The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
E. J. Mittemeijer - One of the best experts on this subject based on the ideXlab platform.
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the effect of substrate orientation on the Kinetics of ultra thin oxide film growth on al single crystals
Acta Materialia, 2008Co-Authors: F. Reichel, Lars P. H. Jeurgens, E. J. MittemeijerAbstract:The Kinetics of ultra-thin (<1.5 nm) oxide-film growth on bare Al{1 1 1}, Al{1 0 0} and Al{1 1 0} substrates in the temperature range of 350–600 K at pO2=1×10-4Pa was investigated by real-time in situ spectroscopic ellipsometry. It follows that the oxide-film growth Kinetics depends strongly on the parent metal substrate orientation. On Al{1 0 0} and Al{1 1 0}, the growth Kinetics can be subdivided into an initial, very fast oxidation stage and a subsequent very slow oxidation stage, which is characterized by the occurrence of a near-limiting oxide-film thickness that increases with increasing temperature. On Al{1 1 1}, the initial, very fast growth rate decreases more gradually with increasing oxidation time and an unexpected decrease of oxide-film thickness, for an oxidation time of 6000 s, with increasing temperature up to 475 K is observed. The rate-limiting step(s) and mechanism(s) of the oxidation process were identified by a quantitative model description of the oxide-film growth Kinetics on the basis of coupled currents of electrons (by both tunneling and thermionic emission) and cations under influence of a surface-charge field. It followed that the unexpected decrease of the oxide-film thickness with increasing temperature on Al{1 1 1} is due to a slow increase of the (relatively low) activation energy barrier for cation transport in combination with a constant Kinetic Potential due to the surface-charge field within the amorphous oxide-film regime (up to T ⩽ 450 K). For Al{1 0 0} and Al{1 1 0}, the energy barrier for cation transport, as well as the Kinetic Potential, increase with increasing temperature due to, as compared to Al{1 1 1}, a more gradual amorphous-to-crystalline transition, which already starts at lower temperatures T < 400 K.
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The role of the initial oxide-film microstructure on the passivation behavior of Al metal surfaces
Surface and Interface Analysis, 2008Co-Authors: F. Reichel, Lars P. H. Jeurgens, E. J. MittemeijerAbstract:An unexpected passivation behavior is reported for the low temperature oxidation of bare Al{111} substrates, which is characterized by an unusual decrease of the oxide-film thickness with increasing temperature (at constant time) in the amorphous oxide-film regime (as established by angle resolved-X-ray photoelectron spectroscopy, real-time In situ spectroscopic ellipsometry and low energy electron diffraction). Modeling of the oxide-film growth Kinetics on the basis of the coupled-currents of cations and electrons in a surface-charge field shows that the decrease of oxide-film thickness with increasing temperature is due to a slow increase of the rate-limiting activation energy barrier for cation transport, W, with increasing temperature in combination with a constant Kinetic Potential due to the surface-charge field up to the amorphous-to-crystalline transition temperature at about 450 K. On Al{100} a more gradual amorphous-to-crystalline transition is observed, which is associated with concurrent increases of not only the energy barrier W, but also the Kinetic Potential, resulting in the usually observed increase of the near-limiting thickness with increasing temperature.
Ju Li - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of thermal transport in dilute nanocolloids.
Physical Review Letters, 2007Co-Authors: Jacob Eapen, Ju LiAbstract:Thermal conduction modes in a nanocolloid (nanofluid) are quantitatively assessed by combining linear response theory with molecular dynamics simulations. The microscopic heat flux is decomposed into three additive fluctuation modes, namely, Kinetic, Potential, and collision. For low volume fractions (
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mechanism of thermal transport in dilute nanocolloids
Physical Review Letters, 2007Co-Authors: Jacob Eapen, Ju LiAbstract:Thermal conduction modes in a nanocolloid (nanofluid) are quantitatively assessed by combining linear response theory with molecular dynamics simulations. The microscopic heat flux is decomposed into three additive fluctuation modes, namely, Kinetic, Potential, and collision. For low volume fractions (<1%) of nanosized platinum clusters which interact strongly with xenon host liquid, a significant thermal conductivity enhancement results from the self correlation in the Potential flux. Our findings reveal a molecular-level mechanism for enhanced thermal conductivity in nanocolloids with short-ranged attraction and offer predictions that can be experimentally tested.
A Pouquet - One of the best experts on this subject based on the ideXlab platform.
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interplay of waves and eddies in rotating stratified turbulence and the link with Kinetic Potential energy partition
EPL, 2015Co-Authors: R Marino, Duane Rosenberg, Corentin Herbert, A PouquetAbstract:The interplay between waves and eddies in stably stratified rotating flows is investigated by means of world-class direct numerical simulations using up to 30723 grid points. Strikingly, we find that the shift from vortex- to wave-dominated dynamics occurs at a wave number k R which does not depend on the Reynolds number, suggesting that the partition of energy between wave and vortical modes is not sensitive to the development of turbulence at the smaller scales. We also show that k R is comparable to the wave number at which exchanges between Kinetic and Potential modes stabilize at close to equipartition, emphasizing the role of Potential energy, as conjectured in the atmosphere and the oceans. Moreover, k R varies as the inverse of the Froude number as explained by the scaling prediction proposed, consistently with recent observations and modeling of the Mesosphere–Lower Thermosphere and of the ocean.
F. Reichel - One of the best experts on this subject based on the ideXlab platform.
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the effect of substrate orientation on the Kinetics of ultra thin oxide film growth on al single crystals
Acta Materialia, 2008Co-Authors: F. Reichel, Lars P. H. Jeurgens, E. J. MittemeijerAbstract:The Kinetics of ultra-thin (<1.5 nm) oxide-film growth on bare Al{1 1 1}, Al{1 0 0} and Al{1 1 0} substrates in the temperature range of 350–600 K at pO2=1×10-4Pa was investigated by real-time in situ spectroscopic ellipsometry. It follows that the oxide-film growth Kinetics depends strongly on the parent metal substrate orientation. On Al{1 0 0} and Al{1 1 0}, the growth Kinetics can be subdivided into an initial, very fast oxidation stage and a subsequent very slow oxidation stage, which is characterized by the occurrence of a near-limiting oxide-film thickness that increases with increasing temperature. On Al{1 1 1}, the initial, very fast growth rate decreases more gradually with increasing oxidation time and an unexpected decrease of oxide-film thickness, for an oxidation time of 6000 s, with increasing temperature up to 475 K is observed. The rate-limiting step(s) and mechanism(s) of the oxidation process were identified by a quantitative model description of the oxide-film growth Kinetics on the basis of coupled currents of electrons (by both tunneling and thermionic emission) and cations under influence of a surface-charge field. It followed that the unexpected decrease of the oxide-film thickness with increasing temperature on Al{1 1 1} is due to a slow increase of the (relatively low) activation energy barrier for cation transport in combination with a constant Kinetic Potential due to the surface-charge field within the amorphous oxide-film regime (up to T ⩽ 450 K). For Al{1 0 0} and Al{1 1 0}, the energy barrier for cation transport, as well as the Kinetic Potential, increase with increasing temperature due to, as compared to Al{1 1 1}, a more gradual amorphous-to-crystalline transition, which already starts at lower temperatures T < 400 K.
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The role of the initial oxide-film microstructure on the passivation behavior of Al metal surfaces
Surface and Interface Analysis, 2008Co-Authors: F. Reichel, Lars P. H. Jeurgens, E. J. MittemeijerAbstract:An unexpected passivation behavior is reported for the low temperature oxidation of bare Al{111} substrates, which is characterized by an unusual decrease of the oxide-film thickness with increasing temperature (at constant time) in the amorphous oxide-film regime (as established by angle resolved-X-ray photoelectron spectroscopy, real-time In situ spectroscopic ellipsometry and low energy electron diffraction). Modeling of the oxide-film growth Kinetics on the basis of the coupled-currents of cations and electrons in a surface-charge field shows that the decrease of oxide-film thickness with increasing temperature is due to a slow increase of the rate-limiting activation energy barrier for cation transport, W, with increasing temperature in combination with a constant Kinetic Potential due to the surface-charge field up to the amorphous-to-crystalline transition temperature at about 450 K. On Al{100} a more gradual amorphous-to-crystalline transition is observed, which is associated with concurrent increases of not only the energy barrier W, but also the Kinetic Potential, resulting in the usually observed increase of the near-limiting thickness with increasing temperature.
Jacob Eapen - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of thermal transport in dilute nanocolloids.
Physical Review Letters, 2007Co-Authors: Jacob Eapen, Ju LiAbstract:Thermal conduction modes in a nanocolloid (nanofluid) are quantitatively assessed by combining linear response theory with molecular dynamics simulations. The microscopic heat flux is decomposed into three additive fluctuation modes, namely, Kinetic, Potential, and collision. For low volume fractions (
-
mechanism of thermal transport in dilute nanocolloids
Physical Review Letters, 2007Co-Authors: Jacob Eapen, Ju LiAbstract:Thermal conduction modes in a nanocolloid (nanofluid) are quantitatively assessed by combining linear response theory with molecular dynamics simulations. The microscopic heat flux is decomposed into three additive fluctuation modes, namely, Kinetic, Potential, and collision. For low volume fractions (<1%) of nanosized platinum clusters which interact strongly with xenon host liquid, a significant thermal conductivity enhancement results from the self correlation in the Potential flux. Our findings reveal a molecular-level mechanism for enhanced thermal conductivity in nanocolloids with short-ranged attraction and offer predictions that can be experimentally tested.
