Abstract
A fundamental study is performed on the surface plasmon resonance (SPR) of metal@semiconductor microsphere photocatalyst to uncover its broadband absorption mechanism over the visible wavelength region. Finite element method studies show that an interference pattern is uniquely generated inside the semiconductor microsphere due to the optical reflection and refraction at the interface between the microsphere and the catalytic medium. By embedding plasmonic nanoparticles (NPs) into the microsphere, an interference-induced broadband absorption enhancement over the entire visible region can be achieved as compared to other plasmonic structures. Based on the properties of the interference, the broadband absorption enhancement can be obtained everywhere inside the microsphere and is particularly large at the microsphere hot-zone. Studies also show that microsphere consisting of higher refractive index semiconductor can maximize the interference-induced broadband absorption enhancement. Besides, NPs with different materials can be mixed to tune the overall absorption band for flexible energy harvesting and enhanced selectivity. At the same time, the evanescent nature of the SPR near field could be better exploited to enhance the catalytic rate if locating the NPs close to the microsphere surface. Our findings could help experimentalists to design optimized metal@semiconductor microsphere photocatalyst to more efficiently utilize the solar power to drive chemical transformation.