67 research outputs found
Thermally-driven phase transitions in freestanding low-buckled silicene, germanene, and stanene
Low-buckled silicene, germanene, and stanene are group graphene
allotropes. They form a honeycomb lattice out of two interpenetrating ( and
) triangular sublattices that are vertically separated by a small distance
. The atomic numbers of silicon, germanium, and tin are larger to
carbon's (), making them the first experimentally viable two-dimensional
topological insulators. Those materials have a twice-energy-degenerate
atomistic structure characterized by the buckling direction of the
sublattice with respect to the sublattice [whereby the atom either
protrudes {\em above} () or {\em below} () the
atoms], and the consequences of that energy degeneracy on their elastic and
electronic properties have not been reported thus far. Here, we uncover {\em
ferroelastic, bistable} behavior on silicene, which turns into an {\em average}
planar structure at about 600 K. Further, the creation of electron and hole
puddles obfuscates the zero-temperature SOC induced band gaps at temperatures
as low as 200 K, which may discard silicene as a viable two-dimensional
topological insulator for room temperature applications. Germanene, on the
other hand, never undergoes a low-buckled to planar 2D transformation, becoming
amorphous at around 675 K instead, and preserving its SOC-induced bandgap
despite of band broadening. Stanene undergoes a transition onto a crystalline
3D structure at about 300 K, preserving its SOC-induced electronic band gap up
to that temperature. Unlike what is observed in silicene and germanene, stanene
readily develops a higher-coordinated structure with a high degree of
structural order. The structural phenomena is shown to have deep-reaching
consequences for the electronic and vibrational properties of those two
dimensional topological insulators.Comment: 16 pages, 21 figures. Originally submitted on December 5, 202
Vortex-oriented ferroelectric domains in SnTe/PbTe monolayer lateral heterostructures
Heterostructures formed from interfaces between materials with complementary properties often display unconventional physics. Of especial interest are heterostructures formed with ferroelectric materials. These are mostly formed by combining thin layers in vertical stacks. Here the first in situ molecular beam epitaxial growth and scanning tunneling microscopy characterization of atomically sharp lateral heterostructures between a ferroelectric SnTe monolayer and a paraelectric PbTe monolayer are reported. The bias voltage dependence of the apparent heights of SnTe and PbTe monolayers, which are closely related to the type-II band alignment of the heterostructure, is investigated. Remarkably, it is discovered that the ferroelectric domains in the SnTe surrounding a PbTe core form either clockwise or counterclockwise vortex-oriented quadrant configurations. In addition, when there is a finite angle between the polarization and the interface, the perpendicular component of the polarization always points from SnTe to PbTe. Supported by first-principles calculation, the mechanism of vortex formation and preferred polarization direction is identified in the interaction between the polarization, the space charge, and the strain effect at the horizontal heterointerface. The studies bring the application of 2D group-IV monochalcogenides on in-plane ferroelectric heterostructures a step closer
Microscopic manipulation of ferroelectric domains in SnSe monolayers at room temperature
Two-dimensional (2D) van der Waals ferroelectrics provide an unprecedented
architectural freedom for the creation of artificial multiferroics and
non-volatile electronic devices based on vertical and co-planar heterojunctions
of 2D ferroic materials. Nevertheless, controlled microscopic manipulation of
ferroelectric domains is still rare in monolayer-thick 2D ferroelectrics with
in-plane polarization. Here we report the discovery of robust ferroelectricity
with a critical temperature close to 400 K in SnSe monolayer plates grown on
graphene, and the demonstration of controlled room temperature ferroelectric
domain manipulation by applying appropriate bias voltage pulses to the tip of a
scanning tunneling microscope (STM). This study shows that STM is a powerful
tool for detecting and manipulating the microscopic domain structures in 2D
ferroelectric monolayers, which is difficult for conventional approaches such
as piezoresponse force microscopy, thus facilitating the hunt for other 2D
ferroelectric monolayers with in-plane polarization with important
technological applications
A Molecular Platinum Cluster Junction: A Single-Molecule Switch
We present a theoretical study of the electronic transport through
single-molecule junctions incorporating a Pt6 metal cluster bound within an
organic framework. We show that the insertion of this molecule between a pair
of electrodes leads to a fully atomically engineered nano-metallic device with
high conductance at the Fermi level and two sequential high on/off switching
states. The origin of this property can be traced back to the existence of a
HOMO which consists of two degenerate and asymmetric orbitals, lying close in
energy to the Fermi level of the metallic leads. Their degeneracy is broken
when the molecule is contacted to the leads, giving rise to two resonances
which become pinned close to the Fermi level and display destructive
interference.Comment: 4 pages, 4 figures. Reprinted (adapted) with permission from J. Am.
Chem. Soc., 2013, 135 (6), 2052. Copyright 2013 American Chemical Societ
Charge Transport through Graphene Junctions with Wetting Metal Leads
[[sponsorship]]原子與分子科學研究所[[note]]已出版;[SCI];有審查制度;具代表性[[note]]http://gateway.isiknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=Drexel&SrcApp=hagerty_opac&KeyRecord=1530-6984&DestApp=JCR&RQ=IF_CAT_BOXPLO
Conductance modulation of metallic carbon nanotubes by remote charged rings
We calculate the effects of a longitudinal electrostatic
perturbation on a metallic single-wall carbon nanotube and
demonstrate conductance modulation. Such external modulation would
be completely screened in bulk 3D metals but is possible in SWNTs
because their electrons are quasi–two-dimensional and can interact
with a nearby system of charges. The resultant modulation of the
conductance is determined by the strength of the self-consistent
potential and its periodicity over shorter or longer distances. We
employ the zero-temperature single-particle Green's function
transport approach in the empirical tight-binding approximation to
quantify the modulation of conductance and also consider the limit
of a superlattice
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