Sharif Digital Repository

Semiconducting lead sulfide film was deposited on Stainless Steel (SS) electrode by cyclic voltammetry (CV) at room temperature. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry were used to investigate the electrochemical properties of PbS film in Na2SO4 solution. The voltammetric results showed that oxidative dissolution of PbS film occurred at about 0.21 V vs. Ag/AgCl and total film detachment from the surface occurs with increasing potential. It is concluded that the electrode surface was not passivated by sulfur produced from oxidative dissolution of PbS film. Also, cathodic reduction of the film continued to beyond the hydrogen evolution at -1.35 V vs. Ag/AgCl.... 

A Bandgap circuit capable of generating a reference voltage of less than 1 V with high PSRR and low temperature sensitivity is proposed. High PSRR achieved by means of an improved current mode regulator which isolates the bandgap voltage from the variations and the noise of the power supply. A vigorous analytical approach is presented to provide a universal design guideline. The analysis unveils the sensitivity of the circuit characteristic to device parameters. The proposed circuit is fabricated in a 0.18μm CMOS technology and operates down to a supply voltage of 1.2 V. The circuit yields 20 ppm/°C of temperature coefficient in typical case and 50 ppm/°C of temperature coefficient in worst... 

Titanium dioxide is a cheap, chemically stable and non-toxic material. However its photocatalytic properties are unstable and it is a modest semiconductor and a mediocre insulator. For several applications it would be interesting to make it either more insulating or more conducting. The goal of this work was to modify the photocatalytic properties of nano-crystalline TiO2 powders by wet chemical routes and hydrothermal methods to understand the mechanism leading to these modifications The principal factors that influence the photocatalytic properties are on the one hand the concentration and nature of the chemical and physical conditions in TiO2, and on the other hand the morphology of the... 

Nowadays, gasochromic Pd/WO3 coatings as optically switchable materials have become more applicable for hydrogen sensors and smart windows. In this study, WO3 films were prepared by Pulsed Laser Deposition (PLD) and spin-coating sol-gel techniques. For deposition of Pd, first a layer of PdCl2 was obtained via a simple drop-drying process by dropping PdCl2 solution onto WO3 substrates and drying them at room temperature. Then Pd nanoparticles were synthesized via hydrogen gas exposure that causes reduction of the PdCl2 layer. According to Scanning Electron Microscope (SEM) observations before hydrogen reduction, many individual nanoparticles or fractal-like constructions of palladium were... 

Carbon nanotubes were electrodeposited in acetonitrile solution at room temperature using Cu, and Fe-Ni nanoparticles as nucleation sites on HF-etched Si(100) wafer substrate. The electrochemical behavior of the deposition was investigated by voltammetry and chronoamperometry techniques. In order to obtain the optimum growth condition, the deposition critical parameters including current density range, potential and time were studied and calculated. Carbon nanotubes with approximate external diameter of 40-100 nm were fabricated under potentiostatic condition and diffusion control at - 20 V in 4-6 h. The film crystallinity was investigated by means of X-ray diffraction and the tubes... 

By co-deposition via RF-Sputtering and RF-PECVD methods and using Cu target and acetylene gas, we prepared Cu@Cu2O coreshell nanoparticles on the a-C:H thin film at room temperature. Mie absorption of Cu cores, scattering from Cu2O shell and luminescence that rises from carrier transfer in Cu@Cu2O interface were employed to fit the whole range of visible extinction spectrum of these coreshells. From simulation it was found that scattering and luminescence have an important effect on the energy, width and shape of LSPR absorption peak. Shift of LSPR peak is more affected by the dielectric coefficient of shell than Cu core size particularly for Cu core diameter above 4 nm. Also, the LSPR... 

A polymeric manganese(II) complex with the general formula [Mn(O 2CCH2NH2CH2CO2) 2(H2O)2]n from reaction of iminodiacetatic acid and manganese(II) perchlorate under nitrogen in water, was synthesized and characterized. The structure of the complex was determined using single-crystal X-ray diffraction, elemental analysis, IR and UV-vis spectra. This complex exhibited excellent catalytic activity and selectivity for oxidation of various alcohols and sulfides to the corresponding aldehydes/ketone and sulfoxides using urea hydrogen peroxide and oxone (2KHSO 5·KHSO4·K2SO4), respectively, as oxidants under air at room temperature. The easy preparation, mild reaction conditions, high yields of the... 

Bismuth ferrite, BiFeO 3, is almost the only material that is simultaneously magnetic and a strong ferroelectric at room temperature. As a result it is the most investigated multiferroic material. In this study, bismuth ferrite thin films were deposited on silicon wafer (100) and glass by pulsed-laser deposition and their structural, optical, and electrical properties were measured. Our study indicates that Bi richness in these films can stimulate formation of oxygen vacancy in the system which in its turn leads to delocalization of carriers and a more intensified photoconductivity response. X-ray diffraction analysis revealed formation of BiFeO 3 (BFO), but it also showed formation of Bi 2O... 

There are many works on annealing process of SPDed bulk metals but there are limited works on annealing process of SPDed sheets. Therefore, in this study the annealing response after constrained groove pressing (CGP) of low carbon steel sheets has been investigated. These sheets are subjected to severe plastic deformation at room temperature by CGP method up to three passes. Nano-structured low carbon steel sheets produced by severe plastic deformation are annealed at temperature range of 100 to 600 °C for 20 min. The microstructural changes after deformation and annealing are studied by optical microscopy. The effects of CGP strain and annealing temperature on microstructure, strength and... 

The ZnO nanowires have been synthesized using vapor-liquid-solid (VLS) process on Au catalyst thin film deposited on different substrates including Si(1 0 0), epi-Si(1 0 0), quartz and alumina. The influence of surface roughness of different substrates and two different environments (Ar + H2 and N2) on formation of ZnO nanostructures was investigated. According to AFM observations, the degree of surface roughness of the different substrates is an important factor to form Au islands for growing ZnO nanostructures (nanowires and nanobelts) with different diameters and lengths. Si substrate (without epi-taxy layer) was found that is the best substrate among Si (with epi-taxy layer), alumina and... 

In this study, the effect of film preparation conditions on the gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films (containing 18 and 28wt% vinyl acetate) was investigated. Film blowing and phase inversion methods were applied in the production of PE and EVA films, respectively. The permeation of pure oxygen and carbon dioxide gases was measured at room temperature. The results indicated that with the increase of PE film thickness, permeability and solubility of O2 and CO2 in these films decreased; but the diffusivities of gases through PE films increased. In addition, in the case of EVA copolymers, by increasing the content of vinyl acetate, the... 

In order to define a new temperature correction factor in this study, accurate experimental values were presented for permeability and diffusivity of carbon dioxide and methane in imidazolium-based room temperature ionic liquid: [bmim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) immobilized on an inorganic membrane support. Results were presented as a function of temperature and pressure for temperatures within 300-320K and pressures below 50kPa. According to the literature, experimental values of permeability and diffusivity for CH4 in [bmim][PF6] vs. temperature are reported for the first time in this study. Results obtained for CO2 permeability revealed good agreement with data... 

We prepared Cu nanoparticles in a-C:H thin films by co-deposition of RF-sputtering and RF-PECVD methods at room temperature. By increasing Cu content in these films a nonmetalmetal (NM) transition is observed. This transition is explainable by the power law of percolation theory. The critical metal content is obtained 56% and the critical exponent is obtained 1.6, which is larger than the exponent for 2 dimension systems and smaller than the one for 3 dimension systems. The electrical conductivity of dielectric samples was explained by tunneling. Activation tunneling energy that was obtained from temperature dependence of electrical resistivity correlates with near infrared absorption peak... 

In this paper, considering the problems of common finite element (FE) codes that consider simple constitutive equations, a developed FE code that considers a new constitutive model is used to simulate the behavior of copper sheets under severe plastic deformation (SPD). The new proposed constitutive model, that considers dislocation densities in cell interiors and cell walls of material as true internal state variables, can investigate all stages of flow stress evolution of material during large plastic deformations and also can explain the effects of strain rate magnitude on the mechanical response of material, during room temperature SPD. The proposed FE analysis is used to investigate the... 

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150-220 °C range as a function of time initially shows linear mass... 

The synthesis of functionalized benzothiadiazine 1,1-dioxide derivatives was achieved through a novel three-component intramolecular C–H activation reaction of trichloroacetonitrile, benzenesulfonyl chloride, and various primary amines. This reaction was performed in the presence of catalytic copper(I) and L-proline as the ligand in tetrahydrofuran at room temperature. © 2018 Elsevier Ltd  

An automated technique based on purge-and-trap coupled to gas chromatography with mass spectrometric detection has been developed and optimized for the trace determination of five of the most important water odorants; 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, 2,4,6-trichloroanisole and geosmin. The extraction method was absolutely solvent-free. Analytes were purged from 20 ml of water sample containing sodium chloride at room temperature by a flow of He and trapped on a Tenax sorbent. The desorption step was performed with helium and temperature programming and desorbed analytes were directly transferred to a gas chromatograph coupled to a mass... 

Background: Hepatitis B virus surface antigen (HBsAg) is an important protein in both diagnosis and prevention of hepatitis B infection. In the current study, a piezoelectric immunosensor based on antibody-antigen interaction was designed to detect HBsAg. A quartz crystal microbalance system was employed to detect antibody-antigen interaction. Methods: At first, an oscillator was designed to measure the resonant frequency affected by the reactants using IC 74LVC1GX04. Antibody against HBsAg was immobilized on 10 MHz AT-cut quartz crystal. The surface modifications were monitored by atomic force microscopy (AFM) and contact angle measurements. Different concentrations of antibody were used... 

Tunable microwave absorption characteristics are highly desirable for industrial applications such as antenna, absorber, and biomedical diagnostics. Here, we report BiNdxCrxFe1-2xO3 (x = 0, 0.05, 0.10, 0.15) nanoparticles (NPs) with electromagnetic matching, which exhibit tunable magneto-optical and feasible microwave absorption characteristics for microwave absorber applications. The experimental results and theoretical calculations demonstrate the original bismuth ferrite (BFO) crystal structure, while Nd and Cr injection in the BFO structure may cause to minimize dielectric losses and enhance magnetization by producing interfacial defects in the spinel structure. Nd and Cr co-doping plays... 

The novel coumarin-3-carboxamides (=2-oxo-2H-1-benzopyran-3-carboxamides) 5a-5g containing lipophilic spacers were synthesized through the Ugi-four-component reaction (Scheme 1). The reactions of aromatic aldehydes 1, 4,4'-oxybis[benzenamine] or 4,4'-methylenebis[benzenamine] as diamine 2, coumarin-3-carboxylic acid (=2-oxo-2H-benzopyran-3-carboxylic acid; 3), and alkyl isocyanides 4 lead to the desired substituted coumarin-3-carboxamides 5a-5g at room temperature with high bond-forming efficiency. These novel coumarin derivatives exhibit brilliant fluorescence at 544 nm in CHCl 3