743 research outputs found
Amorphous thin GeSbTe phase-change films prepared by radical-assisted metal-organic chemical vapor deposition
AbstractAmorphous thin Ge2Sb2Te5 films were deposited by MOCVD (metal organic chemical vapor deposition) on three-dimensional structures. Ammonium gas, used as a reactant, reduced the deposition temperature to 150°C, which is lower than that of metal-organic precursors. Introducing nitrogen and hydrogen radicals made by decomposition of the ammonium gas further reduced the growth temperature. The lowest growth temperature producing a realistic growth rate was 100°C. Phase-change memory cells made of MOCVD-grown films were confirmed to have operation and reliability characteristics as good as those of conventional cells made of sputter-deposited films
EFFECT OF HIGH TEMPERATURE AND HIGH HUMIDITY TREATMENT ON BENDING PROPERTIES OF WOOD
Japanese cedar (Cryptomeria Japonica D. Don) 110 110 1000-mm green boxed-heart timbers were dried under high temperature (110-140C) and high humidity (0.01-0.24 MPa gauge pressure) conditions until the weight remained unchanged. Then strength properties were examined. Wood became brittle because of the high temperature and high humidity treatment. We hypothesize that the wood was seriously damaged by hydrolysis because of the long treatment time used in this study and that the large cross-sectional area and high set gauge pressure lengthened the time of water loss from the wood. We considered viscosity and plasticity, rather than elasticity, to be the main factors that contributed to the decrease of work for rupture
Characterizing Data Assimilation in Navier-Stokes Turbulence with Transverse Lyapunov Exponents
Data assimilation (DA) reconstructing small-scale turbulent structures is
crucial for forecasting and understanding turbulence. This study proposes a
theoretical framework for DA based on ideas from chaos synchronization, in
particular, the transverse Lyapunov exponents (TLEs). The analysis with TLEs
characterizes a critical length scale, below which the turbulent dynamics is
synchronized to the larger-scale turbulent dynamics, indicating successful DA.
An underlying link between TLEs and the maximal Lyapunov exponent suggests that
the critical length scale depends on the Reynolds number. Furthermore, we
discuss new directions of DA algorithms based on the proposed framework.Comment: 5 pages, 3 figure
Suppression of nucleation density in twisted graphene domains grown on graphene/SiC template by sequential thermal process
We investigated the growth of twisted graphene on graphene/silicon carbide
(SiC-G) templates by metal-free chemical vapor deposition (CVD) through a
sequential thermal (ST) process, which exploits the ultraclean surface of SiC-G
without exposing the surface to air before CVD. By conducting control
experiments with SiC-G templates exposed to air (AirE process), structural
analysis by atomic force microscopy revealed that the nucleation density of CVD
graphene (CVD-G) was significantly suppressed in the ST process under the same
growth condition. The nucleation behavior on SiC-G surfaces is observed to be
very sensitive to carbon source concentration and process temperature. The
nucleation on the ultraclean surface of SiC-G prepared by the ST process
requires higher partial pressure of carbon source compared with that on the
surface by the AirE process. Moreover, analysis of CVD-G growth over a wide
temperature range indicates that nucleation phenomena change dramatically with
a threshold temperature of 1300{\deg}C, possibly due to arising of etching
effects. The successful synthesis of twisted few-layer graphene (tFLG) was
affirmed by Raman spectroscopy, in which analysis of the G' band proves a high
ratio of twisted structure in CVD-G. These results demonstrate that metal-free
CVD utilizing ultraclean templates is an effective approach for the scalable
production of large-domain tFLG that is valuable for electronic applications.Comment: Authors' original version submitted to Crystal Growth & Design. Main
manuscript: 23 pages, 6 figures. Supporting information: 1 page
Observation of finite excess noise in the voltage-biased quantum Hall regime as a precursor for breakdown
We performed noise measurements in a two-dimensional electron gas to
investigate the nonequilibrium quantum Hall effect (QHE) state. While excess
noise is perfectly suppressed around the zero-biased QHE state reflecting the
dissipationless electron transport of the QHE state, considerable finite excess
noise is observed in the breakdown regime of the QHE. The noise temperature
deduced from the excess noise is found to be of the same order as the energy
gap between the highest occupied Landau level and the lowest empty one.
Moreover, unexpected finite excess noise is observed at a finite source-drain
bias voltagesmaller than the onset voltage of the QHE breakdown, which
indicates finite dissipation in the QHE state and may be related to the
prebreakdown of the QHE.Comment: 8 pages, 8 figure
Observations of High Energy Cosmic-Ray Electrons from 30 GeV to 3 TeV with Emulsion Chambers
We have performed a series of cosmic-ray electron observations using the
balloon-borne emulsion chambers since 1968. While we previously reported the
results from subsets of the exposures, the final results of the total exposures
up to 2001 are presented here. Our successive experiments have yielded the
total exposure of 8.19 m^2 sr day at the altitudes of 4.0 - 9.4 g/cm^2. The
performance of the emulsion chambers was examined by accelerator beam tests and
Monte-Carlo simulations, and the on-board calibrations were carried out by
using the flight data. In this work we present the cosmic-ray electron spectrum
in the energy range from 30 GeV to 3 TeV at the top of the atmosphere, which is
well represented by a power-law function with an index of -3.28+-0.10. The
observed data can be also interpreted in terms of diffusive propagation models.
The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of
cosmic-ray electron sources at distances within ~1 kpc and times within ~1x10^5
yr ago.Comment: 38 pages, 10 figures, 3 tables, Accepted for publication in Ap
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