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Molecular adsorption and mobility on two-dimensional materials provide sensitive probes of nanoscale energy dissipation and adsorbate–substrate interactions. In particular, comparing structurally similar but electronically distinct systems such as graphene and hexagonal boron nitride (h-BN) offers a route to understanding how surface polarity, electronic structure, and substrate coupling govern molecular motion [1,2]. Using helium spin-echo (HeSE) spectroscopy, we investigate the nanoscale dynamics of weakly interacting molecules on graphene/Ni(111) and h-BN/Ni(111), where the fast molecular motion is often inaccessible to real-space methods [3]. For benzene, we find thermally activated jump diffusion on both substrates, but with clear differences of the microscopic mechanism: on h-BN/Ni, the motion includes additional confined dynamics such as in-plane rotations and significant contributions from longer-range jumps, whereas on graphene/Ni diffusion is dominated by nearest-neighbour hopping and is more strongly influenced by inter-adsorbate repulsion. Correspondingly, the activation barrier is lower on h-BN, with ≈ 30 meV, and approximately 1.5 times higher on graphene. Water likewise exhibits distinct mobility on the two surfaces, with lower activation energies and stronger rotational–translational coupling on h-BN/Ni(111) than on graphene/Ni(111), revealing a substantially different dynamical regime despite the close structural similarity of the substrates [4].
[1] Unravelling the Epitaxial Growth Mechanism of Hexagonal and Nanoporous Boron Nitride: A First-Principles Microkinetic Model, small 21, 2405404 (2025).
[2] How does intercalation affect the structure and dynamics of bilayer graphene? Carbon 238, 120156 (2025).
[3] Nanoscale Motion of Organic π-Conjugated Molecules: Exploring van der Waals Forces, Friction, and Quantum Effects. Nanoscale Horiz. 10, 3158 (2025).
[4] Understanding water behaviour on 2D material interfaces through single-molecule motion on h-BN and graphene Nat. commun. 16, 10465 (2025).