Mazarei Elham, Penschke Christopher, Saalfrank Peter
Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam, Germany.
Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam, Germany.
ACS Omega. 2023 Jun 5;8(24):22026-22041. doi: 10.1021/acsomega.3c02068. eCollection 2023 Jun 20.
Graphene is well-known for its unique combination of electrical and mechanical properties. However, its vanishing band gap limits the use of graphene in microelectronics. Covalent functionalization of graphene has been a common approach to address this critical issue and introduce a band gap. In this Article, we systematically analyze the functionalization of single-layer graphene (SLG) and bilayer graphene (BLG) with methyl (CH) using periodic density functional theory (DFT) at the PBE+D3 level of theory. We also include a comparison of methylated single-layer and bilayer graphene, as well as a discussion of different methylation options (radicalic, cationic, and anionic). For SLG, methyl coverages ranging from 1/8 to 1/1, (i.e., the fully methylated analogue of graphane) are considered. We find that up to a coverage θ of 1/2, graphene readily accepts CH, with neighbor CH groups preferring positions. Above θ = 1/2, the tendency to accept further CH weakens and the lattice constant increases. The band gap behaves less regularly, but overall it increases with increasing methyl coverage. Thus, methylated graphene shows potential for developing band gap-tuned microelectronics devices and may offer further functionalization options. To guide in the interpretation of methylation experiments, vibrational signatures of various species are characterized by normal-mode analysis (NMA), their vibrational density of states (VDOS), and infrared (IR) spectra, the latter two are obtained from ab initio molecular dynamics (AIMD) in combination with a velocity-velocity autocorrelation function (VVAF) approach.
石墨烯因其独特的电学和力学性能组合而闻名。然而，其零带隙限制了石墨烯在微电子领域的应用。石墨烯的共价功能化一直是解决这一关键问题并引入带隙的常用方法。在本文中，我们使用周期性密度泛函理论（DFT）在PBE+D3理论水平上系统地分析了单层石墨烯（SLG）和双层石墨烯（BLG）与甲基（CH）的功能化。我们还对甲基化的单层和双层石墨烯进行了比较，并讨论了不同的甲基化选项（自由基、阳离子和阴离子）。对于SLG，考虑了甲基覆盖率范围从1/8到1/1（即完全甲基化的类石墨烷类似物）。我们发现，在覆盖率θ达到1/2之前，石墨烯很容易接受CH，相邻的CH基团更喜欢特定位置。在θ>1/2时，接受更多CH的趋势减弱，晶格常数增加。带隙的变化不太规律，但总体上随着甲基覆盖率的增加而增加。因此，甲基化石墨烯在开发带隙调谐的微电子器件方面显示出潜力，并可能提供进一步的功能化选项。为了指导甲基化实验的解释，通过正常模式分析（NMA）、它们的振动态密度（VDOS）和红外（IR）光谱来表征各种物种的振动特征，后两者是通过从头算分子动力学（AIMD）结合速度-速度自相关函数（VVAF）方法获得的。
