bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lattice-Gas Models of Electrochemical Adsorption: Static and Dynamic Aspects
Authors: Rikvold Per Arne , Wieckowski Andrzej , Ramos Raphael A. 
Published: June 2019

ABSTRACTWe discuss applications of statistical-mechanical lattice-gas models to electrochemical adsorption. Our strategy to describe specific systems includes microscopic model formulation, calculation of zero-temperature phase diagrams, numerical simulation of thermody-namic and structural quantities at nonzero temperatures, and estimation of effective, lateral interactions. We report applications to adsorption on single-crystal electrodes, presenting simulated and experimental coverages and voltammetric currents for urea on Pt(100) and the underpotential deposition of Cu on Au(111) in sulfuric acid. We also discuss an extension of the method to study time-dependent phenomena far from equilibrium.
Dynamical Processes at the Solid / Liquid Interface
Authors: Giesen M. , Dietterle M. , Stapel D. , Ibach H. , Kolb D. M. 
Published: June 2019

ABSTRACTWe have investigated transport processes on a stepped Ag(111) surface in an aqueous electrolyte by analyzing the equilibrium step fluctuations as a function of the electrode potential. No influence of the electrolyte and the potential was found in the regime of negative potentials with respect to the saturated calomel electrode. As the potential becomes positive and approaches the dissolution limit, the increasing magnitude of the step fluctuations and the change in the time dependence indicate a rapid exchange of silver atoms with the electrolyte long before the silver begins to dissolve.
An in Situ Small Angle Neutron Scattering Investigation of Ag0.7Au0.3 Dealloying Under Potential Control
Authors: Corcoran Sean G. , Wiesler David G. , Sieradzki Karl 
Published: June 2019

ABSTRACTIn situ small angle neutron scattering (SANS) was used to characterize the formation of the random 3-dimensional porous structure created during the dealloying of a Ag0.7Au0.3 alloy under potential control. Using a model developed by N.F. Berk (Phys. Rev. Lett., 58 (1987) 2718) for the scattering properties of random porous media, we were able to characterize the average ligament width as a function of time during the dealloying process. We find that the coarsening of the average ligament width is strongly dependent upon the value of the applied potential. Our results represent the first in situ nanoscale characterization of the 3-dimensional formation of porosity in a dealloying system under potential control.
Planar Ferrite Materials for Millimeter-Wave Applications
Authors: McKnight Stephen W. , Oliver Steven A. , How Hoton , Vittoria Carmine 
Published: June 2019

ABSTRACTTransferred-film technology provides a path to the integration of self-biased hexaferrite film devices into MMIC circuits. While progress is being made on the growth of thick oriented films of barium hexaferrite doped with aluminum and scandium by pulsed laser deposition or liquidphase epitaxy, we have demonstrated prototype devices using available yttrium-iron-garnet films and thinned bulk hexaferrites. Insertion losses less than 2dB and isolation greater than 20dB have been demonstrated, and theoretical modeling indicates that insertion losses less than 0.5 dB are accessible with optimized materials and through matching the active circuit components to the ferrite device. The prospects of accessing ferrite non-reciprocal, non-linear, and tunable functions at frequencies up to and exceeding 100 GHz through devices integrated onto microwave IC substrates without the use of DC biasing magnets are the driving force of this research.
Controlled Injection of Holes into ALQ3 Based Oleds by Means of An Oxidized Transport Layer
Authors: Mathai Mathew K. , Higginson Keith A. , Hsieh Bing R. , Papadimitrakopoulos Fotios 
Published: June 2019

ABSTRACTIn this paper we report a method for tuning the extent of hole injection into the active light emitting tris- (8-hydroxyquinoline) aluminum (Alq3) layer in organic light emitting diodes (OLEDs). This is made possible by modifying the indium tin oxide (ITO) anode with an oxidized transport layer (OTL) comprising a hole transporting polycarbonate of N,N'-bis(3-hydroxymethyl)-N,N'-bis(phenyl) benzidine and diethylene glycol (PC-TPB-DEG) doped with varying concentrations of antimonium hexafluoride salt of N,N,N',N'-tetra-p-tolyl-4,4'-biphenyldiamine (TMTPD+ SbF6-). The conductivity of the OTL can be changed over three orders of magnitude depending on salt loading. The analysis of hole and electron current variations in these devices indicates that optimizing the conductivity of the OTL enables the modulation of hole injection into the Alq3 layer. The bipolar charge transport properties for OLEDs in which the interfacial carrier injection barriers have been minimized, are governed by the conductivities of the respective layers and in this case it is shown that the variable conductivity of the OTL does allow for better control of the same. Accordingly, varying the concentration of holes in the device indicates that beyond an optimum concentration of holes, further hole injection results in the formation of light quenching cationic species and the initiation of oxidative degradation processes in the Alq3 layer, thus accelerating the intrinsic degradation of these devices. The variable conductivity of the OTL can hence be used to minimize the occurrence of these processes.
Synthesis and Characterization of the First 1:2 Ordered Perovskite Ruthenate
Authors: Rijssenbeek Job , Malo Sylvie , Saito Takashi , Caignaert Vincent , Azuma Masaki , Takano Mikio , Poeppelmeier Kenneth R. 
Published: June 2019

AbstractPerovskite-like mixed metal ruthenates are of interest owing to their varied electronic and magnetic properties, which are heavily dependent on the ordering of the transition metals. We report the synthesis and structural characterization of the first 1:2 ordered perovskite ruthenate, Sr3CaRu2O9. The structure was determined from a combination of powder X-ray, electron and neutron diffraction data and is characterized by a 1:2 ordering of Ca2+ and Ru5+ over the sixcoordinate B-sites of the perovskite lattice. Sr3CaRu2O9 is the first example of this structure-type to include a majority metal with d electrons (Ru(V), d3). The relationship of this material to the K2NiF4-type Sr1.5Ca0.5RuO4 (i.e., Sr3CaRu2O8) highlights the dramatic effects of the ruthenium valence on the resultant structure. Remarkably, these two structures can be quantitatively interconverted by the appropriate choice of reaction temperature and atmosphere.
Improvement in Ferroelectric Properties of Sol-Gel Derived SrBi2Ta2O9 thin films with seeding layers
Authors: Leu Ching-Chich , Chien Chao-Hsin , Yang Ming-Jui , Yang Ming-Che , Huang Tiao-Yuan , Lin Hung-Tao , Hu Chen-Ti 
Published: June 2019

AbstractThe effects of a seeding layer, which was deposited on Pt/TiO2/SiO2/Si substrates using magnetron sputtering, on the characteristics of sol-gel-deposited strontium-bismuth-tantalate (SBT) thin films are investigated. The seeding layer serves as nucleation sites so homogeneous crystalline SBT films of bismuth-layered structure (BLS) with fine grains are successfully obtained by 750°C rapid thermal annealing in O2 ambient. The remanent polarization (2Pr) improves from 12.1 to 18.8 μC/cm2 with the addition of the seeding layer. In addition, the seeding layer also results in a lower nucleation temperature, allowing the use of 700°C annealing for 10 min to grow SBT films that are fully crystallized with BLS phase and shows good ferroelectric properties. Finally, crystallinity and microstructures of SBT films are found to be strongly dependent on the thickness of the seeding layer. Optimum Ta-seeded SBT thin film crystallized at 700°C for 10min depicts a higher 2Pr value (12.9 μC/cm2 (@5V) than that of the un-seeded films crystallized at 750°C for 1min.
Enhanced polarization in strained BaTiO3 from first principles
Authors: Neaton J. B. , Hsueh C.-L. , Rabe K. M. 
Published: June 2019

AbstractThe structure, polarization, and zone-center phonons of bulk tetragonal BaTiO3 under compressive epitaxial stress are calculated using density functional theory within the local density approximation. The polarization, computed using the Berry-phase formalism, increases with increasing tetragonality and is found to be enhanced by nearly 70% for the largest compressive misfit strain considered (-2.28%). The results are expected to be useful for the analysis of coherent epitaxial BaTiO3 thin films and heterostructures grown on perovskite substrates having a smaller lattice constant, such as SrTiO3.
Misfit Strain Driven Phase Transformations in Epitaxial Barium Strontium Titanate Films
Authors: Ban Z.-G. , Alpay S. P. 
Published: June 2019

AbstractWe develop phase diagrams for single domain epitaxial barium strontium titanate films on cubic substrates as a function of the misfit strain based on a Landau-Devonshire phenomenological model similar to the one developed by Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)]. Unusual ferroelectric phases that are not possible in single crystals and bulk ceramics are demonstrated in epitaxially constrained BST films. The misfit strain is correlated with the film thickness quantitatively by taking into account the formation of misfit dislocations that relieve epitaxial stresses during deposition. Theoretical estimation of the dielectric constant of (001) Ba0.7Sr0.3TiO3 and Ba0.6Sr0.4TiO3 films grown on Si, MgO, LaAlO3, and SrTiO3 substrates as a function of film thickness is provided. It is shown that the selection of the substrate and the film thickness can be chosen as design parameters to manipulate the internal stress level in the film to achieve enhanced dielectric response.
Theoretical Prediction and Experimental Confirmation of Charge Transfer Vibronic Excitons and Their Phase in ABO3 Perovskite Crystals
Authors: Eglitis R. I. , Vikhnin V. S. , Kotomin E. A. , Kapphan S. E. , Borstel G. 
Published: June 2019

AbstractThe current theoretical and experimental knowledge of new polaronic-type excitons in ferroelectric oxides - charge transfer vibronic excitons (CTVE) is discussed. It is shown that quantum chemical Hartree-Fock-type calculations using a semiempirical Intermediate Neglect of Differential Overlap (INDO) method (modified for ionic/partly ionic solids) as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE existence. Our INDO calculations for KTaO3 and KNbO3 have demonstrated that the triplet exciton is a triad centre containing one active O atom and two Ta atoms sitting on the opposite sites from this O atom. The total energy of a system is lowered by the combination of Coulomb attraction between electron and hole and the vibronic effect in this charge transfer vibronic exciton. It is shown by means of our INDO calculations that polaronic-type CTVE in ferroelectric oxides could lead to the formation of a new crystalline phase. The ground state energy of this phase consisting of strongly correlated CTVEs lies within an optical gap of a pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as by the ferroelectric ordering.
Elastic Properties of Calcium Oxide Perovskites
Authors: Ross Nancy L. , Angel Ross J. , Kung Jennifer , Chaplin Tracey D. 
Published: June 2019

AbstractThe equations of state and axial moduli of the CaBO3 perovskites (B=Zr,Sn,Ti,Ge) and CaFeO2.5 with the brownmillerite structure have been determined using high-pressure, singlecrystal X-ray diffraction. The bulk modulus-specific volume relationship for the Ca-perovskites is nonlinear, with CaSnO3 and CaZrO3 displaying anomalous stiffening (higher bulk moduli) than previously reported and predicted [1,2]. The axial moduli of the a- and c-axes decrease steadily by ∼30% from the least-distorted of the Pbnm perovskites, CaGeO3, to the most distorted, CaZrO3, while the b-axis shows little change. The net result is a threefold increase in the anisotropy of the axial moduli of CaSnO3 and CaZrO3 (∼21%) relative to CaGeO3 and CaTiO3 (∼4-8%). The bulk modulus of CaFeO2.5 falls significantly below the trend for the stoichiometric perovskites. The introduction of 1/6 vacancies on the oxygen positions softens the perovskite structure by 25%.
Coupling of Lattice Dynamics to Spin Transitions in La1-xSrxCoO3
Authors: Louca Despina , Sarrao J. L. 
Published: June 2019

AbstractLa1-xSrxCoO3 is distinct because of its unique spin transitions subjecting the system to variable spin-lattice coupling. Pair density function analysis provided strong evidence for local lattice distortions associated with a Jahn-Teller active mode that is directly correlated to the change in the magnetic/conductive states of this system. The presence of Jahn-Teller distortions also serves as an indication for the intermediate spin configuration. Measurements of the dynamic structure function, S(Q, ω), showed that several phonon peaks fluctuate with carrier density and temperature. Such changes were not seen in an otherwise identical structure, LaAlO3. These phonon peaks are quite unusual and are most likely due to localized modes that appear to be dispersionless.
Formation Enthalpies of Tetravalent Lanthanide Perovskites by High Temperature Oxide Melt Solution Calorimetry
Authors: Ushakov S. V. , Cheng J. , Navrotsky A. , Wu J. R. , Haile S. M. 
Published: June 2019

AbstractHigh-temperature oxide melt solution calorimetry was used to measure formation enthalpies for several compositions of perovskites of nominal stoichiometry BaPrO3 and BaCeO3. Samples were synthesized from chemical solution methods followed by calcination at 1100-1300°C. PrO2 was synthesized by oxidation of Pr6O11 in an oxygen flow at 280°C. The samples were characterized by microprobe, thermogravimetric and differential thermal analyses. Cell parameters were refined by the Rietveld method. Barium excess in the samples with respect to ideal stoichiometry was detected. Drop solution enthalpies were measured in a Calvet type twin microcalorimeter, using 3Na2O·4MoO3 solvent at 702°C. Preliminary values of the formation enthalpy of BaPrO3 and BaCeO3 from oxides were -70 ±10 kJ/mol and -51 ±10 kJ/mol, respectively. They fall on the normal trend of energetics versus Goldschmidt tolerance factor and do not show any special stabilization of BaPrO3 relative to other MLnO3 perovskites.
Nb polarization in Ferroelectric Perovskites KNbO3 and (PbZn1/3Nb2/3O3)0.88-(PbTiO3)0.12
Authors: Mamontov E. , Dmowski W. , Egami T. 
Published: June 2019

AbstractXANES measurements have demonstrated that Nb polarization in (PbZn1/3Nb2/3O3)0.88-(PbTiO3)0.12 is small compared to that in KNbO3. This finding disproves the view of Nb5+ as invariably ferroelectrically active cation, and demonstrates that its polarizability depends on the Asite cations. Our results do not support conventional view of relaxor behavior in Pb(B'1/3Nb2/3)O3 ferroelectrics as a consequence of disruption of the connectivity of polarizable Nb5+ ions by their non-polarizable B' counterparts. Instead, they speak in favor of scenario in which relaxor behavior is caused by randomness of the local direction of Pb polarization due to chemical disorder on the B-sites of the perovskite structure.
From Ferroelectric to Quantum Paraelectric: KTa1-xNbxO3 (KTN), a Model System
Authors: Samara George A. 
Published: June 2019

AbstractThe ABO3 perovskite oxides constitute an important family of technologically important ferroelectrics whose relatively simple chemical and crystallographic structures have contributed significantly to our understanding of ferroelectricity. They readily undergo structural phase transitions involving both polar and non-polar distortions from the ideal cubic lattice. This paper focuses on the mixed perovskite system KTa1-xNbxO3, or KTN, which has turned out to be a model system. While the end members KTaO3 and KNbO3 might be expected to be similar, in reality they exhibit very different properties. Their mixed crystals, which can be grown over the whole composition range, exhibit a rich set of phenomena whose study has added greatly to our current understanding of the phase transitions and dielectric properties of these materials. Included among these phenomena are soft mode response, ferroelectric (FE)-to-relaxor (R) crossover, quantum mechanical suppression of the transition, the appearance of a quantum paraelectric state and relaxational effects associated with dipolar impurities. Each of these phenomena is discussed briefly and illustrated. Some emphasis is on the unique role of pressure in elucidating the physics involved.
Surface Potential Mapping of Patterned Self-Assembled Monolayers by Scanning Probe Microscopy
Authors: Getty R. Ross , Alvarez Rodolfo , Bonnell Dawn A. , Sharp Kenneth G. , Percec Simona , Hietpas Paula B. 
Published: June 2019

AbstractSurface potentials of a number of patterned conducting and insulating self-assembled monolayers (SAMs) were measured by scanning surface potential microscopy (SSPM) as part of a study in molecular electronics. Differences in surface potential were measured for insulating and conducting molecule SAMs on gold. The SAMs were patterned by microcontact printing. High contrast patterns were observed by surface potential even when little imaging was possible in standard AFM modes. Surface potential differences of a few mV to 500 mV were observed under ambient conditions between adjacent SAMs of different compositions or between SAMs and the unmodified substrate.
Electron Holographic Nano-Characterization of Gold Catalyst at Interface
Authors: Ichikawa S. , Akita T. , Okumura M. , Haruta M. , Tanaka K. 
Published: June 2019

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”
Mechanical Behaviour of Nanocrystalline Copper Related to Grain-boundary Structure
Authors: Champion Y. , Langlois P. , Guérin-Mailly S. , Langlois C. , Hÿtch M. J. 
Published: June 2019

AbstractUnderstanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.
Design of Transition Metal Oxide and Hybrid Mesoporous Materials
Authors: Sanchez Clément , Crepaldi Eduardo L. , Bouchara Anne , Cagnol Florence , Grosso David , Soler-Illia Galo J. de A. A. 
Published: June 2019

AbstractMesostructured transition metal (Ti, Zr, V, Al and Ce-Zr) oxide-based hybrid thin films, templated by poly(ethylene oxide)-based surfactants or block copolymers, have been prepared reproducibly, displaying 2D-hexagonal (p6m) or 2D-centred rectangular (c2m) structure. By carefully adjusting the variables involved it is possible to combine both high organisation and excellent optical quality. TiO2 and ZrO2-based materials show thermal stability up to 400-550°C. The elimination of the template can be conducted efficiently and gives rise to high surface area mesoporous films. For the other metal oxide hybrids the inorganic framework is much more fragile, and requires a precise sequence of post-treatments to be stabilised. In addition, original and homogeneous macrotextures shaped with coral-like, helical or macroporous sieves morphologies have been obtained following a nanotectonic approach based on the template-directed assembly by poly-γ-benzyl-L-glutamate (PBLG) of organically functionalised CeO2 crystalline nanoparticles.
Growth of Carbon Nanotubes with Controlled Morphologies
Authors: Dong Lifeng , Jiao Jun , Mosher Catherine L. , Foxley Sean 
Published: June 2019

AbstractThe alignment, orientation and morphologies of multi-walled carbon nanotubes (MWNTs) can be tailored by controlling catalyst deposition on porous silicon substrates. During the growth of MWNTs, H2 promoted the growth of carbon nanotubes and prevented the formation of amorphous carbon particles. With the introduction of H2, the average diameter of MWNTs decreased from 130 nm to 15 nm, and the average growth rate of nanotubes increased from 50 nm/s to 145 nm/s. The use of CH4 as the carbon source resulted in single-walled carbon nanotubes (SWNTs) with an average diameter of 2 nm, and the use of C2H2 as the carbon source resulted in MWNTs with an average diameter of 15 nm.