The initial stages of melting of graphene between 4000 K and 6000 K

Abstract

Graphene and its analogues have some of the highest predicted melting points of any materials. Previous work estimated the melting temperature for freestanding graphene to be a remarkable 4510 K. However, this work relied on theoretical methods that do not accurately account for the role of bond breaking or complex bonding configurations in the melting process. Furthermore, experiments to verify these high melting points have been challenging. Practical applications of graphene and carbon nanotubes at high temperatures will require a detailed understanding of the behavior of these materials under these conditions. Therefore, we have used exclusively reliable ab initio molecular dynamics calculations to study the initial stages of melting of freestanding graphene monolayers between 4000 and 6000 K. To accommodate large defects, and for improved accuracy, we used a large 10 x 10 periodic unit cell. We find that the system can be heated up to 4500 K for 18 ps without melting, and 3-rings and short lived broken bonds (10-rings) are observed. At 4500 K, the system appears to be in a quasi-2D liquid state. At 5000 K, the system is starting to melt. During the 20 ps simulation, diffusion events are observed, leading to the creation of a 5775 defect. We calculate accurate excitation energies for these configurations, and the pair correlation function is presented. The modified Lindemann criterion was calculated. Graphene and nanotubes together with other proposed high melting point materials would be interesting candidates for experimental tests of melting in the weightless environment of space.

Repeated photoporation with graphene quantum dots enables homogeneous labeling of live cells with extrinsic markers for fluorescence microscopy

“…It is indeed known that laser-induced heating can cause AuNPs to melt (1063 ℃ melting point) and/or fragment 18 , 19 . The exact reason why this phenomenon does not occur for GQDs is not known, but it may be linked to their much higher melting temperature of ~4000–6000 ℃ 20 . In comparison, TEM images showed that the size of the GQDs is more gradually reduced upon subsequent laser pulses (Figure S4 ), most likely due to removal of CO 2 /CO 2 H groups.…”

Graphene thermal break-down induced by anharmonic bending mode

“…It is significant, however, that the very form of Hamiltonian (11) indicates the crucial role of multiphonon processes in the occurrence of conditions for the transition of graphene into a phase with abnormally large fluctuations of the bending component of the strain tensor. Since the formation of defects (in the case of graphene, this may be the already mentioned Stone-Wales defects [9,10]) is due to precisely multi-phonon processes, the theory proposed in this paper is naturally linked with ideas about the melting of a crystal as the result of its "softening" due to the thermal creation of defects [3,6,8].…”

“…Really, besides the value W S− E ≈ 4.6 eV [9,10] indicated in the Introduction, in the literature one can find calculated values from 4.8 eV and 5.2 eV [37] to 5.8 eV [38] and even 6.0 eV [39]. It should be borne in mind that the estimation of ∞ T should rather be associated not with W S− E , but with the height of the barrier, which separates the ground state of graphene and the state in the presence of the Stone-Wales defect.…”

Ultrathin 2D metal–organic framework nanosheets prepared via sonication exfoliation of membranes from interfacial growth and exhibition of enhanced catalytic activity by their gold nanocomposites

“…AlB 6 , Cu 2 Si) [12][13][14][15][16][17] have enriched the "family" of 2D nanomaterials. 18,19 These layered nanomaterials exhibit many unique properties compared with zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, three-dimensional (3D) networks, and their bulk counterparts, 18,[20][21][22] which have attracted considerable efforts for exploration of other 2D nanomaterials. Recently, 2D metal-organic framework (MOF) nanosheets, a new class of crystalline porous materials constructed by linking metal nodes (e.g., metal ions, clusters) with organic ligands (e.g., carboxylate ligands, other negatively charged ligands), 23 have attracted increasing research interest.…”