is also briefly discussed.     

Synthesis, characterization and optical properties of sheet-like ZnO

Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 °C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV-vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

Solvothermal synthesis of In(OH)3 nanorods and their conversion to In2O3

In this work, we demonstrate that monodisperse indium hydroxide (In(OH)₃) nanorods constructed with parallel wire-like subunits have been fabricated via a acrylamide-assisted synthesis route without any template. NH₃ from the hydrolysis of acrylamide acts as the OH⁻ provider. The structure and morphology of as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TG). A detailed mechanism has been proposed on the basis of time-dependent experimental results. Furthermore, by annealing In(OH)₃ precursors at 500 °C for 3 h in air, In₂O₃ samples were obtained with the designed morphology.     

Morphological and physicochemical properties of spin-coated poly(3-octylthiophene)/polystyrene composite thin films

Poly(3-octylthiophene) (P3OT) was synthesized by direct oxidation of 3-octylthiophene with FeCl₃ as oxidant. Molecular weight of P3OT polymer was measured by size exclusion chromatography. Homogeneous poly(3-octylthiophene) (P3OT) and polystyrene (PS) composite films have been synthesized by spin-coating technique from toluene with different polymer concentrations. The doped films were obtained by immersion for 30 s in a 0.3 M ferric chloride (FeCl₃) solution in nitromethane. A classical percolation phenomenon was observed in the electrical properties of these blends, it was smaller than 5% of P3OT in the blend. Surface topographical changes were studied by atomic force microscopy (AFM). AFM images of the composite films revealed surface morphology variation as a function of different P3OT concentration in PS, phase segregation was observed, and PS is shown to segregate to the surface of the films. The higher PS solubility, in comparison with the P3OT solubility, in toluene resulted in PS/P3OT bilayers. The films exhibited pit and island like topography, the pit size changed with the polymer concentration. Optical absorption properties of the polymeric films were analyzed in pristine and doped state. In doped state, the bipolaronic bands at 0.5 and 1.6 eV are shown in a 4% conductive polymer in the PS/P3OT film. Finally thermogravimetric analysis was also made on the simple and composite polymers.     

Microstructural changes in the upper surface of austenitic steel induced by ion sputtering and gas nitriding

The results of investigations of the influence of ion sputtering parameters applied as a pre-treatment on the formation of a nitrided layer during gas nitriding are presented. Previous work had shown that a low reproducibility of layer composition occurred after gas nitriding, thought to be the result of uncontrolled variation of sputtering parameters during the plasma initiation. In the present studies a two-stage sputtering process in nitrogen at a pressure of 3-5 Pa was used: firstly for a few seconds to 1 min with the plasma parameters 1.8 kV and 3 mA/cm², and secondly followed by sputtering with the parameters 1.35 kV, 0.5 mA/cm² for 15 min. The samples were gas nitrided immediately following these processes in 100% ammonia. It was found that even a few seconds of the first plasma treatment enabled magnetic “expanded austenite” to be formed in the layer. Surface layers were analysed using grazing angle X-ray diffraction (GXRD), light microscopy (LM), scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), magnetic and atomic force microscopy (AFM and MFM) and electron probe micro analysis (EPMA) that revealed a complex microstructure. The results have emphasised the need for good control over plasma sputtering parameters in the initial process stage.     

Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol–gel derived titania powders

Undoped, 0.05 and 0.5 mol% Ni-doped TiO₂ powders were prepared by a modified sol–gel route. The doping effects on the microstructure and magnetism for the powdered samples have been systematically investigated. Doping of Ni in TiO₂ inhibited rutile crystal growth. The probable reason for this is discussed on the basis of band calculation based analysis of electronic structures of 3d transition metal-doped TiO₂ and the energetic, transformation kinetics and phase stability of anatase over rutile as the function of particle size. Room temperature ferromagnetism (RTFM) with the saturation magnetization of 12 m emu g⁻¹ and Curie temperature as high as 820 K is observed only in case of 0.05 mol% Ni:TiO₂ powdered sample, whereas undoped TiO₂ was diamagnetic and 0.5 mol% Ni:TiO₂ was paramagnetic in nature. The role of any magnetic impurity or any Ni metal in the origin of the RTFM has been ruled out by energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) analysis, whereas magnetic force microscopy (MFM) established the presence of magnetic domains, supporting the intrinsic diluted magnetic semiconductor behavior. The observed ferromagnetism has been attributed to the spin ordering through exchange interaction between holes trapped in oxygen orbitals adjacent to Ni substitutional sites.     

A combined template and closed space sublimation approach to the synthesis of single-crystalline CdS nanowires and their optical properties

High-quality single-crystalline CdS nanowires about 40 nm in diameter have been successfully synthesized without any catalyst at ambient pressure by combining the closed space sublimation (CSS) technique with porous anodic alumina membrane (AAM) template method. Extensive characterizations of the nanowires have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and UV-Visible absorption spectroscopy. A band gap of 2.38 eV is determined from the UV-Vis absorption spectrum obtained from the nanowire sample. Our facile technique may in principle also be used for synthesizing other one-dimensional (1D) materials with high vapor pressure and axial nanowire heterostructures.     

Molten salt synthesis of single-crystal Co3O4 nanorods

The synthesis of the single-crystal Co₃O₄ nanorods by molten salt approach was reported for the first time. The products were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and Selected-area electron diffraction (SAED). TEM results indicate that these nanorods have diameters of about 150 nm and lengths of about 2 μm. According to the analysis of the SAED and HRTEM results, we drew the conclusion that these nanorods grew along an unusual [− 1,− 1,15] direction by Ostwald ripening mechanism.     

Preparation and characterization of α-Fe2O3 polyhedral nanocrystals via annealing technique

Polyhedral nanocrystals of α-Fe₂O₃ are successfully synthesized by annealing FeCl₃ on silicon substrate at 1000 °C in the presence of H₂ gas diluted with argon (Ar). Uniformly shaped polyhedral nanoparticles (diameter ~ 50-100 nm) are observed at 1000 °C and gases flow rate such as; Ar = 200 ml/min and H₂ = 150 ml/min. Non-uniform shaped nanoparticles (diameter ~ 20-70 nm) are also observed at an annealing temperature of 950 °C with lower gases flow rate (Ar = 100 ml/min and H₂ = 75 ml/min). Nanoparticles are characterized in detail by field-emission electron microscopy (FE-SEM), energy dispersive X-ray (EDX) and high resolution transmission electron microscopy (HRTEM) techniques. HRTEM study shows well resolved (110) fringes corresponding to α-Fe₂O₃, and selected area diffraction pattern (SADP) confirms the crystalline nature of α-Fe₂O₃ polyhedral nanoparticles. It is observed that polyhedral formation of α-Fe₂O₃ nanocrystals depends upon annealing temperature and the surface morphology highly rely on the gas flow rate inside the reaction chamber.     

Tailor of ZnO morphology by heterogeneous nucleation in the aqueous solution

The umbrella-like ZnO nanostructures have been prepared by the morphological tailoring in the aqueous solution at 95 °C in the addition of heterogeneous seeds such as MnO₂ and CdS nanoparticles. The morphology and structure of as-synthesized umbrella-like ZnO nanostructures have been characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), electron energy loss spectroscopy (EELS), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The heterogeneous seeds play the critical role for the formation of umbrella-like ZnO nanostructures. Furthermore, the formation mechanism of the umbrella-like nanostructures has been phenomenally presented.     

Synthesis and optical properties of single-crystalline GaN nanorods

Single-crystalline GaN nanorods were successfully synthesized on Si(1 1 1) substrates through ammoniating Ga₂O₃/Mo films deposited on the Si(1 1 1) substrate by radio frequency magnetron sputtering technique. The as-synthesized nanorods are 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). Scanning electron microscopy (SEM) displays that the GaN nanorods are straight and smooth with diameters in the range of 100-200 nm and lengths typically up to several micrometers. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N. The representative photoluminescence spectrum at room temperature exhibits a strong and broad emission band centered at 371.1 nm, attributed to GaN band-edge emission. The growth process of GaN nanorod may be dominated by vapor-solid (VS) mechanism.     

Hydrothermal synthesis of spindle-like ZnS hollow nanostructures

Spindle-like hollow nanostructures of zinc sulfide (ZnS) have been successfully synthesized by hydrothermal process using a simple surfactant emulsion template. The morphologies of ZnS nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FE-SEM). It is found that most of the products including twin ellipsoids with connected hollow cores are reminiscent of spindle-like structures. The lengths, widths and the thickness of the shell are in the range of 1-2 μm, 300-450 nm and 20-40 nm, respectively. Selected area electron diffraction (SAED) and X-ray powder diffraction (XRD) patterns show that the shell is composed of sphalerite ZnS polycrystals.     

Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853 K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16 Pa and rf power of 85 W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO₂ and NO₃ bonding structures when the films are deposited at temperatures higher than 673 K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO₃ bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.     

PEG-300 assisted hydrothermal synthesis of 4ZnO·B2O3·H2O nanorods

4ZnO·B₂O₃·H₂O is commonly used as a flame-retardant filler in composite materials. The microstructure of the powder is of importance in its applications. In our study, for the first time, one-dimensional (1D) nanostructure of 4ZnO·B₂O₃·H₂O with rectangle rod-like shape has been synthesized by a hydrothermal route in the presence of surfactant polyethylene glycol-300 (PEG-300). The nanorods have been characterized by X-ray powder diffraction (XRD), inductively coupled plasma with atomic emission spectroscopy (ICP-AES), thermogravimetry (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) equipped with selected area electron diffraction (SAED) as well as high-resolution transmission electron microscopy (HRTEM). These nanorods are about 70 nm in thickness, 150-800 nm in width and have lengths up to a few microns. 4ZnO·B₂O₃·H₂O nanorods crystallize in the monoclinic space group P2₁/m, a = 6.8871(19) Å, b = 4.9318(10) Å, c = 5.7137(16) Å, β = 98.81(21)° and V = 191.779(71) Å³.     

Thermal, dielectric and microwave absorption properties of polyaniline-CoFe2O4 nanocomposites

The present paper deals with the synthesis of conducting ferromagnetic polyaniline-CoFe₂O₄ (PC) nanocomposites via one-step chemical oxidative polymerization of aniline in the presence of CoFe₂O₄ nanoparticles (30-40 nm). These nanocomposites of PC have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Extended thermal analysis has revealed that the activation energy of these nanocomposites varies from 75.3 to 84.3 kJ/mol as compared to the activation energy of 50.3 kJ/mol for polyaniline-DBSA. In addition, dielectric and microwave absorption properties of the nanocomposites have been measured in the frequency range of 12.4-18 GHz (Ku-band) which demonstrate that more than 99% attenuation of microwaves (SE_A = 21.5 dB) has been achieved using these nanocomposites. Systematic investigations reveal that the CoFe₂O₄ nanoparticles in the polyaniline matrix have phenomenal effect in determining the microwave absorption properties of the nanocomposites.     

Monodisperse ceria nanospheres: Synthesis,characterization, optical properties,and applications in wastewater treatment

Monodisperse ceria nanospheres have been synthesized by a facile solvothermal method, and their morphology and microstructures have been revealed by a combination of X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and N₂ adsorption. It is demonstrated that the as-synthesized powders are highly uniform CeO₂ in spherical shape with cubic fluorite structure. HRTEM and XRD studies show that each ceria nanosphere is composed of dozens of nanocrystals with the average size of 8.5 nm. The direct optical band gap of the ceria nanospheres estimated from the ultraviolet–visible absorption spectrum is 2.7 eV, which is evidently red-shifted with respect to the bulk material (E_g = 3.19 eV); the reduced band gap could be resulted from the high concentration of grain boundaries and defects present in the ceria nanospheres. In addition, the ceria nanospheres exhibit a strong blue luminescence at 504 nm and a broad orange luminescence centered at 645 nm. As a result of the large specific surface area, ceria nanospheres are revealed to be an excellent sorbent for the removal of poisonous pollutants present in water, such as chromium ions and rhodamine B. The removal efficiency of chromium ions is as high as ∼94%.     

Formation of crystalline AlN nanotubes by a roll-up approach

In this study, aluminum nitride (h-AlN) nanotubes with high crystallinity and yield have been prepared by AlP and NaN₃ in a stainless steel autoclave at 350 °C. The samples were studied by powder X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and HRTEM in detail. The lengths of the AlN nanotubes are about 1 μm with most of the tube ends are open. The AlN nanotube preferentially grow along the [001] direction. The results demonstrate that the bending and roll-up of a thin layer to form tubular nanoscrolls is a thermally driven process. One-dimensional preferential growth was explained in terms of the crystallographic feature of hexagonal AlN.     

Synthesis and characterization of carbon nanoribbons and single crystal iron filled carbon nanotubes

Carbon nanoribbons and single crystal iron filled multiwall carbon nanotubes (MWCNTs) have been synthesized by simple pyrolysis technique. SEM investigation shows that the material consist mainly carbon nanoribbons and carbon nanotubes (CNTs). X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), electron energy dispersive X-ray (EDX), transmission electron miscroscopy (TEM) and highresolution transmission electron miscroscopy (HRTEM) studies reveal carbon nanotubes are filled with α-Fe. Closer inspection of HRTEM images indicated that the bcc structure α-Fe nanowires are monocrystalline and Fe (1 1 0) plane is indeed perpendicular to the G (0 0 2) plane, whereas orientation of (0 0 2) lattice planes of carbon nanoribbon is perpendicular to the axis of growth. Magnetic properties studied by superconducting quantum interference device (SQUID) at 300 K and 10 K exhibited coercivity of 1037 Oe and 2023 Oe. The large coercitivity is strongly attributed to the small size monocrystalline single phase α-Fe, single domain nature of the encapsulated Fe crystal, magnetocrystalline shape anisotropy and ferromagnetic behaviour of localized states at the edges of the carbon nanoribbons.     

Hydrothermal synthesis and luminescent properties of Y2O3:Tb and Gd2O3:Tb microrods

One-dimensional (1D) Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ microrods have been successfully prepared through a large-scale and facile hydrothermal method followed by a subsequent calcination process in N₂/H₂ mixed atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectra (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-formed products via the hydrothermal process could transform to cubic Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ with the same morphology and slight shrinking in size after a postannealing process. Both Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ microrods exhibit strong green emission corresponding to ⁵D₄ → ⁷F₅ transition (542 nm) of Tb³⁺ under UV light excitation (307 and 258 nm, respectively), and low-voltage electron beam excitation (1.5 → 3.5 kV), which have potential applications in fluorescent lamps and field emission displays.