Annealing effects on the optical and morphological properties of ZnO nanorods on AZO substrate by using aqueous solution method at low temperature

Vertically aligned ZnO nanorods (NRs) on aluminum-doped zinc oxide (AZO) substrates were fabricated by a single-step aqueous solution method at low temperature. In order to optimize optical quality, the effects of annealing on optical and structural properties were investigated by scanning electron microscopy, X-ray diffraction, photoluminescence (PL), and Raman spectroscopy. We found that the annealing temperature strongly affects both the near-band-edge (NBE) and visible (defect-related) emissions. The best characteristics have been obtained by employing annealing at 400°C in air for 2 h, bringing about a sharp and intense NBE emission. The defect-related recombinations were also suppressed effectively. However, the enhancement decreases with higher annealing temperature and prolonged annealing. PL study indicates that the NBE emission is dominated by radiative recombination associated with hydrogen donors. Thus, the enhancement of NBE is due to the activation of radiative recombinations associated with hydrogen donors. On the other hand, the reduction of visible emission is mainly attributed to the annihilation of OH groups. Our results provide insight to comprehend annealing effects and an effective way to improve optical properties of low-temperature-grown ZnO NRs for future facile device applications.     

Parallel enzymatic and non-enzymatic formation of zinc protoporphyrin IX in pork

Zinc protoporphyrin is formed in pork homogenates in both enzymatic and non-enzymatic reactions. Ferrochelatase is active in formation of the highly fluorescent pigment known from Parma ham as demonstrated by inhibition with N-methylmesoporphyrin and by thermal inactivation. A non-enzymatic transmetallisation reaction, exchange of iron in myoglobin by zinc(II), is demonstrated by Pb(II) inhibition of zinc protoporphyrin formation at low Pb(II) concentrations, but promoted at higher Pb(II) concentrations. The non-enzymatic reaction is characterised as a slow bimolecular reaction between protoporphyrin IX and zinc(II) with a second-order rate constant of 0.63 l mol⁻¹ s⁻¹ at 35 °C and a high energy of activation of 98 kJ mol⁻¹ for acetone:water (3:1, v/v) as solvent. Zinc protoporphyrin formation is concluded to be thermodynamically controlled with a formation constant of 4 × 10⁵ M (35 °C, acetone:water (3:1)). An efficient inhibition of formation of zinc protoporphyrin by nitrite is related to myoglobin as substrate and involves both enzymatic and non-enzymatic reactions.     

Biological performance of zinc borate-incorporated particleboard: Effects of leaching on efficacy

The decay and termite resistance and effects of a robust leaching process on the efficacy of zinc borate-incorporated particleboard were examined. Particleboards (300 × 300 × 15 mm) prepared from particles of mixed wood species generated from demolished construction materials were incorporated with zinc borate at target retentions of 0%, 1%, 1.5% and 2% of the particle weight. An in-line treatment method was utilized to introduce the powdered chemical during the blending stage. ICP analysis indicated that the amount of zinc borate was not lost during manufacturing. Standard static bending tests demonstrated that there was no significant loss in mechanical properties. The decay and termite tests indicated that the efficacy of zinc borate at a higher retention was enough to suppress the biological activity, even after application of a robust leaching process.     

Going from green to white color electroluminescence through a nanoscale complex of Zinc (II)

In this paper, we report application of four novel Nano Zinc (II) complexes as the emitter dyes in organic light emitting diodes (OLEDs). The Nano Zinc (II) complexes emission, particularly its absorption, fluorescence spectra and quantum yield, tuned by varying sizes which affects environments of the Zinc (II) ion. OLED Devices with Nano Zinc (II) complexes were fabricated, giving rise to devices with peak emission ranging from 498 to 541 nm. Here, we have successfully employed sonoelectrochemical method for fabricating white OLEDs. The white emission ascribed to the exciton emission in Nano Zinc (II) complex emitter and from exciplex formation at the interface of PVK/Nano Zinc (II) complex. The experimental results demonstrate that this approach is ideal for color tuning of single and multilayer conducting semiconducting thin films used in the fabrication of organic electronic devices such as OLEDs.     

Performance enhancement of poly (vinylidene fluoride-co-hexafluoro propylene)/polyethylene oxide based nanocomposite polymer electrolyte with ZnO nanofiller for dye-sensitized solar cell

Nanocomposite polymer electrolytes (NCPEs) were prepared by blending poly (vinylidene fluoride-co-hexafluoro propylene) copolymer (PVdF-HFP) and polyethylene oxide (PEO) polymers and incorporation of ZnO inorganic nanofiller (PVdF-HFP:PEO:EC:PC:NaI:I₂:ZnO). The highest ionic conductivity value of 8.36 mS cm⁻¹ was recorded when 3 wt.% of ZnO inorganic nanofiller was incorporated into the NCPE system. Temperature-dependant ionic conductivity behaviour of NCPEs was analysed and proven to follow the Arrhenius thermal activated model. Structural studies of NCPEs were carried out using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analysis. NCPEs were used to fabricate Dye-sensitized solar cells (DSSCs). Enhancements in the solar light to electricity conversion efficiency (η) of DSSCs were observed in the presence of ZnO inorganic nanofiller in the NCPE system and NCPE with 3 wt.% ZnO represented the highest η of 7.33% under full sun irradiation.     

Growth mechanism and gas-sensing characteristics of organic-additive-free zinc oxide of various shapes

Zinc oxide is widely used in gas sensors, solar cells, and photocatalysts because of its wide bandgap and exciton binding energy of 60 meV in various metal oxides. To use ZnO as a gas sensor, it is necessary to synthesize it with surface defects and a large specific surface area. In this study, hydrothermal synthesis without surfactants was employed to obtain organic-additive-free ZnO. For morphology control, we varied the ratio of the hydroxide ion concentration to the zinc ion concentration. To confirm the growth mechanism of ZnO, we performed X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. Raman spectroscopy and photoluminescence measurements were performed to analyze the surface properties. The Brunauer–Emmett–Teller method and probe stations were used to measure the specific surface area and sensitivity of the gas sensor, respectively. The results confirmed that flower-shaped ZnO is the most suitable gas-sensing material.     

Optical properties and electrical resistivity of boron-doped ZnO thin films grown by sol–gel dip-coating method

Sol–gel dip-coating was used to grow ZnO thin films doped with various concentrations of B ranging from 0 to 2.5 at.% on quartz substrates. The effects of B doping on the absorption coefficient (α), optical band gap (E_g), Urbach energy (E_U), refractive index (n), refractive index at infinite wavelength (n_∞), extinction coefficient (k), single-oscillator energy (E_o), dispersion energy (E_d), average oscillator strength (S_o), average oscillator wavelength (λ_o), moments M₋₁ and M₋₃, dielectric constant (ε), optical conductivity (σ), and electrical resistivity (ρ) of the BZO thin films were investigated. The transmittance spectra of the ZnO and BZO thin films show that the transmittance of the BZO thin films was significantly higher than that of the ZnO thin films in the visible region of the spectrum and that the absorption edge of the BZO thin films was blue-shifted. The BZO thin films exhibited higher E_g, E_U, and E_o and lower E_d, λ_o, M₋₁ and M₋₃ moments, S_o, n_∞, and ρ than the ZnO thin films.     

Transparent amorphous zinc oxide thin films for NLO applications

This review focuses on the growth and optical properties of amorphous zinc oxide (ZnO) thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz and glass substrates at temperature equal to 350 K. The amorphous nature of the films was verified by X-ray diffraction. Atomic Force Microscopy was used to evaluate the surface morphology of the films. The optical characteristics of amorphous thin films have been investigated in the spectral range 190–1100 nm. Measurement of the polarized optical properties was shows a high transmissivity (80–99%) and low absorptivity (<5%) in the visible and near infrared regions at different angles of incidence. Linear optical properties were investigated by classic and Time-Resolved Photoluminescence (TRPL) measurements. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. An innovative TRPL technique has enabled the measurement of the photoluminescence decay time as a function of temperature. TRPL measurements reveal a multiexponential decay behavior typical for amorphous thin films. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm in picosecond regime for investigations of the nonlinear optical properties. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications in the optical switching devices based on refractive index changes. Presented spectra confirm high structural and optical quality of the investigated zinc oxide thin films.     

Strontium and zinc co-substituted nanophase hydroxyapatite

It is well documented that biological hydroxyapatite (HA) differs from pure and synthetically produced HA, and contains of a mixture of calcium phosphate (CaP) phases in addition to a range of impurity ions, such as strontium (Sr²⁺), zinc (Zn²⁺), magnesium (Mg²⁺), fluoride (F^-) and carbonate(CO₃^2-), but to name a few. Further to this, biological apatite is generally in the form of rod (or needle-like) crystals in the nanometre (nm) size range, typically 60 nm in length by 5–20 nm wide. In this study, a range of nano-hydroxyapatite (nHA), substituted nHA materials and co-substituted nHA (based on Sr²⁺ and Zn²⁺) were manufactured using an aqueous precipitation method. Sr²⁺ and Zn²⁺ were chosen due to the significant performance enhancements that these substitutions can deliver. The materials were then characterised using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) techniques. The TEM results show that all of the samples produced were nano-sized, with Zn-substituted nHA being the smallest crystals around 27 nm long and 8 nm wide. The FTIR, XRD and XPS results all confirm that the materials had undergone substitution with either Sr²⁺ and Zn²⁺, for Ca²⁺ within the HA lattice (or both in the case of the co-substituted materials). The FTIR results confirmed that all of the samples were carbonated, with a significant loss of hydroxylation as a consequence of the incorporation of Sr²⁺ and Zn²⁺ into the HA lattice. None of the materials synthesised here in this study contained any other impurity CaP phases. Therefore this study has shown that substituted and co-substituted nanoscale apatites can be prepared, and that the degree of substitution (and the substituting ion) can have a profound effect of the attendant materials’ properties.     

Closed cell ZA27–SiC foam made through stir-casting technique

Closed cell zinc aluminum alloy (ZA27)–SiC composite foam has been synthesized using conventional stir-casting technique and CaH₂ as foaming agent. The synthesized foams are characterized in terms of its micro-architectural characteristics and deformation responses under compressive loading. It is observed that ZA27–SiC foams could be easily foamed without any difficulty. The density of the developed foam ranges from 0.25 gm/cc to 0.45 gm/cc due to the variation of CaH₂ percentage. The plateau stress and energy absorption of these foams follow power law relationship with relative density. Wherein, the densification strain follows a linear relationship with the relative density.