Anisotropic Electron Transport in Highly Aligned Carbon Nanotube Films

Carbon nanotubes (CNTs) present significant potential for advances in numerous scientific areas and have diverse applications from electronics to medicine. However, realizing this potential has been stymied by challenges in transitioning from isolated nanotube studies to macroscopic CNT networks. The complexities in ensemble-scale CNT properties include defects, accidental dopants, physical deformations, and inter-tube junctions. In this study, we delved into the intricacies of inter- and intra-nanotube electron transport by applying current perpendicular and parallel to the CNT alignment direction in macroscopically aligned CNT films. Temperature-conductivity measurements showcased highly anisotropic behaviors based on the current direction with respect to the CNT alignment direction. For current parallel to the CNT alignment, from room temperature to a sample-specific temperature of about 100 K, conductivity exhibited metallic behavior due to phonon backscattering. Afterward, a decrease in conductivity was observed with further temperature reductions, possibly caused by weak localization. Conversely, when the current was perpendicular to the alignment direction, variable-range hopping conduction manifested from room temperature to 2 K. These observations elucidate the microscopic anisotropic electron transport mechanisms in aligned CNT films. Through a deeper understanding of inter- and intra-tube electron transport, we aim to propel the optimization and application of macroscopic CNT materials for future technological advancements.