Thermal Diffusivity of a Single Carbon Nanocoil: Uncovering the Correlation with Temperature and Domain Size

The helical geometries and polycrystalline-amorphous structure of carbon nanocoils (CNCs), an exotic class of low-dimensional carbon nanostructures, distinguish them from carbon nanotubes and graphene. These distinct structures result in very different energy transport from that in carbon nanotubes and graphene, leading to important roles in applications as wave absorbers, near-infrared sensors, and nanoelectromechanical sensors. Here we report a systematic study of the thermal diffusivity (alpha) and conductivity (kappa) of CNCs from 290 to 10 K and uncover their property structure aspects. Our room-temperature alpha study reveals a correlation between alpha and the line diameter (d): alpha = (5.43 X 10(4) X e(-d/37.7) + 9.5) X 10(-7) m(2)/s. Combined with the Raman-based grain size (L-a) characterization, alpha and L-a are correlated as alpha = [81.2 X (L-a - 3.32)(1.5) + 9.5] X 10(-7) m(2)/s. With temperature decreasing from 290 K to 10 K, alpha has a 1-1.6-fold increase, and kappa shows a peak around 75 K. To best understand the defect level and polycrystalline amorphous structure of CNCs, the thermal reffusivity (Theta = alpha(-1)) of CNCs is studied and compared with that of graphite and graphene foam from 290 K down to 10 K. Very interestingly, CNC's Theta linearly decreases with decreased temperature, while Theta of graphite and graphene foam have an exponential decrease. The extrapolated 0 K-limit Theta is determined by low-momentum phonon scattering and gives a structure domain size of CNC samples (d = 455, 353, and 334 nm) of 1.28, 2.03 and 3.24 nm. These sizes are coherent with the X-ray diffraction results (3.5 nm) and the Raman spectroscopy study and confirm the correlation among d, L-a, and alpha.