金属插入对石墨烯物化性质调控的理论研究

Recent experiments indicate that metal intercalation is a very effective method to manipulate the graphene-adatom interaction and control metal nanostructure formation on graphene. Materials based on graphene especially for graphene intercalant compound have been attracted extensive attentions since it can be considered as novel materials which have potential applications in microelectronic devices, energy storage, spin transport, surface catalysis and biology. However, a key question is mass transport, i.e., how atoms deposited uniformly on graphene populate different areas depending on the local intercalation. This project based on transition metal and rare earth metal intercalant between graphene and SiC substrate, will be mainly focus on the metals intercalation mechanism, stable geometry, magnetic properties as well as electronic properties by using first-principles calculations and transition state theory together with classical crystal growth theory. The purpose of this proposal is to investigate the distribution of electrostatic potential of transition metal and rare earth metal intercalation into graphene and SiC interface with different forms, and to explore the induced oscillatory electric field. On the other hand, this work scheme is aiming at revealing the reason why the deposited metal show the selective adatom mass transport on partially intercalated graphene. We proposed a diffusion mechanism that leads to selective adatom mass transport on partially intercalated graphene. By using this mechanism, different metal intercalation can induce different doped graphene patches by charge transfer from the intercalant to graphene. This redistribution of the electrons makes the electrostatic potential lower in the intercalated graphene areas and thus induces a strong electric field across the boundary between the intercalated and non-intercalated domains. This field provides significant driving force for biased diffusion of the positively charged metal adatoms toward the non-intercalated domains and can account for the unusual nucleation observed exclusively only on these areas. Similar mechanism can be applied to other systems where intercalation leads to spatial variation of the work function. It can be exploited as a general method to prepare patterned graphene and control the nucleation sites of metallic islands. The results of this research project can serve as a basis for future experimental and theoretical studies of metal intercalation between graphene and SiC substrate.

以石墨烯为基础的碳质材料,尤其是石墨烯-衬底层间插入复合物成为近十年来基础研究和新型材料开发的热点。其在微电子器件、能源存储、电子和自旋输运、催化以及生物等多个领域具有广泛的应用前景。本项目拟采用第一性原理基态结构能量计算和过渡态理论搜索方法，再结合经典晶体生长理论，以过渡金属和稀土金属插入石墨烯-SiC 衬底界面为研究对象，从热力学稳定性和动力学反应路径两个方面来深入研究过渡金属和稀土金属在石墨烯与 SiC 衬底界面的插入机理、稳定构型、磁性和电子结构性质。尤其是关注过渡金属和稀土金属以不同形式在石墨烯与 SiC 衬底界面插入后对石墨烯表面静电势的影响以及静电势的改变对石墨烯样本表面金属原子吸附、扩散、成核的影响，进一步探索在过渡金属和稀土金属插入后对金属纳米材料的生长以及在宏观上密度、形貌等特征的影响规律，从而给予实验研究有力的理论指导。

石墨烯-衬底插层复合物不仅在基础科学研究方面具有重大意义，更在微电子、光电子、储能等器件革新方面有广泛的应用前景。本项目利用第一性原理结构优化和过渡态搜索方法结合经典晶体生长理论对石墨烯-衬底插层复合物表面和界面输运性质进行详细研究。研究结果表明衬底有助于金属原子插入，且缺陷辅助机制是实验上最有可能的插入机制，考虑衬底后能垒分别降低了24%、79%、100%，表明衬底效应不可忽略；金属、非金属插层对石墨烯晶格和电子性质的影响，发现金属插层与石墨烯之间为弱相互作用，对石墨烯晶几何结构和电子结构影响较小；不同插层结构对石墨烯表面静电势的分布影响不同，发现界面处静电势分布不均匀，且金属插层与非金属插层致使石墨烯表面静电势分布不同，这种静电势的重新分布主要来源于插入层向石墨烯层的电荷转移；研究发现不同插层结构表面吸附原子的吸附以及扩散具有选择性，而不是各向同性的这种选择性的根源来自于交替静电势诱导产生的交替电场，纳米粒子在交替电场驱动下选择性扩散进而影响生长形貌。本项目解决了石墨烯-碳化硅衬底表面以及界面质量输运问题，部分解决了插层对纳米材料生长形貌的影响问题。已发表SCI学术论文13篇，参加国际会议2人次，国内会议5人次，组织会议1次，邀请专家来校访问6人次。