Electrodeposition Of Semiconductor Materials And Their Morphology Control By Ionic Liquids

It is well-known that semiconductor materials are used extensively in many fields, such as aerospace industry and electronics industry. Cu₂O is a p-type semiconductor that has potential applications in solar energy conversion and catalysis. Cuprous oxide can be used in photocatalytic degradation of organic pollutants and in the decomposition of water into hydrogen and oxygen under visible light. Cuprous oxide microspheres can also be served as cathode materials for lithium ion batteries. Copper(â… ) bromide crystals are of interest because they are good ionic conductors with very low partial electronic conductivity and wide band gap semiconductors with unusual photoluminescence. Copper(â… ) bromides have been used as catalysis in organic synthesis, batteries, gas sensors and lasers. Therefore, the study of the preparation of Cu₂O and CuBr crystals has very important significance. Electrodeposition is a well known solution process that can be applied in the growth of semiconductor films from aqueous or nonaqeous solutions. The advantages of electrodeposition compared with other techniques include low process temperature, low cost and capability of controlling grain size, morphology and chirialty of the deposited films. In this paper, the Cu₂O and CuBr crystals have been obtained through electrodeposition, their morphologies have been tuned by ionic liquids, and the optical properties of CuBr crystals have also been studied. The content and innovation of this thesis are listed as following:(1) Morphology control of electrodeposited Cu₂O crystals in aqueous solutions using room temperature hydrophilic ionic liquids. The particle size and morphology of materials known to have a great impact on their performance. Synthesis of controllable size and shape of the material is essential to their application. The ability to tune the shape of inorganic crystals is of extraordinary importance because their electronic structure, bonding, surface energy, and chemical reactivities are directly related to their surface morphology. In this paper, the ionic liquids have been first used as surfactant in the electrodeposition of Cu₂O process. The truncated octahedral, octrohedral, and spherical shapes of electrodeposited Cu₂O crystals can be obtained by adding a small amount of hydrophilic RTILs, ([MEIM]⁺[ES]^-), in the aqueous deposition solution. The possible mechanism of the formation of different morphologies has been discussed. This may provide a new and facile way to control the morphology of other electrodeposited semiconductor materials on conducting substrates using RTILs. The ability of control the morphologies of electrodeposited materials has broad application prospects in areas such as catalysis, sensors and optoelectronic devices.(2) Room temperature electrodeposition of highly oriented CuBr on indium tin oxide glass substrate. Several methods have been developed to grow copper(â… ) bromide thin films based on vapor-phase techniques, such as radio frequency magnetron sputtering, molecular beam epitaxy, and high vacuum deposition method. However, these methods require high temperature, high vacuum, complex facility, and rigid experimental procedures and would greatly hinder their universal applications. In this paper, we developed a simple electrochemical deposition process to produce highly oriented CuBr crystals first time. The results of XRD showed that the electrodeposited CuBr crystals have strong preferential (111) out-of-plane orientations. The results of PL showed that there are a strong emission peak appeared at 2.94 ev and a small emission peak at 3.32 eV for the electrodeposited CuBr crystals. The peak at 2.94 eV is contributed by the bound-exciton luminescence of CuBr and the peak at 3.32 eV is contributed by the free-exciton luminescence of CuBr. The intensity of the bound-exciton luminescence is much stronger than that of the free-exciton luminescence. Morphology control of electrodeposited CuBr crystals by [Bmim][BF₄] ionic liquids has also been explored. Further study on optical or conductive properties of the electrodeposited CuBr affected by their size, shape and orientations would be very interesting. The simple electrodeposition process can also be extended to grow other metal halides, such as CuCl, CuI and lanthanide halides.(3) CuBr prepared through electrochemical/chemical method. In the fifth chapter, we developed another path to prepare the CuBr crystals. CuBr crystals have been obtained by chemical reactions of HBr and the electrodeposited Cu₂O under certain conditions. This approach combined the electrodeposition and chemical reactions and might provide a simple and workable solution to prepare other semiconductor materials.In conclusion, in this thesis, the room temperature ionic liquids have been first time used in the morphology control of electrodeposited semiconductor crystals, Cu₂O. The simple electrodeposition process and electrochemical/chemical process have been developed to prepare highly oriented CuBr crystals and the optical properties of the CuBr crystals have also been studied.