In the world of materials science, two-dimensional fullerene networks have been making waves, and for good reason. These structures, composed of carbon molecules, are catching the eye of researchers due to their unique bonding topologies and impressive mechanical strength. A recent study has taken a deep dive into the elastic and thermal transport properties of two specific phases of these networks: the quasi-hexagonal phase (qHP) and the quasi-tetragonal phase (qTP) C$_{24}$ monolayers.
The researchers, Qing Li, Haikuan Dong, Penghua Ying, and Zheyong Fan, developed a machine-learned potential called NEP-C$_{24}$. This tool is designed to accurately model the behaviors of both the qHP and qTP phases. Using this model, they were able to systematically explore the properties of these materials.
The study revealed that both C$_{24}$ phases exhibit a markedly enhanced stiffness compared to C$_{60}$ monolayers. This is attributed to the combination of reduced molecular size and an increased density of covalent bonds. The qTP C$_{24}$ monolayer, with its four-fold symmetry, shows nearly isotropic elastic properties and thermal conductivities along its two principal axes. On the other hand, the chain-like, misaligned bonding topology of the qHP C$_{24}$ monolayer leads to pronounced in-plane anisotropy.
The team also employed homogeneous nonequilibrium molecular dynamics and spectral decomposition analyses. These methods revealed that low-frequency acoustic phonons, specifically those below 5 THz, dominate heat transport. The directional variations in phonon group velocity and mean free path govern the anisotropic response in qHP C$_{24}$. Real-space heat flow visualizations further highlighted that phonon transport in these fullerene networks is dominated by strong inter-fullerene covalent bonds, rather than weak van der Waals interactions.
This research establishes a direct link between intermolecular bonding topology and phonon-mediated heat transport. It provides valuable guidance for the rational design of fullerene-based two-dimensional materials with tunable mechanical and thermal properties. As we continue to push the boundaries of materials science, studies like this one will be instrumental in shaping the future of technology and innovation.
