Studies On The Preparation, Characterization And Properties Of Nano-scale CdS With Quasi One-Dimensional, Two-Dimensional And Superlattice Structure

Chapter one : Nanomaterial is the major direction which the materials have been developing at present. Surface effect and quantum confinement effect from nanomaterials have briefly been described in this chapter. And current situation and future direction of the synthesis of â…¡-â…¥group semiconductor nanocrystals were summarized with main line of the synthesis of CdS nanomaterial. Synthetic methods and fluorescent property of the â…¡-â…¥group semiconductor nanocrystals especially CdS with zero-dimension, one-dimension, two-dimention and three-dimension are emphatically introduced. Finally, we have also reviewed the progress that â…¡-â…¥group semiconductor nanocrystals with high quantum yield were applied in front fields such as bioassay, clinical diagnosis, biolabeling and imaging. Chapter two: The synthesis of CdS quantum dots with high quantum yield was described in detail using CH3CSNH2 as sulphur source. The high-quality CdS quantum dots can self-assemble to hexagonally ordered superlattice structure. The structural characterization and optical properties of CdS quantum dots were determined by TEM, SAED, XRD, PL and UV-Vis spectra. Investigation on nucleation/annealing temperature, annealing time, the concentration of the precursor, dispersed solvent was performed systematically. Results indicated: CdS quantum dots with excellent optical properties can be obtained at relative lower temperature when our reaction system was applied. The control of annealing time contributes to improving fluorescent property. The size of nanoparticles and position of fluorescence peak can be tuned by the temperature and the concentration of the precursor. Proper solvent will increase fluorescence intensity too. This method described here have advantages as follows: high quantum yield of high-quality product. superlattice from self-assembly of CdS quantum dots. and method is simple, safe, energy-saving, easily controlled, etc.. Above-mentioned method can be applied to the synthesis of other sulphide semiconductor nanomaterials and has potential application in industry. Chapter three: For the first time two-dimensional nano-scale CdS (nanoplates) were prepared under stabilization and template effect of starch with polyol. And CdS nanoplates with shapes such as triangular, disk, rod, square, etc. have been obtained when experimental conditions changed. The two-dimensional CdS nanoplates were characterized by TEM, SAED, XRD, UV-Vis, PL, Raman. Results showed: the shapes of CdS nanoplates depend on reactant concentration, aging time, the fashion of adding Na2S solution and are allowed to alter. Formation mechanism of CdS nanoplates was preliminary discussed. Chapter four: Quasi one-dimensional CdS nanoparticle chains were prepared at high temperature while soluble starch with polyol was utilized as capping agent and stabilizing agent and solution containing CH3CSNH2 was refluxed. Characterization and spectra such as TEM, SAED, XRD, UV-Vis, PL were employed to study the structure and properties of nanoparticle chains. And various kinds of influence factors were discussed. The results showed: pH of the solution not only plays a decisive role in controlling over the size of nanoparticles but also influences shapes. High temperature can speed up the orientation growth to form CdS nanorod. Additionally, ultrasonication was used and turned nanochains to bunche-like aggregates, which has offered a convenience manufacture way for practical application in photoelectric technology need solid nanomaterials with special shapes.