Nanoindentation of thin graphdiyne films: Experiments and molecular dynamics simulation Kailu Xiao a, c , Jiaofu Li b, c , Xianqian Wu a, c, * , Huibiao Liu b, c, ** , Chenguang Huang a, c , Yuliang Li b, c a Key Laboratory of Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China b Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100081, China c School of Engineering Science, University of Chinese Academy of Sciences, Beijing, 100049, China article info Article history: Received 9 July 2018 Received in revised form 30 November 2018 Accepted 9 December 2018 Available online 10 December 2018 abstract Graphdiyne possesses not only high strength but also excellent ductility, making it possible to be used in future high-performance protective structures. In this paper, the mechanical properties of graphdiyne were firstly measured by AFM experiments, and the failure behavior during low velocity perforation was also investigated by molecular dynamics (MD) simulations. Firstly, the elastic modulus was measured to be about 218.5 GPa by AFM experiments, which is about half of its ideal value due to various defects and the layer numbers of the synthesized graphdiyne film. Then, the nanoindentation processes of graph- diyne films were investigated by MD simulations, and the elastic modulus and strength were simulated to be about 489.04 GPa and 33.95 GPa, respectively. The failure behavior of the graphdiyne film was also studied in atomic level. Sequential broken of C^C, C]C and CeC bonds and recombination of the broken bonds were observed to form a unique lathy crack. Furthermore, the effects of loading speed and indenter radius on the mechanical response of graphdiyne were investigated. A revised formula was developed for analyzing the mechanical properties of films in AFM experiments under various loading conditions. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Two-dimensional (2D) materials have attracted great attention due to excellent properties such as high strength and high thermal conductivity after graphene is discovered. It has found various potential applications such as electricity, chemistry, and energy storage [1e5]. Most of 2D materials have remarkable mechanical strengths [6e9] and high electronic performance [10, 11]. Graph- diyne [12, 13], one of the new carbon allotropes, exhibits outstanding properties, which derives from its unique structure consisting of sp 2 and sp hybridized carbon atoms. The presence of acetylene can decrease the binding energy so that the electronic and optical properties can be modulated, which is superior to graphene and carbon nanotubes [14, 15]. Unlike graphene, the structure of graphdiyne has diacetylene (C^CeC^C) linkages between benzene rings, making it more flexible and ductile than graphene. Nevertheless the strength of the graphdiyne will be sure to lower because of lower atom density when compared to graphene. It is well known that the strength and ductility of a material has always been competitive mechanism. However, graphdiyne could balance the competition between its strength and ductility in some extent, indicating its promising application in engineering industries such as impact protective coating for micro-projectiles. There is considerable body of litera- ture that addresses the mechanical behavior of graphdiyne by theoretical analysis and MD simulation. Cranford et al. [16] derived basic scaling laws for the cumulative effects of additional acetylene repeats through a spring-network framework, allowing prediction of mechanical performance of other extended graphdiyne struc- tures. Based on their calculation, the in-plane stiffness of a mono- layer graphdiyne was estimated to be 170.4N/m, and the strength * Corresponding author. Key Laboratory of Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China. ** Corresponding author. Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100081, China. E-mail addresses: wuxianqian@imech.ac.cn (X. Wu), liuhb@iccas.ac.cn (H. Liu). Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon https://doi.org/10.1016/j.carbon.2018.12.029 0008-6223/© 2018 Elsevier Ltd. All rights reserved. Carbon 144 (2019) 72e80