Sharif Digital Repository

The interesting properties of metallic nanowires provide many applications in electronic sensors. In this project, we have synthesized Pd nanowires using electrodeposition method. These nanowires are useful for hydrogen sensors by measuring field ionization current in gas. In this project, Pd nanowires were synthesized by electrochemical deposition method in PCT template with 100 nm pore size. The used solution was contained 2mM PdCl2 + 0.1M HCl. The best reduction potential was determined about -0.2V and the best time for synthesizing nanowires was 7 minutes. Chronoampermetric diagrams showed four steps, capacitive current, growth in the holes, reaching to the surface of PCT and the growth... 

Recently, the applications of two dimension materials have been increased in nanotechnology. Among this group of material the Transition metal dichalcogenide due to their energy gap and their particular optical features has attracted much attention. For instance MoS2 is a most famous material in this familyand as a semiconductor has an indirect energy gap about 1.3 eV in the bulk status and 1.9 eV in monolayer. In this project, we investigated the Nano-sheet optical properties of MoS2 by using of tunneling spectroscopy. In this procedure a thin probe is close to the surface until a quantum tunneling occurs between the probe and the sample. By measure the tunneling current we can achieve much... 

In this thesis, adsorption of Carbon monoxide and Hydrogen on graphene, by DFT calculation has been studied. Also effect of strain on some electrical properties, such as band structure, electrical conductivity and Density of states, for pristine graphene and adsorption CO and H2 on it has been probed. This results show that with strain up to 12% on pristine graphene , we won’t have any band gap on Fermi surface and energy adsorption for Carbon monoxide on strained graphene (up 12%) increase up 400 per cent. Also for strained graphene (12%) on Carbon monoxide adsorption condition we will have energy band gap almost a few electron volt on Fermi surface. In general this results express... 

In recent decade energy crisis causes research on luminescent devises gains special importance. Particularly, hybrid LEDs (organic- nanocrystal) have been studied by a number of researches due to their advantages. Easy fabrication and narrow spectrum of radiation are mentioned as the most important benefits. The emissive layer is the most important part in these diodes which made of semiconductor nanoparticles. There are a variety of chemical methods for synthesis of semiconductor nanoparticles. We focus on aqueous method for nanoparticles synthesis because of its advantages. Alloyed semiconductor nanoparticles of ZnxCd1-xS were selected for this research work. The manifest features of the... 

In this thesis, gas sensors were fabricated based on resonance frequency shift of quartz crystal with covering of polymer fibers and carbon nanostructure materials.¬ Sensing materials were used in two different types of polyvinylpyrrolidone (PVP) and Graphene oxide. Electrospining was used as an efficient, simple and low cost approach for producing polymer and composite fibers with 280nm to 4um diameters. In addition, the effects of changing various parameters such as the concentration of polymer solution and electrospining process time were investigated. Images taken with a scaning electron microscope indicated that the concentration of polymer solution effectively can affect morphology,... 

In this research, metal oxides and hydroxides with carbon materials and conductive polymers (CPs), as well as transition metal oxysulfide nanostructures (TMOS), hybrid of Tin oxide and sulfie and polyphasphate-reduced graphene oxide (PPO-RGO) have been used as an active electrode materials for supercapacitors. In the first section of thesis, Tiron and graphene oxide (GO) were used as an anionic dopants to increase the capacity and stability of polypyrrole (PPy). In order to increase the capacity of Tiron/PPy/GO nanocomposite, vanadium oxide (V2O5) was used. The Tiron/PPy/GO/V2O5 nanocomposite was deposited on a stainless steel (SS) as a substrate via one-step electrochemical deposition... 

Dye-sensitized solar cells (DSCs) are third generation of solar cells, which composed of a porous layer of wide band gap semiconductor such as TiO2, covered with a molecular dye that absorbs sunlight, and a counter electrode contacted by a liquid redox electrolyte. Photovoltaic performance is the collective measure of light harvesting, charge separation and charge collection efficiencies. Light harvesting has a significant role in improvement of photovoltaic performance. Molecular engineering of dyes to improve absorption spectrum or to have a broad absorption spectrum,andlight scattering layes are approaches for this porpuse. This research is focused on photon management in DSCs using... 

This study tries to introduce chemical coatings to reducing evaporation from Lake Urmia(LU). In LU, average annual evaporation is estimated at more than 1,000 mm, more than 80% of evaporation occurring in the warmer months of the year. Therefore, by reducing water evaporation, especially in the warmer months of the year, the most crucial factor in water outflow from LU can be reduced.At first, on the scale of class A evaporation pan in Tehran, three kinds of chemical coatings constituted stearic acid, jojoba oil, and fatty alcohols of style and stearyl to reduce evaporation from the LU is investigated. Then the best coating that includes combine of style and stearyl alcohols with stearic... 

Molybdenum disulfide (MoS2) nanoflakes, a two-dimensional crystal with tunable bandgap depends on number of layers, is a promising candidate for future nanoelectronic devices. In the present research, flower shaped MoS2 nanoflakes have been synthesized via hydrothermal method. As part of the research, the growth of triangular MoS2 monolayer up to 10 micrometers has optimized by carring out several chemical vapor deposition experiments with varying deposition parameters. The prepared samples were characterized using optical, scanning electron, and atomic force microscopes, x-ray diffraction analysis, and Raman spectroscopy. Based on the experimental results, the growth mechanism has been... 

Reducing water evaporation is one of the ways to overcome the low precipitation and drought conditions in water reservoirs. For this purpose, extensive studies have been investigated on physical and chemical coatings on lakes and reservoirs. Physical methods often involve the use of floating covers on the water surface to block evaporation by shading, most of which are only suitable for reservoirs with surface areas smaller than 5 hectares. In chemical methods, the evaporation can be decreased by nanomaterial coating, usually, containing long-chain molecules, which by spraying them on the surface, molecular monolayers are formed. In this study, the effect of nanometer coatings on the surface... 

Developing a simple, cost effective and accurate detection method for L-lysine (Lys), L-leucine (Leu) and glycine (Gly) as the important analytes in clinical diagnostics, biological processes and food industries is of great interest. Therefore, in the first part of this research, cellulose nanofibrils (CNFs) were coated on a quartz crystal microbalance (QCM) surface by spin coating to achieve a QCM biodetector for Gly. Thus, the two-layer CNFs coating was selected as sensing film and was applied for following experiments. In the next step, the coated QCMs were carefully characterized before and after interaction with Gly using water contact angle (WCA), Fourier transform infrared... 

Two-dimensional nanostructures can significantly absorb solar irradiation, due to diverse energy levels, large effective surfaces, layered and porous structures with adjustable physical and chemical properties. Mono and multilayers of graphene, as the first isolated 2D materials with special band-structure of a zero-band gap, along with impressive optical properties, tunable light interaction, and adjustable optical properties by chemical doping or structural defects, have great potential for the next generation of nanophotonic devices. So, graphene is an appropriate candidate for absorption, frequent reflection, and energy conversion of electromagnetic waves at the frequency range of the... 

Electrical arc discharge in ambient air, vacuum, reactive gas and other environment is an appropriate method for synthesis of different nanostructures. This method can provide stable and ultra pure nanostructures with diverse applications. In this research we focus on synthesis and analysis of titanium nitride nanoparticles in liquid nitrogen(lack of oxygen)by Electrical arc discharge . At the beginning a reactor for the electrical arc discharge process designed and implemented. Titanium nanoparticles have synthesis by this method analyzed. Several characterization techniques such as X-ray diffraction (XRD), dynamic light scattering (DLS), X-ray photo electron spectroscopy (XPS), scanning... 

Production of nano-particles using arc-discharge method in a liquid nitrogen environment is a proficient way of forming nitride Particles whose formation by other methods is difficult and expensive. Amongstall, Titanium nitride (TiN) is of significant importance because of its high formidability and its optical and electrical metal properties due to plasmonic electrons. This research studies the production of titanium nitride Nano-particles using arc-discharge method and investigates optical properties and features, specially dielectric constant and optical extinction coefficient. Modeling interband Transitions is also discussed to revise Drude's electron theory. First, in experimental... 

Organic light emitting diodes (OLEDs) are one of the main subjects of research in the organic electronic advanced technology. There are many advantages for OLEDs like self-emitting, high efficiency, wide vision angle, high contrast, and rapid response time. The main challenge in this area is the long-time stability of performance in air ambiance. Although the encapsulation process could overcome the instability problem, it increases the final cost. In this project, metal oxides have been utilized for the injection of electrons and holes in hybrid light emitting diodes (HyLEDs). In the first stage, inverted structure of HyLEDs with ZnO and MgxZn1-xO layers was fabricated and characterized.... 

Ionic polymer metal nanocomposites (IPMNCs) are among the advance materials which have been widely used recently as smart materials. These nanocomposites, which are made of polymeric layers (Nafion) plated by metallic or non-metallic conductive electrodes, show large deformations under low applied voltages. The advance materials like these nanocomposites have resolved the problems of the conventional actuators and helped in producing accurate systems.
Several methods have been used to predict the behavior of IPMNCs which any of them consider some simplifying assumptions. In these materials physical phenomena happen at the molecular scale and deformations observed at the large scale.... 

Oxygen gas has many applications and is used in respiration, welding, methanol production, steel industry, rocket fuel and most importantly fuel cells. Today, due to the environmental pollution caused by fossil fuels, the use of clean energy production methods such as fuel cells has received much attention. In hydrogen fuel cells, electrical energy is generated using oxygen and hydrogen gases through an electrochemical process. One of the common methods of producing these gases is electrolysis of water in which the kinetics of anodic reaction (oxygen evolution) have led to many researches in the field of improving metal and non - metal electrocatalysts, especially based on carbon...