Titanium monomers and wires adsorbed on carbon nanotubes: a first principles study

In this work a theoretical study of Ti monomers and wires interacting with an (8, 0) semiconductor single-wall carbon nanotube (SWNT), by inside as well as outside faces, is presented. Spin-polarized total-energy ab initio calculations, based on the density functional theory, are used to describe the structural, electronic and magnetic properties of the studied systems. The most stable configurations for monomers are found to be over the centre of a C-C bond for inside and over the midpoint of the centre of the hexagonal site for outside. Considering that the Ti atoms on the tube surface tend to form continuous wires, to allow a comprehensive view of the interaction of the Ti wires with the SWNT surface, we present a complete understanding, both from inside and outside the nanotube. Our calculations have shown that the most stable configuration is with the wire inside the tube, with the resulting electronic structures showing a metallic system with high hybridization between the Ti and C atoms and a large charge transfer from Ti to C atoms. For Ti wire adsorbed inside the tube the low spin configuration is shown to be more stable than high spin configuration and the opposite behaviour is observed for the corresponding outside case. These novel results are relevant for the understanding of Ti atoms covering and filling SWNTs, demonstrating the high stability of these systems and suggesting that they can be useful for future use in nanodevices, in particular for spintronics and nanosensors.