(220g) Thermal Conductivity of Interlayer-Bonded Bilayer Graphene

Graphene-based metamaterials and derivatives are well-known for their tunable thermomechanical properties through structural modification facilitated by chemical functionalization and defect engineering of graphene. Inserting sp³-hybridized interlayer C-C bonds in bilayer or few-layer graphene is a type of structural modification that has been pursued successfully for the tunability of thermal and mechanical properties of multi-layered graphene sheets. Examples of such structurally modified few-layer graphene configurations include, but are not limited to, interlayer-bonded twisted bilayer graphene (IB-TBG), interlayer-bonded graphene bilayers with randomly distributed individual interlayer bonds (RD-IBGs), and two-dimensional (2D) diamond or diamane consisting of fully interlayer-bonded graphene bilayers. 2D diamond superstructures in IB-TBG with the periodicity of the Moiré superlattice pattern of twisted bilayer graphene (TBG) are generated from TBG through insertion of interlayer C-C bonds as a result of patterned hydrogenation of each graphene layer [1,2]. If the chemical functionalization of the graphene layers is not patterned, interlayer C–C bonding does not occur in a periodic arrangement and, instead of 2D diamond superstructures, RD-IBGs are formed. In general, such interlayer-bonded bilayer graphene sheets are expected to be uniquely promising materials, which combine the exceptional properties of graphene and diamond.

To this end, here, we report results from a systematic analysis of thermal transport in interlayer-bonded bilayer graphene sheets based on molecular-dynamics (MD) simulations. We find that the introduction of interlayer C-C bonds in IB-TBG 2D diamond superstructures causes an abrupt drop in the thermal conductivity of pristine, non-interlayer-bonded bilayer graphene, while further increase in the interlayer C-C bond density (2D diamond fraction) leads to a monotonic increase in the thermal conductivity of the resulting superstructures with increasing 2D diamond fraction toward the high thermal conductivity of 2D diamond (diamane) [3]. We also find that a similar trend is exhibited in the thermal conductivity of RD-IBGs as a function of interlayer C-C bond density, but with the thermal conductivity of the IB-TBG 2D diamond superstructures consistently exceeding that of RD-IBGs at a given interlayer bond density [3]. We analyze the MD simulation results employing effective medium and percolation theories and explain the predicted thermal conductivity dependence on interlayer bond density on the basis of lattice distortions induced in the bilayer structures as a result of interlayer bonding [3]. Our findings demonstrate that the thermal conductivity of IB-TBG 2D diamond superstructures and RD-IBGs can be precisely tuned by controlling interlayer C-C bond density and have important implications for the thermal management applications of interlayer-bonded few-layer graphene derivatives, including their use as heat sinks in nanoelectronic devices.

[1] A. S. Machado, D. Maroudas, and A. R. Muniz, Appl. Phys. Lett. 103, 013113 (2013).

[2] M. Chen, A. R. Muniz, and D. Maroudas, ACS Appl. Mater. Interfaces 10, 28898–28908 (2018).

[3] A. Mostafa, A. Ramasubramaniam, and D. Maroudas, Appl. Phys. Lett. 122, 133101 (2023).