Folds naturally appear on nanometrically thin materials, also called “2D materials”, after exfoliation, eventually creating folded edges across the resulting flakes. We investigate the adhesion and flexural properties of single-layered and multilayered 2D materials upon folding in the present work. This is accomplished by measuring and modeling mechanical properties of folded edges, which allows for the experimental determination of the bending stiffness (κ) of multilayered 2D materials as a function of the number of layers (n). In the case of talc, we obtain κ ∝ n 3 for n ≥ 5, indicating no interlayer sliding upon folding, at least in this thickness range. In contrast, tip-enhanced Raman spectroscopy measurements on edges in folded graphene flakes, 14 layers thick, show no significant strain. This indicates that layers in graphene flakes, up to 5 nm thick, can still slip to relieve stress, showing the richness of the effect in 2D systems. The obtained interlayer adhesion energy for graphene (0.25 N/m) and talc (0.62 N/m) is in good agreement with recent experimental results and theoretical predictions. The obtained value for the adhesion energy of graphene on a silicon substrate is also in agreement with previous results.

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We propose, based on results of first-principles calculations, that nanoporous graphene and h-BN might be efficiently produced from B−C−N layers as precursors. In our calculations, we find that the removal of the h-BN islands that naturally occur in BN-doped graphene, forming nanoporous graphene, requires less energy than if pristine graphene is used as a precursor. The same reduction ΔE f in pore formation energy is found for nanoporous h-BN obtained from graphenedoped BN as a precursor. ΔE f is found to increase linearly as a function of the number of B−C and N−C bonds at the island boundary, with the slope being nearly the same for either porous graphene or porous h-BN. This is explained by an analytical bond-energy model. In the case of porous graphene, we find that the pore formation energy would be further reduced by passivation by pyridinic and quaternary remnant nitrogen atoms at the pore edges, a mechanism that is found to be more effective than the passivation by hydrogen atoms. Both mechanisms for pore formation energy reduction should lead to a possibly efficient method for nanoporous graphene production.

Folds naturally appear on nanometrically thin (also called 2D) materials after exfoliation, eventually creating folded edges across the resulting flakes. In the present work, we investigate the adhesion and flexural properties of single and multilayered 2D materials upon folding. This is accomplished by measuring and modeling mechanical properties of folded edges, which allow the experimental determination of the scaling for the bending stiffness (κ) of a multilayered 2D material with its number of layers (n). In the case of talc, we obtain κ proportional to n3 for n ≥ 5, establishing that there is no interlayer sliding upon folding, at least in this thickness range. Such a result, if applicable to other materials, would imply that layers in folds might be either compressed (at the inner part of the fold) or stretched (at its outer part), leading to changes in their vibrational properties relative to a flat flake. This hypothesis was confirmed by near-field tip-enhanced Raman spectroscopy of a multilayer graphene fold.