Wang Yi, Shen Lang, Wang Yu, Hou Bingya, Gibson George N, Poudel Nirakar, Chen Jihan, Shi Haotian, Guignon Ernest, Cady Nathaniel C, Page William D, Pilar Arturo, Dawlaty Jahan, Cronin Stephen B
Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
Faraday Discuss. 2019 May 23;214(0):325-339. doi: 10.1039/c8fd00141c.
Plasmon resonant grating structures provide an effective platform for distinguishing between the effects of plasmon resonant excitation and bulk metal absorption via interband transitions. By simply rotating the polarization of the incident light, we can switch between resonant excitation and non-resonant excitation, while keeping all other parameters of the measurement constant. With light polarized perpendicular to the lines in the grating (i.e., TE-polarization), the photocatalytic reaction rate (i.e., photocurrent) is measured as the angle of the incident laser light is tuned through the resonance with the grating. Here, hot holes photoexcited in the metal are used to drive the oxygen evolution reaction (OER), producing a measurable photocurrent. Using TE-polarized light, we observe sharp peaks in the photocurrent and sharp dips in the photoreflectance at approximately 9° from normal incidence, which corresponds to the conditions under which there is good wavevector matching between the incident light and the lines in the grating. With light polarized parallel to the grating (i.e., TM), we excite the grating structure non-resonantly and there is no angular dependence in the photocurrent or photoreflectance. In order to quantify the lifetime of these hot carriers, we performed transient absorption spectroscopy of these plasmon resonant grating structures. Here, we observe one feature in the spectra corresponding to interband transitions and another feature associated with the plasmon resonant mode in the grating. Both features decay over a time scale of 1-2 ps. The spectral responses of grating structures fabricated with Ag, Al, and Cu are also presented.
表面等离子体共振光栅结构提供了一个有效的平台，用于区分表面等离子体共振激发和通过带间跃迁的体金属吸收的影响。通过简单地旋转入射光的偏振方向，我们可以在共振激发和非共振激发之间切换，同时保持测量的所有其他参数不变。当光的偏振方向垂直于光栅中的线条（即TE偏振）时，随着入射激光的角度通过与光栅的共振进行调整，测量光催化反应速率（即光电流）。在这里，在金属中光激发产生的热空穴用于驱动析氧反应（OER），产生可测量的光电流。使用TE偏振光，我们观察到在垂直入射约9°处光电流出现尖锐峰值，光反射率出现尖锐下降，这对应于入射光与光栅中的线条之间具有良好波矢匹配的条件。当光的偏振方向平行于光栅（即TM）时，我们非共振地激发光栅结构，并且光电流或光反射率没有角度依赖性。为了量化这些热载流子的寿命，我们对这些表面等离子体共振光栅结构进行了瞬态吸收光谱测量。在这里，我们在光谱中观察到一个对应于带间跃迁的特征和另一个与光栅中的表面等离子体共振模式相关的特征。这两个特征都在1 - 2皮秒的时间尺度上衰减。还展示了用银、铝和铜制造的光栅结构的光谱响应。
