High conducting nanowires obtained from uniform titanium covered carbon nanotubes

We have shown that Ti atoms can form continuous coating of carbon nanotubes at different amount of coverage. The circular cross section changes to a square-like form, and the semiconducting tube becomes ferromagnetic metal with high quantum ballistic conductance. Metallicity is induced not only by the metal-metal coupling, but also by the band gap closing of SWNT at the corners of the square. The magnetic properties of Ti coated tubes depend strongly on the geometry, amount of Ti coverage and also on the elastic deformation of the tube. While the magnetic moment can be pronounced significantly by the positive axial strain, it can decrease dramatically upon the adsorption of additional Ti atoms to those already covering the nanotube. Besides, electronic structure and spin-polarization near the Fermi level can also be modified by radial strain. Our results have been obtained by the first-principles, spin-relaxed pseudopotential plane wave calculations within the density functional theory. © TÜBİTAK

Magic gold nanotubes

In recent ultra-high-vacuum transmission-electron-microscopy experiments evidence is found for the formation of suspended gold single-wall nanotubes (SWNTs) composed of five helical strands. Similar to carbon nanotubes, the (n,m) notation defines the structure of the gold SWNTs. Experimentally, only the (5,3) tube has been observed to form among several other possible alternatives. Using first-principles calculations we demonstrate that gold atoms can form both freestanding and tip-suspended, chiral, single-wall nanotubes. Although freestanding, infinite (5,5) tube is found to be energetically the most favorable, the experimentally observed (5,3) tube, suspended between two tips, corresponds to a local minimum in the variation of string-tension with the radius of the structure, which explains the experimental finding. Similarly, we predict the (4,3) tube as a favorable structure yet to be observed experimentally. Analysis of band structure, charge density, and quantum ballistic conductance suggests that the current on these nanowires is less chiral than expected, and there is no direct correlation between the numbers of conduction channels and helical strands. © TÜBİTAK