Variation Of Chemical Potential Research Articles

Lithium Adsorption on Graphene at Finite Temperature

The increasing demand for high-energy-density lithium-ion batteries motivates a search for alternative electrode materials. Experimentally obtained graphene-based structures have been suggested to replace the state-of-the-art graphitic anode. For a thorough characterization of Li adsorption on graphene, we study the interaction of Li with graphene both at zero and finite temperatures. The zero-temperature study was carried out by means of density functional theory (DFT), accounting for van der Waals (vdW) interactions, whereas the finite temperature behavior was studied by Monte Carlo techniques with a DFT-derived Li–graphene interaction potential constructed via cluster expansion method. Our calculations reveal two distinct types of orderings of Li on graphene, Li-gas (dispersed Li-ion) and Li-cluster phases. The zero-temperature calculations show that, even when vdW is included, the Li–graphene interaction is mainly electrostatic and phase separation to pristine graphene and bulk Li is energetically most favorable. However, at nonzero temperatures, entropy contribution to free energy allows the lesser-ordered Li-gas and Li-cluster states to be more favorable at sufficiently low concentrations: at temperatures below 400 K and concentrations below 1Li:6C, Li-gas and Li-cluster phases coexist whereas at higher concentrations, only clusters remain stable. At temperatures above 400 K, Li-gas phase can be stabilized with respect to Li cluster or Li bulk at higher concentrations. Furthermore, small variations in chemical potential are shown to be enough to change that concentration threshold. Finally, we show that the Li-cluster phases can have Li-island or Li-stripe ordering; however, Li stripes appear due to the finite size of the simulation cell and therefore the Li-island phase is expected to dominate in the thermodynamic limit instead.

Distinguishing topological Majorana bound states from trivial Andreev bound states: Proposed tests through differential tunneling conductance spectroscopy

Trivial Andreev bound states arising from chemical potential variations could lead to zero-bias tunneling conductance peaks at finite magnetic fields in class $D$ nanowires, precisely mimicking the predicted zero-bias conductance peaks arising from the topological Majorana bound states. This finding raises a serious question on the efficacy of using zero-bias tunneling conductance peaks, by themselves, as evidence supporting the existence of topological Majorana bound states in nanowires. In the current work, we provide specific experimental protocols for tunneling spectroscopy measure- ments to distinguish between Andreev and Majorana bound states without invoking more demand- ing nonlocal measurements which have not yet been successfully performed in nanowire systems. In particular, we discuss three distinct experimental schemes involving response of the zero-bias peak to local perturbations of the tunnel barrier, overlap of bound states from the wire ends, and most compellingly, introducing a sharp localized potential in the wire itself to perturb the zero-bias tun- neling peaks. We provide extensive numerical simulations clarifying and supporting our theoretical predictions.

Controlling theoretically total absorption in hybrid-cavity resonator with one graphene monolayer outside cavity

Total absorption is realized theoretically in a graphene-outside-cavity resonator. The structure is composed of the FP-Fano hybrid resonance cavity. Changing the thickness of grating exciting Fano resonance, the absorption-mode number can be tuned effectively. For the focused double-mode absorption, the resonances behave insensitively with the variation of chemical potential of graphene. Varying the geometry of grating can control the coupling extent of two modes. Also, by manipulating the period number of two-side multilayers around graphene, the absorption, shift and number of modes are governed.

(Invited) Influence of Mechanical Stress on Lithium Chemical Potential in Lithium Ion Battery Electrodes

In solid-state ionic devices, such as all-solid-state lithium ion batteries (ASSLIBs) and solid oxide fuel cells (SOFCs), mechanical stress is introduced at the electrode/electrolyte hetrointerfaces due to differences in the crystal structures and the chemical/thermal expansion coefficients. A mechanical strain at the heterointerface might affect thermodynamic and kinetic properties of the electrodes and the electrolyte, resulting in the performance deterioration or improvement of the devices. Although such a so-called “mechano-electro-chemical coupling effect” has been empirically demonstrated by many researches, the origins of the effect are not fully understood so far. In this presentation, we will discuss the influence of mechanical stress on thermodynamic properties of solid-state ionic materials. As a model case, lithium chemical potential in electrode materials for ASSLIBs under mechanical stress was investigated. A dense thin film electrode of LiCoO2, Li2MnO4 or LiFePO4 was deposited on a plate of solid-state lithium ion conductors, and the variation of the lithium chemical potential in the electrode was evaluated by measuring electromotive force under compressively- and tensely-strained conditions. Electromotive force accompanied by mechanical strain could be clearly observed, demonstrating a “mechano-electro-chemical coupling effect”. The influence of mechanical stress was different depending on the kinds of electrode material. The observed change in the electromotive force could be thermodynamically related to the lithium partial molar volume of the electrodes.

Designing Smart Materials for Efficient Electrosynthesis of Fuels and Environmental Remediation: The Story of Transition Metal Chalcogenides

Energy harvesting from solar and water has created ripples in materials energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. Another aspect that has become more relevant is the electroreduction of atmospheric carbon dioxide into fuel or other value-added chemicals, thereby offering environmental remediation without the need to store large amounts of pressurized CO2. It has become very apparent that hydrogen-on-demand technology needs to be developed to complement the growth of hydrogen fuel economy without adding on to the process cost by storing hydrogen in pressurized tanks or non-reactive framework. In this regards, water electrolysis leading to generation of oxygen and hydrogen on demand, has been one of the most promising routes towards sustainable alternative energy generation and storage without depleting fossil-fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited by the anodic oxygen evolution reaction (OER), which is a kinetically sluggish, electron-intensive uphill reaction. A slow OER process also slows the other half-cell reaction, i.e. the hydrogen evolution reaction (HER) at the cathode. Hence, designing efficient catalysts for OER and HER process from earth-abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have focused on transition metal chalcogenides as efficient electrocatalysts for several energy conversion processes. Recently we have discovered that these transition metal selenides are highly efficient electrocatalyst for electroreduction of CO2 to higher hydrocarbons such as ethanol, acetic acid, and acetaldehyde at reasonably low potential (-0.7 to -1.5 V) under ambient conditions. In this presentation we will first present that CO2 electroreduction with Ni, Cu and V-based selenides, and present a thorough investigation of the reaction products and their evolution as a function of applied potential and reaction time. We will also discuss about the selectivity of product formation by controlling catalyst composition and applied potential. For water splitting reactions, we had proposed the idea that these chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal site, compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chemical potential around the transition metal center, [e.g. lowering the Ni2+ --> Ni3+ oxidation potential in Ni-based catalysts where Ni3+ is the actually catalytically active species]. Based on such hypothesis, we have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, Cu, and Ni-Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm2 [Ni3Se2 - 200 - 290 mV; Co7Se8 - 260 mV; FeNi2Se4-NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe2Se4 - 210 mV; CoNi2Se4 - 190 mV; Ni3Te2 – 180 mV]. We will also highlight the importance of this increasing covalency in enhancing OER catalytic activity with the help of experimental evidence in the chalcogenide series (Ni3S2, Ni3Se2, Ni3Te2). We will illustrate how the Ni(II) --> Ni(III) oxidation potential is indeed lowered within the selenide coordination compared to the oxide, in pure single crystals of the seleno-based coordination complex which is devoid of any surface impurities and adsorbates. To complement the experimental observations, we have also performed DFT calculation and will discuss how the OH adsorption energy varied between the oxide and chalcogenides surfaces and the implication of such variation in terms of catalytic activity. The later part of the talk will be focused on designing nanostructures for these catalysts and integrating them with nanostructured photoanode arrays to create an efficient solar-to-fuel energy conversion device as well as artificial photosynthetic units. We will illustrate growth of nanostructured (nanopillars and nanotubes) photoanode arrays through confined electrodeposition on lithographically patterned nanoelectrodes, and decorating them with nanostructured chalcogenide based electroctalaysts, and how this technique can be utilized for a hybrid energy conversion device. Results encompassing efficient photoelectrocatalytic performance of CdSe-NiSe, CdTe-Ni3Te2, CuInSe2-NiSe2 and Fe3Se4-NiSe hybrid nanocomposite will be presented.

Analyzing the effect of graphene's chemical potential on the performance of a plasmonic sensor in infrared

SPR sensor based on ‘glass substrate-Ag film-insulating layer-graphene’ plasmonic structure is proposed in the NIR region. The influence of graphene chemical potential (μ) on the sensor's performance, measured in terms of figure-of-merit (FOM), has been analyzed in detail. The analysis suggests that the variation of chemical potential does not affect much the detection sensitivity and detection limit but it affects the FWHM of SPR curve. The variation of FOM with μ follows a certain pattern. In summary, the maximum and almost constant sensing performance may be achieved for 0.9 < μ < 1 eV for graphene monolayer. Also, CaF2 substrate provides much better FOM compared with 2S2G and Si substrates at any value of μ.

Intrinsic energy conversions for photon-generation in piezo-phototronic materials: A case study on alkaline niobates

The creations of photons in response to mechanical stimulus in a crystal that has noncentral symmetry are the great fundamental physics responsible for numbers of important technologies. The underlying mechanism and complete theory for a precise explanation of the mechanical-photonic energy conversion phenomena is vital important. We take commercial piezoelectric LiNbO3 matrics as the example to interpret the detail mechanisms of energy conversions for the photon-generation through a native point defects study. It was found the Frenkel and Schottky type complex pairs as well as the antisite pair defects acting as energy harvesting and migration centers, which are very easy to form and active. It does to be the extra deep electron or hole traps levels near the valence or conduction band edge, respectively. That is the substantial energy reduction via a spontaneous equilibrium transformation from the complementarily charged individuals into agglomerated complexes. Such energy gain for both two processes turns to be independent to the variations of synthesis chemical potentials. In addition, the complex defects actually form independent to the variations of the chemical potentials. This leads to a coupling and exchange effect by them to continuously collect and transport host charges along the path via localized states to the deep recombination levels. The initiating energy barrier is small which ambient thermal stimulation or quantum tunneling can accomplish. The native sensitizers such as VNb2O5, VLiNbO3, NbLi are also the energy conversion centers to non-radiative resonant energy transfer onto the activator center at the Oi to transfer the energy into photon emissions. A generalized energy conversion mechanism has been unraveled in this work. This gives a solid theoretical reference for developing the mechanical-photonic energy conversion materials.

A dynamically tunable plasmonic multi-functional device based on graphene nano-sheet pair arrays

Dynamically tunable plasmonic multi-functional is particularly desirable for various nanotechnological applications. In this paper, graphene nano-sheet pair arrays separated by a substrate, which can act as a dynamically tunable plasmonic band stop filter with transmission at resonance wavelength lower than 1%, a high sensitivity refractive index sensor with sensitivity up to 4879 nm/RIU, figure of merit of 40.66 and a two circuit optical switch with the modulation depth up to 0.998, are proposed and numerically investigated. These excellent optical performances are calculated by using FDTD numerical modeling and theoretical deduction. Simulation results show that a slight variation of chemical potential of the graphene nano-sheet can achieve significant resonance wavelength shifts. In additional, the resonance wavelength and transmission of this plasmonic device can be tuned easily by two voltages owing to the simple patterned graphene. These studies may have great potential in fabrication of multi-functional and dynamically tunable optoelectronic integrated devices.

Insight into mechanical properties and thermoelectric efficiency of Zr2CoZ (Z = Si, Ge) Heusler alloys

We investigated the electronic, mechanical and thermoelectric properties of Zr2CoZ (Z = Si, Ge) Heusler alloys using the first-principles calculation. From the analysis of various elastic constants, the shear and Young’s moduli, Poisson’s ratio, the ductile nature of the alloys is predicted. Thermoelectric coefficients viz., Seebeck, electrical conductivity and figure of merit show Zr2CoZ alloys as n-type thermoelectric materials showing linearly increasing Seebeck coefficient with temperature. The value of total absolute Seebeck coefficients at 1200 K of Zr2CoSi and Zr2CoGe are 60 µV K−1 and 40 µV K−1 respectively mainly because of the existence of almost flat conduction bands along L to Г directions of high symmetry Brillouin zone. Further, the chemical potential variation of power factor confirms the n-type doping fruitful to increase their TE performance. The figure of merit achieves an upper-limit of 0.95 at 850 K and can favour their use for waste heat recovery at higher temperatures and thermoelectric spin generators.

Raman micro-spectroscopy as a viable tool to monitor and estimate the ionic transport in epithelial cells

The typical response to the lowering of plasma Na+ concentration and blood pressure in our body involves the release of aldosterone from the adrenal glands, which triggers the reabsorption of sodium in the kidney. Although the effects of aldosterone on this physiological mechanism were extensively studied in the past decades, there are still some aspects to be fully elucidated. In the present study, we propose for the first time a new approach based on Raman spectroscopy to monitor the ionic activity in aldosterone-treated A6 renal epithelial cells. This spectroscopic technique is capable of probing the cells through their thickness in a non-destructive and nimble way. The spectroscopic variations of the Raman bands associated to the O-H stretching of water were correlated to the variations of ionic concentration in the intracellular and extracellular fluids. The increase of Na+ concentration gradients was clearly visualized in the cytosol of aldosterone-treated cells. The enhancement of the Na+ current density induced by aldosterone was estimated from the variation of the ionic chemical potential across the intracellular space. In addition, the variation of the O-H Raman bands of water was used to quantify the cell thickness, which was not affected by aldosterone.

Investigating Transition Metal Chalcogenides for Efficient Oxygen Evolution Electrocatalysis: The Effect of Covalency and Directionality

Water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-air batteries, fuel cells, to solar-to-fuel energy conversion systems. Oxygen and Hydrogen evolution reaction (OER and HER respectively) are the two half reactions for water electrolysis, amongst which OER is the most challenging uphill process with a high electron count. Hence, designing efficient catalysts for OER process from earth-abundant resources has been one of the primary concerns for advancing this field. Recently transition metal chalcogenides has been identified as efficient OER electrocatalysts. We have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, and Ni-Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm2 [Ni3Se2 - 200 - 290 mV; Co7Se8 - 260 mV; FeNi2Se4-NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe2Se4 - 210 mV; NiCo2Se4 - 190 mV]. We have proposed the idea that one of the primary reasons these selenides show a much better OER catalytic activity is due to increasing covalency in the metal-selenium bond compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chemical potential around the transition metal center, specifically, lowering the Ni2+ --> Ni3+ oxidation potential (Ni3+ being the actually catalytically active species). In this presentation we will highlight the importance of this increasing covalency in enhancing the catalytic activity with the help of experimental evidence in selenide compositions ranging from binary Ni-selenides (Ni3Se2, NiSe2, NiSe), ternary mixed metal selenides (Ni-Co-Se, Ni-Fe-Se) as well as seleno-based molecular complex containing NiSe4 tetrahedral core. We will illustrate how the Ni(II) --> Ni(III) oxidation potential is indeed lowered within the selenide coordination compared to the oxide, in pure single crystals of the seleno-based coordination complex which is devoid of any surface impurities and adsorbates. We will also emphasize the lattice-plane-dependent catalytic activity through the example of electrodeposited NiSe2 which shows that if grown along the <311> direction exposing the Ni-rich terminating lattice plane, this catalyst can exhibit lowest overpotential at 10 mA/cm2 (140 mV) that has been reported so far for OER in alkaline medium. All of these selenide electrocatalysts has been characterized with pxrd, SEM, TEM, Raman, XPS, EDS and detailed electrochemical studies including LSV, CV, chronoameprometry, chronopotentiometry, determination of Faradaic efficiency, and ECSA. Through this presentation we will offer insight into possible reasons these selenides outperform most of the known OER electrocatalysts, which will hopefully initiate discussion and efforts to fully understand and utilize their full potential.

Influence of basicity and MgO/Al2O3ratio on the viscosity of blast furnace slags containing chloride

The viscosities of CaO–SiO2 –Al2 O3 –MgO–CaCl2 slags under conditions of CaCl2 = 0–10%, C/S = 0.90–1.30 and MgO/Al2 O3 = 0.40–0.67 have been experimentally measured to elucidate the effect of chlorine, basicity and MgO/Al2 O3 ratio on the viscous behavior of the blast furnace slag. Slag viscosity gradually increases with decreasing temperature, then sharply increases at the critical temperature, and it decreases with increasing chlorine content at temperatures over 1673 K. The critical temperature decreases from 1660 K to 1590 K with increasing chlorine content from 0% to 10% CaCl2 ; this may be attributed to the variation of chemical potential of primary solid phase caused by adding chloride. Slag viscosity diminishes with increase in basicity, while MgO/Al2 O3 ratio does not significantly affect the viscosity at temperatures higher than 1645 K. The tendency of the effect of basicity on the slag viscosity corresponds closely with that of corresponding CaO–SiO2 –Al2 O3 –MgO slags obtained from literature, while the trend of MgO/Al2 O3 ratio influence is distinct from that. The activation energy of chlorine-containing slags under the range of 182.8 kJ/mol to 213.8 kJ/mol generally decreases with increasing chlorine content, basicity and MgO/Al2 O3 ratio in slags. Due to the dual effect of the variation of polymerization and the primary phase by adding chloride, the MgO/Al2 O3 ratio almost has no influence on the viscosity of the chlorine-containing slags at higher temperatures.

Spatial and temporal variability in the potential of river water biofilms to degrade p-nitrophenol

In order to predict the fate of chemicals in the environment, a range of regulatory tests are performed with microbial inocula collected from environmental compartments to investigate the potential for biodegradation. The abundance and distribution of microbes in the environment is affected by a range of variables, hence diversity and biomass of inocula used in biodegradation tests can be highly variable in space and time. The use of artificial or natural biofilms in regulatory tests could enable more consistent microbial communities be used as inocula, in order to increase test consistency. We investigated spatial and temporal variation in composition, biomass and chemical biodegradation potential of bacterial biofilms formed in river water. Sampling time and sampling location impacted the capacity of biofilms to degrade p-nitrophenol (PNP). Biofilm bacterial community structure varied across sampling times, but was not affected by sampling location. Degradation of PNP was associated with increased relative abundance of Pseudomonas syringae. Partitioning of the bacterial metacommunity into core and satellite taxa revealed that the P. syringae could be either a satellite or core member of the community across sampling times, but this had no impact on PNP degradation. Quantitative PCR analysis of the pnpA gene showed that it was present in all samples irrespective of their ability to degrade PNP. River biofilms showed seasonal variation in biomass, microbial community composition and PNP biodegradation potential, which resulted in inconsistent biodegradation test results. We discuss the results in the context of the mechanisms underlying variation in regulatory chemical degradation tests.

Measurement of Chemical Potential in Bcy Electrolyte with Varying Thickness and Configuration Using Embedded Reference Electrodes

The correlation between internal chemical potential, and durability of anode-supported BCY (yttria-doped barium cerate) electrolyte cells, was investigated as a function of electrolyte thickness and configuration. Internal hydrogen and oxygen chemical potentials were measured using embedded Pt probes. As the electrolyte thickness decreased, the internal chemical potential became dominated by the gases surrounding the cathode, indicating that the thin BCY cell may be vulnerable to water vapor produced at the cathode during operation. BCY cells with BZY (yttria-doped barium zirconate) protecting at the cathode side (bi-layer cells) showed a small chemical potential variation through the electrolyte region close to the electrode side, indicating significant electronic conduction.Constant-current tests were conducted on thin (~ 10 µm) and thick (~ 35 µm) BCY single layer cells, and also on BCY-BZY bi-layer cells, especially under negative voltage conditions. Consistent with the results of the internal chemical-potential measurements, the thin BCY single layer cell showed a significant rate of degradation due to changes in BCY composition in the electrolyte and cathode, while the thick BCY single layer cell showed much better durability, regardless of the sign of cell voltage. The bi-layer cell was stably operated under any severe operating conditions, because of the BZY protecting layer against water vapor’s attack and its significant electronic conduction close to the cathode/electrolyte interface. Thus, the present work shows the effect of BCY electrolyte thickness and configuration on the durability of BCY based cells, in terms of their internal chemical potential.

Topological phase transition in a ladder of the dimerized Kitaev superconductor chains**Project supported by the National Natural Science Foundation of China (Grant No. 11274102), the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-11-0960), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20134208110001).

We investigate the topological properties of a ladder model of the dimerized Kitaev superconductor chains. The topological class of the system is determined by the relative phase θ between the inter- and intra-chain superconducting pairing. One topological class is the class BDI characterized by the ℤ index, and the other is the class D characterized by the ℤ2 index. For the two different topological classes, the topological phase diagrams of the system are presented by calculating two different topological numbers, i.e., the ℤ index winding number W and the ℤ2 index Majorana number ℳ, respectively. In the case of θ =0, the topological class belongs to the class BDI, multiple topological phase transitions accompanying the variation of the number of Majorana zero modes are observed. In the case of θ =π/2 it belongs to the class D. Our results show that for the given value of dimerization, the topologically nontrivial and trivial phases alternate with the variation of chemical potential.

Membrane fouling in a membrane bioreactor: High filtration resistance of gel layer and its underlying mechanism

A membrane bioreactor (MBR) was continuously operated to investigate mechanisms of fouling caused by the gel layer in this study. Agar was used as a model foulant for gel layer formation, and filtration resistance of gel layers was systematically assessed. The results showed that gel layer possessed unusually high specific filtration resistance (SFR) and high measured porosity as compared with cake layer. Current knowledge cannot explain the contradiction between high filtration resistance and high porosity of gel layer. A new fouling mechanism based on Flory-Huggins theory was then proposed. Filtration resistance of agar gel layer was found to be independent of pH and ionic strength, but linearly increase with gel thickness. The results are accordant with the mechanism deductions. Simulation of the mechanism model showed that the filtration resistance induced by mixing chemical potential variation was comparable to the experimental data of filtration resistance of agar gel layer, indicating that the proposed mechanism is the predominant mechanism responsible for the high filtration resistance of gel layer. The proposed mechanism was further verified from the bound water viewpoint.

Three-Dimensional Analysis of Coarsening Dynamics in Porous Materials for Electrochemical Energy Conversion and Storage: Direct Measurement and Visualization of Changes in Local Surface Curvature

High operating temperature affords solid oxide fuel cells (SOFCs) fuel flexibility, favorable kinetics, enhanced transport properties and high quality heat for secondary thermodynamic cycles.1 Elevated temperatures, however, present challenges to ensuring cell durability.2 Coarsening of nickel in the Ni-YSZ anode is one such challenge that can lead to significant performance degradation. The fundamental driving force Δμ for coarsening phenomena is given by Eq. 1.3 The expression, which assumes isotropic interfacial energy, indicates that the chemical potential μ of a curved interface differs from that of a flat interface μ 0 by the factor VmγH, where H is mean curvature, γ interfacial energy and Vm molar volume. Δμ = μ - μ 0 = VmγH (1) Eq. 1 makes evident that variations in interface curvature, i.e., interface shape, directly correspond to variations in chemical potential. Furthermore, it follows from Eq. 1 that microstructural coarsening is fundamentally related to variations in interface shape. The link between interface shape and coarsening propensity is well known and methods have been developed to directly measure interfacial curvature distributions for complex morphologies in 3-D.4,5 In this work, these techniques are applied to 3-D images obtained by x-ray nanotomography to study coarsening in microstructures obtained from Ni-YSZ solid oxide fuel cell anodes aged for varying lengths of time. This work builds on a previous characterization of the same samples.6 The curvature measurements collected suggest that a combination of coarsening and morphological instability, which leads to channel pinch-off, severely diminish the connectivity of the anode’s Ni network and, in addition, lead to a significant loss of both nominal and effective triple-phase boundary (TPB) density. Both the loss of connectivity and TPB density coincide with cell performance degradation that was observed in the aging experiment7 from which the anode samples were taken. References Singhal, S. C.; Kendall, K. High Temperature Solid Oxide Fuel Cells, Elsevier, 2003.Yokokawa, H.; Tu, H.; Iwanschitz, B.; Mai, A. Fundamental mechanisms limiting solid oxide fuel cell durability. J. Power Sources 2008, 400-412.Voorhees, P. W. The Theory of Ostwald Ripening. J. Stat. Phys. 1985, 231-252.Glicksmann, M. E.; Voorhees, P. W. Ostwald Ripening and Relaxation in Dendritic Structures. Metall. Trans. A, 1984, 995-1001.Mendoza, R.; Savin, I.; Thornton, K.; Voorhees, P. W. Topological complexity and the dynamics of coarsening. Nat. Mater., 2004 385-388.Nelson, G. J.; Grew, K. N.; Izzo, J. R. Jr.; Lombardo, J. J.; Harris, W. M.; Faes, A.; Hessler-Wyser, A.; Van herle, J.; Wang, S.; Chu, Y. S.; Virkar, A. V.; Chiu, W. K. S. Three-dimensional microstructural changes in the Ni-YSZ solid oxide fuel cell anode during operation. Acta Mater., 2012 3491-3500. 7. Faes, A.; Hessler-Wyser, A.; Presvytes, D.; Vayenas, C. G.; Van herle, J. Nickel-Zirconia Anode Degradation and Triple Phase Boundary Quantification from Microstructural Analysis. Fuel Cells, 2009 841-851. Acknowledgements Financial support from the National Science Foundation (Award CBET-1134052) and an Energy Frontier Research Center on Science Based Nano-Structure Design and Synthesis of Heterogeneous Functional Materials for Energy Systems (HeteroFoaM Center) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award DE-SC0001061) is gratefully acknowledged. X-ray nanotomography was performed with Dr. Steve Wang at the Advanced Photon Source supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. Ni-YSZ samples were provided by MER Dr. J. Van herle (Ecole Polytechnique Federale de Lausanne, Switzerland).

Investigation of the tunable plasmonic whispering gallery mode properties for graphene monolayer nanodisk cavities

Tunable graphene plasmonic whispering gallery mode nanodisks formed by nanoscale chemical potential variation on an infinite freestanding graphene monolayer at near-infrared wavelength range are proposed and numerically investigated in this paper. The Q-factor of a high-order whispering gallery mode of 136 and an extremely small mode volume of 4.8×10−7 (λ0/n)3 with a large Purcell factor of 1.7×108 is achieved in a cavity radius of 10nm. This graphene based nanodisk cavity structure with an ultrasmall mode volume and large Purcell factor is a promising candidate for high efficiency plasmonic emitting sources, filters, or a key component in the fields of transformation plasmonics and plasmonic integrated circuits technique in the future.

Distortion of surface plasmon polariton propagation on graphene due to chemical potential variation

The variation of graphene chemical potential owing to surface plasmon polariton excitation and its influence on the propagation properties of the latter is systematically examined in this paper. Although the chemical potential is controlled via a constant electric field bias, the excitation of the highly confined surface wave can considerably affect it, thus disrupting the wave natural propagation. To this aim, the propagation properties of the surface wave are extracted to reliably estimate the aforesaid distortion effect with regard to frequency. Numerical results, obtained in terms of an accurate finite-difference time-domain scheme, certify this interesting convention. Furthermore, the electrodynamic forces on the free electrons of the graphene layer are calculated to justify the electrostatic assumption.

Modulation of mechanical resonance by chemical potential oscillation in graphene

The classical picture of the force on a capacitor assumes a large density of electronic states, such that the electrochemical potential of charges added to the capacitor is given by the external electrostatic potential and the capacitance is determined purely by geometry. Here we consider capacitively driven motion of a nano-mechanical resonator with a low density of states, in which these assumptions can break down. We find three leading-order corrections to the classical picture: the first of is a modulation in the static force due to variation in the internal chemical potential, the second and third are change in static force and dynamic spring constant due to the rate of change of chemical potential, expressed as the quantum (density of states) capacitance. As a demonstration, we study a capacitively driven graphene mechanical resonators, where the chemical potential is modulated independently of the gate voltage using an applied magnetic field to manipulate the energy of electrons residing in discrete Landau levels. In these devices, we observe large periodic frequency shifts consistent with the three corrections to the classical picture. In devices with extremely low strain and disorder, the first correction term dominates and the resonant frequency closely follows the chemical potential. The theoretical model fits the data with only one adjustable parameter representing disorder-broadening of the Landau levels. The underlying electromechanical coupling mechanism is not limited the particular choice of material, geometry, or mechanism for variation in chemical potential, and can thus be extended to other low-dimensional systems.