bluuebunny/crossref_metadata_2025 huggingface dataset:
Volume-Based Considerations for the Metal-Insulator Transition of CMR Oxides
Authors: Neumeier J. J. , Cornelius A. L. , Hundley M. F. , Andres K. , McClellan K. J.
Published: April 2011

The sensitivity of ρ to changes in volume which occur through: (1) applied pressure, (2) variations in temperature, and (3) phase transitions, is evaluated for some selected CMR oxides. It is argued that the changes in volume associated with (2) and (3), which are referred to as self pressures, are equivalent in magnitude to changes in volume resulting from pressures in the range of 0.18 to 0.45 GPa. Through consideration of thermal expansion and electrical resistivity data, it is shown that these self pressures are responsible for large features in the electrical resistivity and are an important component for the occurrence of the metallicity below Tc. It is suggested that this is a manifestation of a strong volume dependence of the electron phonon coupling in the CMR oxides.
Raman Investigation of the Layered Manganese Perovskite La1.2Sr1.8Mn2O7
Authors: Romero D. B. , Podobedov V. B. , Weber A. , Rice J. P. , Mitchell J. F. , Sharma R. P. , Drew H. D.
Published: April 2011

We report the results of a detailed polarization and temperature dependence study of the Raman scattering from La1.2Sr1.8Mn2O7. The Raman spectra reveal three general spectral features. First, there are sharp peaks due to long-wavelength optic phonons. Phonons, attributed to the distortion of the MnO6 octahedra, reveal an anomalous behavior which correlates with the transition from a paramagnetic-insulating (PI) to a ferromagnetic-metallic (FM) phase at a critical temperature Tc. Second, there is an electronic continuum that is suppressed for ω < 500 cm−1 at T ≪ Tc. Third, broad peaks between 400 cm1 to 800 cm−1 seen in the PI state, surprisingly, disappear in the FM state. The implications of these results are discussed.
X-Ray Induced Insulator-Metal Transitions in CMR Manganites
Authors: Kiryukhin V. , Casa D. , Keimer B. , Hill J. P. , Vigliante A. , Tomioka Y. , Tokura Y.
Published: April 2011

In this work we report a study of the photoinduced insulator-to-metal transition in manganese oxide perovskites of the formula Pr1-xCaxMnO3. The transition is closely related to the magnetic field induced insulator-to-metal transition (CMR effect) observed in these materials. It is accompanied by a dramatic change in the magnetic properties and lattice structure: the material changes from an insulating charge-ordered canted antiferromagnet to a ferromagnetic metal. We present an investigation of the transport and structural properties of these materials over the course of the transition (which usually takes about an hour to complete). The current-voltage characteristics exhibited by the material during the transition are highly nonlinear, indicating a large inhomogeneity of the transitional state. Possible practical applications of this novel type of transition are briefly discussed. We also report a high-resolution x-ray diffraction study of the charge-ordering in these materials. The temperature dependent charge ordering structure observed in these compounds is more complex than previously reported.
Paramagnetic Susceptibility of the CMR Compound La1-xCaxMnO3
Authors: Goodwin D. H. , Neumeier J. J. , Lacerda A. H. , Torikachvili M. S.
Published: April 2011

Measurements and analysis of the paramagnetic susceptibility of La1-xCaxMnO3+y (0 ≤ x ≤ 1) are reported. The magnetization was also measured in large fields (H ≤ 18 tesla) for a specimen of La0.79Ca0.21MnO3+y. The paramagnetic susceptibility is observed to be strongly enhanced for most compositions studied, including a number of antiferromagnetic compositions. This behavior is attributed to the existence of magnetic polarons.
Molecular Dynamics Study of Lithium Diffusion in Lithium-Manganese Spinel Cathode Materials
Authors: Cygan Randall T. , Westrich Henry R. , Doughty Daniel H.
Published: April 2011

A series of molecular dynamics computer simulations of the self-diffusion of lithium in pure and several doped lithium-manganese spinel materials has been completed. The theoretical approach is part of an effort to understand the mechanisms and rates of lithium diffusion, and to evaluate the structural control of the cathode materials upon lithium intercalation (charge-discharge) process. The molecular dynamics approach employs a fully ionic forcefield that accounts for electrostatic, repulsive, and dispersion interactions among all ions. A reference unit cell comprised of 56 ions (Li8Mn3+8Mn4+8O32) is used to perform the simulations under constant volume and constant pressure constraints. All atomic positions are allowed to vary during the simulation. Simulations were completed for the undoped and doped LiMn2O4 at various levels of lithium content (based on the number of lithium ions per unit cell and manganese oxidation state). The molecular dynamics results indicate an activation energy of approximately 97 kJ/mole for self-diffusion of lithium in the undoped material. Lithium ion trajectories from the simulations provide diffusion coefficients that decrease by a factor of ten as the cathode accumulates lithium ions during discharge. Molecular dynamics results for the doped spinel suggest a decrease in the diffusion rate with increasing dopant ion.
Structure and Electrochemical Potential Simulation for the Cathode Material Li1+xV3O8
Authors: Benedek R. , Thackeray M. M. , Yang L. H.
Published: April 2011

The structure and electrochemical potential of monoclinic Li1+xV3O8 were calculated within the local-density-functional-theory framework by use of plane-wave-pseudopotential methods. Special attention was given to the compositions 1+x=1.2 and 1+x=4, for which x-ray diffraction structure refinements are available. The calculated low-energy configuration for 1+x=4 is consistent with the three Li sites identified in x-ray diffraction measurements and predicts the position of the unobserved Li. The location of the tetrahedrally coordinated Li in the calculated low-energy configuration for 1+x=1.5 is consistent with the structure measured by x-ray diffraction for Li1.2V3O8. Calculations were also performed for the two monoclinic phases at intermediate Li compositions, for which no structural information is available. Calculations at these compositions are based on hypothetical Li configurations suggested by the ordering of vacancy energies for Li4V3O8 and tetrahedral site energies in Li1.5V3O8. The internal energy curves for the two phases- cross near 1+x=3. Predicted electrochemical potential curves agree well with experiment.
Ab INITIO CALCULATION OF THE LixCoO2 PHASE DIAGRAM
Authors: Der Ven Anton Van , Aydinol Mehmet K , Ceder Gerbrand
Published: April 2011

The electrochemical properties of the layered intercalation compound LiCoO2 used as a cathode in Li batteries have been investigated extensively in the past 15 years. Despite this research, little is known about the nature and thermodynamic driving forces for the phase transformations that occur as the Li concentration is varied. In this work, the phase diagram of LixCoO2 is calculated from first principles for x ranging from 0 to 1. Our calculations indicate that there is a tendency for Li ordering at x = 1/2 in agreement with experiment [1]. At low Li concentration, we find that a staged compound is stable in which the Li ions selectively segregate to every other Li plane leaving the remaining Li planes vacant. We find that the two phase region observed at high Li concentration is not due to Li ordering and speculate that it is driven by a metal-insulator transition which occurs at concentrations slightly below x < 1.
Thin Film Synthesis of Novel Electrode Materials for Solid-Oxide Fuel Cells
Authors: Jankowski Alan F. , Morse Jeffrey D.
Published: April 2011

Electrode materials for solid-oxide fuel cells are developed using sputter deposition. A thin film anode is formed by co-deposition of nickel and yttria-stabilized zirconia. This approach is suitable for composition grading and the provision of a mixed-conducting interfacial layer to the electrolyte layer. Similarly, synthesis of a thin film cathode proceeds by co-deposition of silver and yttria-stabilized zirconia. The sputter deposition of a thin film solid-oxide fuel cell is next demonstrated. The thin film fuel cell microstructure is examined using scanning electron microscopy whereas the cell perfomance is characterized through current-voltage measurement and corresponding impedance spectroscopy.
Novel Proton Exchange Membrane for High Temperature Fuel Cells
Authors: Bhamidipati M. , Lazaro E. , Lyons F. , Morris R. S.
Published: April 2011

This research effort sought to demonstrate that combining select phosphonic acid additives with Nafion could improve Nafion's high temperature electrochemical performance. A 1:1 mixture of the additive with Nafion, resulted in a film that demonstrated 30% higher conductivity than a phosphoric acid equilibrated Nafion control at 175°C. This improvement to the high temperature conductivity of the proton exchange membrane Nafion is without precedent. In addition, thermal analysis data of the test films suggested that the additives did not compromise the thermal stability of Nafion. The results suggest that the improved Nafion proton exchange membranes could offer superior electrochemical performance, but would retain the same degree of thermal stability as Nafion. This research could eventually lead to portable fuel cells that could oxidize unrefined hydrocarbon fuels, resulting in wider proliferation of fuel cells for portable power.
Effects of Microstructure on Oxygen Permeation in Some Perovskite Oxides
Authors: Zhang K. , Yang Y. L. , Jacobson A. J. , Salama K.
Published: April 2011

The effects of microstructure on the oxygen permeation in SrCo0.8Fe0.2O3-δ(SCFO) and La0.2 Sr0.8 Fe0.8Cr0.2 O3 (LSFCO) was investigated using disc samples fabricated under different processing conditions. The microstructure of LSFCO remained unchanged when the sintering temperature was increased from 1300 to 1450 °C, but the average grain size of SCFO increased considerably when the sintering temperature was increased from 930 to 1200 °C. The change in grain size was found to have a strong effect on the oxygen permeation flux in SCFO, which increased considerably as the grain size was decreased. This indicates that the contribution of the grain boundary diffusion to the steady state oxygen flux in SCFO is substantial and grain boundaries provide faster diffusion paths in oxygen permeation through the samples.
Synthesis and Preliminary Electrochemical Characterization of LiNi0.5Co0.5O2 Powders Obtained by the Complex Sol-Gel Process (CSGP)
Authors: Deptula A. , Lada W. , Olczak T. , Croce F. , Ronci F. , Ciancia A. , Giorgi L. , Brignocchi A. , Di Bartolomeo A.
Published: April 2011

Complex Sol-Gel Process (CSGP) was applied to the preparation of LiNi0.5Co0.5O2. Starting sol-solutions were prepared in two different ways: I, in which aqueous ammonia was added to a starting solution of Li+-Ni2+-Co2+ acetate-ascorbate, and II in which LiOH was added to a solution of Ni2+- Co2+ and NH4+ acetate-ascorbate. It was found that in the absence of ascorbic acid, or at its lower content (≤0.2 M on 1M σ Li+- Ni2+- Co2+) precipitation of Ni hydroxides occurred. Regular sols were concentrated ∼3 times, gelled and dried at 140°C. Intensive foaming was observed for samples during further heating. Consequently for scaling up to 200g in a run a preliminary long drying procedure followed by self-ignition step (∼400°C) was introduced. Thermal transformation of the gel to solid was studied by TG, DTA, XRD and IR. The main feature of this step is carbonate formation. The final structure LiNi0.5Co0.5O2 is observed after heating for Ih at 800°C. For larger scale production the extension of firing time was necessary. Electrochemical properties of the LiNi0.5Co0.5O2 compound, prepared by the CSGP were evaluated and considered satisfactory.
Electrochemical Li Insertion in Lamellar (Birnessite) and Tunnel Manganese Oxides (Todorokite)
Authors: Duncan M. J. , Leroux F. , Nazar L. F.
Published: April 2011

A comparison of Li insertion in manganese oxide phases with a tunnel (todorokite) framework, its two-dimensional layered precursor (birnessite/buserite), and Li-exchanged materials are presented. The results outline the effect of the MnO6 octahedral arrangement and framework composition on the electrochemical response. The interlayer cations in the lamellar materials are exchangeable for Li, giving rise to a lithiated birnessite that displays a sustainable capacity of 125 mAh/g. For todorokite, molten salt exchange using LiNO3 results in displacement of water from the tunnels, and incorporation of additional Li into the structure. Some of this Li is extractable during charge, resulting in a reversible capacity of 172 mAh/g in the voltage window 4.2–2.0V.
X-ray Absorption and NMR Studies of LiNiCoO2 Cathodes Prepared by a Participate Sol-Gel Process
Authors: Rostov S. , Wang Y. , denBoer M. L. , Greenbaum S. , Change C. C. , Kumta Prashant N.
Published: April 2011

We have synthesized lithiated nickel oxide-based cathode materials containing stoichiometric and excess lithium using a new low temperature colloidal paniculate sol-gel process. The process yields a xerogel precursor that transforms to the crystalline oxide at 800 °C in 2h. We studied the Li environment with nuclear magnetic resonance (NMR) and that of the transition metal ions with x-ray absorption spectroscopy. We measured samples of LiNi1−xCoxO2, with x = 0 and 0.25. The effect on each composition of the incorporation of 5 mol % Li was also examined. The precursor material appears to have no Ni3+, as indicated x-ray absorption measurements, and is highly disordered, showing little sign of interatomic correlations beyond the nearest neighbor in extended x-ray absorption fine structure (EXAFS) spectra. The 7Li NMR line widths and spin-lattice relaxation (T1) behavior are dominated by strong interactions with the paramagnetic Ni3+. The presence of 5 % excess Li causes almost no change in NMR line width or T1 in the mixed (Ni/Co) cathode, but does produce an almost 30% reduction in line width for the pure LiNiO2, implying that Co stabilizes the structure. The near-edge x-ray absorption measurements show the local Ni environment is relatively unaffected by Co substitution, a result confirmed by EXAFS analysis. The heat-treated samples are highly ordered, and both the near-edge and extended analysis imply Co substitutes primarily for Ni2+, not Ni3+. The Jahn-Teller distortion is apparent in both the stoichiometric and Li-excess materials.
On the Electroanalytical Characterization of LixCoO2, LixNiO2 and LiMn2O4 (Spinel) Electrodes in Repeated Lithium Intercalation-Deintercalation Processes
Authors: Aurbach D. , Levi M. D. , Levi E. , Markovsky B. , Salitra G. , Teller H. , Heider U. , Heider L.
Published: April 2011

This paper reports on electroanalytical studies of the intercalation-deintercalation of lithium into lithiated transition metal oxides which are used as cathodes for Li ion batteries. These include LixCoO2 LixNiO2 and LixMn2O4 spinel. The basic electroanalytical response of these systems in LiAsF6 1M/EC-DMC solutions was obtained from the simultaneous use of slow and fast scan cyclic voltammetry (SSCV), potentiostatic intermittent titration (PITT) (from which D vs. E was calculated), and impedance spectroscopy (EIS). Surface sensitive FTIR spectroscopy and XRD were also used for surface and 3D characterization, respectively. A large and important denominator was found in the electrochemical behavior of lithium intercalation-deintercalation into these transition metal oxides and graphite. The use of the electroanalytical response of these systems as a tool for the study of stabilization and failure mechanisms of these materials as cathodes in rechargeable Li batteries is demonstrated and discussed.
Influence of Water and Other Contaminants in Electrolyte Solutions on Lithium Electrodeposition
Authors: Fujieda T. , Koike S. , Higuchi S.
Published: April 2011

Electrochemistry of a nickel electrode in propylene carbonate [PC] containing LiClO4, LiCF3SO3, LiPF6 was studied through a micro electrode (φ =25 μ m) techniques in the wide potential range between +4.5 and -0.2 V vs. Li/Li+. Common pronounced peaks were observed in the potential range positive to lithium electrodeposition on nickel in all electrolyte solutions examined. Thus, these peaks can be attributed to reactions related to Li+ or commonly contained contaminants such as water and acids. In particular, the peak which appeared at the most negative potential seemed to be underpotential deposition (UPD) of lithium.

To prove this hypothesis a nickel electrode in highly dried PC (water content : 3 – 8 ppm) intentionally contaminated with a small amount of water and CF3COOH was examined via cyclic voltammetry. Changing the content of water and acid (and its ratio) in PC resulted in a variety of voltammograms and one of them was identical to the one observed in PC containing lithium electrolytes. These facts preclude the existence of UPD of lithium on nickel in the electrolyte solutions. Instead, the existence of NiOH on nickel and its redox reaction mechanism have been postulated. The mechanism is consistent with the experimental facts : a nickel electrode passivates in PC with a small amount of water, and a small amount of acid, CF3COOH, can prevent passivation. The vicinity of the electrode surface may be exposed to an alkaline atmosphere owing to the reduction product of water. This seems to be the cause of troubles we run into with the electrodes at cathodic potentials
Passive-Film Formation on Metal Substrates in IM LiPF6/EC-DMC Solutions
Authors: Guidotti Ronald A. , Nelson Gerald C.
Published: April 2011

The initial irreversible capacity loss in lithium-ion cells has been attributed to passive-film formation on the carbon and graphite anodes during the first intercalation. We have examined the nature of these passive films on select metal substrates. We studied film formation on Cu, 304 stainless steel, and Mo cycled in a 1M LiPF6/ethylene carbonate (EC)-dimethyl carbonate (DMC) solution (1:1 v/v) over a potential range of 3 V to below 0 V. Film formation occurs readily on each of the metals and involves both solvent and salt species. The composition, thickness, and distribution of the films depends strongly on the substrate. The redox processes that occur during film formation and the potential for Li plating are highly dependent on the substrate composition.
Pyrrole Copolymers with Enhanced Ion Diffusion Rates for Lithium Batteries
Authors: Calvert Paul , Gardlund Zack , Huntoon Trey , Hall H. K. , Padias Anne
Published: April 2011

Copolymers of pyrrole with a polyether-substituted pyrrole were tested as cathodes for lithium batteries. The charge and discharge characteristics showed that anion transport was much faster in the copolymer than in polypyrrole. As a result these electrodes store and release much more charge at higher current densities but are similar to polypyrrole at low currents. Pulse and relaxation measurements of the ion diffusion showed that this difference was due to a ten-fold increase in the anion diffusion coefficient.
New 7Li-NMR Evidence for Lithium Insertion in Disordered Carbon
Authors: Wang S. , Matsui H. , Matsumura Y. , Yamabe T.
Published: April 2011

In fully-charged carbon materials, we tried to determine the nature of the interaction between Li species and carbon using variable temperature measurements of the Li Knight shift Only one interaction between the Li species and graphite carbon was observed from room temperature to -10°C. However, while only one average interaction between the Li species and the disordered carbon was observed at room temperature, three kinds of interactions were observed at low temperature. These results provide direct evidence for the model which explains why the discharge capacity of the carbon electrode with a disordered structure as an anode can exceed the theoretical capacity of a graphite anode in lithium ion rechargeable batteries.
Commercial Cokes and Graphites as Anode Materials for Lithium - Ion Cells
Authors: Derwin David J. , Kinoshita Kim , Tran Tri D. , Zaleski Peter
Published: April 2011

Several types of carbonaceous materials from Superior Graphite Co. were investigated for lithium ion intercalation. These commercially available cokes, graphitized cokes and graphites have a wide range of physical and chemical properties. The coke materials were investigated in propylene carbonate based electrolytes and the graphitic materials were studied in ethylene carbonate / dimethyl solutions to prevent exfoliation. The reversible capacities of disordered cokes are below 230 mAh / g and those for many highly ordered synthetic (artificial) and natural graphites approached 372 mAh / g (LiC6). The irreversible capacity losses vary between 15 to as much as 200 % of reversible capacities for various types of carbon. Heat treated cokes with the average particle size of 10 microns showed marked improvements in reversible capacity for lithium intercalation. The electrochemical characteristics are correlated with data obtained from scanning electron microscopy (SEM), high resolution transmission electron microscopy (TAM), X - ray diffraction (XRD) and BET surface area analysis. The electrochemical performance, availability, cost and manufacturability of these commercial carbons will be discussed.
Electrochemical Properties of Nitrogen-Substituted Carbon and Organofluorine Compounds
Authors: Nakajima T. , Koh M. , Dan K.
Published: April 2011

The CxN samples(C14N-C62N) prepared with a nickel catalyst had the higher crystallinity and less pyridine-type nitrogens existing at the edge of graphene layers than CxN prepared in the absence of a catalyst. With increase in the deposition temperature of CxN, the cy-cleability for electrochemical intercalation-deintercalation of lithium ions was improved and the profile of the charge-discharge curve approached that of graphite due to increase in the crystallinity and decrease in the incorporated nitrogens. CxN-coated graphites demonstrated gradual increase in the potential at the last stage of lithium ion deintercalation process.

The effect of fluoroester-mixing in 1 M LiClO4-EC/DEC was also investigated at a low temperature. It was found that CHF2COOCH3 with a low molecular weight and a small number of fluorine atoms was effective as a mixing agent.
Effects of Processing Conditions on the Physical and Electrochemical Properties of Carbon Aerogel Composites
Authors: Tran T. D. , Lenz D. , Kinoshita K. , Droege M.
Published: April 2011

The carbon aerogel/carbon paper composites have physical properties similar to those of monolithic carbon aerogels but do not require supercritical extraction during fabrication. The resorcinol-formaldehyde based carbon aerogel phase is intertwined between the fibers of a commercial carbon paper. The resulting composites have variable densities (0.4–0.6 g/cc), high surface areas (300–600 m2/g), and controllable pore sizes and pore distribution. The effects of the resorcinol-formaldehyde concentrations (50–70% w/v) and the pyrolysis temperature (600–1050°C) were studied in an attempt to tailor the aerogel microstructure and properties. The composite physical properties and structure were analyzed by transmission electron microscopy and multipoint-BET analyses and related to electrochemical capacitive data in 5M KOH. These thin carbon aerogel/carbon paper composite electrodes are used in experiments with electrochemical double-layer capacitors and capacitive deionization.
Reactions of Lithium with Small Graphene Fragments: Semi-Empirical Quantum Chemical Calculations
Authors: Radosavljević Marko , Papanek Peter , Fischer John E.
Published: April 2011

Semi-empirical and ab initio calculations [1], as well as inelastic neutron spec-troscopy [2], demonstrate that Li can bind to protonated “edge carbons” to create a moiety analogous to the organolithium monomer C2H2Li2. This provides a possible additional channel for Li uptake in high capacity Li-ion battery anodes based on low-T pyrolyzed soft carbons. Here we show that similar reactivity is exhibited by polyaro-matic hydrocarbons with the protons removed (taken as surrogates for the structural units in hard carbons). In the deprotonated PAH'es the Li serves to saturate dangling bonds, maintaining sp2 hybridization, whereas Li added to PAH'es creates sp3 carbons at the edges. In both cases this extra reactivity occurs in parallel with the usual intercalation. These findings have implications for further development in Li-ion rechargeable battery technology.
Electrical Properties of Novel Anodic Films Formed in Nonaqueous Electrolyte Solutions
Authors: Mizutani F. , Takeuchi S. , Nishiwaki T. , Sato N. , Ue M.
Published: April 2011

An aluminum alloy (Al - 1.0% Si - 0.5% Cu) was anodized in nonaqueous electrolyte solutions containing propylene carbonate (PC), ethylene glycol (EG), or γ-butyrolactone (GBL) as a solvent. MIM (metal-insulator-metal) elements using these anodic films were made to evaluate their electrical properties. Leakage current of the anodic films formed in the nonaqueous solutions was lower than those formed in aqueous electrolyte solutions. These novel films are useful as a high insulating film used for a gate insulator in thin film transistor liquid crystal displays (TFT-LCD).
Electromagnetic Properties of Soils
Authors: Sant Amarina J. C. , Klein K. A.
Published: April 2011

Electromagnetic waves can be used to characterize geomaterials and to monitor geo-processes. Permittivity, conductivity, and magnetic permeability measurements provide complementary information. Furthermore, events at different frequencies, such as the various polarization mechanisms, suggest multiple internal scales within materials. Three laboratory studies are presented: characterization of kaolinite-water mixtures with permittivity data, monitoring soil-cement hydration with conductivity measurements, and characterization of kaolinite-iron mixtures with magnetic permeability data. Laboratory techniques face inherent limitations, in particular, low frequency permittivity measurements of highly conductive specimens are not feasible. Likewise, field techniques are restricted by the compromise between the desired resolution and the achievable skin depth.
Resistometric Mapping using a Scanning Tunneling Microscope
Authors: Lang C I , Tapson J
Published: April 2011

We present a method whereby spatial variations in the resistivity of bulk conductive specimens may be detected on the same scale as the microstructural variations from which they arise. This technique, a new development of scanning tunneling potentiometry, offers significant benefits for microstructural characterization and for investigation of microstructure/resistivity relationships in metallic materials.
Time Domain Response of Electrical Ceramics Micro to Megaseconds
Authors: Modine F. A.
Published: April 2011

The electrical properties of ceramics can be measured in either the time domain or in the frequency domain. But for electrically nonlinear ceramics such as varistors, time-domain measurements provide insights that are different and more relevant to material performance as well as being more physically incisive. This article focuses specifically on the electrical properties of ZnO varistors, but much of it is of relevance for other materials, in particular those materials with grain-boundary barriers and disordered ceramics or glasses. The interpretation of electrical measurements in the time domain is profoundly influenced by such practical matters as source impedance and waveform characteristics. Experimental results are presented for both high and low source impedance relative to that of a test varistor, and the difference in experimental difficulty and ease of interpretation is described. Time-domain measurements of capacitance and of the inductive response of varistors to large, fast electrical pulses are presented and their implications for varistor theory are given. Experimental evidence is given of short- and long-term memory in varistors. These memory phenomena are ascribed respectively to the life time of holes that become trapped in barriers and to polarization currents originating from deep electron traps. Polarization current measurements are presented for a wide range of time and temperature. The power-law time dependence and “universal” behavior of these currents is discussed. The exponent that describes the power law behavior is seen to change with temperature, and the change is interpreted as a double transition from diffusive to dispersive transport that originates with current from two different electron traps.
Non-Debye and CPA Behaviors of Ionic Materials
Authors: Wang J. C
Published: April 2011

Non-Debye and constant-phase-angle (CPA) behaviors associated with the bulk and interfacial processes involving ionic materials are discussed in terms of complex impedance, admittance, and dielectric spectra. The yielding of a CPA and/or a broad non-Debye dielectric loss peak in a spectrum from fractal, pore, and ion-hopping models are compared and reviewed. The observed wide frequency ranges of the CPA behavior suggest that the fractal and pore models, which require a wide range of special structures down to very fine scales, may not be realistic. The ion-hopping model treats the bulk and interfacial processes as a chemical reaction having a thermally-activated Arrhenius form. Because of thermal fluctuations, the activation energies for ion hopping (e.g., in a potential double-well) have a double-exponential distribution which yields a non-Debye dielectric loss peak and a CPA spectrum over a wide frequency range above the loss peak. The distribution also has a special temperature dependence which may explain the invariance of dielectric spectral shapes with temperature, an observation by Joscher. The construction of CPA elements (in a generalized Warburg impedance form) using three distinct types of resistor-capacitor networks are presented and used to aid the discussion.
Measurement of Stratified Distributions of Dielectric Properties and Dependent Physical Parameters
Authors: Mamishev A. V. , Du Y. , Lesieutre B. C. , Zahn M.
Published: April 2011

Recent advances in ω-k (frequency-wavenumber) interdigital dielectrometry are described. Using this technology, information about the microstructure of dielectric materials is obtained by applying to the sensor-dielectric interface a spatially periodic electric potential swept in frequency from 0.005 Hz to 10,000 Hz. The penetration depth of the electric field is proportional to the spatial wavelength of the electric potential. Application of multi-wavelength electrode arrangements allows measurement of stratified distributions of complex dielectric permittivity. Calibration techniques serve to relate the distributed dielectric properties of materials to other physical variables, such as density, porosity, cracking, lamination, and diffusion of contaminants into the material. The specific problem treated in this paper is in the measurement of moisture concentration distribution in transformer pressboard during the diffusion of water molecules from ambient transformer oil. The output of interdigital sensors is strongly influenced by the microgranularity of the material's surface. Although this dependence complicates interpretation of the measurements in some applications, the variation of the output may also be used to characterize the shape of the surface on the microscale.
Extended D.C. Electrical Transport Measurements on the Mixed Conductor Cu3Cs2
Authors: Lemaire P. K. , Benoit J. , Speel R.
Published: April 2011

D.C. electrical transport measurements have been done over the temperature range 200 K. to 450 K on the mixed conductor Cu3.0CS2 This work extends the original work done on CuxCS2 over the temperature range 260 K to 350 K. Above 220 K, the voltage versus time curves follow the Yokota model for mixed conductors. Below 220K, the voltage versus time curves were practically constant, suggesting very little ionic transport below this temperature, and an electronic conductivity of the order of 10−5 (Ω cm)−1 at 200 K. At ambient temperatures, the ionic conductivity and electronic conductivity were both of the order of 10−3 (Ω cm)−1, and the chemical diffusion coefficient found to be of the order of 10−6 cm2s−1, in agreement with earlier work on Cu3CS2. Above 220 K, the ionic conductivity versus temperature plots were of the Arrhenius form with an activation energy of about 0.36 eV. The jump time and residence time were estimated to be of the order of 10−12s and 10−6s respectively, confirming hopping as the mode of ionic transport. The electronic conductivity versus temperature plot confirmed thermal activation as the mode of electronic transport. The results suggest CuxCS2 to be very stable and the Yokota model, with very little modification, to be very reliable for the analysis of these mixed conductors.
Dielectric Spectroscopy of Insulator/Conductor Composites
Authors: Kolcan Julie Runyan , Gerhardt Rosario , Ruh Robert , McLachlan David S.
Published: April 2011

The dielectric properties of composites are affected in different ways by a number of parameters. These include the electrical properties of both the filler and matrix, the wetting properties of the matrix on the filler, the size and shape of the filler, and the amount of the filler. Most composite systems have been studied via dc resistivity measurements which clearly show the effect of the addition of a second phase to an insulating matrix. However, frequency dependent measurements can provide additional insight into the mechanisms controlling the electrical response. The frequency dependence of the dielectric properties of composites will be shown. The permittivity and admittance plots of BN/B4C composites will be given and the relevance of the trends seen in them will be discussed.
Understanding Coating and Substrate Heterogeneities using Electrochemical Impedance Methods
Authors: Mierisch A. M. , Taylor S. R.
Published: April 2011

This study examines natural breakdown events on organic coated AA 2024-T3 coated using Local Electrochemical Impedance (LEI) mapping (M) and spectroscopy (S). LEIM was able to identify not only different types of defects on this system, but also provided information about the kinetics and stages of development of these defects. Supportive evidence regarding the impedance characteristics of these defects was provided by Capillary Electrophoresis (CE). Data from early stages of defect development indicate that an increased impedance develops at the site. This is related to either the development of aggregated water or electrolyte, as well as corrosion product development. Direct evidence of defect healing is also provided.
Scaling Behavior of the Complex Conductivity of Graphite-Boron Nitride Percolation Systems
Authors: Wu Jungie , McLachlan D S
Published: April 2011

Measurements of both components of the complex AC conductivity σ*m of continuum percolation systems, based on Graphite and hexagonal Boron Nitride, over a large frequency range, for samples near the conductor insulator composition, are reported. The results of the real part of σ*m (σmr) above the critical volume fraction (φc) and the imaginary component (σmi = iωεoεmr) below φo are shown to have the correct power law dispersion behavior, but only if the non-universal exponents measured in previously described DC experiments are used. It is also shown that all the results can be scaled, as is predicted by percolation theory, so as to lie on two continuous curves, one below and one above φc. Unfortunately the actual ωc values used to scale the experimental results are found not to be in good agreement with theoretical predictions.
Conductivity and Noise Measurements in 3D Percolative Cellular Structures
Authors: Chiteme C. , McLachlan D. S.
Published: April 2011

Conductivity results and 1/f noise (Sav) measurements from some systems with a cellular structure (composites in which small conductor particles embed on the surface of larger and regular insulator particles) are given. The usual DC percolation parameters (φc,t & s) were obtained from fitting the results to the Percolation equations. φc values for the systems have been found to lie in the range 0.01 – 0.07, while both non-universal and close to universal values have been measured for the exponents s and t. In addition, 1/f or flicker noise results on the systems give an additional exponent ω from the relationship Sav/Vdc2 = KRω. For the systems measured so far, the exponent ω is observed to take different values ω1 close to and ω2 further away from the conductor-insulator transition, but on the conducting side (ω > ωc). The very different values (s, t & ω), obtained for the various conducting powders, in the same macroscopic structure, indicates that the way the powders distribute themselves on the insulating particles is a major factor in determining the exponents.
Electromechanical Study of Carbon Fiber Composites
Authors: Wang Xiaojun , Fu Xuli , Chung D.D.L.
Published: April 2011

Electromechanical testing involving simultaneous electrical and mechanical measurements under load was used to study the fiber-matrix interface, fiber residual stress and marcelling (fiber waviness) in carbon fiber composites. The interface study involved single fiber pull-out while the fiber-matrix contact resistivity was measured. The residual stress study involved measuring the resistance of a single fiber embedded in the matrix while the fiber was tensioned at its exposed ends. The marcelling study involved measuring the resistance of a composite in the through-thickness direction while tension was applied in the fiber direction.
Electrical Measurement of the Bandgap of N+ and P+ SiGe Formed by Ge Ion Implantation
Authors: Nishiyama Akira , Arisumi Osamu , Yoshimi Makoto
Published: April 2011

N+ and p+ SiGe layers were formed in the source regions of SOI MOSFETs in order to suppress the floating-body effects by means of high-dose Ge implantation. The bandgaps of the layers were evaluated by measuring the temperature dependence of the base current of the source/channel/drain lateral bipolar transistors. It has been found that the reductions of the bandgaps due to the SiGe formation by the Ge implantation were relatively small, compared to those obtained by the theoretical calculation for heavily doped SiGe. It was also found that the bandgap reduction was larger for n+ layers than that for p+ layers.
In situ Characterization of Functional Organic Thin Films by Energy Dispersive Grazing Incidence X-ray Diffraction
Authors: Yoshida Yuji , Takiguchi Hiroshi , Tanigaki Nobutaka , Yase Kiyoshi
Published: April 2011

We are investigating well-ordered highly crystalline thin films made using organic molecular beam deposition (OMBD) since it is important to control the formation mechanism at the initial growth process. Then, we developed a new in situ technique of energy dispersive grazing incidence X-ray diffraction utilized within an ultrahigh vacuum system. This technique (in situ ED-GID) makes it possible to examine the crystal structure, orientation and morphology of organic thin films during deposition without any damage to the film. In the present review, we examined the growth process of thin films of functional organic dyes, fullerene (C60) and p-sexiphenyl (6P) by using this in situ ED-GID. The crystal strucutre and molecular orientation in epitaxially-grown thin films were confirmed during the initial stages of growth. Also, the morphology of C60 thin films was examined during the deposition. As a result, it was confirmed that the decay curves of X-ray fluorescence indicate different island growth in C60 thin films.
Monitoring of Sidewall Spacer Etch by Optical Emission Spectroscopy and Mass Spectroscopy
Authors: Min K. , Chambers J. J. , Parsons G. N. , Hauser J. R.
Published: April 2011

Selective etch of SiO2/poly Si in a high density CF4+D2 plasma generated by ECR (Electron Cyclotron Resonance) system was studied. The end point detection of the SiO2 sidewall spacer etch was monitored using optical emission spectroscopy and mass spectrometer. SEM cross sectional analysis was conducted to confirm the end point detection and spacer formation.
Rotating-Compensator Multichannel Ellipsometry: Applications in Process Development for Nanocrystalline Diamond Thin Films
Authors: Collins R. W. , Lee Joungchel , Rovira P. I. , An Ilsin
Published: April 2011

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to characterize nanocrystalline diamond thin film growth processes by plasma-enhanced chemical vapor deposition (PECVD). With the newly-designed instrument, a time resolution of 32 ms is possible for spectra (1.5˜4.0 eV) in the Stokes vector of the light beam reflected from the surface of the growing film. Several advantages of the rotating-compensator over the simpler rotating-polarizer multichannel ellipsometer design are demonstrated here for diamond thin film growth. These include the ability to: (i) resolve the sign ambiguity in the p–s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the film/substrate. The degree of polarization has been applied to characterize the time evolution of light scattering during the nucleation of the diamond, as well as the time evolution of thickness non-uniformity over the probed area of the growing film. In this paper, a brief description of calibration and data reduction for the new instrument is also provided.
In-situ RF diagnostic for PECVD process control
Authors: Raoux S. , Liu K. S. , Guo X. , Silvetti D.
Published: April 2011

The fabrication of advanced integrated circuits requires increased accuracy in process monitoring and active control. As higher production yields are required, the technology is moving from statistical process control to in-situ diagnostic techniques. A set of experiments was conducted to explore the feasibility of using radio frequency (RF) impedance probes to detect deviation of electrical characteristics of process chambers during wafer fabrication. A probe was integrated on a plasma-enhanced chemical vapor deposition (PECVD) chamber to explore the sensitivity of the reactor electrical characteristics on the events of process drift or input parameter variation. We measured RF the voltage, current and harmonics, the phase angle and the impedance magnitude for a capacitively coupled reactor. A single frequency (13.56MHz) process for depositing Si0 2 and a dual frequency (13.56MHz+35OkHz) process for Si3N4 deposition were characterized. We investigated the dependence of the RF signature and process parameters such as RF power, pressure, gas flow and electrode spacing. We observed that there is a correlation between the film properties (especially stress) and the plasma electrical characteristics. Furthermore, RF probes can be used to detect chamber malfunctions such as lost of RF ground or wafer-out-of-pocket events.
Characterization of a Solid-Source Delivery System for Metal Organic Chemical Vapor Deposition by In-Situ Laser Reflectance
Authors: Dubourdieu C. , Kim G. Y. , Meyer J. D. , Gallois B.
Published: April 2011

Specular laser reflectance (He-Ne laser) has been used to monitor in-situ and in real time the growth rate and the index of refraction of oxide films during chemical vapor deposition. This technique has been implemented on an inverted vertical stagnation-flow reactor equipped with a solid-source delivery system. Yttria deposited on silicon has been chosen as a starting material to characterize the reactor and the precursor delivery system capabilities. The experimental reflectance curves have been fitted to a simple three-layer (gas/film/substrate) model allowing the determination of the growth rate and of the refractive index. The growth rate has been studied as a function of various key processing parameters: the source feeding rate, the powder packing density, the oxygen partial pressure and the total pressure. The change in reflectivity has also been recorded during pulsed-delivery growth. Nanometer-scale resolution is obtained which demonstrates that this method can be extended to the study of multilayer oxide structures.
Microstructure And Mechanical Properties Of Electroplated Cu Films For Damascene Ulsi Metallization
Authors: Dubin V. M. , Morales G. , Ryu C. , Wong S. S.
Published: April 2011

Copper has been deposited for filling sub-0.5 μm trenches by using electroplating. Electroplating with pulse plating conditions provides the high deposition rate (0.5–1 μm/min) and defect-free filling the 0.25 μm trenches and vias of high aspect ratio (>4:1). Enhanced copper electroplating at the trench bottom has been achieved. The median grain size of electroplated copper was measured to be about 1 jim and the lognormal standard deviation is about 0.4 μm. Strong <111> texture was observed in electroplated Cu film. Low stress of electroplated Cu films and excellent adhesion of plated Cu to sputtered Cu seed were observed.
Coherency and Loss of Coherency in Multilayers
Authors: Hazzledine P. M. , Grinfeld M. A. , RAO S. I.
Published: April 2011

A multilayer consisting of parallel sided, elastically isotropic layers with thicknesses much smaller than their dimensions in the plane of the layers may develop large coherency stresses when the layers are thin enough. General formulae are given for the stress tensors in a flat periodic fully coherent multilayer which may contain any number of layers, each with different lattice parameters, elastic constants and thicknesses. As the thicknesses of the layers increase there is an increasing tendency for the interfaces to become incoherent thereby relaxing the elastic stresses, at the expense of creating higher energy interfaces between the layers. This tendency is particularly marked for unusually thick or unusually rigid layers or for layers with very large or small lattice parameters. Unlike the case of thin films on massive substrates, there is no single thickness at which coherency is lost. In this paper, the loss of coherency is explored by searching for energy minima in irregular multilayers.
The Hardness and Wear of Electrochemically Grown Tantalum Oxide
Authors: Mulivor A. W. , Mann A. B. , Searson P. C. , Weihs T. P.
Published: April 2011

For several metallic systems, including tantalum, barrier (non-porous) oxide layers up to 200 nm thick can be grown quickly and efficiently using electrochemical techniques. The thickness of the oxide layer has been found to be linearly proportional to the voltage applied during the electrochemical growth process. These oxides can cause a substantial increase in both the hardness and wear-resistance of the surface. Ex-situ Micro and Nano indentation testing of the Ta/ Ta2O5 system has clearly shown that the indentation hardness increases with oxide thickness, even for indentation depths much greater than the oxide thickness. AFM imaging of indentations and analysis of nanoindentation curves suggests this increased hardness is due to the oxide impeding the pile-up of material at the edges of the indentation, which changes the geometry of the contact. Tribometer testing of various oxide thicknesses has shown that the oxide plays a similar role in preventing wear, specifically by preventing the transfer of material between the two contacting bodies and spreading the load over a greater area. Thus, the electrochemical growth of Ta2O5 provides a convenient method for providing protective hard coatings.