11,701 research outputs found
Atomic structure, energetics, and dynamics of topological solitons in Indium chains on Si(111) surfaces
Based on scanning tunneling microscopy and first-principles theoretical
studies, we characterize the precise atomic structure of a topological soliton
in In chains grown on Si(111) surfaces. Variable-temperature measurements of
the soliton population allow us to determine the soliton formation energy to be
~60 meV, smaller than one half of the band gap of ~200 meV. Once created, these
solitons have very low mobility, even though the activation energy is only
about 20 meV; the sluggish nature is attributed to the exceptionally low
attempt frequency for soliton migration. We further demonstrate local electric
field-enhanced soliton dynamics.Comment: 5 pages, 3 figure
Composition dependence of electronic structure and optical properties of Hf1-xSixOy gate dielectrics
Copyright © 2008 American Institute of Physics. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditionsComposition-dependent electronic structure and optical properties of Hf1âxSixOy 0.1 x 0.6 gate
dielectrics on Si at 450 °C grown by UV-photo-induced chemical vapor deposition UV-CVD have
been investigated via x-ray photoemission spectroscopy and spectroscopy ellipsometry SE . By
means of the chemical shifts in the Hf 4f, Si 2p, and O 1s spectra, the HfâOâSi bondings in the
as-deposited films have been confirmed. Analyses of composition-dependent band alignment of
Hf1âxSixOy / Si gate stacks have shown that the valence band VB offset Ev demonstrates little
change; however, the values of conduction band offset Ec increase with the increase in the silicon
atomic composition, resulting from the increase in the separation between oxygen 2p orbital VB
state and antibonding d states intermixed of Hf and Si. Analysis by SE, based on the TaucâLorentz
model, has indicated that decreases in the optical dielectric constant and increase in band gap have
been observed as a function of silicon contents. Changes in the complex dielectric functions and
band gap Eg related to the silicon concentration in the films are discussed systematically. From the
band offset and band gap viewpoint, these results suggest that Hf1âxSixOy films provide sufficient
tunneling barriers for electrons and holes, making them promising candidates as alternative gate
dielectrics.National Natural Science Foundation of China and Royal Society U.K
Systematic Determination of Absolute Absorption Cross-section of Individual Carbon Nanotubes
Determination of optical absorption cross-section is always among the central
importance of understanding a material. However its realization on individual
nanostructures, such as carbon nanotubes, is experimentally challenging due to
the small extinction signal using conventional transmission measurements. Here
we develop a technique based on polarization manipulation to enhance the
sensitivity of single-nanotube absorption spectroscopy by two-orders of
magnitude. We systematically determine absorption cross-section over broad
spectral range at single-tube level for more than 50 chirality-defined
single-walled nanotubes. Our data reveals chirality-dependent one-dimensional
photo-physics through the behaviours of exciton oscillator strength and
lifetime. We also establish an empirical formula to predict absorption spectrum
of any nanotube, which provides the foundation to determine quantum
efficiencies in important photoluminescence and photovoltaic processes
Bandwidth-Controlled Insulator-Metal Transition and Correlated Metallic State in 5 Transition Metal Oxides SrIrO (=1, 2, and )
We investigated the electronic structures of the 5 Ruddlesden-Popper
series SrIrO (=1, 2, and ) using optical
spectroscopy and first-principles calculations. As 5 orbitals are spatially
more extended than 3 or 4 orbitals, it has been widely accepted that
correlation effects are minimal in 5 compounds. However, we observed a
bandwidth-controlled transition from a Mott insulator to a metal as we
increased . In addition, the artificially synthesized perovskite SrIrO
showed a very large mass enhancement of about 6, indicating that it was in a
correlated metallic state
Optimizing the Resource Requirements of Hierarchical Scheduling Systems
Compositional reasoning on hierarchical scheduling systems is a well-founded formal method that can construct schedulable and optimal system configurations in a compositional way. However, a compositional framework formulates the resource requirement of a component, called an interface, by assuming that a resource is always supplied by the parent components in the most pessimistic way. For this reason, the component interface demands more resources than the amount of resources that are really sufficient to satisfy sub-components. We provide two new supply bound functions which provides tighter bounds on the resource requirements of individual components. The tighter bounds are calculated by using more information about the scheduling system.
We evaluate our new tighter bounds by using a model-based schedulability framework for hierarchical scheduling systems realized as Uppaal models. The timed models are checked using model checking tools Uppaal and Uppaal SMC, and we compare our results with the state of the art tool CARTS
Avian influenza viruses in Korean live poultry markets and their pathogenic potential
AbstractWe surveyed live-poultry markets in Korea in 2003 and isolated 9 H9N2, 6 H3N2, and 1 H6N1 influenza viruses. Antigenic and phylogenetic analyses showed that all 9 H9N2 isolates were of A/Chicken/Korea/25232-96006/96-like lineage (which caused disease in chickens in Korea in 1996) but were different from H9N2 viruses of southeastern China. They had at least 4 genotypes and replicated in chickens but not in mice. The H3N2 and H6N1 viruses were new to Korea and were probably reassortants of avian influenza viruses from southeastern China and recent Korean H9N2 viruses. All 8 segments of the H3N2 viruses formed a single phylogenetic cluster with 99.1 to 100% homology. The H3N2 viruses replicated in chickens and mice without preadaptation, but the H6N1 virus did not. Our results show an increasingly diverse pool of avian influenza viruses in Korea that are potential pandemic influenza agents
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