Review on Zinc Oxide Nanoparticles: Antibacterial Activity and Toxicity Mechanism

Antibacterial activity of zinc oxide nanoparticles(Zn O-NPs) has received significant interest worldwide particularly by the implementation of nanotechnology to synthesize particles in the nanometer region. Many microorganisms exist in the range from hundreds of nanometers to tens of micrometers. Zn O-NPs exhibit attractive antibacterial properties due to increased specific surface area as the reduced particle size leading to enhanced particle surface reactivity. Zn O is a bio-safe material that possesses photo-oxidizing and photocatalysis impacts on chemical and biological species. This review covered Zn O-NPs antibacterial activity including testing methods, impact of UV illumination, Zn O particle properties(size, concentration, morphology, and defects), particle surface modification, and minimum inhibitory concentration. Particular emphasize was given to bactericidal and bacteriostatic mechanisms with focus on generation of reactive oxygen species(ROS) including hydrogen peroxide(H2O2), OH-(hydroxyl radicals), and O2-2(peroxide). ROS has been a major factor for several mechanisms including cell wall damage due to Zn O-localized interaction, enhanced membrane permeability, internalization of NPs due to loss of proton motive force and uptake of toxic dissolved zinc ions.These have led to mitochondria weakness, intracellular outflow, and release in gene expression of oxidative stress which caused eventual cell growth inhibition and cell death. In some cases, enhanced antibacterial activity can be attributed to surface defects on Zn O abrasive surface texture. One functional application of the Zn O antibacterial bioactivity was discussed in food packaging industry where Zn O-NPs are used as an antibacterial agent toward foodborne diseases. Proper incorporation of Zn O-NPs into packaging materials can cause interaction with foodborne pathogens, thereby releasing NPs onto food surface where they come in contact with bad bacteria and cause the bacterial death and/or inhibition.

Hydrogen Gas Sensor Based on Nanocrystalline SnO_2 Thin Film Grown on Bare Si Substrates

In this paper, high-quality nanocrystalline SnO_2 thin film was grown on bare Si(100) substrates by a sol–gel method. A metal–semiconductor–metal gas sensor was fabricated using nanocrystalline SnO_2 thin film and palladium(Pd)metal. The contact between Pd and nanocrystalline SnO_2 film is tunable. Ohmic barrier contact was formed without addition of glycerin, while Schottky contact formed by adding glycerin. Two kinds of sensor devices with Schottky contact were fabricated(Device 1: 8 h, 500 °C; Device 2: 10 h, 400 °C). The room temperature sensitivity for hydrogen(H_2) was120 and 95 % in 1000 ppm H_2, and the low power consumption was 65 and 86 l W for two devices, respectively. At higher temperature of 125 °C, the sensitivity was increased to 195 and 160 %, respectively. The sensing measurements were repeatable at various temperatures(room temperature, 75, 125 °C) for over 50 min. It was found that Device 1 has better sensitivity than Device 2 due to its better crystallinity. These findings indicate that the sensors fabricated on bare Si by adding glycerin to the sol solution have strong ability to detect H_2 gas under different concentrations and temperatures.

Composition Dependence of Surface Phonon Polariton Mode in Wurtzite InxGa1-xN （0 ≤ x ≤ 1） Ternary Alloy

We present a theoretical study on the composition dependence of the surface phonon polariton （SPP） mode in wurtzite structure α-InxGa1-xN ternary alloy over the whole composition range. The SPP modes are obtained by the theoretical simulations by means of an anisotropy model. The results reveal that the SPP mode of α-InxGa1-xN semiconductors exhibits one-mode behaviour. From these data, composition dependence of the SPP mode with bowing parameter of-28.9 cm^-1 is theoretically obtained.

Effects of CW CO₂Laser Annealing on Indium Tin Oxide Thin Films Characteristics

In this work ITO thin film annealing was carried out using a CW CO2 laser beam for ITO thin film annealing over a 1 cm2 area with a temperature higher than 250°C to obtain ITO grains with excellent structural quality thin films. The obtained ITO films were characterized for crystallization, surface morphology, electrical and optical properties, which has theoretical significance and application value. ITO thin films are deposited on glass substrates by sputter coater system (RF) from a high density target (In2O3-SnO2, 90-10 wt%). After deposition, ITO thin films have been irradiated by CW CO2 laser (λ = 10.6 μm) with power ranging from 1 to 10 watt. These films were annealed at temperatures 250°C, 350°C, and 450°C in the air for 20 minutes using different laser power. The main incentive was to develop a low temperature process for ITO thin films, which typically required a 350°C anneal to crystallize and achieve optimum optical and electrical properties. The XRD results showed that 350°C temperature laser annealing could crystallize ITO with a strong (222) preferred orientation and its grain size increased from 29.27 nm to 48.63 nm. The structure, optical transmission, energy gap, resistivity and sheet resistance of the ITO thin films were systematically investigated as a function of laser post annealing temperature. It was found that the lowest resistivity was 2.9 × 10-4 Ω-cm and that sheet resistance was 14.5 Ω/sq. And the highest optical transmittance (98.65%) of ITO films was obtained at 350°C annealing temperature.

Interaction between Kaolin and Urea in Organoclay and Its Impact on Removing Methylene Blue from Aqueous Solution

Interaction between kaolin (particle size 53 and 106 μm) and urea was studied by infrared spectroscopy and powder X-ray diffraction. Interaction was found to be dependent on the particle size of kaolin raw material. Nature of interaction achieved through the formation of hydrogen bonds between urea and both AlOH and Si-O surface of kaolinite. Effect of temperature on equilibrium adsorption of methylene blue (MB) from aqueous solution using kaolin also studied, the results were analyzed by Langmuir and frendlich isotherms. Thermodynamic parameters such as ΔG, ΔH and ΔS were calculated. Results suggested that the MB adsorption on kaolin was spontaneous and exothermic process.

Effect of TiO₂Thin Film Morphology on Polyaniline/TiO₂Solar Cell Efficiency

Nanocrystalline titanium dioxide (TiO2) thin films were prepared by using sol-gel through spin- coating method. An assembly of indium tin oxide (ITO)/TiO2/polyaniline (PANI)/Ag was made in a sandwich panel structure. The obtained junction shows rectifying behavior. Additionally, the I/V characteristic indicates that a P-N junction at nanocrystalline PANI/TiO2 interface has been created. In this experimental study, we depended only on the ratio between titanium and PANI in the process of preparing sol-gel (PANi/TiO2 at 20% wt). The largest open circuit voltage of 656 mV and short current density of 0.00315 mΑ/cm2 produce 0.0004% power conversion solar cell (η) under simulated solar radiation (50 mW/cm2). The thin films of PANI and titanium oxide (TiO2)/ PANI composites were synthesized by sol-gel technique. Pure TiO2 powder with nanoparticle size of less than 25 nm and PANI were synthesized through chemical oxidative polymerization of aniline monomers. The composite films were characterized by high resolution X-ray diffraction, Fourier transform infrared spectroscopy, field effect scanning electron microscopy, and UV-vis spectroscopy. The results were compared with the corresponding data on pure PANI films. The intensity of diffraction peaks for PANI/TiO2 composites is lower than that for TiO2. The characteristic of the FTIR peaks of pure PANI shifts to a higher wave number in TiO2/PANI composite, which is attributed to the interaction of TiO2 nanoparticles with PANI molecular chains.

InGaN/GaN laser diode characterization and quantum well number effect

The effect of quantum well number on the quantum efficiency and temperature characteristics of In- GaN/GaN laser diodes （LDs） is determined and investigated. The 3-nm-thick In0.13Ca0.87N wells and two 6-am-thick GaN barriers are selected as an active region for Fabry-Perot （FP） cavity waveguide edge emitting LD. The internal quantum efficiency and internal optical loss coefficient are extracted through the simulation software for single, double, and triple InGaN/GaN quantum wells. The effects of device temperature on the laser threshold current, external differential quantum efficiency （DQE）, and output wavelength are also investigated. The external quantum efficiency and characteristic temperature are improved significantly when the quantum well number is two. It is indicated that the laser structures with many quantum wells will suffer from the inhomogeneity of the carrier density within the quantum well itself which affects the LD performance.

A study of the operating parameters and barrier thickness of Al_(0.08)In_(0.08)Ga_(0.84)N/Al_xIn_yGa_(1-x-y)N double quantum well laser diodes

The operating parameters such as the internal quantum efficiency （η）, internal loss （α） and transparent threshold current density （J0） of double quantum well laser diodes were investigated and identified using the program, Integrated System Engineering-Technical Computer Aided Design （ISE-TCAD）. Various thicknesses （6, 7, 8, 10, 12 rim） of AlxInyGa1-x-yN barriers with （3 nm） Al0.08In0.08Ga0.84N wells as an active region were studied. The lowest threshold current （lth）, and the highest output power （Pop） were 116 mA and 196 mW respectively, at barriers thickness of 6 nm, Al mole fraction of 10% and In mole fraction of 1%, at an emission wavelength of 359.6 nm.

Far Infrared Optical Properties of Bulk Wurtzite Zinc Oxide Semiconductor

Polarized far infrared （FIR） reflectance technique was applied to study the optical properties of a bulk wurtzite zinc oxide （ZnO） single crystal. Room temperature polarized FIR reflectance spectra were taken at various angles of incidence, from 20°to 70°. The theoretical polarized FIR reflectance spectra were simulated based on the anisotropic dielectric function model. Good agreement was achieved between the experimental and the theoretical FIR reflectance spectra. Through this work, a complete set of reststrahlen parameters of a bulk wurtzite ZnO at the Brillouin zone centre was obtained. Additionally, other FIR optical properties such as the real and the imaginary parts of the complex dielectric function, real and imaginary parts of the refractive index, the absorption coefficient and the reciprocal of the absorption coefficient were also obtained by using numerical calculation.

Laser-induced etching parameters impact on optical properties of the silicon nanostructures

Porous silicon (PS) was fabricated by laser-induced etching (LIE) process. The objective of this study is to investigate the selected LIE parameters to control size and shape of nanostructures,which are considered important factors in semiconductor device applications. Photoluminescence output intensity becomes stronger due to the increase in the number of emitted photons on the porous surface. There is a dramatic increase in photoluminescence intensity due to the increase of porosity as a function of laser power density. The increase in electrolyte concentration is an important parameter to accelerate the dissolution reaction on the interface layer between the electrolyte solution and wafer surface. PS spectra displayed a stronger Raman intensity than crystalline bulk Si;also the PS spectrum was shifted and broadened as a function of LIE parameters.

Effects of Nitridation Temperature on Characteristics of Gallium Nitride Thin Films Prepared Via Two-Step Method

In this research,the growth of GaN thin films on c-plane sapphire（0001） substrates via two-step method without the assist of buffer layer and catalysts was demonstrated.First,gallium oxide（Ga_2O_3） thin films were deposited on sapphire substrates by radio frequency magnetron sputtering method.The deposited Ga_2O_3 thin films were then nitridated at various temperatures.In this research,attention is focused on the influence of nitridation temperatures on the structural and optical properties of the synthesized GaN thin films.It is revealed that 950 ℃ is the optimal nitridation temperature for synthesizing hexagonal wurtzite GaN thin film with preferential（0002） growth direction.