Wang Yu, Aravind Indu, Cai Zhi, Shen Lang, Gibson George N, Chen Jihan, Wang Bo, Shi Haotian, Song Boxiang, Guignon Ernest, Cady Nathaniel C, Page William D, Pilar Arturo, Cronin Stephen B
Department of Physics, University of Connecticut, Storrs, Connecticut 06269, United States.
Ciencia Inc., East Hartford, Connecticut 06108, United States.
ACS Appl Mater Interfaces. 2020 Apr 15;12(15):17459-17465. doi: 10.1021/acsami.0c00066. Epub 2020 Apr 3.
We demonstrate the hot electron injection of photoexcited carriers in an Ag-based plasmon resonant grating structure. By varying the incident angle of irradiation, sharp dips are observed in the reflectance with p-polarized light (electric field perpendicular to grating lines) when there is wavevector matching between the incident light and the plasmon resonant modes of the grating and no angle dependence is observed with s-polarized light. This configuration enables us to compare photoelectrochemical current produced by plasmon resonant excitation with that of bulk metal interband absorption simply by rotating the polarization of the incident light while keeping all other parameters of the measurement fixed. With 633 nm light, we observed a 12-fold enhancement in the photocurrent (i.e., reaction rate) between resonant and nonresonant polarizations at incident angles of ±7.6° from normal. At 785 nm irradiation, we observed similar resonant profiles to those obtained with 633 nm wavelength light but with a 44-fold enhancement factor. Using 532 nm light, we observed two resonant peaks (with approximately 10× enhancement) in the photocurrent at 19.4° and 28.0° incident angles, each corresponding to higher order modes in the grating with more nodes per period. The lower enhancement factors observed at shorter wavelengths are attributed to interband transitions, which provide a damping mechanism for the plasmon resonance. Finite difference time domain (FDTD) simulations of these grating structures confirm the resonant profiles observed in the angle-dependent spectra of these gratings and provide a detailed picture of the electric field profiles on and off resonance.
我们展示了在基于银的等离子体共振光栅结构中光激发载流子的热电子注入。通过改变辐照入射角，当入射光与光栅的等离子体共振模式之间存在波矢匹配时，对于p偏振光（电场垂直于光栅线），在反射率中观察到尖锐的下降，而对于s偏振光则未观察到角度依赖性。这种配置使我们能够通过旋转入射光的偏振，同时保持测量的所有其他参数不变，将等离子体共振激发产生的光电流与块状金属带间吸收产生的光电流进行比较。使用633 nm光，我们在与法线成±7.6°的入射角下，观察到共振和非共振偏振之间的光电流（即反应速率）增强了12倍。在785 nm辐照下，我们观察到与633 nm波长光获得的类似共振曲线，但增强因子为44倍。使用532 nm光，我们在19.4°和28.0°入射角下观察到光电流中的两个共振峰（增强约10倍），每个峰对应于光栅中每个周期具有更多节点的高阶模式。在较短波长下观察到的较低增强因子归因于带间跃迁，它为等离子体共振提供了一种阻尼机制。这些光栅结构的有限差分时域（FDTD）模拟证实了在这些光栅的角度相关光谱中观察到的共振曲线，并提供了共振和非共振时电场分布的详细图像。
