Significant reduction in thermal conductivity of carbon nanotubes by amorphous gate oxides

Carbon nanotubes (CNTs) possess extremely high intrinsic thermal conductivity, which is generally considered to suppress current saturation caused by self-heating. However, in practical applications, CNTs are often covered by amorphous gate oxides, and their influence on thermal conductivity has not been studied. To fill this gap, we systematically study the effect of the nanogap between CNTs and amorphous oxides (SiO₂, Al₂O₃, and HfO₂) on their thermal conductivity using molecular dynamics simulations. The results show that when the nanogap is minimized, all three amorphous oxides significantly reduce the thermal conductivity of CNTs, with Al₂O₃ having the strongest effect, reducing thermal conductivity by nearly five times. Harmonic phonon analysis reveals that this material dependence originates from interfacial phonon mode coupling. Based on vibrational density of states analysis, it was found that amorphous Al₂O₃ overlaps most with CNTs at low frequencies (0-30 THz), leading to strong interfacial phonon mode coupling. Besides, spectral energy density analysis further reveals that interfacial interaction enhances anharmonic phonon scattering and significantly shortens phonon lifetime, which is the main mechanism underlying the reduction in thermal conductivity. As the nanogap increases, the interface phonon coupling gradually weakens and the thermal conductivity of CNTs recovers and approaches its intrinsic value at approximately 12.5 Å. This study not only clarifies the crucial role of the nanogap in thermal transport in the CNT/oxide systems but also provides a theoretical basis for the thermal management design of high-performance CNT-based electronic devices.