可调谐碳纳米管薄膜THz表面等离子波导及传导特性研究

Terahertz surface plasmon waveguides have attracted interest because of their unique ability to support low-loss THz wave that are localized near the surface of an interface. In this project, tunable carbon nanotube film surface plamon waveguide and transmission properties at terahertz range have been presented. First, carbon nanotube films are grown by chemical vapor deposition. The influence of preparation process on the conductivity properties have been studied, and the carrier concentration in semiconducing carbon nanotube is changed to analyze the tunable electrical properties of carbon nanotube film. Second, the dielectric parameters are obtained by comparing the theoretical calculation with the result of THz time domain spectroscopy of carbon nanotube film. Then the waveguide structure is designed and the parameters are optimized in order to finding the effect law of geometric parameters on the surface wave transmission properties. Eventually, THz surface waveguide has been manufactured and the transmission properties of surface plasmon wave have been studied. All the results of this project are expected to solve the weakness of high-loss and weak limitation for the current THz waveguide, and promote the research and development of the high-sensitive, tunable THz wave devices.

THz表面等离子波导以低损耗、高局域化之优点限制和传导THz波而成为国际研究热点之一。本项目提出利用碳纳米管薄膜来实现THz表面等离子波波导并对其可调谐传导特性进行深入研究。主要内容包括：利用化学气相淀积法制备碳纳米管薄膜，研究制备工艺对其导电性能的影响，并通过光照改变半导体性碳纳米管的载流子浓度以分析薄膜的可调谐导电特性；对制备的碳纳米管薄膜进行THz时域光谱测试分析并和理论计算对比，以获得THz波段的碳纳米管薄膜介电参数；进行波导结构设计和参数优化分析，通过数值仿真获得几何结构参数对表面波传播特性影响的规律；最后制备出能够传导THz表面波的波导并进行实验测试以揭示传导THz表面波的本质。本项目的预期成果有望解决目前THz波波导的弱限制和高损耗等问题，能够促进高灵敏、可调谐传感功能的THz波器件研究和开发。

导体/介质界面的表面等离子激元与局域化等离子开启了光学研究领域前所未有的深度和广度，在近场光学、光路集成以及单分子光传感领域具有广泛的应用。这将对低频光波段特别是应用于太赫兹波段的高灵敏近场成像与生物传感的高度局域化波导以及超聚焦的新颖现象的研究具有重要意义。本项目利用化学气相沉积法在硅衬底上制备多壁碳纳米管阵列后通过拉伸方法获得不同厚度的多壁碳纳米管薄膜，然后利用激光雕刻方法设计出碳纳米管薄膜的一维/二维周期性微观波导结构并通过实验改进薄膜厚度以及完善微观结构；从理论和实验两方面分析了碳纳米管薄膜在太赫兹波段的折射率、电导率和介电常数以及产生太赫兹表面等离子波传导特性。实验结果表明，碳纳米管薄膜在太赫兹波段的介电特性与金属在可见光波段的介电特性相似，表现出良好的导体特性。同时，对太赫兹波通过多壁碳纳米管薄膜波导的透射增强现象与增强机理进行了研究，得到在共振频率处传输增强80%以上，远远超出经典孔径理论预测的1.3%。此外，对碳纳米管薄膜在太赫兹波段的偏振特性进行了探索性研究，获得了极化比能达到99.4%的好结果。