Structural evaluation along the nanotube length for super-long vertically aligned double-walled carbon nanotube arrays

By performing Raman spectroscopic and electrochemical measurements along the nanotube length, we have demonstrated that there is a concentration gradient of structural defects along the tube length for super-long (ca. 5 mm) vertically aligned double-walled carbon nanotubes (SLVA-DWNTs) produced by water-assisted CVD growth. An increase in the structural defect content along the nanotube length from the top to bottom end was observed in the present study due to the bottom growth process and the decay of the catalyst reactivity with the growth time. The newly observed defect content gradient facilitated us to tune the nanotube electrochemistry along its length and to deposit metal particles in a length-specific fashion.