Institute of Physical Chemistry, University of Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg, Germany.
Nanotechnology. 2017 Feb 10;28(6):064002. doi: 10.1088/1361-6528/aa52e4. Epub 2017 Jan 9.
A consistent set of 2D elastic and fracture properties of hexagonal boron nitride (h-BN) monolayers (boronitrene) and molybdenum disulfide (MoS) nanosheets is derived. Reported literature values for Young's moduli and fracture strengths, based on experiments and DFT calculations, were used to estimate the line or edge energy with a local 2D bond-breaking model. Consistent information was obtained for intrinsic fracture properties. The basic mechanical properties of boronitrene are roughly 25% lower than the corresponding graphene values. This is consistent with the tensile bond force model, and the lower ionic-covalent bonding energy of sp-hybridized B-N bonds in comparison with sp-hybridized carbon bonds. While the intrinsic stiffness and strength of MoS correlate with the strength of its constituent chemical bonds, DFT calculations of the line or edge energy scale with roughly two times the Mo-S bonding energy, whereas the 2D bond-breaking model yields a correlation similar to that found for h-BN. Additional failure properties such as the fracture toughness and strain energy release rate were determined. Together with the intrinsic strengths a Griffith plot of the effective strength of defective h-BN and MoS versus the square root of half the defect size of single defects such as (multi)vacancies and micro-cracks exhibits a slope similar to that of the graphene plot.
本文得到了一套一致的二维弹性和断裂特性的六方氮化硼（h-BN）单层（硼烯）和二硫化钼（MoS）纳米片。基于实验和密度泛函理论（DFT）计算，报道的文献中的杨氏模量和断裂强度值被用于通过局部二维键断裂模型来估计线或边缘能。得到了一致的内在断裂特性信息。硼烯的基本力学性能比相应的石墨烯值低约 25%。这与拉伸键力模型一致，并且 sp 杂化的 B-N 键的离子共价键能比 sp 杂化的碳键低。虽然 MoS 的固有刚度和强度与其组成化学键的强度相关，但线或边缘能的 DFT 计算与 Mo-S 键能大致两倍的比例相关，而二维键断裂模型则给出了与 h-BN 相似的相关性。还确定了其他失效特性，如断裂韧性和应变能释放率。与内在强度一起，有效强度的 Griffith 图显示了有缺陷的 h-BN 和 MoS 的有效强度与单个缺陷（如多空位和微裂纹）的缺陷尺寸的平方根成反比，其斜率类似于石墨烯的斜率。
