Zilio Pierfrancesco, Dipalo Michele, Tantussi Francesco, Messina Gabriele C, de Angelis Francesco
Istituto Italiano di Tecnologia, 16163, Genova, Italy.
Light Sci Appl. 2017 Jun 30;6(6):e17002. doi: 10.1038/lsa.2017.2. eCollection 2017 Jun.
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.
我们展示了一种等离子体纳米电极结构的理论和实验研究，该结构能够将成束的热电子注入水环境中。在这种方法中，电子在水中被有质动力加速至能够激发或电离水分子的能量。这种能力由纳米电极结构（从金属基板伸出）实现，该结构允许在结构顶端产生强烈的等离子体热点，同时保持与几乎无限电荷库的电连接。通过记录透过水介质传输的电流对电子注入进行实验监测，而通过观察激光功率超过适当阈值时产生的气泡来确认电子加速。通过一种数值方法来理解其中涉及的复杂物理过程，该方法明确模拟了电磁热点的产生、通过多光子吸收逐个电子的注入、有质动力的加速以及通过随机弹性和非弹性散射的电子 - 水相互作用。该模型预测了气泡成核的临界电子密度，与实验结果非常吻合，并揭示了从等离子体热点到自由电子云的能量转移效率在水中比在真空中高得多（高17倍）。由于其高动能和大还原电位，这些提出的湿热电子可能在光催化、电化学过程和热电子驱动化学中提供新的机会。
