2,724 research outputs found
Depletion-Isolation Effect in Vertical MOSFETs During the Transition From Partial to Fully Depleted Operation
A simulation study is made of floating-body effects (FBEs) in vertical MOSFETs due to depletion isolation as the pillar thickness is reduced from 200 to 10 nm. For pillar thicknesses between 200–60 nm, the output characteristics with and without impact ionization are identical at a low drain bias and then diverge at a high drain bias. The critical drain bias Vdc for which the increased drain–current is observed is found to decrease with a reduction in pillar thickness. This is explained by the onset of FBEs at progressively lower values of the drain bias due to the merging of the drain depletion regions at the bottom of the pillar (depletion isolation). For pillar thicknesses between 60–10 nm, the output characteristics show the opposite behavior, namely, the critical drain bias increases with a reduction in pillar thickness. This is explained by a reduction in the severity of the FBEs due to the drain debiasing effect caused by the elevated body potential. Both depletion isolation and gate–gate coupling contribute to the drain–current for pillar thicknesses between 100–40 nm
Humans\u27 Bonding with their Companion Dogs: Cardiovascular Benefits during and after Stress
This study examined whether having one\u27s companion dog present during and after stress posed similar cardiovascular benefits as having a close friend present, even when the relationship quality for both the companion dog and friend was highly positive. Positive aspects of relationship quality for participants\u27 dog and friend were not associated with one another, suggesting that these relationships exist independently. Additionally, compared to participants with a close friend present, those with their dog present had lower heart rate and diastolic blood pressure (p\u27s \u3c .05) while undergoing the stressors, and tended to have lower heart rate and systolic blood pressure (p\u27s \u3c .09) when recovering from stressors. This study indicates that even when relationship quality is similarly high for companion dogs and friends, dogs may be associated with greater reductions in owners\u27 cardiovascular reactivity to stress, particularly if there is a potential for evaluation apprehension in the human friendships. These findings support the value of the human- companion animal relationship in promoting human welfare
Effects of atomic short-range order on the properties of perovskite alloys in their morphotropic phase boundary
The effects of atomic short-range order on the properties of
Pb(Zr_{1-x}Ti_x)O_3 alloy in its morphotropic phase boundary (MPB) are
predicted by combining first-principles-based methods and annealing techniques.
Clustering is found to lead to a compositional expansion of this boundary,
while the association of unlike atoms yields a contraction of this region.
Atomic short-range order can thus drastically affect properties of perovskite
alloys in their MPB, by inducing phase transitions. Microscopic mechanisms
responsible for these effects are revealed and discussed.Comment: 4 pages, with 2 postscript figures embedded. Uses REVTEX4 and
graphicx macro
Phase diagram of Pb(Zr,Ti)O3 solid solutions from first principles
A first-principles-derived scheme, that incorporates ferroelectric and
antiferrodistortive degrees of freedom, is developed to study
finite-temperature properties of PbZr1-xTixO3 solid solutions near its
morphotropic phase boundary. The use of this numerical technique (i) resolves
controversies about the monoclinic ground-state for some Ti compositions, (ii)
leads to the discovery of an overlooked phase, and (iii) yields three
multiphase points, that are each associated with four phases. Additional
neutron diffraction measurements strongly support some of these predictions.Comment: 10 pages, 2 figure
Vortex-to-Polarization Phase Transformation Path in Pb(ZrTi)O Nanoparticles
Phase transformation in finite-size ferroelectrics is of fundamental
relevance for understanding collective behaviors and balance of competing
interactions in low-dimensional systems. We report a first-principles effective
Hamiltonian study of vortex-to-polarization transformation in
Pb(ZrTi)O nanoparticles, caused by homogeneous electric
fields normal to the vortex plane. The transformation is shown to (1) follow an
unusual {\it macroscopic} path that is symmetry non-conforming and
characterized by the occurrence of a previously unknown structure as the
bridging phase; (2) lead to the discovery of a striking collective phenomenon,
revealing how ferroelectric vortex is annihilated {\it microscopically}.
Interactions underlying these behaviors are discussed
Domain Size Dependence of Piezoelectric Properties of Ferroelectrics
The domain size dependence of piezoelectric properties of ferroelectrics is
investigated using a continuum Ginzburg-Landau model that incorporates the
long-range elastic and electrostatic interactions. Microstructures with desired
domain sizes are created by quenching from the paraelectric phase by biasing
the initial conditions. Three different two-dimensional microstructures with
different sizes of the domains are simulated. An electric field is
applied along the polar as well as non-polar directions and the piezoelectric
response is simulated as a function of domain size for both cases. The
simulations show that the piezoelectric coefficients are enhanced by reducing
the domain size, consistent with recent experimental results of Wada and
Tsurumi (Brit. Ceram. Trans. {\bf 103}, 93, 2004) on domain engineered
Comment: submitted to Physical Review
Kinetic Monte Carlo Simulations of Crystal Growth in Ferroelectric Alloys
The growth rates and chemical ordering of ferroelectric alloys are studied
with kinetic Monte Carlo (KMC) simulations using an electrostatic model with
long-range Coulomb interactions, as a function of temperature, chemical
composition, and substrate orientation. Crystal growth is characterized by
thermodynamic processes involving adsorption and evaporation, with
solid-on-solid restrictions and excluding diffusion. A KMC algorithm is
formulated to simulate this model efficiently in the presence of long-range
interactions. Simulations were carried out on Ba(Mg_{1/3}Nb_{2/3})O_3 (BMN)
type materials. Compared to the simple rocksalt ordered structures, ordered BMN
grows only at very low temperatures and only under finely tuned conditions. For
materials with tetravalent compositions, such as (1-x)Ba(Mg_{1/3}Nb_{2/3})O_3 +
xBaZrO_3 (BMN-BZ), the model does not incorporate tetravalent ions at
low-temperature, exhibiting a phase-separated ground state instead. At higher
temperatures, tetravalent ions can be incorporated, but the resulting crystals
show no chemical ordering in the absence of diffusive mechanisms.Comment: 13 pages, 16 postscript figures, submitted to Physics Review B
Journa
Poling effect on distribution of quenched random fields in a uniaxial relaxor ferroelectric
The frequency dependence of the dielectric permitivity's maximum has been
studied for poled and unpoled doped relaxor strontium barium niobate
(SBN-61:Cr). In both cases the maximum
found is broad and the frequency dispersion is strong. The present view of
random fields compensation in the unpoled sample is not suitable for explaining
this experimental result. We propose a new mechanism where the dispersion of
quenched random electric fields, affecting the nanodomains, is minimized after
poling. We test our proposal by numerical simulations on a random field Ising
model. Results obtained are in agreement with the polarization's measurements
presented by Granzow et al. [Phys. Rev. Lett {\bf 92}, 065701 (2004)].Comment: 7 pages, 4 figure
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