JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2019 | Volume:13 | Issue:2|Papers Count:8

In this work, the efficiency of inactivation of a cold argon plasma jet at atmospheric pressure (APPJ) on the basis of a lowcurrent spark discharge into microorganisms with different characteristics of the cell walls was evaluated. Gram-negative bacteria Escherichia coli M17, gram-positive bacteria Bacillus subtilis 534 and Bacillus cereus IP 5832, and the yeast Saccharomyces cerevisiae were seeded on cultured Petri dishes. A plasma jet with an average power of 0. 85 W and a flow rate of argon of 6. 7 l/min was directed perpendicular to the Petri dishes with agar. The distance to the agar varied from 0. 5 to 3 cm, and the treatment time varied from 5 to 300 s. The efficiency of inactivation was assessed by measuring the area of inactivation zones (where there was no growth of microorganisms). It was shown that gram-negative bacteria E. coli M17 is most susceptible to exposure to the plasma jet, and gram-positive bacteria B. cereus IP 5832 and yeast S. cerevisiae are most stable. It is established that an increase in the treatment time of plasma jets of a low-current spark allows effective inactivation of microorganisms over a much larger area.

The properties of L10-FePt nanoparticles can be improved in the presence of MgO and Ag interlayers in direct sputtering and annealing method, respectively. Such properties are crystal and compound ordering, nanostructure and crystal orientation. In this work, FePt nanoparticles in ferromagnetic L10-fct phase were synthesized using sputtering method on Ag and MgO layers. According to XRD analyses, the impact of the presence of these two kinds of interlayer on crystal structure and its orientation has been investigated. Furthermore, the effect of the presence of 10% Ag on these properties has been studied and their granular layer nanostructures were characterized through the FE-SEM analysis. The results show that the presence of Ag as nanocompound and interlayer is desirable on declining the transition temperature and controlling the size during annealing. The presence of MgO as a sublayer in direct synthesis leads to the formation of 10 nm monosize smaller nanoparticles. According to VSM analysis, MgO and Ag sublayers have increased the magnetic coercivity of the FePt nanoparticles by 3. 4 times and 3. 7 times, respectively.

Different optical characterization techniques have been performed on a series of microcrystalline silicon thin films deposited using very high-frequency-assisted plasma-enhanced chemical vapor deposition process. The constant photocurrent method has been employed to study the defects states in density of states spectra of hydrogenated microcrystalline silicon thin films. The photocurrent measurements demonstrate anisotropy in the optoelectronic properties of the material. We have analyzed the optical absorption coefficient from UV spectroscopy and with the help of constant photocurrent method. The spectra have been analyzed in broad region and are presented for both the cases, i. e., surface and bulk light scatterings. The spectra were interpreted in terms of disorder, resulting defect density, crystalline/amorphous volume fractions and material morphology. The subgap-related parameters such as absorption coefficient, characteristic energy E0 of tail states and density of subgap defect states together with an estimate of the bandgap of silicon films prepared at various crystalline fractions have also been estimated. The density of localized tail states is found to fall exponentially toward the gap with band tail width of about 110 meV.

In this paper, examples of all types of signal injection such as different signal, harmonic signal and multiple signal injections in a TWT including hollow electron beam near frequency 1800 MHz and within input powers lower than TWT saturation power has been analyzed using approximate analytical solution of S-MUSE model. Later, the results obtained from approximate analytical solution with large signal code LATTE, that is a Lagrangian model, have been tested and simulated so that the effect of input phase difference between drive and injected wave and the effect of input powers on the amplification value of drive and generated second-order harmonic waves were investigated. The phase difference between drive and harmonic waves is a key parameter in harmonic injection for increasing the output power of drive and second-order harmonic frequencies.

Al-doped ZnO (AZO) thin films are deposited on glass substrate by sol– gel spin coating using zinc acetate dihydrate as a precursor with different molar concentrations varying from 0. 35 to 0. 75 mol/L. To investigate the structural, electrical, optical and morphological properties of AZO films, XRD, four-point probes, HE measurement, UV– Vis spectrometry and SEM with EDX are used. Thickness of the thin film is measured by a surface profilometer. The structural characteristics show a hexagonal wurtzite structure with a (002)-preferred orientation. Optical study reveals that transmittance is very high (up to 90%) within the visible region and optical band gap, Eg varies from 3. 25 to 3. 29 eV with Zn concentration. The carrier concentration increases and resistivity decreases with the increase in Zn concentration. Thin films fabricated with 0. 75 mol/L of Zn concentration exhibit the best electrical property. SEM study shows non-uniform surface of the films where EDX confirms the formation of AZO. The results revealed by this study prompt a high interest to use AZO as transparent conductive oxide for advanced applications such as displays, solar cells and optoelectronic devices.

Because of the interesting features of the organic/inorganic halide perovskite (e. g., CH3NH3PbX3, X = Cl, Br) materials, such as long electron– hole diffusion length, high absorption coefficient and adjustable band gap, they have attracted a great deal of attention. In this research, CH3NH3PbX3 (X = Br, Cl) are synthesized and perovskite-based single-layer and perovskite-based bilayer diodes are fabricated. Using electron beam deposition technique, thin films of CH3NH3PbX3 (X = Br, Cl) hybrids with excellent homogeneity are manufactured. Absorption spectrum, X-ray spectrum and photoluminescence spectrum of organic/ inorganic halide perovskites along with electroluminescence spectra, SEM micrographs and current– voltage characteristic of perovskite-based light-emitting diodes are investigated. Perovskite-based bilayer diodes are evaluated for the first time. The difference between the emission wavelengths of single-layer and bilayer diodes is the main characteristic of bilayer diodes.

The main goal of this work is to find natural rock materials that can be used as effective gamma rays shielding at minimal cost, reliability and wide applications. It must be at particular weight and volume (lighter and more protection). Natural bentonite clay can be used as shelters from nuclear waste because of its large availability and low cost. Bentonite clay was used in two forms naturally as it is from its ores and in ground phase. Natural bentonite was cut into cylindrical pellets at different thicknesses; also, the other form pressed into cylindrical pellets with different thicknesses and different pressing pressures (50, 100 and 150 bar). The different samples are coated with polyvinyl alcohol polymer to prevent nuclear waste leakage through porosity of clay. Chemical analysis and density are measured for all samples. Bentonite clay was found naturally in nanometer scale because it is formed from volcanic ash deposits. The nanoparticle size was determined by dynamic light scattering and Williamson– Hall size analysis using XRD patterns and the help of X-powder program. The particle size of natural bentonite was found to be 59. 79 nm. The microstructure was characterized by scanning electron microscope and transmission electron microscopy. The linear and mass attenuation coefficients of nano-structured bentonite clay (natural and pressed) were determined at 662 keV energy of 137Cs; at 1173 and 1332 keV energies of 60Co, gamma ray sources were determined by using NaI(Tl) scintillation detector. The experimental results showed that the ground bentonite pressed at 150 bar gave the highest linear and mass attenuation coefficients than other samples. The theoretical and the experimental calculations of mass attenuation coefficient were found to be in a good agreement.

In the present study, the optical characterization of borate glasses with composition 35Li2O − 10ZnO − 55B2O3 − xMnO2: x = 0, 0. 5, 1. 0, 1. 5, and 2. 0 wt% has been investigated. The absorption spectra measurements within the wavelength domain 200– 1000 nm have been carried out. The optical energy gap of the investigated samples using the absorption spectrum fitting (ASF) model has been calculated. The molar refraction, molar polarizability, reflection loss, optical transmission for the samples were estimated. The metallization criterion, dielectric constant, refractive index, and energy band metallization criterion for the studied glasses were estimated. Magnetic property measurements for all glass samples were carried out at 300 K. Additionally, the prospects of gamma-ray interactions with the investigated glasses have been achieved through studying the total mass attenuation, coherent, Compton, photoelectric, and pair production interactions at photon energy in the range of 0. 356– 1. 330 MeV. Results reveal that the optical and magnetic properties of the investigated glasses change with changing the MnO2 concentration. Studied glasses can be used as a candidate for optical fiber and optical devices application. In the other hand, at lower gamma photon energy range, the photoelectric absorption dominates with the glasses, while as the energy increases, the probability of Compton scattering and pair production become the most dominate interactions.