Early stages of Ti-O cluster growth on carbon nanotubes by ab initio calculations

Ti-O combined with carbon nanotubes are excelled candidates for many technological applications. The early stages of growth comprise octahedral (Oh) anatase or rutile nanoparticles depending on the tetrahedral (Th) precursors. However, the underline mechanisms are still unknown. Here, we present results of a systematic study of Th or Oh clusters on (4,0) and (8,0). We found that although the Th may exist in several conformations, with well localized electronic states, the Oh is unstable. We found that due to charge localization and the emergence of C dangling bonds at the Fermi level, Th could be considered as more active compared to Oh that adopts the tube's C(2p)-C(2p) π-like features. In addition, when parallel to the tubes and along the zigzag chiral direction, the linear rutile-like trimers on zigzag (8,0), armchair (5,5), and (3,0)@(12,0) multiwall were clearly found to be energetically favored, while when vertically aligned, equi-probable rutile or spinal anatase-like growth is expected. At the Fermi level, the charge is localized at the Ti-O trimer, when on (5,5) and (3,0)@(12,0) cases, rendering Ti-O active. These results could enlighten the early stages of Ti-O growth on SWCNT providing useful information in the field of nanoelectronics and nanotechnology.