Unusual thermal transport behavior in self-assembled fullerene nanorods

Abstract

In this work, fullerene (C₆₀) nanorods were prepared by a surfactant-assisted self-assembly method. Although the orientation of molecular alignment remains unchanged from one end to the other end in these C₆₀ nanorods, they cannot be rigorously treated as single crystals because of the existence of amorphous-like regions formed by a high density of defects such as stacking faults and vacancy clusters. The partially crystalline and partially amorphous structure results in unusual thermal transport behavior in C₆₀ nanorods, which cannot be classified into either typical crystalline-like or typical glass-like behavior. The thermal resistances of the C₆₀ nanorods decrease with increasing temperature and reach a plateau around 100 K, which can be attributed to the combined effect of Einstein localized vibration in C₆₀ molecules, intracluster vibration, and phonon-defect scattering. Accompanied with depositing Pt/C composites at two ends of a C₆₀ nanorod to improve thermal contact between Pt electrodes and the C₆₀ nanorod, tensile strain may be introduced in the C₆₀ nanorod due to contraction, which enhances thermal resistance, especially in the low temperature range. Ultralow thermal conductivity (less than 0.06 W m⁻¹ K⁻¹) is observed for self-assembled C₆₀ nanorods at room temperature, which is significantly lower than the thermal conductivity of bulk C₆₀ single crystals and polycrystalline C₆₀/C₇₀ compacts but on the same order of magnitude as the lower limit of thermal conductivity of amorphous carbon.