Tailoring Optical and Plasmon Resonances in Core-Shell and Core-Multishell Nanowires.

摘要

Semiconductor nanowires (NWs) are sub-wavelength structures which exhibit strong optical (Mie) resonances in the visible range. In addition to such optical resonances, the localized surface plasmon resonances (LSPR) in metal and semiconductor (or dielectric) based core-shell (CS) and core-multishell (CMS) NWs can be tailored to achieve novel negative-index metamaterials (NIM), extreme absorbers, invisibility cloaks and sensors. Particularly, in this dissertation, the versatility of CS and CMS NWs for the design of negative-index metamaterials in the visible range and, plasmonic light harvesting in ultrathin photocatalyst layers for water splitting are studied.;Utilizing the LSPR in the metal layer and the magnetic dipole resonance in the semiconductor shell under traverse electric (TE) polarization, semiconductor-metal-semiconductor CMS NWs can be designed to exhibit spectrally overlapping electric and magnetic resonances in the visible range. NWs exhibiting such double resonances can be considered as meta-atoms and arrayed to form polarization dependant, low-loss NIM.;Alternatively, by tuning the LSPR in the TE polarization and the optical resonance in the transverse magnetic (TM) polarization of metal-photocatalyst CS and semiconductor-metal-photocatalyst CMS NWs, the absorption within ultrathin (sub-50 nm) photocatalyst layers can be substantially enhanced. Notably, aluminum and copper based NWs provide absorption enhancement remarkably close to silver and gold based NWs respectively. Further, such absorption is polarization independent and remains high over a large range of incidence angles and permittivity of the medium.;Due to the tunability of their optical properties, CS and CMS NWs, are expected to be vital components for the design of nanophotonic devices. An outlook has been presented highlighting some of the potential applications of such nanowires beyond negetive-index metamaterials and extreme absorption.