The adhesive interactions between graphene and substrates by blister tests
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A blister test and associated analysis was developed to characterize the interfacial adhesion between graphene and copper and silicon substrates to which it has been transferred. Chemical vapor deposition grown graphene had been transferred to a highly polished copper or silicon substrate from its seed foil. The graphene/photoresist or graphene/PDMS/photoresist composite film was pressurized with deionized water through a hole in the substrate and the deflection of the membrane was measured by a full field interference method. Different mixed-mode conditions were achieved by varying the thickness of the backing layers. The measured adhesion energy for the graphene/copper and graphene/silicon interfaces showed a strong dependence on the mode-mix. The deflection profiles were modeled by plate, membrane theory and finite element analysis. The variation of energy release rate with blister radius and thickness for graphene/copper and graphene/silicon interfaces were obtained. The traction-separation relations of the graphene/copper interface were determined in the modified blister tests. The blister profiles and normal crack opening displacements were measured by two synchronized camera. Cohesive zone models associated with traction-separation relations were developed to study the damage initiation and crack propagation under various mixed-mode conditions. It was determined that the maximum normal and shear strength, which governed damage initiation, was independent of the mode-mix. The softening parameter, which governed damage evolution, was also independent of the mode mix. The numerical solution for and experimental measurements of the pressure vs. blister radius and deflection, as well as NCOD were in good agreement. A model for the variation of traction-separation relations with mode-mix was developed based on an asperity shielding model. The delamination paths of the graphene/photoresist, and graphene/PDMS/photoresist samples and the quality of graphene after the blister test were confirmed by Raman spectroscopy. The use of pressure could provide a path to large-scale graphene transfer.