In addition, it is found that the trilateral structure is an interim state in the evolution process from a pristine hexagonal this website structure to the 5–7 structure. A 5-3-6 structure including this trilateral structure and its adjacent structures would evolve into another 5–7 structure, the right one in Figure  2d, through bond breaking and

bond reforming. Furthermore, a single-chain structure, shown in Figure  2e, can be observed during the fracture process, which can also be found in [26]. Afterwards, the single chain was broken and the indenter totally pierced through the graphene film. Figure 2 Evolution of graphene lattice fracture at different indentation depths. This group of figures shows the process from the state at which the indentation depth reaches

the critical depth to the state the graphene film is totally ruptured with an indenter radius of 2 nm, loading speed of 0.20 Å/ps, and aspect ratio of 1.2. (a) At critical moment: indentation depth 55.95 Å, load 655.08 nN; (b) first broken bond emerged: indentation depth 55.97 Å, load 635.60 nN; (c) pentagonal-heptagonal (5–7) and trilateral structures emerged: indentation depth 55.99 Å, load 426.04 nN; (d) three 5–7 structures: indentation depth 56.01 Å, load 310.45 nN; (e) single-chain structure emerged: indentation depth 56.51 Å, load 112.03 nN; (f) fracture of the chain: indentation depth 56.61 Å, load 93.70 nN. Generally speaking, elastic deformation which is reversible selleck inhibitor and plastic deformation which is irreversible are two

typical kinds of deformation of an object or material in the view of engineering. In order to determine whether the deformation of the graphene film is elastic or plastic, a set of experiments of loading-unloading-reloading processes are conducted. As shown in Figure  3, during the continuous loading process of the indenter on the graphene medroxyprogesterone film, it can be found that the graphene film mainly takes on two stages in sequence: Figure 3 Load–displacement curve of loading-unloading-reloading process with maximum indentation depth smaller than the critical indentation depth. Stage I. The unloading process is done before the indentation depth reaches the critical depth, d c. The graphene sheet almost can make a complete recovery, i.e., restore its selleck compound initial structures, and the curves of reloading processes almost perfectly match the initial loading curve while the unloading curve shows very small deviations from the initial one, as shown in the inset of Figure  3. In general, the almost-perfect coincidence is due to the fact that the carbon covalent bonds and the graphene lattice structure are not destroyed. It can be concluded that there is no plastic deformation in this stage, i.e., the graphene undergoes elastic deformation. Stage II, i.e., the yellow region in Figure  3.