Graphene is often in contact with other materials through weak van der Waals (vdW) interactions. Of particular interest is the graphene-polymer interface, which is constantly subjected to dynamic loading in applications, including flexible electronics and multifunctional coatings. Through in situ cyclic loading, we directly observed interfacial fatigue propagation at the graphene-polymer interface, which was revealed to satisfy a modified Paris’ law. Furthermore, cyclic loading through vdW contact was able to cause fatigue fracture of even pristine graphene through a combined in-plane shear and out-of-plane tear mechanism. Shear fracture was found to mainly initiate at the fold junctions induced by cyclic loading and propagate parallel to the loading direction. Fracture mechanics analysis was conducted to explain the kinetics of an exotic self-tearing behavior of graphene during cyclic loading. This work offers mechanistic insights into the dynamic reliability of graphene and graphene-polymer interface, which could facilitate the durable design of graphene-based structures.

The subsurface imaging capabilities of atomic force acoustic microscopy (AFAM) was investigated by imaging graphite flakes suspended over holes in a silicon dioxide substrate.

Photothermal excitation of the cantilever for use in subsurface imaging with atomic force microscopy was compared against traditional piezoelectric excitation. Photothermal excitation alleviates issues commonly found in traditional piezoelectrics such as spurious resonances by producing clean resonance peaks through direct cantilever excitation. A calibration specimen consisting of a 3 × 3 array of holes ranging from 200 to 30 nm etched into silicon and covered by graphite was used to compare these two drive mechanisms. Photothermal excitation exhibited a signal-to-noise ratio as high as four times when compared to piezoelectric excitation, utilizing higher eigenmodes for subsurface imaging. The cleaner and sharper resonance peaks obtained using photothermal excitation revealed all subsurface holes down to 30 nm through 135 nm of graphite. In addition, we demonstrated the ability of using photothermal excitation to detect the contact quality variation and evolution at graphite–polymer interfaces, which is critical in graphene-based nanocomposites, flexible electronics, and functional coatings.