Studies On Preparation Of CdS Nanocrystals By Hydrothermal And Solvothermal Techniques

Nano-scaled semiconducting materials have attracted considerable attentions due to their unique potential applications in future nanodevices. Amongâ…¡-â…¥group, CdS is an important semiconductor with direct band gap of about 2.42ev, and has wide applications in optoelectronic devices. It is still a challenging task to achieve morphology- and size- controlled growth of CdS nanostructures by a facile technique. Number work has shown technological perspective of hydro- and solvothermal routes to CdS nanostructures because of their facility, low cost and large scale production.The dissertation mainly focused on syntheses of CdS nanocrystals by the two techniques.CdS submicro- and micro-spheres assembled by nanoparticles were synthesized by hydrothermal route at low temperature. One-dimensional nanostructures, nanorods of CdS, were synthesized by solvothermal technique using ethylenediamine as solvent. The influences of synthetic conditions on the growth of CdS nanostructures were studied in details and their growth mechanisms were discussed.X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM)and high resolution TEM (HRTEM) were employed to examine the structures, morphologies and micro-structure of the products. The optical properties of products were analyzed by Photoluminescence (PL) spectra and Raman spectra (Raman). The main results of the dissertation are summarized as follows:1,Solvents, reaction temperature and reaction time were key factors of hydro- and solvothermal synthesing CdS nanocrystals.2,The different cadmium sources would affect the structures and morphologies of the products grown in ethylenediamine. The evolution of CdS nanorods from nanoparticles was achieved by solvothermal re-crystallization technique assisted by proper additives. It was found that thiourea and Na2S2O3 could facilitate one-dimensional growth of CdS nanorods.3,The Raman modes of CdS nanocrystals appear a red shift , which is believed to be related with size-effect and crystallinity of the products, and the Photoluminescence spectra of CdS nanocrystals appear a blue shift.