Proton Transport Through Monolayer Graphene: Supposed Quantum Tunnelling and the Singular Regime of One-Atom-Thick Barriers}Supposed Quantum Tunnelling and the Singular Regime of One-Atom-Thick Barriers

Description Reports of proton transport through monolayer graphene are frequently interpreted as evidence of quantum tunnelling through an atomically thin carbon barrier. This work argues that such an interpretation misidentifies the physical regime being tested. At the one-atom thickness limit, only sp²-bonded carbon lattices are structurally stable; sp³-bonded diamond lattices cannot exist without dimensional depth or chemical passivation. As a result, a “one-atom-thick carbon barrier” is necessarily planar, dynamically flexible, and incapable of perfect closure. Proton permeability in monolayer graphene therefore does not probe tunnelling through a rigid or chemically generic carbon barrier, but instead reflects the unavoidable dynamical openness intrinsic to two-dimensional lattices at minimal thickness. This perspective reframes the sharp suppression of proton transport observed in bilayer graphene as a structural closure effect rather than a simple exponential dependence on barrier thickness. By clarifying the dimensional constraints governing atomic-scale barriers, the note resolves apparent inconsistencies in experimental and theoretical interpretations and highlights the singular, non-generic nature of the one-atom-thick regime.