In this research, zinc oxide nanorods are synthesized by two approachs; solvothermal method and thermal decomposition method, and studied their structural and optical properties. The main precuesor for both processes is zinc acetate dehydrate. Using hydrothermal method, zinc oxide nanorods are coated by zinc sulfide (ZnS) and converted to ZnO/ZnS core/shell nanorods. For this purpose thioacetamide is used to replace oxygen atoms with sulfur atoms. Then the optical properties of core/shell nanorods are also studied by ultraviolet-visible spectroscopy (UV-Visible) and photoluminescence photometry (PL). Results show that optical properties of coated nanostructures by secondary material, with larger band gap, improve. Following, polymer nanofibers containing zinc oxide nanorods are produced by electospinning method. In this process utillized polymer is polyvinyl alcohol (PVA). For alignment of nanofibers containing nanorods, twe parallel collectors with different distances are used. The applied parameters in electrospinning process are: 15 cm for distance between nozzle and collector, 25 kV for devices voltage and 0.3 ml/h for injection rate of solution. In general, the scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible spectroscopy and photoluminescence photometry are used to investigate different properties of nanofibers and nanorods.

Belonging to single-dimensional nanomaterials and with unique structures, Hollow nanofibers have become the focus of many researchers in the last few decades. In addition to having an outer surface, these type of nanofibers have also include an interior surface, which make them potential structures for applications in many different applied fields. In this project, with the goal of fabricating SnO2 hollow nanofibers and studying their structural and optical properties, single-needle electrospinning method has been employed. With proper control of electrospinning conditions, composite nanofibers, including polymer and salt precursor, were first produced and finally, by adjusting the increase rate of calcination temperature hollow nanofibers were fabricated. Also, the mechanism governing the formation of tubular-shaped fibers, in particular, was studied. At the end, the structural and optical properties of hollow nanofibers of Tin dioxid were investigated. For analyzing and investigating the nanofibers properties, different techniques including Scanning Electron Microscopy (SEM), Filed Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), Fourier Transform Infrared spectrometry (FT-IR), UV-visible spectrometry and photoluminescence spectroscopy (PL) are employed. The results show that the hollow nanofibers diameters are in the range of 200-300 nm at 600°C calcination temperature. It should be noted that in this thesis, the photocatalytic properties of the resulting fibers for the removal of two toxic dyes, as one of the most important applications of hallow nanofibers of Tin Dioxide, have also been investigated, results of the tests are presented.

One of the major issues in Nanotechnology is the ability to align the nanostructures. Among these structures, aligned nanofibers have found many applications in the science and technology .From different methods of production of such nanofibers, electrospining method, for its simplicity, controllability, cost and possibility of large scale production, has attracted many research and industrial groups. The goal of our research has been to produce and study aligned ribbons and yarns of YBa2Cu3O7-δ ceramic nanofibers. The result of this research will be presented in this thesis. Three methods are used to align nanofibers; two parallel electrode, a rotating cylinder and rotating disc. TGA and DTA analyses are used to study of the optimum sintering temprature of nanofibers. Morphology structural properties of nanofibers are studied by scanning electron microscopy (SEM),¬ X-ray diffraction (XRD) and Fourier transform infrared spectroscopy(FTIR).Magnetic properties of samples are also measured by ac magnetic susceptibility method .Results indicate nanofibers produced by rotating disk are very well aligned in comparison to the two other methods Finally, result of production of twisted superconductor yarn with fiber size of 100 nm and length of 2 cm will be also presented.

In this thesis, ZnO nanofibers with different morphologies such as mats and yarns are produced by electrospinning method. Zinc acetate and polyvinylpyrrolidone are used to producte composit nanofibers. The fibers are heat treated first in oven and then in furnace. For Electrospinning of aligned fiber two different collecting set up, one a grounded plate and the others rotating disk are examined. Electrospinning parameters of these two set-up 15cm distance between nozzle and grounded plate, 5cm distance betweene nozzle and rotating disk, high voltage of 20kV, constant flow rate of 0.3ml/h. After preparation, structural and optical properties of ZnO yarns have been studied. For this purpose, TGA, SEM, XRD, FTIR, UV-Visible and PL analysis are carried out. The results show that the ZnO twisted yarns at with an average diameter about 80-150nm with unique characteristic can be fabricated.

  Nanotechnology has opened up a new research area for investigators. Nano-optics is an important fields discussed in the nano nanotechnology. Modulation doped quantum wells (MDQW) have been an important research topic in nano-optic during the last two decades. MDQW has wide applications in ultrafast optoelectronic devices such as semiconductor lasers and infrared detectors. Nanoscale physical phenomena can be studied using quantum mechanic rules and numerical simulations.
In this thesis, we study and investigate the effect of laser radiation on optical properties of doped quantum well. The potential that governed such system when irradiated by laser beam, that is called dressed potential, can be extracted from floquet theory.
Here at first we use this theory to calculate the dressed potential by analytical methods, then by substituting this potential in schrodinger equation and using selfconsistence solution of schrodinger and poisson equations in hartree approximation by numerical methods we have obtained energy levels and eigen functions. By using this results and equations of nonlinear optics, changes in optical propertiesof the system are studied. Results show that potential profile in presence of laser radiation is subjected to a large variation and subsequently wave functions and energy levels of the system have been changed. This changes have caused shift in resonance peaks of optical properties in system.

 

 Electron guns are considered important and useful devices in atomic and molecular physics. In general, an electron gun includes parts such as an electron source, extracting and accelerating electrods and also focussing lenses. In this study, a low energy electron diffraction system with thirteen electrodes is designed and simulated. Simion 3D software version¬ 7.0 has been used for this study. To underestand and characterize the gun and achieve the best operating parameters involving gun’s electrodes, different parts of the gun has been studied separately, and the effect of energy and distribution of electrons is also investigated. We have also studied the effect of temperature in the source on the performance of the gun.
Finally, the performance of complete electron gun system is simulated and the best operating parameters are achieved. The results will be presented in this thesis.

Abstract: One of the most common methods for evaluation of products dealing with charged particles interaction with material surface is electron spectrometer. Electron spectrometer consists of different components, one of which is energy analyzer. So far, various types of electron energy analyzers, for use in electron spectroscopy and each with its own characteristics, have been designed and constructed. In this thesis, after the introduction and study of different types of electrostatic analyzers, the detailed relationships the two most important one's; the cylindrical mirror analyzer (CMA), and cylindrical deflecting analyzer (CDA), are discussed. Afterward, the CMA has been chosen for simulation and characterization using Simion Software version 7. By selecting initial operating parameters of CMA, including the energy and entrance angle of electron beam, maximum entrance angle and initial diameter of beam, applying appropriate potential, performance of CMA is investigated. Also, the effect of distance between CMA electrode on the electron beam trajectory in the analyzer has been studied. In addition to improve the performance a new type of CMA geometry with a third electrode is designed and studied. The simulation results of this structure are compared with two electrode geometry. Results indicate a better focussing at the output of CMA as well as about 41.0138% improvement in overal performance of the new system. Results also indicate adding a third electrode will have no affect on the efficiency the electron beam transfer.

Electrospining is one of the methods used in producing polymer fibers in nano scale. This method is mostly considered valuable for its simplicity, quality control and high accuracy. In this research, first the electrospun polymeric nanofibers of poly(methyl methacrylate) have been produced. Then the effects of the most important parameters such as PMMA concentration in the polymeric solution, the distance between the nozzle head and the collector and the applied voltage on fibers diameter have been studied. The morphology of electrospun nanofibers has also been studied by SEM. In order to analyse the physical interference of methylene blue dye and PMMA the FTIR test was taken and then with the help of UV spectrophotometer the maximum absorption of dye was measured. Finally the stability of the dyed nanofibers were analysed through the flourometer method.
Upon completion of the experiments, it was concluded that the decrease in the polymer concentration, the distance between the nozzle head and the collector and an increase in the voltage results in nanofibers with smaller diameters (up to 133nm). The results of FTIR had indicated surface absorption of the dye by polymer molecules. The flourometric results showed that the intensity of fluorescent in nanofibers would not change in time and only a slight decrease in fluorescent intensity (less than 8.9%) were observed. Finally results show the PMMA nanofibers make a suitable and stable platform for methylene blue.
 

 With numerous application of electron beams in electron-optic systems such as spectrometers and-electron lithography systems, a precise study of the physical behavior of the beams is important. Space charge is one of the most important factors affective on electron beams. However, this effect is ignored in order to avoid its complexity in electron-optic systems. But space-charge effect plays an important role in many applications of high density electron beams. Therefore In this study, first we will study the principles of the electron optic, the electron sources, and the production methods of electrons. This is followed by the study of different aberrations in electron optics systems. Then we will study and simulate the formation of space charge region. Then we will simulate a thermionic cathode and study the effect of the cathode temperature and different size of anode radius, on the current that is limited by the space charge effect. At the end with regard to this study, a typical electron gun will be designed, simulated and finally optimized

semiconductor quantum dots, because of their electronic structures and controllablity of their shapes and sizes, are highly regarded. One of the most interesting subjects in quantum dots field is the ability to have tunable optical emission frequency caused by quantum confinement effect. In these Thesis, first we study quantum dots and then due to the abundant use of quantum dots in solar cells, we study the properties of these dots embedded in silicon di-oxide matrix. The study is performed based on the application of the effective mass approximation framework and solving schrodinger differential equation for electrons in conduction band of silicon and zinc oxcide quantum dots in dielectric matrixes. Then, linear and nonlinear optical properties of intersubband of these dots, such as linear and nonlinear susceptibility, refractive index changes and absorption coefficient have been studied. Also, the effect of different dielectric matrixes, including oxide, carbid and nitride matrices has been checked on quantum dots. At the end, the stark effect on a silicon quantum dots in a silicon dioxide matrix is investigated.

This thesis present a details description of a new type Quantum Dots Sensitized Solar Cells (QDSSC) based on ZnO nanofibers as their photo anodes. For its ease of operation and controllability on related parameters, Electrospinning has been used in production of these nanofibers. The thesis will report on CdS quantum dots made by SILAR technique. Also, it will report on production of Cu2S layers on conductive glass FTO as cathodes.
For production of nanofibers a simple configuration of electrospinning technique with defined parameters is used. The ZnO nanofibers with average diameter of 350 nm are fabricated on a conductive and transparent FTO substrate. In order to understand the effect of heat treatment on production of ZnO nanofibers from electrospun fibers, the fibers are heat treated in different temperatures of 450, 500, 550, 600 and 700 °C. The data analyses have revealed that the temperature of 500°C is the best fitted temperature on structure, size and diameter of the ZnO nanofibers. The effects of adhesion between nanofibers and substrate (FTO) on efficiency of QDSSCs have also been investigated. Three adhesion methods, namely aqueous solution, Dr Blade and PEG, are used for this investigation. The results will be discussed. Also, the effects of the numbers of SILAR procedures on structural properties and the efficiencies of the solar cells are studied and their results will be presented. In this regard, quantum dots of different sizes with the least of 4¬nm diameter will be reported. Finally, the studies of crystallographic, structural and optical properties of nanofibers and quantum dots as well as efficiencies of solar cells, performed with different analytical techniques such as XRD, SEM, TEM, UV-Visible and solar simulator, are presented.
 

Abstract:Today, Nanofibers are very attractive structures among researches of different disciplines for their high sensing capabilities, and their usages in producing electronics components as well as optical fiber devices. In this thesis, we have investigated the modes propagation of electromagnetic waves (EM) into an optical waveguide. For this study, the propagation of an EM wave into an electrospun polymer nanofiber with diameters of 200, 400 and 600 nm are investigated. The input range of wavelengths, for these calculations, is in optical range of 400-680 nm. Characteristic parameters in EM propagation in waveguides such as poynting vector, total electric energy, electric and magnetic fields are studied. The results show that for shorter wavelengths and smaller diameters the calculated values of these parameters are higher in comparison to their values for longer wavelengths and larger diameters. The results of simulation in 660-nm-wavelength show that in the range of 200-410 nm of nanofiber diameter, the fundamental mode of HE11, so called a single-mode waveguides, is generated. The above simulations are done on nanofibers with clear surface with no porosity. For making structures of these nanofibers close to those that are made by electrospinning method, we have first set porosity along the length of these nanofibers, and then have repeated the above simulations for 200 and 600 nanometer diameters. As a result of this investigation it is shown that porous nanofibers have higher values of poynting vector and also higher total energy densities compare to non-porous nanofibers. Therefore, it is concluded, because of porosities, the electrospun nanofibers exhibit notable features compare to those of non–porous structures in transporting EM waves in waveguides.

 

Today, the interaction of ions with solid surfaces has found many applications for surface analysis in microscopic and spectroscopic studies. In this thesis, the interactions of ions and electrons with different surfaces are studied. 5000 Ga ions are selected and their interactions are studied with Carbon and Copper surfaces in the range of 110 nm and 80 nm, respectively. Also the interactions of 4000 He ions with Silicon surface in the scale of 900 nm are studied. These surfaces have been studied and investigated in terms of their relative masses with respect to those of incoming ions. Following, with regards to comparison between ions and electrons interaction, the interaction of 10000 electrons with Carbon, Copper and silicon surfaces are investigated. The study of ions and electrons beams interactions with surfaces has been performed using SRIM-TRIM version 2013 and CASINO version 2013 softwares, respectively. The effects of beams energy and interaction angle have been investigated and compared. Finally, from the results of simulation of Ga ions interactions, the desired energy ranges equal to 0.5 up to 30 KeV, for use in microscopic and spectroscopic studies have been obtained. With the goal of causing minimum damage to the target surface, the reasonable angle range for Ga ions from 0 to 30 degree has been obtained.The accepted values of energies and angles for use of He ions in ion microscopes are in the range of 25 to 70 KeV and 45 to 90 degrees (with respect to vertical line), respectively. In the interaction of electrons with surfaces energy range of 0 to 50 KeV is also reasonable. This can be the best applicable range of energy in the study of surfaces for electron microscopes. The results show that for high contrast pictures from surfaces, it is desirable to increase the interaction angles of electrons. Finally, the comparison between the results of interaction of electrons and ions with surfaces has been presented. In these investigations the initial interacting parameters are in the range of experimental values and the measured parameters are introduced and optimized for applications in ions and electrons microscopes.

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In this thesis GdBa2Cu3O7-x(a high temperature ceramic superconductor) nanofibers from a precursor polymer solution are produced, using electrospinning method. Precursor polymer water solution contains polyvinyl pyrrolidone (PVP) and a mixture of Gadolinium Nitrite, Barium Nitrite, and Cupper Nitrite with mass ratio of 5/1 (polymer/nitrite). using above method (electrospinning) and with following condition; solution density of 55%, voltage of 18 kV, distance between collector plate and nuzzle of 12 cm and injection solution rate of 1 ml/h, fibers with diameters of the order of 470 nm and average length of greater than 10 µm are produced.
The SEM pictures of GdBa2Cu3O7-x fibers indicate that with increasing the potential, the distance between collector plate and nuzzle, and solution density the diameter of fibers will reduce, however with increasing the injection solution rate the diameter of fibers will increase.For nitrogen liberation, the produced fibers are heated to a temperature of 200 oc and kept at this temperature for 12 hours.
The SEM pictures at this stage indicate that the fiber diameters are increased to about 1µm.This increased diameter of the fibers could be predicted with understanding of the reaction between citric acid and nitrites. after this step the calcination processes are done on the fibers at a temperature of 900 centigrade degree. Following the calcination, in order to achieve a superconducting phase transition, the fibers are subjected to a cooking process in a temperature of 930 centigrade degree for 12 hours. X-Ray diffraction patterns of the cooked-sintered samples indicate that the GdBa2Cu3O7-x superconducting phase are created. The SEM pictures, at this stage, indicate that after sintering process the acquired fiber diameters are largely decreased.
Finally with the use of measurement software, the average diameter of produced nanofibers is estimated to be of the order of 90 nm.