Sharif Digital Repository

Studying the behavior of piezoelectric materials containing self-assembled quantum wires and quantum dots is of great interest. This work is devoted to analytical and exact determination of the electro-elastic fields associated to quantum wires and quantum dots in piezoelectric mediums. The present work accounts for: (1) different shapes and orientations of quantum wires and quantum dots, (2) different types of anisotropy, and (3) high concentrations of quantum wires and quantum dots, that is, the corresponding interaction is considered properly. The presented solution is valid for general anisotropy and different shapes of quantum wires and quantum dots. In this work, periodic and... 

In this research we focus on fabrication and characterization of Dye and Cadmium based Quantum Dot Sensitized Solar Cells (QDSCs) based on TiO2 nanostructures. TiO2 nanorods were synthesized with a simple chemical method. TiO2 nanorods, TiO2 nanorod/TiO2 and ZnO nanoparticle composite structures were integrated as photoanode in dye sensitized solar cells (DSSCs). Incorporation of TiO2 nanoparticles into the bare nanorods increased the efficiency more than 45%. Monitoring electron transport properties of the cells, pointed out the crucial role of electronic structure of composite film components on the performance of cells. Suitable morphology of TiO2 nanorods, led us to use them, to make a... 

In this project, we have studied the geometric and electronic structures of CdS nano-particles. The bulk CdS is known to be a semiconductor with the experimental energy gap of 2.42eV which is more than twice the theoretical resuls based on LDA or GGA energy functionals used in the density functional theory. However the calculations based on Kohn-Sham formalism used in DFT (KS-DFT) predicts the geometric structure of bulk semiconductors fairly well. Therefore, we have employed the KS-DFT formalism for our CdS nano-particles and have used the Gaussian as well as SIESTA computer codes to predict the geometric structures of these nano-semiconductor-particles. For calculating their electronic... 

Optical bistability is one of the most important results of nonlinear optics. The term optical bistability refers to the situation in which two different output intensities are possible for a given input intensity. Interest in optical bistability stems from its potential usefulness as a switch for use in optical communication and in optical computing. Optical bistability is resulted by nonlinear phenomena such as kerr effect, two photon absorption and saturable absorber. In this thesis, we study the optical bistability in a double-coupler ring resonator, in which the right half of ring is made of an erbium doped fiber amplifier for compensating the loss by the gain of EDFA, and the left half... 

Conventionally all objects radiate most of its energy in the from of infrared waves, therefore, infrared photodetectors for detecting objects is important and more study is done on improve the detecting parameters. The proposed structures are developed from bulk to quantum well and quantum dots in recently years. In this work at reason insensitivity to incident light polarization, flexible operation wavelength, high operation temperature, inherent photovoltaic effect, low capture probability we study the structure of quantum dot infrared photodetectors and then for improve the detecting parameters structure of two layers quantum dot separated with a layer thin barrier (bilayer). And then a... 

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... 

In recent years utilization of quantum dots for stem cells detection and clean energy production has received intensive attention. Graphene and its derivatives have been widely studied because of their effectiveness on electronical and optoelectronical devices, chemical sensors, nanocomposites, and energy storage. By use of metal nanoparticles, such as AuNPs, we can develop properties of graphene, and control them via shifting the absorption peak wavelength and increasing its biocompatibility. In this research, hybrid nanoparticles of gold-graphene as core-shell and conjugated by polymeric linkers containing amine or thiol functions are synthesized. Our purpose is stabilization the... 

The light emitting diodes is composed of an electron transport layer and hole transport layer. The electrons and holes go to the middle region called active region through these transmit regions, and they emit light from themselves by recombination in this area. In our structure, the active region consists of quantum dots. The emitted light characteristics depend on these dots to great extent. In this thesis, we first describe the processes in this type of device, and then we will review the well-known structures that have been reported so far. In chapter 4 discusses the important characteristics of the active region, including the size of the quantum dots and the wetting layer, and we... 

Levodopa [L-3, 4-dihydroxyphenylalanine, or L-DOPA] is an important neurotransmitter used for the treatment of neural disorders such as Parkinson’s disease. Abnormal L-Dopa concentrations in biological fluids can be used for evaluation of diseases such as Parkinson’s diseases. In the first part of this thesis, a rapid and sensitive method for levodopa detection was reported which is based on in situ formation of polylevodopa nanoparticles. The assay is very simple and low cost and uses only NaOH and HCl as reagents. Under alkaline conditions, levodopa is spontaneously oxidized to its quinone derivative and shows the fluorescence properties. The fluorescence signal of the oxidation product of... 

Solution-processed quantum dots (QDs) have attracted significant attention for the low-cost fabrication of optoelectronic devices. Here, we synthesized PbS QDs via hot injection method and passivated the trap states by using short thiols and dopant elements for photovoltaic application. In order to study the effect of dopants on photovoltaic application, PbS QDs were doped by using three different cations: Cadmium, Calcium, and Zinc. The results showed that Cd dopant has a better improvement than Ca and Zn dopants in order to increase the efficiency of the PbS QDs solar cells. We achieved solar power conversion efficiencies of 5.81% using Cd therapy. Recently, hybrid nanocomposites... 

Coupling of optical and mechanical degrees of freedom through radiation pressure was, first, observed in the experiments for detection of gravitational waves. Recent experimental advances have granted reality to the long-hankered-after coupling between microscopic and macroscopic systems. In the first step, this thesis will review different aspects of cavity Optomechanics, such as: cooling, side-band formation and dynamics of an Optomechanical cavity. Then we will go further and study the Optomechanical dynamics of a cavity in the presence of an atom. To do so, we will analyze the entanglement, created between the center of mass motion of the atom and the mirror and will probe into its... 

Over the past two decades, several studies have been investigated on synthesis and properties of semi-conductor quantum dots because of their applications in sensors, LEDs, detectors, solar cells, etc. One of challenging issues in synthesizing these nano-particles is their size distribution. In this study, Cadmium Selenide was synthesized by the method of colloidal synthesis. X-ray diffraction showed that the crystalline nano-particles have wurtzite structure. For obtaining a uniform size distribution, effect of various parameters such as molar ratio of components and reaction temperature on the growth kinetics of these particles, were studied. Results showed that molar ratio of Selenium to... 

This thesis cantain two section. In the first section a novel extracting medium based on magnetic molecularly imprinted polymers (MIPs) nanoparticles was synthesized by chemical polymerization for micro-solid phase extraction. In this work, the modified chitosan magnetite nanoparticles (MNP-CS) was synthesized by co-precipitating Fe2+ and Fe3+ in the chitosan solution [1,2]. The characteristic properties of Fe3O4@MIPs nanoparticles were determined using Fourier transform infrared spectrometer. Extraction efficiency of the novel extracting medium was compared with MNP-CS sorbents for the determination of RhB in aqueous samples, via quantification by spectrofluorimetry. The obtained results... 

The use of magnetic compounds for drug delivery and magnetic imaging has been studied in many studies. The easy use of magnetic particles makes them widespread. By applying a magnetic field, the particles reach the desired position and return to the original state by cutting off the field. The use of these magnetic materials in the nanoscale also adds other benefits, including: convenient and rapid transfer of nanoparticles, rapid repulsion of the kidneys, reducing the risk of overdose, etc. In recent years, the use of quantum dots for the diagnosis and treatment of tumors has attracted much attention. The use of hybrid quantum dots and magnetic nanoparticles can incorporate the desired... 

Boron Nitride Quantum Dots, as a new member of Heavy-metal-free Quantum dots has attracted many attention due to their unique properties. The hyroxylate functionalized BNQDs was synthesized with two steps fabrication approache which were contained mechanical milling and solvothermal process. It has been shown that 12 hours for mechanical milling and 24 hours for solvothermal process would be the most optimum time that produce well disperse functionalized BNQDs . The characterization results have proved that the as-prepared BNQDs have lateral size at around 5 nm with thickness in range of 4-6 layers. Also, it has been demonstrated that OH functional groups can attache into the surface of...