Sharif Digital Repository

The interesting properties of metallic and semiconductor nanowires provide many applications in electronic and optoelectronic devices. In this project, we have synthesized Cu and CdSe nanowires using electrodeposition method. To adjust deposition bath conditions and characterize the structure of deposit first we prepared CdSe thin film on ITO substrates. The used solution was contained 0.1 M CdSO4+ 0.1 mM SeO2 in the acidic situation with pH=2.5. The best reduction potential was determined about -0.5 V. The XPS and XRD analyses showed that the ratio of cadmium to selenium in the films was 1:1 and the film’s structure is amorphous. Optical band gap of the cadmium selenide films was obtained... 

Different molybdenum oxide nano/micro structure thin films were synthesized by thermal evaporation method under various growth conditions such as deposition time, temperature and evaporation source-substrate distance. Molybdenum oxide nanostructures grown on Si(100) such as nanowalls, nanostars and nanowires were characterized with scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). Shape and type of nanostructures were determined with SEM, AFM and HRTEM analysis. XPS analysis showed that the synthesized nanostructures contained Mo6+, Mo5+, Mo4+ and... 

Platinum nanowires were prepared by electrodeposition in polycarbonate membrane, with different average diameter of nanowires about 15, 50 and 100 nm and the height about 6 µm. Kinetics of electrodeposition process were studied by electrochemical techniques such as voltammetry and chronoamperometry methods. Diffusion coefficient was then calculated from the electrochemical parameters and consequently the density of primer nuclei was extracted. The morphology of Pt nanowires was characterized by SEM, TEM and EDX. The results show that growing Nanowires on the surface of template is branch-like. The electro-oxidation of methanol and hydrogen on this electrode is investigated at room... 

Electrochemical supercapacitors are the charge-storage devices having high power density.The materials in the nano-size form with high surface area and high porosity give the best performances as the electrode materials for supercapacitors because of their distinctive characteristics of conducting pathways, and nanoscale dimensions. Therefore, the synthesis and the capacitive characterization of the high surface area nanomaterials such as nanotubes, nanowires,etc, have been carried out extensively in the past few years. In this research Polyaniline nanowires were electrochemically deposited on stainless steel electrode with the technique of Choronoamperometry and pulse Voltammetry and... 

In this work, mechanical behavior of Ni nanowires with various dimensions under tensile loading at different temperatures and strain rates was simulated by molecular dynamics. Lennard-Jones and Sutton-Chen potential functions were utilized. The relationship between the tensile properties of Ni nanowires and temperature, strain rate, aspect ratio and crystal orientation was studied. It was shown that with increasing the aspect ratio of the nanowires the strength of the material decreases. A change in the fracture mode of the nanowire from slippage at low strain rates (<10 m/s) to amorphous deformation at high loading rates was observed. The crystal orientation was found to influence the... 

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... 

By considering the effect of surface/interface stress, classical problems of the interaction between dislocations and inhomogeneities are addressed. Especifically two distinct problems are solved, the first one is consisted of an edge dislocation located near an elliptical nano-inhomogeneity and the second one hasa screw dislocation laid in the core-shell nanowire. The stress field as well as the image force on the dislocation are calculated and discussed in detail. Results show that by decreasing the dimension of the problem to nano-scale, the differences between classical elasticity and surface approachincrease rapidly. By considering the effect of the surface/interface stress, new... 

Dye-sensitized solar cells were introduced by M. Gratzel in 1991. These solar cells have a power conversion efficiency of about 12% over the AM1.5 full sun. Traditionally, a liquid electrolyte redox system is used to regenerate the dye. Due to stability issues, a solid hole transport material has been employed to replace the liquid electrolyte as an attempt to create solid-state Dye-sensitized solar cell (ssDSC). Over past few years power conversion efficiency of ssDSCs has improved considerably and reached over 7%.
Here, ss-DSCs based on TiO2 nanoparticles as photoelctrode and P3HT as hole transport material were fabricated and characterized. We used three different methods; dip... 

Phase transformation in Ni-Ti shape memory alloys (SAM) have been investigated quite frequently due to their shape recovery by thermal cycling. With emerging of nanotechnology, the martensitic/austenite phase transformation in SAM at nanoscale has become of interest for MEMS and NEMS applications. In this work, molecular dynamic simulation (MD) was utilized to study the phase transformation and shape memory effect in Ni-Ti nanowires. EAM/Alloy and EAM/FS potential functions were used. The potential energy versus temperature and time for the phase transformation was calculated and combined with the radius distribution function (RDF) in order to study the changes in the crystal structure.... 

In this project, the equilibrium structure of clamped-free silicon nano-beams is investigated using molecular dynamics (MD) simulations. Four main interatomic potentials for silicon nanostructures, i.e. Tersoff, MEAM, Stillinger-Weber and EDIP, are implemented in the current study. Using aforementioned potentials, the structural stability of Si nano-beams are studied and effects of thickness, width, length, size, lattice direction, facets of cross section, and temperature on the equilibrium structure of nano-beams are investigated. The conducted simulations demonstrate that equilibrium structure of nano-beam is completely dependent on the type of atomic potential used for modeling.... 

Li-ion batteries have been widely applied as power sources for portable electronic devices. Recently, Li-ion batteries are considered as the most promising energy storage technology for electric vehicle applications however, fundamental improvements are needed. TiO2 (B) is attractive candidate for anodes in rechargeable Li-ion batteries, due to their low cost, non-toxicity and favorable channel structure for fast lithium mobility. It is predicted that synthesis of doped nanostructure of this material, through reducing the diffusion pathway and formation of crystal defects, will increase the capacity of TiO2(B). In this investigation, Co and V doped TiO2(B) nanowires are synthesized by... 

Amongst different methods for synthesis one-dimensional TiO2 nanostructures, hydrothermal process has various advantages such as use of water as growth media and can be defined as an environmentally friendly processing. Hydrothermal processing parameters including processing temperature and time, nature of titanium source and its primary particle size, concentration of titanium source, drying temperature, annealing temperature and re-hydrothermal process have significant influence on crystal structure and morphology of the final product. These parameters were investigated in the present study. Therefore, five different titanium sources including three TiO2 powders and two TiO2 sols as well... 

In this research, two type of graphene quantum dots (GQDs) have synthesized including, normal GQDs and nitrogen-doped GQDs (N-GQDs). Then, each of GQDs were deposited on the 1 dimensional zinc oxide (ZnO) nanostructures namely nanowires (NWs) and branched hierarchical (BH) systems. Then, photocatalytic activity of the samples were studied in photodegradation of methylene blue (MB) and methylene orange (MO) under visible light. First, ZnO nanowires (ZnO NWs) were fabricated by anodization of zinc sheet possessing wurtzite crystal structure with their average length and diameter measured in the range of 50-60 μm and 170-300 nm, respectively. Then, normal GQDs were synthesized by... 

Titanium dioxide (TiO2) is a transparent n-type semiconductor with wide band gap which makes it suitable for applications such as solar cells. TiO2 dye-sensitized solar cells (DSSCs) transform the visible light energy to the electrical energy by excitation of absorbed dye. In the present study, TiO2 nanowires and nanoparticles were synthesized by hydrothermal and sol-gel methods, respectively. The effect of TiO2 morphology on photovoltaic performance of the cells was studied by fabrication of single layer DSSCs containing pure nanowires, pure nanoparticles and mixture of nanowires and nanoparticles with various weight ratios. The results revealed that, DSSC made of 10 wt% nanowires and 90...