bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal Chemistry of Chemically Delithiated Layered Oxide Cathodes of Lithium Ion Batteries
Authors: Manthiram A. , Venkatraman S.
Published: April 2011

The structural and chemical stabilities of layered Li1-xCoO2-δ, Li1-xNi0.85Co0.15O2-δ and Li1-xNi0.5Mn0.5O2-δ (0 ≤ (1-x) ≤ 1) cathodes have been investigated by chemically extracting lithium from the corresponding LiMO2 with the oxidizer NO2BF4 in acetonitrile medium. While Li1-xCoO2-δ and Li1-xNi0.85Co0.15O2-δ begin to form a P3-type and a new O3-type (designated as O3') phases, respectively, for (1-x) < 0.5 and (1-x) < 0.3, Li1-xNi0.5Mn0.5O2-δ maintains the initial O3-type structure without forming any second phase. Chemical analysis with a redox titration indicates that the Li1-xCoO2-δ, Li1-xNi0.85Co0.15O2-δ, and Li1-xNi0.5Mn0.5O2-δ systems begin to lose oxygen from the lattice, respectively, for (1-x) < 0.5, < 0.3 and < 0.4, which is accompanied by an onset of a decrease in the c parameter. The oxygen loss signals chemical instability and the trend in instability correlates with the charging voltage profiles of the cathodes.
Carbon Coated Silicon Powders As Anode Materials For Lithium Ion Batteries
Authors: Gulbinska M. , Galasso F. S. , Suib S. L. , Iaconetti S. , Russell P. G. , DiCarlo J. F.
Published: April 2011

Novel lithium ion battery anode materials consisting of carbon-coated silicon were prepared. Chemical vapor deposition (CVD) methods were used in the syntheses of these composite materials with toluene being used as the precursor for carbon coatings on silicon powder. The temperature of carbon deposition was 950°C and the deposition time was 30 min for powdered substrates. Carbon-coated silicon powders were analyzed by HRSEM, TEM, and Raman spectroscopy. Coin cells were made and cycled to evaluate the electrochemical performance of carbon-coated silicon powders. Coated materials performed well during the initial coin cell testing. Silicon wafers (orientation <111>) were also used as the substrates for carbon coatings. Silicon wafers were coated for 40 seconds at 950°C. Auger spectroscopy and XPS depth profiling were used to analyze the thin films of toluene-derived carbons on silicon wafers.
Synthesis and Electrochemical Behaviour of Ramsdellite LiCrTiO4
Authors: García-Alvarado F. , Martín-Gil M. , Kuhn A.
Published: April 2011

A ramsdellite with composition LiCrTiO4 has been obtained by heating the spinel of same composition to high temperature. The new ramsdellite has been investigated in view of its possible use as an electrode material in lithium rechargeable batteries. Lithium can be partially extracted from ramsdellite LiCrTiO4 and further intercalated into, by contrast to the spinel of same composition. The average operating voltage during lithium extraction is 4 Volts vs. lithium, and the process produces a specific capacity of 90 mAh/g at 0.1 mA/cm2. On the other hand, upon reduction from open circuit voltage, lithium can be reversibly intercalated into the ramsdellite polymorph at ca. 1.5 V vs. lithium yielding a rechargeable capacity of 110 mAh/g at 0.1 mA/cm2.
Kinetics of Oxygen Exchange in Sr(Ti0.65Fe0.35)O3
Authors: Schneider Th. , Wagner S. F. , Menesklou W. , Ivers-Tiffée E.
Published: April 2011

Current limiting electrochemical pumping cells (amperometric sensors) based on zirconia are commonly used for engine control applications. Fast resistive-type sensors adapted from semiconducting metal oxides are a promising alternative for future exhaust gas monitoring systems. Therefore among the interesting characteristics of the materials system Sr(Ti0.65Fe0.35)O3, including high sensitivity and temperature independence at high oxygen partial pressures (pO2 > 10-4 bar), a short response time (t90 = 30 ms) is obviously the most salient.

The latter is determined by the kinetics of the oxygen surface transfer and subsequent diffusion of oxygen vacancies V‥O. For thin samples and low temperatures the surface transfer is dominant, since bulk diffusion usually occurs very fast. The presented model is based on the frequency-domain analysis of amplitude and phase shift of the response signal obtained from a pO2 modulation in a fast kinetic measurement setup. This method allows both the measurement of response times in the sub-millisecond range as well as the distinction of the behaviour either controlled by volume diffusion or by surface transfer reaction in Sr(Ti0.65Fe0.35)O3 ceramics.
The Effect of Composition on the Wetting Behavior and Joint Strength of the Ag-CuO Reactive Air Braze
Authors: Scott Weil K. , Coyle Chris A. , Kim Jin Yong , Hardy John S.
Published: April 2011

As interest in high temperature electrochemical membrane devices for energy and gas generation has intensified, it has become apparent that developing an appropriate method of hermetically joining the ceramic and metallic components in these devices will be critical to their success. A recently developed technique referred to as reactive air brazing (RAB) has shown promise in the joining of components for planar solid oxide fuel cells (pSOFC) and oxygen generators. In the study described below, the relationship between braze composition, substrate wetting, and joint strenth was investigated to gain further understanding of the RAB process. It was found that braze wettability and joint strength are inversely related for the simple binary Ag-CuO braze system.
Optimization of the sintering of Aurivillius phases using D-optimal statistical design
Authors: Peterson M.S. , Misture S.T.
Published: April 2011

A statistical model has been employed to determine the optimal sintering times and temperatures for Bi2Sr2Nb2TiO12. The phase of interest was made in pure form by solid-state synthesis. Bi2O3 was used as a sintering aid to decrease sintering temperatures and increase densification. The amount of Bi2O3 added and the sintering temperature had a statistical impact on density, while the heat treatment time did not.
Ultra CO Tolerant PtMo/PtRu anodes for PEMFCs
Authors: Ball Sarah C , Thompsett David
Published: April 2011

Progress has been made in designing an anode electrode that can tolerate CO levels of several thousand ppm which are a typical output of a fuel processor consisting of a reformer and water-gas-shift unit only. The combination of a PtMo catalyst that is capable of electrochemically oxidising CO and a PtRu catalyst that can tolerate high levels of CO2 arranged in a bilayer configuration, has been shown to tolerate 2000 ppm CO in H2 with a relatively small loss in fuel cell performance. Further improvements in the ability to tolerate higher levels of CO with lower performance losses are expected due to improved PtMo catalyst design.
Fuel Cell Applications of Nanotube-Metal Supported Catalysts
Authors: Gennett T. , Landi B. J. , Elich J. M. , Jones K. M. , Alleman J. L. , Lamarre P. , Morris R. S. , Raffaelle R. P. , Heben M.J.
Published: April 2011

Novel carbon materials with nanometer dimensions are of potentially significant importance for a number of advanced technological applications. Within this report we describe the results for the electrochemical characterization of a series of single walled carbon nanotube (SWNT) metal supported catalysts as cathodes for basic fuel cell systems. Compared to the typical carbon black electrocatalysts, the nanotube supported platinum catalyst resulted in up to a 140% improvement in the efficiency for a proton exchange membrane (PEM) fuel cell.
The Effect of the Nano and Microstructure of PtRu/C Electrocatalysts Towards Methanol and Carbon Monoxide Oxidation
Authors: Sugimoto Wataru , Kawaguchi Tomoyuki , Murakami Yasushi , Takasu Yoshio
Published: April 2011

Nanoparticul ate Pt50Ru50 supported on a carbon black (CB) were prepared by an impregnation method and the effect of the nano and microstructure towards the electrocatalytic oxidation of methanol and carbon monoxide were evaluated. The in-house prepared PtRu nanoparticles were well-alloyed and finely dispersed on CB, as revealed by XRD and FESEM. FESTEM-EDX analysis of isolated PtRu single nanoparticles indicated that although the majority of the binary particles had a metal composition in accordance to the nominal ratio, some compositional deviation was observed. The activity towards electrocatalytic oxidation of methanol and preadsorbed carbon monoxide is discussed based on the nano and microstructure.
Bipolar Plate-Supported Solid Oxide Fuel Cells for Auxiliary Power Units
Authors: David Carter J. , Cruse Terry A. , Bae Joong-Myeon , Ralph James M. , Myers Deborah J. , Kumar Romesh , Krumpelt Michael
Published: April 2011

This paper presents an advanced design and fabrication concept for a solid oxide fuel cell (SOFC). The concept is based on a laminate repeat unit comprised of a thin electrolyte, cermet anode, metallic gas flow fields, and a metallic bipolar plate. The laminate is sintered in a singlestep process in a controlled atmosphere, and the cathode is applied and sintered in situ during the initial heating of the cell (or stack). Observations about the types of cracks that formed in the electrolyte during the sintering process guided the development of the sintering protocol to yield the desired product. Cells with power densities exceeding 250 mW/cm2 have been tested.
Study of Ammonia Formation During The Autothermal Reforming of Hydrocarbon Based Fuels
Authors: Khan A.R. , Zhao James , Polevaya O. Y.
Published: April 2011

Ammonia formation in autothermal reforming process was studied in Nuvera's Modular Pressurized Flow Reactor facility. Experiments were conducted to study and compare different catalysts for their ammonia formation characteristics. Different hydrocarbon fuels were reformed and effects of fuel structure and operating conditions on ammonia formation were investigated. Reformate generated was analyzed for ammonia contamination by using FTIR spectroscopy.
Microemulsion-Templated Synthesis of Highly Active High-Temperature Stable Partial Oxidation Catalysts
Authors: Kirchhoff Mark , Specht Ullrich , Veser Götz
Published: April 2011

Highly active catalysts for high-temperature partial oxidation reactions have been synthesized based on a microemulsion-templated sol-gel synthesis. The catalysts were tested with the direct catalytic oxidation of methane to synthesis gas and showed excellent selectitivites towards syngas combined with very high activity and low ignition temperatures. Furthermore, a surprisingly high long term stability was observed at these high-temperature conditions of T > 900°C. The catalyst therefore seem very promising candidates for high-temperature partial oxidation and hydrogen production from hydrocarbon fuels.
Miniature Fuel Processors for Portable Fuel Cell Power Supplies
Authors: Holladay Jamie , Jones Evan , Palo Daniel R. , Phelps Max , Chin Ya-Huei , Dagle Robert , Hu Jianli , Wang Yong , Baker Ed
Published: April 2011

Miniature and microscale fuel processors that incorporate novel catalysts and microtechnology-based designs are discussed. The novel catalyst allows for methanol reforming at high gas hourly space velocities of 50,000 hr-1 or higher while maintaining a carbon monoxide levels at 1% or less. The microtechnology-based designs extremely compact and lightweight devices. The miniature fuel processors, with a volume less than 25 cm3, a mass less than 200 grams, and thermal efficiencies of up to 83%, nominally provide 25 to 50 watts equivalent of hydrogen, which is ample for the portable power supplies described here. With reasonable assumptions on fuel cell efficiencies, anode gas and water management, parasitic power loss, the energy density was estimated at 1700 Whr/kg. These processors have been demonstrated with a CO cleanup method and a fuel cell stack. The microscale fuel processors, with a volume of less than 0.25 cm3 and a mass of less than 1 gram, are designed to provide up to 0.3 watt equivalent of power with efficiencies over 20%.
Model Simulation of Powder Compaction by Complex Mold Based on Deformation Behavior of Free Particles Measured by Compression Test
Authors: Hashimoto Hitoshi , Sun Zheng Ming , Park Yong Ho , Abe Toshihiko
Published: April 2011

Discrete element method (DEM) is one of the excellent procedures for model simulation of behavior of granular assemblies. A two-dimensional DEM simulation of powder compaction by a complex mold was conducted by considering the deformation behavior of individual particles measured by a compression test of free particles. Spherical copper particles were used as a model material in this study. The particles (particle size ranges from 38 to 125microns) were individually compressed between parallel platens to measure compressive load and displacement in the loading direction. From the measured load and displacement data, force-displacement relations at contacts between the particles, and between the particles and mold wall were determined. In the simulation, the two-dimensional complex mold consisting of three stages (upper stage:3-mm wide and 1-mm deep, middle stage:2-mm wide and 1-mm deep, lower stage:1-mm wide and 1-mm deep) was charged with the copper powder consisting of spherical particles with size range of 50 to 200microns and was pressed under four press conditions. Forces at all contacts were calculated by using the determined force-displacement relations and each particle's position was traced by solving equations of motion for each particle. Pressure at each wall of the mold and density distribution in the powder compact were calculated as results of the simulation. It was found that the increase in the pressure at each wall corresponds to the increase in the density of the powder near the wall.
Dynamic Behavior of an Intruder in a Granular Couette Flow
Authors: Liu Jian , Rosato Anthony D.
Published: April 2011

This paper reports on three-dimensional, steady discrete element simulations of a single large spherical intruder in a gravity-free granular Couette flow of uniform particles with diameterd.The non-equilibrium nature of the flow is characterized by the depth profile of granular temperature, which decreases inwards toward the center. An intruder of size φ =D/dmigrates away from the walls at a rate that increases with φ and wall velocityU.Computations indicated that the intruder's motion is induced by the high pressure near the wall.
Energy Absorption and Recovery in Tapered Granular Chains: Small Chains and Low Tapering
Authors: Pfannes Jan , Sen Surajit , Chakravarti Soumya , Surve Farhat I.
Published: April 2011

Shock absorption traditionally exploits visco-elastic devices, fluid viscous dampers and friction dampers, or “soft” materials. Recent work on impulse propagation in granular assemblies suggests that it may be possible to absorb shock waves using a different variety of shock absorbers and thus unlock the possibility of building structures that are significantly more shock absorbent than is currently possible, an issue of relevance to concerns of security. These new shock absorbers are composed of granular materials and exploit the nonlinear energy propagation properties in assemblies of granular materials. They have the potential to partially recover the energy of the absorbed shock waves for useful purposes, a property that might allow one to design devices to convert the incident energy to other useful forms. The basic physics of the “tapered chain shock absorber” is briefly discussed in this work.
The Cymbal as an Instructional Device for Materials Education
Authors: White Mary Anne , MacMillan Peter
Published: April 2011

The materials chemistry behind the production of a cymbal provides an opportunity for exploration of a number of materials topics, which could well resonate with students.
Using Interactive Multimedia Tools to Teach Materials Characterization Techniques in the Undergraduate Curriculum
Authors: Prüβner Karin , Pingel Klaus , Becker Jens , Dressel Horst-Peter , Undynko Alexander , Reiner Christof , Schlosser Marc , Christ Hans-Jürgen
Published: April 2011

The paper describes an ongoing project at the University of Siegen to develop multimedia teaching/learning software for materials characterization techniques in an effort to improve the quality of teaching and learning and to increase interest in scientific and engineering subjects in younger students. We have developed a modular web-based teaching platform that uses multimedia tools to provide access to and information about state-of-the-art analytical techniques, visualize complex physical concepts, and use interactive and animated modules to improve student learning.
An Instructional Two-Dimensional Diffraction Laboratory Using Patterns Created with Electron-Beam Lithography
Authors: Inglefield Colin , Anthon Royce
Published: April 2011

An instructional laboratory in two-dimensional diffraction is discussed. The experiment is appropriate for undergraduate students in materials science, solid-state physics (as was the case with our group), modern physics, or optics. The experiment is performed using visible light from a laser incident on a 2D lattice of gold dots deposited with electron beam lithography on a glass substrate. The pattern is microscopic with a lattice constant on the same order of magnitude as the wavelength of light used. Students observe the diffraction pattern, and then quantitatively determine the positions of maxima. These data are used by the students to reconstruct the (real space) microscopic lattice. The students can simulate the experiment with software that computes reciprocal lattice and diffraction patterns for an arbitrary 2D lattice.
Non-Destructive Techniques for the Characterization of Structural Materials: Materials Science & Engineering Curriculum for the Education of an Innovative Model
Authors: Moropoulou Antonia , Aggelakopoulou Eleni , Avdelidis Nicolas P. , Koui Maria
Published: April 2011

In this paper, the example of the Materials Science and Engineering (MSE) Curriculum that exists as a scientific direction in the undergraduate programme of the Chemical Engineering School, in the National Technical University of Athens (NTUA), in Greece, is presented. The course content includes several tools, such as theoretical lessons, laboratory modules - nondestructive testing (NDT) and instrumental techniques - semi industrial scale devices, fieldworks and a dissertation thesis. The presented curriculum can be regarded as an innovative educational model for chemical engineering students that choose to become involved in the field of MSE.
Alignment and Deposition of Single Wall Carbon Nanotubes under the Influence of an Electric Field
Authors: Jaynes Paul , Tiano Thomas , Roylance Margaret , Carey Charles , McElrath Kenneth
Published: April 2011

Single wall carbon nanotubes have aroused a great deal of interest because of their unique combination of electrical, physical and mechanical properties. However, the widespread use of SWNTs in composites and electronic devices is limited because of the difficulty of dispersing and processing these materials. This paper describes a method for depositing and aligning SWNTs from a dispersed solution onto a substrate under the influence of an electric field. Results indicate that SWNTs can be aligned in bulk in the direction of electric field lines, and that individual SWNT ropes may be deposited between two electrodes. The extent and type of deposition depends upon the electrode geometry and processing time. Electrical alignment of SWNTs is an enabling technology allowing manipulation of nanomaterials using standard processing. It could eventually lead to a wide range of products, such as nanocomposites with aligned fillers and nanoelectronic devices.
Wireless and RF Module Packaging using Low Loss Ceramic and Low Loss Organic Materials
Authors: Logothetis James J. , Amey Daniel I. , Mobley Timothy P.
Published: April 2011

This presentation describes the basics of Multi-Mix® and Green Tape™ Low Temperature Cofired Ceramic (LTCC) technologies. The design and performance of a 28 GHz mixer package using a GaAs MMIC and the 943 Green Tape™ LTCC system with embedded capacitance technology is described including the tradeoffs, advantages and compatibility of Multi-Mix® and Green Tape™ technologies. A design approach combining the technologies offers the designer new options to meet the ever-increasing demands of high frequency packaging.
Micr owave Dielectric Properties of (1-x)CaTiO3-xNd(Mg1/2Ti1/2)O3 Ceramics System
Authors: Huang Cheng-Liang , Chen Yuan-Bin , Lo Ching-Wen
Published: April 2011

The microwave dielectric properties of (1-x)CaTiO3-xNd(Mg1/2Ti1/2)O3 (0.1≤x≤1.0) have been investigated. The system forms a solid solution throughout the entire compositional range. The dielectric constant decreases from 152 to 27 as x varies from 0.1 to 1.0. In the (1-x)CaTiO3-xNd(Mg1/2Ti1/2)O3 system, the microwave dielectric properties can be effectively controlled by varying the x value. A maximum quality factor Qxf=43000GHz (where f is the resonant frequency) was achieved for samples with x=0.9, although the dielectric properties varied with sintering temperature. The Qxf value of (1-x)CaTiO3-xNd(Mg1/2Ti1/2)O3 almost increased up to 1500°C, after which it decreased. At 1400°C, 0.1CaTiO3-0.9Nd(Mg1/2Ti1/2)O3 ceramics gives a dielectric constant εr of 42, a Qxf value of 35000 (GHz) and a τf value of -10 (ppm/°C).
Microwave Dielectric Properties of LaScO3-TiO2 Materials
Authors: Kwon Do-Kyun , Lanagan Michael T. , Shrout Thomas R.
Published: April 2011

From fundamental ionic polarizability concepts, LaScO3 was projected as a candidate dielectric material for microwave application. The microwave dielectric properties of LaScO3 were obtained as the dielectric permittivity of 24, Q×f of 18,000 GHz, with a temperature coefficient of resonant frequency (TCF) of −69 ppm/°C. Solid solutions and polyphase assemblages were investigated in the LaScO3-TiO2 system as a function of TiO2 content, and correlated with the microwave dielectric properties. Orthorhombic perovskite LaScO3 transformed to tetragonal symmetry with Ti substitution on the B-site of LaScO3 owing to the ionic radius difference between Sc3+ and Ti4+. With this phase transition, the formation of A-site vacancies (VLa‴) resulted in the precipitation of a La deficient secondary phase. The substitution of Ti also affected the dielectric properties. The dielectric constant increased and TCF became less negative with increased TiO2 addition. However, the Q×f value decreased, due to the formation of the secondary phase. For the case of the 0.6LaScO3-0.4TiO2 composition, a dielectric K of 40, Q×f of 6,000 GHz and nearly zero TCF were obtained.
High-Density, Low-loss MOS Decoupling Capacitors integrated in a GSM Power Amplifier
Authors: Roozeboom F. , Kemmeren A. , Verhoeven J. , van den Heuvel E. , Kretschman H. , Frič T.
Published: April 2011

High-density MOS capacitors have been fabricated with ∼ 30 nF/mm2 specific capacitance on highly-doped Si-wafers with arrays of macropores with ∼ 2 μm diameter. Using the Bosch process [1] these pores were dry-etched to depths of ∼ 30 μm or more. The enlarged Si-surface thus obtained serves as a substrate for capacitors fabricated by fully MOS-compatible processing.

Wafers were fabricated with a top electrode of poly-Si and Al and ‘ONO’ (i.e. oxide / nitride / oxide) dielectric stacks showing 7–10 MV/cm electrical breakdown field and leakage < 1 nA/mm2 @ 20 V. These wafers were thinned to 380 μm and sawn into dies, representing 40 nF capacitors. Typically low loss factors such as ESR < 50 mΩ and ESL < 20 pH and resonance frequencies of ∼ 0.1 GHz were found for 40 nF capacitor dies. Next, 40 nF dies were mounted by wire bonding on Al2O3 or laminate substrate as supply-line decoupling capacitors in complete GSM power amplifier test modules. RF decoupling and transmission were measured and compared to identical test modules with conventional discrete ceramic capacitors. The MOS capacitors showed very efficient decoupling, resulting in superior signal stability as measured in the 0 – 1 GHz range (less noisy, free from oscillations).

The new capacitor is very suitable for integrated decoupling purposes, e.g. supply-line decoupling in RF wireless communication and analog and mixed-signal systems.
RF-MEMS: Materials and technology, integration and packaging
Authors: Tilmans Harrie A. C.
Published: April 2011

MEMS technology is rapidly emerging as an enabling technology to yield a new generation of highperformance RF-MEMS passives, like switches, tunable capacitors, high-Q resonators and tunable filters. This paper presents the progress in RF-MEMS device and package development with focus on relevant technology and material issues. The importance of wafer-level or 0-level packaging of the RF-MEMS devices is elucidated. Examples of 1-level packaging, e.g., chip-on-board or plastic molded 1-level package, are briefly described. The paper concludes in stipulating how integration of RF-MEMS passives with other passives (as inductors, LC filters, SAW devices) and active circuitry (RFICs) can lead to so-called “RF-MEMS system-in-a-package (RF-MEMS-SiP)” modules. The evolution of the RF-MEMS-SiP technology is illustrated using IMEC's microwave multi-layer thin film MCM-D technology.
Photodefinable Metal Oxide Dielectrics: A Novel Method for Fabricating Low Cost RF Capacitive MEMS Switches
Authors: Wang Guoan , Jeyakumar Augustin , Papapolymerou John , Henderson Clifford L.
Published: April 2011

In this paper, a novel approach for fabricating low cost capacitive RF MEMS switches using directly photodefinable high dielectric constant metal oxides has been developed. In this approach, a radiation sensitive metal-organic precursor is deposited via spin coating and converted patternwise to a high dielectric constant metal oxide via ultraviolet exposure. The feasibility of this approach is demonstrated by fabricating bridge-type and cantilever-type switches with a nitride/metal-oxide/nitride dielectric film stack. These switches exhibited significantly higher isolation and load capacitances as compared to comparable switches fabricated using a simple silicon nitride dielectric.
Pyroelectric Properties of Ferroelectric Thin Films: Effect of Internal Stresses
Authors: Sharma A. , Ban Z.–G. , Alpay S. P.
Published: April 2011

A thermodynamic model is employed to analyze the effect of internal stresses on the pyroelectric response of ferroelectric thin films. The pyroelectric coefficient as a function of the misfit strain is calculated for (001) Ba0.6Sr0.4TiO3 epitaxial thin films by taking into account formation of misfit dislocations that relieve epitaxial stresses during deposition. It is shown that the pyroelectric response is highly dependent on the misfit strain in epitaxial thin films. Enhanced pyroelectric coefficient can be achieved by adjusting the misfit strain via substrate selection and film thickness especially in the vicinity of the ferroelectric to paraelectric phase transformation.
Deposition Of BaTiO3 Thin Films And MgO Buffer Layers On Patterned GaAs Substrates For Integrated Optics Applications
Authors: Chen Ding-Yuan , Murphy Timothy E. , Phillips Jamie D.
Published: April 2011

This work addresses the need for thick layers of ferroelectric thin films on semiconductors for integrated optics applications. The deposition of BaTiO3 thin films with MgO buffers on patterned GaAs substrates is presented as an approach to achieve crack-free optical waveguiding structures. Cracking and peeling of the thin films are observed on patterns with lateral dimensions exceeding 60 microns and nearly crack-free thin films for patterns with lateral dimensions of a few microns. The cracking and peeling of the thin films is attributed to thermal expansion mismatch during the heating and cooling steps of the deposition process. A thin film stress and fracture model is used to analyze the phenomenon. Reduced cracking and peeling on the patterned features are attributed to strain relief on the patterned features. The inclusion of thick AlxOy buffer layers obtained through wet-oxidation of AlGaAs prior to BaTiO3/MgO deposition are presented as a means of obtaining electro-optic waveguide structures on GaAs.
An Effective Way to Suppress the Pyrochlore Phase Formation in SBT Thin Films
Authors: Jung Se-Yeon , Kwak Woo-Chul , Hwang Seung-Joon , Sung Yun-Mo
Published: April 2011

Sr0.7Bi2.4Ta2O9 (SBT) thin films were deposited on Pt/Ti/SiO2/Si substrates with and without a seed layer of ∼40 nm thickness using sol-gel and spin coating methods. The influence of seed layer on the phase formation characteristics of SBT thin films was investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. Formation of pyrochlore as well as Aurivillius phase was observed in both the unseeded and seeded SBT films heated at 740°C. However, it was revealed that Aurivillius phase formation was enhanced in seeded SBT thin films and pyrochlore phase formation was highly suppressed. In this study, two possible mechanisms for the suppression of pyrochlore phase formation were proposed from the perspectives of activation energy difference for Aurivillius and pyrochlore phase formation and Bi-ion diffusion to pyrochlore phase.
Polarization Enhancement of Nd-Modified Bismuth Titanate Prepared by Pulsed Laser Deposition at Low Temperature
Authors: Wenbiao Wu , Akira Shibuya , Minoru Noda , Masanori Okuyama
Published: April 2011

Neodymium-modified Bi4Ti3O12(BNdT) thin films have been prepared by pulsed laser deposition (PLD), aiming to realize enhanced ferroelectric properties by a low temperature treatment. When deposited at 500°C, the film shows P-E hysteresis having twice remanent polarization 2Pr of 78.8 μC/cm-2, coercive force Ec of about 250 kV/cm, and leakage current of less than 10-7 A/cm2 from -50 to +50 kV/cm. Good fatigue properties of BNdT films deposited at 5 Hz have been obtained up to 1010 cycles of 500 kHz bipolar square pulses, with less than 25% decrease of +Pr and -Pr.
Preparation and Characterization of Ba1-xSrxTiO3 Based Thin Films for Pyroelectric Applications
Authors: Hubbard C. W. , Cole M. W. , Ervin M. , Wood M.
Published: April 2011

The use of pyroelectric thin films in uncooled IR detectors has many advantages over the present IR detector technology, which requires extensive cooling for operation. These advantages include reduced weight, reduced footprint, reduced complexity, increased reliability, and decreased maintenance. Ba1-xSrxTiO3 (BST), based thin films are ideal candidates for use in these devices due to their tailorable materials properties. These properties include a high dielectric constant, low dielectric loss, high electrical resistivity, as well as a high pyroelectric constant. BST thin films were doped with Mg in varying amounts, from 0 to 20mol%. The thin films were deposited via metalorganic solution deposition (MOSD) on Pt/Ti/SiO2/Si substrates. Annealing temperatures ranged from 500 to 750 °C. The films were characterized for structural, microstructural, compositional, surface morphological, dielectric and insulating properties. Glancing angle x-ray diffraction (GAXRD) was used to determine crystallinity, phase formation and film orientation. Field emission scanning electron microscopy (FESEM) and cross sectional transmission electron microscopy (TEM) were employed to access surface morphology and microstructure. The Materials Detectivity Figure of Merit (FOM), D*, [D*=pi/(CV(ε0εrtanδ)1/2] was used to evaluate the film's detectivity response. Our results show that undoped Ba60Sr40TiO3, with a value D*= 0.08 (cm3/J)1/2, appears to out perform Pb based pyroelectric thin films, thus making it a viable candidate for IR pyroelectric detector applications.
Ferroelectric Domain Structure and Local Piezoelectric Properties of Sol-Gel Derived Pb(Zr1-xTix)O3 Films
Authors: Bdikin I. K. , Shvartsman V. V. , Kholkin A. L. , Kim Seung-Hyun
Published: April 2011

High-resolution domain studies are performed on Pb(Zr1-xTix)O3 (PZT) films of different thicknesses and compositions (x=0.30, 0.48, and 0.70) by piezoresponse force microscopy (PFM). Depending on the composition, the orientation of the films is varied from purely (111) (related to the orientation of Pt bottom electrode) to a more random texture. Statistical processing of the obtained domain images is used to analyze the correlation between the composition of the films and their nanoscale piezoelectric properties. It is shown that the virgin (unpoled) films possess large piezoelectric activity comparable to that after local poling (self-polarization effect). This corresponds to a clear predominance of the domains with polarization oriented from the free surface of the film to the bottom electrode. Both the average piezoelectric signal and half-width of the piezoelectric histograms depend on the composition and thickness of the films. The largest local piezoelectric coefficient and the broadest distribution are found for tetragonal (x=0.70) films with almost pure (111) texture. The results are discussed in terms of texture and PFM instrumentation effects on local piezoelectric measurements.
Compositionally Asymmetric Tri-Color Superlattices Grown by Pulsed Laser Deposition
Authors: Lee H. N. , Christen H. M. , Rouleau C. M. , Senz S. , Lee S. K. , Hesse D. , Lowndes D. H.
Published: April 2011

Compositionally asymmetric tri-color superlattices (TCS) with a combination of BaTiO3/SrTiO3/CaTiO3 have been grown by pulsed laser deposition (PLD) on atomically-flat SrRuO3-covered (001) SrTiO3 substrates. Conducting SrRuO3 films with single-terrace steps that closely mimic those of the SrTiO3 substrate also were grown by PLD and serve as bottom electrodes. In order to achieve atomic control of each layer, we have calibrated precisely the number of laser pulses required to grow one unit-cell-thick layers (∼200 for a laser spot of 0.4 mm2). These conditions allowed recording of pronounced oscillations of the reflection high-energy electron diffraction (RHEED) specular spot intensity over the entire growth run - even for TCS layers totaling more than 1000 nm in total thickness.
Low Temperature Crystallization of Bismuth Layer-Structured Ferroelectric Thin Films Using Lead Titanate Sol-Gel Templating Technique and Their Electrical Properties
Authors: Karasawa Junichi , Kijima Takeshi , Natori Eiji , Shimoda Tatsuya
Published: April 2011

The crystal structure and electrical properties of lead titanate (PbTiO3: PT) sol-gel network templated bismuth layer-structured ferroelectric (BLSF) thin films were systematically investigated as a function of the doping amount of lead titanate sol-gel solution and annealing temperature. The starting solutions of lead titanate sol-gel templated BLSF were prepared by adding lead titanate sol-gel solution to BLSF solutions such as strontium bismuth tantalate (SrBi2Ta2O9: SBT), bismuth titanate (Bi4Ti3O12: BiT) and lanthanum-doped bismuth titanate ((Bi,La)4Ti3O12: BLT). These solutions were spin-coated on platinized silicon wafers and pyrolized on a hot plate, then crystallized at 550°C – 738°C by RTA (Rapid Thermal Annealing). The crystallized films with sputtered platinum top electrodes were post-annealed for electrical property measurements. In the case of SBT-PT, it was found that the added lead titanate so-gel network has no remarkable effect on lowering the BLSF (m=2) crystallization temperature but rather enhances the pyrochlore phase. In the case of BiT-PT, the bismuth layered-structure was confirmed at the temperature down to 550°C as the amount of lead titanate sol-gel network is increased. The major layered-structure, however, was not desired m=3, but unexpected m (e.g m=4 or higher). In the case of BLT-PT, lowering the BLSF (m=3) crystallization temperature down to 638°C was finally achieved within proper amount of lead titanate sol-gel network without drastic drop of ferroelectricity. A 2Pr of 32 μC/cm2 was obtained in 0.96BLT-0.04PT thin film.
Time-domain Terahertz Spectroscopy of Strontium Bismuth Tantalate Thin Films
Authors: Kotani K. , Misra M. , Kawayama I. , Tonouchi M.
Published: April 2011

We have measured the dielectric and optical properties of pulsed laser deposited SrBi2Ta 2O9 and Sr0.8Bi2.2Ta2O9 thin films on MgO substrate in THz frequency region by THz time-domain spectroscopy. The imaginary parts of the dielectric constant of both the samples show broad peaks in the frequency range 0.5–1.0 THz, which may be due to the soft mode in SBT in this frequency spectrum. The difference in the real part of the dielectric constant of Sr0.8Bi2.2Ta2O9 thin films is small for MHz and THz frequencies. On the other hand, the value of real part of dielectric constant of SrBi2Ta2O9 thin films in THz frequency range is much smaller than that in MHz frequency region, indicating that SrBi2Ta2O9 is not simply displacive ferroelectric material.
Low-Temperature Synthesis and Dielectric Properties of Single-Phase Lead Zirconate Titanate Thin Film with a Nano Particle Seeding Technique
Authors: Tanase Tomokazu , Kobayashi Yoshio , Miwa Takao , Konno Mikio
Published: April 2011

The low temperature synthetic method, which combines chemical solution deposition and nm-seeding technique, was applied to the fabrication of lead zirconate titanate (PZT) thin films. Nano-crystallines of barium strontium titanate (BST) particles were prepared by the hydrolysis reaction of the complex alkoxides. PZT precursor solutions containing the BST particles were spin-coated on Pt/Ti/SiO2/Si substrates to film thickness of 500 − 800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and crystallized PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10-6 A/cm2 at applied electric field from 0 to 64 kV/cm.
Low Temperature Dielectric Properties of BST/ZrO2 Multilayer Films
Authors: Sahoo Santosh K. , Agrawal D. C. , Majumder S. B. , Katiyar R. S. , Mohapatra Y. N.
Published: April 2011

Thin films of Ba1-x SrxTiO3 (BST) are being actively investigated for applications in dynamic random access memories (DRAM) because of their properties such as high dielectric constant, low leakage current, and low fatigue. Several approaches have been used to improve the properties of thin films such as doping with aliovalent dopants, graded compositions, and layered structures. We have found that interposing layers of an electronic insulator such as ZrO2 in between BST layers results in a significant reduction in the leakage current. In this paper the low temperature electrical properties of these multilayer structures are reported. The structures consist of alternate layers of Ba0.8Sr0.2TiO3 and ZrO2 deposited by a sol-gel process on platinized Si substrates. The thickness and the number of layers are varied while keeping the total thickness of the film constant. Multiple peaks in the dielectric constant vs temperature plots at all frequencies are observed in the multilayered films. The properties of the multilayer films are a complex function of the number of layers and their thicknesses. A structure with several thin layers of ZrO2 interposed between the BST layers produces smoother plots than a single layer of ZrO2 of same total thickness. This is attributed to more uniform distribution, as determined by XPS, of ZrO2 in the multilayer structure due to smaller diffusion distances.
Microwave Measurements of Ferroelectric Thin Films: Techniques, Error and Limitations
Authors: Petrov Peter Kr.
Published: April 2011

This paper examines the problem of evaluating the microwave properties of thin ferroelectric films patterned as planar capacitors. Two types of microwave measurements of ferroelectric thin films are considered: reflection and resonance type measurements. Algorithms are presented for evaluation of capacitance-permittivity and dielectric loss. Using sensitivity analysis, the error and limitations associated with these measurements are estimated. The end result is a series of formulae that use the network analyser's measurement data to calculate the capacitance-permittivity, the dielectric loss, and the associated error.
Property Design of SrBi2Ta2O9 by Defect Engineering
Authors: Noguchi Yuji , Miyayama Masaru
Published: April 2011

Defect engineering is shown to be an effective to design for remanent polarization (Pr) and coercive field (Ec) in SrBi2Ta2O9 (SBT). Cation vacancies and oxygen vacancies are shown to play an essential role in the polarization properties. The ceramic samples were prepared by a solid-state reaction, and high-density ceramics (over 95% of the theoretical density) were used for the measurements of polarization and dielectric properties. High-resolution neutron powder diffraction revealed that trivalent-cation (Bi, rare-earth elements [RE=La, Ce, Pr, Nd, Sm]) substitution induces Sr vacancies in the perovskite blocks for the requirement of charge neutrality. The substitution of La with Sr vacancies (La0.33Sr0.5Bi2Ta2O9) increased 2Pr from 13 μC/cm2 (SBT) to 16 μC/cm2, and the 2Ec value (41 kV/cm) was much smaller than that of SBT (57 kV/cm). Nd-substituted SBT showed the same Pr of La-SBT, while 2Ec (140 kV/cm) of Nd-SBT (x=0.5) was much higher than that of La-SBT. The higher Ec found for Nd-SBT is attributed to partial Nd substitution at the Ta site with the creation of oxygen vacancies. The control of Ec for RE-SBT is discussed in terms of Sr vacancies and oxygen vacancies.
Fabrication of Ru/Bi4−xLaxTi3O12/Ru Ferroelectric Capacitor Structure Using a Ru Film Deposited by Metalorganic Chemical Vapor Deposition
Authors: Furukawa Taisuke , Kuroiwa Takeharu , Fujisaki Yoshihisa , Sato Takehiko , Ishiwara Hiroshi
Published: April 2011

A Ru/ Bi 4-xLaxTi 3O12/Ru (Ru/BLT/Ru) capacitor structure with Ru top electrodes deposited by metalorganic chemical vapor deposition (MOCVD) was fabricated. On a Ru film deposited by MOCVD, BLT film was formed by a sol-gel method and crystallized in vacuum. Depositing a conformal Ru film on a BLT/Ru structure by MOCVD, Ru/BLT/Ru stack with smooth and flat surface was successfully formed. Then, ferroelectric Ru/BLT/Ru capacitors were fabricated through a dry etching process. It exhibited both good ferroelectric properties (2Pr =16 μC/cm2) and low leakage current density (J =10−7 A/cm2), suggesting that Ru film deposited by MOCVD showed sufficient properties for the tope electrode of Ru/BLT/Ru structures.
Single- and Multi-target Pulsed Laser Deposition of Thin BSTO films: Preparation, Microstructure and Electrical Properties
Authors: Sarma Kumaravinothan , Petrov Peter Kr. , Alford Neil McN.
Published: April 2011

A comparative study of microstructure and electrical properties of BaxSr1-xTiO3 films made by single- and multi-target pulsed laser deposition was carried out. The films were epitaxially grown on both LaAlO3 and MgO substrates. The structural properties of all samples were investigated using X-ray diffraction and Raman spectroscopy. The elemental composition of the samples was investigated using energy dispersive X-ray analysis. For electrical properties examination, a simple capacitor structure was patterned on the film surface. Thin films made using both methods exhibit similar structural and electrical properties; however the samples made by a multi-target method underwent phase transition in a broader temperature region. The results prove the possibility of using the multi-target pulse laser deposition as a more flexible method for engineering thin film stoichometry.
Ferroelectric Films and Multilayers with Ultrahigh Dielectric Constants
Authors: Li Kewen , Zou Kevin , Wang Yanyun , Jiang Hua , Chen Xuesheng
Published: April 2011

This work presents a systematic study of ferroelectric films and multilayers made by a metal-organic chemical liquid deposition method. BaxSr1-xTiO3, Pb(Mg1/3Nb2/3)O3-PbTiO3, and Pb(Zn1/3Nb2/3)O3-PbTiO3 films, as well as multilayers incorporated with these materials have been grown at different conditions. Ultrahigh dielectric constant (∼6700) has been achieved in the PMN/PZN-PT multilayers when the sublayer thickness approached to nanometer scale, where interfaces become dominant. When the sublayer materials with desired Curie temperatures were properly chosen, the temperature dependent dielectric constant of the multilayer structure could be greatly reduced. These nanostructured multilayers may find very important applications where temperature variation is a key concern. Pb doping in BaxSr1-xTiO3 was found very efficient in increasing the dielectric constant and reducing the loss. It is believed that the addition of Pb improved the film density and reduced the grain boundary defects.
Long Retention Performance of a MFIS Device Achieved by Introducing High-k Al2O3/Si3N4/Si Buffer Layer
Authors: Fujisaki Yoshihisa , Iseki Kunie , Ishiwara Hiroshi
Published: April 2011

We introduced high-k Al2O3/Si3N4 buffer layer in MFIS (Metal-Ferroelectric-Insulator-Semiconductor) devices to reduce the leakage current though the buffer (I) layer. We prepared the buffer layer by nitridizing Si substrate by atomic nitrogen radicals and then deposited Al2O3 film using ALD (Atomic Layer Deposition) technique. The interface state density between the ALD-Al2O3/Radical-Si3N4 stacked insulator and a Si substrate is as low as 1011 cm-2eV-1. The current density less than 10-9 A/cm2 is realized under the 1V bias application using films with the capacitance density of 12fF/μm2. The c-axis oriented Bi3.45La0.75Ti3O12 (BLT) ferroelectric films were deposited to make MFIS structure. With this structure, we obtained the retention time as long as 1.5×106 sec (about 17 days). This excellent retention character is attributable to the high insulating property of the ALD-Al2O3/Radical-Si3N4 stacked insulator and also attributable to the perfect elimination of defects at the interfaces in the MFIS structure.
Selective Deposition of C-axis Oriented Pb5Ge3O11 on the Patterned High k Gate Oxide by MOCVD Processes
Authors: Li Tingkai , Hsu Sheng Teng , Ulrich Bruce , Evans Dave
Published: April 2011

For the high density FeRAM applications, the integration process-induces damages such as etching damage that degrades the properties of FRAM devices and the high surface roughness of ferroelectric thin film that results in the difficulty for alignment are critical issues. In order to solve these problems, selective deposition process is developed to simplify the integration processes and improve the properties of FeRAM memory devices. Based on the differential deposition rates of ferroelectric materials on high-k oxide and silicon dioxide, we can selectively deposit a c-axis oriented PGO thin film on the patterned high-k oxide such as ZrOx (x=0–2), HfOx (x=0–2), TiO2, and their mixtures other than on SiO2. By patterning the high-k dielectric, the PGO deposition is limited to just the preferred pattern high-k area. SEM, EDX and x-ray measurements further confirm that the c-axis oriented PGO thin films are selectively deposited on the high-k gate oxide other than on the field SiO2 including alignment mark area, which will eliminate the roughness problem for the alignments. Also the etching damage is eliminated since there is no need to etch the PGO film, which improved the properties of FeRAM devices.
Smart Heterostructures Based on Solid Solution ZnCdHgTe
Authors: Khlyap Galina M. , Sydorchuk Petro G. , Polit Jacek , Oszwaldowsky Macej
Published: April 2011

Current – voltage (IVC) and capacitance – voltage (CVC) of heterostructures (Cd, Zn)Te/ZnCdHgTe are studied for the first time. Thin films ZnxCdyHg1-x-yTe were grown on monocrystalline (111) CdTe and ZnTe substrates by PLE technology. Deposition was carried out on substrates held at temperatures near 290 K. The thickness of investigated films was estimated to be about 5 μm. Electric characteristics of the as-grown structures were examined under T = 77–290 K in the wide range of applied bias. All investigated samples have demonstrated diode-like IVC and CVC under test signal frequency f = 1 kHz. Heterostructures CdTe/ZnCdHgTe have exhibited a room temperature photosensitivity in spectral range 0.50–0.65 μm.