Electronic transport in semiconductor-metal hybrid nanostructure studied by cryogenic scanning tunneling spectroscopy and ultrafast absorption measurements

Semiconductor-noble metal core-shell hybrid nanostructures (HNs) are promising and versatile systems due to quantum confinement-induced multiple functionalities. In future nanoplasmonic devices, the interaction between the strong intrinsic optical nonlinearities of excitonic nanostructures and the ability of metallic nanostructures to locally concentrate electromagnetic fields are the most important open subjects. Moreover, the band-structure and photo-physical properties of these HNs can be engineered by changing the overall orientation of the core-shell structure. In this work, an attempt has been made to investigate the band-structure modification with the formation geometry of HNs by low temperature (4K) scanning tunneling spectroscopy at the single nanoparticle level. The band-gap and the spectral feature above the band-gap due to electronic transport exhibit a specific trend with the change in the semiconductor core size and noble-metal shell thickness. We have investigated exciton-plasmon interaction mediated charge transfer process through these modified band-structures using ultra-fast absorption spectroscopy. The charge transfer is found to occur on a picosecond time-scale and is sensitive to the change of the core-shell geometry.