Plasmon induced ultrafast injection of hot electrons in Au nanoislands grown on a CdS film

Abstract

Metal nanoparticle semiconductor heterostructures exhibit unique optoelectronic properties and have potential applications in energy harvesting, photodetectors, photocatalysts, and optoelectronic devices. The hot carriers are formed at the metal nanostructure semiconductor interface, and their efficient injection into the surrounding media (semiconductor) is a great challenge and understanding the physics behind the charge transfer is currently a topic of global research. Herein, we report the investigation on the hot electron injection in the Au nanoislands formed on a CdS film using ultrafast femtosecond spectroscopy. When the Au–CdS film is excited with visible light (above the band gap), a complete bleaching effect is observed. However, when it is excited with the photon energies below the band gap of the CdS film, an absorption signal is observed over a broad spectral range. The ultrafast charge transfer dynamics studied herein indicate the possibility of the plasmons formed in the Au nanoislands, which directly decay nonradiatively by injecting electrons in the conduction band of the CdS film and charge recombination with the Au nanoislands. Finally, we demonstrate the charge transfer in the metal semiconductor hybrid, which exhibits a significant alteration in the ultrafast optical properties compared to its individual components and is dependent on the excitation energy and can thus be exploited in the light harvesting devices.