908 research outputs found
Kinetically-controlled thin-film growth of layered - and NaCoO cobaltate
We report growth characteristics of epitaxial -NaCoO and
-NaCoO thin films on (001) sapphire substrates grown by
pulsed-laser deposition. Reduction of deposition rate could change structure of
NaCoO thin film from -phase with island growth mode to
-phase with layer-by-layer growth mode. The
-NaCoO thin film exhibits spiral surface growth with
multiterraced islands and highly crystallized texture compared to that of the
-NaCoO thin film. This heterogeneous epitaxial film growth
can give opportunity of strain effect of physical properties and growth
dynamics of NaCoO as well as subtle nature of structural change.Comment: accepted for publication in Applied Physics Letter
Graphyne: Hexagonal network of carbon with versatile Dirac cones
We study alpha, beta, and gamma graphyne, a class of graphene allotropes with
carbon triple bonds, using a first-principles density-functional method and
tight-binding calculation. We find that graphyne has versatile Dirac cones and
it is due to remarkable roles of the carbon triple bonds in electronic and
atomic structures. The carbon triple bonds modulate effective hopping matrix
elements and reverse their signs, resulting in Dirac cones with reversed
chirality in alpha graphyne, momentum shift of the Dirac point in beta
graphyne, and switch of the energy gap in gamma graphyne. Furthermore, the
triple bonds provide chemisorption sites of adatoms which can break sublattice
symmetry while preserving planar sp2-bonding networks. These features of
graphyne open new possibilities for electronic applications of carbon-based
two-dimensional materials and derived nanostructures.Comment: 5 pages, 5 figures, 1 tabl
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