▎ 摘　　要

Due to the atomistic thinness of graphene, it is non-trivial to measure fracture behaviors of freestanding graphene without any underlying materials. In this study, we present a methodology for measuring the fracture behavior of freestanding natural graphene with single crystallinity using an in situ tensile tester under a scanning electron microscope. A pre-crack was introduced in a freestanding graphene specimen using focused ion beam. Crystallographic information, geometric dimensions, and layer numbers of the graphene specimen were characterized before fracture testing using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. Taking the advantages of the in situ fracture test, we measured load-displacement data of single-crystalline bilayer graphene and observed an exciting fracture behavior during the crack extension along its zig-zag direction. Young's modulus and the stress field of the specimen at the moment of fracture were evaluated from the measured data and finite element analysis. The present study provides a direct pathway to fracture mechanics tests of natural graphene under uniaxial tension, and could be an insightful cornerstone for fracture mechanics tests of other two-dimensional materials or atomically thin film. (C) 2016 Elsevier Ltd. All rights reserved.