Metal/Si Nanowire Arrays for Hot Electron Catalysis

Area of Science:

• Materials Science
• Nanotechnology
• Photocatalysis

Background:

• High-refractive index substrates are crucial for enhancing plasmonic nanostructures in photocatalysis.
• Limited understanding exists regarding the interplay of near-field enhancement, hotspot accessibility, and material choice in plasmon-driven reactions.

Purpose of the Study:

• To investigate the use of hexagonally-arranged vertically-aligned silicon nanowire (VA-SiNW) arrays as substrates for plasmon-driven photocatalysis.
• To explore the influence of different metal nanostructures (Au nanoparticles, Au/Ag nanoshells) on silicon nanowires for enhanced catalytic performance.

Main Methods:

• Fabrication of VA-SiNW arrays integrated with gold nanoparticles and gold/silver nanoshells.
• In situ Raman spectroscopy to monitor plasmon-driven dimerization of p-nitrothiophenol (p-NTP) to 4,4'-dimercaptoazobenzene (DMAB).
• Evaluation of photocatalytic activity using different excitation wavelengths and substrates, including 4-mercaptobenzoic acid decarboxylation.

Main Results:

• VA-SiNWs significantly enhance local electric fields, boosting Surface-Enhanced Raman Spectroscopy (SERS) and hot electron catalysis.
• Despite strong near-field enhancement, Au nanoparticle/SiNW arrays showed lower reaction rates due to steric hindrance in confined hotspots.
• Ag/SiNW arrays exhibited higher photocatalytic activity, particularly with 532 nm excitation, and demonstrated capability in oxidation reactions via reactive oxygen radicals.

Conclusions:

• VA-SiNW arrays serve as effective high-surface-area photonic supports for plasmon-driven chemical reactions.
• Optimizing plasmon-driven photocatalysis requires balancing field enhancement, hotspot accessibility, and the choice of plasmonic metal.
• This study provides critical insights into designing efficient plasmonic nanostructures for photocatalytic applications.