1,887 research outputs found
Substrate-induced band gap opening in epitaxial graphene
Graphene has shown great application potentials as the host material for next
generation electronic devices. However, despite its intriguing properties, one
of the biggest hurdles for graphene to be useful as an electronic material is
its lacking of an energy gap in the electronic spectra. This, for example,
prevents the use of graphene in making transistors. Although several proposals
have been made to open a gap in graphene's electronic spectra, they all require
complex engineering of the graphene layer. Here we show that when graphene is
epitaxially grown on the SiC substrate, a gap of ~ 0.26 is produced. This gap
decreases as the sample thickness increases and eventually approaches zero when
the number of layers exceeds four. We propose that the origin of this gap is
the breaking of sublattice symmetry owing to the graphene-substrate
interaction. We believe our results highlight a promising direction for band
gap engineering of graphene.Comment: 10 pages, 4 figures; updated reference
Strain-induced energy band gap opening in two-dimensional bilayered silicon film
This work presents a theoretical study of the structural and electronic
properties of bilayered silicon films under in-plane biaxial strain/stress
using density functional theory. Atomic structures of the two-dimensional
silicon films are optimized by using both the local-density approximation and
generalized gradient approximation. In the absence of strain/stress, five
buckled hexagonal honeycomb structures of the bilayered silicon film have been
obtained as local energy minima and their structural stability has been
verified. These structures present a Dirac-cone shaped energy band diagram with
zero energy band gaps. Applying tensile biaxial strain leads to a reduction of
the buckling height. Atomically flat structures with zero bucking height have
been observed when the AA-stacking structures are under a critical biaxial
strain. Increase of the strain between 10.7% ~ 15.4% results in a band-gap
opening with a maximum energy band gap opening of ~168.0 meV obtained when
14.3% strain is applied. Energy band diagram, electron transmission efficiency,
and the charge transport property are calculated.Comment: 18 pages, 5 figures, 1 tabl
Band gap opening by two-dimensional manifestation of Peierls instability in graphene
Using first-principles calculations of graphene having high-symmetry
distortion or defects, we investigate band gap opening by chiral symmetry
breaking, or intervalley mixing, in graphene and show an intuitive picture of
understanding the gap opening in terms of local bonding and antibonding
hybridizations. We identify that the gap opening by chiral symmetry breaking in
honeycomb lattices is an ideal two-dimensional (2D) extension of the Peierls
metal-insulator transition in 1D linear lattices. We show that the spontaneous
Kekule distortion, a 2D version of the Peierls distortion, takes place in
biaxially strained graphene, leading to structural failure. We also show that
the gap opening in graphene antidots and armchair nanoribbons, which has been
attributed usually to quantum confinement effects, can be understood with the
chiral symmetry breaking
Anomalous temperature dependence of the band-gap in Black Phosphorus
Black Phosphorus (BP) has gained renewed attention due to its singular
anisotropic electronic and optical properties that might be exploited for a
wide range of technological applications. In this respect, the thermal
properties are particularly important both to predict its room temperature
operation and to determine its thermoelectric potential. From this point of
view, one of the most spectacular and poorly understood phenomena is, indeed,
the BP temperature-induced band-gap opening: when temperature is increased the
fundamental band-gap increases instead of decreasing. This anomalous thermal
dependence has also been observed, recently, in its monolayer counterpart. In
this work, based on \textit{ab-initio} calculations, we present an explanation
for this long known, and yet not fully explained, effect. We show that it
arises from a combination of harmonic and lattice thermal expansion
contributions, which are, in fact, highly interwined. We clearly narrow down
the mechanisms that cause this gap opening by identifying the peculiar atomic
vibrations that drive the anomaly. The final picture we give explains both the
BP anomalous band-gap opening and the frequency increase with increasing volume
(tension effect).Comment: Published in Nano Letter
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