A research team from Institute of Mechanics, Chinese Academy of Sciences demonstrated that outstanding strengths and large plastic-like strain can be achieved in layered 3D monolayer amorphous carbon composites. The research has been published in Nano Letters, a flagship journal in the field of materials science (Xie & Wei, 2021. Roughening for strengthening and toughening in monolayer carbon based composites. Nano Lett. doi: https://doi.org/10.1021/acs.nanolett.1c01462).

　　Three-dimensional aggregation of graphene is dramatically weak and brittle due primarily to the prevailing interlayer van der Waals interaction. In this report, we demonstrate that outstanding strengths and large plastic-like strain can be achieved in layered 3D MAC composites. Starting from the key issues of scale-up, we explore the influence of roughness and flexibility of atomic-layer carbon on the mechanical properties of their stacked 3D composites. Counterintuitively, defect-rich monolayer amorphous carbon sheets, when stacking up layer by layer, can reach extremely high strength on the order of several gigapascal. Opposite to most other stacked hierarchical structures exhibiting abrupt or progressive failure, MAC layered materials show plastic-like deformation after the peak stress, which leads to high work-to-fracture. Such mechanical behavior is also sensitive to the thickness of building blocks that the thinner blocks give rise to higher strength and more gradual failure. It is clear that both surface roughening and out-of-plane flexibility of MAC are the key factors counting for the high strength and gradual failure in 3D MAC. The conclusions seem to be general for other types of atomic scale films, and our results pave a new strategy in enhancing toughness in van der Waals heterostructures to effectively avoid catastrophic failure.

　　This research was supported by the NSFC Basic Science Center for 'Multiscale Problems in Nonlinear Mechanics' (No. 11988102) and (No. 11790291), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB22020200).

　　Figure: Outstanding strengths and plastic-like strain are achieved simultaneously in composites stacking by MACs. Side view of the stacked hexagonal MAC sheets structure and the atomic network of the selected region (left). Mechanical behavior of the stacked structure of different sheet size (right).