Sharif Digital Repository

The need for further improving the operation of the electronic and optoelectronic devices to raise the speed of the circuits, and to decrease their power dissipation, has led many researchers to investigate the structure of 2D material, such as graphene, transition metal dichalcogenides (TMDs) as MoS2, and other 2D compounds such as BN, due to their prominent electronic properties. TMDs have the highest significant potential for the next generation transistors due to their salient semiconductor characteristics such as electron mobility, band gap, and conductivity. For instance, Graphene is a favorable candidate for analog devices due to zero bandgap. Regarding the importance of bandgap in... 

In this research, molybdenum and tungsten catalysts modified with cobalt and nickel on a carbon support have been synthesized and investigated in the oxidation desulfurization process. A model fuel was used to evaluate the synthesized catalysts. This model fuel was n-decane. dibenzothiophene was also used as a sulfur model. The synthesized catalysts were subjected to various analyzes such as XRD, FTIR, Raman, BET-BJH, NH3-TPD, TEM and ICP-OES for structural evaluation. On the other hand, synthetic parameters such as metal loading rate, molar or weight ratio of secondary metal (cobalt and nickel) to primary metal (molybdenum and tungsten) and molar ratio of citric acid to primary metal as... 

A global concern has arisen owing to rapid industrial development and population growth, resulting in energy scarcity and earth pollution. In this regard, developing green and sustainable methods for producing clean energy and solving environmental pollution problems have absorbed enormous attention. Among various auspicious strategies, semiconductor photocatalysis has been widely studied in recent years owing to its capabilities to obtain hydrogen as an energy carrier, to remove organic pollutants, and to reduce CO2 emission by converting solar energy into chemical energy. Recently, a metal-free semiconductor photocatalyst based on graphitic carbon nitride, g-C3N4, has received much... 

In this dissertation, Hydrogen storage in the solids based was investigated. The carbon-based structure used is the graphene that decorated with metal atoms to increase intermolecular interactions and increase the adsorption weight capacity. The structure of graphene has been considered due to its properties such as low density, high heat transfer coefficient and high specific surface area. Initially, the structure of pure graphene was investigated using the molecular dynamics method for hydrogen storage and it was shown that the interaction between hydrogen molecules and pure graphene is very weak and it can’t be a good option for use in cars. Then, the structures of graphene reinforced... 

To account for certain essential features of material such as micro-structure effects and dispersive behaviour and optical branches in dispersion curves, a fundamental departure from classical elasticity to generalized continuum theories is required. Among the generalized continuum mechanics, micromorphic elasticity is capable of capturing these physical phenomena completely. In the mathematical framework of micromorphic elasticity, in addition to the traditional elastic moduli tensors, some additional tensors are introduced in the pertinent governing equations of motion. A precise evaluation of the numerical values of the aforementioned elastic moduli tensors in the realm of the... 

Unique properties of Gold at nanoscale have made it one of the most popular substances used in nanotechnology. The interaction of Gold and Thiolates is one of the most favorite fields of research. Extensive studies about this interaction have revealed the importance and usage of this system in future technology. Due to difficulties of experimentationat nanoscale, computer simulations arevery important. Although interatomic potentials lead to higher computational speeds, they have deficiencies in precise simulation of some phenomena. Ab-initio methods, such as density functional theory, provide powerful tools to increase the accuracy. In this research, the interaction of gold and thiolates... 

Density Functional Theory is one of the most robust Ab-intio methods for describing the structural and electronic properties of a wide range of materials. The ability to predict the material properties changes due to targeted material manipulation at the atomic scale has reduced the cost of many empirical experiments. It has improved the knowledge and understanding of the investigation and producing new materials and devices. Tow dimensional heterostructures are highly regarded due to their unique optoelectronic properties, potential application in nanoelectronic devices, energy storage devices, solid-state devices, and photovoltaic devices. In this study, the two-dimensional materials... 

In this study, orthosilicate materials with chemical formula of Li2MSiO4 (M one or two transition metal/metals) were investigated experimentally and theoretically as cathode material of Li-ion batteries. The most important material in this category i.e. Li2FeSiO4 was synthesized by three methods including nitrate-based sol-gel, oxalate-based solid state reaction and oxide-based solid state reaction. Based on XRD and SEM evaluations, grain size of synthesized powders was estimated to be between 15 to 100 nanometers. Of these three methods, oxide-based solid state reaction was employed in this study for the first time. This syntheses method is very important due to the significant lower... 

Sulfur dioxide is known as an acidic gas and one of the standard pollutants in determining air quality. This gas mostly enters into the atmosphere by flue gas causing many environmental problems. In order to remove this gas, various methods are used. One of the suitable methods to reduce the emission of this pollutant in low concentrations is the use of Metal-Organic Frameworks (MOF) as an adsorbent. One of these Metal-Organic Frameworks is NH2-MIL-53(Al) that owing to its relatively good stability under wet and acidic conditions, has been chosen to adsorb sulfur dioxide in this research. In most studies on SO2 adsorption, often MOFs with a long synthesis time, high synthesis cost, and/or... 

Position sensors are an integral part of electric machine control systems. There are different ways to determine the position. The most common methods are using resolvers or optical encoders. Resolver is the recommended in harsh environments where there is wide temperature variation, vibration, and dust. Despite their good features, resolvers face challenges such as eccentricity, short circuit fault, single-phase disconnection, and non-ideal signal voltage. The Resolver chosen in this research is the variable reluctance resolver with variable air gap length. Although this type of resolvers is cheaper than wound rotor resolvers, but its position error is high under electrical and mechanical... 

The purpose of this research is to introduce a heterostructure for Vertical Tunneling Field-Effect Transitors, calculating its band structure and finding the tight binding hopping parameters of its structure. To do this, we must first study different kinds of heterostructures and choose the most suitable one among them. In this research, we selected the three-layer graphene eSoM2-BN-Gr_h for its high on/off current ratio (〖10〗^6). To find the band structure, first we should construct unit cell and then find its crystal structure after relaxation. The lattice constant for graphene and is the same, but the lattice constant of graphene andeSoM2-BN-Gr_h is different . The number of atoms in the... 

In this thesis the effects of impurities and different defects on electrical and magnetic properties of monolayer and bilayer graphene is investigated. Calculations are performed using density function theory. Alloying monolayer graphene with boron and nitrogen the energy gaps of 0.7 and 0.6 eV are obtained, respectively. Moreover, we show that BN is a good candidate for opening the band gap in graphene. Alloying monolayer graphene with BN the energy gap of 1.2 eV is obtained. Another way of opening band gap is to somehow break the symmetry between layers of the bilayer graphene. By alloying one layers of bilayer graphene with B, N or B-N, although the symmetry of layers is broken, each... 

In this paper effect of Nitrogen and Boron doping on the quantum conductance of semiconductor carbon nanotubes is investigated. Calculations are performed using density function theory in conjunction with Green function techniques and the quantum conductance is calculated. Transmission and conductance of the electronic devices in nanometer scale depend on band structure and density of states. Our results show that quantum conductance of semiconductor carbon nanotube is increased by replacing Nitrogen and Boron in its structure. The value of increasing conductance depends on the type of impurity. It is greater for Nitrogen doping in comparison with Boron. Effect of strain on the quantum... 

The sustainable development in societies and the global energy challenge requires usage of clean energy systems that have attracted the attention of many researchers in recent decades. One of the major challenges in generating renewable resources is the problem of energy storage and imbalance between supply and demand cycles. Hydrogen as one of the clean energy carriers and due to having the highest energy density in terms of weight, is one of the important research topics. From this point of view, the preparation of electrocatalysts for hydrogen production, based on available materials, via simple and environmentally friendly production methods, was considered in this research.... 

The ternary 122-type AeFe2As2 (Ae=Ba,Sr,Ca) compounds are antiferromagnetic metals with the orthorhombic lattice structure at ambient pressure and low temperature. By applying mechanical pressure, structural, magnetic and superconducting transitions occur in these compounds. The isovalent doping of Ba with Sr and Ca elements induces chemical pressure and reduces the onset pressure of these transitions. The main purpose of this thesis is to investigate and compare the effects of mechanical and chemical pressures on the structural and magnetic phase transition in the 122 compounds. To achieve this purpose, we have done first-principle calculations for many properties such as the structural... 

In this thesis the structure and potential energy surfaces of Lidocaine and bupivacaine were studied by DFT method at B3LYD level calculation using 6-311++G basis set. Both compounds were calculated in water, dimetylsulfoxide, and carbontetracholoride as the solvent using the PCM model.Since the molecules meant to be studied were polar, level of energy in polar solvent is higher than non-polar solvent . The most considerable increase was observed in the amount of energy at 0.01 hartree for water compared with carbon tetracholoride. By changeing in solvent environment the most considerable difference in bond length was observed as 0.01 Ǻ.The spin spin coupling constants 1JCH, 2JCH, 2JHH,... 

The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing. 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states. Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) investigations suggest that silicon vacancy point defects in SiC possess properties similar to those of the NV center in diamond. We provide a new theoretical frame to explain a wider range of experimental results. Employing a proposed generalized Hubbard model, with the help of electronic structure programs, DFT, second quantization, and various computational approaches, we obtain new... 

In this research, Synthesis, characterization and photoelectrochemical application of two dimensional MoS2 and WS2 nanosheets have been carefully investigated. And finally, based on theoritical and experimental analysis results, the mechanisms of the observed photoelectrochemical (PEC) activities were suggested.The ab initio density functional calculations about Mo1-xWxS2 monolayer deposited over a TiO2 (110) substrate revealed a shift in band position of the Mo1-xWxS2 in favor of photoelectrochemical water splitting. Moreover, increase of W concentration in Mo1-xWxS2 could improve the charge separation and increase the effective mass ratio leading to an extension of the electron–hole... 

Optimized structure of the chlorophyll a and b molecules was obtained for LDA and GGA approximation by SIESTA package. Calculation illustrate that tails are curved in the optimized structure for both chlorophyll a and chlorophyll b molecules; in addition, Antennas, which are attached to the head of molecules, are located in optimized-spatial state. This optimized structure of chlorophyll a is similar to the calculated structure in ref [42]. Electrical dipole are calculated from ground state electron density of chlorophylls. Total electrical dipole of chlorophyll a for GGA and LDA approximation are 4.662 and 4.813 Debay, and these value for chlorophyll b are 1.435 and 1.302 Debay,... 

Iron based superconductors that are studied more in recent years, have the same and different features with copper oxide high temperature superconductors which they can help in solving problems related to high temperature superconductors. In addition, these compounds have attractive physical characteristics such as superconductivity despite of presence of magnetic Iron element or other magnetic elements like nickel and cobalt (In other superconductivity groups, low doping of magnetic elements destroys superconductivity) and also concurrent presence of magnetic and superconductivity phases. The most reported transition temperature in these compounds is 56.3K in Gd0.8Th 0.2FeAsO compound....