【作者】 曾亚萍；

【导师】 王岩国；

【作者基本信息】 湖南大学 ， 物理学， 2013， 博士

【摘要】 金属硫族化物纳米材料作为半导体材料中一个重要的成员因其优异的光电性质显示出其在光学、磁学、电学、生物医学、电化学和太阳能电池等领域广泛的应用前景。但是这些光电性质具有尺寸、形貌和化学组分依赖特性。因此，合理设计、可控合成具有特殊光学、电学和磁学性质的金属硫族化物纳米材料已成为纳米生物医学、光电器件、催化等前沿领域的研究热点。制备具有新颖形貌的金属硫族化物纳米晶、并探索其生长机制，进而实现对尺寸、维度及物性的调控，这对于研究纳米结构与材料物性的关联，实现按照人们的意愿合成具有某些特殊性质的材料，从而组装成各种功能器件具有重要意义。尽管当前人类对金属硫族化物的纳米制备与合成已经取得了较大的发展，但这些进展主要集中在对二元金属硫族化物的控制合成上，对于三元及三元以上的硫族化物的可控合成还不尽完善。因此，大量、廉价并且高效地合成与组装不同组份与形貌的多元金属硫族化物纳米材料无论从基础研究，还是从性能和应用的角度来看，都有着特殊重要的意义。本论文主要从可控合成三元Cu-Bi-S系列化合物及四元Cu2ZnSnS/Se4系列纳米材料出发，探究了它们的形貌结构以及生长机理，并研究了这些化合物的光电学、电化学性能、光学带隙以及光伏性能等。另外，本文还研究了ZnSe-Au纳米线所形成的接触在通过电流自加热后其微结构的变化，以及发生应变后ZnSe纳米线内部电学性能以及热学性能的变化。所取得的具体成果如下：（1）利用水热法可控的制备了同时具有八角形与六角形两种外形的Cu9BiS6纳米片、以及结晶性较好的CuBiS2纳米线。分析了他们的微结构以及优先生长面与优先生长方向。通过分析其光学带隙发现，Cu9BiS6纳米片的禁带宽度为1.25eV，CuBiS2纳米线的禁带宽度为1.1eV，两者都与太阳光谱中的可见光谱非常匹配，因此是一种较好的光伏备选材料。（2）一步水热法合成了具有多层次结构的Cu3BiS3纳米花，通过对其生长机制的探究发现，这种花状结构的形成可归结为一个自腐蚀过程，其参与的可逆反应使得内部的晶核向外生长，并最终形成了多孔结构。这种Cu3BiS3多孔结构的光学带隙大约为1.2eV。作为一种新的锂离子电池阳极材料，它的首次放电与充电容量分别为676与564mAhg-1，初始库伦效率为83.4%。初始放电值要高于二元Bi2S3的理论放电值（625mAhg-1），而二元Bi2S3正是因为硫元素较高的质量容量以及铋元素很大的体积容量才被用在锂离子电池阳极材料。（3）用湿化学方法合成了四元Cu2ZnSnS4纳米颗粒。这种颗粒直径较小，仅为10nm左右。XRD确定其晶体结构为四方晶系的锌黄锡矿。SEM观察确定Cu2ZnSnS4纳米颗粒单分散性较好，无明显团聚。紫外-可见吸收光谱法测定其光学带隙大约为~1.5eV。由场诱导光电压谱（简称FISPS）测量的表面光生电荷性能证实Cu2ZnSnS4纳米颗粒在激发光波长为630nm左右发生明显的光伏响应，与其带隙1.5eV对应，说明光照引起的是一个带带直接跃迁。（4）本章通过原位焦耳热的方法，利用透射电子显微镜（TEM），在金与硒化锌纳米线所形成的接触处（M-S）达到了可控的界面合金化处理。TEM检测显示，金电极在M-S接触处原位熔化了，并且硒化锌纳米线的尖端被熔化后的金所覆盖。实验结果证实，反向偏置的M-S接触的合金化处理是因为在这个接触处所存在的肖特基势垒具有很高的阻抗值，这与阴极控制模式相吻合。因此，原位焦耳热的方法是一种行之有效的方法，可以用来改善基于金属-半导体-金属纳米结构的纳米电子器件的性能。（5）本章通过原位TEM技术研究了应变对ZnSe纳米线中载流容量的影响。在TEM的观察下，使用一个可移动的探针电极在纳米线轴向施加压缩应力，能够在单根ZnSe纳米线中的选定区域创建应变。仔细操作可移动探针电极，诱发应变在ZnSe纳米线弯曲的曲率级别上可控。原位电流诱导焦耳热的方法证实了，在对抗焦耳热方面单根ZnSe纳米线中应变的部分比未发生应变的部分有更好的性能。因此，通过特意创建应变，ZnSe纳米线的载流容量得到了有效增强。实验结果也证实了，在同一根纳米线中，电导率与热导率会因为引入的应变而发生明显的增长。更多还原

【Abstract】 Crystalline metal sulfides as a typical and important group of semiconductorshave attracted extensive investigation due to their unique optical, magnetic andelectrical properties and the intriguing prospects for developments in photovoltaicsolar cells, biological labeling and medical diagnostics, etc. However, the uniquephotoelectrical properties of colloidal semiconductor nanocrystals exhibit distinct size-,shape-and composition dependence. Thus, developing general and facile syntheticapproaches that yield metal sulfides nanocrystals with precise control over not only thesize and shape but also the chemical composition is highly desirable for bothfundamental studies and practical applications. At present, a wealth of methods hasbeen developed for the synthesis of metal sulfide nanocrystals, but these developmentsare mainly concentrated in the controlled synthesis of binary sulfide. It is not desirableto controllable synthesis of ternary sulfides or even multiple sulfides. Therefore,large-scale, low-cost and effective synthesis and assembling of the metal sulfides withdifferent morphologies have a special significance both from the point ofnanoscientific and nanotechnological views.In this paper, we mainly focus on the issues related to the facile synthesis,morphology control and growth mechanism of ternary and quaternary metal sulfides.Then we have characterized the photoelectric property, optical band gap andphotovoltaic performance of these compounds. Further more, this paper also studiedthe internal electrical properties of the binary ZnSe nanowires under applied strain.The main contents are as follows:(1) Single crystalline Cu9BiS6nanoplates and composite structure CuBiS2nanowires have been synthesized via a hydrothermal route by using different sovlents.The morphology of these nanoplates identified by electron microscope was thehexagonal and octagonal configurations respectively. And the CuBiS2nanowires wereproved to be the twin crystal. The microstructures and growth direction of these twokind of nanostructures were analysed carefully by TEM photos. Optical diffusereflectance measurement demonstrated that these Cu9BiS6nanoplates and CuBiS2nanowires have a band gap of1.25eV and1.1eV respectively, which matched thesolar spectrum very well, thus were confirmed to be the alternative photovoltagematerials. (2) Flower-like hierarchical nanostructures with Cu3BiS3nanosheets asbuilding blocks formed by in situ corrosion of matrix Cu3BiS3microspheres weresynthesized via a facile hydrothermal method. Their morphology, microstructure, andcrystalline phase were characterized by scanning electron microscopy (SEM),transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively.Pore-size distribution analysis indicated that both mesopores and micropores existed inthe as-obtained products, which are favourable for increasing of surface-to-volumeratio. The optical band-gap of the hierarchical Cu3BiS3nanostructures was estimatedto be~1.2eV by UV-vis spectroscopy. Electrochemical measurements were also usedto investigate the electrochemical Li+intercalation performance for the flower-likeCu3BiS3nanostructures. The results showed that the initial discharge capacity of thenanosheets based Cu3BiS3hierarchical structures is676mAhg-1which is lager thanthe thereotical value of Bi2S3(625mAhg-1), but it degraded quickly duringsubsequent cycles, and further improvement in cyclic stability is still needed forpractical application in lithium-ion batteries.(3) Cu2ZnSnS4nanoparticles have been prepared by wet chemical method. Thecrystal structure analyzed by XRD coincides to stannite with tetragonal symmetry andlattice parameters a=0.5427nm and c=1.0848nm. Morphology of these nanoparticlescharacterized by SEM coincides to the well-dispersed nanospheres with the diameterranging from5nm to10nm. The band gap has been estimated to be about1.5eVbased on the corresponding Uv-vis absorption spectra.(4) Controllable interfacial alloying is achieved at a Au-ZnSe nanowire (M-S)contact via in situ Joule heating inside transmission electron microscopy (TEM). TEMinspection reveals that the Au electrode is locally molten at the M-S contact and the tipof the ZnSe nanowire is covered by the Au melting. Experimental evidences confirmthat the alloying at the reversely biased M-S contact is due to the high resistance of theSchottky barrier at this M-S contact, coincident to cathode-control mode.Consequently, in situ Joule heating can be an effective method to improve theperformance of nanoelectronics based on a metal-semiconductor-metal nanostructure.(5) The effect of strain on the current carrying capacity of ZnSe nanowire hasbeen studied by in situ transmission electron microscopy (TEM). Under TEMinspection the strain can be created at the selected position in a single ZnSe nanowireby the compressive stress applied along its axial direction using a movable probeelectrode. The induced strain is controllable in the magnitude of curvature of the ZnSenanowire bent by careful manipulation of the movable probe electrode. In situ current-induced Joule heating has confirmed that the strained segment in a single ZnSenanowire exhibited better ability than the unstrained segments against Joule heating.Consequently, the current carrying capacity of the ZnSe nanowire can be effectivelyenhanced by intentionally created strain. The experimental results have also provedthat a significant increase of the electrical conductance and the thermal resistance canbe achieved simultaneously in a single nanowire by the intentionally designed andcreated strain.更多还原