|Alternative Title||Study on the physical and mechanical behaviors of defective carbon nanostructures|
|Place of Conferral||北京|
Low-dimensional carbon allotropes, such as graphene, have been broadly explored due to their outstanding and special properties. While the existent of defects in large-area graphene films is inevitable and grain boundaries (GBs) and Stone-Wales defect are commonly presented in form of pentagon and heptagon rings. These defects may significantly influence the interaction between graphene and the other interfaces. Although graphene has been broadly explored due to their outstanding mechanical properties, there exist significant challenges in retaining such properties of basic building blocks when scaling them up to three-dimensional materials and structures for many technological applications. The realized mechanical properties of 3-D carbon materials, by staggering graphene sheets or vertically grown carbon nanotube arrays, are significantly lower than those of individual graphene sheets or individual CNTs. The huge gap in mechanical properties between the low-dimensional carbon allotropes and their 3-D derivatives originates from the dissimilar bonding characteristics between carbon atoms within graphene or CNTs and the architectured 3-D engineering materials: The intra-structure bonding is covalent in nature, while van der Waals bonding dominates between different layers/tubes or with other materials. Such heterogeneous bonding leads to property inheritance that is a mission impossible.
We demonstrate the feasibility of constructing stable 3-D architectured C-honeycomb with covalent bonding. The specific strength of C-honeycomb could be the best in structural carbon materials. Its strong anisotropic Poisson’s effect may be utilized to design multi-functional structures with applications ranging from biomedical engineering to energy and environment systems. With the growing interest for 3-D nano-architectured functional materials, the well patterned two-level hexagonal structures in C-honeycomb pave a new strategy in achieving desirable properties that are comparable with carbon allotropes.
We also reporte a first-principles study on how grain boundary defects in graphene may influence the adsorption of lithium. The adsorption energy for Li atoms trapping in 5-, 7-, and 8-rings is much lower than the counter-part of Li atoms and pristine graphene. Such defective graphene could adsorb more Li atoms, and may reach the speculated ratio of 1:1 for C-Li adsorption. In a contrast study of lithium on fullerenes of different size, we find that the adsorption energy decreases with increasing size of fullerenes, but does not approach the energy when Li atoms adsorb on flat graphene. The energy in carbon nanotubes, however, converges to the adsorption energy between Li atoms and flat graphene if the radius of carbon nanotubes is sufficiently large. It hence indicates that while curvature plays a role in the enhanced adsorption in fullerenes, the twelve 5 rings in a fullerene ball is the primary factor accounting for the enhanced lithium adsorption.
Besides, we also show that the wrinkle formation of graphene grown on Cu substrates is strongly dependent on the crystallographic orientations. The wrinkle-free feature of graphene is attributed to the strong interaction of graphene with Cu(111) that enable strain energy retaining in graphene lattice instead of wrinkles formation. Moreover, the defects direction and orieation distribution of defects in graphene can influence the formation and elimination of wrinkle on different crystallographic orientations of Cu. All of our research provide a theoretical basis for experimental growth of wrinkle-free graphene.
The graphene interlayer also can weaken the interaction between AlN and sapphire, thus the compressive strain in AlN and tensile strain in sapphire is largely relaxed. The effective relaxation of strain further leads to fast epitaxial growth of AlN on sapphire. We also investigate the mechanics of borophene under uniaxial and biaxial tension. We find that the failure behavior, Young’s modulus and Poisson’s ratio of both the monolayer and bilayer borophene are highly anisotropic: Poisson’s ratio is negative when tension is along the atomic ridge direction.
|庞震乾. 含缺陷碳构筑结构的物理力学行为研究[D]. 北京. 中国科学院大学,2018.|
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