Study On Controllable Preparation, Growth And Optical Properties Of CdS Nanostructures

Cadmium sulfide （CdS） is one of important II-VI,wide band semiconductors which iswidely used in photocatalysis,solar cells,field emission devices and so on. In thispaper,self-assembly CdS nanobelts and CdS nanorods, CdS/ZnS composite nanorods inwhich Zn ions replaced Cd ions and Zn-doped CdS dendritic nanostructures wereprepared by the thermal evaporation method,solvothermal method and hydrothermalmethod.The obtained products were characterized by X-ray diffraction （XRD）, scanningelectron microscopy （SEM）, transmission electron microscopy （TEM）, ultravioletvisible absorption （UV-Vis）， Raman scattering and photoluminescence （PL）spectroscopy to obtain the structural and optical properties. The main contents are asfollows:1. CdS quantum dots directed self-assemble nanobeltsCdS nanoparticles self-assemble nanobelts were controllable prepared by anaccurately designed thermal-evaporating method with CdS powder as raw material. Theresult of XRD and TEM showed that the size of the nanoparticles was about3nm.Thisnanostructure presented single-crystalline characteristic.The samples were characterizedand analyzed by HRTEM and SAED,and found that the nanoparticles aggregated along[21|-1|-0],[011|-0] and [0001]crystal directions. Two Raman peaks(at299.0and603.5cm^-1)of the CdS nanobelts shift toward lower frequency. A symmetrical intensive peakcentered at2.43eV was observed in PL spectrum of CdS nanobelts. This novel CdSnanobelts are promising candidates for future applications in optoelectronicnanodevices.2. Controllable preparation of CdS nanorods and the influence of reaction timeand temperature on its crystal quality and optical propertiesThis chapter studied the structure and optical properties of CdS nanorod in detail by asolvent-thermal method in ethylenediamine at different temperature and time.Thesamples were characterized and analyzed by XRD and TEM,and found that thesolvent-thermal temperature at200℃is an optimal reaction temperature for preparingCdS nanorods. The growth of single-crystalline CdS nanorods followed three steps;（a）CdS nuclei formed by reacting Cadmium chloride dihydrate and thiourea in ethylenediamine at200℃,（b） CdS nuclei grew into thin nanowhiskers after1h reaction,（c） the growth of CdS nanorods based on nanowhiskers via a Ostwald ripening process.Further,Raman and PL spectra were used to study the optical properties of CdSnanorods.3. CdS/ZnS composite nanorodsCdS/ZnS composite nanorods were controllable prepared by two-step syntheticmethod. The samples were characterized and analyzed by XRD,TEM and SAED,andfound that the samples have symmetrical,black streaks on the samples’ surface whichwere formed by Zn ions replacing Cd ions.CdS/ZnS composite nanorods still presentedsingle-crystalline characteristic.The band gaps in ultraviolet visible absorption spectradecreased as the reaction time increased. At the same time,we used Raman and PLspectrum to study their optical properties.The PL spectra of samples with different timeare found that the quality and surface defects of the crystal increased as the reactiontime increased. The peaks of Raman spectra are correspond to the first-order（1LO） andsecond-order （2LO） longitudinal optical phonon bands of CdS respectively.4. Zn-doped CdS dendritic nanostructuresZn-doped CdS nanostructures were synthesized for the first time by direct doped,hydrothermal method.The samples were characterized and analyzed by XRD,SEM,EDSand TEM and found that it presented single-crystalline characteristic and some growedalong equivalent crystal directions（[21|-1|-0],[1|-1|-20]and[1|-21|-0]）respectively. The bandgap is slightly broadened by doping Zn which is observed in UV-vis spectrum.Thegreen emission band gets stronger and the infrared emission band gets weaker in PLspectrum of Zn-doped dendritic CdS nanostructures.