Facile hydrothermal synthesis of flowerlike ZnOnanorods without catalysts

A very simple hydrothermal method (one step) was used at low temperature to synthesis flower-like ZnOnanorods on glass substrate without any template, catalyst or buffer layer before the reaction. Flower-like ZnOnanorods were synthesized by hydrothermally heating 0.1 M precursor solution of hexahedral zinc nitrate Zn(NO3)2.6H2O, hexamethylenetetramine (HMT) and NaOH were the starting materials for the chemical reaction under stirring. The field emission scanning electron microscopy (FE-SEM) images showed that the flower-like structures were formed in 3.5 h hydrothermally-heated for sample, whereas the experimental pattern of the films by X-ray diffraction show that diffraction peaks can be assigned to the wurtzite hexagonal-shaped ZnO as shown in the (FE-SEM) images, also the morphology of the films studied by atomic force microscope (AFM) shows that the films have high roughness. The energy gap was estimated and optical behavior was investigate

Surface plasmon resonance effects of gold colloids on optical properties of N719 dye in ethanol

In this work, the light absorption and emission effects of gold nanoparticles on some optical properties of N719 dye solution were studied via transmission electron microscopy, UV-vis absorption, and photoluminescence spectroscopy measurements. A facile method to fabricate four gold colloidal solutions with different concentrations containing ~15 nm gold nanoparticles was presented through pulsed laser ablation of a gold target immersed in ethanol, followed by a post-ablated size modification process. As-prepared gold colloids with different concentrations were mixed with certain dye solution. The absorption and fluorescence enhancement that resulted from the interaction between the dipole moments of the day and the surface plasmon resonance of gold nanoparticles were found to be strongly dependent on the gold colloid concentration. Fluorescence was enhanced by around 9-fold, which was achieved for the dye solution with the highest gold nanoparticles concentration

Optical and electrical correlation effects in ZnO nanostructures: Role of pulsed laser annealing

This paper reports the preparation and characterization of some high quality polycrystalline ZnO nanofilms (ZNFs) deposited on silicon (Si) substrates via sol gel allied spin coating process. The properties of such deposited ZNFs were modified by Nd:YAG pulsed laser annealing at varied wavelengths. The impact of pulse laser wavelengths on the structural, morphological, optical and electrical characteristics of these nanofilms was evaluated. Annealing at third harmonic generation wavelength of 355 nm was found to produce ZNFs with much better polycrystallinity and strong lattice orientation than the one annealed at the fundamental wavelength of 1064 nm. Furthermore, annealing at the second harmonic generation wavelength of 532 nm could produce a typical ZnO crystal with apparent orientation. The observed modifications in the films structure and morphology were attributed to the laser treatment-mediated thermal effect. FESEM analysis of the films revealed the existence of varied nanostructures depending on the laser wavelength. Photoluminescence (PL) emission spectra of ZNFs exhibited a broad UV excitonic band and a narrow visible band related to defects. The laser irradiation induced generation of the oxygen vacancies were observed to reduce the electrical resistivity of the films and altered the optical band gap energies. Sample annealed at 355 nm disclosed the lowest resistivity of 23.532 × 10-3 O cm. Raman spectra of ZNFs confirmed the existence of hexagonal ZnO wurtzite structure. The narrowing of the E2high (437 cm-1) Raman phonon mode due to further annealing indicated an improvement in the films crystallinity and reduction in the local atomic defects related to the oxygen vacancy (VO+2). XPS analyses showed an improvement crystallinity and chemisorption of oxygen into the grain boundaries of the films due to the laser treatment in air at lower wavelength. In short, the pulsed laser annealing of ZNFs were established to be far more efficient process for the oxidation of Zn to ZnO than conventional annealing procedures

Sol-gel grown aluminum/gallium co-doped ZnO nanostructures: Hydrogen gas sensing attributes

Aluminum (Al) and Gallium (Ga) co-doped ZnO nanostructures (AGZO NSs) were prepared on p-type Si(100) substrate using sol-gel united spin coating method. Ga contents were varied from 1 to 5 at% at fixed Al doping (1 at%). Synthesized samples were annealed at 500 °C for 3 h. The structural, morphological, and electrical property of the optimum sample (containing 3 at% of Ga) were determined. Optimum AGZO NSs enclosing highest density of nanorod (NR) arrays were selected to fabricate a hydrogen gas (H2) sensor. As-grown AGZO NSs revealed hexagonal wurtzite structure with mean grain size ≈ 41.20 nm and resistivity ≈ 0.6475 × 10−2 Ω cm. The gas sensing attributes of the developed sensor was evaluated for two different temperatures (at 100 and 150 °C) under varying gas H2 contents (from 250 to 1750 ppm). Furthermore, the selectivity of the AGZO NSs for three different gases such as H2, CO and CH4 were examined. The sensitivity of the sensor at 100 °C was augmented sharply from 60% to 385% with the increment of H2 gas contents from 250 to 1750 ppm. This enhancement was attributed to the increases of hydrogen gas current (IH) and good stability of the air atmosphere. The synthesized AGZO NSs have high potential for gas sensing, photovoltaic and field emission applications