Terahertz transmission properties of four metamaterials

We investigated the power transmission properties of four metamaterials in terahertz regime. The measured results reveal a global maximum transmission peak at 2.52 THz, and some local transmission peaks. In order to find a best metamaterials with relatively high transmission efficiency, we compared measured power transmission performances of four types of metamaterials microstructures, and analyzed their transmission differences.     

Terahertz generation and amplification in graphene nanoribbons in multi-frequency electric fields

We study theoretically a multi-frequency response of electrons in confined graphene subject to DC–AC driven fields. We explore the possibility for using graphene nanoribbons (GNRs) to generate and amplify terahertz (THz) radiations in electric field domainless regime. We discover two main important schemes of generation; when the frequencies are commensurate, THz generation is due to wave mixing and when they are non-commensurate, a single strong field suppresses space charge instability and any weak signals can get amplified.     

Tunable electronic transmission gaps in a graphene superlattice

The transmission in graphene superlattices with adjustable barrier height is investigated using transfer-matrix method. It is found that one could control the angular range of transmission by changing the ratio of incidence energy and barrier height. The transmission as a function of incidence energy has more than one gaps, due to the appearance of evanescent waves in different barriers. Accordingly, more than one conductivity minimums are induced. The transmission gaps could be controlled by adjusting the incidence angle, the barrier height, and the barrier number, which gives the possibility to construct an energy-dependent wavevector filter.     

Terahertz plasmon-emitting graphene-channel transistor

In this work we propose and analyze the possibility of creating terahertz plasmon-emitting graphene-channel transistor. It is shown that at electric pumping the damping of the terahertz plasmons can give way to their amplification, when the real part of the dynamic conductivity of graphene becomes negative in the terahertz range of frequencies due to the interband population inversion.     

Band gap opening and optical absorption enhancement in graphene using ZnO nanocluster

Electronic, optical and transport properties of the graphene/ZnO heterostructure have been explored using first-principles density functional theory. The results show that Zn₁₂O₁₂ can open a band gap of 14.5 meV in graphene, increase its optical absorption by 1.67 times covering the visible spectrum which extends to the infra-red (IR) range, and exhibits a slight non-linear I–V characteristic depending on the applied bias. These findings envisage that a graphene/Zn₁₂O₁₂ heterostructure can be appropriate for energy harvesting, photodetection, and photochemical devices.     

垂直电场下扭转双层石墨烯光学吸收性质的理论研究

层间扭转角度是对石墨烯物理性质宽波段可调谐的一个新参量.本文采用2°<θ<15°扭转角度下的连续近似模型,获得了不同扭转角度双层石墨烯分别在有、无电场下的能带结构,通过电子-光子相互作用跃迁速率,计算模拟了范霍夫奇点附近电子带内跃迁和带间跃迁所引起的光学吸收谱.结果表明,在无外加电场时,带间跃迁吸收峰的位置随着扭转角度的增大而发生从红外到可见光波段的蓝移,且吸收系数增大,带内跃迁的光学吸收系数相对于带间跃迁高出2个数量级;而存在外加电场时,两个范霍夫奇点在波矢空间的位置发生偏移,带间跃迁吸收峰发生分裂,且两个分裂的吸收峰位置随着电场强度的不断增大而反向行进.上述研究结果对石墨烯材料在光电器件方面的应用有一定指导作用.     

Hot-electron transport in graphene driven by intense terahertz fields

We investigate transport properties of graphene driven by intense terahertz (THz) fields, considering impurity, acoustic-phonon and optical phonon scatterings. The time evolutions of drift velocity and electron temperature are analyzed and the phase shift and distortion of drift velocity are demonstrated. We also examine the terahertz photoconductivity, finding that the suppression of linear dc mobility is greatly enhanced with decreasing frequency of the radiation.     

夹心式太赫兹微流控芯片

许多生物大分子的振动和转动能级都落在THz波段范围内,因此可以采用THz光谱技术定性地鉴别生物样品。但是大部分生物分子的活性需在液体环境中才能表现出来,而水作为极性物质对THz波具有较强的吸收特性。因此,在THz光谱技术中通常采取各种措施来减少水的影响,以防止水溶液中生物样品的信息被掩盖。该研究设计了两种可利用透射式太赫兹时域光谱(THz-TDS)系统检测的夹心式微流控芯片,通过减小THz与水的作用距离来减少水对THz的吸收,从而达到高透过率的目的。微流控芯片采用环烯烃共聚物(Zeonor 1420R)作为基片和盖片,聚二甲基硅氧烷(PDMS)作为沟道夹层,利用THz-TDS系统对该芯片进行了测试,测得该芯片在0.2～2.6 THz频率范围内的透过率可以达到80％以上。在微流控芯片中分别加入去离子水、1,2-丙二醇以及二者在不同体积比下的混合溶液,并测量了它们的透射谱。结果表明,不同比例溶液的THz光谱明显不同,说明该芯片在测量液态样品方面的可行性。此外,用该芯片分别研究了不同浓度的氯化钾和碘化钾溶液,发现氯化钾溶液随着浓度的增加THz透过率减弱,而碘化钾溶液则相反。初步认为,电解质改变了水溶液中的氢键密度,从而导致溶液对THz吸收的改变。     

旋转双层石墨烯的电子结构

本文将第一性原理和紧束缚方法结合起来, 研究了层间不同旋转角度对双层石墨烯的电子能带结构和态密度的影响. 分析发现, 旋转双层石墨烯具有线性的电子能量色散关系, 但其费米速度随着旋转角度的减小而降低. 进一步研究其电子能带结构发现, 不同旋转角度的双层石墨烯在M点可能会出现大小不同的的带隙, 而这些能隙会增强双层石墨烯的拉曼模强度, 并由拉曼光谱实验所证实. 通过对比双层石墨烯的晶体结构和电子态密度, 发现M点处带隙来自于晶体结构中的“类AB堆垛区”. 关键词： 旋转双层石墨烯 第一性原理 紧束缚 电子结构     

吡虫啉的太赫兹(THz)光谱研究

由超短激光脉冲产生的脉冲波是具有较宽频带的电磁辐射,属于远红外波段,该波段电磁波与物质的相互作用是个崭新的研究领域。文章利用太赫兹时域光谱技术测量了室温下吡虫啉在0.2～2.0 THz范围内的吸收谱和折射率谱。结果表明吡虫啉在此波段有明显的特征吸收峰且吸收系数随频率的增加而增大,折射率也随频率的增加而有所增大,其平均折射率为1.65。实验研究的同时,运用半经验理论计算了吡虫啉分子的结构及其在太赫兹波段的振动频率,并根据计算结果对实验数据进行了解析。计算结果与实验光谱吻合得很好,实验光谱的特征吸收峰是由分子的集体振动及扭转形成, 不同的吸收峰位对应分子不同的振转模式。实验和理论研究的对比表明：分子的远红外吸收特征对于分子的结构和空间排列非常敏感,THz-TDS是研究生物分子集体振动模式和构象结构的好方法。     

真皮革和人工革在太赫兹波段的光谱研究

皮革检测鉴定的市场需求缺口巨大,不同种类皮革,尤其是不同种类真皮革无损、无标记检测具有重要的应用价值。利用太赫兹时域光谱技术系统地测试了不同种类真皮革和人工革的太赫兹透射光谱,计算了不同真皮革和人工革的太赫兹吸收系数和折射率。在0.2~1.5 THz范围内,不同种类皮革的太赫兹吸收系数和折射率数值大小具有明显差异,真皮革大于人工革;且真皮革中,爬行类皮革>鱼类皮革>哺乳类皮革。进一步地,猪、牛、羊真皮革在25~80 ℃加热过程中太赫兹时域光谱振幅变化均在60 ℃左右出现拐点,而人工革无拐点;且猪、牛、羊真皮革变化趋势各异。为了验证皮革太赫兹光谱产生差异的原因,首先对代表性皮革牛皮革、人造革和合成革的主要组成成分牛皮胶原蛋白、聚氯乙烯（PVC）和聚氨酯（PU）进行了太赫兹光谱测试,牛皮胶原蛋白的太赫兹吸收系数和折射率大于聚氯乙烯和聚氨酯;并且在25~80 ℃加热过程中胶原蛋白出现变化拐点,而聚氯乙烯无。实验结果显示,皮革主要组成成分的太赫兹光谱特征的数值差异和变化趋势与对应皮革相同,表明不同种类皮革间差异性的太赫兹光谱特征主要来源于其组成成分的不同。基于此,太赫兹光谱技术有望用于皮革的快速、准确、无损、无标记检测,用于区分不同种类真皮革和人工革,尤其是分辨来源于爬行动物、哺乳动物和鱼类的真皮革。     

Tunable Fano resonances in the ballistic transmission and tunneling lifetime in a biased bilayer graphene nanostructure

Dynamics of the Dirac fermions, in particular the transmission coefficient and the resonant tunneling lifetime are studied across a bilayer graphene electrostatic double barrier structure modulated by an in plane homogeneous electric field. Asymmetric Fano type resonances are noted for the first time in the transmission spectrum of the bilayer graphene nanostructures and are found to be highly sensitive to the direction of incidence of the charge carriers and the applied homogeneous electric field. The effect of the external field on the extended and the evanescent modes is also analysed. Resonant tunneling lifetime is found to be highly anisotropic in nature. The chiral carriers are either accelerated or decelerated by the electric field depending on the energy of the quasi-bound states, the angle of incidence and the magnitude of the applied field. Effects of the external field on the localization of the chiral carriers are also discussed.     

太赫兹光谱用于成品油的识别

用太赫兹时域光谱(THz-TDS)技术研究了90#、93#、97#汽油和-10#柴油在0.25—1.5THz波段的响应特性。结果表明,不同油品其太赫兹响应图谱确实存在明显的差异,并从成分上分析了产生这些差异的原因。在成品油中,吸收系数受醇类添加剂的影响很大,芳烃次之,直链烷烃很少;折射率主要受成分中碳数的影响同时芳烃的作用也很大。通过吸收系数和折射率的不同能够实现成品油的鉴别和区分。     

光栅-液晶复合结构太赫兹移相器

随着太赫兹技术及其应用的快速发展,各类太赫兹控制器件需求也随之增加,作为太赫兹系统重要器件之一,太赫兹波移相器成为当前研究热点.已有移相器存在着尺寸较大、结构复杂、相移量较小等问题,为克服上述缺陷,提出一种光栅-液晶复合结构太赫兹移相器,该器件结构为石英、石墨烯、液晶盒、光栅结构、石墨烯和石英组成.通过改变石墨烯电极上...     

First-principles study of lithium intercalated bilayer graphene

Lithium intercalated bilayer graphene has been investigated using first-principles density functional theory calculations. Results show that there exist AB and AA stacking sequences for bilayer graphene in which the latter is more favorable for the Li storage and the former will evolve into the latter with the intercalation of Li ions. The relationship between the interlayer distance of two graphene sheets and the intercalated capacity of Li ions is discussed. It is found that structural defect is identified to store Li ions more favorably than pristine bilayer graphene and an isolated C atom vacancy in bilayer graphene can capture three Li ions between two graphene sheets.     

Electronic transport of bilayer graphene with asymmetry line defects

In this paper,we study the quantum properties of a bilayer graphene with(asymmetry) line defects.The localized states are found around the line defects.Thus,the line defects on one certain layer of the bilayer graphene can lead to an electric transport channel.By adding a bias potential along the direction of the line defects,we calculate the electric conductivity of bilayer graphene with line defects using the Landauer-Biittiker theory,and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene.This one-dimensional line electric channel has the potential to be applied in nanotechnology engineering.     

有机磷农药甲基对硫磷的太赫兹(THz)光谱研究

运用太赫兹时域光谱技术(THz-TDS)与理论模拟相结合的方法研究了有机磷农药甲基对硫磷在THz波段的光谱特性。在室温氮气环境中得到了样品在0.2～2.0 THz波段的吸收谱和折射率谱。表明其特征吸收峰分别位于0.65,1.33,1.81和1.91 THz处,其平均折射率为1.39。同时运用密度泛函理论(DFT)计算了甲基对硫磷分子的结构及其在太赫兹波段的振动频率,计算结果与实验数据吻合较好。研究结果表明,实验光谱的特征吸收峰是由分子的集体振动及扭转形成,不同的吸收峰位对应分子不同的振转模式。     

盐酸克伦特罗的太赫兹光谱研究

应用太赫兹时域光谱技术获取了盐酸克伦特罗在0.2～2.6 THz波段的光谱特征,并计算获得了盐酸克伦特罗在室温下的折射率谱和吸收谱.分别理论计算了克伦特罗分子、盐酸克伦特罗分子和盐酸克伦特罗晶体的振动频率.根据理论计算和实验光谱的对比,对盐酸克伦特罗的THz特征吸收峰进行了分析指认.实验结果显示,基于固体仿真的方法能够...     

基于石墨烯和二氧化钒的太赫兹宽带可调谐超材料吸收器

太赫兹超材料吸收器作为一种重要的太赫兹功能器件,被广泛应用于生物医学传感、电磁隐身、军用雷达等多个领域.但这种传统的超材料吸收器结构具有可调谐性差、功能单一、性能指标不足等缺点,已经无法满足复杂多变的电磁环境的要求,因此可调谐超材料吸收器逐渐成为了太赫兹功能器件领域的研究热点.为实现超材料吸收器吸收特性的调谐,通常从调...