Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215, United States.
ACS Nano. 2012 Sep 25;6(9):7998-8006. doi: 10.1021/nn3026468. Epub 2012 Aug 24.
Metamaterial-based perfect absorbers utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. For most of the reported absorbers, the absorption occurs only at a single wavelength where plasmon resonances are excited in the nanostructures. Here we introduce a dual-band perfect absorber based on a gold nanocross structure. Two bands of maximum absorption of 94% are experimentally accomplished by breaking the symmetry of the cross structure. Furthermore, we demonstrate the two bands can be readily tuned throughout the mid-infrared with their associated resonances giving rise to large near-field enhancements. These features are ideal for multiband surface-enhanced infrared spectroscopy applications. We experimentally demonstrate this application by simultaneously detecting two molecular vibrational modes of a 4 nm thick polymer film utilizing our proposed absorber. Furthermore, in response to variations in the interaction strength between the plasmonic and molecular dipoles, we observe an anticrossing behavior and modification in the spectral line shape of the molecular absorption peak, which are characteristic of the coupling between the two modes.
基于超材料的完美吸收体利用固有损耗，通过适当的结构设计，在特定波长下实现近于 unity 的吸收。对于大多数报道的吸收体，吸收仅发生在纳米结构中激发等离子体共振的单个波长处。在这里，我们介绍了一种基于金纳米十字结构的双频完美吸收体。通过打破十字结构的对称性，实验实现了两个最大吸收率为 94%的吸收带。此外，我们证明通过与大近场增强相关的共振，这两个波段可以在整个中红外范围内轻松调谐。这些特性非常适合多频表面增强红外光谱应用。我们通过利用我们提出的吸收体同时检测 4nm 厚聚合物薄膜的两个分子振动模式，实验证明了这一应用。此外，对于等离子体和分子偶极子之间相互作用强度的变化，我们观察到交叉行为和分子吸收峰的光谱线形状的改变，这是两种模式之间耦合的特征。
