Design, Preparation And Properties Of Nanostructured Copper Oxides And Chalcogenides

As important p-type semiconductors, nanostructured copper oxides and chalcogenides have great potential applications in thermoelectronics, optoelectronics, catalysis, sensing, superconductors and solar cells. In this dissertation, a variety of nanostructured copper oxides and chalcogenides have been prepared by different chemical methods. The optical properties and humidity-sensing properties of them have been studied. The main points are summarized as follows:1.A series of well-aligned arrays of Cu_2-xSe, Cu₇S₄ and Cu_2-xSe/Cu₂O sheath-like nanotubes have been synthesized by using Cu(OH)₂ nanorods as sacrificial templates. Arrays of Cu(OH)₂/Cu_2-xSe core/shell nanorods are obtained by immersing the Cu(OH)₂ nanorod arrays in Se^2- source solution, then arrays of Cu_2-xSe sheath-like nanotubes with close tips have been prepared after the completely dissolution of the inner Cu(OH)₂ core in ammonia solution. Similarly, arrays of Cu₇S₄ sheath-like nanotubes have also been prepared after the reaction of Cu(OH)₂ nanorod arrays and Na₂S solution coupled with the post-treatment in ammonia solution. The diameter of the copper chalcogenides nanotubes is in the range of 400-600 nm, and the wall thickness of the nanotubes is estimated to be about 60-70 nm. Great difference in solubility product (K_sp) between the copper chalcogenide wall and the Cu(OH)₂ core materials is crucial for the direct replacement of one type of anions by the other. Arrays of Cu_2-xSe/Cu₂O nanotubes with heterojunction constructed from Cu_2-xSe thin sheaths and Cu₂O hollow nanospheres have been fabricated with the reaction of Cu(OH)₂/Cu_2-xSe core/shell nanorods and ascorbic acid solution by Kirkendall effect. The diameter of the Cu₂O hollow nanospheres is in the range of 100-150 nm.2.Well-aligned arrays of Cu₇S₄ and Cu_2-xSe nanotubes with double walls have been designed and successfully prepared via a novel inward lithography method. This new method is based on layer-by-layer chemical conversion and inward etching of the sacrificial templates, which is essentially a kind of lithography inside the Cu(OH)₂ nanorods. The key step of the process involves repeated formation of the copper chalcogenide wall and the dissolution of the Cu(OH)₂ core for two consecutive cycles. The wall thickness of the nanotubes can be controlled by varying the reaction time between Cu(OH)₂ nanorod arrays and Na₂S solution (or Se^2- source solution) while the interlayer between the inner and outer tubes can be adjusted by varying the reaction time between Cu(OH)₂ nanorod and ammonia solution.3. Ultra-long crystalline Cu_2-xSe nanowire bundles with uniform diameters of 65-120 nm and lengths of 100-150μm constructed from ultra-thin nanowires with diameters less than 10 nm have been prepared by evaporating the mixture of Cu(NO₃)₂ solution and alkaline selenium aqueous solution. Growth of the Cu_2-xSe nanowire bundles is demonstrated by an evaporation of solvent H₂O to induce self-assembly coupled with crystal splitting mechanism. The Cu_2-xSe nanowire bundles are successfully used as photoluminescence-type sensors for the first time. The PL intensity response of the Cu_2-xSe nanowire bundles to humidity has been investigated at room temperature, which shows excellent linearity in sensitivity, long lifetime, fast response and recovery.