15 research outputs found
Graphene allotropes: stability, structural and electronic properties from DF-TB calculations
Using the density-functional-based tight-binding method we performed a
systematic comparative study of stability, structural and electronic properties
for 12 various types of graphene allotropes, which are likely candidates for
engineering of novel graphene-like materials.Comment: 12 pages, 4 figure
Fluorographynes: Stability, Structural and Electronic Properties
The presence in the graphyne sheets of a variable amount of sp2/sp1 atoms,
which can be transformed into sp3-like atoms by covalent binding with one or
two fluorine atoms, respectively, allows one to assume the formation of
fulorinated graphynes (fluorographynes) with variable F/C stoichiometry. Here,
employing DFT band structure calculations, we examine a series of
fluorographynes, and the trends in their stability, structural and electronic
properties have been discussed as depending on their stoichiometry: from C2F3
(F/C= 1.5) to C4F7 (F/C= 1.75).Comment: 13 pages, 3 table
Electronic Properties of TiO Nanotubes
quasi-one-dimensional (1D) titania nanostructures - single-walled nanotubes
formed by rolling [101] planes of TiO (anatase phase) are modeled and their
electronic properties and bond orders indices are studied using the
tight-binding band theory. We show that all zigzag (n,0)- and armchair
(n,n)-like nanotubes are uniformly semiconducting, and the band gap trends to
vanish as the tube diameters decrease. It was established that the zigzag (n,0)
nanotubes configurations are more likely to form when the diameters are larger
1 nm. The Ti-O covalent bonds were found to be the strongest interactions in
TiO tubes, whereas Ti-Ti bonds proved to be much weaker.Comment: 7 pages, 4 figure
Transport properties of MoS
We report about results from density functional based calculations on structural,
electronic and transport properties of one-dimensional MoS2 nanoribbons with
different widths and passivation of their edges. The edge passivation influences the
electronic and transport properties of the nanoribbons. This holds especially for
nanoribbons with zigzag edges. Nearly independent from the passivation the armchair
MoS2 nanoribbons are semiconductors and their band gaps exhibit an almost
constant value of 0.42Â eV. Our results illustrate clearly the edge priority
on the electronic properties of MoS2 nanoribbons and indicate problems
for doping of MoS2 nanoribbons
Structure and stability of molybdenum sulfide fullerenes
MoS2 nanooctahedra are believed to be the smallest stable closed-cage structures of MoS2, i.e., the genuine inorganic fullerenes. Here a combination of experiments and density functional tight binding calculations with molecular dynamics annealing are used to elucidate the structures and electronic properties of octahedral MoS2 fullerenes. Through the use of these calculations MoS2 octahedra were found to be stable beyond nMO > 100 but with the loss of 12 sulfur atoms in the six corners. In contrast to bulk and nanotubular MoS2, which are semiconductors, the Fermi level of the nanooctahedra is situated within the band, thus making them metallic-like. A model is used for extending the calculations to much larger sizes. These model calculations show that, in agreement with experiment, the multiwall nanooctahedra are stable over a limited size range of 104-105 atoms, whereupon they are converted into multiwall MoS2 nanoparticles with a quasi-spherical shape. On the experimental side, targets of MoS2 and MoSe2 were laser-ablated and analyzed mostly through transmission electron microscopy. This analysis shows that, in qualitative agreement with the theoretical analysis, multilayer nanooctahedra of MoS2 with 1000-25 000 atoms (Mo + S) are stable. Furthermore, this and previous work show that beyond ???105 atoms fullerene-like structures with quasi-spherical forms and 30-100 layers become stable. Laser-ablated WS2 samples yielded much less faceted and sometimes spherically symmetric nanocages.close332