Optical and electrical measurements at the nanoscale

Abstract

Plasmonics modes, or photon states coupled to the collective oscillations of electrons in metallic structures, are very attractive for applications where small size and strong intensity of light are required, as for bio and chemical sensors, solar cells and photodetectors. The effcient use of plasmonic structures in these fields is due to their advantageous properties such as broadly tunable optical behaviour coupled with catalytically active surfaces and high efficiency of trapping and concentrating of light. Indeed, as the optical properties of these plasmonic materials are highly tunable (by varying size and shape) across the entire visible spectrum they provide an extremely efficient platform for light absorption and collection. Nevertheless, such strong light confinement in plasmonic systems requires the storage of part of the energy in the motion of free-electrons, which are excited out of equilibrium and subject to ohmnic losses. These out of equilibrium carrier are highly energetic and if extracted can be used as catalyzer of chemical reaction at the surface of the plasmonic structure with extremely precise control. In this work a combination of optical and electrical measurements is used to further explore the understanding of the underlying physics at the base of plasmon enhancement and hot carrier production. By probing electrical and optical properties, we try to disclose a tighter link between oscillation of the electromagnetic field and the generation of energetic electron that once out of equilibrium with the oscillation of the field can be harvested with different purposes. After realizing that the acceptor of these energetic carries needs to be placed in the vicinity of the plasmonic structure and spatially localised in the region of highest field of the structure under exam, so to increase the probability of extraction of such energetic carriers from the structure, as well to maximize their energy. I first investigate new manipulation techniques capable of driving a target object to the sphere of action of a plasmonic structure, and then explore the possible way to extract such energetic carriers at two different possible interfaces the metallic/semiconductor one and the metallic/molecular one.