Heterostructuring quantum dot nanomaterials

Abstract

In this research, various kinds of heterostructured nanomaterials are fabricated. For example, semicon-ductor-metal hybrid structure and graphene oxide/nanocrystal (NC) nanocomposites. In chapter 2, we demonstrate photocatalytic reduction of methylene blue in the infrared region, using PbSe/CdSe/CdS core/shell/shell heterostructure nanocrystals(HNCs) with type II or quasi-type II band offsets. Varying deposition rates of the CdS shell result in NCs of diverse morphologies ranging from spheres to pyramids to tetrapods. The faceted shapes enable the selective growth of Au tips, which help increase photocatalytic activity since the Au tips serve as an electron sink. Comparative studies reveal that the photocatalytic activity appears to correlate with the integral overlap of electron and hole wavefunctions. Tetrapod-shaped HNCs with Au tips show considerably higher photocatalytic activity for the reduction of methyelene blue than sphere or pyramid-shaped HNCs of equivalent composition arrangement. In chapter 3, graphene oxide/NC composites are synthesized by using electrostatic attraction between graphene oxide and NCs and we demonstrate crystalline transformation of various kinds of NCs on graphene oxide. Emergence of novel two-dimensional (2-D) templates, e.g., graphene oxide, has signified new intriguing opportunities to couple NCs electronically to the microscopic 2-D contacts. A promising approach to uniform dispersion of inorganic NCs on the 2-D interfaces is to graft them through chemical bonding. The 2-D dispersion would offer a unique opportunity to address one of the primary challenges in the field of nanotechnology: ful-filling excellent chemical and physical properties of the NCs in electronic solid-state devices. In this study, we blended colloidal NCs with graphene oxide in aqueous solution in attempts to bind the NCs on reactive sites of the graphene oxide surface, thereby achieving uniform loading. Interestingly, the NCs undergo significant crys-...