Bouaamlat Hussam, Seitsonen Ari Paavo, Bussetti Gianlorenzo, Yivlialin Rossella, De Rosa Stefania, Branchini Paolo, Tortora Luca
National Institute for Nuclear Physics - Roma Tre Division, via della Vasca Navale 84, Rome I-00146, Italy.
Département de Chimie, École Normale Supérieure, 24 rue Lhomond, Paris F-75005, France.
Phys Chem Chem Phys. 2024 Apr 24;26(16):12269-12281. doi: 10.1039/d3cp05706b.
Complex phenomena characterize the intercalation of ions inside stratified crystals. Their comprehension is crucial in view of exploiting the intercalation mechanism to change the transport properties of the crystal or obtaining a fine control of crystal delamination. In particular, the relationship between the concentration and nature of intercalated ions and surface structural modifications of the host stratified crystal is still under debate. Here, we discuss a theoretical effort to provide a rationale for some structural changes observed on the highly oriented pyrolytic graphite (HOPG) surface after electrochemical treatment in perchloric and sulphuric acid solutions. The formation of the so-called nano-protrusions on the basal plane of intercalated graphite was previously observed with scanning tunneling microscopy (STM). In this work, we employed both STM and density functional theory (DFT) simulations to elucidate the physical and chemical mechanisms driving the emergence of these nano-protrusions. The DFT results show that, in a bilayer graphene system, the presence of a single ion can generate a nano-protrusion with 2.49 Å height and 21.27 Å width. In the deformed area, the C-C bond length is stretched by about 2.5% more than the normal graphene bond. These values are of the same dimensional scale as those reported in previous STM experimental results. However, the simulated STM images obtained by increasing the amount of intercalated ions per area suggest that the presence of more than one ion is needed for the deformation of the uppermost graphite layer during the early stages of intercalation. In contrast, in a multilayer graphene system, no significant surface deformation is detected when ions are intercalated between the third and fourth layers. Charge analysis indicates an altered distribution of the charges as a consequence of the intercalation. The charge transfer from graphene layers to the intercalated ions results in a surface layer more prone to oxidation.
复杂的现象表征了离子在层状晶体内部的嵌入过程。鉴于利用嵌入机制来改变晶体的传输特性或实现对晶体分层的精确控制，对这些现象的理解至关重要。特别是，嵌入离子的浓度和性质与主体层状晶体表面结构改性之间的关系仍存在争议。在此，我们讨论一项理论研究工作，旨在为在高氯酸和硫酸溶液中进行电化学处理后在高度取向热解石墨（HOPG）表面观察到的一些结构变化提供理论依据。先前通过扫描隧道显微镜（STM）观察到嵌入石墨基面形成了所谓的纳米突起。在这项工作中，我们同时使用STM和密度泛函理论（DFT）模拟来阐明驱动这些纳米突起出现的物理和化学机制。DFT结果表明，在双层石墨烯系统中，单个离子的存在可产生高度为2.49 Å、宽度为21.27 Å的纳米突起。在变形区域，C-C键长比正常石墨烯键长拉伸约2.5%。这些值与先前STM实验结果报道的尺寸规模相同。然而，通过增加每单位面积嵌入离子的数量获得的模拟STM图像表明，在嵌入早期，最上层石墨层的变形需要不止一个离子的存在。相比之下，在多层石墨烯系统中，当离子嵌入第三层和第四层之间时，未检测到明显的表面变形。电荷分析表明，嵌入导致电荷分布发生改变。从石墨烯层到嵌入离子的电荷转移导致表面层更易于氧化。
