Hot Electron Driven Photocatalysis on Plasmon-resonant Grating Nanostructures.

Y. Wang,I. Aravind,Zhi Cai,L. Shen,G. Gibson,Jihan Chen,Bo Wang,Haotian Shi,Boxiang Song,E. Guignon,N. Cady,William Page,Arturo Pilar,S. Cronin

Published 2020 in ACS Applied Materials and Interfaces

ABSTRACT

We demonstrate hot electron injection of photoexcited carriers in 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 633nm light, we observe a 12-fold enhancement in the photocurrent (i.e., reaction rate) between resonant and non-resonant polarizations at incident angles of ±7.6o from normal. At 785nm irradiation, we observe similar resonant profiles to those obtained with 633nm wavelength light but with a 44-fold enhancement factor. Using 532nm light, we observe two resonant peaks (with approximately 10X enhancement) in the photocurrent at 19.4o and 28.0o 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.

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