435 research outputs found
Graphite based Schottky diodes formed on Si, GaAs and 4H-SiC substrates
We demonstrate the formation of semimetal graphite/semiconductor Schottky
barriers where the semiconductor is either silicon (Si), gallium arsenide
(GaAs) or 4H-silicon carbide (4H-SiC). Near room temperature, the forward-bias
diode characteristics are well described by thermionic emission, and the
extracted barrier heights, which are confirmed by capacitance voltage
measurements, roughly follow the Schottky-Mott relation. Since the outermost
layer of the graphite electrode is a single graphene sheet, we expect that
graphene/semiconductor barriers will manifest similar behavior.Comment: 5 pages, 3 figures, 1 tabl
Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers
We investigate valley exciton dynamics in MoSe2 monolayers in polarization-
and time-resolved photoluminescence (PL) spectroscopy at 4K. Following
circularly polarized laser excitation, we record a low circular polarization
degree of the PL of typically . This is about 10 times lower than the
polarization induced under comparable conditions in MoS2 and WSe2 monolayers.
The evolution of the exciton polarization as a function of excitation laser
energy and power is monitored in PL excitation (PLE) experiments. Fast PL
emission times are recorded for both the neutral exciton of ps and for
the charged exciton (trion) of 12 ps.Comment: 4 pages, 3 figure
Ab-initio electron transport calculations of carbon based string structures
First-principles calculations show that monatomic strings of carbon have high
cohesive energy and axial strength, and exhibit stability even at high
temperatures. Due to their flexibility and reactivity, carbon chains are
suitable for structural and chemical functionalizations; they form also stable
ring, helix, grid and network structures. Analysis of electronic conductance of
various infinite, finite and doped string structures reveal fundamental and
technologically interesting features. Changes in doping and geometry give rise
to dramatic variations in conductance. In even-numbered linear chains strain
induces substantial decrease of conductance. The double covalent bonding of
carbon atoms underlies their unusual chemical, mechanical and transport
properties.Comment: 4 pages, 4 figure
Half-metallic properties of atomic chains of carbon-transition metal compounds
We found that magnetic ground state of one-dimensional atomic chains of
carbon-transition metal compounds exhibit half-metallic properties. They are
semiconductors for one spin-direction, but show metallic properties for the
opposite direction. The spins are fully polarized at the Fermi level and net
magnetic moment per unit cell is an integer multiple of Bohr magneton. The
spin-dependent electronic structure can be engineered by changing the number of
carbon and type of transition metal atoms. These chains, which are stable even
at high temperature and some of which keep their spin-dependent electronic
properties even under moderate axial strain, hold the promise of potential
applications in nanospintronics.Comment: 11 pages, 3 figures, 1 table
Silicon and III-V compound nanotubes: structural and electronic properties
Unusual physical properties of single-wall carbon nanotubes have started a
search for similar tubular structures of other elements. In this paper, we
present a theoretical analysis of single-wall nanotubes of silicon and group
III-V compounds. Starting from precursor graphene-like structures we
investigated the stability, energetics and electronic structure of zigzag and
armchair tubes using first-principles pseudopotential plane wave method and
finite temperature ab-initio molecular dynamics calculations. We showed that
(n,0) zigzag and (n,n) armchair nanotubes of silicon having n > 6 are stable
but those with n < 6 can be stabilized by internal or external adsorption of
transition metal elements. Some of these tubes have magnetic ground state
leading to spintronic properties. We also examined the stability of nanotubes
under radial and axial deformation. Owing to the weakness of radial restoring
force, stable Si nanotubes are radially soft. Undeformed zigzag nanotubes are
found to be metallic for 6 < n < 11 due to curvature effect; but a gap starts
to open for n > 12. Furthermore, we identified stable tubular structures formed
by stacking of Si polygons. We found AlP, GaAs, and GaN (8,0) single-wall
nanotubes stable and semiconducting. Our results are compared with those of
single-wall carbon nanotubes.Comment: 11 pages, 10 figure
Supermetallic conductivity in bromine-intercalated graphite
Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to
in-plane charge conductivities which increase monotonically with intercalation
time toward values (for ~6 at% Br) that are significantly higher than Cu at
temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic
susceptibility measurements confirm that the Br dopes the graphene sheets with
holes while simultaneously increasing the interplanar separation. The increase
of mobility (~ 5E4 cm^2/Vs at T=300 K) and resistance anisotropy together with
the reduced diamagnetic susceptibility of the intercalated samples suggests
that the observed supermetallic conductivity derives from a parallel
combination of weakly-coupled hole-doped graphene sheets.Comment: 5 pages, 4 figure
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