Synthesis And Characterization Of One Dimensional Semiconductor Nanostructures

Preparation of nano-materials is the most active branch of the nano-science and technology (nano-ST). Nano-materials have taken great progress since 80 years of last century. One dimensional (1 D) nanostructures (nanotube, nanowire, nanorod, nanobelt ect.) and their assemblies (such as nanoarry, nanoscale pattern materials) have been the focus of this area for the present, owing to their unique potential application in mesophysics and fabrication of nanodevices.Therefore, it has been one of the important frontiers in modern materials science research and development directions of nano-science research.Though the research of quasi-1D nanomaterials already has been got considerable progresses, it still remains a significant challenge to achieve controllable synthesis of 1D nanomaterials with desired morphologies, components, and structures, which is a foundation and prerequisite for the applications of nanomaterials. Focusing on the research of controlled synthesis of 1D nanomaterials and relative physical properties, we have done a series of work. The growing process of several nanostructures synthesized by simple thermal evaporation have been investigated in this master dissertation .And some surface modification based on SiNWs have also been studied.First, hierarchical nanohelices of sulfur doped zinc oxide were synthesized by the simple thermal evaporation method. The as-synthesized material has a relatively high yield on the substrate and shows a high degree of reproducibility. The deposited material has a dominant morphology, which consists of helices of S-doped ZnO. The morphology of the S doped ZnO nanohelix was more complex than that observed for ZnO, which composes of spine and branch two different parts. By Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM), we try to understand the formation process. The growth of the spine occurred rather fast during the growing process. The presence of polar surfaces results in coiling of the spine to form a helix that minimizes the electrostaticinteraction energy of the polar surfaces. The diameter of the nanohelix and nanoring is from 1 to 8 micrometers, while the width is about 100~600nm. Both polar surface and dopant have an effect on the side branches. They are densely packed to form an aligned and ordered array that follows the coiling geometry of the helix. This hierarchical nanohelix may have novel mechanical, optical, and electrical properties.Second, germanium oxide nanowires and dendritic nanostructures were fabricated by simple thermal evaporation of a powder mixture of Ge and GeO2 without metal catalyst. The as-synthesized samples were analyzed by SEM,TEM and X-ray diffraction (XRD) .It indicated that the diameter of germanium oxide nanowires and the stems part of the dendritic nanostructures rang from 100 to 400nm, while the length can be as long as several tens of micrometers. The diameter of the branch nanowires is quite uniform, which is about 30~50nm. However, its length is also about several micrometers. Germanium oxide nanowires is main products on the relative low-temperature growth zone, while germanium oxide dendritic nanostructures is a dominant morphology of deposited on the relative high-temperature growth zone. Various morphologies have a close relation with different growth mechanism. All of the data confirms that the growth of germanium oxide nanowires and the stems part of the dendritic nanostructures followed the oxide-assisted growth mechanism. It could be deduced that the branches part appears to follow two concurrent processes: vapor-liquid-solid (VLS) and oxide-assisted growth (OAG) process. There were few articles reported about this novel structure before.Third, aligned nanomaterials arrays were synthesized by simple evaporation of a powder mixture of ZnO and ZnS by using Au as catalyst. It was found that at the bottom of the samples is ZnO-ZnS aggregate, while the upside is well-aligned nanostructure according to SEM obervation. The height of arrays is about 500nm, and the diameter is from 80 to 125nm. EDX analysis indicates that the as-synthesized samples mainly contain Zn, O, S, Au and C. Zn, O and S are from source materials ZnO and ZnS. Au comes from catalyst and sputtering of gold process, while C is from conductive adhesive. XRD data showed that the structures of ZnO and ZnS are both wurtzite, and the preferred growth direction was along <001>direction. This nanostructure with growing strongly along the same direction may perform well mechanical and electrical properties have wide scope of applications.Fourth,Using vapor-phase growth method and strictly controlling the growth conditions, a mass of silicon nanowires were fabricated by simple thermal evaporation method .The oxide layer was removed by immersing the as-synthesized SiNWs into a 5% hydrogen fluoride solution. The reactions of SiNWs with metal ions were carried out by immersing the etched SiNWs into silver nitrate and gold chloride solutions of different concentrations. The reactions between silicon wafer and metal ions have been studied by others. However, interaction of SiNWs with metal ions in solution is a complex surface electrochemistry system. It was proposeed that the silicon at the surface of the SiNWs can be employed to readily reduce silver (â… ) and gold (â…£) ions to metal aggregates on the SiNWs surface, while, the silicon at surface was re-oxidized at room temperature. The reaction products by varying the concentration of Ag and Au ions in the solution had been characterized with TEM. Therefore, the optimum reaction conditions have been found through series experiments. This approach for synthesis of metal nanostructures offered a potential method for the preparation of desired metal catalysts and application of nanosensor.