【作者】 王彬；

【导师】 胡礼中；

【作者基本信息】 大连理工大学 ， 微电子学与固体电子学， 2014， 博士

【摘要】 由于石墨烯具有的独特的晶体结构、优异的电学、光学等方面的性质,使得其在光电子器件、复合材料和储能器件等领域有着广阔的应用前景。与其他制备石墨烯的方法相比,利用化学气相沉积(CVD)法在过渡族金属上制备大面积可转移的石墨烯薄膜有着明显的优势。但是,由于受到石墨烯生长条件以及成核机制的限制,CVD法制备的石墨烯薄膜在提高质量以及均匀性等方面面临巨大挑战。而材料的制备是系统研究其性能并且成功应用的前提和基础。本论文基于CVD法的石墨烯制备(以钼膜和铜箔为衬底)和表征,所开展的主要工作和得到的结论如下：1.利用自行改装的CVD设备,在钼膜衬底上成功制备出高质量的石墨烯薄膜。拉曼光谱测试结果证明了生长时间、降温速率和钼膜厚度对生长的石墨烯质量有很大影响。通过优化生长时间(15min)和降温速率(10℃/s),在200nm厚的钼膜上获得了IG/I2D约为0.26、半高宽约为30.4cm-1的石墨烯薄膜。并且证明了钼基上石墨烯的生长机理为碳的溶解析出机制。2.通过实验对比,发现铜衬底的表面形态,例如粗糙度和晶界对石墨烯的成核有着重要影响。通过对铜箔进行机械化学抛光,降低了铜箔表面的粗糙度,在抛光后的铜箔上生长石墨烯,大大降低了石墨烯的成核密度。扫描电子显微镜和光学显微镜显示石墨烯优先在铜的晶界和表面划痕处成核。在抛光后的铜衬底上生长出了六角单晶石墨烯晶畴,并且通过优化生长参数提高了晶畴的大小。通过两步合成法在抛光的铜衬底上生长出连续的石墨烯薄膜,霍尔测试结果显示其电学特性远优于在未抛光铜衬底上生长的石墨烯薄膜。3.对CVD方法生长的六角形石墨烯晶畴在常压下进行氢气刻蚀,观察到氢气刻蚀在石墨烯表面产生了网络状和线状结构的刻蚀条纹,并且刻蚀条纹的密度和宽度随着刻蚀时间的增加而增大。经过电子背向散射衍射(EBSD)测试,证明了刻蚀条纹的形态与铜衬底面的晶向有关,不同的晶向可导致刻蚀条纹不同的形状和密度。通过对比实验,证明了刻蚀条纹是由于降温过程中形成的褶皱产生氢化现象引起的。此外,通过扫描电子显微镜(SEM)观察,进一步解释了石墨烯褶皱处氢气刻蚀的过程。更多还原

【Abstract】 As a novel two-dimension carbon specy, graphene has attracted significant attention due to its unique physical properties such as crystallographic quality, electronic structure and high optical transparency, which have significant potential in optoelectronic devices, composite materials and energy storages. Compared with other graphene synthesis processes, graphene grown on transition metals via chemical vapor deposition (CVD) has the distinct advantage of providing extremely large-area graphene films transferable to other substrates. However, as limited by the growth and nucleation mechanism, it remains a challenge to control the quality and uniformity of CVD graphene, whose natural polycrystalline structure has greatly degraded its electrical performance. Since the preparation of materials is the premise and basis for the systematic study of its properties and applications, we study on the synthesis and characters of graphene grown on Mo and Cu substrate by chemical vapor deposition in this paper. The main results are summarized as follows:1. High quality graphene on single-crystal Mo (110) films has been successfully synthesized by a modified CVD equipment. The micro-Raman spectroscopy indicated that the thickness of Mo films, cooling rate and growing time play significant roles in the quality of as-grown graphene films. By optimizing the growth time (15min) and cooling rate (10℃/s), we achieved high quality graphene films with the small ratio IG/I2d≈0.26and the FWHM(2D)≈30.4cm-1on200nm-thick Mo films. Our experiments also suggested that graphene growth on Mo was a dissolution and segregation process.2. The morphology of copper surface such as roughness and grain boundary were found to be crucial roles for forming nucleation seeds of graphene domain. We reduced the nucleation seed density via polishing the Cu substrate by chemical mechanical method. Scanning electron microscope and optical microscope images indicated that it was preferential to form nucleation seeds along the Cu grain boundary and scratched area of the polished Cu substrate. We demonstrated that a very flat surface of Cu substrate was beneficial for growing hexagonal single-crystal graphene domain and could enhance the homogeneity and electronic transport properties of graphene films.3. Hexagonal single-crystal graphene domains were grown on copper (Cu) foil via chemical vapor deposition and were etched with hydrogen at950℃from7to60min at atmospheric pressure. Numerous trenches were observed on the initial graphene domains after etching, and the trench patterns were closely associated with the Cu crystal orientation. We proved that the etching trenches were caused by the hydrogenation of the wrinkles formed during the cooling down process. The etching process on the wrinkles was also examined and explained by SEM.更多还原