Charge induced frustration in C60 monolayers on h-BN/Ni(111)

Abstract

Frustration in a system occurs when all interacting components cannot reach their minimum energy simultaneously. We report on the development of a frustrated adsorption configuration of a C60 monolayer on epitaxial hexagonal boron nitride (h-BN) grown on Ni(111). In the low-temperature adsorption configuration, we discover non-periodic patterns with striped and zigzag elements, which are characteristic of frustrated systems, formed by molceules with different orientational alignement. Using scanning probe techniques, we investigate these complex patterns' structural and electronic properties. We find two distinct C60 species, one of which is neutral, and the other is charged due to a locally preferred energy level alignment that favors an electron transfer from the Ni(111). Discharging single or multiple intrinsically charged C60 molecules creates local changes in the electrostatic potential, shifting the energy of surrounding molecular orbitals. This allows us to measure the inter-fullerene Coulomb interactions, which plays a crucial role in the formation of the frustrated structure. Monte Carlo simulations derived from the antiferromagnetic Ising model replicate the experimentally observed frustration pattern by considering competing attractive and repulsive intermolecular interactions. As such, the C60 h-BN/Ni(111) system opens a window for essential insights into charge-induced frustration and intermolecular interactions.