252 research outputs found
Soft X-ray Photoemission Studies of the HfO2/SiO2/Si System
Cataloged from PDF version of article.Soft x-ray photoelectron spectroscopy with synchrotron radiation was employed to study the valence-band offsets for the HfO2/SiO2/Si and HfO2/SiOxNy/Si systems. We obtained a valence-band offset difference of -1.05+/-0.1 eV between HfO2 (in HfO2/15 Angstrom SiO2/Si) and SiO2 (in 15 Angstrom SiO2/Si). There is no measurable difference between the HfO2 valence-band maximum positions of the HfO2/10 Angstrom SiOxNy/Si and HfO2/15 Angstrom SiO2/Si systems. (C) 2002 American Institute of Physics
Cascade Boltzmann - Langevin approach to higher-order current correlations in diffusive metal contacts
The Boltzmann - Langevin approach is extended to calculations of third and
fourth cumulants of current in diffusive-metal contacts. These cumulants result
from indirect correlations between current fluctuations, which may be
considered as "noise of noise". The calculated third cumulant coincides exactly
with its quantum-mechanical value. The fourth cumulant tends to its
quantum-mechanical value at high voltages and to a positive value
at V=0 changing its sign at .Comment: 6 pages, 2 eps figures, typo corrected, minor change
A Discrete and Bounded Envy-free Cake Cutting Protocol for Four Agents
We consider the well-studied cake cutting problem in which the goal is to
identify a fair allocation based on a minimal number of queries from the
agents. The problem has attracted considerable attention within various
branches of computer science, mathematics, and economics. Although, the elegant
Selfridge-Conway envy-free protocol for three agents has been known since 1960,
it has been a major open problem for the last fifty years to obtain a bounded
envy-free protocol for more than three agents. We propose a discrete and
bounded envy-free protocol for four agents
Simultaneous imaging of dopants and free charge carriers by STEM-EELS
Doping inhomogeneities in solids are not uncommon, but their microscopic
observation and understanding are limited due to the lack of bulk-sensitive
experimental techniques with high-enough spatial and spectral resolution. Here,
we demonstrate nanoscale imaging of both dopants and free charge carriers in
La-doped BaSnO3 (BLSO) using high-resolution electron energy-loss spectroscopy
(EELS). By analyzing both high- and low-energy excitations in EELS, we reveal
chemical and electronic inhomogeneities within a single BLSO nanocrystal. The
inhomogeneous doping leads to distinctive localized infrared surface plasmons,
including a novel plasmon mode that is highly confined between high- and
low-doping regions. We further quantify the carrier density, effective mass,
and dopant activation percentage from EELS data and transport measurements on
the bulk single crystals of BLSO. These results represent a unique way of
studying heterogeneities in solids, understanding structure-property
relationships at the nanoscale, and opening the way to leveraging nanoscale
doping texture in the design of nanophotonic devices
Nanometer Scale Dielectric Fluctuations at the Glass Transition
Using non-contact scanning probe microscopy (SPM) techniques, dielectric
properties were studied on 50 nanometer length scales in poly-vinyl-acetate
(PVAc) films in the vicinity of the glass transition. Low frequency (1/f) noise
observed in the measurements, was shown to arise from thermal fluctuations of
the electric polarization. Anomalous variations observed in the noise spectrum
provide direct evidence for cooperative nano-regions with heterogeneous
kinetics. The cooperative length scale was determined. Heterogeneity was
long-lived only well below the glass transition for faster than average
processes.Comment: 4 pages, 4 embedded PS figures, RevTeX - To appear in Phys. Rev. Let
Variability in bioreactivity linked to changes in size and zeta potential of diesel exhaust particles in human immune cells
Acting as fuel combustion catalysts to increase fuel economy, cerium dioxide (ceria, CeO(2)) nanoparticles have been used in Europe as diesel fuel additives (Envirox™). We attempted to examine the effects of particles emitted from a diesel engine burning either diesel (diesel exhaust particles, DEP) or diesel doped with various concentrations of CeO(2) (DEP-Env) on innate immune responses in THP-1 and primary human peripheral blood mononuclear cells (PBMC). Batches of DEP and DEP-Env were obtained on three separate occasions using identical collection and extraction protocols with the aim of determining the reproducibility of particles generated at different times. However, we observed significant differences in size and surface charge (zeta potential) of the DEP and DEP-Env across the three batches. We also observed that exposure of THP-1 cells and PBMC to identical concentrations of DEP and DEP-Env from the three batches resulted in statistically significant differences in bioreactivity as determined by IL-1β, TNF-α, IL-6, IFN-γ, and IL-12p40 mRNA (by qRT-PCR) and protein expression (by ELISPOT assays). Importantly, bioreactivity was noted in very tight ranges of DEP size (60 to 120 nm) and zeta potential (−37 to −41 mV). Thus, these physical properties of DEP and DEP-Env were found to be the primary determinants of the bioreactivity measured in this study. Our findings also point to the potential risk of over- or under- estimation of expected bioreactivity effects (and by inference of public health risks) from bulk DEP use without taking into account potential batch-to-batch variations in physical (and possibly chemical) properties
Instability, Intermixing and Electronic Structure at the Epitaxial LaAlO3/SrTiO3(001) Heterojunction
The question of stability against diffusional mixing at the prototypical
LaAlO3/SrTiO3(001) interface is explored using a multi-faceted experimental and
theoretical approach. We combine analytical methods with a range of
sensitivities to elemental concentrations and spatial separations to
investigate interfaces grown using on-axis pulsed laser deposition. We also
employ computational modeling based on the density function theory as well as
classical force fields to explore the energetic stability of a wide variety of
intermixed atomic configurations relative to the idealized, atomically abrupt
model. Statistical analysis of the calculated energies for the various
configurations is used to elucidate the relative thermodynamic stability of
intermixed and abrupt configurations. We find that on both experimental and
theoretical fronts, the tendency toward intermixing is very strong. We have
also measured and calculated key electronic properties such as the presence of
electric fields and the value of the valence band discontinuity at the
interface. We find no measurable electric field in either the LaAlO3 or SrTiO3,
and that the valence band offset is near zero, partitioning the band
discontinuity almost entirely to the conduction band edge. Moreover, we find
that it is not possible to account for these electronic properties
theoretically without including extensive intermixing in our physical model of
the interface. The atomic configurations which give the greatest electrostatic
stability are those that eliminate the interface dipole by intermixing, calling
into question the conventional explanation for conductivity at this interface -
electronic reconstruction. Rather, evidence is presented for La indiffusion and
doping of the SrTiO3 below the interface as being the cause of the observed
conductivity
Soft x-ray photoemission studies of Hf oxidation
Charging of oxide films under x rays is an important issue that must be taken into consideration for determination of core-level binding energies as well as valence band offsets. Measurements are taken as a function of time, thickness, and annealing condition. Photoemission results show the presence of metallic Hf with the 4f7/2 binding energy of 18.16 eV, and at least one clear suboxide peak
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