FABRICATION AND CHARACTERIZATION OF INTEGRATED NANOSTRUCTURES & THEIR APPLICATIONS TO NANOPHOTONICS

Book excerpt: Current developments in optical devices are being directed toward nanocrystals based devices, where photons are manipulated using nanoscale optical phenomenon. Nanochemistry is a powerful tool for making nanostructures based on such nanocrystals. In this dissertation, various applications such as photodetectors/photovoltaics, photonic crystals and plasmonic applications involving nanoparticles and organic: inorganic hybrid systems have been investigated. The hall marks of quantum dots are well defined excitonic absorption and sharp emission profiles and their unique behavior comprises intense and immune to photobleaching luminescence, photon upconversion, slow exciton relaxation, multiexciton generation due to impact ionization, enhanced lasing, etc. Various quantum dots such as Indium Phosphide (InP), Cadmium Sulphide (CdS), Cadmium Selenide (CdSe), InP-CdS type-II core-shell, Lead Sulphide (PbS), Lead Selenide (PbSe) etc.^have been prepared via hot colloidal synthesis and have been extensively characterized spectroscopically as well as structurally. These quantum dots were utilized for making solution processed organic: inorganic hybrid photodevices. Photodetecting device with enhanced efficiency has been fabricated using physical blend of PbSe and carbon nanotubes. Type-II quantum dots (InP-CdS) were also utilized for making solar cells and their efficiency was found to be much more than their parent quantum dots (InP and CdS). Photonic composite materials, such as polymers doped with nanoparticles, have attracted a great deal of attention because of relative ease and flexibility of their engineering as well as improved performance for applications in photonic or optoelectronic devices. 2D Photonic Crystals of enhanced structural and optical properties were fabricated by doping small amount of colloidal gold nanoparticles and patterned via multi-beam interference lithography.^Spontaneous emission of quantum rods doped in such photonic crystal was controlled by simple azimuthal rotation of photonic crystals. Detailed studies have been performed to understand the underlying phenomenon/physics. Plasmonic nanostructures are also very attractive due to their ability to tune the plasmonic response by changing geometry. Plasmonic nanoarrays have been prepared by templating in porous alumina template and have been found to show extended response in infrared region owing to transverse plasmon coupling in nanoarrays. We have also prepared several planar optically active structures via two-photon lithography. In situ reduction of metal salt with simultaneous polymerization of SU-8 was utilized for making all plasmonic nanostructures. Detailed studies involving expected chemical reaction and structural/optical properties have been performed to characterize the same.