Queensland Micro and Nano Technology Centre, Nathan Campus, Griffith University, 170 Kessels Road, Nathan, QLD 4111, Australia.
Department of Engineering Mechanics and Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
J Chem Phys. 2013 Dec 14;139(22):224704. doi: 10.1063/1.4839615.
Via a novel experiment, Liu et al. [Phys. Rev. B 85, 205418 (2012)] estimated the graphite binding energy, specifically the cleavage energy, an important physical property of bulk graphite. We re-examine the data analysis and note that within the standard Lennard-Jones model employed, there are difficulties in achieving internal consistency in the reproduction of the graphite elastic properties. By employing similar models which guarantee consistency with the elastic constant, we find a wide range of model dependent binding energy values from the same experimental data. We attribute some of the difficulties in the determination of the binding energy to: (i) limited theoretical understanding of the van der Waals dispersion of graphite cleavage, (ii) the mis-match between the strong bending stiffness of the graphite-SiO2 cantilever and the weak asymptotic inter-layer forces that are integrated over to produce the binding energy. We find, however, that the data do support determination of a maximum inter-layer force that is relatively model independent. We conclude that the peak force per unit area is 1.1 ± 0.15 GPa for cleavage, and occurs at an inter-layer spacing of 0.377 ± 0.013 nm.
通过一项新颖的实验，Liu 等人 [Phys. Rev. B 85, 205418 (2012)] 估算了石墨的结合能，特别是解理能，这是块状石墨的一个重要物理性质。我们重新检查了数据分析，并注意到在使用的标准 Lennard-Jones 模型中，在再现石墨弹性性质时存在难以实现内部一致性的问题。通过使用类似的模型来保证与弹性常数的一致性，我们从相同的实验数据中发现了广泛的、依赖模型的结合能值。我们将结合能确定中的一些困难归因于：（i）对石墨解理的范德华色散的理论理解有限，（ii）石墨-SiO2 悬梁的强烈弯曲刚度与被积分以产生结合能的弱渐近层间力之间不匹配。然而，我们发现数据确实支持确定一个相对独立于模型的最大层间力。我们得出结论，解理的单位面积峰值力为 1.1 ± 0.15 GPa，发生在层间间距为 0.377 ± 0.013 nm 处。
