【作者】 曾健；

【导师】 刘杰； 李公平；

【作者基本信息】 中国科学院研究生院（近代物理研究所） ， 粒子物理与原子核物理， 2014， 博士

【摘要】 石墨材料具有诸多优点，如高的熔沸点、良好导热导电性、稳定的化学性质、耐腐蚀、抗热震性、良好可塑性及良好的中子减速性能，非常适合用作核反应堆快中子慢化材料。在高温气冷堆中，石墨是唯一可选择的结构材料和反射层材料。高温中子辐照会在石墨中引起晶格原子离位，产生缺陷和扰动，并引起理化性能和宏观尺寸的变化，因此石墨的辐照效应研究始终是国际上的热点研究课题。石墨烯作为单层的石墨材料，具有优异的电学、热学以及光学性能，是构建其它维数碳材料的基本单元，对其辐照效应的研究一方面可以提高对石墨、碳纳米管、富勒烯等碳同素异构体材料辐照效应的认识。另外也可以为石墨烯的应用提供有价值的参考数据。本论文采用机械剥离法成功获得石墨烯样品，借助近物所重离子加速器HIRFL和德国GSI的直线加速器UNILAC提供的快重离子（SHI），以及近物所320kV高压平台提供的高电荷态离子（HCI），对高定向石墨（HOPG）、纳米厚度的HOPG及石墨烯样品进行辐照。辐照后样品采用激光共聚焦拉曼光谱仪、X射线光电子谱仪、扫描隧道显微镜、透射电子显微镜及原子力显微镜进行检测，实验结果分三个部分进行详细分析和讨论。快重离子辐照实验结果表明，(1)辐照后HOPG表面有纳米尺寸小丘状潜径迹形成，且有sp3杂化相产生。sp3相产额与电子能损和离子总注量有关。辐照后的样品拉曼D峰与D′峰与G峰面积比(ID/IG)随辐照注量的增加而增大，服从T-K关系。(2)薄层HOPG的辐照损伤与其厚度有关，越薄损伤越严重，单层石墨烯损伤最严重。通过检测样品的拉曼D峰与D′峰的峰高比ID/ID′，讨论了不同厚度样品中可能存在的缺陷类型。(3)实验观测到辐照后石墨烯出现纳米直径的孔洞。Raman测试表明电子能损值是影响石墨烯辐照损伤程度的重要因素。通过改进Lucchese的理论模型，对辐照后石墨烯ID/IG值随潜径迹间距(Ld)变化参数进行拟合。获得了石墨烯损伤程度与入射离子的电子能损dE/dx和单核能的关系，可以用于石墨烯SHI辐照损伤的预测。(4)对比HOPG与石墨烯实验结果发现，石墨烯比块体石墨更容易产生辐照损伤；石墨烯ID/IG值随辐照注量变化出现拐点，而在现有注量范围内石墨的ID/IG值并无拐点出现；在石墨中发现的离子速度效应在石墨烯中并未观察到。高电荷态离子辐照实验表明，(1)辐照后HOPG表面有小丘状潜径迹形成，在部分小丘状突起顶端检测到新的HOPG晶格结构。(2)通过对Lucchese的理论模型进行改进，成功拟合了石墨与石墨烯的实验数据。拟合结果表明，石墨与石墨烯的ID/IG随注量的变化趋势不同，差异源于辐照后石墨烯中存在结构完全损伤区与激活区，两种竞争机制导致了石墨烯ID/IG的三个变化阶段。而HOPG只有激活区，所以石墨ID/IG只有两个变化阶段。对比快重离子与高电荷态离子在HOPG与石墨烯中引起的辐照效应可以得出，(1)相同辐照注量条件下，在HOPG中，HCI辐照将导致比SHI辐照更大的拉曼D峰与G峰峰高比(ID/IG)，然而在石墨烯中，两种离子辐照引起的ID/IG并无明显差异。(2)石墨烯中，HCI将导致比SHI更大的激活区半径rA。更多还原

【Abstract】 Graphite materials have many advantages, such as high melting and boiling points,good thermal and electrical conductivity, stable chemical property, corrosion resistance,thermal shock resistance and good plasticity. What’s more important is it can slowdown the fast neutrons. Thus graphite is the ideal neutron moderation materials whichcould be used in nuclear reactors. In high-temperature gas-cooled reactor, graphite isthe only choice for structure and reflector materials. Heat neutron irradiation inducesatom displacement, results in defects and disturbance which would further lead to thephysical and chemical properties and even the macroscopic dimensions changes of thegraphite. Therefore, the study of irradiation effects in graphite is always a veryimportant research topic all over the world. Graphene is single layer graphite, whichcould be viewed as the building block for various carbon allotropes. In addition,graphene has excellent electrical, thermal and optical properties. The investigation ofthe irradiation effects on graphene paves a way to understand the property of carbonallotropes. Moreover, it could provide valuable experimental data for the applicationof graphene.In this thesis, monolayer graphene samples were successfully fabricated bymicromechanical cleavage technique. Both of Swift Heavy Ions (SHI) and HighlyCharged Ions (HCI) were used to irradiate Highly Oriented Pyrolytic Graphite(HOPG), HOPG films with thickness of several nanometers and monolayer graphene.SHI were provided by the accelerator HIRFL of IMP and the linear acceleratorUNILAC of GSI. HCI were offered by320kV high-voltage platform of IMP. Afterirradiation, the samples were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning tunneling microscopy, transmission electronmicroscopy and atomic force microscopy. The detailed analysis and discussion of theexperimental results are divided into three parts as follows.The results of irradiation effects caused by SHI indicate that:(1) Nanoscalehillock latent tracks and sp3component were detected on the irradiated HOPG surface.The amount of hybridization (Isp3/Isp2) strongly depends on the electronic energy lossand the fluence of incident ions in the samples. The area ratio of Raman D and D′peak to G peak (ID/IG) increases with the increasing ion fluence, this is correspondingto the T-K relation.(2) The irradiation damage of HOPG films depends on thethickness of the samples. It’s much easier to induce defects into thinner films thanthicker ones. The results showed that the monolayer graphene has the weakest anti–irradiation properties. The possible defect types in samples with different thicknesswere also discussed via different intensity ratio ID/ID′.(3) Nanoscale holes wereobserved in monolayer graphene by TEM. Raman test shows that the electronic energyloss (dE/dx)eplays an important role in the degree of damage in graphene. Lucchese’stheoretical model was improved in this work to study the evolution of ID/IGwith latenttrack spacing (Ld) of graphene irradiated by SHI. In the improved model, the directrelationships of the damage in graphene to the impacting ions parameters includingelectronic energy loss dE/dx and impact ion energy ε were concluded. With this model,the irradiation effects of graphene caused by SHI could be predicted well.(4) Bycomparing the irradiation effects of HOPG and graphene, we found that monolayergraphene is much easier to be damaged than bulk graphite. A turning point wasdetected in the evolution progress of ID/IGwith the fluence obtained from graphene,while such point was never found in HOPG in the fluence range of this work. Thevelocity effect was measured in HOPG However, it was not observed in graphene inthis experiment.The results of the HCI irradiation experiment were concluded as following:(1)Hillock latent tracks were detected on the irradiated HOPG surface.Compressed HOPG lattice structure was imaged on the top of some latent tracks.(2)The Lucchese’s phenomenological model was improved to give full line fitting of theexperiment data of HOPG and graphene. According to the improved model, the energetic ions may cause both structurally disordered and activated regions ingraphene. The competing mechanism of these two regions results in three variationregions of the ID/IGof graphene. In HOPG, however, only activated region is inducedby energetic ions, then two variation regions of ID/IGobtained from HOPG has bedetected.The different irradiation results of the HOPG and graphene caused by SHI andHCI were discussed. The main results show that:(1) Under the same irradiation ionfluence, the greater intensity ratios of the D peak to G peak (ID/IG) were found inHOPG impacted by HCI than that by SHI. While no obvious differences of ID/IGweredetected in graphene irradiated by those two different kinds of ions.(2) Comparing thegraphene samples impacted by SHI and HCI ions, the larger radius of the activatedregion rAin HCI irradiated graphene was observed.更多还原