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

Indu Aravind,Zhi Cai,Bofan Zhao,Yu Wang,George N Gibson,Yi Wang,Sisi Yang,Stephen B Cronin,William D Page,Nathaniel C Cady,Ernest Guignon,Jahan M Dawlaty,Arturo Pilar,Lang Shen

doi:10.3390/cryst11020118

Abstract

Metallic grating structures have been shown to provide an effective platform for generating hot electrons and driving electrochemical reactions. Here, we present a systematic theoretical study of the surface plasmon resonance in different corrugated metallic grating structures using computational electromagnetic tools (i.e., the finite difference time domain (FDTD) method). We identify the corrugation parameters that produce maximum resonant field enhancement at commonly used wavelengths for photocatalytic applications (633 nm and 785 nm) in different material systems, including Ag, Au, Cu, Al, and Pt. The absorption spectra of each grating structure have been fitted with the analytical equation obtained from Coupled Mode Theory. We then extracted the absorptive and radiative loss rates. The field enhancement can be maximized by matching the absorption and radiation losses via tuning the geometric parameters. We could improve the average field enhancement of 633 nm and 785 nm modes by a factor of 1.8× and 3.8× for Ag, 1.4× and 3.6× for Au, and 1.2× and 2.6× for Cu. The optimum structures are found to be shallower for Ag, Au, and Cu; deeper for Pt; and to almost remain the same for Al. The gratings become flat for all the metals for increasing the average field enhancement. Overall, Ag and Au were found to be the best in terms of overall field enhancement while Pt had the worst performance.

Highlights

Hot electrons photoexcited in plasmon-resonant metal nanostructures have been studied extensively over the past decade in the context of novel chemistry, as well as solid state devices [1,2,3,4,5]
Theoretical studies have revealed that hot carriers are generated via direct transitions above the interband transition threshold in commonly used plasmonic materials gold, silver, copper, and aluminum [10,11]
In the work presented here, we systematically study the geometric effects in these corrugated structures on the generation of surface plasmon polaritons and resulting hot carrier generation in commonly used plasmonic metals Ag, Au, Al, Cu, and Pt

Summary

Introduction

Hot electrons photoexcited in plasmon-resonant metal nanostructures have been studied extensively over the past decade in the context of novel chemistry, as well as solid state devices [1,2,3,4,5]. Corrugated metallic grating nanostructures have emerged as an effective platform for generating plasmon-enhanced hot carriers in the visible range [13,14,15]. 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. In the work presented here, we systematically study the geometric effects in these corrugated structures on the generation of surface plasmon polaritons and resulting hot carrier generation in commonly used plasmonic metals Ag, Au, Al, Cu, and Pt. Based on the material choice, the optimum geometry can be chosen to maximize the field enhancement and thereby the hot carrier generation rate

Methods

Theory

Corrugated Grating Structure

Tuning the Corrugation for Each Material