Preparation And Surface-enhanced Raman Scattering Investigations Of Carbon Chains

A one-dimensional carbon chain has a diameter of an atom, in which the carbon atoms exist in the form of a triple bond conjugated structure(polyyne) or cumulative double bonds(cumulune). One-dimensional carbon-atom wire has been observed in many carbon-based materials and structures, such as in free carbon clusters in the gas phase, in sp-sp2 systems and in liquids. Because of potentially downscale devices to the atomic level, studies on it are gradually increasing in recent years.The content of this thesis can be divided into two parts: the first part is the preparation, separation and characterizations of one-dimensional carbon chains. The second part is the preliminary exploration on the preparation of sp-sp2 carbon materials.In the first section, we prepared hydrogen-capped polyyne by arc discharge in liquid. Using several different currents in different liquid, we got polyyne as well as carbon nanotubes, graphene-like structures and other ancillary products. The effect of different currents on yield of polyyne and ancillary products is discussed. Ultra-violet absorption spectra results show that the best current range of preparation is 10-20 A. For lower current, the yield is too small; and for larger current, the yield of polyyne reduces and affiliated products such as carbon nanotubes, graphene- like structures increases. The formation mechanism of polyyne is discussed by analysis of these products. After that, the as-prepared polyyne are subjected to size separation by high-performance liquid chromatography. Size-separated polyyne(C2nH2 with n=4~6) are investigated by surface-enhanced Raman scattering(SERS) spectroscopy in Ag colloid and dried Ag colloid. The Raman intensity and position of polyyne’s α band change significantly as the Ag colloid runs dry. The interaction between sp chains and Ag nanoparticles used as a SERS active medium is considered. There may be a progress of Ag–C8–H mode turning to Ag–C8–Ag mode. Furthermore, an inference is proposed that the C10H2 and C12H2 chains transform to shorter ones.The second part is the preliminary exploration on the preparation of sp-sp2 hybridized carbon materials. Applying Ag colloid as an effective surface-enhanced material in Raman measurement, we confirmed that the sp-sp2 carbon materials were produced by low current arcing under H2 atmosphere of low pressure and the formation mechanism was analyzed. In addition, the as-prepared polyyne were inserted into carbon nanotubes(CNTs). Heat-treatment was performed on this polyyne@CNT structure at several temperatures. The results showed that the 600 ℃ heat-treated polyyne@CNT samples remain stable structure. And as the heat-treatment temperature rose, Raman peaks of polyyne@CNT moved to the left until disappeared at 800 ℃. It indicated that some polyyne were destroyed or escaped from carbon nanotubes.