Anharmonic suppression of ultra-narrow graphene nanoribbons confined in carbon nanotubes through host–guest interactions

One-dimensional (1D) graphene nanoribbons (GNRs) hold significant promise for graphene-based nanodevices, but their reduced dimensionality leads to enhanced anharmonicity, which strongly impacts their physical properties, such as thermal conductivity. In this work, we demonstrate that the anharmonicity of GNRs can be effectively suppressed when confined within single-walled carbon nanotubes (SWNTs). Using temperature-dependent Raman spectroscopy, we observe a reduced temperature coefficient for the G mode in 7-atom-wide armchair GNRs (7AGNRs) encapsulated within SWNTs, compared to freestanding 7AGNRs, indicating a weakened anharmonic effect, which leads to a remarkable enhancement of over 50% in the thermal conductivity of the confined 7AGNRs. First-principles calculations of charge differential density reveal that host–guest interactions in this 1D vdW heterostructure strengthen the covalent bonds of GNRs through in-plane charge transfer from GNR atoms to their bands, induced by the built-in field of the SWNT. This enhanced bonding suppresses anharmonic effects in the confined GNRs, as further confirmed by the behavior of the CH in-plane bending mode (CH-ipb) and D mode in Raman spectra. Our findings establish a direct structure–thermal property relationship in 1D van der Waals heterostructures, demonstrating that nanoconfinement engineering can overcome the inherent anharmonic limitations of low-dimensional nanomaterials.