Variable-force Microscopy for Advanced Characterization of Horizontally Aligned Carbon Nanotubes

Atomic force microscopy (AFM) performed with variable-force imaging was recently demonstrated to be an accurate method of determining the diameter and number of sidewalls of a carbon nanotube (CNT). This AFM technique provides an alternative to transmission electron microscopy (TEM) when TEM imaging is not possible due to substrate thickness. We have used variable-force AFM to characterize horizontally aligned CNTs grown on ST-cut quartz. Our measurements reveal new aspects of horizontally aligned growth that are essential for enhancing the performance of CNT-based devices as well as understanding the growth mechanism. First, previously reported optimal growth conditions produce a large spread in CNT diameters and a significant fraction of double-walled CNTs. Second, monodispersity is significantly improved when growth temperature is reduced. Third, CNTs with diameters up to 5 nm align to the substrate, suggesting the interaction between CNTs and the quartz lattice is more robust than previously reported.