Metal/Si Nanowire Arrays for Hot Electron Catalysis

ABSTRACT

The application of high–refractive index substrates to boost near‐field enhancements in plasmonic nanostructures for photocatalysis remains limited. Here, we combine hexagonally‐arranged vertically‐aligned silicon nanowire (VA‐SiNW) arrays with Au nanoparticles and Au/Ag nanoshells to study the plasmon‐driven dimerization of p‐nitrothiophenol (p‐NTP) into 4,4′‐dimercaptoazobenzene (DMAB). In situ Raman spectroscopy reveals that VA‐SiNWs can enhance local electric fields at the metal nanostructures, which we use for SERS and hot electron catalysis. Despite producing the strongest near‐field enhancement and the highest SERS response, AuNPs/SiNW arrays do not deliver the highest reaction rates, indicating that near‐field intensity alone does not govern catalytic performance. This discrepancy is attributed to steric hindrance within highly confined hotspots at the Au/Si interface. Compared with the Au‐based substrates, Ag/SiNW arrays show higher photocatalytic activity, with 532 nm excitation dramatically accelerating p‐NTP photoreduction. Ag/SiNW arrays also photocatalyze 4‐mercaptobenzoic acid decarboxylation, demonstrating their ability to drive oxidation reactions via the generation of reactive oxygen radicals. Overall, our results indicate that VA‐SiNW arrays can serve as high‐surface‐area photonic supports for plasmon‐driven chemistry and highlight the critical interplay between field enhancement, hotspot accessibility, and metal choice in optimizing hot electron‐induced photocatalytic performance.