Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371.
ACS Nano. 2014 Apr 22;8(4):3796-806. doi: 10.1021/nn500527f. Epub 2014 Apr 1.
Tailoring optical properties of artificial metamaterials, whose optical properties go beyond the limitations of conventional and naturally occurring materials, is of importance in fundamental research and has led to many important applications such as security imaging, invisible cloak, negative refraction, ultrasensitive sensing, and transformable and switchable optics. Herein, by precisely controlling the size, symmetry, and topology of alphabetical metamaterials with U, S, Y, H, U-bar, and V shapes, we have obtained highly tunable optical response covering visible-to-infrared (vis-NIR) optical frequency. In addition, we show a detailed study on the physical origin of resonance modes, plasmonic coupling, the dispersion of resonance modes, and the possibility of negative refraction. We have found that all the electronic and magnetic modes follow the dispersion of surface plasmon polaritons; thus, essentially they are electronic- and magnetic-surface-plasmon-polaritons-like (ESPP-like and MSPP-like) modes resulted from diffraction coupling between localized surface plasmon and freely propagating light. On the basis of the fill factor and formula of magnetism permeability, we predict that the alphabetical metamaterials should show the negative refraction capability in visible optical frequency. Furthermore, we have demonstrated the specific ultrasensitive surface enhanced Raman spectroscopy (SERS) sensing of monolayer molecules and femtomolar food contaminants by tuning their resonance to match the laser wavelength, or by tuning the laser wavelength to match the plasmon resonance of metamaterials. Our tunable alphabetical metamaterials provide a generic platform to study the electromagnetic properties of metamaterials and explore the novel applications in optical frequency.
人工超材料的光学性质可以超越传统和自然材料的限制，对基础研究具有重要意义，并导致了许多重要的应用，如安全成像、隐形斗篷、负折射、超灵敏传感、可变形和可切换光学等。在此，我们通过精确控制 U、S、Y、H、U 形和 V 形字母超材料的尺寸、对称性和拓扑结构，获得了覆盖可见光到近红外（vis-NIR）光频的高度可调谐光学响应。此外，我们对共振模式的物理起源、等离子体耦合、共振模式的色散以及负折射的可能性进行了详细研究。我们发现所有的电子和磁模式都遵循表面等离激元极化激元的色散关系；因此，它们本质上是由局域表面等离激元和自由传播光之间的衍射耦合产生的电子和磁表面等离激元样（ESPP-like 和 MSPP-like）模式。基于填充因子和磁导率公式，我们预测字母超材料在可见光学频率下应该具有负折射能力。此外，我们通过调谐共振以匹配激光波长，或通过调谐激光波长以匹配超材料的等离子体共振，展示了单层分子和飞摩尔食品污染物的特定超灵敏表面增强拉曼光谱（SERS）传感。我们的可调谐字母超材料为研究超材料的电磁性质和探索光学频率的新应用提供了一个通用平台。
