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 5nm align to the substrate, suggesting the interaction between CNTs and the quartz lattice is more robust than previously reported.
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