14,813 research outputs found
Structural difference rule for amorphous alloy formation by ion mixing
We formulate a rule which establishes a sufficient condition that an amorphous binary alloy will be formed by ion mixing of multilayered samples when the two constituent metals are of different crystalline structure, regardless of their atomic sizes and electronegativities. The rule is supported by the experimental results we have obtained on six selected binary metal systems, as well as by the previous data reported in the literature. The amorphization mechanism is discussed in terms of the competition between two different structures resulting in frustration of the crystallization process
Heterostructure by solid‐phase epitaxy in the Si〈111〉/Pd/Si (amorphous) system
When a thin film of Pd reacts with a 〈111〉 Si substrate, a layer of epitaxial Pd_2Si is formed. It is shown that Si can grow epitaxially on such a layer by solid‐phase reaction
Gravitational energy from a combination of a tetrad expression and Einstein's pseudotensor
The energy-momentum for a gravitating system can be considered by the tetard
teleparalle gauge current in orthonormal frames. Whereas the Einstein
pseudotensor used holonomic frames. Tetrad expression itself gives a better
result for gravitational energy than Einstein's. Inspired by an idea of Deser,
we found a gravitational energy expression which enjoys the positive energy
property by combining the tetrad expression and the Einstein pseudotensor,
i.e., the connection coefficient has a form appropriate to a suitable
intermediate between orthonormal and holonomic frames.Comment: 5 page
Scanning Tunneling Spectroscopic Studies of the Effects of Dielectrics and Metallic Substrates on the Local Electronic Characteristics of Graphene
Atomically resolved imaging and spectroscopic characteristics of
graphene grown by chemical vapor deposition (CVD) on copper
foils are investigated and compared with those of mechanical
exfoliated graphene on SiO_2. For exfoliated graphene, the local
spectral deviations from ideal behavior may be attributed to strain
induced by the SiO_2 substrate. For CVD grown graphene, the
lattice structure appears strongly distorted by the underlying
copper, with regions in direct contact with copper showing nearly
square lattices whereas suspended regions from thermal relaxation
exhibiting nearly honeycomb or hexagonal lattice structures. The
electronic density of states (DOS) correlates closely with the
atomic arrangements of carbon, showing excess zero-bias
tunneling conductance and nearly energy-independent DOS for
strongly distorted graphene, in contrast to the linearly dispersive
DOS for suspended graphene. These results suggest that graphene
can interact strongly with both metallic and dielectric materials in
close proximity, leading to non-negligible modifications to the
electronic properties
New variables, the gravitational action, and boosted quasilocal stress-energy-momentum
This paper presents a complete set of quasilocal densities which describe the
stress-energy-momentum content of the gravitational field and which are built
with Ashtekar variables. The densities are defined on a two-surface which
bounds a generic spacelike hypersurface of spacetime. The method used
to derive the set of quasilocal densities is a Hamilton-Jacobi analysis of a
suitable covariant action principle for the Ashtekar variables. As such, the
theory presented here is an Ashtekar-variable reformulation of the metric
theory of quasilocal stress-energy-momentum originally due to Brown and York.
This work also investigates how the quasilocal densities behave under
generalized boosts, i. e. switches of the slice spanning . It is
shown that under such boosts the densities behave in a manner which is similar
to the simple boost law for energy-momentum four-vectors in special relativity.
The developed formalism is used to obtain a collection of two-surface or boost
invariants. With these invariants, one may ``build" several different mass
definitions in general relativity, such as the Hawking expression. Also
discussed in detail in this paper is the canonical action principle as applied
to bounded spacetime regions with ``sharp corners."Comment: Revtex, 41 Pages, 4 figures added. Final version has been revised and
improved quite a bit. To appear in Classical and Quantum Gravit
Spreading of Latex Particles on a Substrate
We have investigated both experimentally and theoretically the spreading
behavior of latex particles deposited on solid substrates. These particles,
which are composed of cross-linked polymer chains, have an intrinsic elastic
modulus. We show that the elasticity must be considered to account for the
observed contact angle between the particle and the solid substrate, as
measured through atomic force microscopy techniques. In particular, the work of
adhesion computed within our model can be significantly larger than that from
the classical Dupr\'{e} formula.Comment: 7 pages, 7 figures, to appear in Europhys. Let
Time Delay Predictions in a Modified Gravity Theory
The time delay effect for planets and spacecraft is obtained from a fully
relativistic modified gravity theory including a fifth force skew symmetric
field by fitting to the Pioneer 10/11 anomalous acceleration data. A possible
detection of the predicted time delay corrections to general relativity for the
outer planets and future spacecraft missions is considered. The time delay
correction to GR predicted by the modified gravity is consistent with the
observational limit of the Doppler tracking measurement reported by the Cassini
spacecraft on its way to Saturn, and the correction increases to a value that
could be measured for a spacecraft approaching Neptune and Pluto.Comment: 5 pages, LaTex file, no figures. Corrections to Table
Evidence for Strain-Induced Local Conductance Modulations in Single-Layer Graphene on SiO_2
Graphene has emerged as an electronic material that is promising for device applications and for studying two-dimensional electron gases with relativistic dispersion near two Dirac points. Nonetheless, deviations from Dirac-like spectroscopy have been widely reported with varying interpretations. Here we show evidence for strain-induced spatial modulations in the local conductance of single-layer graphene on SiO_2 substrates from scanning tunneling microscopic (STM) studies. We find that strained graphene exhibits parabolic, U-shaped conductance vs bias voltage spectra rather than the V-shaped spectra expected for Dirac fermions, whereas V-shaped spectra are recovered in regions of relaxed graphene. Strain maps derived from the STM studies further reveal direct correlation with the local tunneling conductance. These results are attributed to a strain-induced frequency increase in the out-of-plane phonon mode that mediates the low-energy inelastic charge tunneling into graphene
New positive small vacuum region gravitational energy expressions
We construct an infinite number of new holonomic quasi-local gravitational
energy-momentum density pseudotensors with good limits asymptotically and in
small regions, both materially and in vacuum. For small vacuum regions they are
all a positive multiple of the Bel-Robinson tensor and consequently have
positive energy.Comment: 4 page
Monte Carlo Study of Topological Defects in the 3D Heisenberg Model
We use single-cluster Monte Carlo simulations to study the role of
topological defects in the three-dimensional classical Heisenberg model on
simple cubic lattices of size up to . By applying reweighting techniques
to time series generated in the vicinity of the approximate infinite volume
transition point , we obtain clear evidence that the temperature
derivative of the average defect density behaves
qualitatively like the specific heat, i.e., both observables are finite in the
infinite volume limit. This is in contrast to results by Lau and Dasgupta [{\em
Phys. Rev.\/} {\bf B39} (1989) 7212] who extrapolated a divergent behavior of
at from simulations on lattices of size up to
. We obtain weak evidence that scales with the
same critical exponent as the specific heat.As a byproduct of our simulations,
we obtain a very accurate estimate for the ratio of the
specific-heat exponent with the correlation-length exponent from a finite-size
scaling analysis of the energy.Comment: pages ,4 ps-figures not included, FUB-HEP 10/9
- …