圆柱形光子晶体中电磁波的模式和带隙

利用电磁波在一维圆柱光子晶体中径向受限的条件,推导出电磁波在一维圆柱光子晶体中各个模式满足的关系式。研究了各个模式的特征。计算出TE波和TM波各模式的禁带随模式量子数、圆柱半径以及入射角的变化规律。得出了一些不同于一维非受限光子晶体带隙的新结构。     

一维矩形光子晶体中电磁波的传输特性

利用一维矩形光子晶体中电磁波横向受限的条件,推导出电磁波在其中各个模式满足的关系式,从而研究了电磁波各模式的特性.通过色散法研究了电磁波的传输特性随模式量子数和矩形边长的变化规律,得出了一些不同于一维非受限光子晶体的新特征,即一维矩形光子晶体的禁带由模式量子数确定,禁带频率中心和频率宽度与模式量子数和边长有关.     

Effect of the mutual rectification of two electromagnetic waves with perpendicular polarization planes in a superlattice based on graphene

The effect of the mutual rectification of two electromagnetic waves with perpendicular polarization planes in a superlattice based on graphene was investigated. It was shown that, due to the nonadditive nature of the electronic spectrum of a superlattice based on grapheme, a constant term of current arises along its axes. The dependence of the constant of current density on the intensity of an electromagnetic wave is oscillatory in nature.     

一种电磁带隙结构的快速分析方法

 使用直接传输方法分析有限周期Mushroom-like 电磁带隙结构的表面波带隙,与无限周期的电磁带隙结构表面波色散能带图相比,该方法能大大缩短分析时间。将电磁带隙结构放置于波导底面,通过计算波导的传输系数,分析了不同波导高度和电磁带隙结构周期数对带隙范围的影响。加工了Mushroom-like电磁带隙结构样品,并使用一对探针耦合的方法测量了电磁带隙结构的TE和TM表面波带隙,实验结果表明使用直接传输方法确定的表面波带隙与测量数据吻合良好,证明了此方法的有效性。     

Interaction of terahertz electromagnetic waves with periodic gratings of graphene micro- and nanoribbons

An original mathematical model of the interaction of terahertz (THz) electromagnetic waves with periodic gratings of graphene micro- and nanoribbons is based on the solution to the boundary-value problem of diffraction for the Maxwell equations with electrodynamic boundary conditions and material equations. The electrodynamic calculations of the transmission coefficients of the TEM wave versus frequency are performed for the 2D grating of graphene micro- and nanoribbons at several chemical potentials, grating periods, and geometrical sizes of ribbons. The results of the calculations show that the transmission spectrum exhibits a minimum in the THz range if the electric field of the wave is perpendicular to the graphene ribbons. The minimum is due to the plasmon resonance of the fundamental mode in graphene, and the absorption peaks at higher frequencies in the upper part of the THz range are related to the highorder plasmon modes.     

On transmittance and localization of the electromagnetic wave in two-dimensional graphene-based photonic crystals

Two-dimensional graphene-based photonic crystal (GPC) formed by a periodic array of the homogeneous dielectric cylinders etched in the alternating graphene and dielectric layers and its inverse counterpart are considered. The transmittance of the photonic crystal is obtained. The waveguide due to the localization of the electromagnetic wave on the lattice defect that breaks the translational symmetry of the GPC of two different topologies is studied. The different topologies of GPC are characterized by different photonic band structures with different widths of photonic band gaps (PBG) and provide different frequencies for the localized electromagnetic wave due to the defect. The frequencies of the localized mode for both type of the GPC, located inside the lowest PBG, are in the range of THz or tens of THz depending on the topology of the GPC. It is shown that the photonic band gap always can be tuned by changing the chemical potential of graphene to provide formation of the localized photonic mode due to the defect. The technological advantages of the GPC, as well as the opportunity to tune the PBG and the frequency of the localized electromagnetic wave in the terahertz region of spectrum for the GPC are discussed.     

Substrate-induced bandgap in the spectrum of an epitaxial graphene layer

It has been shown that a bandgap can appear in the spectrum of a graphene bilayer formed on the surface of a semiconductor. Bandgap widths have been estimated for various SiC polytypes. The predicted effect is important for the practical applications of graphene.     

Graphene-based one-dimensional photonic crystal

A novel type of one-dimensional (1D) photonic crystal formed by an array of periodically located stacks of alternating graphene and dielectric stripes embedded into a background dielectric medium is proposed. The wave equation for the electromagnetic wave propagating in such a structure is solved in the framework of the Kronig-Penney model. The frequency band structure of the 1D graphene-based photonic crystal is obtained analytically as a function of the filling factor and the thickness of the dielectric between the graphene stripes. The photonic frequency corresponding to the electromagnetic wave localized by a defect of the photonic crystal formed by an extra dielectric placed in the position of one stack of alternating graphene and dielectric stripes is obtained.     

Electronic,thermal, and optical properties of graphene like SiCx structures: Significant effects of Si atom configurations

We investigate the electronic, thermal, and optical characteristics of graphene like SiC_x structure using model calculations based on density functional theory. The change in the energy bandgap can be tuned by the Si atomic configuration, rather than the dopants ratio. The effects of the concentration of the Si atoms and the shape of supercell are kept constant, and only the interaction effects of two Si atoms are studied by varying their positions. If the Si atoms are at the same sublattice positions, a maximum bandgap is obtained leading to an increased Seebeck coefficient and figure of merit. A deviation in the Wiedemann-Franz ratio is also found, and a maximum value of the Lorenz number is thus discovered. Furthermore, a significant red shift of the first peak of the imaginary part of the dielectric function towards the visible range of the electromagnetic radiation is observed. On the other hand, if the Si atoms are located at different sublattice positions, a small bandgap is seen because the symmetry of sublattice remains almost unchanged. Consequently, the Seebeck coefficient and the dielectric function are only slightly changed compared to pristine graphene. In addition, the electron energy loss function is suppressed in Si-doped graphene. These unique variations of the thermal and the optical properties of Si-doped graphene are of importance to understand experiments relevant to optoelectronic applications.     

About the linewidth of cyclotron resonance in band-gap graphene

The critical amplitude of circularly polarized electromagnetic wave when the hysteresis of cyclotron absorption takes place, was found for band-gap graphene. The dependence of critical amplitude on the gap value and on the relaxation time was investigated. The conditions of applicability of linear theory describing the electromagnetic response of band-gap graphene in a non-zero magnetic field were found. The power of the circularly polarized electromagnetic radiation absorbed by band-gap graphene in the presence of a magnetic field was calculated. The linewidth of cyclotron absorption was shown to be not zero even for pure band-gap graphene.     

Gap opening and tuning in single-layer graphene with combined electric and magnetic field modulation

The energy band structure of single-layer graphene under one-dimensional electric and magnetic field modulation is theoretically investigated. The criterion for bandgap opening at the Dirac point is analytically derived with a two-fold degeneracy second-order perturbation method. It is shown that a direct or an indirect bandgap semiconductor could be realized in a single-layer graphene under some specific configurations of the electric and magnetic field arrangement. Due to the bandgap generated in the single-layer graphene,the Klein tunneling observed in pristine graphene is completely suppressed.     

电磁偏置各向异性石墨烯界面的传播矩阵

基于电磁场边界条件和相位匹配,推导出电、磁偏置下呈各向异性的石墨烯导电界面的传播矩阵,并进一步给出各向异性石墨烯界面的反透射系数解析解;该传播矩阵耦合了基本的横电波和横磁波极化,并包括偏置电、磁场的影响.将跨石墨烯界面传播矩阵嵌入各向同性分层介质传播矩阵,获得的新传播矩阵可用于解析分析平面电磁波以任意角度入射含各向异性...     

Tuning the bandgaps in a magnonic crystal–ferroelectric–magnonic crystal layered structure

A dispersion relation has been obtained for the hybrid electromagnetic spin wave in a magnonic crystal–ferroelectric–magnonic crystal layered structure. The mechanisms of the bandgap formation in this structure have been revealed, and the ability to double tune bandgap characteristics by means of the electric and magnetic fields has been shown.     

Calculation of electron spectra and some problems in the thermodynamics of graphene layers

The expressions for the energy spectra of monolayer, bilayer, and multilayer graphene, as well as epitaxial graphene, are derived using the quantum Green’s functions method. Analytic expressions are obtained for the densities of states of these systems. It is shown that a bandgap can appear the spectrum of an epitaxial graphene bilayer. A number of problems in the thermodynamics of electrons in free and epitaxial graphene layers are considered as applications. Analytic expressions are obtained for the chemical potential and heat capacity in the limiting cases of low and high temperatures. Quantum oscillations of heat capacity in graphene are analyzed taking into account the Coulomb interaction. The Berry phase of epitaxial graphene is investigated.     

基于开口环的可调谐滤波器及其电磁带隙

基于开口谐振环上加载变容二极管设计可调谐滤波器,很好地实现了电磁波带隙的可调.在单环开口谐振环缝隙处或者双环开口谐振环的两环之间加载变容二极管,改变加载变容管上得的电压,改变该结构的分布参量而达到滤波器可调性能.同时通过数值计算分析了该滤波器结构对电磁波的频率响应函数,指出其形成电磁波带隙的物理机制,为了消除开口谐振环的磁谐振效应而关闭开口谐振环的缝隙实验进行了验证.研究表明基于变容管开口环的可调谐滤波器所形成的电磁波带隙中,有的带隙是源于磁谐振机制.有的带隙是源于电谐振机制.对该滤波器形成带隙物理机制的研究,可以更好地理解开口谐振环,有助于其在光学和微波波段器件的设计.     

Design of a type of broadband metamaterial absorber based on metal and graphene

In this paper, we demonstrate a kind of broadband metamaterial perfect absorber using both graphene and metal resonator elements. Through step by step design and simulation, wider absorption band from about 4.22 THz to 7.48 THz with average absorption rate up to 98.21% is achieved in the absorption spectrum. In addition, the absorber has characteristics of polarization insensitivity and wide incident angle due to its inherent rotational symmetry. Moreover, the absorption band can be adjusted by changing the chemical potential of the graphene. The superiorities of broadband, high absorption rate, polarization independent and wide-angle characteristics make it have potential application prospects in electromagnetic wave absorbing, signal sensing and detection, and other optoelectronic devices.     

Br掺杂对石墨烯带隙影响的实验研究

石墨烯独特的结构和性能使其在纳米电子、半导体器件等领域成为研究的热点,但其零带隙的特性严重限制了其应用.采用化学气化沉积法制备了多层石墨烯,并使用溴蒸汽对制备的多层石墨烯进行掺杂,分析研究了溴蒸汽化学掺杂对石墨烯带隙的影响.为了对比溴蒸汽掺杂对石墨烯带隙的影响,使用633 nm He-Ne光分别测量了石墨烯掺杂前和掺杂后的拉曼光谱,根据拉曼光谱计算了石墨烯费米能级移动与掺杂溴蒸汽之间的关系.实验结果表明:溴蒸汽掺杂对石墨烯拉曼光谱G带产生影响;随着掺杂溴蒸汽体积的增加,拉曼光谱G带向高频移动并逐渐趋于稳定;G带和2D带强度比也迅速增加,并最终趋于稳定.费米能级的移动与G峰位置成线性关系,利用G峰峰值位置与费米能级实验关系式计算了溴掺杂后石墨烯的费米能级,分析了化学掺杂对石墨烯带隙的影响.     

Complete low-frequency bandgap in a two-dimensional phononic crystal with spindle-shaped inclusions

A two-dimensional phononic crystal(PC) structure possessing a relatively low frequency range of complete bandgap is presented. The structure is composed of periodic spindle-shaped plumbum inclusions in a rubber matrix which forms a square lattice. The dispersion relation, transmission spectrum and displacement field are studied using the finite element method in conjunction with the Bloch theorem. Numerical results show that the present PC structure can achieve a large complete bandgap in a relatively low frequency range compared with two inclusions of different materials, which is useful in low-frequency noise and vibration control and can be designed as a low frequency acoustic filter and waveguides. Moreover,the transmission spectrum and effective mass are evaluated to validate the obtained band structure. It is interesting to see that within the band gap the effective mass becomes negative, resulting in an imaginary wave speed and wave exponential attenuation. Finally, sensitivity analysis of the effect of geometrical parameters of the presented PC structure on the lowest bandgap is performed to investigate the variations of the bandgap width and frequency.     

Ultrashort pulses in graphene with Coulomb impurities

We have investigated the propagation of an electromagnetic field in graphene with impurities, including the two-dimensional case. The spectrum of electrons for the graphene subsystem is taken from a model that takes into account Coulomb impurities. Based on Maxwell’s equations, we have obtained an effective equation for the vector potential of the electromagnetic field. It has been revealed that the pulse shape depends on free parameters.     

Rb吸附石墨烯纳米带电子性质和光学性质的研究

本文基于密度泛函理论的第一性原理方法了计算了Rb、O和H吸附石墨烯纳米带的差分电荷密度、能带结构、分波态密度和介电函数,调制了石墨烯纳米带的电子性质和光学性质,给出了不同杂质影响材料光学特性的规律.结果表明本征石墨烯纳米带为n型直接带隙半导体且带隙值为0.639 eV;Rb原子吸附石墨烯纳米带之后变为n型简并直接带隙半导体,带隙值为0.494eV;Rb和O吸附石墨烯纳米带变为p型简并直接带隙半导体,带隙值增加为0.996eV;增加H吸附石墨烯纳米带后,半导体类型变为n型直接带隙半导体,且带隙变为0.299eV,带隙值相对减小,更有利于半导体发光器件制备.吸附Rb、O和H原子后,石墨烯纳米带中电荷密度发生转移,导致C、Rb、O和H之间成键作用显著.吸附Rb之后,在费米能级附近由C-2p、Rb-5s贡献;增加O原子吸附之后,O-2p在费米能级附近贡献非常活跃,杂化效应使费米能级分裂出一条能带;再增加H原子吸附之后,Rb-4p贡献发生蓝移,O-2p在费米能级附近贡献非常强,费米能级分裂出两条能带.Rb、O和H的吸附后,明显调制了石墨烯纳米带的光学性质.