Surface Plasmon-Mediated Chemical Solution Deposition of Cu Nanoparticle Films

The photothermal heating of plasmonic metal nanostructures can be exploited for bottom-up nanofabrication via surface plasmon-mediated chemical solution deposition (SPMCSD). Herein, we demonstrate the versatility of this plasmon-mediated strategy with a rapid deposition (<i>t</i> ≈ 5 min) of metallic copper nanoparticles (Cu NPs) on a silver (Ag) film on nanosphere (AgFON) substrate under low-power, visible-light irradiation (<i>I</i>₀ = 2.0 W/cm², λ > 435 nm). The resultant plasmonic nanostructures exhibit significant optical extinction and enriched chemical affinity for Raman probe molecules, rendering the hybrid AgFON/Cu substrate a suitable plasmonic platform for chemical sensing via surface-enhanced Raman scattering (SERS)

Solvent Control of Surface Plasmon-Mediated Chemical Deposition of Au Nanoparticles from Alkylgold Phosphine Complexes

Bottom-up approaches to nanofabrication are of great interest because they can enable structural control while minimizing material waste and fabrication time. One new bottom-up nanofabrication method involves excitation of the surface plasmon resonance (SPR) of a Ag surface to drive deposition of sub-15 nm Au nanoparticles from MeAuPPh₃. In this work we used density functional theory to investigate the role of the PPh₃ ligands of the Au precursor and the effect of adsorbed solvent on the deposition process, and to elucidate the mechanism of Au nanoparticle deposition. In the absence of solvent, the calculated barrier to MeAuPPh₃ dissociation on the bare surface is <20 kcal/mol, making it facile at room temperature. Once adsorbed on the surface, neighboring MeAu fragments undergo ethane elimination to produce Au adatoms that cluster into Au nanoparticles. However, if the sample is immersed in benzene, we predict that the monolayer of adsorbed solvent blocks the adsorption of MeAuPPh₃ onto the Ag surface because the PPh₃ ligand is large compared to the size of the exposed surface between adsorbed benzenes. Instead, the Au–P bond of MeAuPPh₃ dissociates in solution (<i>E</i>_a = 38.5 kcal/mol) in the plasmon heated near-surface region followed by the adsorption of the MeAu fragment on Ag in the interstitial space of the benzene monolayer. The adsorbed benzene forces the Au precursor to react through the higher energy path of dissociation in solution rather than dissociatively adsorbing onto the bare surface. This requires a higher temperature if the reaction is to proceed at a reasonable rate and enables the control of deposition by the light induced SPR heating of the surface and nearby solution

Surface Plasmon-Driven Water Reduction: Gold Nanoparticle Size Matters

Water reduction under two different visible-light ranges (λ > 400 nm and λ > 435 nm) was investigated in gold-loaded titanium dioxide (Au-TiO₂) heterostructures with different sizes of Au nanoparticles (NPs). Our study clearly demonstrates the essential role played by Au NP size in plasmon-driven H₂O reduction and reveals two distinct mechanisms to clarify visible-light photocatalytic activity under different excitation conditions. The size of the Au NP governs the efficiency of plasmon-mediated electron transfer and plays a critical role in determining the reduction potentials of the electrons transferred to the TiO₂ conduction band. Our discovery provides a facile method of manipulating photocatalytic activity simply by varying the Au NP size and is expected to greatly facilitate the design of suitable plasmonic photocatalysts for solar-to-fuel energy conversion