Controllable Synthesis And Formation Mechanism Of Micron And Nanoscale Metal Selenides And Tellurides

The goal of this dissertation is to explore and study novel synthetic methods and routes to synthesize semiconductor metal selenides and tellurides micro and nano-scale materials with controlled structures and various novel morphologies. Based on the hydrothermal and solvothermal technique,we developed an ethanolamine based reaction system in this thesis.Taking metal selenides and tellurides as example,by adjusting the reaction parameters,such as the molar ratio of raw materials,the volume ratio of solvents,the concentration of surfactants and so on,the crystal structure and the morphology of the products can be effectively controlled.The main contents can be summarized as follows:1.An ethanolamine and water mixed solution route was developed for the synthesis of CdSe nanocrystallines with controllable phase and morphology.The phase transition of CdSe nanocrystallines from zinc blende to wurtzite phase can be controlled by varying the volume ratio of ethanolamine and water in their mixed solution,and the morphologies of the CdSe nanocrystals are controlled simultaneously.2.A reaction solution made of ethanolamine and polyethylene glycol-20000 (PEG)was developed to synthesis of CdSe nanorod-assembled microtubes. Experiment revealed that both the solvent ethanolamine and surfactant PEG-20000 played a key role in the formation of nanorod-assembled microtubes.According to the experimental results,a possible formation mechanism was proposed using PEG micelle rods as soft templates to prepare CdSe nanorod-assembled microtubes.3.A reaction solution made of ethanolamine and Polyvinyl Alcohol(PVA)was proposed to synthesis of nickel selenides crystals with tunable phase and morphology. It was found that the phase of the products could be controlled by adjusting the Ni/Se ratio of the raw materials.With the ratio of Ni/Se increase from 1:3 to 3:1, NiSe₂,NiSe₂ and NiSe,NiSe,NiSe and Ni₃Se₂ can be successively obtained. Furthermore,by controlling the quantity of PVA added in the reaction,the products with different morphologies could be obtained.4.A reaction solution made of ethanolamine and glucose was proposed to controlled synthesis of metal chalcogenides(such as Bi₂Se₃ and CoTe)with different morphologies.The morphologies of the products could be greatly adjusted by varying the experimental parameters.Based on the above results,the possible mechanisms were proposed.(1)Using Bi(NO₃)₃·5H₂O and SeO₂ as raw materials, flower-like Bi₂Se₃ nanocrystals were prepared in the ethanolamine and glucose reaction solution.It was found that flower-like Bi₂Se₃ nanocrystals were formed based on the flower-like Se nanocrystals.The prepared flower-like Bi₂Se₃ nanocrystals kept the original morphology of flower-like Se nanocrystals.(2)In the same reaction solution,using COSO₄·7H₂O instead of Bi(NO₃)₃·5H₂O and TeO₂ instead of SeO₂,we prepared CoTe nanotubes.The experiment indicated that Te nanorods could be formed in the intermediate reaction process.With the reaction time prolonged,CoTe nanoparticles layers could be formed based on the Te nanorods,finally,CoTe nanotubes could be formed after the reaction time prolonged to 16 h.Based on the above results,an in-situ template-directed synthesis process was proposed to prepare CoTe nanotubes.5.A simple reversible chemical reacting process under hydrothermal conditions was proposed to grow t-Se crystals.By controlling the concentration of MnCl₂·4H₂O, the alkaline strength of the solution was controlled,and the initial concentration of the Se nuclei was controlled simultaneously.As a result,t-Se aligned microrod bundles,microtubes and dendrites could be obtained.