Research On Fabrication And Properties Of Semiconductor-based LSPR Materials

Currently the research in the field of plasmonics has spurred a tremendous amount of interest, which is a phenomenon that arises from the wave of charge density fluctuations on the surface of the metal driven by the electromagnetic field of the light. However, the conventional plasmonic materials such as gold and silver suffer from shortcomings, which restrict severely the realization of plasmonics devices. Therefore, semiconductor-based LSPR materials should be better alternative plasmonic materials in the near-infrared region as a result of metallic properties and own special advantages. Doping mechanism and bandgap structure in semiconductors can reduce losses.The LSPR properties of semiconductor-based LSPR materials can be modified by alter their compostion, size and morphology. We have developed servral facile approaches to the synthesis of semiconductor-based nanomaterials with adjustment of doping concentration, size and shape to realize the excellently controlled LSPR properties in the near-infrared region. The primary significant results are listed as follows:(1) Indium tin oxide nanoparticles (ITO NPs)have been synthesized by the rapid thermal injection method. The doping Sn concentration in ITO NPs could be controlled via changing the %Sn in the initial feed from 0 to 30%. We demonstrate that LSPR frequencies of ITO NPs can be manipulated from 1600 to 1993 nm in near-infrared band. Furthermore, we demonstrate that the SPR peaks can also be tuned by the size of ITO NPs, from 6.3 to 16.2 nm in the case of uniform doping. And the LSPR peaks can be tuned from 1600 to 1978 nm. Besides, single crystalline ITO NPs with nanoflower morphology by 3D oriented attachment synthesized through the one-pot method exhibit LSPR absorption peak features of red-shifting and broadening.(2) Through the analysis of XPS spectra of the O1s core levels, the intensity ratio of oxygen vacancy has been achieved 27.3% when the Sn doping concentration is 10% which means that ITO NPs with 10% Sn doped have the highest electron density. Furthermore, once the Sn doping concentration exceeds 15%, partial Sn4+ ions have already been reduced to Sn2+which decrease the conductivity of the ITO NPs.(3) The ITO NPs were spin-coated onto 2 centimeter-wide quartz substrates, forming uniform ITO thin film with the thickness of 2.2μm after repeating 20 times. The thickness of thin film was controlled by the times of the spin-coating. ITO thin film has transparency of 83% in the visible spectral range and low resistivity (Rs=790 Ω/sq) via controlled thermal annealing at 300 ℃ for 1 h under Ar and 5% H2. To identify the potential of ITO nanoparticles assembly used as SERS-active substrate, we demonstrate the capable of enhancing Raman signal using R6G and DAPI in our ITO assembly systems with Raman spectroscopy.(4) Through the one-pot method, we synthesized the digenite Cu7.2S4 and covellite CuS nanodisks with a pronounced LSPR peak around 1422 and 1057 nm respectively. The Cu7.2S4 nanodisks assemblies can be effectively employed as a SERS-active substrate that the Raman signal of pure R6G dye enhanced significantly. We controlled Cu7.2S4 and CuS nanodisks orientation to form stacked structures by chemically modifying the surface with hydrophobic capping ligands. And Cu2+ ions acted as oxidizing agents, yielding void formation process in the Cu2-xS nanodisks core region in case of the Kirkendall effect via etching experiments. Monodisperse Cu2-xSe NPs were synthesized by using rapid thermal injection. The LSPR properties can be modified by altering the initial concentrations ratio of Cu and Se, which can affect the final phase of Cu2-xSe NPs.