MOVPE生长的InGaN/GaN单量子阱的光致发光和光吸收特性

研究了用金属有机物气相外延(MOVPE)法在蓝宝石衬底上生长的In组分浓度保持不变的InGaN/GaN单量子阱结构在室温下的发光特性和光吸收特性.实验结果表明,在InGaN厚度<3nm时,随着样品InGaN势阱层宽度的增加(1nm),光致发光(PL)谱的发光峰值波长出现明显的红移33nm现象,而且发光强度下降8%,谱线半峰全宽(FWHM)展宽,通过对样品的透射、反射光谱研究发现,量子阱层窄(1.5nm)的样品在波长接近红外区时出现无吸收的现象,即R+T达到了100%,而在阱层较宽的样品中没有发现这一现象,对引起这些现象的原因进行了讨论.这些结果有助于开发和优化三族氮化物半导体光电器件的进一步研究工作.     

太赫兹波段表面等离子光子学研究进展

表面等离子光子学是研究金属、 半导体纳米结构材料独特的光学特性, 是目前光子学中最有吸引力、 发展最快的领域之一. 伴随着微/纳制造技术与计算机模拟技术的进步, 表面等离子光子学在可见光、 红外、 太赫兹以及微波频域得到了广泛研究, 在高灵敏生化传感、 亚波长光波导、 近场光学显微、 纳米光刻等领域有潜在的应用价值. 特别是人工超材料的发展, 为自然界长期缺乏响应太赫兹波的材料和器件奠定了基础, 从而也促进了太赫兹波段表面等离子光子学的研究. 本文从太赫兹表面等离子波的激发、 传导、 最新应用及未来发展趋势等几个方面进行了回顾和讨论, 将最新研究成果展示给读者.     

基于纳观域碳纳米管的太赫兹波天线研究

基于碳纳米管独特的结构特点建立了以其为基础的Pocklington积分方程,并设计了一种全新的碳纳米管太赫兹(THz)波天线.数值仿真和理论计算结果表明,碳纳米管能够产生高频THz电磁辐射,半波长为60μm、半径为2.712nm的单壁碳纳米管偶极天线在-10dB反射系数以下可以实现2.5THz与7.6THz的双频带工作,带宽分别为8.4%与2.7%,由其构成的纳米管天线阵可以获得10.3dB的高增益特性.所得结果有助于在纳观域开展高频THz波辐射源及天线的研究与设计. 关键词： 太赫兹波 碳纳米管 天线 辐射源     

Electromagnetic scattering of the carbon nanotubes excited by an electric line source

An analytical solution is presented for the electromagnetic scattering from an infinite-length metallic carbon nanotube and a carbon nanotube bundle.The scattering field and scattering cross section are predicted using a modal technique based on a Bessel and Hankel function for the electric line source and a quantum conductance function for the carbon nanotube.For the particular case of an isolated armchair (10,10) carbon nanotube,the scattered field predicted from this technique is in excellent agreement with the measured result.Furthermore,the analysis indicates that the scattering pattern of an isolated carbon nanotube differs from that of the carbon nanotube bundle of identical index (m,n) metallic carbon nanotubes.     

Electromagnetic scattering of the carbon nanotubes excited by an electric line source

An analytical solution is presented for the electromagnetic scattering from an infinite-length metallic carbon nanotube and a carbon nanotube bundle. The scattering field and scattering cross section are predicted using a modal technique based on a Bessel and Hankel function for the electric line source and a quantum conductance function for the carbon nanotube. For the particular case of an isolated armchair (10, 10) carbon nanotube, the scattered field predicted from this technique is in excellent agreement with the measured result. Furthermore, the analysis indicates that the scattering pattern of an isolated carbon nanotube differs from that of the carbon nanotube bundle of identical index (m, n) metallic carbon nanotubes.     

提高太赫兹时域光谱仪测量速度研究

太赫兹时域光谱仪的测量速度是一个非常重要的指标,为了提高光谱仪的测量速度需要提高延迟线的扫描速度。实验研究了扫描速度、时间常数、采样率对太赫兹时域光谱仪信号品质的影响。研究结果表明,当时间常数为10 ms时,提高扫描速度不会对信号幅度造成较大改变;而当时间常数为30,100和300 ms时,随着扫描速度的提高,信号幅度会迅速降低,且时间常数越大信号幅度衰减越快,因此,为了避免在提高测量速度时导致信号品质的劣化,应尽量设置较小的时间常数。另一方面,当采集一定时域长度的信号时,扫描速度越高,采集到的采样点数越少,时域波形失真越严重,因此在提高扫描速度时,不仅需要减小锁相放大器时间常数,同时还需要相应的提高采样率以避免因采集点数减少而造成信号波形的失真。该结果可为提高太赫兹时域光谱仪的测量速度提供参考。     

Terahertz radiation from armchair carbon nanotube dipole antenna

This paper investigates the electromagnetic radiation characteristics of a metallic, large aspect ratio single walled carbon nanotube antenna in the terahertz frequency region below 12.5 THz. The key features of terahertz pulse have been revealed on the carbon nanotube antenna in comparison with conventional photoconductive switching. The terahertz waveforms, radiation power and their field distributions have been evaluated and are analysed. The Fourier transformed spectra over the whole frequency range demonstrate that the carbon nanotube antenna can be used as radiation source for broadband terahertz applications.     

碳纳米管薄膜周期结构的太赫兹表面等离子波特性研究

在获得太赫兹波段碳纳米管薄膜的介电特性基础上,利用数值THz时域光谱技术研究了碳纳米管薄膜栅周期结构的表面等离子激元的传播特性和局域化现象. 研究结果表明,在栅周期为168 μm时,频率在0.5-2.5 THz之间出现两个等离子模式的共振峰值,分别位于0.99 THz和1.95 THz,这与理论计算结果相符合. 数值计算的表面等离子激元传播距离与理论预测值相一致,达到了146 μm. 此外,分析了栅厚度与栅宽度变化对表面等离子波特性的影响. 关键词： 太赫兹 碳纳米管 表面等离子波     

Three-dimensional surface current loops in broadband responsive negative refractive metamaterial with isotropy

We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to the polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.