Chemical Potential Distribution Research Articles

Ultrabroad Band Rainbow Capture and Releasing in Graded Chemical Potential Distributed Graphene Monolayer

We propose and numerically analyze a scheme to trap a broadband surface plasmon polariton (SPP) wave on a sheet of monolayer graphene with gradient chemical potential distribution. Different frequency components of the incident wave are trapped at different locations according to the chemical potential, resulting in “rainbow trapping” effect. By appropriately tuning the chemical potential distribution over the graphene sheet, graphene conductivity distribution is modified so that the trapped SPP wave is released. In the proposed structure, the group velocity of the trapped SPP waves is as low as the 10−8 times of the light speed in free space, and the lifetime of the trapped SPP wave is 3.14 ps when the relaxation of the graphene is 0.5 ps. This slow light system offers advantages simultaneously including broadband operation, ultracompact footprint, and dynamic control of group velocity without any complicated and expensive device geometry engineering.

Effect of surface Si redistribution on the alignment of Ge dots grown on pit-patterned Si(001) substrates

Thermally activated redistribution of Si surface atoms is found to be a crucial factor for the growth of aligned Ge dots on pit-patterned Si(001) substrates. A phenomenon of Si accumulation around the edge of pits significantly alters the substrate surface morphology. As the pit spacing is reduced to below 100 nm, a convex morphology developed between adjacent pits causes a chemical potential distribution that drives the Ge dots into the pits. In addition, the pits of an etching depth greater than 60 nm will evolve into truncated inverted pyramids with sharp base corners that provide deep potential wells for the confinement of Ge dots. Perfectly aligned Ge dots are obtained on pit-patterned Si substrates with this range of pit spacing and etching depth. We also find that the initial geometric shape of the pits does not affect the spatial arrangement of Ge dots.

Direct Evaluation of Oxygen Chemical Potential Distribution in an SOFC Cathode by In Situ X-Ray Absorption Spectroscopy

Oxygen chemical potential distribution in a porous La0.6Sr0.4CoO3-δ (LSC64) electrode on a Ce0.9Gd0.1CoO1.95- δ (GDC) electrolyte under polarization was evaluated by using in situ X-ray absorption spectroscopy (XAS) at P(O2) = 10-2 bar and 873 K. The application of synchrotron X-ray focused into the submicrometer size enabled us to experimentally clarify the oxygen potential distribution in the vicinity of electrode/electrolyte interface with the position resolution of micrometer. Electrochemical impedance spectroscopy (EIS) measurements, followed by the analysis assuming the transmission line model (TLM) as an equivalent circuit, were performed with the same electrochemical cell for the XAS measurements. Based on the results by in-situ micro XAS and EIS measurements, the effective reaction area in the porous LSC64 electrode was discussed.

Electrochemical Measurements on Cells, I: Simulation of Potential Distribution with an Embedded Probe

Finite element analysis is used to calculate electrochemical potential distributions of charged species and chemical potential distributions of neutral species in solid electrolytes of electrochemical cells. Potential distributions of charged species follow the Laplace equation; while that of neutral species are related to the potentials of charged species through the local chemical equilibrium. Simulations with different cell geometries and transport parameters show that an embedded probe with electrically insulating coating along the probe surface (with tips uncoated) is required for the measurement of electrochemical potential of electrons within a solid electrolyte. Simulation also shows that by optimizing both electronic and ionic conductivities, cell stability can be improved.

Evaporation-Induced Branched Structures from Sessile Nanofluid Droplets

We investigate the formation of branched nanoparticle aggregates resulting from the evaporation of sessile nanofluid droplets of the copper water-based nanofluids experimentally. Both symmetric and asymmetric drying patterns were found as the sessile droplet evaporated. A kinetic Monte Carlo (KMC) approach is developed to explain the drying process in a circular domain, representing the top view of a drying sessile droplet. It is found that the lattice-gas-based Monte Carlo model can describe the nanoparticle self-assembly into a solid highly branched aggregate. While the chemical potential function is coupled to the nondimensional spherical droplet size during evaporation, the results reveal that the fingering contact line instabilities can emerge under a given condition and force the formation of a branched nanoparticle structure. The pattern comparison shows that the simulation results have a qualitative agreement with the experiments. The parameter study shows that the model parameters, such as domain diameter, chemical potential distribution, particle interaction energy, and so on, have significant influence on the resulting patterns.

Nanostructurization caused by first order phase transitions in systems with hopping dynamics

Abstract A system with thermally activated hopping dynamics is considered in the framework of the lattice fluid model in situations when no constrains on concentration gradients are assumed. Attractive nearest neighbor interparticle interactions and discrete particle energy levels are taken into account. On the basis of local equilibrium distribution function the expressions for the mean potentials and the chemical potential distribution at a given particle concentration distribution are derived in the quasichemical approximation. The closed system of differential-difference evolution equations for the particle concentration distribution is evaluated. Several case studies of formation of nanostructures accompanied by first order phase transitions are considered. They include situations when the symmetry of initially metastable constant concentration distribution is violated by temperature, interparticle interaction or concentration perturbation. In the latter case two dimensional structures are observed. The final nanostructured states remain stable when fluctuations are taken into consideration.

On the steady-state chemical potential profiles in bilayer solid electrolytes

Abstract

Thermodynamic and SIMS analyses on the role of proton/water in oxygen reduction process and related degradations in solid oxide fuel cells

Roles of Secondary Ion Mass Spectrometry and the local thermodynamic equilibrium approximation are discussed in understanding high temperature electrochemical processes. Fundamental issues are first considered on metal dense electrode (Pt/Au) and oxide electrolyte (YSZ/GDC) systems; the so-called three phase boundary (TPB) mechanism is dominant for YSZ systems, whereas for the GDC systems, a new proton/water mechanism is dominant; protons play an important role in a such way that the cathodic reaction of protons to form water vapors takes place at TPBs, while evaporated water vapors are transported on the GDC surface; oxide ions are transported to the anode and protons are circulated to the TPBs of the cathode; another effect of water vapors is to enhance oxygen isotope exchange reactions over a whole area of surface and a resulting flow of 18O inside GDC masks the charge transfer process in the SIMS analyses. A local proton flow in the proton/water mechanism provides a drastic change in the distribution of chemical potential of water vapors under the dense electrodes, leading to the pore formation or the non-homogenized cation distribution. Concerning industrial issues, two degradation topics are analyzed on drastic changes in chemical potential distribution caused by electrode reactions or by non-uniform flows of oxide ions inside electrolyte.

Effect of dissipative processes on the near-surface inhomogeneity of a hollow cylinder

UDC 539.3 We formulate the basic relations of a mathematical model of mechanics of elastic deformable systems that describes the formation of a near-surface inhomogeneity caused by both the process of local mass displacement and dissipative processes. On this basis, we solve the problem of the stationary stressstrain state of an infinite hollow cylinder. It is shown that the near-surface inhomogeneity of the distribution of stresses and chemical potential is characterized by two parameters. One of them is related to the local mass displacement, and the other is a consequence of dissipative processes in the body.

Structural and vibrational study of 3- or 5-methyl substituted 2-N-ethylamino-4-nitropyridine N-oxides

X-ray crystal structures of two isomers C8H11N3O3, i.e. 2-N-ethylamino-5-methyl-4-nitropyridine N-oxide (EN5MPO) and 2-N-ethylamino-3-methyl-4-nitropyridine N-oxide (EN3MPO) have been determined. The different substitutions of the CH3 groups lead to change of the unit-cell structure, molecular and intermolecular arrangement. Both structures are monoclinic, space group P21/c and P21/n with a parallel and antiparallel orientation along the a-axis, respectively. In each of the two subunits, the methyl carbons and N-atoms of the nitro group are almost coplanar with the pyridine ring, but the N-oxide bonds are inclined from this plane. The crystal structures are stabilized by a set of the weak inter- and intramolecular hydrogen bonds of the NH⋯O type. The structures of both isomers have been confirmed by the results of IR and Raman spectra measurements, quantum chemical calculations and potential energy distribution (PED). The role of methyl group introduced in 3 or 5 position of 2-N-ethylamino-4-nitropyridine N-oxide has been analysed.

Electrochemical Behaviors of Nickel/Yttria-Stabilized Zirconia Anodes with Distribution Controlled Yttrium-Doped Barium Zirconate by Ink-jet Technique

The relationship between the electrochemical performance of an anode in a solid oxide fuel cell and the distribution of yttrium-doped barium zirconate (BZY) in the electrochemically active zone of nickel (Ni)/yttria-stabilized zirconia (YSZ) anodes was investigated to clarify the promoting effect of BZY on electrochemical reaction. After BZY was injected into Ni/YSZ anodes using an ink-jet technique for control of the distribution of BZY, the anode performance improved in both humidified H2 and dry CH4 fuels. The performance of the BZY-infiltrated Ni/YSZ anodes depended on the distribution of BZY; an increasing gradient of BZY from the electrolyte side to the anode surface side was particularly effective in improving the performance. These results suggest that the optimum amount of infiltrated BZY to enhance the electrochemical reaction depended on the distribution of the oxygen chemical potential in the Ni/YSZ anodes. According to the competitive adsorption equilibrium of reactants and the Langmuir-type reaction on the surface of Ni at the triple-phase boundary, the oxygen coverage was a critical factor in the electrochemical reaction and depended on the oxygen chemical potential. In conclusion, the enhanced electrochemical reaction in the BZY-infiltrated Ni/YSZ anodes was therefore due to the increased oxygen coverage.

Thermally induced morphology evolution of pit-patterned Si substrate and its effect onnucleation properties of Ge dots

We demonstrate the effect of the pre-growth heat treatment process on the nucleationproperties of Ge dots grown on pit-patterned Si(001) substrates. The prefabricated 200 nmdiameter pits inherently evolve into truncated inverted pyramids (TIPs) with⟨110⟩ base edgesand a 7°–9° sidewall slope during heat treatment; this morphology transformation is robust against variationsin shape and orientation of the pit patterns. Uniform Ge dots with an areal density of4 × 109 cm − 2 were obtained on the Si substrates having TIPs. Each TIP containsfour aligned Ge dots locating symmetrically with respect to ⟨110⟩. These dots exhibit an elliptical dome shape with major axis oriented along⟨100⟩. The nucleation position, shape and spatial orientation of these Ge dots coincide with thecalculated surface chemical potential distribution of the TIP.

Particle rearrangement during sintering of heterogeneous powder mixtures: A combined experimental and theoretical study

We studied the morphology evolution of individual three-particle W–Cu–W agglomerates during sintering anneals at 1000 °C. The angle between the lines connecting the centers of W and Cu particles decreased during annealing, provided its initial value was different from 180°. While the W particles retained their spherical shape during sintering, the shape of Cu particles changed significantly after long sintering times. Both the rate of the particles’ rearrangement and the linear shrinkage of the particle pairs determined in the experiments increased with decreasing initial angle between the particles. We proposed an analytical model of sintering of cylindrical three-wire agglomerates controlled by self-diffusion of Cu atoms along the surface of Cu wire and along the W–Cu interphase boundary. The proposed model incorporates a thermodynamic method for calculating the distribution of chemical potential of metal atoms moving along the rigid cylindrical interphase boundary. The predictions of the model were in good agreement with the experimental data, underlying an important role played by capillary-driven diffusion in rearrangement of particles during sintering.

Void Formation at the Interface of the Duplex Scale Formed on Fe-5Cr Alloy at 773 K

Void formation in a duplex scale formed on Fe-5Cr alloy at 773 K has been elucidated by oxygen chemical potential distribution, the flux of oxide ion and its divergence. The calculation predicts that voids preferentially form at the interface between inner and outer scales in the low oxygen partial pressure in which the predominant defect of iron is interstitial ion. The flux of oxide ion changes discontinuously at this interface and the divergence of the flux gives voids. Calculated volume fraction of voids at this interface is in good agreement with that has been measured.

Quantitative Analysis on Internal Oxide Precipitates in Fe–1 mass%Si Alloy Formed at 1473K in Ar–17.6%H2–12.2%H2O

Surface defects formed on Si-containing steels in hot-rolling process depend largely on the character of the scale composed of FeO and Fe2SiO4 (FeO+Fe2SiO4 oxide scale) during de-scaling. The formation of FeO+Fe2SiO4 oxide scale is influence by internal oxide precipitates. In order to elucidate quantitatively the internal oxidation, it is required to analyze the distributions of number, radius and volume of internal oxide precipitates in internal oxidation zone (IOZ).Internal oxidation of Fe–1 mass%Si alloy was examined at 1473K in Ar–17.6%H2–12.2%H2O where an outer scale of FeO does not form. The growth rate of IOZ was obeyed the parabolic rate law, indicating that the rate-determining step was the diffusion of oxygen through alloy. SiO2 precipitated from the internal oxidation front to 0.23±0.02 of normalized thickness of IOZ, and Fe2SiO4 precipitated from the position to the gas/alloy interface, depending on the chemical potential distribution of oxygen. Fe2SiO4 is formed by the reaction between SiO2, Fe and dissolved oxygen in IOZ. The number of precipitates in unit volume is reciprocally proportional to depth in IOZ, suggesting that the grain growth of oxide obviously affected the distribution. The radius of the precipitates was proportional to the cubic root of depth so that the volume of the precipitate was proportional to depth. These results elucidated that the volume fraction of precipitates in IOZ was constant.

Three-dimensional numerical analysis of mixed ionic and electronic conducting cathode reconstructed by focused ion beam scanning electron microscope

Three-dimensional microstructure of mixed ionic and electronic conducting cathode, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428), is obtained by a dual-beam focused ion beam-scanning electron microscope, and its overpotential is predicted by the lattice Boltzmann method. Gaseous, ionic and electronic transport equations coupled with electrochemical reaction at the gas/solid interface in the three-dimensional microstructure are solved with an assumption of local equilibrium in the solid oxide. The gas transport is modeled by the dusty gas model. The numerical simulation is conducted under the current density conditions of 0.01, 0.05, 0.1 and 0.2A/cm2. Predicted cathode overpotentials agreed well with the experimental results. However, predicted overpotential was very large at O2=20%, T=973K and i=0.2A/cm2 case due to the decline of ionic conductivity at low oxygen partial pressure. Three-dimensional chemical potential and current vector distributions inside LSCF microstructure are presented. Ionic and electronic current stream lines are uniform and smooth, which indicates good ionic and electronic conductions as well as wide electrochemically active areas inside the LSCF microstructure. Present method will be an effective tool for investigating local oxygen potential field which affects local reactions, diffusions and physical properties of the MIEC cathodes.

Elastodynamic response of thermoelastic diffusion due to inclined load

PurposeThe paper's aim is to investigate a two‐dimensional deformation of homogeneous, anisotropic generalized thermoelastic diffusion as a result of an inclined load by applying Laplace and Fourier transforms. The inclined load is assumed to be a linear combination of a normal load and a tangential load.Design/methodology/approachAs an application, concentrated and distributed loads have been taken to illustrate the utility of the approach. The transformed solutions are inverted numerically, using a numerical inversion technique.FindingsThe variations of normal displacement, temperature distribution and chemical potential distribution due to different sources for different angle of inclinations with distance have been shown graphically to depict the effect of diffusion and anisotropy. A special case is also deduced from the present investigation.Originality/valueIt can contribute to the theoretical consideration of the seismic and volcanic sources since it can account for the deformation fields in the entire volume surrounding the sources region.

InAs quantum wire induced composition modulation in an In0.53Ga0.37Al0.10As barrier layer grown on an InP substrate

Composition modulations are observed by transmission electron microscopy in In0.53Ga0.37Al0.10As barrier layers that overgrow both single- and multilayer InAs quantum wire structures grown on an InP substrate. Indium-rich (gallium-deficient) regions were observed in the region of the barrier layer lying directly above individual quantum wires, while indium-deficient (gallium-rich) regions were detected in the barrier above the gaps between adjacent underlying quantum wires. The magnitude of such modulation was typically 7% (atomic percent) for both indium and gallium as estimated from the energy dispersive x-ray analysis. The origin of such composition modulations was determined by modeling the chemical potential distribution for indium and gallium on the growth front of the barrier layer at the initial capping stage of the quantum wires with finite element simulations. It is found that the number and positions of the indium-rich regions are determined by the combined effects of strain and surface energy distributions on the barrier material capping the quantum wires. Moreover the estimated magnitudes of the composition modulation for both indium and gallium from the finite element models are in good agreement with the experimental observations. This method provides a simple way to understand the origin of, and to estimate the magnitude of the quantum wire-induced composition modulation in the barrier layer.

Numerical study on the difference in mechanism between vapor-solid and vapor-liquid-solid solidification processes

In the vapor-liquid-solid (VLS) nanowire growth, nanowires can be constructed utilizing the difference in the mechanism of crystallization between the vapor-solid (VS) process (outside the solvent droplet) and the VLS process (inside the droplet). We performed a series of separate molecular dynamics simulations for a VLS system and a VS system under equivalent nonequilibrium conditions to clarify the different mechanisms of the solid growth process in both systems and to understand how a liquid substance can catalyze the solidification. The detailed observation of the chemical potential distribution during the steady solid growth state clearly outlines the processes that limit the growth rate. We found that the most dominant process limiting the growth rate is mass transport in the solvent liquid. We also show numerically and analytically that the mass transport rate is proportional to the diffusion constant and also to the solubility of in the solvent, and that a high solubility in the solvent can almost compensate for the disadvantage of a small diffusion constant. Although remarkable catalytic effect by the solvent at least in the linear nonequilibrium region could not be observed, our results suggest that the VLS process would catalyze the solid growth using liquid substance with higher solubility or in a nonlinear nonequilibrium state.

Analysis of Deformation Due to Various Sources in Micropolar Thermodiffusive Elastic Medium

Within the framework of investigation, a general solution to the field equations of micropolar thermodiffusive elastic medium for two-dimensional problem based on the concept of Lord and Shulman [1] theory are obtained by employing Laplace and Fourier transforms. The application of distributed sources has been considered to show the utility of the problem. The transformed components of displacement, stress, temperature distribution and chemical potential distribution are inverted numerically using a numerical inversion technique. Impact of relaxation time, diffusion and micropolarity on these resulting quantities are presented graphically. Some special cases of interest are also deduced from present investigation.