Navegando por Assunto "Grafeno"

Agora exibindo 1 - 17 de 17

Acesso aberto (Open Access)
Análise de estruturas planares em THz baseadas em grafeno
(Universidade Federal do Pará, 2016-01-28) NASCIMENTO, Clerisson Monte do; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/0684541646225359
In this work we analyse the properties of scattering of electromagnetic waves in graphene surfaces and the planar plasmonic based devices made of the same material, both in THz frequency region. The work is presented in form of four scientific papers. In the first one a numerical analysis of the plasmonic waves propagation in graphene elements is performed. The influence of geometrical configuration, chemical potential variation, angle of incidence and polarizations is analysed. That results give us the information to project two devices (the second and third) based on frequency selective surfaces (FSS) on THz range and that are composed only by graphene elements and dielectric substrates without the insertions of different metals. The first device consists in a THz electromagnetic filter made by an planar array of graphene ring-shaped elements placed in both sides of a dielectric substrate. The second device presents new multifunctional graphene device that can operate either as an electromagnetic, dynamically controlled, filter or as an eletromagnectic switch. Both devices operates based on Fano resonance effect. The fourth paper presents a new method of analysis of periodic planar structure, based on group theory approach. This method takes account the transversal and longitudinal components of induced current in the structure. By using this, one can obtain more information about the device properties than by using exitenting methods, which uses only longitudinal components of the induced currents. As application, we suggest an analyse a periodic array of graphene elements.
Acesso aberto (Open Access)
Análise de ressonâncias eletromagnéticas em estrutura periódica de discos de grafeno magnetizadosd na faixa de terahertz
(Universidade Federal do Pará, 2023-02-27) SILVA, Amanda Evangelista da; OLIVEIRA, Cristiano Braga de; http://lattes.cnpq.br/2012907724305086; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
Since its isolation in 2004, graphene has shown to be a promising material, as it allows strong interaction of charge carriers with terahertz (THz) radiation. This extensive interaction with light is due to the excitation of surface plasmon polaritons (SPPs) thus providing several applications in the areas of THz photonics. In the presence of an external magnetic field, the cyclotron resonance dominates in the THz spectra. In this work we analyze several resonance modes (dipole, quadrupole, hexapole and modes with azimuthal symmetry) that can exist in the graphene disk in an arrangement with periodic square unit cells. We calculated the resonances with magnetization by an external DC magnetic field ranging up to 3T and compared them with the case of the same structure without magnetization where it was observed that the presence of the magnetic field results in the splitting of some resonant modes. The resonant characteristics are numerically obtained using the COMSOL Multiphysics software in two distinct and complementary studies: the eigenfrequency calculation regime referring to the natural modes of resonance and the plane wave excitation with normal incidence. Floquet boundary conditions on the four sides of the unit cells are used to simulate the in-plane periodic structure of graphene. The unit cell side (i.e. the period of the matrix) used in the numerical calculation is A = 9µm, the radius of the graphene disk is D = 3µm. The problem of excitation of some modes is discussed from the point of view of the circular symmetry that, to generate the resonance peaks in this regime, had to be broken through a subtle cut in the shape of a rectangular slit of size Lx = 10nm by Ly = 550nm starting axially from the edge. The disk is modeled as a two-dimensional element, and this provides a good approximation of the atomic thickness of a single layer of this material. Conductivity is modeled by the semi-classical Drude model. The discussion of resonator properties is fulfilled in terms of graphene currents and electromagnetic fields outside graphene. Potential applications of the obtained results are Faraday and Kerr rotators, controllable filters and absorbers for THz photonic circuits
Acesso aberto (Open Access)
Análise numérica de sensor de ressonância plasmônica de superfície baseado em grafeno na faixa de terahertz
(Universidade Federal do Pará, 2022-06-24) SILVA, Wêndria Cunha da; COSTA, Karlo Queiroz da; http://lattes.cnpq.br/7932708321834647
This work proposes a Terahertz plasmonic refraction index sensor based on Single-Layer Graphene operating as a refractometer in the Terahertz range. The configuration used is Kretschmann, where one of the variables that monitors the reflectivity is the chemical potential. The sensor was theoretically analyzed by the finite element method (FEM), using a bidimensional-based model structure. In it, the reflectivities and the field distributions were calculated for different parameters, such as sample thickness, operating frequency, incidence angle, chemical potential variation and electrical permittivity. Firstly, a study was made to determine the best operating frequency, the sensor’s angle of incidence and minimum sample thickness that the sample should have Subsequently, the numerical model was compared with the analytical model obtained through two literatures.. From the numerical results, parametric analyzes were performed to verify variations in sensitivity, full width at half maximum (FWHM) and resolution, all parameters of device quality. Numerical results are compared with theoretical concepts available in the literature and in recently published works.
Acesso aberto (Open Access)
Circulador de 4 portas baseado em um ressonador elíptico de grafeno na região terahertz.
(Universidade Federal do Pará, 2020-01-20) OLIVEIRA, Thiago Lima de; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
A new type of four-port circulator based on graphene for the terahertz frequency range is proposed and analyzed in this work. It consists of two parallel waveguides coupled laterally to a magnetized resonator in the shape of an ellipse. The cross section of the components has a three-layer structure consisting of graphene, silica dioxides and silicon. The graphene resonator is normally magnetized in its plane by an external DC magnetic field. The physical principle of the device is based on the dipolar resonance of the resonant cavity of magnetized graphene. Using the Theory of Magnetic Groups, we were able to analyze the scattering matrices of the symmetry components of the device. In addition, the Temporal Coupled Modes Theory was used in order to analytically analyze the characteristics of the device. The influence of different parameters on the characteristics of the circulator was investigated using the Comsol Multiphysics software. Numerical simulations demonstrate the isolation of ports 3 and 4 around -32.6 dB and -16.2 dB, insertion losses around -2.5 dB, reflection around -20.3 dB and 5.7 % bandwidth with the center frequency of 5.03 THz. The DC magnetic field of applied polarization is 0.8 T. The central frequency of the circulator can be controlled by the change in the Fermi energy of graphene. Finally, a comparison was made between the numerical and analytical model of the device, using the aforementioned tools.
Acesso aberto (Open Access)
Circuladores de grafeno de banda ultralarga para região THz
(Universidade Federal do Pará, 2019-06-07) SILVA, Samara Leandro Matos da; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
Non-reciprocal components are indispensable parts of many microwave and optical systems. In the future, THz communication systems will also require these components. Existing publications show that the bandwidth of graphene-based circulators in the THz region can be 10% to 20% with the use of rather complicated structures. The suggested circulators are formed by a graphene junction with concave pattern connected to the waveguides. Graphene is supported by SiO2/Si layers. The circulating behavior is based on the nonsymmetry of the graphene conductivity tensor that appears due to magnetization by a DC magnetic field normally applied to the plane of the graphene. We discuss the main parameters that define the bandwidth and its influence on it. Circulators have record bandwidth that is twice as high as those published. We have shown that the circulator Y can have the bandwidth of 42% in the frequency range (2.75 ÷ 4.2) THz, with the insulation better than −15 dB and the larger insertion losses that −2 dB, provided by the DC magnetic field polarization of 1.5 T and the chemical potential of 0.15 eV. For the two 4-port circulators we achieved a bandwidth of 44% for the same physical parameters.
Acesso aberto (Open Access)
Dispositivos não-recíprocos baseados em grafeno na região de THz
(Universidade Federal do Pará, 2019-02-28) CASTRO, Wagner Ormanes Palheta; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
Four new types of nonreciprocal graphene-based devices operating in the Terahertz region are suggested and theoretically analyzed in this work. They are two three-port circulators with Y and W geometries and two power dividers with different geometries. The cross section of the components has a three-layer structure, composed of graphene, silica and silicon. The planes of the figures of these components consist of a circular resonator of graphene and waveguides connected to it. The graphene resonator is magnetized normally of its plane by an external DC magnetic field, and the physical principle of operation of the devices is based on the dipole resonance of the magnetized graphene resonator. Using the Magnetic Group Theory, we analyze the scattering matrices of the symmetrical components of the devices. In addition, for the analysis of the circulators, the Analytical Temporal Coupled Mode Theory was also used. Numerical simulations were performed by a full wave computational program and the calculations demonstrate isolation levels better than -15 dB for both the circulators and the dividers. The Y-circulator has insertion losses around - 2.6 dB, bandwidth of 7.4% at the center frequency of 5.38 THz, whereas the circulator W showed insertion losses of - 2 dB, bandwidth of 4.5% at the center frequency of 7.5 THz. The DC bending magnetic field in the two cases was 0.45 T and 0.56 T, respectively. The power dividers have shown to posses the division of the signal between the two output ports of -4.4 dB with in the frequency band of 4.5% and 3.4% with magnetic filed of 0,8 T. The influence of geometric and physical parameters on the characteristics of the circulators is discussed. The frequency bands of the devices can be controlled dynamically by changing bias voltage applied between the graphene layer and the substrate.
Acesso aberto (Open Access)
Espalhamento eletromagnético no grafeno através de transformadas de impedância
(Universidade Federal do Pará, 2019-02-22) PIRES, Andrey Viana; COSTA, Karlo Queiroz da; http://lattes.cnpq.br/7932708321834647
Graphene is a two-dimensional material with good electrical properties that make possible new telecommunications applications in telecommunications on the terahertz range. This work presents an alternative analysis of the scattering problem in a graphene sheet using the impedance transform. The Green functions, electromagnetic fields and properties of the plasmonic surface wave on the graphene are demonstrated. The numerical results show the spatial field distributions and spectral analysis of the plasmonic wave as a function of media properties, frequency and chemical potential. The results show that the impedance transform is adequate for scattering analysis in graphene sheets because it uses the natural autofunctions of the problem.
Acesso aberto (Open Access)
Estruturas photonic band gap em antena de microfita com aplicações em microondas e terahertz
(Universidade Federal do Pará, 2019-08-16) OLIVEIRA, Jorge Everaldo de; COSTA, Marcos Benedito Caldas; http://lattes.cnpq.br/7636226766852440
In this work we are analyzing the simulations of two microstrip antennas. The first is an antenna using the ceramic material Bismuth Niobate (BiNbO4) doped with Vanadium Pentoxide (V2O5) on the substrate. The antenna patch was designed with indented power line to facilitate matching of impedances and the substrate with air holes was placed just below the patch to further decrease the losses. The second is a nano-antenne with Graphene Patch in the Terahertz range and PBG (Photonic Band Gap) substrate with triangular mesh, and holes in the following height configurations h1, h2 and h3. At time h1 the substrate is fully drilled, while at heights h2 the holes will be made top to bottom of the substrate and the height h3 is the antenna with substrate drilled from the bottom up to the middle of the substrate. Therefore three antennas are created in these geometries using a triangular hole network. The arrangement of the holes in the dielectric substrate constitute the PBG structure, to increase the performance and efficiency of these antennas, extinguishing surface waves in the substrate of microstrip antennas. The adopted geometry also improves antenna parameters such as efficiency and bandwidth. The commercial software HFSS and CST were used for the simulations of the antennas. After the numerical simulation steps the results of the parameters of these devices were obtained. The first antenna (periodic lattice with ceramic substrate) obtained a return loss of -36.21 dB, at a resonance frequency of 10,26 GHz, with a bandwidth of 2.18 GHz. In the simulations of the antennas of microstrip with Patch of graphene the antenna h3 obtained double transmission band with chemical potential of graphene of 0,3 eV.
Acesso aberto (Open Access)
Filtro eletromagnético baseado em grafeno operando na região THz.
(Universidade Federal do Pará, 2024-04-04) SANTOS, Luis Eduardo de Sena dos; CASTRO, Wagner Ormanes Palheta; http://lattes.cnpq.br/4322608238580829; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
In this study, a compact nanoscale plasmonic filter was proposed and numerically analyzed. The plasmonic filter is based on graphene nanoribbons coupled to a disc-shaped graphene resonator with horizontal side cuts and 45o orientation, deposited on a dielectric substrate of silica (SiO2) and silicon (Si) , operating in the THz region. We investigated simple structures that allow tuning the resonance frequency of the resonator. This work provides a viable solution for graphene plasmonic nanofilter structures for future use in highly integrateds plasmonic device applications in THz and FIR regions.
Acesso aberto (Open Access)
Modelagem por MOM de um dipolo de grafeno com múltiplos potenciais químicos
(Universidade Federal do Pará, 2023-10-27) JESUS, Luiz Eduardo Moreira de; COSTA, Karlo Queiroz da; http://lattes.cnpq.br/7932708321834647
In this dissertation, the potential of graphene in the terahertz frequency range was explored, particularly its ability to control the radiation pattern and impedance of a graphene dipole antenna by varying the chemical potential in multiple controllable segments. Two dipole antennas were analyzed, one with four graphene segments and another with six graphene segments, where each segment can have its chemical potential controlled directly. The study used the Method of Moments with graphene surface impedance values to calculate input impedance, gain, surface current distribution, and radiation pattern. The variations in chemical potentials were divided into symmetric and asymmetric groups, allowing adjustments to the second resonance and the angle of maximum gain in the radiation pattern, respectively. Compared to four-segment antennas, the six-segment antenna exhibited increased gain in the symmetric group with little variation in the second resonance. Furthermore, the gain of the six-segment antennas showed a notable increase at the point of maximum deviation while maintaining nearly constant angular displacement. This study paves the way for highly adjustable and efficient graphene antennas with promising applications in communication technology and radiation. Future work may explore various chemical potentials, other antenna geometries, and optimization techniques in simulation.
Acesso aberto (Open Access)
Projeto de um demultiplexador de cristal fotônico bidimensional baseado em grafeno para aplicação em sistemas por divisão de comprimento de onda (WDM).
(Universidade Federal do Pará, 2024-03-15) SILVA, Alan dos Reis; COSTA, Marcos Benedito Caldas; http://lattes.cnpq.br/7636226766852440
This work presents an eight-channel 2D photonic crystal demultiplexer based on graphene for application in optical systems that use the wavelength division multiplexing technique - WDM. The optical device was designed based on a square crystalline lattice of silicon dielectric rods immersed in air and is formed by three main parts: Bus waveguide; Octagonal resonator rings and L-curve waveguides. The COMSOL multiphysics software and the Legumes python packages were used to study and simulate the designed structure. In analyzing the simulation results, the resonant wavelength, spectral width, quality factor, transmission efficiency, spacing between channels and the level of electromagnetic interference (Crosstalk) for the eight channels of the demultiplexer were evaluated. Furthermore, the analysis of the results occurred from two different perspectives, in the first of which the relationship between the transmission parameters of the demultiplexer with the variation in the chemical potential of graphene was analyzed and in the second the application of the device in WDM systems was explored. In general, the analyzes carried out proved to be considerable regarding the application of the photonic device in optical wavelength division multiplexing (WDM) systems.
Acesso aberto (Open Access)
Sistema de automação IoT para gestão de ativos no cenário da indústria 4.0
(Universidade Federal do Pará, 2023-07-10) GOMES, Woldson Leonne Pereira; SERUFFO, Marcos César da Rocha; http://lattes.cnpq.br/3794198610723464; SILVEIRA, Antonio da Silva; http://lattes.cnpq.br/1828468407562753
The fourth industrial revolution has several pillars, with the Internet of Things and Big Data being one of the most prominent. These technologies make it possible to collect and analyze large data sets in real time, allowing the development of models for the most diverse situations, from consumer behavior to the prevention of manufacturing failures. In this context, the present work addresses the development of a complete architecture for the implementation of an automation system for Industry 4.0, at the hardware and software level, based on the collection of temperature, hour meter, vibration and current data in electric motors of a primary aluminum industry. From the measured variables, vibration data can be obtained in the frequency domain, phase imbalance and Kalman filter estimation. A multicriteria decision algorithm was adopted to assist in choosing the programming language. After elaborating this systematic, a set of solutions was obtained that made the development of the system feasible, which was validated in a controlled experimental setup. The automation system developed was called IOTCORE, which performs the collection of variables in real time, with low latency, high performance, and makes it possible to transmit, store and visualize the data in several supervisory systems.
Acesso aberto (Open Access)
Superfície seletiva de frequências inteligente baseada em grafeno
(Universidade Federal do Pará, 2019-09-02) PAIVA, Rodrigo Rodrigues; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, a formulation based on the finite-difference time-domain (FDTD) and on the exponential matrix methods is developed for modeling thin graphene sheets. This formulation is validated by reproducing problems involving graphene frequency selective surfaces (FSS) known from literature. Then, we propose in this work a smart graphene FSS device. Smartness is obtained by means of a unity cell formed by a graphene ring with a graphene sheet placed in its aperture. By properly regulating the chemical potentials of the graphene elements, two frequency-tunable modus operandi are obtained: single- or dual-band rejection modes. When the device operates in its dual-band rejection mode, either of the rejection bands can be shifted individually in the frequency spectrum. Additionally, both rejection bands can also be reconfigured simultaneously. With the device operating in single-band rejection mode, it is also possible to shift its rejection band in the frequency spectrum.
Acesso aberto (Open Access)
Theoretical study of plasmonically induced transparency effect in arrays of graphene-based double disk resonators
(Sociedade Brasileira de Micro-ondas e Optoeletrônica, 2019-03) PORTELA, Gianni Masaki Tanaka; DMITRIEV, Victor Alexandrovich; OLIVEIRA, Cristiano Braga de; CASTRO, Wagner Ormanes Palheta
In this paper, we consider coupled disk-shaped resonators separated by a thin dielectric substrate that can be used as frequency-tunable filters or as electromagnetic switches in the terahertz frequency band. The two disks are electromagnetically coupled and resonate with dipole plasmonic modes. By using a Temporal Coupled-Mode Theory based approach, we show how to analytically calculate the frequency response of such structures.The analytical results are in good agreement with those obtained from computational simulations based on the finite element method.
Acesso aberto (Open Access)
Transporte eletrônico em alótropos de carbono análogo ao grafeno
(Universidade Federal do Pará, 2018-04-20) SANTOS, Júlio César da Silva dos; SILVA JÚNIOR, Carlos Alberto Brito da; http://lattes.cnpq.br/5067093267673117; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
Carbon-based nanostructured materials have become of great interest to the scientific community due to the properties that these materials present in the technological area. Among the most varied structures derived from carbon, graphene, an allotropic form of carbon having a two-dimensional (2D) hexagonal structure formed from the hybridization of sp² carbon, has great prominence with electrical, thermal and optical properties that exhibit great prospects for future applications technological developments. Recently, a new allotropic form of graphene, consisting of 5-6-7 carbon aromatic rings, has been theoretically proposed. This 2D allotrope with sp² hybridization is energetically comparable to graphene and more favorable to other carbon allotropes. In this work, we propose two hybrid structures or heterojunctions formed by graphene - phagraphene - graphene with zigzag edges at the upper and lower end without (zzG - zzPG - zzG) and with Hydrogen (zzGNR - zzPGNR - zzGNR) coupled to metallic graphene Leads of Hamada index (3,3). The heterojunction constituted by Hydrogen at the ends form nanoribbon (NR). Later, we did a study of the electronic properties of the heterojunctions without the electrodes and of electronic transport of the devices with and without Hydrogen. In order to carry out the calculations of electronic and transport properties, we used the DFT and DFT-NEGF methodology in the Landauer-Büttiker formalism, as implemented in the SIESTA/TRANSIESTA code. Our results show a strong topological insulator behavior with an indirect gap of 0.011eV for zzG-zzPG-zzG in V = 0V and an indirect gap semiconductor of 0.025eV for zzGNR-zzPGNR-zzGNR in V = 0V with phase transition (insulation -metal) for Vmin = -0.5V. Thus, various features of electronic devices for regions of direct (V> 0) and reverse (V <0) polarization in heterojunctions are suggested as: (i) zzG-zzPG-zzG for V> 0 shows four regions corresponding to resistor (I), FET (II), NDR (III) and switch (IV), and for V <0 show five regions corresponding to resistor (I), NDR (II), limiter-switch (III), NDR (IV) and limiter-switch (V). (ii) zzGNR-zzPGNR-zzGNR for V> 0 exhibits FET characteristic and for V <0 it exhibits one NDR with tunnel diode behavior.
Acesso aberto (Open Access)
Transporte eletrônico em nanofitas de grafeno sob a influência de fatores externos, via primeiros princípios
(Universidade Federal do Pará, 2012) NASCIMENTO, Clerisson Monte do; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/0684541646225359
Graphene was the first two-dimensional structure obtained experimentally. Its crystalline lattice is a hexagonal network with a unique atom thick, known as "Honeycomb". Cuts in graphene sheets, which favour a certain direction, generate the so-called graphene nanoribbons. Although graphene behaves like a metal, without considering spin polarization or any type of doping, nanoribbons can present metallic, semi-metallic or semiconductor behaviour, depending on the direction of the cutting and/or on the width of the ribbon. In the case of the semiconductor nanoribbons, the width of the band gap can depends directly on the width of the nanoribbon. Generally, the treatment is predominantly computational, for example, the DFT (Density Functional Theory), in order to obtain characteristics such as dispersion curves for nanoribbons, or the treatment can also be experimental. In this work, we first present the diagrams of energy band and the curves of density of states for semiconductor graphene nanoribbons of different widths and in the absence of external influences. Methods of first principles were used to obtain these curves and the method of Green functions of non-equilibrium was used to obtain the electronic transport. Subsequently, we investigated the influence of the hydrogenation, of the temperature and of the mechanical stress over the system, in order to analyse the behaviour of the electronic transport with and without external influences. It is noteworthy that the graphene nanoribbons present real possibilities of application in nanoelectronic devices, such as nanodiodos and nanotransistores. For this reason, it is important to understand how external factors affect the properties of such materials. So, it is expected that the properties of electronic devices are also influenced in the same way as the properties of the nanoribbons are influenced too.
Acesso aberto (Open Access)
Transporte eletrônico em um alótropo de grafeno nanofitas de bifenileno com bordas hidrogenadas
(Universidade Federal do Pará, 2024-11-06) SOUZA, Lucas Pessoa de; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
Carbon-based nanostructured materials have aroused considerable interest in the scientific community due to their remarkable technological properties. Among the various carbon structures, graphene stands out as an allotropic form with a two-dimensional (2D) hexagonal structure, resulting from the sp² hybridization of carbon. In this work, we investigated the electronic properties of structures based on a 2D allotropic form of carbon, composed of rings of 4, 6 and 8, called Biphenylene. The research used the hydrogenation of the top of Biphenylene nanosheets, with the aim of exploring applications in molecular electronics. To achieve this, we employ Density Functional Theory (DFT) to optimize the structures and combine DFT with the Non-Equilibrium Green Functions method to obtain electronic transport properties. The band structure results indicate that, among the unit cells analyzed, the Biphenylene cell behaves as a conductive material when analyzed in the zigzag direction, while in the archmair direction they present characteristics of semiconductors. Regarding electronic transport properties, the Biphenylene nanodevice demonstrates behaviors like those of a field effect transistor in the studied range. Specifically, the zzBFNRH-O device, which exhibits field-effect transistor characteristics in the range of 0.00 V to 0.07 V, the same behavior we can observe for the zzBFNRH-H device, which exhibits the behavior of a field effect transistor for ranges from 0.00V to 0.50V. We can observe the behavior of the archBFNRH-O device where it indicates the behavior of a metal, presenting current conduction values after 0.10V. The archBFNRH-H device presents the behavior of a semiconductor, which indicates a gap of 1.8eV. We can observe that when the device width increases, this gap decreases. These results demonstrate that structures based on Biphenylene present themselves as a promising alternative for the development of nanodevices and applications in molecular electronics.