【作者】 刘金养；

【导师】 王晓平；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2013， 博士

【摘要】 石墨烯是一种由碳原子以sp2杂化轨道组成的六角型晶格单原子层二维晶体。石墨烯有许多独特的性质,它是零带隙的半金属半导体材料,具有超高的费米速度(光速的1/300)、载流子迁移率(达到200,000cm2V-1s-1)和热导率(～5000W/mK),良好的透光特性(单层石墨烯的吸收-2.3%)和优异的力学性能(弹性模量和抗拉强度分别达到1.1TPa和125GPa),因此在透明电极、晶体管、传感器、能源存储、高强度复合材料等方面存在广泛的应用前景。另一方面,石墨烯具有原子级的平整度、良好的生物兼容性、去局域化的π键以及良好的化学惰性,为研究表面增强拉曼及其机理提供了一个全新的平台；同时,它丰富的表面有利于石墨烯-半导体复合结构的设计、集成和制备。本文基于石墨烯的上述特性,侧重开展石墨烯及其新型纳米复合结构在表面增强拉曼光谱以及光电探测方面的应用基础研究。本论文共有五章,各章内容简述如下：在第一章中,我们首先简要回顾了石墨烯的发现历史、主要制备方法和性质,以及石墨烯各种潜在的应用前景。接着介绍了表面增强拉曼光谱和光电探测器的基本原理、研究现状与发展趋势,以及石墨烯在表面增强拉曼光谱和光电探测器研究中的应用前景。最后,概述了本论文的选题背景和科学意义。在第二章中,我们设计和制备了金属／石墨烯／金属三明治纳米结构的新型表面增强拉曼衬底,解决了表面增强拉曼效应研究中精确构筑“热点”和放置分子这些长期存在的问题。在金属／石墨烯／金属纳米结构中,通过改变石墨烯、金属纳米颗粒大小以及金属纳米颗粒的种类实现了对电磁场“热点”的调节；通过石墨烯对分子的吸附,实现了将分子精确放置于复合纳米结构的等离子体激元“热点”处。此外,我们发现金属／石墨烯／金属纳米结构的表面增强拉曼效应还与激发光的入射倾角相关,在合适的角度下,能够进一步增强拉曼信号。该结构有超高的灵敏度,能够探测到50nM溶液浓度的RhB分子信号。在第三章中,我们发展了一种通过金属纳米颗粒局域催化分解碳制备多孔石墨烯的新方法,并将之应用于表面增强拉曼光谱。该方法中,通过调节Cu薄膜的厚度可以调节多孔石墨烯中孔的大小、密度以及边缘长度。以RhB为检测分子,我们发现多孔石墨烯有比纯石墨烯衬底更强的拉曼化学增强特性,同时发现其化学增强能力同多孔结构中的边缘长度相关。通过拉曼光谱表征和电输运测量,我们推断多孔石墨烯中大量的边缘结构可实现自发的p型掺杂,从而导致显著的拉曼化学增强。此外,多孔石墨烯的孔洞边缘还可以高效吸附待测分子,实现对分子拉曼增强的快速检测。这些结果表明,多孔石墨烯可以用作一种快速、高效拉曼增强检测的优质衬底。在第四章中,我们利用水热反应制备出无表面活性剂的氧化锌纳米颗粒／还原石墨烯复合结构,并研究了其光电响应特性。研究发现复合结构中氧化锌单晶纳米颗粒的平均直径为5纳米,这些颗粒均匀分布在还原石墨烯表面,其密度可以通过反应物的浓度进行有效调节。我们进一步构建了基于这种复合结构的光电探测器,该探测器对紫外光的响应很快,光电流响应变化可达四个量级,表明该复合结构特别适合作为替代材料用于设计和构建高性能的紫外光探测器件。在第五章中,我们展望了石墨烯研究中的一些挑战和发展趋势。更多还原

【Abstract】 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.更多还原