On Chip Plasmonic Monopole Nano-Antennas and Circuits
On Chip Plasmonic Monopole Nano-Antennas and Circuits
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DOI：
10.1021/nl202528h
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发表时间：
2011-12-01
期刊：
影响因子：
10.8
通讯作者：
Altug, Hatice
中科院分区：
文献类型：
--
作者：
Adato, Ronen;Yanik, Ahmet A.;Altug, Hatice
许多射频 (RF) 天线设计的类似物（例如半波偶极子和八木宇田）已成功适应光学频率范围，为生物传感、光电检测和发射器控制方面的重要进展打开了大门。然而，考虑到单极天线在射频应用中的广泛使用，单极天线的例子非常罕见。单极天线很有吸引力，因为它们具有易于设计、紧凑的几何形状，并且能够很好地隔离接地层的干扰。然而，通常，需要将天线元件定向为垂直于半无限接地平面，这需要三维结构并且与基于芯片的制造技术不兼容。我们在这里首次提出并证明，单极天线元件可以通过使用小纳米棒作为线反射器，由以传统平面几何形状制造的单元件纳米颗粒制成。该结构具有紧凑的几何形状，反射器元件提供类似于射频对应物的隔离措施。这种隔离在导电耦合状态下持续存在，允许多个单极子组合成单个纳米粒子，但仍然独立运行。这与之前的几项研究形成鲜明对比，这些研究观察到传导耦合粒子的光谱响应存在巨大变化。我们可以通过使用标准射频天线理论中的电路方程对系统进行建模来解释这些影响。我们的模型准确地描述了这种行为以及结构的详细共振调谐。作为具体的实际应用，单极共振被精确调谐到所需的蛋白质吸收带，从而增强其光谱特征。此外，导电耦合的精确建模和所证明的电子隔离对于包含多个天线和其他载流元件的复杂等离子体电路的设计应该具有普遍意义。
Analogues of many radio frequency (RF) antenna designs such as the half-wave dipole and Yagi-Uda have been successfully adapted to the optical frequency regime, opening the door for important advances in biosensing, photodetection, and emitter control. Examples of monopole antennas, however, are conspicuously rare given the element's extensive use in RF applications. Monopole antennas are attractive as they represent an easy to engineer, compact geometry and are well isolated from interference due the ground plane. Typically, however, the need to orient the antenna element perpendicular to a semi-infinite ground plane requires a three-dimensional structure and is incompatible with chip-based fabrication techniques. We propose and demonstrate here for the first time that monopole antenna elements can be fashioned out of single element nanoparticles fabricated in conventional planar geometries by using a small nanorod as a wire reflector. The structure offers a compact geometry and the reflector element provides a measure of isolation analogous to the RF counterpart. This isolation persists in the conductive coupling regime, allowing multiple monopoles to be combined into a single nanoparticle, yet still operate independently. This contrasts with several previous studies that observed dramatic variations in the spectral response of conductively coupled particles. We are able to account for these effects by modeling the system using circuit equations from standard RF antenna theory. Our model accurately describes this behavior as well as the detailed resonance tuning of the structure. As a specific practical application, the monopole resonances are precisely tuned to desired protein absorption bands, thereby enhancing their spectroscopic signatures. Furthermore, the accurate modeling of conductive coupling and demonstrated electronic isolation should be of general interest to the design of complex plasmonic circuits incorporating multiple antennas and other current carrying elements.