Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
J Phys Chem A. 2011 Nov 24;115(46):13269-80. doi: 10.1021/jp207179x. Epub 2011 Oct 25.
In this work, we have investigated the hyperthermal collisions of atomic oxygens with graphene through molecular dynamics simulations using the ReaxFF reactive force field. First, following Paci et al. (J. Phys. Chem. A 2009, 113, 4677 - 4685), 5-eV energetic collisions of atomic oxygen with a 24-atom pristine graphene sheet and a sheet with a single vacancy defect, both functionalized with oxygen atoms in the form of epoxides, were studied. We found that the removal of an O(2) molecule from the surface of the graphene sheet occurs predominantly through an Eley-Rideal-type reaction mechanism. Our results, in terms of the number of occurrences of various reactive events, compared well with those reported by Paci et al. Subsequently, energetic collisions of atomic oxygen with a 25-times-expanded pristine sheet were investigated. The steady-state oxygen coverage was found to be more than one atom per three surface carbon atoms. Under an oxygen impact, the graphene sheet was always found to buckle along its diagonal. In addition, the larger sheet exhibited trampoline-like behavior, as a result of which we observed a much larger number of inelastic scattering events than those reported by Paci et al. for the smaller system. Removal of O(2) from the larger sheet occurred strictly through an Eley-Rideal-type reaction. Investigation of the events leading to the breakup of a pristine unfunctionalized graphene sheet and the effects of the presence of a second layer beneath the graphene sheet in an AB arrangement was done through successive impacts with energetic oxygen atoms on the structures. Breakup of a graphene sheet was found to occur in two stages: epoxide formation, followed by the creation and growth of defects. Events leading to the breakup of a two-layer graphene stack included epoxide formation, transformation from an AB to an AA arrangement as a result of interlayer bonding, defect formation and expansion in the top layer, and finally erosion of the bottom layer. We observed that the breakup of the two-layer stack occurred through a sequential, layer-by-layer, erosion process.
在这项工作中，我们通过使用 ReaxFF 反应力场的分子动力学模拟研究了原子氧与石墨烯的超热碰撞。首先，我们遵循 Paci 等人的方法（J. Phys. Chem. A 2009, 113, 4677-4685），研究了 5eV 能量的原子氧与具有环氧官能团的 24 个原子原始石墨烯片和具有单个空位缺陷的石墨烯片之间的碰撞。我们发现，从石墨烯片表面去除 O(2)分子主要通过 Eley-Rideal 型反应机制发生。我们在各种反应事件发生次数方面的结果与 Paci 等人的报道吻合良好。随后，我们研究了原子氧与 25 倍扩展的原始石墨烯片的高能碰撞。发现稳态氧覆盖率超过每个三个表面碳原子一个原子。在氧气冲击下，石墨烯片总是沿着对角线弯曲。此外，较大的片表现出蹦床样行为，因此我们观察到比 Paci 等人报道的更小系统更多的非弹性散射事件。较大的片上 O(2)的去除严格通过 Eley-Rideal 型反应发生。通过在结构上用高能氧原子连续冲击，研究了原始未官能化石墨烯片的破裂事件以及 AB 排列下第二层存在的影响。发现石墨烯片的破裂分两个阶段发生：环氧化物形成，然后缺陷的产生和增长。导致双层石墨烯堆叠破裂的事件包括环氧化物形成、层间键合导致 AB 排列转变为 AA 排列、缺陷形成和上层扩展，以及最后底层侵蚀。我们观察到双层堆叠的破裂是通过顺序的、逐层的侵蚀过程发生的。
