Experimental evidence of diffuson-dominated thermal transport in amorphous diamond-like carbon nanowires

Abstract

Amorphous carbon is widely employed as protective and dielectric layers in microelectronics, where its thermal transport properties play a critical role in heat dissipation. Although vibrational excitations in amorphous solids are generally classified into propagons, diffusons, and locons, the dominant heat carriers in amorphous carbon remain actively debated. In this work, we synthesize amorphous diamond-like carbon (DLC) nanowires (mass density: 1.71 g/cm3; sp3 fraction: 55.7%) and measure their thermal conductivity from 20 to 300 K using a suspended thermal bridge method. The measured thermal conductivity is slightly lower than previously reported for DLC films, due to relatively low mass density and sp3 ratio that govern thermal transport in amorphous carbons. Remarkably, the thermal conductivity exhibits a steep, nearly linear temperature dependence, in clear deviation from the predictions of the amorphous limit model. Further molecular dynamics simulations and quasi-harmonic Green–Kubo lattice dynamics calculations reproduce the experimental trend and reveal that heat conduction is overwhelmingly dominated by diffusons (98% at 300 K) in the frequency range of 4–60 THz. The nearly linear temperature dependence arises from the combined effects of the linear scaling of mode-specific heat with temperature and the weak temperature dependence of mode diffusivity. These results provide direct experimental evidence for diffuson-dominated thermal transport in amorphous DLC nanostructures and offer important physical insight for the design of disordered carbon materials with tailored thermal properties for nanoscale electronic applications.