Sharif Digital Repository

In this study, graphene oxide/gold/methylene blue (GO/Au/MB) ternary composites were synthesized and characterized through UV–vis, FTIR, XRD, XPS, SEM, and TEM analyses towards plasmon-enhanced singlet oxygen (1O2) generation. Through using gold nanoparticles and MB photosensitizers, the visible light adsorption capability of GO was enhanced by 115%. Moreover, applying this ternary composite as a photocatalyst under visible light interestingly revealed a drastic step-increase of 14% (i.e., from 9 to 23%) in the conversion of photooxygenation of Anthracene. This behavior was rationalized using finite-difference time-domain (FDTD) simulations which confirms the plasmonic field of gold... 

In this paper, a sufficient reciprocity condition for general time-periodic modulated bianisotropic media is extracted from first principles. Reciprocity of various cases of significant importance, including stationary bianisotropic media, time-varying (TV) isotropic media, TV anisotropic media, and TV bianisotropic media, are investigated using this condition. We prove that synchronous time modulation of stationary bianisotropic yet reciprocal media (chiral, pseudochiral, and achiral) does not lead to nonreciprocity, unless the modulation function breaks time reversal symmetry. This is in contrast to recently published research. The theoretical results are validated using in-house finite... 

In this paper, we propose a reversible Feynman gate utilizing the interference effect for optical communications and computing. The plasmonic waveguides are created by placing a suspended graphene sheet, held by two SiO2 ridges, 10 nm above the Si ribs. The Finite-difference time-domain (FDTD) method is used to simulate the proposed gate in frequency and time domains. Simulation results show that high extinction ratios as much as (15.12 dB) and 13 dB are achievable at the wavelength of 10 μm for the output bits P and Q, respectively. The device is immune against ± 20% variations in the width of the Si ribs due to fabrication errors and its performance can be controlled by setting the... 

NMZ ferrites doped with rare earth having spinel composition Ni0.5Mn0.3Zn0.2X0.02Fe1.98O4, whereas X = Y, Pr and Gd were synthesized by sol gel auto-ignition method. XRD, FESEM, VSM and VNA were used to determine the phase, microstructural, magnetic and electromagnetic properties of rare earths doped NMZ ferrite. XRD analysis confirms the single phase of the rare earths doped NMZ ferrite. FESEM images shows Pr doped NMZ ferrite has less agglomerations and more porous structure as compared to NMZ and other rare earths doped NMZ ferrites. Magnetic analysis shows the enhancement in saturation magnetization and remanence with the doping of Y, Pr and Gd in NMZ ferrite. Dielectric properties were... 

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were... 

NMZ ferrites doped with rare earth having spinel composition Ni0.5Mn0.3Zn0.2X0.02Fe1.98O4, whereas X = Y, Pr and Gd were synthesized by sol gel auto-ignition method. XRD, FESEM, VSM and VNA were used to determine the phase, microstructural, magnetic and electromagnetic properties of rare earths doped NMZ ferrite. XRD analysis confirms the single phase of the rare earths doped NMZ ferrite. FESEM images shows Pr doped NMZ ferrite has less agglomerations and more porous structure as compared to NMZ and other rare earths doped NMZ ferrites. Magnetic analysis shows the enhancement in saturation magnetization and remanence with the doping of Y, Pr and Gd in NMZ ferrite. Dielectric properties were... 

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were... 

Plasmonic nanostructures have emerging applications in solar cells, photodynamic therapies, surface-enhanced Raman scattering detection, and photocatalysis due to the excitation of localized surface plasmons. The exciting electric field resulting from the collective oscillation of free electrons is highly dependent on the dielectric medium, shape, size, composition, and configuration of plasmonic nanostructures. From an engineering perspective, one can tune the optimal properties in the desired applications of geometrical parameters such as the shape, size, and nanoparticles' configuration. Such optimization should be performed analytically (with exact solutions) or numerically (with... 

In this paper, it is shown that non-reciprocity can be observed in time-varying media without employing spatiotemporal modulated permittivities. We show that by using only two one-dimensional Fabry–Perot slabs with time-periodic permittivities having quadrature-phase difference, it is possible to achieve considerable non-reciprocity in transmission at the incidence frequency. To analyze such a scenario, generalized transfer matrices are introduced to find the wave amplitudes of all harmonics in all space. The results are verified by in-house finite-difference time-domain simulations. Moreover, in order to have a simple model of such time-varying slab resonators, a time-perturbed coupled-mode... 

This paper is concerned with the investigation of an optical band-pass filter based on subwavelength surface plasmon polaritons. The transmission characteristics are numerically analyzed by the finite-difference time-domain method, and simulation results reveal that the structure has a band-pass filtering characteristic. The metal–insulator–metal plasmonic nanostructure is implemented by several vertical rectangular cavities across an optical waveguide. The metal and dielectric materials utilized for the realization of the filter are silver and air, respectively. Furthermore, the performance can be efficiently modified by tuning the geometric parameters such as the cavities’ length and width... 

We report the effect of the geometric parameters on transparency and conductivity in a metallic nanowire mesh as a transparent electrode. Today, indium tin oxide and fluorine-doped tin oxide are used as the transparent electrode for displays and solar cells. Still, there is a definite need for their replacement due to drawbacks such as brittleness, scarcity, and adverse environmental effects. Metallic nanowire mesh is likely the best replacement option, but the main issue is how to find the optimal structure and how to get the best performance. Since the interaction of light with nanowire mesh is complicated, there is no straightforward rule with a simple analytical solution. We developed a... 

Passive localisation of non-cooperative targets through their electromagnetic emissions is an attractive issue. This localisation task can be carried out using multitude of receiver sites being linked together. This multiplicity, however, brings about difficulties in organising and coordinating the sites. One can even claim that the method is no longer passive considering the necessary communication links between the sites. On the other hand, single-site localisation methods basically overcome these difficulties eliminating the need for inter-site communications. In this study, a single-site localisation method is presented and analysed. This method is applicable to scenarios with a large... 

An inverted organic solar cell (IOSC) with nanograting array as anode of the cell has been simulated and analyzed using a combined electrical and optical approach. We have used finite difference time domain (FDTD) method for optimizing device structure. We have compared the characteristics of the IOSC with grating structure with a reference IOSC without grating structure. As a result, an improvement of 11% and 26% in power conversion efficiency (PCE) and short circuit current (JSC) compared to the reference structure was achieved. An analysis is provided on the origin of reduced fill factor (FF) in the IOSC with grating structure. We also have discussed about disadvantage of using optical... 

Subradiant modes can exhibit sharper spectral response, and lower radiative loss compared to the super-radiant modes of plasmonic nanostructures. Selective excitation of these modes is challenging, and has practical importance. In this paper, a systematic procedure for determining, and individually exciting the subradiant modes of a plasmonic nanostructure is presented by utilizing our previously reported T-matrix formulation. As an example, we calculate various modes of a gold nanodimer, and determine the incident field required for exciting a subradiant mode of this nanostructure. This field is then generated by a modified zone plate lens. The expansion of scattered field, as well as the... 

A method to simulate an open boundary problem within the finite difference time domain approach for the emission of photo-conductive antennas is presented here. For this purpose, we use convolutional perfectly matched layers (CPMLs). In these devices, the semiconductor region, where transient currents are present in simulation time, is considered to be an 'active' medium. This medium is extended virtually beyond its boundaries or the computational domain limits. We explain in this communication how to simulate the transient state of a semiconductor in a CPML region as well as the potential of the method developed to solve conventional practical applications  

A coupled transmission line model whose parameters are analytically given is provided for fast and accurate analysis of miscellaneous plasmonic structures with metal-dielectric-metal (MDM) arrangement. The coupling of surface plasmons supported by the planar metal-dielectric interfaces is included in the proposed model and thereby the effects of the first non-principal mode of the MDM waveguide are considered. In particular, MDM bends, junctions, and stubs are studied. Using rigorous numerical solutions, e.g., the finite-element method and the finite-difference time-domain, it is shown that the proposed model is accurate in all those cases  

Bluetooth headsets are one of the popular accessories of mobile phones because of their convenience. It is necessary to assess the impact of electromagnetic waves on the human head when a person is using a headset. In this paper different scenarios closely modeling the situations that a subject may use the headset in real life are simulated. Simulations are performed for two types of materials commonly used to manufacture the headsets, namely silicone and acetal, and for two different orientation angle of the headset on the ear. Specific Absorption Rate (SAR) and path loss values are then obtained for two different environments, the open space and inside a car. SEMCAD-X software is used as a... 

It has been proposed that emission spectrum of random lasers with magnetically active semiconductor constituents can be made tunable by external magnetic fields. By employing the FDTD method, the spectral intensity and spatial distribution of electric field are calculated in the presence of an external magnetic field. It is numerically shown that due to the magneto-optical Voigt effect, the emission spectrum of a semiconductor-based random laser can be made tunable by adjusting the external magnetic field. The effect of magnetic field on the localization length of the laser modes is investigated. It is also shown that the spatial distribution of electric field exhibited remarkable... 

Time-dependent model is presented to simulate random lasers in the presence of an inhomogeneous gain medium. PbSe quantum dots (QDs) with an arbitrary size distribution are treated as an inhomogeneous gain medium. By introducing inhomogeneity of the PbSe QDs in polarization, rate, and Maxwell's equations, our model is constructed for a one-dimensional disordered system. By employing the finite difference time-domain method, the governing equations are numerically solved and lasing spectra and spatial distribution of the electric field are calculated. The effect of increasing the pumping rate on the laser characteristics is investigated. The results show that the number of lasing modes and... 

We substitute different types of photonic crystal waveguide components by approximate transmission line circuits. The proposed distributed circuits exploit the analogy of wave propagation in photonic crystal waveguides and transmission lines. They are either cascaded to each other or inserted like stubs to imitate wave propagation within the photonic structure. Notable examples, e.g. coupled waveguide-cavity systems, sharp 90° bends, and T-junctions, are studied in detail. It is shown that analysis of the proposed circuits here can yield accurate enough results and thus substitute the brute-force numerical methods. The privilege of having analytical models is exploited to improve the...