Morphology Controllable Rapid Synthesis Of Copper Selenide Nanomaterials,characterization And Optical Properties

Micro/nano structured copper selenide is a typical p-type semiconductor with band gap1.2².3 eV,which is widely used in solar cells,gas sensor and thermoelectric converter.In this thesis,a few copper selenide products were synthesized using two methods and their morphologies,structures and optical properties were studied by SEM,XRD,TEM,PL spectra and UV-Vis absorption spectra.Besides,the morphology and structure of Cu?OH?₂ and CuO precursors were also studied.The contents are as follows:1.Copper hydroxide nanotube arrays and copper oxide micro-spheres with nanosheets hierarchical structure have been synthesized using one step method at 0? and room temperature,respectively.The morphology and phase of the products were characterized.The effects of temperature,reaction time and reactant dosage on the morphology of the products were analysized.Different precursors were used for synthesis of copper selenide products.The results show that the phase and morphology of the precursor have a greater impact on the morphology of the resulting copper selenide product.2.Hexagonal Cu_2-xSe microplates with lateral sizes of around 5-8 ?m and 500 nm in thickness were synthesized by hydrothermal method using CuCl2 and Se powder as raw materials,hydrazine hydrate as a reducing agent and oleylamine as an auxiliary agent.A simple solution route was used for rapid synthesis of copper selenide using cupric hydroxide nanotubes as a precursor and NaBH4 as a reductant at room temperature.The obtained hexagonal nanosheets film on the surface of the copper foil has a size of only tens of nanometers.The morphology,composition and optical properties of these two kinds of hexagonal structures were studied by SEM?XRD?PL spectra and UV-vis absorption spectra.The results show that its main component is also Cu_2-xSe,the average size of the primary particles and the band gap are also similar to that of the hexagonal microplate although the larger difference in sizes of the two hexagonal copper selenides.Besides,the fluorescence emission spectra of the two samples also display a similar fluorescence emission band in the wavelength of 400 500 nm with the peak at 420 nm.3.Cubic phase of Cu_2-xSe?x=0.23?tubes assembled by nanocubes were prepared at room temperature using highly ordered Cu?OH?₂ nanotube array as a sacrificial template,which were further converted to Cu_2-xSe?x=0.13?quasi-tubes assembled by intercrossed nanosheets with prolonging reaction time.The formation mechanism of the two Cu_2-x Se nanostructures and their optical properties were studied.The results show that the nanocubes,the hierarchical structure of the tubular Cu_1.77 Se,were densely accumulated by many parallel thin nanosheetswhich disassembled gradually to individual intercrossed nanosheets with prolonging reaction time.The formation of the tubular Cu_1.77 Se assembled by nanocubes follows the ‘Kirkendall effect',while the evolution from the Cu_1.77 Se tubes assembled by nanocubes to Cu1.87 Se quasi-tubes assembled by nanosheets could be attributed to the ‘Ostwald ripening' process.The band gap energies of the two products decrease from 1.98 to 1.36 eV,along with the hierarchical structure changing from nanocube to nanosheet.Besides,the reaction conditions have a large effect on the morphology of the sample.With increasing reaction temperature,morphology evolution from Cu?OH?₂ nanotube precursor to copper selenide assembled by cubes and then to nanosheet structure is accelerated.The dosages of Na2SO3 and NaOH must be controlled in the suitable value to maintain the tubular morphology and the amount of Se powder also must be kept more than 0.12 g.The kinds of the reductants also affect the morphology of the products.