A study on the optical and electrical properties of direct-patternable ZnO films incorporated various contents of Pt nanoparticles

Platinum nanoparticles were synthesized by the methanol reduction method, and their size was controlled to 3 nm on average using PVP [poly(N-vinyl-2-pyrrolidon)] as a protecting unit. Various contents of Pt nanoparticles were incorporated into ZnO solutions which were synthesized by a sol-gel process. ZnO films with Pt nanoparticles of various content were annealed at 500 °C and 600 °C for 1 h. The crystallinity increased with the annealing temperature and also slightly with the content of Pt nanoparticles. The sheet resistance of ZnO films decreased with the incorporation of Pt nanoparticles, however the decreasing behavior was not maintained with increasing content of Pt nanoparticles. A shift of valence band maximum energy of ZnO film with Pt nanoparticles to higher energy was also observed due to electron transfer from Pt nanoparticles to ZnO film. The optical transmittance was 88 ± 2% in the visible region for all the ZnO films. Well-defined 60 μm wide direct-patterned ZnO films containing Pt nanoparticles of 0.5 atomic percent could be formed without using dry etching process.     

Highly luminescent silica-coated ZnO nanoparticles dispersed in an aqueous medium

Highly luminescent silica-coated ZnO nanoparticles dispersed in an aqueous medium were synthesized using the sol-gel process. The samples prepared at various temperatures exhibited an emission peak at around 480 nm (blue color) and a quantum efficiency of 60% at maximum by the quantum confinement effect of ZnO nanoparticles, with diameters ranging from 3.1 to 3.5 nm, under ultraviolet excitation. No degradation of the quantum efficiencies and no peak shifting in the emission spectra were observed for 7 days following the preparation, which indicated no growth of ZnO nanoparticles in the aqueous medium.     

Characterization of undoped and Co doped ZnO nanoparticles synthesized by DC thermal plasma method

ZnO nanopowders doped with 5 and 10 at% cobalt were synthesized and their antibacterial activity was studied. Cobalt doped ZnO powders were prepared using dc thermal plasma method. Crystal structure and grain size of the particles were characterized by X-ray diffractometry and optical properties were studied using UV-vis spectroscopy. The particle size and morphology was observed by SEM and HRTEM, revealing rod like morphology. The antibacterial activity of undoped ZnO and cobalt doped ZnO nanoparticles against a Gram-negative bacterium Escherichia coli and a Gram-positive bacterium Bacillus atrophaeus was investigated. Undoped ZnO and cobalt doped ZnO exhibited antibacterial activity against both E. coli and Staphylococcus aureus but it was considerably more effective in the cobalt doped ZnO.     

Low temperature synthesis of fluorescent ZnO nanoparticles

Fluorescent ZnO nanoparticles have been prepared by mixing aqueous solutions of zinc nitrate and ammonium carbonate in the presence of a non-ionic surfactant, Tween-80. Increased concentrations of the surfactant were found to affect both the morphology and purity of the synthesized ZnO nanoparticles. XRD, SEM, FTIR, TGA and Confocal laser scanning microscopy were employed to characterize the as-prepared samples. ZnO nanoparticles ranging in particle size from 11 to 15 nm were formed at the reaction temperature of 70-80 °C. The results of FTIR and TGA analysis indicate the self assembly of Tween molecules on the surface of ZnO nanoparticles. A bright emission in the visible region from the as-prepared ZnO nanoparticles was recorded using confocal laser scanning microscopy. This property of the as-prepared nanoparticles may find potential application in bio-imaging.     

Self-aligned nanocrystalline ZnO hexagons by facile solid-state and co-precipitation route

In this study, we report the synthesis of well-aligned nanocrystalline hexagonal zinc oxide (ZnO) nanoparticles by facile solid-state and co-precipitation method. The co-precipitation reactions were performed using aqueous and ethylene glycol (EG) medium using zinc acetate and adipic acid to obtain zinc adipate and further decomposition at 450 °C to confer nanocrystalline ZnO hexagons. XRD shows the hexagonal wurtzite structure of the ZnO. Thermal study reveals complete formation of ZnO at 430 °C in case of solid-state method, whereas in case of co-precipitation method complete formation was observed at 400 °C. Field emission scanning electron microscope shows spherical morphology for ZnO synthesized by solid-state method. The aqueous-mediated ZnO by co-precipitation method shows rod-like morphology. These rods are formed via self assembling of spherical nanoparticles, however, uniformly dispersed spherical crystallites were seen in EG-mediated ZnO. Transmission electron microscope (TEM) investigations clearly show well aligned and highly crystalline transparent and thin hexagonal ZnO. The particle size was measured using TEM and was observed to be 50–60 nm in case of solid-state method and aqueous-mediated co-precipitation method, while 25–50 nm in case of EG-mediated co-precipitation method. UV absorption spectra showed sharp absorption peaks with a blue shift for EG-mediated ZnO, which demonstrate the mono-dispersed lower particle size. The band gap of the ZnO was observed to be 3.4 eV which is higher than the bulk, implies nanocrystalline nature of the ZnO. The photoluminescence studies clearly indicate the strong violet and weak blue emission in ZnO nanoparticles which is quite unique. The process investigated may be useful to synthesize other oxide semiconductors and transition metal oxides.     

Structure and size control of ZnO nanoparticles by applying high pressure to ambient liquid in liquid-phase laser ablation

We synthesized ZnO nanoparticles by laser ablation of a Zn target in water at pressures up to 30 MPa. We observed the enhancement of the crystallinity of synthesized ZnO nanoparticles when high pressure was applied to ambient water. In addition, we found that ZnO nanoparticles with smaller sizes were synthesized by pressurizing ambient water. Considering our previous understanding on the effect of high pressure applied to ambient liquid, the controls of the structure and the size of nanoparticles were considered to be obtained via the controls of the dynamics of laser ablation plasma and ablation-induced cavitation bubble.     

Complex dynamics of a particle in an oscillating potential field

In this paper, Mg-doped ZnO nanoparticles were synthesized by the facile sol–gel method. The crystalline structure, characteristic absorption bands and morphology of the obtained Mg-doped ZnO nanoparticles were studied by XRD, FTIR and TEM. The thermal degradation behaviour of the samples was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The effect of Mg concentrations and annealing temperatures on the antibacterial properties of the obtained nanoparticles was investigated in detail. The results indicated that doping Mg ions into ZnO lattice could enhance its antibacterial activity. Antibacterial assay demonstrated that Mg-doped ZnO with 7% Mg content annealed at 400 ^°C had the strongest antibacterial activity against Listeria monocytogenes (98.7%). This study indicated that the inhibition rate of ZnO nanoparticles increased with the formation of granular structure and the decrease of ZnO size due to the doping of Mg ions into the ZnO lattice.     

Ferromagnetic behavior of high-purity ZnO nanoparticles

ZnO nanoparticles with the wurtzite structure were prepared by chemical methods at low temperature in aqueous solution. The size of the nanoparticles is in the range from about 10 to 30 nm. Ferromagnetic properties were observed from 2 K to room temperature and above. Magnetization versus temperature, M(T), and isothermal M(H) measurements were obtained. The coercive field clearly shows ferromagnetism above room temperature. An exchange bias was observed, and we related this behavior to the core-shell structure present in the samples. The chemical synthesis, structure, and defects in the bulk related to oxygen vacancies are the main factors for the observed magnetic behavior.     

ZnO nanoparticles favours heterogeneous nucleation in PET–ZnO nanocomposites

The structural and chemical properties with non-isothermal crystallization kinetics of PET–ZnO nanocomposites have been reported in this article. ZnO nanoparticles have been synthesized via chemical route with average diameter 19 nm which made confirm by transmission electron microscopy and X-ray diffractometer (XRD) techniques. PET–ZnO nanocomposites have been prepared by solution casting method. The structural and chemical changes occurred in poly (ethylene terephthalate) after inclusion of ZnO nanoparticles have been studied with the help of XRD and Fourier transform infrared spectroscopy, respectively. It was observed from differential scanning calorimeter that ZnO nanoparticles work as nucleating agent for heterogeneous nucleation in PET matrix under non-isothermal crystallization process. The combined Avrami and Ozawa models have been proved adequate to explain non-isothermal crystallization kinetics of PET–ZnO nanocomposites, and also, ZnO nanoparticles have been caused to reduce crystallization activation energy in pristine PET as per the applied Kissinger model.     

Tailoring Cu2−xTe quantum-dot-decorated ZnO nanoparticles for potential solar cell applications

Cu_2−xTe QDs on ZnO nanoparticles were synthesized using a successive ionic layer absorption and reaction technique (SILAR) at room temperature. The as-synthesized QDs which were distributively deposited on ZnO nanoparticles surface were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction and high-resolution transmittance microscope (HR-TEM). It revealed that the average diameter of the QDs was ∼2 nm. The synthesized Cu_2−xTe QDs were solely orthorhombic Cu_1.44Te phase. The growth mechanism was supposed that it based on ions deposition. The energy gap of as-synthesized Cu_2−xTe QDs was determined ∼1.1 eV and the smallest energy gap of 0.76 eV was obtained, equal to that of bulk material. Raman spectroscopy and FTIR were also used to study the Cu_2−xTe QDs on ZnO nanoparticles. These characteristics suggest a promising implication for a potential broadband sensitizer of QDSCs.     

Finite size effects in ZnO nanoparticles: An electron paramagnetic resonance (EPR) analysis

ZnO nanoparticles were synthesized by solid coprecipitation method with consecutive high energy ball milling procedure. By reducing the particle size of ZnO to nano dimensions strong nano‐size effects were observed. In order to characterize the ZnO defect structure, EPR has been applied. It was observed that below 50 nm the surface defects play a dominant role in the electronic properties of ZnO. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis, effect of capping agents, structural, optical and photoluminescence properties of ZnO nanoparticles

Zinc oxide nanoparticles were synthesized using chemical method in alcohol base. During synthesis three capping agents, i.e. triethanolamine (TEA), oleic acid and thioglycerol, were used and the effect of concentrations was analyzed for their effectiveness in limiting the particle growth. Thermal stability of ZnO nanoparticles prepared using TEA, oleic acid and thioglycerol capping agents, was studied using thermogravimetric analyzer (TGA). ZnO nanoparticles capped with TEA showed maximum weight loss. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for structural and morphological characterization of ZnO nanoparticles. Particle size was evaluated using effective mass approximation method from UV-vis spectroscopy and Scherrer's formula from XRD patterns. XRD analysis revealed single crystal ZnO nanoparticles of size 12-20 nm in case of TEA capping. TEA, oleic acid and thioglycerol capped synthesized ZnO nanoparticles were investigated at room temperature photoluminescence for three excitation wavelengths i.e. 304, 322 and 325 nm, showing strong peaks at about 471 nm when excited at 322 and 325 nm whereas strong peak was observed at 411 for 304 nm excitation.     

Green synthesis of gold and silver nanoparticles using gallic acid: catalytic activity and conversion yield toward the 4-nitrophenol reduction reaction

In the present report, gallic acid was used as both a reducing and stabilizing agent to synthesize gold and silver nanoparticles. The synthesized gold and silver nanoparticles exhibited characteristic surface plasmon resonance bands at 536 and 392 nm, respectively. Nanoparticles that were approximately spherical in shape were observed in high-resolution transmission electron microscopy and atomic force microscopy images. The hydrodynamic radius was determined to be 54.4 nm for gold nanoparticles and 33.7 nm for silver nanoparticles in aqueous medium. X-ray diffraction analyses confirmed that the synthesized nanoparticles possessed a face-centered cubic structure. FT-IR spectra demonstrated that the carboxylic acid functional groups of gallic acid contributed to the electrostatic binding onto the surface of the nanoparticles. Zeta potential values of ?41.98 mV for the gold nanoparticles and ?53.47 mV for the silver nanoparticles indicated that the synthesized nanoparticles possess excellent stability. On-the-shelf stability for 4 weeks also confirmed that the synthesized nanoparticles were quite stable without significant changes in their UV–visible spectra. The synthesized nanoparticles exhibited catalytic activity toward the reduction reaction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. The rate constant of the silver nanoparticles was higher than that of the gold nanoparticles in the catalytic reaction. Furthermore, the conversion yield (%) of 4-nitrophenol to 4-aminophenol was determined using reversed-phase high-performance liquid chromatography with UV detection at 254 nm. The silver nanoparticles exhibited an excellent conversion yield (96.7–99.9 %), suggesting that the synthesized silver nanoparticles are highly efficient catalysts for the 4-nitrophenol reduction reaction.     

Low frequency Raman scattering from acoustic phonons confined in ZnO nanoparticles

We report here the first observation of the low frequency Raman scattering from acoustic phonons in semiconducting zinc oxide (ZnO) nanoparticles without embedding in any solid matrix. ZnO nanoparticles (size 5-10 nm) with nearly spherical shape have been synthesized using a chemical route. A shift in the phonon peaks toward higher frequencies along with broadening was observed with a decrease in particle size. The size dependence of the acoustic phonons in ZnO nanoparticles is explained using Lamb's theory that predicts the vibrational frequencies of a homogeneous elastic body of spherical shape. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar vibrations (l = 2) of the spheroidal mode due to the confinement of acoustic vibrations in ZnO nanoparticles.     

Synthesis and surface modification of ZnO:Cu nanoparticles by silica and PMMA

ZnO nanoparticles doped with Cu were synthesized by solid state reaction using different precursor routes and varying growth environment. Average crystallite size varied from 40 to 100 nm depending upon synthesis temperature, lower temperature favouring smaller particle size. Scanning electron microscope (SEM) images showed that particles synthesized at 250 °C were in the shape of nanorods but those synthesized at 900 °C had spherical shape. Luminescence emission showed marked dependence on the growth conditions varying from ultraviolet (UV) emission to green emission. For making the luminescent nanoparticles bio-compatible, a bioinorganic interface on ZnO:Cu nanoparticles was created by coating them with inert silica. Surface modification of ZnO:Cu was also done with lipophilic polymethylmethacrylate (PMMA). ZnO:Cu nanoparticles showed hexagonal wurtzite structure and the coating of silica was confirmed with the presence of two extra peaks due to silica in the XRD spectra. Thermogravimetric analysis (TGA) and FTIR spectroscopy indicated that PMMA molecules were adsorbed on the surface of ZnO:Cu nanoparticles. SEM images revealed that PMMA adsorption improved the dispersibilty of ZnO:Cu nanoparticles.     

Growth mechanism of ZnO nanorod/Fe3O4 nanoparticle composites and their photocatalytic properties

ZnO nanorods/Fe₃O₄ nanocomposites as the recyclable photocatalyst were synthesized by a co-precipitation method, with microwave assistant by dropping alkaline solution with Fe₃O₄ nanoparticles into the aqueous of zinc salt. These Fe₃O₄ nanoparticles were the nucleated centers for the ZnO nanorods growth so that these nanorods ended with aggregated Fe₃O₄ nanoparticles. The growth processes and mechanism are explained as those insoluble zinc hydroxides prefer to nucleate on the surface of Fe₃O₄ nanoparticles (heterogeneous nucleation) rather than nucleated as isolated ZnO nanostructures (homogeneous nucleation). These nanocomposites have strong photocatalytic ability to reduce RhB and moderate magnetization, which make them being good recyclable photocatalysts.     

Enhancement in SERS intensities of azo dyes adsorbed on ZnO by plasma treatment

Surface‐enhanced Raman scattering (SERS) spectra of azo dyes (methyl orange and p‐methyl red) adsorbed on ZnO nanoparticles were observed. Hydrothermally synthesized ZnO nanoparticles were characterized by powder X‐ray diffraction and X‐ray photoelectron spectroscopy. The ZnO nanoparticle size, monitored with X‐ray diffraction, was tuned by calcination to optimize SERS intensities. The observed SERS effect of azo dyes adsorbed on ZnO can be ascribed to charge‐transfer resonance effect. Time‐dependent density functional theory was used to calculate the optical spectra and interpret the chemical enhancement observed in the experiment. The SERS enhancement factors for methyl red on ZnO were boosted by nearly four times and twice with O₂ plasma and H₂ plasma, respectively. However, plasma treatment showed no effect on the enhancement factors of methyl orange on ZnO. We conclude that plasma‐induced defect formation and band gap shift in ZnO and the coupling of energy levels between ZnO and azo dye molecules are responsible for the observed enhancement of SERS intensities. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of barium doping on the physical properties of zinc oxide nanoparticles elaborated via sonochemical synthesis method

The aim of this work is to study the effect of barium (Ba) doping on the optical, morphological and structural properties of ZnO nanoparticles. Undoped and Ba-doped ZnO have been successfully synthesized via sonochemical method using zinc nitrate, hexamethylenetetramine (HMT) and barium chloride as starting materials. The structural characterization by XRD and FTIR shows that ZnO nanoparticles are polycrystalline with a standard hexagonal ZnO wurtzite crystal structure. Decrease in lattice parameters from diffraction data shows the presence of Ba²⁺ in the ZnO crystal lattice. The morphology of the ZnO nanoparticles has been determined by scanning electron microscopy (SEM). Incorporation of Ba was confirmed from the elemental analysis using EDX. Optical analysis depicted that all samples exhibit an average optical transparency over 80%, in the visible range. Room-temperature photoluminescence (PL) spectra detected a strong ultraviolet emission at 330 nm and two weak emission bands were observed near 417 and 560 nm. Raman spectroscopy analysis of Ba-doped samples reveals the successful doping of Ba ions in the host ZnO.     

Fabrication of three-dimensional ZnO with hierarchical structure via an electrodeposition process

A novel three-dimensional (3D) hierarchical structured ZnO was prepared on TiO₂ nanoparticles film by electrodeposition process from aqueous ZnCl₂ solution. The hierarchical structured ZnO was observed by scanning electron microscopy. The results showed that the deposition time had an obvious effect on the morphology of the ZnO structures. Accordingly, a possible growth mechanism was proposed. Furthermore, the room-temperature optical properties of hierarchical structured ZnO were investigated by photoluminescence spectrum, indicating that a strong green emission peak centered at 542 nm.     

Synthesis of ZnO nanoparticles using nanosecond pulsed laser ablation in aqueous media and their self-assembly towards spindle-like ZnO aggregates

ZnO nanoparticles were fabricated by pulsed laser ablation (PLA) of a Zn metal in aqueous media, and aging effects on the morphology and photoluminescence properties of ZnO nanoparticles were investigated. The crystalline phase and particle morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that small, well-defined ZnO nanoparticles were obtained by PLA of a Zn plate in aqueous media, and subsequent aging of the obtained ZnO nanoparticle suspension produced in cetyltrimethylammonium bromide (CTAB) solution led to the formation of spindle-like ZnO aggregates. However, in deionized water not the spindle-like ZnO aggregates but fluffy round aggregates were obtained. High-resolution transmission electron microscopic (HRTEM) observation indicated that the spindle-like ZnO aggregates were composed of many well-defined nanoparticles. Spindle-like aggregates exhibited strong exciton emission, while green emission could be suppressed via an aging process in the presence of CTAB. Moreover, thin films prepared by electrophoretic deposition (EPD) of ZnO nanoparticles after PLA in the presence of CTAB also possessed highly elongated aggregate structures that were possibly formed by surrounding the ZnO nanoparticles with double layers of CTAB molecules.