Growth and optical and field emission properties of flower-like ZnO nanostructures with hexagonal crown

Flower-like zinc oxide (ZnO) nanostructures with hexagonal crown were synthesized on a Si substrate by direct thermal evaporation of zinc power at a low temperature of 600 °C and atmospheric pressure. Field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and photoluminescence were applied to study the structural characteristics and optical properties of the product. The result indicated that the flower-like product with many slender branches and hexagonal crowns at the ends were single-crystalline wurtzite structures and were preferentially oriented in the <001> direction. The photoluminescence spectrum demonstrated a strong UV emission band at about 386 nm and a green emission band at 516 nm. The field emission of the product showed a turn-on field of 3.0 V/µm at a current density of 0.1 μA/cm², while the emission current density reached about 1 mA/cm² at an applied field of 5.9 V/μm.     

Effects of ethylenediamine to water ratios on cadmium sulfide nanorods and nanoparticles produced by a solvothermal method

Cadmium sulfide nanorods and nanoparticles were successfully produced by a solvothermal reaction at 200 °C for 24 h using ethylenediamine and water as pure and mixed solvents. The products were analyzed by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. In pure ethylenediamine, they show the hexagonal structure CdS nanorods with 0.2-2 μm long and 30 nm diameter, and the 1LO and 2LO modes at 299.36 and 600.72 cm^− 1, respectively. Growth of CdS nanorods is along the [001] direction, interpreted by HRTEM images and SAED patterns. In the 50:50 vol.% of ethylenediamine:water mixed solvents, the length of CdS nanorods decreased to 100-200 nm. The CdS nanoparticles were produced when pure water was used.     

Ferromagnetism in Gd-doped CdS dilute magnetic semiconducting nanorods

Cd _x Gd_1?x S (x = 0–0.15) nanorods have been synthesized by solvothermal technique. X-ray diffraction study reveals that pure and Gd-doped CdS nanorods exhibits hexagonal wurtzite structure. Transmission electron microscopy reveals nanorods like morphology of synthesized CdS having 14 and 26 nm size of pure and 15 % doped CdS nanorods. UV–Visible absorption study confirms the blue shift in the energy band energy due to the quantum confinement effects. Photoluminescence spectra confirm the defect free nature of the synthesized nanorods with peaks emerging around 528 and 540 nm due to the green emission. The magnetic study shows that the pure and Gd-doped CdS nanorods exhibits ferromagnetic character and the magnetisation increased by five times from 0.074 to 0.422 emu/g upon Gd-doping.     

Synthesis and characterization of silver molybdate nanowires, nanorods and multipods

Silver molybdate nanowires, nanorods and multipods like structures have been prepared by an organic free hydrothermal process using ammonium molybdate and silver nitrate solutions. The powder X-ray diffraction (PXRD) patterns reveal that the silver molybdate belongs to anorthic structure. The thickness, 200–500 nm, for silver molybdate nanorods/wires and 2–5 μm for microrods are identified from SEM images. UV-visible spectrum of silver molybdate nanorods/nanowires shows maximum absorbance at 408 nm. Photo-luminescence (PL) spectrum exhibits UV emission at 335 nm, violet emission at 408 nm and a weak green emission at 540 nm. The influence of hydrothermal synthesis conditions on silver molybdate nanowires, nanorods and multipods compositions were established.     

Rapid synthesis of ZnO ellipsoidal nanostructures in large scale and their photoluminescence properties

ZnO ellipsoidal nanostructures with uniform ellipsoidal morphologies have been synthesized using different hydroxide anion precursors by an ultra-fast, facile (90 °C) solution-phase method without the assistance of sonication or any surfactants. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) measurements. Based on the experimental results, a growth mechanism of ZnO nanostructures was proposed. The obtained ZnO nanostructures exhibit a weak UV emission band at ~ 385 nm and a relatively stronger orange emission band at ~ 615 nm. The solution-phase method is simple, convenient for large-scale fabrication of ZnO ellipsoidal nanostructures.     

Solvothermal synthesis of hexagonal ZnO nanorods and their photoluminescence properties

Pure hexagonal ZnO nanorods were synthesized by low-temperature (90 °C) solvothermal treatment of zinc acetate in 40-80 wt.% hydrazine hydrate aqueous solutions. The products were characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. They show a strong UV emission at around 380 nm upon excitation at 360 nm using a Xe lamp at room temperature. The influence on the quality of the nanorods was investigated while the content of the solvent changed. The as-synthesized ZnO nanorods are promising materials for nanoscale optoelectronic devices due to their excellent UV emission properties.     

Thickness dependent growth of needle-like and flower-like ZnO nanostructures

Needle-like nanorods and micron-scale flower-like structures of ZnO were synthesized by thermal evaporation of metallic zinc films with different thicknesses, followed by thermal annealing. Needle-like nanorods of ZnO were found through out the sample surface after annealing of the 1.3 μm thick Zn film. Three-dimensional crystalline nanorod-based flower-like structures of ZnO were also observed after annealing of the relatively thick (3.3 μm) Zn film. Thermal annealing of the Zn films was done at 800 °C in air for different time durations (30, 45, and 90 min). The flower size and number increase with increase in film thickness for the same annealing temperature and time. The X-ray diffraction results show that both the needle-like nanorods and flower-like structures are hexagonal wurtzite structure of ZnO. The room temperature PL spectrum shows a strong defect related violet emission peak centered at 441 nm for both the structures. The possible growth process based on root growth technique is proposed.     

Strong quantum confinement effect in nanocrystalline CdS

CdS quantum dots have been prepared by chemical method. The X-ray diffraction results indicated the formation of CdS nanoparticles with hexagonal phase and grain size 2.5 nm. The HRTEM analysis reveals the formation of CdS quantum dots with an average grain size of ~2.5 nm. The X-ray photoelectron spectroscopy spectra exhibit the 3d _5/2 and 3d _3/2 peaks corresponding to cadmium and the S2p _3/2 peak corresponding to sulphur. Optical studies by UV–vis spectroscopy show a blue shifted absorption at 471 nm because of the quantum confined excitonic absorption. The photoluminescence spectra of CdS exhibited a broad green emission band centred at around 494 nm.     

Synthesis and characterization of octahedral PbF2

The novel 3D octahedron-like PbF₂ structures with dimension of 2-4 µm have been successfully synthesized by a simple route at low temperature. The morphologies and structures of as-prepared products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The growth mechanism has been proposed for octahedral PbF₂. It was found that the aging time is important for the formation of 3D octahedron-like PbF₂ structures. The room-temperature photoluminescence measurements revealed a strong blue emission band at 485 nm. It was indicated that the as-prepared octahedral PbF₂ could have the potential application in optoelectronic devices.     

Photoelectrochemical performance of CdS nanorods grafted vertically aligned TiO2 nanorods

In this study, TiO₂ nanorods/CdS nanorods composite samples were successfully synthesized by grafting CdS nanorods on vertically aligned TiO₂ nanorods. A two-step hydrothermal method was used to prepare the samples. Some properties of the samples, such as morphological, structural, and optical properties were characterized by energy-dispersive X-ray detection, field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and ultraviolet-visible spectroscopy. Moreover, photoelectrochemical properties were studied via current-voltage and photocurrent spectrum measurements. The results showed that CdS nanorods grafted on top of TiO₂ nanorods like a lawn. The amount grafted as well as the diameter and crystallinity of CdS nanorods increased first and then decreased as the grafting time increased, due to Ostwald ripening. Under the back-side illumination, the composite film with 2 h grafting time exhibited the highest photocurrent density which was almost twice of that of the pure TiO₂ nanorods.     

Solvothermal synthesis and photoluminescence properties of ZnO nanorods and nanorod assemblies from ZnO2 nanoparticles

Without the use of any extra surfactant or template, hexagonal phase ZnO crystallites consisting of individual nanorods or nanorod assemblies were synthesized simply by solvothermal treatment of several nanometer ZnO₂ nanoparticles in three different solvents (including ethanol, 80 wt.% hydrazine hydrate aqueous solution and ethylenediamine) at 150 °C for 24 h. The structures and optical properties of the resultant products were characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), and room temperature photoluminescence (RTPL) spectra. The RTPL spectra of the resultant products all showed a much stronger ultraviolet bandgap emission peaking at around 387 nm and a weaker emission associated with the defect level. The as-synthesized ZnO crystallites are promising materials for the optoelectronic devices due to their excellent UV emission properties.     

Structural,optical and magnetic properties of cobalt-doped CdS dilute magnetic semiconducting nanorods

Nanostructures of dilute magnetic semiconductors (DMS) in which a part of host material is replaced by a magnetic dopant are the promising candidates for spintronic devices. Pure and cobalt-doped DMS nanorods of CdS have been synthesized by solvothermal method. The effect of doping as well as the size of synthesized nanorods on structural, optical, and magnetic properties has been investigated. Transmission electron microscopy confirms the nanorods' morphology with an average diameter between 7 and 11 nm. Structural study reveals the formation of single phase hexagonal wurtzite structure of CdS with P6₃mc space group. UV–visible absorption spectra confirms that the band gap of the synthesized nanorods lie in the visible region between 2.46 and 2.72 eV. Photoluminescence spectra show defects-free nature of synthesized nanorods. The hump of emission band, around 430 nm in Co-doped CdS nanorods, attributes to the direct transition from the energy states created in CdS. Magnetic study reflects the ferromagnetic character of synthesized nanorods with high magnetic saturation, 0.034, 0.041, 0.070 and 0.090 emu g⁻¹ for, respectively, pure, 5%, 10% and 15% Co-doped CdS nanorods. The observed ferromagnetism in the synthesized nanorods have been explained on the basis of F-center (sulfur vacancy) mediated exchange mechanism and indirect interaction among Co (II) centers.     

Transformation of c-oriented nanowall network to a flat morphology in GaN films on c-plane sapphire

The work significantly optimizes growth parameters for nanostructured and flat GaN film in the 480–830 °C temperature range. The growth of ordered, high quality GaN nanowall hexagonal honeycomb like network on c-plane sapphire under nitrogen rich (N/Ga ratio of 100) conditions at temperatures below 700 °C is demonstrated. The walls are c-oriented wurtzite structures 200 nm wide at base and taper to 10 nm at apex, manifesting electron confinement effects to tune optoelectronic properties. For substrate temperatures above 700 °C the nanowalls thicken to a flat morphology with a dislocation density of 10¹⁰/cm². The role of misfit dislocations in the GaN overlayer evolution is discussed in terms of growth kinetics being influenced by adatom diffusion, interactions and bonding at different temperatures. The GaN films are characterized by reflection high energy electron diffraction (RHEED), field emission scanning electron (FESEM), high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL).     

A simple route to lanthanum hydroxide nanorods

This letter first describes a facile, low-cost, solution-phase approach to the large-scale preparation of lanthanum hydroxide single crystal nanorods at 60 °C without any template and surfactant. X-ray diffraction (XRD) shows that the nanorods are of pure hexagonal structure. The size and morphology of the products were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Lanthanum hydroxide single crystal nanorods are with diameters of approximately 20 nm and lengths of 150-200 nm. The processes of formation and decomposition for the as-prepared lanthanum hydroxide nanorods were discussed.     

One-dimensional cadmium sulfide (CdS) nanostructures by the solvothermal process: Controlling crystal structure and morphology aided by different solvents

Cadmium sulfide (CdS) nanowires and nanorods with different aspect ratios were successfully synthesized by the solvothermal method aided with various solvents, namely ethylenediamine, ethanolamine and triethylene tetraamine. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that, highly pure CdS nanostructures were crystallized with different structures and preferable growth orientations depending on solvent nature. Field emission electron microscope (FE-SEM) images showed that the aspect ratio of CdS nanostructures depends upon the dielectric constant and boiling temperature of solvents. CdS nanostructures with the highest aspect ratio in the form of nanowire were obtained using ethylenediamine, whereas CdS nanorods were produced in the presence of ethanolamine and triethylene tetraamine solvents. The absorption edge of CdS nanowires and nanorods showed a blue shift compared with that of bulk CdS due to an increase in their band gap energies.     

Synthesis of CdS nanorods by reacting CdCl2 nanorods with H2S at room temperature

We report the synthesis of CdS nanorods by reacting CdCl₂ nanorods with H₂S at room temperature. The preparation method was based on CdCl₂ nanorods employed as chemical template. The length and the diameter of the obtained CdS nanorods are about tens micron and 120−300 nm, respectively. The phase and the crystallographic structure of the products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The composition of the products was investigated by X-ray photoelectron spectroscopy (XPS).     

Green hydrothermal synthesis and photoluminescence property of ZnO2 nanoparticles

ZnO₂ nanoparticles were synthesized via a green hydrothermal method using ZnO powder and 30% H₂O₂ aqueous solution as the starting materials, and characterized by X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray (EDX) spectra, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. It was found that suitable reaction temperature (e.g., 80-140 °C) played an important role in obtaining pure cubic phase ZnO₂ nanoparticles. The RTPL spectra disclosed that the as-synthesized ZnO₂ nanoparticles exhibit one strong emission band centered at around 400 nm and one very weak emission band at around 474 nm, which may have originated from the band edge emission and the oxygen vacancy, respectively.     

Optical and electrical properties of ZnO nanoparticle thin films deposited on quartz by sparking process

ZnO nanoparticle thin films were deposited on quartz substrates by a novel sparking deposition which is a simple and cost-effective technique. The sparking off two zinc tips above the substrate was done repeatedly 50-200 times through a high voltage of 10 kV in air at atmospheric pressure. The film deposition rate by sparking process was approximately 1.0 nm/spark. The ZnO thin films were characterized by X-ray diffraction, Raman spectroscopy, UV-vis spectrophotometry, and ionoluminescence at room temperature. The two broad emission peaks centered at 483 nm (green emission) and 650 nm (orange-red emission) were varied after two-step annealing treatments at 400-800 °C. Moreover, the electrical resistivity of the films was likely to be proportional to the peak intensity of the orange-red emission.     

Study of structural and optical properties of Ge doped ZnO films

The Ge doped ZnO films were deposited on quartz substrates by radio frequency magnetron sputtering. The effects of doping and substrate temperature on the structural and optical properties of the Ge doped ZnO films were investigated by means of X-ray diffraction (XRD), UV-visible transmission spectra, X-ray photoelectron spectroscopy and photoluminescence (PL) spectra. The XRD patterns showed that Zn₂GeO₄ phases were formed in the films. With the increase of substrate temperature the crystallization of Zn₂GeO₄ was improved, and that of ZnO phases turned worse, and no diffraction peak of ZnO was observed when the substrate temperature was 700 °C. Obvious ultraviolet (UV) light emission was found due to ZnO grains, and it was much stronger than that of un-doped ZnO films. The enhancement of UV light emission at about 380 nm may be caused by excitons which were formed at the interface between Zn₂GeO₄ and ZnO grains. In the visible region of the PL spectra, the green light emission peak of samples at about 512 nm was associated with defects in ZnO. A red shift of the green light emission peak was observed which can be explained by the fact that there is a luminescence center at about 548 nm taking the place of the defect emission of ZnO with the increase of substrate temperature. The red shift of the green light emission peak and the 548 nm green light emission peaks of the PL spectrum show that some Ge²⁺ should replace the Zn²⁺ positions during the Zn₂GeO₄ grains growth and form the Ge²⁺ luminescence centers in Zn₂GeO₄ grains.     

Synthesis of novel hexagon SnO2 nanosheets in ethanol/water solution by hydrothermal process

The novel hexagon SnO₂ nanosheets are successfully synthesized in ethanol/water solution by hydrothermal process. The samples are characterized by X-ray diffraction (XRD), infrared ray (IR) and transmission electron microscopy (TEM). By changing the reaction conditions, the size and the morphology can be controlled. Comparison experiments show that when the temperature increased from 140 °C to 180 °C, the edge length of the hexagon nanoparticles increases from 300-450 nm to 700-900 nm. On the other hand, by adjusting the ratios of water to ethanol from 2 to 0.5, SnO₂ nanoparticles with different morphologies of triangle and sphere are obtained. When the concentration of NaOH is increased from 0.15 M to 0.30 M, a hollow ring structure can be obtained.