FL - 4th International Conference
Mass, Charge and Spin Transport in Inorganic Materials: Fundamentals to Devices
Session FL-1 - Mass and Charge Transport Mechanisms
FL-1:IL01 Quantum Spintronics: Engineering and Manipulating Atom-like Spins in Semiconductors
D.D. AWSCHALOM, Institute for Molecular Engineering, University of Chicago, Chicago, IL, USA
Semiconductor defects, while generally considered undesirable in traditional electronic devices, can confine isolated electronic spins and are promising candidates for solid-state quantum bits (qubits). Alongside research efforts focusing on nitrogen vacancy centers in diamond, an alternative approach seeks to identify and control new spin systems with an expanded set of technological capabilities, a strategy that could ultimately lead to "designer" spins with tailored properties for future quantum information processing. We discuss recent experimental results identifying such spin systems in various crystal polymorphs of silicon carbide. Using infrared light at near-telecom wavelengths and gigahertz microwaves, we show that these spin states can be coherently addressed at temperatures ranging from 20 K to room temperature. Long spin coherence times allow us to measure magnetic dipole interactions between spin ensembles in inequivalent lattice sites of the same crystal. Since the inequivalent spin states have distinct optical and spin transition energies, these interactions could lead to engineered dipole-coupled networks of separately addressable qubits. These results make SiC a powerful platform for applications that merge quantum degrees of freedom with classical technologies.
FL-1:IL02 Local Investigation of Interference and Quantum Coherence in Ballistic Nanostructures Using a Scanning Gate
A.A. KOZIKOV, C. RÖSSLER, T. IHN, K. ENSSLIN, C. REICHL, W. WEGSCHEIDER, Solid States Physics laboratory, ETH Zürich, Zürich, Switzerland; D. Weinmann, IPCMS, Université de Strasbourg, CNRS UMR 7504, Strasbourg, France
We have measured local transport through a stadium formed by two ballistic constrictions fabricated on a GaAs/AlGaAs heterostructure at 300 mK as a function of the position of a biased metallic tip. We have observed conductance fluctuations inside the stadium and a set of unexpected fringe patterns at the constrictions and in the center of the stadium. We also imaged the transition from electrostatic to magnetic depopulation of subbands in a perpendicular magnetic field. The fringes are interpreted as standing wave patterns between the AFM tip and the top gates leading to quantized conductance plateaus. The fringes form checkerboard patterns, which precisely allows determining the number of transmitted modes in each of the tip-gate constrictions. By placing the tip in the center of the stadium a ring is formed. The number of transmitted modes in the arms of the ring is determined from the checkerboard pattern. Magnetoresitance measurements show periodic conductance fluctuations, the Aharonov-Bohm effect.
In the quantum Hall regime moving the tip inside the constriction brings edge channels closer together, which are backscattered one by one. This is seen in spatially resolved images as wide conductance plateaus, each of which corresponds to its own local filling factor.
FL-1:IL04 Recent Advances in the Theory and Computer Modelling of Interdiffusion in Alloys/Intermetallics and Ionic Compounds
G.E. MURCH, I.V. BELOVA, A.V. EVTEEV, E.V. LEVCHENKO, University of Newcastle, Callaghan, NSW, Australia; P. SOWA, D R. KUZUBSKI, Jagiellonian University, Krakow, Poland
An overview of some recent advances in interdiffusion in binary alloys/intermetallics and ionic compounds will be presented. We cover kinetic topics including the extended Darken-Manning equation in multicomponent alloys, the origin of the vacancy-wind effect in alloys/intermetallics (and the equivalent phenomenon in ionic compounds), the effect on interdiffusion of non-equilibrium vacancy concentrations, and atomic mechanisms of interdiffusion in intermetallics. We also discuss ways of addressing the long-standing problem of performing correct computer simulations of interdiffusion, with examples including interdiffusion in the intermetallic NiAl with the formation of structural vacancies and interdiffusion in core-shell nanoparticles of Ni-Al and Ti-Al.
FL-1:IL05 Mobility of Li Ions in Solids
P. HEITJANS, Leibniz Universität Hannover, Institute of Physical Chemistry and Electrochemistry, Hannover, Germany
Diffusion of lithium has recently gained enormous interest due to the search for better materials for Li ion batteries. However, fundamental research on Li ion mobility, comprising questions about, e.g., the dimensionality of diffusion or the influence of structural disorder, has been intensified as well.
One of the most versatile experimental methods to obtain detailed insights into ionic diffusion in solids is nuclear magnetic resonance (NMR) utilizing spin bearing nuclei, inherent or introduced in the sample. In the case of Li ion conductors these are 6Li and 7Li as well as beta-radioactive 8Li (t1/2=0.8 s) nuclei (beta-NMR) 1.
The various NMR techniques give access to Li jump rates over more than ten decades and the corresponding activation barriers. In systems with a large fraction of interfacial regions, such as nanocrystalline Li ion conductors, the heterogeneous dynamics in the bulk and the interfaces can be discriminated 2.
The examples presented include studies of Li diffusion in potential solid electrolyte, cathode and anode materials which often simultaneously serve as model systems for fundamental diffusion aspects3-6. Besides NMR techniques, comprising the measurement of line shapes, spin-lattice relaxation rates, spin-alignment echo decay rates and site exchange rates by 2D MAS NMR, complementary methods like impedance spectroscopy, mass spectrometry and neutron scattering are being used for the diffusion studies.
1. P. Heitjans et. al., in ‘Diffusion in Condensed Matter’, Springer (2005), p.367.
2. P. Heitjans et al., MRS Bull. 34 (2009) 91.
3. M. Wilkening et al., J. Phys. Chem. C 114 (2010) 19083.
4. A. Duevel et al., J. Phys. Chem. C 116 (2012) 15192.
5. A. Kuhn et al., J. Am. Chem. Soc. 133 (2011) 11018.
6. J. Langer et. al., Phys. Rev. B 88 (2013) 094304.
FL-1:IL07 Effects of Elastic Strain on Oxygen Transport and Reduction Kinetics in Oxides
B. YILDIZ1, ZHUHUA CAI1, A. KUSHIMA1, QIYANG LU1, N. TSVETKOV1, JEONG WOO HAN1, YAN CHEN1, J. FLEIG2, M. KUBICEK2, 1Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA; 2Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria
In this talk, we will discuss recent work that probes quantitatively the mechanisms by which elastic strain impacts surface reactivity and diffusion kinetics in fluorite and perovskite oxides. Computationally, using ab initio and atomistic simulations, we discovered that lattice strain can accelerate the ionic transport in 8%Y2O3-ZrO2 by reducing the ion migration energy barriers. Combining surface chemical characterization on model thin films with ab initio modeling, we demonstrated for the first time that tensile lattice strain favors oxygen exchange kinetics on both the oxygen-deficient (La,Sr)CoO3-d and (La,Sr)MnO3-d and the oxygen-excess Nd2NiO4+d by impacting the energies of oxygen adsorption and dissociation, oxygen vacancy formation, oxygen diffusion, cation segregation and the electron transfer process. The favorable impact of tensile lattice strain on these elementary reactions was validated at the collective level by quantifying the oxygen surface exchange and diffusion kinetics with isotope exchange measurements on (La,Sr)CoO3-d. These results together put forth elastic strain to be an important parameter that couples impressively to the kinetics of charge transport and reactivity in functional oxides.
FL-1:IL08 Direct Evaluation of Electrochemical Reactions in Solid Oxide Fuel Cells under Operation
K. AMEZAWA, Y. FUJIMAKI, T. NAKAMURA, K. NITTA, Y. TERADA, F. IGUCHI, H. YUGAMI, T. KAWADA, Tohoku University, Sendai, Japan
Electrode reactions in solid oxide fuel cells (SOFCs) are gas reactions at interfaces consisting of electrode/electrolyte/gas or electrode/gas phases. In order to clarify reaction mechanisms and to improve the performance of SOFC electrodes, it is indispensable to understand chemical/physical states of the interfaces. For this purpose, we have established novel in situ analytical techniques using X-ray absorption spectroscopy (XAS), which could enable us to investigate electronic structures of SOFC electrolytes and electrodes at elevated temperatures while controlling atmospheric conditions and passing electric current. Particularly, by applying the high flux synchrotron X-ray beam, in situ measurements with a high special resolution (< 1 micrometer) and/or a high time resolution (< 1 second) became available. In this contribution, our recent results on in situ analysis of SOFC electrodes under operation by using above-mentioned techniques will be presented. Throughout such measurements, we could directly evaluate oxygen potential distribution in SOFC electrodes.
FL-1:IL09 Ionic and Electronic Transport under Chemical Potential Gradients
M. MARTIN, Institute of Physical Chemistry, RWTH Aachen University, Aachen, Germany
In oxides which are exposed to thermodynamic potential gradients, i.e. gradients of chemical potentials, electrical potential, temperature, or pressure, transport processes of the mobile components occur. These transport processes and the coupling between different processes are not only of fundamental interest but also the basis for many applications, such as solid oxide fuel cells, oxygen permeation membranes, resistive switching devices etc. In addition, ionic and electronic transport processes may be the origin of degradation processes, such as kinetic demixing, kinetic decomposition, and changes in the morphology of the material . We will discuss the basic phenomena and applications as well.
 M. Martin, Pure Appl. Chem. 75 (2003) 889-903.
FL-1:IL10 Electron Quantum Transport in Disordered Graphene
I. DERETZIS, A. LA MAGNA, CNR-IMM, Catania, Italy
We theoretically review the electronic transport properties of doped and defected graphene systems in the quantum coherent regime. By varying both the width and the length of two-terminal devices from the nano- to the micro-scale, we study localization phenomena, the formation of pseudo-gaps, transport length scales and conductance characteristics for numerous defect/impurity concentrations. When the lateral confinement is strong (i.e. in the case of graphene nanoribbons), we show that localization due to scattering is strongly energy dependent, and this fact leads to the appearance of conductance quasigaps in the spectral region of the resonance states. Moreover, conductance fluctuations are very large in the quasigap regions, indicating significant electrical disorder. We then focus on the conductance variations when gradually passing from the quasi-1D limit (graphene nanoribbons) to the 2D case (graphene). We finally discuss how the resultant conduction characteristics could be exploited for the fabrication of innovative graphene-based nanoscale devices.
FL-1:IL11 Mass Transport in Grain Boundaries: Mechanism and Controversial Subjects
B. BOKSHTEYN, National University of Science and Technology “MISIS”, Moscow, Russia
What is the mechanism of grain boundary diffusion (GBD)? That is a key question which has not a clear answer today. Possibly, there is no unique answer at all.
The prevailing paradigm of 1970th-1980th was there does not exist a fundamental difference between grain boundary (GB) and volume diffusion. Vacancies were believed to be the main defects in GBs which moved by exchanges with single atoms .
Due to the atomistic computer simulations of the last decade (Yu. Mishin and coworkers), GBD is profoundly different from the volume diffusion. It is characterized by a large multiplicity of mechanisms, including collective jumps of two or more atoms up to formation of the liquid “drops” at high enough temperatures.
In this lecture the possible thermodynamic, kinetic and atomistic (computer modeling) methods of problem decision was observed.
The special attention is devoted to the thermodynamic driving forces of GBD, enthalpies of formation and the temperature dependence of different defects, the role of chemical interaction of atoms in GBs, the effects of nonlinear GB segregation, internal stresses, stresses and energy gradient , associates formation, phase transitions in GBs on grain boundary diffusion, collective atomic jumps (“long vacancy” jumps), etc.
FL-1:IL12 Capillary-driven Interdiffusion Along Interphase Boundaries in Solids
E. RABKIN, D. AMRAM, L. KLINGER, Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel
We consider the size and shape evolution in nanocrystalline and nano-particulate solids controlled by diffusion along the interphase boundaries between two immiscible, non-reactive phases. Like in the case of surface diffusion, the atomic diffusion flux along the interphase boundary is driven by the gradient of chemical potential of the atoms at the interface. Yet while in the case of surface diffusion this chemical potential is a local function of surface curvature and surface energy, in the case of interphase boundary the chemical potentials of the components depend on the overall geometry of the system and on boundary conditions at the triple lines. We suggest a variational method of calculating the chemical potentials at the interphase boundary. This method relies on calculating the variations of the total energy of the system caused by infinitesimal relative translations and rotations of the two solid phases abutting the interface.
Our theoretical models are illustrated by the experimental data on sintering of model Cu-W agglomerates, on phase transformations in the nanoparticles of Au-Fe alloys, and on thermal grooving in thin Ni films with "mazed bicrystal" microstructure.
FL-1:L14 Formalism for the Measurement of Tracer Diffusion and Interdiffusion Coefficients in a Single Experiment
I.V. BELOVA, G.E. MURCH, University of Newcastle, NSW, Australia; N.S. KULKARNI, Oak Ridge National Laboratory, TN, USA; Y. SOHN, University of Central Florida, Fl, USA
The capability of SIMS measurements of different isotopes of the same element has generated the need for a new formalism suitable for analyzing interdiffusion when different isotopes of the elements are present. The basis for a formalism for interdiffusion involving the atomic components and their available isotopes has recently been developed . It is generalized further here. The measured concentration profiles can provide a very significant amount of new diffusion information making it possible to measure tracer diffusion coefficients as well as interdiffusion coefficients in a single experiment. The main condition for the successful experimental application of this analysis is in having different abundance(s) of the isotopes at each end of the diffusion couple. This can also be efficiently achieved by implementing a 'sandwich' type of interdiffusion couple with a thin layer of the isotope(s) . Using the new formalism, the tracer diffusion coefficient of the corresponding isotope can be obtained as a function of the composition. The resulting formalism is shown to be very general and independent of kinetic models for binary systems.
 I V Belova, N S Kulkarni, Y H Sohn and G E Murch, Phil. Mag., 93, pp 3515-3526 (2013).
 J.R. Manning, Phys. Rev. A 116 (1959) p. 69.
FL-1:L15 Vacancy Diffusion under a Stress and Kinetic of Nanovoid Growth in Cubic Metals
A.V. NAZAROV, National Research Nuclear University (MEPhI), Moscow, Russia; A.A. MIKHEEV, Moscow State University of Design and Technology, RUSSIA; A.G. ZALUZHNYI, SSC RF Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia
Elastic fields, generating by defects of the structure, influence the diffusion processes. It leads to the alteration of the phase transformation kinetic. One of the chief aims of our work is to obtain general equations for the diffusion fluxes under strain that give the possibility for using these equations at low temperatures, as in this case the strain influence on the diffusion fluxes is manifested in maximal degree. Our approach takes into consideration, that the strains can alter the surrounding atom configuration near the jumping one and consequently the local magnitude of the activation barrier and a rate of atom jump. The rates of atom jumps in different directions define the flux density of the vacancies. Now we take into account, that strain values are different in the saddle point and in the rest atom position, in differ from our consideration that was done by us earlier. As a result in the development of our approach the general equations for the vacancy fluxes are obtained for fcc and bcc metals. In our presentation we are going to discuss the main features of the theory of diffusion under stress and its applications. In particular we examine how elastic stress, arising from nanovoids, influence the diffusion vacancy fluxes and the growth rate of voids in metals.
FL-1:IL17 Percolation of Electronic and Ionic Carrier in Single Phase Materials
S. YAMAGUCHI1, DONGYOUNG KIM2, T. TSUCHIYA3, S. MIYOSHI1, Y. SHIBUYA1, 1Dept. Materials Engg., School of Engg., The University of Tokyo, Tokyo, Japan; 2Samsung Research Center, Korea; 3MANA, NIMS, Japan
A heavily non-linear percolation conductivity of electronic and ionic carriers have been found in recent study on doped perovskite oxide systems: when a perovskite oxides with its chemical formula of A2+B4+O3 are doped with acceptor dopant, MA3+, positively charged electron holes or ionic carriers such as Vö or H･i are formed and strongly localized to dopant. Upon formation of local conduction network of such oxygen octahedra with dopant by increased concentration of dopant, a percolation conductivity prevails. The authors found such percolation conductivity in the Fe-doped BaZrO3 system, which exhibits typical percolation conductivity features of non-linear conductivity against dopant concentration and a knee in the Arrhenius plot of conductivity with apparent activation energy variation at the threshold composition, which is significantly lower than theoretical critical threshold for the cubic site percolation system. On the other hand, none of typical percolation behavior has never been found in heavily doped Pr-BaZrO3 nor Fe-doped SrTiO3 system, but the transition of conductivity dependence from linear to cubic at fairly low critical threshold. The authors propose here a new site percolation model specifically targeting perovskite to cover all these features.
FL-1:IL18 Atomistic Modelling of Diffusion Processes of Light Elements in Metals
J. ROGAL, R. DRAUTZ, ICAMS, Ruhr-Universität Bochum, Bochum, Germany
The mobility of light elements and their segregation behaviour towards point and extended defects play an important role in understanding the mechanical properties of metals. In iron and steels structural defects such as vacancies, grain boundaries, and dislocations can, e.g., trap hydrogen, and a local accumulation of hydrogen at these defects can lead to a degradation of the materials properties. An important aspect in obtaining insight into this so-called hydrogen embrittlement on the atomistic level is to understand the diffusion of hydrogen in these materials.
Modelling the diffusion of hydrogen requires atomistic simulations over extended time scales that go far beyond what can be reached with regular molecular dynamics simulations. Here, we apply a kinetic Monte Carlo (KMC) approach combined with highly accurate ab initio calculations to model hydrogen diffusion in BCC iron in the presence of point and extended defects. All input data to the KMC model, such as available sites, solution energies, and diffusion barriers are obtained using density functional theory. In particular we investigate the effect of different microstructures on the distribution and mobility of hydrogen.
FL-1:L20 Conductivity Manipulation of Metal Single Crystals by Grain Boundary Control and Impurity Doping
SE-YOUNG JEONG, Department of Cogno-Mechatronics Engineering, Pusan National University, Miryang, Republic of Korea; J.Y. KIM, C.-R. CHO, Department of Nano Fusion Technology, Pusan National University, Miryang, Republic of Korea; M.-W. OH, Fundamental and Creativity Research Division, Korea Electrotechnology Research Institute, Changwon-si, Republic of Korea; S. LEE, The Institute of Basic Science, Korea University, Seoul, Republic of Korea; Y.C. Cho, Crystal Bank Research Institute, Pusan National University, Miryang, Republic of Korea; J.-H. YOON, Busan center, Korea Basic Science Institute, Busan, Republic of Korea; G.W. LEE, Korea Research Institute of Standards and Science & Department of Science of Measurement, University of Science and Technology, Daejeon, Republic of Korea; C.H. PARK, Department of Physics Education & RCDAMP, Pusan National University, Busan, Republic of Korea
In this study, we showed an enhancement in electrical conductivity for metal single crystals with impurity addition. Highly crystalline, metal single crystals were grown using the Czochralski method. Grain-free single-crystal copper and silver exhibited higher conductivity (by as much as 10%) compared with standard conductivity values for these metals. Simultaneous heat and pressure treatments were used to enhance the crystallinity, which further improved the conductivity by 12-14%. The enhanced crystal quality significantly affected the accuracy of the measurement system. We then added impurities to the host metal single crystal; incorporation of the impurities into the host metal affected the electron-phonon interactions. Interestingly, we observed anomalous behavior in which the resistivity decreased for small levels of doping. A metal mixed crystal of Ag, with 3 mol% Cu, exhibited an electrical resistivity of 1.35 micro-ohm cm, the lowest resistivity ever reported at room temperature. To explain the abnormal behavior, a variety of mechanisms were evaluated, including the change in the electronic structure and phonon density of states (PDOS). Consequently, we speculate that additional impurities affect the electron-phonon coupling constant.
Session FL-2 - Role of Transport in Materials Development, Properties and Behaviour
FL-2:IL01 Grain Boundary Growth in Evolving Microstructure
A. ZIGELMAN, A. NOVICK-COHEN, Department of Mathematics, Technion-IIT, Haifa, Israel; A. VILENKIN, The Rachah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel
Grain growth depends on the motion of the grain boundaries, which have been assumed since the 1956 paper by Mullins to be governed by mean curvature motion, V=AK, although clearly additional effects may be present. In order to make an accurate connection between theory and experiment, it is necessary to have an accurate estimate for A, the reduced mobility coefficient. A classical tool in this direction are bi-crystals in the half-loop geometry as developed by Shvindlerman et. al. In such bi-crystals a single grain boundary is present whose evolution may be roughly described by the grim reaper solution of the mean curvature motion equation in the plane. However, all real physical systems are actually 3D rather than 2D, and thus there are additional effects which influence the measurements and perturb the grim reaper solution. Some perturbed grim reaper solutions are discussed, and how they influence grain boundary mobility measurements.
FL-2:IL02 Effects of Strain, Orientation, and Microstructure on Oxygen Reduction in SOFC Cathode Materials
M. YAN, J. INFANTE, P.H. LEE, L. YAN, R. CHAO, K.R. BALASUBRAMANIAM, P. A. SALVADOR, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
Surface engineering of electrodes, e.g., infiltration of nanoscale catalysts, holds promise for SOFC performance improvement. Yet, the surface properties of oxides in SOFC conditions are poorly understood. To build correlations between microstructural features and oxygen surface exchange properties, thin flat films of (La,Sr)MnO3, (La,Sr)CoO3, and La2NiO4 were deposited on perovskite, fluorite, rock-salt, and/or Ruddlesden-Popper substrates and characterized structurally and electrically. Chemical surface exchange coefficients, kchem, were measured using electrical conductivity relaxation as function of substrate, orientation, thickness, and epitaxy. Strain states and extended defect populations are demonstrated to influence strongly the magnitude and activation energy (EA) of kchem. Importantly, the fastest exchange rates in SOFC conditions were for films under tensile strains. We demonstrate that significant departures from bulk or ceramic values are observed for the surfaces of epitaxial films and will discuss their implications for SOFC improvement. We also discuss the differences between the cation-deficient (LSM), oxygen-deficient (LSC), and oxygen excess (LNO) materials, with regard to role of microstructural features on oxygen exchange.
FL-2:IL03 Wetting Phase Transition in Grain Boundaries
B.B. STRAUMAL1, 2, B. BARETZKY2, 1Institute of Solid State Physics Russian Academy of Sciences, Chernogolovka, Russia; 2Karlsruher Institut für Technologie (KIT), Institut für Nanotechnologie, Eggenstein-Leopoldshafen, Germany
The grain boundaries can be wetted not only by a liquid phase (melt) but also by a second solid or amorphous phase. If the second (wetting) phase is solid, the contact angle is not obliged to decrease with increasing temperature. If the second (wetting) phase is amorphous, it surrounds the crystalline grains preventing them to contact each other. Such phenomenon was observed in the nanocrystalline ZnO films. Even the wetting of "grain boundaries" in two different amorphous phases can be considered. The as-cast Ni50Nb20Y30 alloy was coarse-grained and contained mainly NiY phase and also NbNi3, Ni2Y, Ni7Y2 and Ni3Y phases. High pressure torsion completely changes the structure. The sample after SPD contained two glassy phases and two other nanocrystalline NiY and Nb15Ni2 phases. Bright field TEM micrographs show the fine 5-10 nm round bubbles of bright Y-rich amorphous phase which are embedded in the darker Nb-rich "grains". In turn, the Nb-rich dark grains are separated by the few nm thick layers of the bright Y-rich amorphous phase. This structure permits one to speak about the mutual wetting of "grain boundaries" in both amorphous phases.
Session FL-3 - Role of Mass and Charge Transport in Application Engineering
FL-3:IL01 Graphene for Low Energy Applications
ZHIHONG CHEN, Purdue University, West Lafayette, IN, USA
Power consumption has become the most pressing challenge in today's electronics world. Both tunneling FET and spin logic devices are widely discussed for low energy post-CMOS applications. Graphene with its unique material properties has been identified as an exceptional channel material for both device concepts. It has been experimentally challenging to realize a tunneling FET with a high tunneling current and a steep subthreshold slope simultaneously. It is understood that the band gap and the effective mass of the channel material and the screening length across the tunneling barrier need to be minimized for a high transmission probability. Bilayer graphene with a sizable bandgap is an appealing material for use in tunneling FETs due to its small effective mass and high mobility. I will show fabrication and measurements of bilayer graphene based tunneling FETs. All spin logic proposes to use pure spin current to carry information through a spin coherence channel and transfer that to an output by spin transfer torque. Multi-layer graphene is an ideal channel material due to its long spin diffusion length. I will present the first experimental measurement of spin transfer torque assisted by an external magnetic field in graphene lateral non-local spin valve devices.
FL-3:IL02 Effects of Lattice Strain on Oxide Ion Diffusivity in Pr2NiO4 Doped with Cu and Ni
T. ISHIHARA, J. HOYODO, J. DRUCE, S. IDA, J.A. KILNER, International Institute for Carbon Neutral Energy Research, Kyushu University, Fukuoka, Japan
Mass transport property and electronic property in nano-size materials are attracting much interest, because such nanosize effects have a possibility to increase the performance of the electrochemical solid state devices such as Solid Oxide Fuel Cells (SOFCs). In order to induce the tensile strain, Cu- and Ga-doped Pr2NiO4+δ (PNCG) with gold particles was chosen because of the relationship between their thermal expansion coefficients (α(PNCG) = 13.5-13.8, α(Au) = 14.2 (x10-6 K-1)).
It was found that tensile strain introduced by Au dispersion was enhanced the electronic and oxide ionic conductivity, and that this enhancement was strongly related to the changing of interstitial oxygen nonstoichiometry. Enhancement of mass transport property was observed at all temperatures. At high temperature only increased interstitial oxygen amount was the reason for increase in oxygen permeation rate, but enlarged oxygen ion mobility by tensile strain was related to the oxygen permeability at low temperature. This result might be related to significant tensile strain at low temperature because thermal tensile strain might relax at sintering temperature. In this report, effects of Au addition on oxygen diffusivity was further discussed based on tracer diffusion technology.
FL-3:IL03 Role of Defects in Non-equilibrium Impurity Transport Applied to Semiconductor Processing
L. PELAZ, M. ABOY, I. SANTOS, P. LÓPEZ, L. MARQUES, Universidad de Valladolid, Valladolid, Spain
Ion implantation is the method traditionally used to introduce dopants in semiconductors for junction formation in logic and memory devices, and recently also in solar cells fabrication. The introduction of energetic ions produces atomic displacements leading to defect concentrations well above the equilibrium values. During subsequent annealing, dopant-defect interactions cause enhanced dopant diffusion and formation of dopant-defect complexes that makes it difficult the realization of low resistivity ultra shallow junctions required in nanometric semiconductor devices. The variety of defects and their interaction with dopants set a complex modeling scenario with a large number of reactions and parameters to be defined. In this work we will present multiscale atomistic simulations to understand the mechanisms of defect generation, their structural and energetic properties and their role in dopant diffusion and activation in semiconductor processing. The understanding of the physics involved in device fabrication provides clues for process optimization.
FL-3:L04 Spin Orientation and Transport in Germanium: Hole and Electron Spin Diffusion Lengths
M. CANTONI, C. RINALDI, S. BERTOLI, R. BERTACCO, CNISM and LNESS - Dipartimento di Fisica, Politecnico di Milano, Como, Italy
Germanium-based spintronic devices have recently deserved great attention, thanks to the compatibility with Silicon-based electronics, the large carrier mobility, the possibility of optical spin pumping and electrical spin manipulation. Moreover, because of the inversion simmetry, the D'yakonov-Perel' spin relaxation mechanism is inhibited in Germanium, leading, in principle, to a larger spin diffusion length than in the non-centrosymmetric GaAs.
In order to characterize the spin diffusion length of carriers in Germanium, in this contribution we report on optical and electronic measurements on epitaxial Fe/MgO/Ge and CoFeB/MgO/Ge heterostructures.
Optical measurements on Fe/MgO/Ge(001) spin-photodiodes [Adv. Mat. 24, 3037 (2012)] in the wavelenght range 400nm-1550nm revealed spin diffusion lengths of about 1 micron for electrons, coherently with literature and confirmed by non-local and Hanle measurements on CoFeB/MgO/Ge devices; for holes, instead, a spin diffusion length of about 200 nm has been extracted, ten times larger than expected, paving the way to germanium-based spintronic devices where holes, instead or in addition to electrons, are employed as spin carriers.
FL-3:IL05 Mass and Charge Transport in Solid Oxide Fuel Cells
T. KAWADA, Tohoku University. Sendai, Japan
Oxide ion transport is obviously a key feature of the electrolyte and electrode materials of solid oxide fuel cells (SOFC). Bulk and interface conductance of oxide ion directly determines the energy conversion efficiency and power density.
In addition, oxygen potential profile build during the operation is an important factor to determine the long term stability and reliability of the cell and stacks. Since complex oxides are used in various parts of SOFC, cation transport driven by the oxygen potential gradient may cause the morphological and compositional instability due to kinetic demixing or decomposition. The stability of LaMnO3-based and La(Co,Fe)O3 based cathode materials have been experimentally investigated in the form of dense bulk ceramics and as porous electrodes. The results are discussed in terms of kinetic decomposition via fast grain boundary diffusion.
The reliability of the cell and stacks are also affected by the potential profile through the distribution of oxygen vacancy concentration and the resulting strain/stress distribution inside the cell. Calculation method and the necessary data were provided for structure analysis with consideration of oxygen potential distribution in SOFC under operation.
FL-3:IL06 Structural and Thermochemical Constraints of Mixed Conducting BSCF and SCF Electrodes for Fuel Cells
J. FRADE, A. YAREMCHENKO, S. MIKHALEV, Department of Materials and Ceramic Engineering, CICECO, University of Aveiro, Aveiro, Portugal
A compilation of literature data suggests guidelines for thermochemical constraints on oxide mixed conducting oxygen electrodes for SOFC and SOEC. Yet, chemical expansion results reported for Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and SrCo0.8Fe0.2O3-δ (SCF) deviate significantly from the main trend for a variety of other perovskite materials. BSCF and SCF were, thus, used to re-examine structural effects on thermochemical constraints of mixed conducting electrodes by simultaneous studies of oxygen stoichiometry and thermochemical expansion in dynamic mode. This minimizes uncertainties concerning kinetics of equilibration at given p(O2) in high-temperature range, and their dependence on microstructural differences demonstrated for bulk ceramics samples. BSCF shows smaller changes of oxygen stoichiometry and also lower chemical expansion compared to SCF and many other mixed conductors, originating from specific structural features such as larger unit cell and weaker sensitivity to temperature and other changes in operation conditions. BSCF also shows much better phase stability under oxygen lean conditions or corresponding cathodic polarization, as expected for SOFC oxygen electrodes. However, these advantages are lost on reverting to oxygen rich or anodic polarization, as required for SOEC. On the contrary, SCF shows enhanced stability under these SOEC conditions and limited stability under prospective SOFC conditions.
FL-3:IL07 Protonic SOFC Based on LaSrSc3 Perovskite-type Proton Conductor
H. YUGAMI, Graduate School of Engineering, Tohoku University, Japan; H. KATO, Tohoku Electric Power Co., Inc, Japan; F. IGUCHI, Graduate School of Engineering, Tohoku University, Japan
High temperature solid oxide fuel cells (SOFCs)have high efficiency and low emissions and contribute to the saving of fossil fuel and the decrease of the CO2 emission bringing about the global warning. Concerning the development of electrolytes, oxide-ion conductors alternative to yttria-stabilized zirconia (YSZ) such as doped CeO2, Sc-SZ and perovskite-type oxides (LaGaO3) etc. have been reported to apply to intermediate temperature SOFCs (IT-SOFCs). Some of perovskite-type oxides show high proton conductivity at high temperature and are expected suitable electrolyte materials for IT-SOFCs. In this paper we review the mixed electrical conductivity properties of LaScO3 and its applicability as electrolyte material for IT-SOFCs by testing the SOFC performance of Pt/LaScO3/Pt single cell configuration. We also investigated the optical absorption spectrum of OH(D)-vibration.by using single crystalline LaScO3 samples.
FL-3:IL08 Mixed Ionic Conduction for Electrochemical Membranes and Fuel Cells
F.M.B. MARQUES, Materials and Ceramic Eng. Dept./CICECO, University of Aveiro, Aveiro, Portugal
Composite electrolyte materials (oxide+salt) can be used in fuel cells, steam electrolyzers but also in selective CO2 separation membranes, amongst other applications. These materials consist of a combination of classical electrolytes used in Solid Oxide Fuel Cells (namely ceria-based electrolytes) with those used in Molten Carbonate Fuel Cells (mixtures of alkaline carbonates). Interestingly, these materials exhibit protonic conduction besides the expected oxide and carbonate-ion conductivity, inherent to their constituent phases.
Considering their recent discovery, there is little information on the exact relevance of each ionic species on the overall ionic transport of these composites. In this work we assess several composites based on distinct ceramic oxides to highlight the role of the ceramic matrix on their performance. Low temperature impedance spectroscopy provides a good basis for data analysis. Tuning the composite composition and microstructure to target functionalities at higher temperatures, namely for CO2 separation membranes, is feasible in this manner.
FL:P01 Effect of Ultrasonic Treatment on the Defect Structure of the Si-SiO2 System
D. KROPMAN, Tallinn University of Technology, Tallinn, Estonia
The effect of ultrasonic treatment(UST) on the defect structure of the Si-SiO2 system is characterized by means of electron spin resonance,metallography,MOS capacitance measurements and secondary ion mass spectroscopy.A non-monotonous dependence of the defect densities on the US wave intensity has been observed.