2,077 research outputs found
Novel Two-dimensional Carbon Allotrope with Strong Electronic Anisotropy
Two novel two-dimensional carbon allotropes comprised of octagons and
pentagons are proposed based on the first-principles calculations. The two
carbon allotropes, named OPG-L and OPG-Z, are found to have distinct
properties. OPG-L is metallic, while OPG-Z is a gapless semimetal. Remarkably,
OPG-Z exhibits pronounced electronic anisotropy with highly anisotropic Dirac
points at the Fermi level. A tight-binding model is suggested to describe the
low-energy quasiparticles, which clarifies the origin of the anisotropic Dirac
points. Such an anisotropic electronic characteristic of OPG-Z is expected to
have wide implications in nano-electronics.Comment: 6 pages, 5 figures (accepted by Physical Review B
Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials - A general bond polarizability model
2D layered materials have recently attracted tremendous interest due to their
fascinating properties and potential applications. The interlayer interactions
are much weaker than the intralayer bonds, allowing the as-synthesized
materials to exhibit different stacking sequences (e.g. ABAB, ABCABC), leading
to different physical properties. Here, we show that regardless of the space
group of the 2D material, the Raman frequencies of the interlayer shear modes
observed under the typical configuration blue shift for AB stacked materials,
and red shift for ABC stacked materials, as the number of layers increases. Our
predictions are made using an intuitive bond polarizability model which shows
that stacking sequence plays a key role in determining which interlayer shear
modes lead to the largest change in polarizability (Raman intensity); the modes
with the largest Raman intensity determining the frequency trends. We present
direct evidence for these conclusions by studying the Raman modes in few layer
graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles
calculations and Raman spectroscopy. This study sheds light on the influence of
stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D
layered materials in general, and leads to a practical way of identifying the
stacking sequence in these materials.Comment: 30 pages, 8 figure
N′-(2-Methoxybenzylidene)nicotinohydrazide
The title compound, C14H13N3O2, was prepared by the reaction of 2-methoxybenzyaldehyde with nicotinic acid hydrazide in methanol. The dihedral angle between the benzene and pyridine rings is 5.9 (3)°. In the crystal structure, molecules are linked by intermolecular N—H⋯O hydrogen bonds, leading to the formation of chains along the c axis; adjacent chains are linked via C—H⋯O and C—H⋯N hydrogen bonds
- …