Epitaxial deposition of silver ultra-fine nano-clusters on defect-free surfaces of HOPG-derived few-layer graphene in a UHV multi-chamber by in situ STM, ex situ XPS, and ab initio calculations.

The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging.

Molecular dynamics simulation studies of structural and mechanical properties of single-walled carbon nanotubes.

Structural and mechanical properties of armchair, zig-zag and chiral single-walled carbon nanotubes are computed by employing Molecular Dynamics simulation technique using Discover code with Compass force field via Materials Studio program developed by the Accelrys. Consistent with the literature, we find that the armchair SWCNT is energetically favored over zig-zag and chiral nanotubes. Predicted structural parameters agree well with experimental observations. Observed radial distribution functions show that the single-walled carbon nanotubes remain crystalline after exposing them to 300 K. The predicted Young's and the Shear moduli were in reasonable agreement with other reports. Our predictions show that the Young's modulus of the tubes increases as the diameter of the tube decreases.

DFT studies of low concentration substitutional doping of transition-metals on single-walled carbon nanotube surface.

Using first principles-density functional theory, a theoretical study of the electronic properties of (5, 5) armchair single-walled carbon nanotube doped with transitions metals (Fe, Co and Ni) is presented. The generalized gradient approximation was used for the exchange-correlation potentials. The energy cut-off of 500 eV was adopted in the study. The main features of electronic band structure and density of states are shown. A systematic comparison of the density of states as well as band structures of pure and doped SWCNT is made. The contribution of the different bands was analyzed from the total and partial density of states curves. These metals are used as catalysts during synthesis of single-walled carbon nanotubes and hence, the choice we have made. Where data is available, the results are compared with previous calculations and with experimental measurements.

Effect of oxygen doping on electrical properties of small radius (2,1) single-walled carbon nanotubes.

We investigated the electrical conductivity of the small radius oxygen-doped (2,1) single-walled carbon nanotubes (SWCNTs) using first-principles density functional theory (DFT). We found that introduction of oxygen does not significantly change the global structure of the SWCNT, and thus the bonding mode of the structure is not remarkably altered. The results show that doping enhances the conductivity of the SWCNT. Oxygen doping increases density of states at the Fermi level, thus the conductivity of the doped SWCNT increases when oxygen is introduced, consistent with experimental observations. These observations were further clarified by comparing band structures of pristine and doped nanotubes.