Synthesis And Characterization Of CdSeS Nanomaterials By Thermal Evaporation Method Under Atmospheric Pressure

As a class of typical ternary II-VI alloyed semiconductor materials, CdSeS alloyed nanostructures have huge potential applications in the field of medicine and optoelectronic devices due to their excellent optical and electrical properties. Consequently, researches on the preparation and application of CdSeS nanostructures have attracted extensive attention.In this dissertation, in atmosphere tube furnace, by employing high-purity CdS and CdSe mixture powder with a molar ratio of 1:1 as evaporation source and high-purity Ar gas as carrier and protective gas, the formation temperature of pure-phase alloyed CdSeS under atmospheric pressure was first explored during high temperature solid phase reaction. Then, via thermal evaporation under atmospheric pressure, using silicon wafer coated with a thin Fe layer as substrate, the effects of thermal evaporation temperature, the distance between evaporation source and the substrate, and Ar gas flow rate on the composition, morphology and crystallinity of CdSeS nanocrystalline films were studied systematically. And the optimum processing parameters for preparing CdSe0.48S0.52 nanocrystalline films with uniform size distribution and good crystallinity were obtained. In addition, multipods-branched CdSeS micro-/nano-structures were successfully prepared.The results showed that by employing high-purity CdS and CdSe mixture powder with a molar ratio of 1:1 as evaporation source and high-purity Ar gas as carrier and protective gas, when the reaction temperature was up to 900 ℃ under atmospheric pressure, pure-phase alloyed CdSeS solid solution could be prepared. Through thermal evaporation under atmospheric pressure, by using silicon wafer coated with a thin Fe layer as substrate, the optimum processing parameters for preparing CdSe0.48S0.52 nanocrystalline films with uniform size distribution and good crystallinity are as follows: evaporation temperature is 1100 ℃, the distance between the substrate and evaporation source is 38 cm, Ar gas flow rate is 200 sccm. The composition of CdSeS nanocrystalline films was influenced by the evaporation temperature, mainly because of sublimation temperature difference berween CdS and CdSe source. The distance between the evaporation source and substrate had a certain influence on the crystallinity and particle size of CdSeS nanocrystalline films, which is mainly due to the substrate surface temperature difference caused by the different distances of substrate from the evaporation source. In an atmosphere tube furnace, by thermal evaporation under atmospheric pressure, using mica wafer treated in 0.2 wt.% HAuCl4 solution as a substrate, when the evaporation temperature was 1100 ℃, Ar gas flow rate was 200 sccm and the distance betwwen evaporation source and the substrate was 22 cm, multipods-branched CdSeS micro-/nano-structures were successfully prepared. The multipods-branched CdSeS micro-/nano-structures has a hexagonal structure and an intrinsic emission peak in their photoluminescence spectra at around 620 nm at the room temperature, and they might be grown by vapor-solid mechanism.