Controlled Synthesis And Optical Property Investigation Of Semiconductor Nanostructured Materials

The object of this dissertation is to explore new"greener"and cheaper controllable synthetic methods to semiconductor nanostructured materials, to characterize their structures, explore their optical properties, and suit their applications. Severl semiconductors nanostructured materials have been invesigated including CdSe and CdTe nanocrystals, Sb₂O₃ nanowires and nanobelts.(1) We report the possible mechanism of forming of CdSe nanocrystals in the high boiling point solvents with long alkane chains and a novel Non-TOP-Based route to zinc-blende CdSe nanocrystals. A new mechanism shows that there exits a redox reaction in the long alkane chain solvents: Se is reduced to H2Se gas; at the same time, the long alkane chains are oxidated to alkene chains; then, the Cd complex reacts with H2Se to form CdSe nanocrystals. Possible chemical reaction equations involved in the process of forming the CdSe nanocrystals have been discussed. The alkene chain and H2Se were detected respectively by a series of experiments to support the new mechanism. Under the guidance of this mechanism, we have developed a much cheaper and greener Non-TOP-Based route for the synthesis of a size series of high-quality zincblende (cubic) CdSe nanocrystals. Low-cost, green, and environmentally friendlier reagents are used, without use of expensive solvents such as trioctylphosphine (TOP) or tributylphosphine (TBP). The new route enables us to achieve high-quality CdSe nanocrystals with sharp ultraviolet and visible (UV-vis) absorption peaks, controllable size (2.0⁵.0 nm), bright photoluminescence (PL), narrow PL full width of half-maximum (fwhm) (29⁴8 nm), and high PL quantum yield (up to 60%) without any size sorting. (2) One of the most highlighted and fastest moving interfaces of nanotechnology is the application of quantum dots (QDs) in biological imaging and dictation. Herein, we adopted an improved method to synthesize a series of bring luminescent water-soluble CdTe quantum dots. The structural characterizations and optical properties are investigated. It was found that the as-synthesized CdTe quantum dots are pH sensitive. We cooperate with Jiacang Yue's group in institute of biophysics, Chinese Academy of Sciences to use pH sensitive CdTe QDs as a proton sensor to detect proton (H+) flux driven by ATP synthesis in chromatophore. We applied the QDs-labeled chromatophores as a virus-detector to detect H9 avian influenza virus based on antibody-antigen reaction. Furthermore, we take the bicolor (i.e. green and orange) CdTe QDs as the effective pH-sensitive fluorescent probes for dual simultaneous and independent detection of viruses. A new bicolor-QDs-biosensors fluorescent measurement system was established for rapid, simultaneous, and independent detection of two different kinds of viruses (i.e. H9 avian influenza virus and MHV68 virus). We believe that the method described in this paper has great potential for multicolor optical encoding detection system.(3) We report a simple solution route to large-scale synthesis of uniform, single-crystalline, and well-faceted orthorhombic antimony trioxide (Sb₂O₃) nanowires with rectangular cross sections by direct air oxidation of bulk metal antimony (Sb) in a mixed solution made of ethylenediamine (EDA) and deionized water (DIW). The as-synthesized products were analyzed by range of methods, such as XRD, SEM, EDX, TEM, SAED, HRTEM, FTIR, Raman, UV-vis absorption, and photoluminescence (PL) spectra. The as-synthesized Sb₂O₃ nanowires with rectangular cross sections are usually hundreds of micrometers in length, typically 80-100 nm in width, and 60-80 nm in thickness. The novel room temperature photoluminescence properties of Sb₂O₃ nanowires with rectangular cross sections displayed a significant UV luminescence with a strong emission band at 374 nm, which was reported for the first time, indicating the as-synthesized products with an optical band gap Eg=3.3 eV. It is expected that as-synthesized Sb₂O₃ nanowires would be a new member of functional materials and used in the manufacture of advanced nanodevices.(4) A facile template-free aqueous solution strategy of oriented attachment assisted self-assembly of Sb₂O₃ nanorods and nanowires into well-defined complex nanostructures is described in this paper. It is demonstrated that at the temperature of 40°C, the Sb₂O₃ nanorods with different lengths (2⁵0μm) and diameters (20¹000 nm) would axially self-assemble into multisegmented coaxial nanowires by an oriented attachment assisted end-to-end self-assembly process. At the temperature of 80°C, the Sb₂O₃ nanowires with diameter of 10³0 nm would radially self-assemble into nanobelts with hundreds of micrometers in length, typically 400¹000 nm in width and 20⁶0 nm in thickness by an oriented attachment assisted side-by-side self-assembly process. The obtained self-assembled nanostructures were analyzed by a series of methods such as XRD, SEM, EDX, TEM, SAED, HRTEM, and photoluminescence. The formation mechanism of the obtained nanostructures was discussed. The oriented attachment assisted self-assembly strategy we presented here may open a new avenue for the controllable self-assembly of nanorods and nanowires into unique complex nanostructured materials.