Morphology engineering of hollow carbon nanotube pillars by oxygen plasma treatment

Oxygen plasma treatment is introduced herein as a novel post-growth fabrication technique to engineer the macroscopic morphology of hollow carbon nanotube (CNT) pillars. Current fabrication techniques for patterned vertically-aligned CNTs only allow for the production of extruded structures with constant cross-sectional area. Oxygen plasma treatment is utilized to rectify this limitation by introducing variation to the cross-sectional area. The results presented herein demonstrate that a conical geometry can be successfully introduced by oxygen plasma treatment to a hollow cylindrical CNT pillar. Using oxygen plasma treatment, the blunt tip of a cylindrical CNT pillar can be controllably sharpened until it reaches a size reduction of more than 93%. A geometric model is presented herein to predict the morphology transformation of a hollow cylindrical CNT pillar during the oxygen plasma treatment. Three distinct phases of CNT structural and morphological evolution induced by oxygen plasma treatment are also identified. A mild CNT functionalization by oxygen adsorbates occurs in the first phase. The second phase is indicated by drastic changes in the macroscopic morphology of CNT pillars. Structural amorphization and collapse of the base of the CNT pillars take place in the final phase.