基于粗粒化分子动力学的自支撑石墨烯镜面屈曲研究

Mirror buckling analysis of freestanding graphene membranes by coarse-grained molecular dynamics method

在扫描隧道显微镜的观测中发现了自支撑石墨烯膜镜面屈曲这一独特现象,目前尚少有研究人员对其进行系统性的研究.对于这种面外变形行为,不论是在实验观测,还是在能量收集系统这种潜在的应用形式中,石墨烯的尺寸都需要达到微米级.先前的研究表明,传统分子动力学适用于纳米尺度石墨烯的计算与分析,由于其计算方法的限制,在处理微米级模型时容易出现计算效率低、耗时长等问题.为了研究微米级尺寸石墨烯膜镜面屈曲现象,本文使用粗粒化分子动力学方法,首先验证该方法的适用性,然后分别施加不同大小的机械载荷和温度载荷在扇形截面不同高跨比的石墨烯膜上以分析各因素带来的影响.计算结果表明机械载荷作用下各个高跨比石墨烯均可以发生镜面屈曲现象,且临界载荷随高跨比的增大而增大;温度载荷作用下,高跨比较小的石墨烯能够发生完全翻转现象,大高跨比情况下温度升高使中心高度下降,但完全翻转较难发生.研究分析各因素对于石墨烯镜面屈曲现象的影响,可以加深对这一特殊现象了解的同时,为能量收集系统的设计提供理论指导.

Up to now,the analysis has rarely been conducted of thermal-mechanical mirror buckling behavior of freestanding graphene membranes discovered in scan tunneling microscope experiments.One of the potential applications of the out-of-plane deformational behavior of graphene membranes is energy harvesting system.Whether in the experiments or for energy harvesting systems,the size of graphene membrane needs to be down to micron scale.According to previous researches,traditional molecular dynamics method is a suitable method to characterize nano-scale mirror buckling.However,owing to the limit of algorithm,when dealing with micro size model by molecular dynamics method,two problems arise:low computational efficiency and too long calculation time.Therefore,for analyzing the mirror buckling of micro size graphene membranes,the coarse-grained molecular dynamics method is utilized in this work.Graphene membranes with a fan-shaped cross section and various depth-span ratios are under mechanical or thermal loads.Effects of each factor on the mirror buckling are investigated.The calculations indicate that for graphene membranes with various depth-span ratios under mechanical load mirror buckling can be observed.And the critical loading increases with the depth-span ratio increasing.Under thermal load graphene membranes only with low depth-span ratios can undergo complete flipping phenomenon.For high depth-span ratio graphene,the center height decreases with temperature rising.However,it is hard to flip over completely.The understanding of the effects of various factors on the mirror buckling phenomenon of graphene membranes can provide theoretical guidance for designing the energy harvesting systems.