【作者】 李晓燕；

【导师】 胡陈果；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2014， 博士

【摘要】 II–VI族半导体因为其独特的物理和化学性质而在数十年来受到人们的广泛关注。ZnS和CdS是重要的两种II–VI族半导体材料，广泛用于光电器件、纳米发电机、气敏、生物荧光材料以及光降解催化剂等。另外，新型的硫族铜化合物纳米材料也作为构建下一代器件的优良的功能材料而受到研究人员的广泛关注，因为这种材料往往表现出很独特的性质。基于这些材料的卓越性能，本论文做了以下一些研究工作：(1)使用改良复合盐媒介法合成了由2–6纳米的超细颗粒自组装而成的纳米颗粒。研究了ZnS纳米颗粒的紫外-可见反射光谱和光致发光谱，发现该ZnS纳米颗粒的带隙比相应的块体材料要窄。带隙变窄来源于超细颗粒在组装时某些晶界面的不匹配而形成的富含缺陷的独特的准单晶结构。将ZnS纳米颗粒作为催化剂，催化降解甲基橙，在模拟太阳光下表现出比商业ZnS粉末更好的催化性质。使用复合盐媒介法合成了单晶CdS纳米颗粒。系统研究了温度、生长时间、盐量对颗粒形貌的影响。发现较低的温度、较短的时间和较多的盐量有利于得到较小的CdS纳米颗粒。将CdS纳米颗粒作为催化剂，在模拟太阳光下催化降解罗丹明B和亚甲基蓝，并与商业TiO2颗粒做了对比。使用加入不同水量的改良复合碱媒介法合成了立方相的CdS线状样品和六方相的纳米棒。发现在复合碱中加入较多的水量很容易得到纯净的六方相的纳米短棒。将CdS纳米短棒作为催化剂，在模拟太阳光下催化降解罗丹明B，表现出比CdS纳米颗粒更好的催化效果。六方相纳米棒的催化优势在于晶体端点处(0001)极性面所具有的超强的催化能力。(2)通过改良复合碱媒介法，在金属Cd片上直接生长出了六方相的三维CdS纳米墙和立方相的CdS纳米颗粒。 CdS纳米晶体的结构相变可以通过调节反应媒介中加入的水量来实现。六方相纳米墙电极比立方相纳米颗粒电极表现出明显的更佳的光电化学性质。表面形貌在光电化学中起到了很重要的作用，三维纳米墙的高比表面积、良好的传输性能保障了其良好的光电化学性质。使用水热法合成了三维的CdS纳米墙。构建了在CdS纳米墙阵列上沉积CdSe层的光电化学传感器。纳米墙的紧密度和厚度可以通过调节反应原料的浓度实现。通过连续离子吸附反应法在CdS纳米墙上沉积了一层均匀的CdSe纳米颗粒，并且通过调节吸附反应的周次可以调节沉积层的厚度。紫外-可见吸收光谱显示CdS/CdSe核壳结构的纳米墙阵列对光的吸收有效展宽到几乎整个可见光范围。纳米墙电极在模拟太阳光下的光电流从沉积前的3.78mA/cm2增加到沉积了CdSe后的8.3mA/cm2。光电化学效应的增强机理在文中有详细讨论。(3)使用改良复合碱媒介法合成了新型KCu7-xS4纳米线。调控了合成时加入的水量、反应时间和碱的种类，得到了理想形貌的样品。通过X射线衍射和旋转透射电子显微镜下不同角度的衍射谱的分析，得出KCu7-xS4纳米线是体心立方结构，其晶格参数为a=b=10.163、c=3.838。该KCu7-xS4纳米线吸收光谱范围包括了整个可见-近红外光谱。KCu7-xS4纳米线制得的膜在室温下的电阻率低至5×10-5·cm，电阻率随温度的变化曲线显示其具有金属性。获得低的热导率是制备高效热电材料的有效途径。然而要想在降低材料热导率的同时不破坏其电导率就是一项颇具挑战性的工作，这需要材料具有“声子玻璃-电子晶格”的特性。人们发现笼形晶格结构的材料可以实现声子玻璃-电子导体以及超离子导电性。实验发现KCu7-xS4纳米线比传统的Cu7S4纳米结构呈现出更加优良的热电性质。在这里，K离子的引入可以使实验合成出的KCu7-xS4晶体成为笼形结构，该晶体呈现超离子导电性，使得材料成为声子玻璃-电子晶体。并且纳米线结构也对热电效应的提高有一定的帮助。用该KCu7-xS4纳米线压制的块体材料具有很低的热导率和高的塞贝克系数。导电率在420K以下保持较高的水平。另外，材料具有大量晶界面，Cu空位缺陷和纳米线的有序排列都有利于热电性质的进一步提高。结果表明，我们可以通过在硫族铜化合物中引入K原子而得到声子玻璃-电子晶体的高效热电材料。更多还原

【Abstract】 Due to their unique physical and chemical properties, II–VI semiconductormaterials have attracted great interest in the last decade. ZnS and CdS are importantII–VI semiconductor, which are considered as the most useful functional materials inthe electroluminescent devices, nano-generator, gas sensors, biological fluorescencematerials as well as photo-degradation catalysts. And novel copper chalcogenidesnanostructrures have attracted much attention as fundamental building blocks for thedevelopment of next generation devices, which have high performance and novelfunctionalities. Based on the excellent properties, the detail studies are described asfollows:(1) ZnS nanoparticles self-assembled from ultrafine particles (2–6nm) have beensynthesized for the first time by the modified composite molten salt method. UV–visreflectance spectrum and photoluminescence of the ZnS nanoparticles were investigated.The narrowed band gap of the ZnS nanoparticles was found owing to novel crystalstructure formed from a lattice-matched ‘coherent interface’ of the agglomeratedultrafine particles. Photocatalytic degradation of methyl orange by the nanoparticlesshows much better photocatalysis than that by the commercial ZnS powder undersimulated sunlight irradiation.Single-crystalline CdS nanoparticles were synthesized for the first time by thecomposite molten salt method. The influence of temperature, growth time and amountof salts on the morphology of CdS nanoparticles was systematically investigated. Itshows that a smaller size of CdS nanoparticles can be obtained under lower temperature,less growth time and more composite salts. Photocatalytic degradation of rhodamine Band methylene blue in presence of the CdS nanoparticles was compared with that inpresence of the commercial TiO2nanoparticles under the simulated sunlight.Single-crystalline cubic CdS wires and hexagonal nanorods have been synthesizedby the composite hydroxide mediated approach by tuning the different amout of water.It shows that the more water in the composite-hydroxide can easily get the purehexagonal phase structure and shorter nanorods. Photocatalytic degradation ofrhodamine B under simulated sunlight irradiation is carried out, it shows that thehexagonal phase structure nanorods have much better photocatalysis than that of thecubic CdS nanoparticles owing to the exposure of (0001) polar facet on the ends of CdS nanorods.(2) Three-dimensional hexagonal CdS nanowalls and cubic nanoparticles werefabricated directly on Cd foils via a modified composite hydroxide mediated approach.The phase transition of CdS nanocrystals from cubic to hexagonal phase can becontrolled by varying the water content in the hydroxide melts. The obviously enhancedphotoelectrochemical performances of the hexagonal nanowalls were found under theillumination of the simulated sunlight in comparison with that of the cubic CdSnanoparticles. The surface morphology plays a vital role in its photoelectrochemicalbehaviors due to the different specific surface area and charge transport, indicating suchthree-dimensional hexagonal CdS nanostructure has prominent advantages inphotoelectrochemical applications.Strategies employed to fabricate high sensitive photoelectrochemical sensor withCdSe deposited on CdS nanowall arrays were investigated. The three-dimensional CdSnanowall arrays were prepared via hydrothermal method. The density and height of theCdS nanowall arrays could be controlled through varying the solution concentration. Auniform CdSe layer was deposited on the CdS nanowall arrays by a successive ioniclayer adsorption and reaction method, and the thickness of CdSe layer could beeffectively controlled by changing deposition cycles. UV–vis absorption spectrademonstrate that the light absorption range of the CdS/CdSe core–shell nanowall arrayscan be almost extended to the whole visible range. The obviously enhancedphotoelectrochemical current of8.3mA/cm2for the heterojunction nanowalls werefound under illumination of the simulated sunlight compared with that of the3.78mA/cm2for bare CdS nanowalls. The enhanced photoelectrochemical performance andformation mechanism of CdS/CdSe core–shell nanowall arrays were discussed in detail.(3) A novel single-crystalline KCu7-xS4nanowires were synthesized by a modifiedcomposite hydroxide mediated approach. The synthesis conditions including watercontent, reaction time and hydroxide type were systematically studied to get an optimalmorphology. Crystal structure of the nanowires was determined by X-ray diffractionand series surveys of diffraction spot configurations in the reciprocal space via TEM,which reveal that the synthesized sample is the body center tetragonal KCu7-xS4with thecell parameter a=b=10.163, and c=3.838. A broad absorption in visible-infraredregion was found. The resistivity of the film made from the KCu7-xS4nanowires is lessthan5×10-5·cm at room temperature and displays a metallicity according totemperature dependent resistance measurement. A low thermal conductivity is a prerequisite for obtaining high efficiencythermoelectric materials. It is a challenge to have low thermal conductivity withoutsimultaneously destroying electric conductivity, which is proposed as ‘phononglass/liquid–electron crystal’. To realize the phonon glass–electron crystal, host–guestcage crystal system is considered, while to realize the phonon liquid–electron crystal,superionic conductivity is needed. The KCu7-xS4nanowire exhibits enhancedthermoelectric properties with respect to the traditional chalcogenide Cu7S4nanostructure. The presence of K ions not only form a clathrate and superionic fluidstructure, which provides phonon glass&liquid–electron crystal, but also adjust theproduct to have a nanowire-like morphology. A low thermal conductivity and largeSeebeck coefficient are achieved when the nanowires are pressed into a bulk material.Higher electrical conductivity is also obtained below420K. In addition, the numerousgrain boundaries, Cu deficiency and the orientated nanowires would further increase thethermoelectric properties. The results indicate a new strategy to obtain high-efficiencythermoelectric materials by introducing kalium in copper chalcogenides to form a newcrystal structure with ‘phonon glass&liquid–electron crystal’ properties.更多还原