Figure 3: Nanomechanical testing of fracture of graphene with a pre-crack.

(a) SEM image showing the in situ tensile testing with a microdevice. Movement of the nanoindenter tip (shown by the block arrow) was converted to pure tension of the specimen on the sample stage by the inclined beams. Inset is the magnified image of the boxed region showing graphene across the gap of the sample stage. (b,c) SEM images showing graphene on the sample stage before and after tensile testing, respectively. The pre-crack (boxed in (b)) was cut by FIB. The scale bar in (b) and its inset is 5 μm and 500 nm, respectively. (d) Selected engineering stress-strain curves of the cracked graphene samples (corresponding to #3 and #5 in Table 1).