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The lack of a detailed mechanistic understanding for plasmon-mediated charge transfer at metal-semiconductor interfaces severely limits the design of efficient photovoltaic and photocatalytic devices. A major remaining question is the relative contribution from indirect transfer of hot electrons generated by plasmon decay in the metal to the semiconductor compared to direct metal-to-semiconductor interfacial charge transfer. Here, we demonstrate an overall electron transfer efficiency of 44 ± 3% from gold nanorods to titanium oxide shells when excited on resonance. We prove that half of it originates from direct interfacial charge transfer mediated specifically by exciting the plasmon. We are able to distinguish between direct and indirect pathways through multimodal frequency-resolved approach measuring the homogeneous plasmon linewidth by single-particle scattering spectroscopy and time-resolved transient absorption spectroscopy with variable pump wavelengths. Our results signify that the direct plasmon-induced charge transfer pathway is a promising way to improve hot carrier extraction efficiency by circumventing metal intrinsic decay that results mainly in nonspecific heating. 

Optical applications of plasmonic nanoparticles depend critically on particle properties such as relative proximity, composition, crystallinity, and shape. The most common nanoparticle fabrication techniques, colloidal synthesis and electron beam lithography, allow the tailoring of some of these parameters, yet do not provide control over all of them. Scanning probe block copolymer lithography (SPBCL), a technique that grows nanoparticles on substrates from precisely deposited precursor droplets, merges the advantages of colloidal synthesis and electron beam lithography, and offers high throughput, precise particle positioning, and composition control. A few challenges with the SBCL method remain: fabrication of optically relevant particle sizes on optically transparent supports, and detailed correlation of their optical and morphological properties. Here, we adapt SPBCL to fabricate large arrays of gold nanoparticles on glass supports. The resulting nanoparticles have varying shapes, and at ∼100 nm in diameter, they support strong plasmon resonances. In order to fully exploit the high-throughput fabrication method, we designed an automated dark-field microscope and correlated the optical behavior to the mechanical properties as determined through electron and pump–probe microscopy. We find that the SPBCL-synthesized nanoparticles are highly crystalline, supporting both plasmon oscillations and mechanical vibrations with lifetimes comparable to colloidal nanospheres. Our work highlights SPBCL as a promising and versatile synthesis approach for plasmonic nanoparticles, leading the way toward extensive screening capabilities for optical properties and hence improved potential applications.