| Graphene is a good two-dimensional material, which is stable and independent on any substrate. It is constructed by single-layer carbon atom with perfect hexagonal structure and possesses of many novel properties for its special structure. Different from ordinary metal and semiconductor, the carrier in graphene is Dirac fermion, which behaves like relativistic particle. Therefore, the graphene can provide a platform to observe and investigate the behavior described by the theory of relativity under mild conditions (room temperature and small magnetic field). Due to its excellent electrical and optical transport properties (such as the mobility>104cm2/V.s and the absorption of2.3%for single layer) and compatibility with the traditional semiconductor technology, it has emerged widely potential applications in the areas of advanced materials, optoelectronics and interdisciplinary research. Tremendous efforts are made on the development and improvement of preparation methods, thorough characterization of its properties and further exploitation of its applications. Chemical oxidation following with reduction is a method with widespread applications for the advantage of mass production and low-cost. Moreover, the structure of chemically derived graphene, containing sp2and sp3hybridized carbon atoms, can be easily modified.Recently, the graphene was found to enable served as a substrate for Raman enhancement of the adsorbed molecules and improvement of Raman to fluorescence signal ratio. The reason is attributed to the chemical enhancement mechanism. It is well known that chemical mechanism and electromagnetic mechanism are the basic interpretation for the surface enhanced Raman scattering (SERS). However, both mechanisms are frequently coexisted on the Raman enhancement, resulting in the difficult to distinguish the effect of each of them. Because the graphene has no surface plasmon resonance in visible light wavelength, it can provide a good platform for study of chemical mechanism. Moreover, we can also modify the surface structure of graphene readily. This is an effective way to manipulation its chemical enhancement and also valuable for deep understanding of the mechanism.In the first chapter, we first introduced the structure and properties of graphene briefly. Then the preparation method for the graphene and the mechanisms of SERS were also presented. The main contents of the thesis were given lastly.In the second chapter, we used the chemically derived graphene as the substrate for SERS measurement. The surface structure of graphene oxide was simply controlled by reduction time and the Raman enhancement for RhB molecules was observed, which also showed dependence on the reduction time of graphene oxide. With the help of X-ray photoelectron spectra, we identified that the Raman enhancement decreased with the decrease of the oxygen-containing groups. We attributed the enhancement behavior to the oxygen-containing groups with strong local dipole moment, which can induce considerable local electric field under the laser excitation.In the third chapter, we further investigated the role of surface dipoles in Raman enhancement through designing and preparing new substrate based on the thermally reduced graphene (RGO). We doped RGO with CF4plasma first and then study the dependence of Raman enhancement on the content of fluorine of the substrate. Combined with electrical measurements, we exclude the effect of resonance charge transfer and exclusively attributed the Raman enhancement to the surface dipoles formed by fluorine doping.In the fourth chapter, we prepared and characterized the graphene-CdS and the graphene-Au hybrids without use of surfactant. The results demonstrated that the surface groups on the reduction graphene could serve as nuclear sites for the formation of various nanoparticles and made the graphene-based composite stable. The ionization of surface groups made the graphene be negatively charged, resulting in well dispersion of graphene and improving the quality of the composites. |
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