Thermolytic Growth of ZnO Nanocrystals: Morphology Control and Optical Properties (original) (raw)
Related papers
Here we report an easy and rapid synthesis technique of wurtzite ZnO nanostructures in the form of flowers, nano-rods and nano-tubes that are achieved by a facile hydrothermal method. A growth mechanism is proposed based on a series of temperature dependent experiments keeping other parameters during the synthesis in the aqueous medium at optimized levels. Pure ZnO results in nano-rods while Sr doped ZnO material forms flower and tube like structures. The XRD and TEM investigations show that ZnO nanostructures possess good crystalline structures with a growth direction along the c-axis of the crystal plane. Raman spectra confirm five phonon vibration modes for ZnO nanostructures at 99, 333, 382, 438 and 582 cm À1 and one more defect induced low intensity peak at 663 cm À1 for Sr doped ZnO. Ultraviolet-visible (UV-vis) spectroscopy shows the band gap energy of ZnO nanostructures decreases from 3.24 to 3.22 eV with the substitution of Sr into the ZnO lattice. Photoluminescence spectra reveal the existence of several defect states in all of the samples. Defect intensity seems negligibly affected by the variation of growth temperature, whereas, Sr doping plays a major role in controlling oxygen and Zn related defects. I–V characteristics of the ZnO and Sr doped ZnO show rectification behaviour of the Schottky diodes.
Synthesis and optical properties of ZnO nanostructures with different morphologies
Optical Materials, 2006
ZnO nanostructures with different morphologies were grown by a low-temperature hydrothermal technique. The morphology, crystallinity and defect content in the nanostructures could be controlled by adjusting the synthesis conditions. Nanostructures prepared with optimum growth conditions were of good structural and optical qualities. Effects of growth conditions and thermal annealing on the optical properties of the nanostructures were studied by Raman and photoluminescence spectroscopy techniques. It is found that the nanostructures grown with particular initial and final pH values of the reaction mixture and air-annealed at about 250°C are of best crystalline and optical quality.
Journal of Luminescence, 2012
Zinc hydroxide particles were prepared by a two-step process employing zinc nitrate hexahydrate, urea, ethylene glycol, water and p-toluene-sulfonic acid monohydrate (p-TSA). We used different concentrations of the reactants as well as different volume ratios of the solvents. ZnO particles were obtained by thermal treatment of the reaction products at two different temperatures: 350 1C and 500 1C. The samples were characterized by scanning field emission electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, BET analysis, thermogravimetry (TG) analysis and photoluminescence (PL) spectroscopy. It was found that after the thermal treatment particles become smaller, with the p-TSA concentration strongly affecting the morphology of the particles. Luminescence properties of the samples probed by PL at 8 K and room temperature exhibited a remarkable correlation with specimens 0 nanomorphology. Luminescent features at $ 2.0-2.2 eV, $ 2.4-2.5 eV, $ 2.65 eV, $ 2.9 eV, $ 3.0-3.1 eV and $ 3.3 eV were observed in most specimens, although their relative intensity and temperature dependence were specific to an individual group of samples visa -vis their growth history and morphology.
2010
ZnO nanostructures have been synthesized by heating a mixture of ZnO/graphite powders using the thermal evaporation and vapor transport on Si(1 0 0) substrates without any catalyst and at atmospheric argon pressure. The in. uence of the source temperature on the morphology and luminescence properties of ZnO nanostructures has been investigated. ZnO nanowires, nanoflowres and nanotetrapods have been formed upon the Si(1 0 0) substrates at different source temperatures ranging from 1100 to 1200 degrees C. Room temperature photoluminescence (PL) spectra showed increase green emission intensity as the source temperature was decreased and ZnO nanowires had the strongest intensity of UV emission compared with other nanostructures. In addition, the growth mechanism of the ZnO nanostructures is discussed based on the reaction conditions. (C) 2010 Elsevier B. V. All rights reserved.
ZnO Nanocrystals by a Non-hydrolytic Route: Synthesis and Characterization
The Journal of Physical Chemistry B, 2003
We report a novel, non-hydrolytic route to ZnO nanocrystals by means of thermal decomposition of zinc acetate (ZnAc 2 ) in alkylamines, in the presence of tert-butylphosphonic acid (TBPA). The slow heating of an alkylamine/TBPA/ZnAc 2 mixture is a simple, safe, and scalable approach to synthesize ZnO nanocrystals from handy chemicals. The obtained ZnO nanocrystals were characterized by UV-vis absorption, photoluminescence (PL) and infrared (FT-IR) spectroscopies, and by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The growth of ZnO particles in the nanoscopic regime and their final size were governed by the TBPA/ZnAc 2 molar ratio in the reaction mixtures. The various roles played by TBPA in the conditions of the synthesis are discussed on the basis of the experimental evidence. The presented synthetic approach provides a unique tool for designing the synthesis of ZnO crystals of a desired size in the nanoscale regime and can be potentially extended to other nanoscale materials.
Synthesis and characterization of ZnO nanocrystals from thermolysis of new precursor
Chemical Engineering Journal, 2009
ZnO nanocrystals were prepared by the thermolysis of Zn-surfactant complexes. The particle sizes of the nanocrystals were from 15 to 25 nm. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and ultraviolet-visible (UV-vis) spectroscopy. The synthesized ZnO nanocrystals have a hexagonal wurtzite structure.
Morphological Control and Photoluminescence of Zinc Oxide Nanocrystals
Journal of Physical Chemistry B, 2005
Nanocrystals of the wide band gap semiconductor zinc oxide of controllable morphologies were synthesized by a simple thermal decomposition method. The predominating factor in determining the morphology (spheres, triangular prisms, and rods) was the solvent, selected on the basis of coordinating power. The nanoparticles were structurally analyzed, and the photoluminescence of each shape was compared. The intensity of the green band emission, common to many ZnO structures, was found to vary with morphology. The strongest green band intensity corresponded to the shape with the largest surface/volume ratio and could be attributed to surface oxygen vacancies. Control over the morphology of ZnO at the nanoscale is presented as a means to control the green band emission.
Effect of the reaction conditions on the formation of the ZnO nanostructures
ZnO nanorods were synthesized through a simple chemical method at low temperature. Different morphologies were obtained changing the order of addition of reactants. The X-ray diffraction data indicated that the samples had hexagonal wurtzite structure. The optical band gap of the ZnO samples calculated using Tauc model was 3.19 eV.
Journal of Crystal Growth
Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the...
Chemical Physics Letters, 2011
A low temperature reaction route via ultrasonication has been demonstrated for the synthesis of ZnO nanoparticles. It is found that the morphology and photoluminescence has strong dependence on the surfactant, triethanolamine (TEA) and chelating agent, citric acid. Polyvinylpyrrolidine (PVP) is used as a capping agent. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), FTIR, UV–Vis absorption and photoluminescence spectra are used to characterize the as-prepared ZnO nanoparticles.TEA acting as a surfactant form a diffuse layer around Zn+2 ions. The surface energies and growth rates of different crystallographic faces with the attachment of ethanolamine leads to spherical nanoparticles. In presence of surfactant as well as chelating agent leads to formation of spherical monodispersed ZnO nanoparticles without any agglomeration. But in the absence of chelating agent as-obtained nanoparticles forming bunches through agglomeration and larger in size.► Effect of surfactant and chelating agent on the formation of ZnO nanoparticles studied in detail. ► Synthesis of ZnO nanoparticles by low temperature reaction route via ultrasonication. ► Due to quantum confinement effects, the band gap of the ZnO nanoparticles is blue shifted compared with the bulk material. ► Band gap of the ZnO nanoparticles is blue shifted compared with the bulk material.