Sharif Digital Repository

The main purpose of this theses is to synthesize graphene by chemical vapor deposition (CVD) of a hydrocarbon gas such as methane on the nickel foam substrate and then to characterize this kind of graphene. Graphene is a single layer of carbon atoms, discovered in 2004, which has led mankind to new eras in all fields by its extraordinary features such as extra high electron mobility, high thermal conductivity, excellent mechanical strength, optical transparence and extra high specific surface. The advantage of this method compared to other methods is that the graphene generated has a better structural quality. Graphene foam firstly, because of the continuity of the foam structure, has better... 

Titanium nanoparticles were synthesized by chemical vapor condensation (CVC) process. Titanium tetrachloride (TiCl4) as titanium’s precursor reacted with potassium as reductant, in vapor phase and the products were titanium nanoparticles encapsulated in potassium chloride. Dried Argon gas was employed as carrier gas. Resulting powders gathered in ethanol bath. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic adsorption spectroscopy (AAS) analysis were used to characterizing the products. The effect of Argon gas flow on nanoparticles size was investigated in this research. The particle size decreases with increasing Argon gas flow. The size of nanoparticles was under... 

For realization of nanosale photonic device required by the future system, electron beams, and scanning probe microscopes have been used to control the site on the subtrate. However, these techniques have a fatal disadvantage because they cannot deal with insulators and Diffraction of light, limiting their application.To overcome this difficulties, we design and implement near-field optical chemical vapor deposition, which enables the fabrication of nanometer-scale structure, while controlling their position. To guarantee that an optical near field is generated sufficiently, we fabricated a sharped W-tip by electrochemical etching. The separation between the W-tip and the substrate was kept... 

The chemical vapor deposition (CVD) of graphene from methane on a copper substrate is the most promising method for production of large-area graphene films. There have been long-standing challenges in this field such as controlling the graphene coverage, film quality, the number of layers, and the nucleation density of graphene domain. These challenges can be overcome by developing a fundamental understanding of the graphene growth process. The main aim of this study is to control nucleation density of graphene domains. Chemical vapor deposition (CVD) graphene is polycrystalline, and grain boundaries in graphene film have been identified to degrade the properties of graphene as a membrane... 

One of the most important world issues is environmental constraints regarding the pollutants released by transportation fuels and refinery products, sulfur reduction being one of the most significant objectives. Deep hydrodesulfurization processes result in great sulfur reduction in refinery streams. However, such harsh process conditions increase undesired side reactions and facilitate coke formation as well as affecting the surfaces. More effective alternatives for hard process conditions are highly active and selective hydrodesulfurization catalysts, which enable the process to be performed at milder pressure and reaction conditions. Catalyst bases play a very important role in hydrogen... 

Carbon-based thin films possess low friction coefficient, low surface roughness, chemical inertness and outstanding biocompatibility. In the present work, TiO2 nanoparticles were covered by a thin film of pyrolytic carbon (PyC) to provide a core-shell morphology. The PyC film was deposited by dehydrogenation of methane in a fluidized bed chemical vapour deposition (FBCVD) reactor at 1100 °C. The prepared specimens were characterized by various analytical methods including XRD, SEM, TEM, AFM, TGA and contact angle measurement techniques. Biocompatibility profiles of the resulting materials were evaluated using MTT and cell cycle assay. The results showed that the thin carbon film strongly... 

Graphene based photodetectors which are modified with quantum dots, are the new generation of detectors. In these supplies an integration of graphene’s unique characteristics like high conductivity and mobility and the high light absorption of quantum dots, are used.In this research graphene by chemical vapor deposition in centimetric large scales, tungsten disulfide quantum dots, boron nitride and graphene quantum dots and 2D tungsten disulfide have been synthesized. In the next step each of them were characterized to modify the quality of used layers in heterostructure.Based on the characteristic tests, quantum dots aspect ratios were 1 to 5 nanometers. Also tungsten disulfide was obtained... 

The fabrication of future electronic and optical devices will require advanced nanofabrication techniques that realize high spatial resolution and high precision in controlling size and position, and that are applicable to various materials. Near-field CVD (NF-CVD) was proposed to solve these problems with no need to perform nanolithography prcesses. NFCVD system has two major subsystems, first vacuum chamber and gas distribution system for delivering parent gases to the chamber and second, a nanopositiong system to keep the probe and the sample in the constant systems.In this dissertation we have set up a piezoelectric nanopositiong system and its driver modules. The positioning accuracy... 

In this study three different methods; hot filament chemical vapor deposition (HFCVD), pulsed laser ablation (PLA) and electrochemical deposition were utilized to prepare catalyst thin films or nanoparticles and thermal chemical vapor deposition (TCVD) was used to grow multiwall carbon nanotubes (MWCNTs). We found that even though the three mentioned techniques have been rarely applied by researchers, they are appropriate and efficient methods to produce catalytic basis for CNT growth. In the TCVD step, liquid petroleum gas (LPG) was applied as carbon source. Although, this gas is a mixture of different hydrocarbons and further contains some sulfur, our results verify that utilizing of LPG... 

Nowadays, silicon based devices especially carbon nanotubes received lots of attentions and advancement from researchers and industries. Because of amazing electrical and mechanical properties and wide range of applications, CNTs are received a lot of attention from nanoelectronics experts. There are lots of CNT growth methods such as: Arc Discharge, Laser Ablation, Surface Decomposition, CVD and PECVD.
In this thesis, we are going to use PECVD method to synthesis CNT. A typical PECVD system includes two parallel electrodes that have been packed in vacuum chamber and gases like argon, hydrogen and NH3 are introduced to chamber as a reactant gas.
In this thesis, firs we had fixed... 

In this work, a novel type electrode based on RuO2 nanoparticles-modified vertically aligned carbon nanotubes (RuO2/MWCNTs) was investigated. ThisRuO2/MWCNTs electrode not only shows a high capacity nature,but also possesses a good response to the pH value. In order to develope this sensor, aligned carbon nanotubes were synthesized by the chemical vapor deposition at first and then modified with RuO2 nanopartcles by sol-gel method. Various parameters affecting the growth of nanotubes, such as substrate type, surface finishing, surface roughness, the growth temperature and carbon feed rate was studiedand and optimal conditions for growth were obtained. At last, aligned nanotubes with a...