Hot Electron Driven Photocatalysis on Plasmon-Resonant Grating Nanostructures

Abstract

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°f rom 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.

Hot Electron Plasmon-Resonant Grating Structures for Enhanced Photochemistry: A Theoretical Study

“…In order to excite the surface plasmon polaritons (SPPs) in the grating structure, the momentum and energy of the incident photons had to match those of the SPPs (i.e., wavevector matching). The incident angles that satisfied this condition at each wavelength were found by solving the following equation [13]:…”

“…More recently, corrugated metallic grating nanostructures have emerged as an effective platform for generating plasmon-enhanced hot carriers in the visible range [13][14][15]. These gratings are fabricated by depositing a plasmonic metal on a corrugated silicon substrate.…”

“…Corrugated Au gratings have also been used to inject photoexcited hot electrons into an aqueous solution and to drive water splitting reactions [7,15]. Photocurrent enhancement has been demonstrated with hot electrons generated in corrugated Ag grating structures [13]. These measurements use a fixed wavelength and scan the incident angle, which enables tuning through the plasmon resonance.…”

Optical Resonator Enhanced Photovoltaics and Photocatalysis: Fundamental and Recent Progress

“…In 2020, Wang et al demonstrated huge PEC current enhancement by using the plasmonic resonant grating structure (Figure 15b). [222] By exploiting the sensitive AC lockin technique, the small photocurrents generated from hot electrons in the metal can be measured. They investigated the incident angle-dependent photocurrent, which showed a significant photocurrent enhancement when the wavevector matches the incident light and resonance of grating.…”

“…Bottom: electric field distribution and absorption spectrum of the Ag grating nanostructure. Reproduced with permission [222]. Copyright 2020, American Chemical Society.…”