17,036 research outputs found
Liquid-Metal-Enabled Synthesis of Aluminum-Containing III-Nitrides by Plasma-Assisted Molecular Beam Epitaxy
Nitride films are promising for advanced optoelectronic and electronic device
applications. However, some challenges continue to impede development of high
aluminum-containing devices. The two major difficulties are growth of high
crystalline quality films with aluminum-rich compositions, and efficiently
doping such films p-type. These problems have severely limited use of
aluminum-rich nitride films grown by molecular beam epitaxy. A way around these
problems is through use of a liquid-metal-enabled approach to molecular beam
epitaxy. Although the presence of a liquid metal layer at the growth front is
reminiscent of conventional liquid phase epitaxy, this approach is different in
its details. Conventional liquid epitaxy is a near-thermodynamic equilibrium
process which liquid-metal assisted molecular beam epitaxy is not. Growth of
aluminum-rich nitrides is primarily driven by the kinetics of the molecular
vapor fluxes, and the surface diffusion of adatoms through a liquid metal layer
before incorporation. This paper reports on growth of high crystalline quality
and highly doped aluminum-containing nitride films. Measured optical and
electrical characterization data show that the approach is viable for growth of
atomically smooth aluminum-containing nitride heterostructures. Extremely high
p-type doping of up to cm and n-type doping of up
to cm in AlGaN films was achieved.
Use of these metal-rich conditions is expected to have a significant impact on
high efficiency and high power optoelectronic and electronic devices that
require both high crystalline quality and highly doped (Al,Ga)N films
New Insights on Low Energy Scattering Amplitudes
The - and - wave phase shifts of low-energy pion-nucleon scatterings
are analysed using Peking University representation, in which they are
decomposed into various terms contributing either from poles or branch cuts. We
estimate the left-hand cut contributions with the help of tree-level
perturbative amplitudes derived in relativistic baryon chiral perturbation
theory up to . It is found that in and
channels, contributions from known resonances and cuts are far from enough to
saturate experimental phase shift data -- strongly indicating contributions
from low lying poles undiscovered before, and we fully explore possible physics
behind. On the other side, no serious disagreements are observed in the other
channels.Comment: slightly chnaged version, a few more figures added. Physical
conclusions unchange
in a supersymmetric theory with an explicit R-parity violation
We studied the process in a
violating supersymmetric Model with the effects from both B- and L-violating
interactions. The calculation shows that it is possible to detect a
violating signal at the Next Linear Collider. Information about the B-violating
interaction in this model could be obtained under very clean background, if we
take the present upper bounds for the parameters in the supersymmetric interactions. Even if we can not detect a signal of in the
experiment, we may get more stringent constraints on the heavy-flavor
couplings.Comment: 16 pages, 6 figure
Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions
Graphene-based vertical heterostructures, particularly stacks incorporated
with other layered materials, are promising for nanoelectronics. The stacking
of two model Dirac materials, graphene and topological insulator, can
considerably enlarge the family of van der Waals heterostructures. Despite well
understanding of the two individual materials, the electron transport
properties of a combined vertical heterojunction are still unknown. Here we
show the experimental realization of a vertical heterojunction between Bi2Se3
nanoplate and monolayer graphene. At low temperatures, the electron transport
through the vertical heterojunction is dominated by the tunneling process,
which can be effectively tuned by gate voltage to alter the density of states
near the Fermi surface. In the presence of a magnetic field, quantum
oscillations are observed due to the quantized Landau levels in both graphene
and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an
exotic gate-tunable tunneling resistance under high magnetic field, which
displays resistance maxima when the underlying graphene becomes a quantum Hall
insulator
Slightly Fluorination of Al₂O₃ ALD Coating on Li₁.₂Mn₀.₅₄Coo.₁₃Ni₀.₁₃O₂ Electrodes: Interface Reaction to Create Stable Solid Permeable Interphase Layer
Improving the performance of cathodes by using surface coatings has proven to be an effective method for improving the stability of Li-ion batteries (LIBs), while a high-quality film satisfying all requirements of electrochemical inertia, chemical stability, and lithium ion conductivity has not been found. In this study, a composite film composed of Al2O3 and AlF3 layers was coated on the surface of Li1.2Mn0.54Co0.13Ni0.13O2 (Li-rich NMC) based electrodes by atomic layer deposition (ALD). By varying the ratio of Al2O3 and AlF3, an optimal coating was achieved. The electrochemical characterization results indicated that the coating with 1 cycle of AlF3 ALD on 5 cycles of Al2O3 ALD (1AlF3-5Al2O3) significantly improved the cycling stability and alleviated the voltage attenuation problem of Li-rich NMC based electrodes by suppressing side reactions between the electrolyte and electrode, as well as inhibiting the transformation of layered Li2MnO3 into a spinel-like phase. After 200 cycles of charge-discharge, the discharge capacity retention of LIB half cells based on 1AlF3-5Al2O3 coated Li-rich NMC electrodes kept at 84%, much higher than that of the uncoated Li-rich NMC (the capacity retention less than 20%)
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