Abstract
We present a theoretical and experimental study of a plasmonic nanoelectrode architecture that is able to inject bunches of hot electrons into an aqueous environment. In this approach, electrons are accelerated in water by ponderomotive forces up to energies capable of exciting or ionizing water molecules. This ability is enabled by the nanoelectrode structure (extruding out of a metal baseplate), which allows for the production of an intense plasmonic hot spot at the apex of the structure while maintaining the electrical connection to a virtually unlimited charge reservoir. The electron injection is experimentally monitored by recording the current transmitted through the water medium, whereas the electron acceleration is confirmed by observation of the bubble generation for a laser power exceeding a proper threshold. An understanding of the complex physics involved is obtained via a numerical approach that explicitly models the electromagnetic hot spot generation, electron-by-electron injection via multiphoton absorption, acceleration by ponderomotive forces and electron-water interaction through random elastic and inelastic scattering. The model predicts a critical electron density for bubble nucleation that nicely matches the experimental findings and reveals that the efficiency of energy transfer from the plasmonic hot spot to the free electron cloud is much more efficient (17 times higher) in water than in a vacuum. Because of their high kinetic energy and large reduction potential, these proposed wet hot electrons may provide new opportunities in photocatalysis, electrochemical processes and hot-electron driven chemistry.
Highlights
The possibility to generate free electrons in water has been attracting interest for several decades in many different fields of chemical and physical sciences because of their extremely high reactivity1
Free electrons have a fundamental role in many photochemical or electrochemical processes, and they participate as a trigger or an intermediate state in an extremely wide variety of chemical, biological or physical processes
We presented experimental data and a numerical model that describe hot-electron injection and acceleration in water by photoexcitation of 3D plasmonic nanoelectrodes
Summary
The possibility to generate free electrons in water has been attracting interest for several decades in many different fields of chemical and physical sciences because of their extremely high reactivity. Free electrons can be considered the most powerful and simple reducing agents in chemistry, showing huge reduction potentials, exceeding more than À5 eV with respect to the normal hydrogen electrode. Free electrons have a fundamental role in many photochemical or electrochemical processes, and they participate as a trigger or an intermediate state in an extremely wide variety of chemical, biological or physical processes. The difficulties originate from the wide range of energy and time scales involved in these processes. Most of the current knowledge comes from experiments of the radiolysis of water produced by a high-energy electron beam or intense laser radiation, which usually result in very different and complex outcomes
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