Sharif Digital Repository

Cadmium sulfide (CdS) nanowires and nanorods with different aspect ratios were successfully synthesized by the solvothermal method aided with various solvents, namely ethylenediamine, ethanolamine and triethylene tetraamine. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that, highly pure CdS nanostructures were crystallized with different structures and preferable growth orientations depending on solvent nature. Field emission electron microscope (FE-SEM) images showed that the aspect ratio of CdS nanostructures depends upon the dielectric constant and boiling temperature of solvents. CdS nanostructures with the highest aspect ratio in the form... 

Methyl 3-dimethylamino-2-cyanocrotonate (MDACC) has a remarkably weak carbon-carbon double bond. It has strong electron-withdrawing groups on one end and electron-donating groups on the other: a so-called push-pull ethylene. To investigate this unusual electronic structure, we have determined the crystal structure and measured both the 13C and 15N NMR chemical-shift tensors. These measurements are supplemented by shielding-tensor calculations done with density functional methods. The large difference (approximately 100 ppm) between isotropic chemical shifts of the two alkenyl carbons reflects a large charge release from the electron-donating side of C=C double bond to the... 

This research reports the preparation and examination of Cadmium Telluride (CdTe) Quantum Dots and doping CdTe QDs with Europium (Eu), Gadolinium (Gd), and Manganese (Mn) prepared in aqueous solution using TGA as a capping agent. Magnetic QDs (MQDs) are important agents for fluorescence (FL) /magnetic resonance (MR) dual-modal imaging due to their excellent optical and magnetic properties. Herein, the chemical bonds, structural, fluorescence, and magnetized properties of CdTe QDs and effect of Mn, Eu, and Gd ions doping on their properties were examined by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTM), Energy-dispersive X-ray spectroscopy (EDX),... 

Herein, we report a new strategy for improving the efficiency and reducing the fabrication cost of dye-sensitized solar cells (DSCs) by elimination of the three- or four-fold layer deposition of TiO2. This is performed by replacing a single layer deposition of mesoporous TiO2 beads, with sub-micrometer size, high surface area and tunable pore size, synthesized by a combination of sol-gel and solvothermal methods. Furthermore, superior electronic properties gained by a reduction in electronic trap states are achieved through doping of pristine TiO2 beads with lithium. The beads have a spherical shape with monodispersed texture consisting of anatase-TiO2 nanocrystals and ultra-fine pores. The... 

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 crystal and electronic structures of normal phase of Ba1-xKxFe2As2 for x = 0.0, 0.5 and 1.0 have been studied by using pseudopotential Quantum Espresso code based on ab-initio density functional theory. Effects of K doping on the crystal structure and lattice parameters have been calculated and compared with the experimental and computational reported data for similar compounds. The metal-metal bonding scenario was used to explain the changes of lattice parameters by K doping. The electronic structure of this system including of density of states and band structure have been calculated and investigated by K doping. One of the interesting results is that a larger peak is appeared near the... 

The effect of pulse reverse current (PRC) method on Ni-Mo coatings electroplated from chloride solution was investigated by various plating parameters such as plating duration, the anodic duty cycle, the anodic current density and the cathodic current density. By increasing the anodic duty cycle and anodic current density, the Mo content of coatings reached 68wt.% and 78wt.%, respectively at cathodic current densities of 500 and 300mAcm-2. The Mo content of coatings increases by the preferential dissolution of Ni on the anodic pulse and also by the replenishment of Mo complexes in the diffusion layer near the substrate surface during the anodic pulse. In comparison with the direct current... 

A comparative investigation has been developed for the stability constants of several amino acid complexes with divalent metal ions, which have been determined by potentiometric pH titration. Depending on the metal ion-binding properties, vital differences in the building complexes were observed. The present study indicates that in some M(L) complexes, metal ions are arranged in carboxyl groups, but in other M(L)complexes, some metal ions are able to build chelate over amine groups. The results mentioned-above demonstrate that for some M(L) complexes, the stability constants are also largely determined by the affinity of metal ions for amine group. This leads to a kind of selectivity of... 

Novel ZnO-carbon and ZnO nanofibers were fabricated by electrospinning of polymer precursor followed by subsequent annealing in nitrogen and air, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) indicated the smooth and beadless nanofibers with wurtzite crystal structure. X-ray photoelectron spectroscopy (XPS) showed the presence of oxygen vacancies (VO) and chemisorbed O2 on the surface of the samples. Band gap narrowing of the ZnO-carbon nanofibers in comparison to ZnO were measured by diffuse reflectance spectroscopy (DRS). Photo-degradation of azo dye under the UV and visible light was evaluated and ZnO-carbon showed an enhancement in... 

Azlactones have been prepared via Erlenmeyer synthesis from aromatic aldehydes and hippuric acid using Fe 2O 3 nanoparticles under ultrasonic irradiation. Short reaction times, easy and quick isolation of the products, and excellent yields are the main advantages of this procedure  

A simple method for synthesising W17O47 nanowires on tungsten oxide thin films deposited by sol-gel method on mica substrate has been reported. After thermally annealing thin films at 700 C in H2 ambient for different durations and subsequently in N2 ambient for 60 min, single-crystalline W17O47 nanowires along h0 01i direction were formed on the surface. Experimental results revealed that annealing under H2 ambient has an important effect on the growth of W17O47 nanowires. According to scanning electron microscopic observations, the synthesised nanowires have ∼70 nm in width and a few microns in length after annealing under H2 ambient for 30min and subsequently under N2 ambient for 60min. A... 

Epitaxial cerium oxide (CeO2) buffer layer has been grown on lanthanum aluminate (LAO) single crystal substrates for fabrication of c-axis oriented YBa2Cu3O7-x (YBCO). Precursor solution of cerium acetylacetonates with viscosity of 0.6 centipoises was spin coated on the 1×1 cm area LAO substrates. The calcination was carried out by very slow ramp (1°C per minute) until the final temperature of 500°C in oxygen flow to remove most of the organic compounds. The final heat treatment has been done at 780°C by a ramp of 20° per minute in gas flow of mixed argon-oxygen with 5 Pa partial pressure of oxygen. The thickness of the deposited CeO2 buffer layer was 20 nm. Then, 100 nm thick YBCO film was... 

The morphological manipulation and structural characterisation of TiO 2-MgO binary system by an aqueous particulate sol-gel route were reported. Different crystal structures including pure MgTiO 3, mixtures of MgTiO 3 and TiO 2 and mixtures of MgTiO 3 and Mg 2TiO 4 were tailored by controlling Mg:Ti molar ratio and annealing temperatures as the processing parameters. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that all compounds crystallised at the low temperature of 500 °C. Furthermore, it was found that the average crystallite size of the compounds depends upon the Mg:Ti molar ratio as well as the annealing temperature, being in the range 3-5 nm at... 

A new strategy for enhancing the efficiency and reducing the production cost of TiO 2 solar cells by design of a new formulated TiO 2 paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO 2 compound. Different TiO 2 pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol-gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO 2 paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO 2... 

Atomistic simulation was used to study the deformation and fracture mechanisms of Ni-Si interfaces under tensile and shear loads dependent on the crystal structure of interface zone. Modified embedded atom method (MEAM) potential was utilized for molecular dynamics (MD) modeling. The simulation includes analysis of common neighbors, coordination number, least-square atomic local strain, and radial distribution function. The profound effect of interface crystallography on the tensile and shear deformation is shown. The highest tensile strength is obtained for interfaces with high plane density due to lowest atomic disorder while under shear loading planes with low density exhibit a high local... 

We have investigated the effect of Ca substitution for Sr site on structural, magnetic and superconducting properties of RuSr2 -x CaxGd1.4Ce0.6Cu2O10 -δ system. In this system, the magnetic coupling of RuO 2 and CuO 2 plays an important role in magnetic and superconducting states. X-ray diffraction analysis shows that all samples are single phase and the lattice parameters decrease continuously by increasing Ca content. The onset superconducting transition temperature is found to decrease with Ca substitution. As Ca content increases, rotation of the RuO 6 octahedron increases and RuO(1)Ru angle decreases. These variations strengthen the magnetic moments in the RuO 2 planes. The enhancement... 

We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal slabs. Modes are poles of reflection and transmission coefficients of multilayered structures. According to this principle, modes can be detected by only pursuing phase variations of transmission coefficients that are equal to π rad. Therefore, extraction of modes becomes fast and simple through... 

A simplified model based on cohesive energy is proposed to estimate the formation energy of Schottky vacancies (VFE) in free-standing metal nanoparticles with BCC and FCC crystal structures. To study the effect of particle size and shape, the surface energy, elastic contraction and average coordination number of particles at the surface and core was considered. It is shown that the energy of vacancy formation in FCC nanoparticles increases with decreasing the size while the effect of particle shape (sphere, cubic and icosahedral) is marginal. In spite of this behavior, BCC nanoparticles exhibit a critical particle size at around 25 Å, at which a minimum VFE is attained. Additionally, the... 

A specific structure of doped graphene with substituted silicon impurity is introduced and ab initio density-functional approach is applied for the energy band structure calculation of the proposed structure. Using the band structure calculation for different silicon sites in the host graphene, the effect of silicon concentration and unit cell geometry on the bandgap of the proposed structure is also investigated. Chemically, silicon-doped graphene results in an energy gap as large as 2eV according to density-functional theory calculations. As the authors will show, in contrast to previous bandgap engineering methods, such structure has significant advantages including wide gap tuning... 

The reaction of dithiocarbamic acid salts with trimethyl orthoformate in the presence of BF3·OEt2 was investigated to give 4-(N,N-dialkyldithiocarbamato)-2-dialkyliminio-1,3-dithietane tetrafluoroborates in good yields. Additionally, a one-pot procedure for the synthesis of 2-iminium-1,3-dithiolanes from the BF3·OEt2 catalyzed reaction of dithiocarbamic acid salts with styrene epoxide is described