bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical and Electrical Properties of Metal Nanoclusters Embedded in a Dielectric Medium
Authors: Dumas-Bouchiat Frédéric , Asad Syed Salman , Champeaux Corinne , Catherinot Alain , Crunteanu Aurelian Stanescu , Blondy Pierre
Published: April 2011

We present the synthesis and optical and electrical characterization of amorphous nanocomposite layers made of metallic nanoclusters embedded in an alumina (Al2O3) matrix (nc-M:Al2O3 with M= Ag, Cu and Co). The nanocomposites, obtained by a pulsed laser deposition (PLD)- derived method, exhibit specific optical plasma resonance absorption in the visible and UV region. The position of the absorption peaks depends on the cluster type and gives information about its dimension and nature (metal or oxide). The results fit well with the size and shape distribution recorded by transmission electron microscopy (TEM). Electrical properties and conduction mechanisms of nc-Co:Al2O3 layers were investigated for different doping levels and in temperature range of 303-473 K. It was concluded that space charge limited currents theory (SCLC) can be assumed as major conduction mechanism, at least for intermediate doping levels (∼9 vol.%).
Forward Active and Blocking Performance of 4H-SiC Bipolar Junction Transistors
Authors: Balachandran Santhosh , Chow T. Paul , Agarwal Anant
Published: April 2011

We evaluate the performance capabilities and limitations of high voltage 4H-SiC based Bipolar Junction Transistors (BJTs). Experimental forward characteristics of a 4kV BJT are studied and simulations are employed to determine the factors behind the higher than expected specific on-resistance (Ron,sp) for the device. The impact of material (minority carrier lifetimes), processing (surface recombination velocity) and design (p contact spacing from the emitter mesa) parameters on the forward active performance of this device are discussed and ways to lower Ron,sp, below the unipolar level, and increase the gain (β) are examined. A correlation between the open base blocking behavior (forward blocking) and the current gain (forward active) for 4H-SiC based high-voltage BJTs with lightly doped collector regions is presented and experimental device characteristics are utilized to verify our numerical analysis.
Electronic Acoustic Sensor
Authors: Bharti Vivek , DeRoos Fred L.
Published: April 2011

The Stethoscope (acoustic sensor) is a fundamental tool for the diagnosis of diseases and conditions of the cardiovascular (CV) system. It serves as the most commonly employed technique for diagnosis of such diseases and conditions in primary health care and in circumstances where sophisticated medical equipment is not available, such as remote areas. The piezoelectric sensor was used as an acoustic sensor. The sensitivity of the sensor was improved more than 20 times with our new design. The signal-to-noise ratio was further improved by using unique sensor housing and by using an electronic amplifier in the differential mode.
Ion Beam Modified Conducting Polymer Composites: Material for Gas Sensing
Authors: Singh Virendra , Kaur Manindar , Singh Tejvir , Chandra Amita , Srivastava Alok
Published: April 2011

A polyaniline based conducting composite was prepared by oxidative polymerisation of aniline in presence of polyvinylchloride (PVC) matrix. The coherent free standing thin films of the composite were prepared by solution casting method. The PVC-polyaniline composite (90:10) of thickness 40 μm was irradiated with 90 MeV C5+ ions at different ion fluence ranging 5× 1011-5× 1013 ions/cm2. The changes in resistance of pristine and irradiated composite in presence of ammonia gas were studied. A general decrease in surface resistance is observed upon irradiation. The sensitivity, response time and recovery time were studied as a function of ion fluence on exposing the sensor material to ammonia gas at ambient condition. It is observed that irradiated composite films are more sensitive and fast in response to ammonia gas. The preliminary results observed are encouraging.
AFM Characterization of Electroactive Polymer Nanocomposites
Authors: Pérez Ricardo , Ounaies Zoubeida , Lillehei Peter , Harrison Joycelyn
Published: April 2011

An AFM-based method is used to probe the electromechanical response of a polyimide-SWNT nanocomposite at the nanoscale level. Our previous investigations on bulk polyimide-SWNT nanocomposites using a fiber optic sensor-based method have shown that the nanocomposites are electroactive and exhibit a quadratic relationship between output displacement and input voltage. In the current study, the composites are probed at the nanoscale using the AFM in contact mode. One goal of the current study is to assess the AFM-based technique in measuring our nanocomposites and verifying their actuation. A second goal is to improve the methodology itself by characterizing a commercially available piezoelectric ceramic, PZT, and a commercially available piezoelectric polymer, PVDF. The experiments are conducted in contact mode under the application of a DC voltage. Values for the strain piezoelectric coefficients d33 are widely reported in the literature and consequently permit to calibrate the methodology applied in the present work.

These findings, coupled with bulk film characterization will be used to shed light on the polyimide-SWNT interaction and its effect on the electroactive mechanism displayed by the nanocomposites.
Poly(Vinyldene Fluoride-Trifluoroethylene-Chlorofluoroethylene) Terpolymer as High-energy-density Capacitor Materials
Authors: Chu Baojin , Zhou Xin , Neese Bret , Zhang Q. M.
Published: April 2011

Recently, PVDF-TrFE-CFE terpolymer was developed in Penn State University. The polymer exhibits relaxor ferroelectric behavior. At room temperature, the low-field dielectric constant can be as high as 50-60, more than ten times larger than other dielectric polymer materials, such as Polypropylene, the most widely-used polymer materials for capacitor applications. Due to the large change of electric field induced polarization and high breakdown field, energy density of the terpolymer can reach ∼10 J/cm3, much larger than other polymer materials. In this paper, experimental results on energy density and non-linear dielectric behavior of the terpolymer will be reported.
Spectroscopic Signature of Aging in δ-Pu(Ga)
Authors: Chung Brandon , Schwartz Adam , Ebbinghaus Bartley , Fluss Michael , Haslam Jeffrey , Blobaum Kerri , Tobin James
Published: April 2011

Plutonium, because of its radioactive nature, ages from the “inside out” by means of self-irradiation damage and thus produces nanoscale internal defects. The self-irradiation induced defects come in the form of Frenkel-type defects (vacancies and self-interstitial atoms), helium in-growth, and defect clusters. At present there are neither experimental nor theoretical models describing the changes in the electronic structure caused by the aging in Pu. This fact appears to be associated primarily with the absence of reasonably convincing spectroscopic evidence of the changes. This paper demonstrates that Resonant Photoemission, a variant of Photoelectron Spectroscopy, has strong sensitivity to aging of Pu samples. The spectroscopic results are correlated with an extra-atomic screening model, and are shown to be the fingerprint of mesoscopic or nanoscale internal damage in the Pu physical structure. This means that a spectroscopic signature of internal damage due to aging in Pu has been established.
Isothermal δ / α′ Transformation and TTT Diagram in a Plutonium Gallium Alloy
Authors: Oudot Benoit Jean-Paul , Blobaum Kerri , Wall Mark , Schwartz Adam
Published: April 2011

Differential scanning calorimetry (DSC) is used as an alternative approach to determining the time-temperature-transformation (TTT) diagram for the martensitic delta to alpha-prime transformation in a Pu-2.0 at% Ga alloy. Previous work sugests that the TTT diagram for a similar alloy exhibits an unusual double-C curve for isothermal holds of less than 100 minutes. Here, we extend this diagram to 18 hours, and confirm the double-C curve behavior. When the sample is cooled prior to the isothermal holds, the delta to alpha-prime transformation is observed as several overlapping exothermic peaks. These peaks are very reproducible, and they are believed to be the result of different kinds of delta to alpha-prime martensitic transformation. This may be due to the presence of different nucleation sites and/or different morphologies.
Structural Chemistry of Thorium Iodates
Authors: Sullens Tyler A. , Almond Philip M. , Albrecht-Schmitt Thomas E.
Published: April 2011

The hydrothermal reaction of Th(NO3)4·xH2O with I2O5 in the presence of KCl results in the crystallization of α-Th(IO3)4(H2O) and β-Th(IO3)4(H2O). The structure of αTh(IO3)4(H2O) is three-dimensional and contains Th4+ cations bound by iodate anions and a coordinating water, creating a tricapped trigonal prismatic environment around the thorium centers. βTh(IO3)4(H2O) is layered, and contains ThO9 units that are best described as capped square antiprisms. Crystallographic data: (193 K, MoKα, λ = 0.71073 Å): α-Th(IO3)4(H2O), monoclinic, space group P21/c, a = 7.2335(3) Å, b = 24.6046(12) Å, c = 7.0150(3) Å, b = 112.1888(8)°, V = 1156.05(9), Z = 4, R(F) = 1.97%; βTh(IO3)4(H2O), monoclinic, space group C2/c, a = 33.928(1) Å, b = 5.7466(2) Å, c = 12.4509(5) Å, b = 107.9896(7)°, V = 2308.8(1), Z = 8, R(F) = 1.63%.
Similarities between the Coordination of Actinide Ions in Solution and the Structures of their Related Crystalline Phases
Authors: Soderholm L. , Skanthakumar S. , Burns Peter C , Forbes Tori
Published: April 2011

High-energy x-ray scattering (HEXS) is used to probe correlations about selected actinide ions in solution. The experiments were designed to favor homoleptic water coordination in order to compare the preferred structural environment of UO22+, NpO2+, and Cm3+ with similar ligands. In addition to comparisons between the three actinide ions in solution, the results from the HEXS studies are also compared with known solid state structures. Marked similarities are found between near- and next-near neighbor coordination in solution and in the solid state.
Complexation of Actinides with Amide Derivatives of Oxydiacetic Acid
Authors: Rao Linfeng , Tian Guoxin
Published: April 2011

Complexation of Np(V), U(VI) and Nd(III) with dimethyl-3-oxa-glutaramic acid (DMOGA) and tetramethyl-3-oxa-glutaramide (TMOGA) was studied in comparison with the complexation with oxydiacetic acid (ODA). Stability constants and enthalpy of complexation were determined by potentiometry, spectrophotometry and calorimetry. Thermodynamic parameters, in conjunction with structural information of solid compounds, indicate that DMOGA and TMOGA form tridentate complexes with the ether-oxygen participating in bonding with actinide/lanthanide ions. The trends in the stability constants, enthalpy and entropy of complexation are discussed in terms of the difference in the hydration of the amide groups and carboxylate groups and the difference in the charge density of the metal ions.
Nanostructures in Uranium Oxocompounds
Authors: Krivovichev Sergey V. , Tananaev Ivan G. , Myasoedov Boris F
Published: April 2011

Examples of uranium-oxide-based nanostructures are considered, including 2D organic-inorganic nanocomposites and nanotubules. In nanocomposites, interfacial interactions between organic and inorganic substructures can be studied by charge-density matching principle. Application of this principle to uranyl compounds requires special attention since surface area of uranyl-based 2D units is higher than that of other inorganic oxysalts units (i.e. metal phosphates). The charge-density matching principle is, however, observed either through tail interdigitation (for long-chain monoamines) or incorporation of acid-water interlayers into organic substructure (for long-chain diamines). In some compounds, protonated amine molecules form cylindrical micelles that involves self-assembly governed by competing hydrophobic/hydrophillic interactions. The flexible inorganic complexes present in the reaction mixture could then form around cylindrical micelles to produce highly undulated 2D sheets or nanotubules.
Presence and Persistence of Uranyl Peroxide Nanoclusters in Contact with Geological Media
Authors: Kubatko Karrie-Ann , Gunderson Katie M. , Antonio Mark , Burns Peter C. , Soderholm L.
Published: April 2011

Recently uranyl peroxide nanoclusters containing 24, 28, and 32 uranyl polyhedra were chemically and structurally characterized under alkaline conditions. Such nanoclusters could conceivable form from oxidative alteration of nuclear waste in a geological repository by incorporating peroxide formed by alpha-radiolysis of water or in tanks where high-level waste is stored. The stability and persistence of uranyl peroxides in the vadose zone will be impacted by their interaction with geological media. Here we report batch experiments of solutions containing monodisperse nanoclusters in contact with crushed welded tuff. Within the first 72 hours, U concentrations in solution remained unchanged; however concentrations of Si, Al, Ca, Mg, Na, and Fe increased due to the dissolution of calcium-bearing aluminum silicate minerals in the welded tuff. Despite the presence of excess Li+ in solution, within two weeks crystals precipitated in which Ca2+ replaced Li+ in the nanocluster cage.
Combinatorial Optimization of Low Electrical Resistivity Pd-based Thin Film Metallic Glass
Authors: Yamauchi Ryusuke , Hata Seiichi , Sakurai Junpei , Shimokohbe Akira
Published: April 2011

In order to optimize low electrical resistivity compositions of Pd-based thin film metallic glass (TFMG), Combinatorial arc plasma deposition (CAPD) was employed. A Pd-based continuous compositionally-graded thin film was deposited using CAPD in the experiments. To deposit the composition-grade of the Pd-rich thin film, the number of shots and the plasma strength were controlled. The deposited thin film was separated into 1,089 samples for measurements. The thickness, composition, phase and relative resistivity of these samples were measured respectively. And three amorphous CAPD samples exhibiting low relative resistivity were selected. To determine whether these were TFMG compositions, their compositions were reproduced on sputter-deposited samples and their Tg and Tx were measured. It was found that the sample of Pd81Cu5Si14 at.% showed the lowest absolute resistivity (60 μΩ·cm) and the largest temperature range of supercooled liquid region (SCLR) i.e., 60 K among all samples. The resistivity was 19% lower than conventional Pd-based TFMG and SCLR was two and half times as large. The tensile strength was higher than the conventional TFMG and the Young's modulus was lower than the conventional one.
Making Combinatorial Libraries of Titanium Based Alloys by Direct Metal Deposition Technique
Authors: Pimenova Natalia , Starr Thomas L.
Published: April 2011

α/β type titanium alloys, such as Ti-6Al-4V and Ti-6Al-7Nb, have been used for orthopedic implant materials because of their combination of biocompatibility, corrosion resistance and mechanical properties. However, toxicity of alloying elements is a concern.

In this project, it is proposed to design the new type of titanium alloys composed of non-toxic elements, such as Ti, Al, and Fe with lower modulus of elasticity and greater corrosion resistance. To find the optimal ratio of components in the Ti-Al-Fe system is important. The composition of the alloy determines its properties. Using combinatorial approach the optimal ratio can be found relatively easily.

Direct metal deposition (DMD) is a novel precise manufacturing process for fabricating metal parts directly from Computer Aided Design (CAD) solid models. The DMD process allows making several layers of different composition on one substrate. One sample includes several Ti-xAl-yFe alloys at once. This combinatorial library dramatically reduces the time and cost of the investigation.

The structure, mechanical and electrochemical properties of each new composition was studied using scanning electron microscopy (SEM) with energy-dispersive X-ray fluorescence analyzer (EDAX ZAF®), and electrochemical polarization method.
Informatics for Combinatorial Experiments: Accelerating Data Interpretation
Authors: Stukowski M. , Suh C. , Rajan Krishna , D. Tall P. , C. Beye A. , G. Ramirez A. , O. Soboyejo W. , L. Benson M. , Liaw P.K.
Published: April 2011

Combinatorial experiments provide a means of generating large amounts of experimental data; however that does not necessarily lead to high throughput interpretation of that data. In this paper we provide a brief summary of how one can use informatics techniques to accelerate data interpretation from high throughput experiments. We provide examples from high throughput nanoindentation and diffraction experiments.
Micro- to Nano-scale Structure and Drug Release Behavior of Solutions and Hydrogels of Poly (lactide)-Poly (ethylene oxide)-Poly (lactide) Triblock Copolymers
Authors: Agrawal Sarvesh Kumar , Sanabria-DeLong Naomi , Jemian Pete R. , Coburn Jeannine M. , Tew Gregory N. , Bhatia Surita R.
Published: April 2011

We have performed for the first time a complete structural characterization of PLA-PEO-PLA in the solution and hydrogel states. Previous studies on hydrogels of these polymers have shown that these gels have excellent mechanical properties suitable for possible application in tissue engineering and drug delivery. We have performed SANS, USAXS and confocal microscopy to relate the change in micro to nano scale self-assembled structure of these polymers in aqueous solution with changes in the block length and stereospecificity of the PLA block. A significant difference in structure and association behavior was seen between the polymers made from amorphous D/L-lactide as compared to those with crystalline L lactide blocks. In the former case spherical micelles were seen to form whereas the latter forms nonspherical polydisperse micellar assemblies. Both polymers form an associative network structure at higher concentrations, leading to gelation. USAXS and confocal microscopy show the presence of large-scale fractal aggregates in the hydrogels of these polymers. The fractal structure was denser for the L lactide series polymers as compared to the D/L-lactide series polymers. These results show that we can tune the microstructure and thereby the mechanical strength of these gels depending upon the specific application we need it for. We also show profiles for release of hydrophobic drug sulindac from 5 weight% solutions of these polymers in phosphate buffer saline. The profiles follows an almost zero order release behavior that continues slowly and steadily over several days and is again found to be strongly dependent on the crystallinity and molecular weight of the PLA block.
Nanocharacterization of Relaxation Properties in Organic Thin Film Electronic Materials
Authors: Gray Tomoko , Overney Rene
Published: April 2011

With increased molecular complexity of organic thin film electronics, novel characterization methods are required to provide nanoscale material property information. Particularly important in polymer thin film electronics are methods characterizing the mobility properties of materials that are in amorphous unsteady states. If the unsteady nature of materials is paired with dimensional and interfacial constraints in anisotropic systems, such as thin films, it produces material systems of great challenges with enormous engineering potentials. Two examples are addressed in this paper, involving desired and undesired supramolecular alignments in polymer thin films, the spectral stability in organic blue-light emitting diodes and the electro-optical (EO) activity in organic non-linear optical (NLO) materials, in conjunction with novel scanning probe microscopy (SFM) based characterization tools. The nanoscopic methods discussed here, i.e., shear modulation force microscopy (SM-FM), and nanoscale isothermal friction analysis (NIFA), offer a quantitative approach for investigating the mobility/stability of organic semiconductor polymer films. Thereby, local properties such as energy barriers for sub-molecular motions (relaxations) and critical transition temperatures can be directly inferred from organic films that are used in actual electronic devices.
Analysis of Electromigration- and Stress-Induced Dynamical Response of Voids Confined in Metallic Thin Films
Authors: Gungor M. Rauf , Cho Jaeseol , Maroudas Dimitrios
Published: April 2011

A theoretical analysis based on self-consistent dynamical simulations is presented of electromigration- and stress-induced surface morphological response of voids confined in metallic thin films. The analysis predicts the onset of stable time-periodic states for the void surface morphological response, which is associated with current-driven wave propagation on the void surface. This time-periodic response is demonstrated under certain electromigration conditions and detailed response diagrams are presented which map the corresponding parameter space to regions of steady, time-periodic, and unstable surface morphological response. The evolution of the electrical resistance of these thin films also is computed, providing an interpretation for experimentally observed time-periodic response of the electrical resistance of metallic interconnect lines on the basis of current-driven void morphological evolution. In addition, we demonstrate significant effects on the electromigration-induced morphologically stable void migration of mechanical stress application in a metallic thin film. Specifically, we find that under certain electromechanical conditions, elastic stress can cause substantial retardation of void motion, as measured by the constant speed of electromigration-induced translation of morphologically stable voids. More importantly, this effect suggests the possibility for complete inhibition of void motion under stress.
Nanocrystalline gold and gold-palladium as effective catalysts for selective oxidation
Authors: Edwards Jennifer , Landon Philip , Carley Albert F. , Herzing Andrew , Watanabe Masashi , Kiely Christopher J. , Hutchings Graham
Published: April 2011

The recent interest in oxidation catalysis provides the focus for this paper. Until recently gold has been overlooked as a key component of both homogeneous and heterogeneous catalysts. However, the observation in the 1980's that nanocrystalline gold supported on oxides was an effective catalyst for low temperature carbon monoxide oxidation has now captured the imagination of many researchers. At present low temperature carbon monoxide oxidation remains an intensely studied field, but in recent years increased emphasis has been placed on using gold catalysts for selective oxidation. For example the oxidation of alkanes, alkenes and alcohols have all been shown to be effective with gold based catalysts. In addition gold palladium catalysts have been shown to be very effective for the direct formation of hydrogen peroxide and this will be described in this paper.
Fabrication of Photonic Crystal Biosensors using Micro-molding of Nanoporous Glass
Authors: Block Ian D. , Chan Leo L , Cunningham Brian T
Published: April 2011

We demonstrate a micro-molding method for submicron patterning of a low-index sol-gel nanoporous glass for the purpose of fabricating large-area (∼3”×”) label-free photonic crystal optical biosensors. SEM images show that the sol-gel exhibited minimal shrinkage and good substrate adhesion and depict precise and uniform pattern transfer over the fabricated area within the limits of measurement resolution. A unique characterization approach accurately and quickly revealed porous glass patterned over a large area with geometrical and material properties uniform within 1%. We suggest that this robust method is an excellent approach for photonic crystal sensor fabrication, and may also find applications in integrated optics and electronics.
The Relation between Catalytic Activity of CO Oxidation and Support Structure in Oxidation Catalysts using Gold Nanoparticles
Authors: Nagano Shiho , Tajiri Koji , Tai Yutaka
Published: April 2011

Thiol-passivated gold nanoparticles were adsorbed on several kinds of support materials such as titania-coated silica aerogels and xerogels etc., and then the thiol was removed by heat treatment. The catalytic activity of the prepared composites for CO oxidation reaction was measured, and the effects of the support on the catalytic activity were investigated. Density of the supports, namely, whether aerogel supports or xerogel ones, hardly affected the catalytic activity. It was found that the catalysts having high catalytic activity could be obtained by this preparation method, even using the xerogels as the support. Calcination of the supports before adsorption of the gold nanoparticles affected the activity. The difference of the catalytic activity was observed between the composites with same gold nanoparticle size, so it was considered that the surface condition of the support materials affects the state of gold nanoparticles in composite.
Synthesis of water-soluble, magnetic Fe/Au nanoparticles
Authors: Brown Katherine A. , Wijaya Andy , Alper Joshua D , Hamad-Schifferli Kimberly
Published: April 2011

We report the synthesis of water soluble, monodisperse Fe/Au bimetallic nanoparticles with an average diameter of 7nm. Synthesis involves simultaneous reduction of Fe3+ and Au3+ in water to yield bimetallic nanoparticles. The elemental content of Fe is 1.5%. Nanoparticles exhibit ferromagnetic behavior as measured by SQUID. These particles can be easily conjugated to thiolated DNA, as evidenced by mobility shifts in agarose gel electrophoresis. Nanoparticles heat in solution to temperatures above 40°C, indicating suitability for hyperthermia.
Parallel and Complementary Detection of Proteins by p-type and n-type Silicon Nanowire Transistor Arrays
Authors: Zheng Gengfeng , Patolsky Fernando , Lieber Charles M.
Published: April 2011

Label-free, real-time, parallel and complementary electrical detection of proteins is demonstrated by p-type and n-type silicon nanowire field-effect transistors in the same arrays. Composed of hundreds of individually electrically addressable nanowire devices with highly sensitive and reproducible performances, these nanowire arrays can be controllably modified by monoclonal antibodies, and show discrete conductance changes characteristic of highly selective binding and unbinding of target proteins, such as prostate specific antigens (PSA), thus providing a general and powerful platform for high-throughput real-time parallel detection and rapid screening of libraries of biomolecules. Studies show that the PSA proteins can be routinely detected at femtomolar concentrations with high selectivity, and simultaneously incorporation of both p-type and n-type silicon nanowire devices enable discrimination against false positive/negative signals. The integrated complementary nanowire sensor arrays open up substantial opportunities for diagnosis and treatment of complex diseases such as cancer, detection of biological threats, and fundamental proteomic and biophysical studies.
Sub-micron Patterning on Polymer Films for Protein Arrays
Authors: Christman Karen L. , Requa Michael V. , Enriquez-Rios Vanessa D. , Mendes Paula , Stoddart J. Fraser , Turner Kimberley L. , Maynard Heather D.
Published: April 2011

Patterning proteins at the sub-micron and nanoscale has many uses, including fabrication of protein arrays for diagnostic and sensor applications. Many groups have reported micron scale protein patterns using photolithography; however, smaller scales have not been realized. In this study, we demonstrate sub-micron protein patterns using photolithography. Patterning is achieved by chemical transformation of pH-reactive polymer films. Site-specific immobilization of streptavidin within a protein resistant background is demonstrated. This methodology could be utilized for the development of high density proteins arrays for biotechnology applications.
Nanostructured alumina doped TiO2 ceramics for gas sensors
Authors: Choi Young Jin , Bandyopadhyay Amit , Bose Susmita
Published: April 2011

Nanostructured TiO2 based ceramics were synthesized using citrate-nitrate auto combustion method with different concentrations of aluminum oxide as dopant. The powder x-ray diffraction data showed that synthesized TiO2 powders, pure as well as alumina doped TiO2 had anatase phase. Dopant concentration was varied between 0 and 15 wt%. Particle size analysis showed that the particle size was in the range of 50 to 80nm for nanosized TiO2 calcined between 600 and 800°C. Average particle size of doped powders was generally less than pure TiO2. BET specific average surface area was between 10 and 25 m2/g. Doping upto 10wt% alumina is not effective in retarding anatase crystallite growth. The resistance of Al doped TiO2 sample is found to be lower than that of pure TiO2. Al2O3 doped TiO2 sensor was found to be selective to CO sensing at an operating temperature of 600 °C.
Surface Stress Effects on the Elastic Behavior of Nanoporous Metals
Authors: Crowson Douglas A. , Farkas Diana , Corcoran Sean G.
Published: April 2011

Atomic scale computer simulations were used to investigate the surface stress induced deformation in nanoporous metals. A phase field model was used to generate digital nanoporous structures that are quantitatively similar to those created experimentally via dealloying. We analyze the important effects of surface relaxations on the macroscopic deformation in these samples as well as in small spherical clusters.
High Sensitive Optical Detection of Bio-Chemicals onto a Silicon Oxide Surface Based on Waveguide Mode
Authors: Fukuda Nobuko , Fujimaki Makoto , Awazu Koichi , Tamada Kaoru , Yase Kiyoshi
Published: April 2011

This work presents high sensitive detection of specific adsorption of proteins onto a silicon oxide (SiOx) surface modified by molecules with a biotinyl-end group. We fabricated a SiOx waveguide by sputtering onto a thin gold film and measured the incident angle-dependence of reflectivity using a polarized He-Ne laser under total internal reflection condition. When the s-polarized light was irradiated to the SiOx waveguide (760 nm) coupled with a prism, the incident angle-dependence of reflectivity showed narrow dips due to excitation of the waveguide mode. The waveguide surface was modified by the molecules with the biotinyl-end group as a protein probe. Specific adsorption of streptavidin in a PBS buffer solution was monitored through time course of the reflectivity change at a constant incident angle, where the waveguide mode was excited. As compared with conventional SPR system using a gold surface, high sensitive detection of the specific adsorption was achieved. Additionally, we fabricated micro-patterned arrays of biotinyl-end layers onto the SiOx waveguide surface by micro-contact printing. Then we observed the specific adsorption behavior on the micro-patterned arrays by the imaging based on the waveguide mode using a CCD camera.
Synthesis of Bimetallic AuPt Nanoparticles in Aqueous Solution and Electrocatalytic Activity
Authors: Njoki Peter N. , Luo Jin , Jacob Aisley , Munawar Rizwan , Khan Bilal , Zhong Chuan-Jian
Published: April 2011

The ability to control composition and size in the synthesis of bimetallic nanoparticles is important for the exploitation of the bimetallic catalytic properties. This paper reports recent findings of an investigation of the synthesis of gold-platinum (AuPt) bimetallic nanoparticles in aqueous solution via reduction of AuCl4− and PtCl42− using a combination of reducing and capping agents. In addition to characterization of the morphological properties of the AuPt nanoparticles using TEM and XRD, the electrocatalytic activity of the carbon-supported AuPt nanoparticle catalysts was also examined for oxygen reduction reaction (ORR) using the rotating disk electrode (RDE) technique. The findings have implications to the design of bimetallic nanoparticle catalysts for fuel cell reactions.
PZT and PLZT thin films on Cu substrates for dielectric and piezoelectric applications: Effect of processing atmosphere and film strain
Authors: Kim Taeyun , Srinivasan Sudarsan , Kingon Angus I
Published: April 2011

PZT (52/48) and PLZT (7/65/35) thin films were prepared by chemical solution deposition (CSD) on Pt/SiO2/Si and Cu foil substrate, respectively. For PZT thin films on Pt/SiO2/Si substrates, pO2 control during thermal treatment affected both perovskite phase formation and orientation, but did not show significant impact on the ferroelectric and dielectric properties. When PLZT thin films (7/65/35) were prepared on Cu foil to tailor ferroelectric/dielectric properties, it was observed that ferroelectric and dielectric properties were significantly affected by the strains, possibly from the coefficient of thermal expansion (CTE) mismatch between PLZT and Cu foil during cooling after high temperature crystallization. It was also experimentally observed that, depending on the direction of applied strain, the PLZT films could be cycled between ferroelectric and paraelectric phases. It was suggested that PZT based thin films on base metal substrate requires very careful processing for optimized electrical performance.
Cohesive Model of Electromechanical Fatigue for Ferroelectric Materials and Structures
Authors: Serebrinsky Santiago Ariel , Arias Irene , Ortiz Michael
Published: April 2011

We develop a phenomenological model of electro-mechanical ferroelectric fatigue based on a ferroelectric cohesive law that couples mechanical displacement and electric-potential discontinuity to mechanical tractions and surface-charge density. The ferroelectric cohesive law exhibits a monotonic envelope and loading-unloading hysteresis. The model is applicable whenever the changes in properties leading to fatigue are localized in one or more planar-like regions, modelled by the cohesive surfaces. We validate the model against experimental data for a simple test configuration consisting of an infinite slab acted upon by an oscillatory voltage differential across the slab and otherwise stress free. The model captures salient features of the experimental record including: the existence of a threshold nominal field for the onset of fatigue; the dependence of the threshold on the applied-field frequency; the dependence of fatigue life on the amplitude of the nominal field; and the size effect on the coercive field. Our results, although not conclusive, indicate that planar-like regions affected by cycling may lead to the observed fatigue in tetragonal PZT. A particularly appealing feature of the model is that it can be incorporated in a very natural and convenient way into a general finite element analysis of structures and devices for fatigue life assessment.
Deposition of Highly (100) Oriented PZT Film Using Lanthanum Nitrate/Nickel Acetate Buffer Layer
Authors: Choi Jong-Jin , Hahn Byung-Dong , Jang Joo-Hee , Yoon Woon-Ha , Park Dong-Soo , Kim Hyoun-Ee
Published: April 2011

Highly (100) oriented Pb(Zr,Ti)O3 [PZT] films were fabricated using lanthanum nitrate/nickel acetate double layers as a buffer layer, regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature, and heating rate. The buffer layer was also acted as a very effective barrier against Pb-Si interdiffusion, thus allowing for the direct deposition of PZT films on Si, SiO2/Si, and glass substrates. The strong orientation was attributed to the formation of a crystalline intermediate phase between the PZT and lanthanum nitrate during annealing. The lanthanum nitrate/nickel acetate double layers became a lanthanum nickel oxide (LaNiO3), which shows good electrical conductivity, after an annealing process at 650°C. The nature and the role of lanthanum nitrate buffer as a layer for the growth of highly (100) oriented PZT films have been studied. The dielectric, ferroelectric, piezoelectric and electrooptic properties of the highly (100) oriented PZT films with a lanthanum nitrate/nickel acetate buffer layer were measured and compared with the values measured from the (111) and (100) oriented PZT films deposited without buffer layer.
Influence of the lead-compound on PZT 30/70 thin film orientation
Authors: Mandeljc Mira , Malič Barbara , Kosec Marija , Dražič Goran
Published: April 2011

Ferroelectric thin films based on Pb(Zr0.30Ti0.70)O3 (PZT 30/70) were prepared by Chemical Solution Deposition from lead oxide or lead acetate and transition metal alkoxides in 2-methoxyethanol at 400 °C. The choice of the lead-compound determines the composition of the PZT-sols and as a consequence the course of the thermal decomposition. In the case of PbO the local atmosphere within the bulk of the film during heating is more reducing, i.e. the partial pressure of oxygen is lower, than in the case of Pb(OAc)2 based film. Thus, in the former case a continuous layer of Pt-Pb phase is formed at 400 °C, while in Pb(OAc)2 based film only a low amount of Pt-Pb inclusions could be determined by TEM.
Electrical Properties of Au/Bi4-xLaxTi3O12 Thin Film/Si Structures and Reduction of Interface States
Authors: Kohno Atsushi , Tomari Hiroyuki
Published: April 2011

Sub-100nm-Thick Polycrystalline Bi4-xLaxTi3O12 (BLT) thin films have been formed on silicon substrates by sol-gel and spin-coating techniques. The analysis of X-ray reflectivity for the BLT/Si structure showed that the BLT film density was slightly lower than the ideal value and the interfacial layer was formed. By Fourier transform infrared spectroscopy (FT-IR) it is confirmed that the formation of the interfacial layer was due to oxidation of Si. Clockwise hysteresis was observed in capacitance-voltage (C-V) characteristics for Au/BLT/p-Si structures at a frequency range between 1 MHz – 1 kHz. The frequency dispersion of the C-V curve was caused by a large amount of interface states at BLT/Si interface. As the film was crystallized at 550°C for 2 h the maximum interface state density was ∼3.4×1011 cm-2ev-1 at 1 kHz. Also, the negative gate-voltage shift of the C-V curve from the ideal curve and the gate-bias dependence of the flat-band voltage were observed, resulting in the presence of undesirable positive charges in the film and the electron injection to the traps near the BLT/Si interface. By post-annealing of the device at 400 °C in oxygen atmosphere the interface states (fast sates) were successfully reduced to a third of the initial value and also the positive charges were significantly diminished.
Ferroelectric Gates for Modulation of 2D Electron Gas at GaN/AlGaN Interfaces
Authors: Stolichnov Igor , Malin Lisa , Muralt Paul , Setter Nava
Published: April 2011

The Pb(Zr,Ti)O3 ferroelectric gate was successfully integrated into the GaN/AlGaN heterostructure with 2D electron gas. The processing conditions were optimized in a way to obtain high quality textured Pb(Zr,Ti)O3 films without destroying the 2D gas situated as close to the interface as 20nm. Study of transport properties in this system demonstrates a possibility to control the 2D gas by switching the spontaneous polarization in the gate. Concentration and mobility of electrons in the 2D gas were monitored using Hall effect and resistivity measurements in a wide temperature range from 4.2K to 300K. The polarization oriented in the direction “from bottom to top” provokes a partial depletion effect in the channel resulting in a conductivity decrease. A correlation between the depletion effect in 2D gas and the change of the spontaneous polarization with temperature has been observed. The depletion effect is found to be reversible so that the initial conductivity in 2D gas can be restored by inversing the spontaneous polarization in the gate. These results suggest that ferroelectric gates integrated into systems with 2D electron gas may be potentially interesting for a number of experiments and applications as a flexible and nondestructive way of making rewritable nanopatterns on semiconductor heterostructures.
Terahertz radiation from multiferroic BiFeO3 thin films as a new approach for ferroelectric memory readout and ferroelectric domain imaging microscopy
Authors: Takahashi Kouhei , Kida Noriaki , Tonouchi Masayoshi
Published: April 2011

We have observed novel terahertz (THz) radiation characteristics of multiferroic BiFeO3 thin films upon illumination of femtosecond laser pulses. The radiated THz pulses from BiFeO3 thin films were shown to originate from an ultrafast modulation of spontaneous polarization, which was introduced by the photoexcited charge carriers. Based on our findings, we briefly present new approaches to nondestructive readout for nonvolatile memory devices and ferroelectric domain imaging microscopy using THz radiation as a sensitive probe.
Three-dimensional observation of nano-scale ferroelectric domain using scanning nonlinear dielectric microscopy
Authors: Cho Yasuo , Sugihara Tomoyuki
Published: April 2011

Three-dimensional domain configuration of multi-domain LiTaO3 is revealed by Scanning Nonlinear Dielectric Microscopy (SNDM). SNDM can measure the polarization components both perpendicular and parallel to the surface of the specimen. These techniques are applied to the both congruent and stoichiometric LiTaO3 crystals. The images obtained by SNDM measurements allow us to confirm the various domain features of LiTaO3 and to understand both similarities and differences between the congruent and stoichiometric compositions.
Recent Developments in Thermodynamic Theory of Ferroelectric Thin Films
Authors: Pertsev Nikolay
Published: April 2011

The nonlinear thermodynamic theory of epitaxial ferroelectric films has predicted several important strain-induced phenomena, which have been already observed experimentally. This justifies further development of this theory aiming at the better understanding of the structure/property relationships in thin-film ferroelectrics. To that end, a number of new theoretical studies have been performed recently. First, the thermodynamic formalism has been extended to epitaxial films grown on dissimilar substrates inducing anisotropic strains and a shear deformation in the film plane. Second, the polarization states and dielectric properties were calculated for polydomain Pb(Zr1-xTix)O3 films deposited on cubic substrates. Third, the effect of depolarizing field on the physical properties of strained single-domain films sandwiched between continuous electrodes was described. The results of these studies will be discussed in this paper.
High Growth Rate Process in a SiC Horizontal Reactor with HCl Addition: Structural and Electrical Characterization
Authors: La Via Francesco , Galvagno Giuseppa , Firrincieli Andrea , Di Franco Salvatore , Severino Andrea , Leone Stefano , Mauceri Marco , Pistone Giuseppe , Abbondanza Giuseppe , Portuese Ferdinando , Calcagno Lucia , Foti Gaetano
Published: April 2011

The growth rate of 4H-SiC epitaxial layer has been increased by a factor 19 (up to 112 μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. The effects of different deposition parameters on the epitaxial growth process have been described in detail. This process can be very promising for high power devices with a breakdown voltage of 10 kV.
Growth of Crystalline Silicon Carbide by CVD Using Chlorosilane Gases
Authors: Loboda Mark , MacMillan M. F. , Wan J. , Chung G. , Carlson E. , Makarov Y. , Galyukov A. , Molnar M. J.
Published: April 2011

The forefront of semiconductor silicon carbide technology now approaches commercialization for both materials and device technology. The commercialization of SiC epitaxy processes requires improvement in defect density, uniformity and repeatability. Especially problematic are graphite particles, gas phase nucleation of particles and the limitations placed on achieving growth rates that can positively impact process costs. When it approached the same historical point of development, silicon epitaxy technology shifted to the use of chlorosilane precursor gases to suppress gas phase nucleation and achieve targeted growth rates. Recent work on SiC epitaxy chemistry now investigates the use of HCl, halocarbons and most recently chlorosilane precursors. This paper will review the original work on gas phase nucleation and its control in silicon epitaxy processes using HCl additives and chlorosilanes. Using established dissociation pathways for chlorosilanes, equilibrium chemical reaction models are used to assess the impact of HCl, halocarbons and chlorosilane precursors on growth rates and particle formation SiC epitaxy. Experimental data is presented on the comparative performance of HCl additive and chlorosilane precursors in SiC epitaxy and film properties.
Effect of Dopant Concentration on High Voltage 4H-SiC Schottky Diodes
Authors: La Via Francesco , Galvagno Giuseppa , Firrincieli Andrea , Di Franco Salvatore , Severino Andrea , Leone Stefano , Mauceri Marco , Pistone Giuseppe , Abbondanza Giuseppe , Portuese Ferdinando , Calcagno Lucia , Foti Gaetano
Published: April 2011

Practical design of high-voltage SiC Schottky rectifiers requires the understanding of the influence of the epitaxial dopant concentration on the reverse and forward characteristics. This work analyzes the correlation between the dopant concentration and the I-V characteristics of Schottky diodes for a critical concentration range where the leakage current variations are more evident. The details of how high temperatures affect the properties of junctions have been carefully described to obtain further improvement in the future by proper device optimization. Dopant concentration of about 1.2 × 1016 cm-3 gives the best results in reverse characteristics without great losses in forward currents.
Growth of Epitaxial γ-Al2O3 Dielectrics on 4H-SiC
Authors: Tanner Carey M. , Lu Jun , Blom Hans-Olof , Chang Jane P.
Published: April 2011

Highly oriented ?-Al2O3 thin films on 4H-SiC were engineered to demonstrate their potential as a crystalline high-k gate dielectric in SiC power MOSFETs. As-deposited Al2O3 thin films grown on 4H-SiC (0001) by thermal atomic layer deposition (ALD) were amorphous as determined by in-situ reflection high-energy electron diffraction (RHEED). Upon annealing in N2 at 1100°C, the film crystallized to the ?-Al2O3 phase as observed by RHEED, high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Based on Fourier transforms of the HRTEM image, an epitaxial relationship of ?-Al2O3 (111) on 4H-SiC (0001) was observed in which ?-Al2O3 (-110) is oriented with 4H-SiC (-12-10). This orientation was further confirmed by XRD analysis in which only the ?-Al2O3 (111) and (222) peaks were observed. An abrupt interface of both amorphous and crystalline Al2O3 with 4H-SiC was determined by HRTEM.