22 research outputs found
First-Principles Study of Chemisorption of Oxygen and Aziridine on Graphitic Nanostructures
Using ab initio plane wave pseudopotential calculations, we study the energetics and structure of adsorbed linear arrays of oxygen and aziridine on carbon nanotubes, graphitic ribbons, and graphene sheets. Chemisorption of arrays of O or NH causes splitting of the CC bond and local deformation of the graphitic structures. The (3,3) nanotube cross section assumes a teardrop-like shape, while graphene sheets warp into a new local geometry around the chemisorbed molecules. The interior of a (3,3) nanotube is less prone to oxidation than the exterior because of steric effects. A zigzag (6,0) nanotube is less reactive and thus chemically more stable than an armchair (3,3) nanotube. The results suggest a partial explanation for the experimentally observed selective etching of metallic carbon nanotubes
GasâSurface Chemical Reactions at High Collision Energies?
Most gasâsurface chemical reactions occur via reaction of adsorbed species to form a thermal-energy (kT) product; however, some instances exist where an energetic projectile directly reacts with an adsorbate in a single-collision event to form a hyperthermal product (with a kinetic energy of a few eV). Here we show for the first time that 30â300 eV F^+ bombardment of fluorinated Ag and Si surfaces produces âultrafastâ F_2^â products with exit energies of up to 90 eV via a multistep direct-reaction mechanism. Experiments conclusively show that the projectile F atom ends up in the fast molecular product despite the fact that the impact energy is far greater than typical bond energies
Dirac Cones and Nodal Line in Borophene
Two-dimensional single-layer
boron (borophene) has emerged as a
new material with several intriguing properties. Recently, the β<sub>12</sub> polymorph of borophene was grown on Ag(111), and observed
to host Dirac fermions. Similar to graphene, β<sub>12</sub> borophene
can be described as atom-vacancy pseudoalloy on a closed-packed triangular
lattice; however, unlike graphene, the origin of its Dirac fermionsÂ
is yet unclear. Here, using first-principles calculations, we probe
the origin of Dirac fermions in freestanding and Ag(111)-supported
β<sub>12</sub> borophene. The freestanding β<sub>12</sub> sheet hosts two Dirac cones and a topologically nontrivial Dirac
nodal line with interesting Dirac-like edge states. On Ag(111), the
Dirac cones develop a gap, whereas the topologically protected nodal
line remains intact, and its position in the Brillouin zone matches
that of the Dirac-like electronic states seen in the experiment. The
presence of nontrivial topological states near the Fermi level in
borophene makes its electronic properties important for both fundamental
and applied research
Can Two-Dimensional Boron Superconduct?
Two-dimensional
boron is expected to exhibit various structural polymorphs, all being
metallic. Additionally, its small atomic mass suggests strong electronâphonon
coupling, which in turn can enable superconducting behavior. Here
we perform first-principles analysis of electronic structure, phonon
spectra, and electronâphonon coupling of selected 2D boron
polymorphs and show that the most stable structures predicted to feasibly
form on a metal substrate should also exhibit intrinsic phonon-mediated
superconductivity, with estimated critical temperature in the range
of <i>T</i><sub>c</sub> â 10â20 K