Design, Fabrication And Properties Of Graphene And Graphene-based Nanocomposites

Graphene is a two dimensional crystal with a single monolayer of carbon atoms packed into a honeycomb lattice with sp2-hybridized. It has attracted great attention and has been studied greatly due to its prominent properties since discovered. For example, it is a semimetal with zero bandgap at room temperature and possesses ultrhigh electron Femi speed (-c/300), mobility (-200,000cm2V-1s-1) and thermal conductivity (-5000W/mK). It also holds good transparency (-98%) and extreme mechanical properties (Young’s modulus and tensile strength are about1.0TPa and125GPa respectively). Therefore, it has a great of potential applications for transparent conductive electrode, field effect transistor, sensor, energy generation and storage as well as a variety of graphene-based nanocomposites. Moreover, graphene is also a unique platform for SERS study due its atomic uniformity, biological compatibility, delocalized π bonds and chemical inertness. In addition, it is feasible to design, combine and synthesis graphene-semiconductor nanocomposites owing to lots of function groups in the graphene derivative. To this end, we focused on how to design, synthesis and characterization of novel graphene nanostructure and the graphene-based nanocomposites for the application in SERS and the photodetector. This dissertation contains five chapters and the contents are outlined as following.In charater one, we first briefly reviewed the history, synthesis strategies, properties and potential applications of graphene. Then we introduced the principle of SERS and photodetector, as well as the research status and trends with the graphene. We also presented the background and motivation of our study.In chapter two, we designed and synthesized metal/graphene/metal (MGM) nanostructure for the application of SERS. With systematic experimental investigations and FDTD simulations, we showed that the MGM nanostructure can not only control the intensity and distribution of the electronmagnetic field "hot spots", but also can put the probe molecules in the exact "hot spots", which are two challenges in SERS. Furthermore, we demonstrated that the field "hot spots" in MGM nanostructure can be readily controlled by the size and the composition of metal NPs as well as the assembled sequence of graphene and NPs, while the target molecules can be anchored to the "hot spots" through absorbed onto the in-between layer of graphene of MGM nanostructure. Additionally, the SERS of MGM are dependent on the incident angle of the excitated light and the signal can be improved with tuning the angle. Finally, we found that the MGM nanostructure can detect Raman signal of RhB as low solution concentration as50nM.In chapter three, we demonstrated a novel method to fabricate the graphene nanomesh based on the local catalytic hydrogenation of carbon in the high temperature. The size, the density, and the edge length of holes of the nanomesh can be facilely tuned through the control of the thickness of the Cu film. The nanomesh showed stronger chemical SERS of RhB molecules as compared to the pristine graphene. Raman characterization revealed that the produced nanomeshes are p-type doped, resulting the dipole moment near the edge of hole to serve as a source for the chemical enhancement. Moreover, the edges in the nanomesh are found to be capable acted as a chemical hot spot (CHS) to quickly trap adsorbed molecules with enhanced Raman intensity. The result provides a way to effectively modify the electronic structure of graphene and also a highly sensitive Raman sensor that offers a rapid and nondestructive in situ detection of molecules.In chapter four, we prepared ZnO NPs-RGO hybrid by simple hydrothermal process without any surfactant. TEM characterization shows the ZnO NPs, with an average diameter of5nm, are uniformally anchored on the surface of RGO sheet. The density of ZnO NPs on the RGO can be readily controlled by the precursor weight ratio of GO to Zn(Ac)2. The UV photodetector constructed by the ZnO NPs-RGO hybrid demonstrates an excellent photoresponse compared to the previous reported. The behavior can be attributed to the improved interfacial contact between ZnO NPs and RGO, resulting in the enhancement of photo-generated carriers transfer from ZnO to RGO. Our results indicate this hybrid providing a novel alternate material for the design and fabrication of high performance UV photodector.In chaper five, we prospected several existing challenges as well as the opportunities for the future researches of the graphene.