bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Hybrid Enzyme-Based Porous Silicon Platform for Chemical Warfare Agent Detection
Authors: Létant Sonia E. , Hart Bradley R. , Kane Staci R. , Hadi Masood Z. , Shields Sharon J. , Cheng Tu-Chen , Rastogi Vipin K. , Del Eckels J. , Reynolds John G.
Published: April 2011

The goal of our research is to combine porous silicon and enzymes in order to build hybrid platforms for extremely selective chemical sensing applications. For this, a new synthetic route to covalently anchor bio-molecules on photo-luminescent porous silicon (PL PSi) while preserving the optical properties of the matrix was developed. The hydride terminated porous silicon surface was covalently functionalized with t-butyloxycarbonyl protected amine by light-assisted hydrosysilation. Protein cross-linker chemistry was then used to extend the linker and immobilize various enzymes. The glu-coronidase enzyme/p-nitro-phenyl-beta-glucoronide substrate test system provided a proof of concept for an enzyme-based porous silicon detector. The enzymatic activity and the luminescence of the porous silicon platform were both retained after the functionali-zation procedure and, charge transfer between the products of the enzymatic breakdown and the silicon quantum dots was demonstrated. The organophosphorous hydrolase enzyme OPAA was then immobilized and tested on p-nitrophenyl-soman, a surrogate substrate for soman. The production of the hydrolysis product, p-nitrophenol, correlated with the reversible luminescence quenching of the porous silicon matrix demonstrating the relevance of the enzyme-based platform for detection applications. This detection scheme, although indirect, takes advantage of the extreme specificity of enzymes. The approach is general and can be implemented for a series of target molecules.
Sol-gel derived porous silica as a constituent material for designing optical fiber chemical sensors
Authors: Tao Shiquan , Fanguy Joseph C. , Xu Lina
Published: April 2011

Sol-gel processes were developed to prepare nano porous silica materials. The obtained porous sol-gel silica (PSGS) materials have been used as constituent materials in designing optical fiber chemical sensors. A PSGS membrane coated on the surface of an optical fiber was used as a transducer for sensing humidity level in air. A PSGS membrane doped with an ammonia indicator dye has been coated on an optical fiber to sense ammonia in air. Both of the coating based sensors are reversible and fast response. In the tested range, relative humidity (RH) in air down to 3% can be detected with the PSGS coated fiber optic sensor. The fiber optic ammonia sensor with ammonia indicator doped PSGS coating can be used to sense ammonia in air down to sub-ppm level. PSGS has also been used as a constituent material in preparing porous silica optical fibers. The obtained porous optical fibers have been used to design optical fiber chemical sensors for sensing humidity, ammonia and volatile organic compounds. A CuCl2 doped PSGS fiber has been tested for sensing ammonia in a high temperature gas sample. Ammonia in the high temperature air gas diffuses into the PSGS fiber, reversibly reacts with CuCl2 doped in the PSGS fiber to form a complex. The formed complex was detected with fiber optic spectrometric method. This sensor can detect ammonia in a high temperature (450 °C) air gas stream down 0.3 ppm. Techniques of preparing PSGS, coating PSGS on an optical fiber, making a porous optical fiber with PSGS as a constituent material will be presented. Examples of optical fiber sensors using PSGS coatings and a PSGS fiber as transducers for gas sensing are presented.
A Titania Nanotube-Array Room-Temperature Sensor for Selective Detection of Low Hydrogen Concentrations
Authors: Varghese Oomman K. , Mor Gopal K. , Paulose Maggie , Grimes Craig A.
Published: April 2011

A tremendous variation in electrical resistance, from the semiconductor to metallic range, has been observed in titania nanotube arrays at room temperature, ≈ 25°C, in the presence of low ppm hydrogen gas concentrations (≤ 1000 ppm). The nanotube arrays are fabricated by anodizing titanium foil in an aqueous fluoride containing electrolyte solution. Subsequently, the arrays are annealed in an oxygen ambient, then coated with a 10 nm layer of palladium by evaporation. Electrical contacts are made by sputtering a small (e.g. 1 mm diameter) platinum disk atop the Pd coated nanotube-array. These sensors exhibit a resistance variation of the order of over 107 (1,000,000,000%) in the presence of 1000 ppm hydrogen at 23°C. To the best of our knowledge this dynamic change in electrical resistance the largest known response of any material, to any gas, at any temperature. The sensors demonstrate complete reversibility, repeatability, high selectivity, no drift and wide dynamic range. The nanoscale geometry of the nanotubes, in particular the points of tube-to-tube contact, is believed to be responsible for the outstanding hydrogen gas sensitivities.
A Novel Theoretical Model for Semiconductor Oxide Gas Sensor
Authors: Shukla Satyajit , Seal Sudipta
Published: April 2011

A new constitutive equation for the gas sensitivity of n-type semiconductor oxide thin film gas sensor has been proposed here based on a single-crystal model. The derived constitutive equation shows the dependence of the gas sensitivity on various critical parameters such as nanocrystallite size, space-charge-layer thickness, reducing gas concentration, bulk charge-carrier-concentration, surface-density of states, oxygen-ion-vacancy concentration, operating temperature, and film thickness. The present theoretical model is applicable to all n-type semiconductor oxides gas sensors.
Gas sensors based on semiconductor oxides: basic aspects onto materials and working principles
Authors: Cristina M. , Giberti Alessio , Guidi Vincenzo , Malagù Cesare , Vendemiati Beatrice , Martinelli Giuliano
Published: April 2011

The properties of the most important semiconductor oxides for gas sensing, such as SnO2, TiO2, WO3 and their modifications due to ion-addition or to catalyzers, have been reviewed. The oxide powders, synthesized via wet chemical routes, have been characterized both as dispersed powders and as sintered films. Deposition of thick film gas sensors was carried out through screen-printing technology. They have been studied comparing the electrical behavior under identical environmental conditions. Potential barrier heights have been measured via stimulated temperature measurements and density of ionized donors obtained via Hall Effect. A theoretical model has been developed to justify the size dependent behavior of nanocrystalline oxides.
Chemical Vapor Depositions of Single Walled Carbon Nanotube thin films and their applications for sensors in aqueous solutions
Authors: Fu Qiang , An Lei , Lu Chenguang , Liu Jie
Published: April 2011

High-density and high-quality single walled carbon nanotubes are directly grown on surface by Chemical Vapor Depositions. We found that those SWNT thin films could be used to fabricate thin film field-effect transistors. Those transistors are very sensitive to surface charges changes in aqueous solutions and could be used tobuild chemical sensors.
Gas Selectivity of Polycrystalline Thick Films of SrPb1−xBixO3−δ
Authors: Michel Carlos R. , Santillán Gloria , Quino Abraham , Chávez Arturo
Published: April 2011

Polycrystalline samples of the perovskites: SrPb1−xBixO3−δ (x = 0, 0.1) were prepared from the dissolution of stoichiometric amounts of Sr(NO3), Pb(NO3)2 and Bi(NO3)3 in aqueous media. The solutions were heat-dried at 75°C obtaining powder precursors. To determine the temperature of formation of these phases, thermal analyses were made on them. Calcination at 650°C for 6 h produced pure samples, which were characterized by X-ray powder diffraction. The surface microstructure of powders was analyzed by scanning electron microscopy, and showed that this preparation procedure yield micron-sized particles, which formed agglomerations. To evaluate their gas sensing behavior, the resulting powders were finely ground and mixed with acetone to form thick-films. The electrical conductivity vs. temperature of films was measured in dry air, O2 and CO2, and resulted that SrPb0.9Bi0.1O3−δ has a better sensitivity to O2 compared to SrPbO3−δ, caused by the partial substitution of lead by bismuth.
Nanomatertials as Low Density Lipoprotein (LDL) Sensors
Authors: Tang Tao , Liu Xiaolei , Li Chao , Lei Bo , Zhang Daihua , Rouhanizadeh Mahsa , Hsiai Tzung , Zhou Chongwu
Published: April 2011

In2O3nanowire and carbon nanotube transistors were used to study the chemical gating effects in response to LDL particles. Low density lipoprotein (LDL) cholesterol in blood constitutes a risk factor for coronary artery disease (heart attack). The interactions of LDL particles with these two different surfaces were investigated. The degree of LDL particles binding to carbon nanotubes was ten-fold higher than to In2O3nanowires possibly owing to the hydrophobic/hydrophilic interactions. The conductance of field effect transistors (FET) based on nanowires and nanotubes showed complementary responses after exposure to LDL particles. While In2O3nanowire transistors exhibited higher conductance accompanied by a negative shift of the threshold voltage, nanotube transistors displayed a lower conductance. This phenomenon was attributed to the complementary doping between the n-type In2O3nanowires and p-type carbon nanotubes.
Printable Electronics: Patterning of Conductive Materials for Novel Applications
Authors: Karwa Anupama , Xia Yu , Clark Daniel M. , Smith Thomas W. , Kahn Bruce E.
Published: April 2011

The convergence of materials science, printing, and electronics promises to offer low cost and high volume production of devices such as transistors, RFID tags, wearable electronics and other novel applications. Although a number of “soft lithographic” techniques have been used to make these devices, they are slow and have a limited production volume [5], [14-15].

Here high volume printing processes like rotary letterpress, flexography and offset lithography have been investigated for patterning conductive materials [1]. The synthesis and development of conducting inks using electrically functional polymers has been studied. The feasibility of using such inks in high volume printing processes has been studied. An attempt has been made to print conductive interdigitated electrodes using these inks to obtain uniform coating properties and appropriate electrical characteristics. Various process parameters like type of substrate, inking time and speed, printing pressure, printing force and ink formulation have been investigated.
Mechanism of the Oxygen Interaction with a Surface of Thin Nanosized Metal Oxide Film
Authors: Brinzari Vladimir I. , Dmitriev Serghei V. , Korotcenkov Ghenadii S.
Published: April 2011

This paper presents result of investigation of the oxygen interaction with a surface of semiconductor metal oxide film. The idea to carry out such research is connected with the key role, which oxygen plays in the processes of impurity gas molecules detection in atmosphere and semiconductor surface sensibilization. Numerical modeling of the interaction was carried out for different temperatures and oxygen partial pressures. Results of modeling are compared with the results of experimental study of oxygen-semiconductor film system.
Low Cost Integrated Sensors Utilizing Patterned Nano-Structured Titania Arrays Fabricated Using a Simple Process
Authors: Samah Zuruzi Abu , Kolmakov Andrei , Moskovits Martin , MacDonald Noel C.
Published: April 2011

Using a novel low-temperature process, we demonstrate the facile integration of crack-free nanostructured titania (NST) as sensing elements in microsystems. Unlike conventional sol-gel methods, NST layers of interconnected nano-walls and nano-wires were formed by reacting Ti surfaces with aqueous hydrogen peroxide solution. Cracks were observed in NST layers formed on blanket Ti films but absent on arrays of patterned Ti pads below a threshold dimension. Analyses using TEM, high resolution SEM, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that NST consists of anatase TiO2 nano-crystals. NST pads were found able to detect oxygen gas of a few ppm. NST pad arrays were integrated on rigid and flexible substrates with potential applications in low cost and wearable sensing systems.
Future Directions of Non-volatile Memory Technologies
Authors: Fazio Albert
Published: April 2011

It expected that for many years to come, the majority of the nonvolatile memories shipped will be based on current mainstream flash technologies, which utilize transistor based charge storage memory cells and multi-level-cell concepts, for storing more than one logic bit in a single physical cell. Moore's law will continue to drive transistor based memory technology scaling but technology complexity will be increasing. In order to meet technology scaling, the mainstream transistor based flash technologies will start evolving to incorporate material and structural innovations. This paper will review the current status and discuss the approaches being explored to provide scaling solutions for future transistor based non-volatile memory products. Based on the introduction of material innovations, it is expected that the planar transistor based flash memory cell can scale into the 32nm node. Further, more complex, structural innovations will be required to maintain further scaling. New memory concepts, not relying on transistors as a basis of the memory cell, provide new opportunities for future low cost memories. Several of these new concepts will be summarized and contrasted with the mainstream transistor based flash memory technologies.
Integration and Performance Improvements of Silicon Nanocrystal Memories
Authors: Hiramoto T. , Kim I. , Saitoh M. , Yanagidaira K.
Published: April 2011

The silicon nanocrystal memory, that is one of the most promising devices for future non-volatile memory, is extensively investigated by experiments and simulation. The silicon nanocrystal memory cells are successfully integrated using the state-of-the-art 0.13 μm DRAM technology. The mechanism of the two-bit-per-cell operation, that is one of the unique features of silicon nanocrystal memory, is investigated and it is shown that the degree of DIBL determines the read scheme of the two-bit-per-cell operation. Moreover, the dependences of memory characteristics on device structures are examined by fabrication and measurements and it is found that the ultra-thin-body SOI and double-gate structures have better memory characteristics.
Optimisation and Simulation of an Alternative nano-flash Memory: the SASEM device.
Authors: Krzeminski C. , Dubois E. , Tang X. , Reckinger N. , Crahay A. , Bayot V.
Published: April 2011

Process simulation are performed in order to simulate the full fabrication process of an alternative nano-flash memory in order to optimise it and to improve the understanding of the dot storage formation. The influence of various parameters (oxidation temperature, nanowire shape) have been investigated.
Improvement of Ferroelectric Properties of Lead Zirconate Titanate Thin Films by Ion-substitution using Rare-earth Cations
Authors: Nakaki Hiroshi , Uchida Hiroshi , Okamoto Shoji , Yokoyama Shintaro , Funakubo Hiroshi , Koda Seiichiro
Published: April 2011

Rare-earth-substituted tetragonal lead zirconate titanate thin films were synthesized for improving the ferroelectric property of conventional lead zirconate titanate. Thin films of Pb1.00REx (Zr0.40Ti0.60)1-(3x /4)O3 (x = 0.02, RE = Y, Dy, Er and Yb) were deposited on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition (CSD). B-site substitution using rare-earth cations described above enhanced the crystal anisotropy, i.e., ratio of PZT lattice parameters c/a. Remanent polarization (Pr) of PZT film was enhanced by Y3+-, Dy3+- and Er3+-substitution from 20 μC/cm2 up to 26, 25 and 26 μC/cm2 respectively, while ion substitution using Yb3+ degraded the Pr value down to 16 μC/cm2. These films had similar coercive fields (Ec) of around 100 kV/cm. Improving the ferroelectric property of PZT film by rare-earth-substitution would be ascribed to the enhancement of the crystal anisotropy. We concluded that ion substitution using some rare-earth cations, such as Y3+, Dy3+ or Er3+, is one of promising technique for improving the ferroelectric property of PZT film.
Semiconductor Nanocrystal Floating-gate Memory Devices
Authors: Dimitrakis P. , Normand P.
Published: April 2011

Current research directions and recent advances in the area of semiconductor nanocrystal floating-gate memory devices are herein reviewed. Particular attention is placed on the advantages, limitations and perspectives of some of the principal new alternatives suggested for improving device performance and reliability. The attractive option of generating Si nanocrystal memories by ion-beam-synthesis (IBS) is discussed with emphasis on the ultra-low-energy (ULE) regime. Pertinent issues related to the fabrication of low-voltage memory cells and the integration of the ULE-IBS technique in manufactory environment are discussed. The effect on device performance of parasitic transistors that form at the channel corner of shallow trench isolated transistors is described in details. It is shown that such parasitic transistors lead to a substantial degradation of the electrical properties of the intended devices and dominates the memory behavior of deep submicronic cells.
A Model of Silicon Nanocrystal Nucleation and Growth on SiO2 by CVD
Authors: Stoker M. W. , Merchant T. P. , Rao R. , Muralidhar R. , Straub S. , White B. E.
Published: April 2011

Silicon nanocrystals can be used in non-volatile memory devices to reduce susceptibility to charge loss via tunnel oxide defects, allowing scaling to smaller sizes than possible with conventional Flash memory technology. In order to optimize device performance, it is desirable to maximize the nanocrystal density and surface coverage, while maintaining sufficient inter-crystallite separation to limit electron tunneling between adjacent crystallites. Ideally, crystallite densities in excess of 1012cm-2 with relatively narrow particle size distributions must be obtained, posing a significant challenge for process development and control. In order to facilitate development of such a process, a rate-expression-based model has been developed for the nucleation and growth of silicon nanocrystals on SiO2 in a CVD process. The model addresses the phenomena of nucleation, growth, and coalescence and includes the effects of exclusion zones surrounding the growing nuclei. The model uses a phenomenological expression to describe the nucleation rate and assumes that following nucleation, crystallite growth is dominated by gas-phase deposition processes, analogous to CVD of polycrystalline silicon. The model-predicted time-evolutions of crystallite densities and crystallite size distributions are consistent with experimental distributions as measured by Scanning Electron Microscopy (SEM). By coupling the model to a reactor-scale model of polysilicon CVD, it is possible to predict variations in the crystallite size distributions at various locations across a wafer as a function of reactor settings (temperature, pressure, flow rates, etc…). This in turn can be used for process control and optimization in order to ensure uniform deposition of nanocrystals in a large-scale manufacturing environment.
Search for magnetism in Co and Fe-doped HfO2 thin films for potential spintronic applications
Authors: Rao M. S. R. , Kundaliya Darshan C. , Dhar S. , Cardoso C. A. , Curtin A. , Welz S. J. , Erni R. , Browning N. D. , Lofland S. E. , Metting C. J. , Ogale S. B. , Venkatesan T.
Published: April 2011

We studied the structural and magnetic properties of dilutely (5 mol%) doped 3d elements (Co and Fe) in PLD grown HfO2 high-k dielectric thin films. Monoclinic phase of HfO2 was stabilized by Co- and Fe- substitution at significantly low growth temperature (∼725 °C). No magnetic moment was observed in Co-doped HfO2 films. On the other hand, 5 mol% Fe-doped HfO2 films grown at different oxygen partial pressures (10-6 torr to 10 mtorr) showed interesting magnetization behavior with varying coercive field due to the segregation of Fe2O3 and Fe3O4 phases. Magnetic force microscopy (MFM) study revealed magnetic impurity phase segregation. Films grown at 1 × 10-4 torr of oxygen partial pressure (O2pp) showed oriented Fe3O4 impurity line (220) and the coercive field (Hc) ∼ 350 Oe. Films grown at higher oxygen partial pressure (1x10-2 torr) showed no impurities and magnetization was absent. Coercive field varied as a function of oxygen partial pressure. This property will be of great interest from the view point of magneto-optic applications.
Oxidation of Si nanocrystals fabricated by ultra-low energy ion implantation in thin SiO2 layers
Authors: Coffin H. , Bonafos C. , Schamm S. , Cherkashin N. , Respaud M. , Ben Assayag G. , Dimitrakis P. , Normand P. , Tencé M. , Colliex C. , Claverie A.
Published: April 2011

The effect of annealing in diluted oxygen on the structural characteristics of thin silicon dioxide layers with embedded Si nanocrystals fabricated by ultra-low energy ion implantation (1 keV) is reported. The nanocrystal characteristics (size, density, coverage) have been measured by spatially resolved Electron Energy Loss Spectroscopy using the spectrum-imaging mode of a Scanning Transmission Electron Microscope. Their evolution has been studied as a function of the annealing duration under N2+O2 at 900°C. An extended spherical Deal-Grove model for the self-limiting oxidation of embedded silicon nanocrystals has been carried out. It shows that stress effects, due to the deformation of the oxide, slows down the chemical oxidation rate and leads to a self-limiting oxide growth. The model predictions show a good agreement with the experimental results.
A novel copper damascene technique for power loaded SAW structures
Authors: Menzel S. B. , Albert M. , Reitz D. , Wendrock H. , Schmidt H. , Weihnacht M. , Wetzig K. , Bartha J. W.
Published: April 2011

The damage of finger electrodes of surface acoustic wave (SAW) structures due to material transport (acoustomigration) forming voids and hillocks is strongly associated with the SAW stress field, the temperature and properties of the fingers material and their configuration. By application of Cu thin films a significant higher performance of SAW structures with respect to power durability, reliability and lifetime is obtained. In the present paper Cu finger electrodes of a special power SAW test structure were fabricated in trenches of STX quartz substrates using the copper damascene technique. In comparison with conventional finger electrodes located on the substrate surface, such an embedded structure enables some new features regarding their acoustical and acoustomigration behavior. So high power SAW load cannot cause fatal failures by shorts between adjacent fingers. This fact is specially important for SAW devices in the GHz range. The trench structuring into the substrate was carried out by reactive ion (RIE) or ion beam etching (IBE) technique using a metallic hard mask. Etched trenches were filled with a conductive Ta-Si-N / Cu-layer system by magnetron sputtering in a cluster tool, and structured by a chemical-mechanical polishing (CMP) process. Subsequently, after cleaning an insulating Ta-based barrier (system Ta-Si-O / Ta-Si-N) layer was deposited on the wafer surface. This covering layer also acts as a protective coating. Such a metallization system enables sufficient bonding properties using Al-wires. First results of electrical measurements show that travelling SAW could be excited in quartz substrates.
Epitaxial Aluminum Electrodes on Theta Rotated Y-X LiTaO3 Piezoelectric Substrate for High Power Durable SAW Duplexers.
Authors: Nakagawara Osamu , Suzuki Hironori , Yamato Shuji , Hasegawa Masayuki , Ieki Hideharu
Published: April 2011

High power durable electrodes have been successfully grown on 38.5° rotated Y-X LiTaO3 piezoelectric substrates featuring epitaxial Al films with a pseudo-homoepitaxial Ti intermediate layer. We found that a two-step process sequence in the deposition temperature of an intermediate layer could make it possible for an Al/Ti structure to grow epitaxially on low-cut-angle Y-X LiTaO3. Specified epitaxial relationship was Al(111)<011>//Ti(001)<100>//LiTaO3(001)<100>. Duplexers with epitaxial Al electrodes had a breakdown power above 6 W and more than ten times longer lifetime in contrast to filters with polycrystalline electrodes of which the breakdown power is 3.4 W. Epitaxial electrodes with extremely less grain boundary can improve power durability because self-diffusion of Al atoms occurs mainly in the grain boundary of the film. Material variation of epitaxial electrodes will be discussed as well.
Three Dimensional Integration with Benzocyclobutene as the Wafer-Bonding Medium
Authors: Kim Sang Kevin , Xue Lei , Tiwari Sandip
Published: April 2011

A successful wafer-scale device layering process for fabricating three-dimensional integrated circuits (3D ICs) using Benzocyclobutene (BCB) is described. In the reported embodiment of the method, a sub-micron thick “donor” device layer is transplanted onto a fully fabricated “host” wafer with BCB as the intervening medium. Experimental results, including RIE study and planarization of BCB processed through the 3D fabrication procedure are reported. We conclude with an approach to alleviate BCB and fabrication induced wafer bowing, which leads to poor wafer to wafer alignment in 3D integration.
Die-on-Wafer and Wafer-Level Three-Dimensional (3D) Integration of Heterogeneous IC Technologies for RF-Microwave-Millimeter Applications
Authors: Lu J.-Q. , Devarajan S. , Zeng A. Y. , Rose K. , Gutmann R. J.
Published: April 2011

Die-on-wafer and wafer-level three-dimensional (3D) integrations of heterogeneous IC technologies are briefly described, emphasizing a specific 3D hyper-integration platform using dielectric adhesive wafer bonding and Cu damascene inter-wafer interconnects to provide a perspective on wafer-level 3D technology processing. Wafer-level 3D partitioning of high Q passive components, analog-to-digital (A/D) converters, RF transceivers, digital processors, and memory is discussed for high-performance RF-microwave-millimeter applications, especially where high manufacturing quantities are anticipated. Design and simulation results of 3D heterogeneous integration are presented. This 3D technology is applicable to smart wireless terminals, millimeter phased array radars, and smart imagers.
Evaluation of Dielectric Permittivity of Barium Titanate Fine Powders
Authors: Tsurumi Takaaki , Sekine Takashi , Kakemoto Hirofumi , Hoshina Takuya , Nam Song-Min , Yasuno Hiroaki , Wada Satoshi
Published: April 2011

Dielectric permittivity (εr) of BaTiO3(BTO) powders was determined by measuring εr of slurries prepared from BTO powder and propylene carbonate as dispersion medium, followed by analyzing with a finite element methods (FEM). The εr of powders depended on their characters such as tetragonality (c/a ratio), density, particle size and specific surface area. In order to extract the effect of each character, a statistical analysis was carried out to represent the εr of powders with an empirical formula, where the c/a ratio, density and particle size were used as parameters. A fairly good agreement between observed data and those expected from the formula was obtained and the contribution of each character to the εr could be determined.
New Garnet Films for Magneto-Optical Photonic Crystals
Authors: Khartsev S.I. , Grishin A.M.
Published: April 2011

Epitaxial La3Ga5O12 (LGG) garnet films and Bi3Fe5O12/La3Ga5O12 (BIG/LGG) heteroepitaxial structures have been synthesized on Gd3Ga5O12(GGG, 111) single crystal. LGG films were grown by Pulsed Laser Deposition (PLD) technique whereas rf-magnetron sputtering was used to grow BIG films. We demonstrate LGG is a promising material to be integrated with a giant Faraday rotator Bi3Fe5O12 in magneto-optical photonic crystals. LGG has a lattice constant 12.772 Å that is bigger than that in GGG (12.384 Å) and closer to that in BIG (12.626 Å). Heteroepitaxial Bi3Fe5O12(2μm)/La3Ga5O12(300nm) structures grown on the GGG(111) single crystal show the Faraday rotation as high as 5.74 deg/μm compared to 5.46 deg/μm in BIG/GGG at λ = 655 nm. Fitting LGG reflectivity spectra to Fresnel formulas yields LGG refractive index n = 1.981 compared to 1.963 in GGG at 655 nm. Dispersion of LGG refraction index follows Sellmeier formula n2 = 1 + 2.78/ [1 – (138nm/λ)2] in the range from 400 nm to 1000 nm.
Nonlinear magneto-optics in garnet magnetophotonic crystals
Authors: Aktsipetrov O.A. , Dolgova T.V. , Fedyanin A.A. , Kapra R.V. , Murzina T.V. , Inoue M. , Yoshida T. , Kobayashi D. , Nishimura K. , Uchida H.
Published: April 2011

In this paper the results of our recent studies of the magnetization-induced nonlinear optical second-order and third-order effects in magnetophotonic crystals and magnetophotonic microcavities are surveyed.

Nonlinear magneto-optical Kerr effect (NOMOKE) both in magnetization-induced second-harmonic generation (MSHG) and magnetization-induced third-harmonic generation (MTHG) is observed in garnet MMC at wavelengths of the resonant microcavity modes. Magnetization-induced variations of MSHG and MTHG intensity as well as magnetization-induced shift of phase and rotation of polarization of second-harmonic and third-harmonic waves are observed in proper - transversal, longitudinal or polar - NOMOKE configurations.

Nonlinear magneto-optical Kerr effect in MSHG intensity is observed in garnet magnetophotonic crystals in the spectral range of photonic band gap (PBG) edges of MPC.The MSHG intensity reveals enhancement by a factor of more than 102 if the fundamental wavelength is tuned in the vicinity of the PBG edge. This enhancement is attributed to the fulfilment of the phase matching conditions for MSHG effect in layered structures with periodic modulation of both optical (magneto-optical) and nonlinear optical parameters.
High-Density Magneto-Optical Recording with DWDD and DTE
Authors: Miyakoshi Toshimori , Shiratori Tsutomu , Miyaoka Yasuyuki , Hozumi Yasushi
Published: April 2011

We have developed a new light intensity modulation recording method called Domain Tail Erasing (DTE). This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of Domain Wall Displacement Detection (DWDD) with that of Light Intensity Modulation Direct Overwrite (LIMDOW). Recording performance nearly identical to that with Magnetic Field Modulation (MFM) was confirmed with this method, using conventional optics with a wavelength of 660 nm and an NA of 0.60. However, the DTE method still requires a bias magnet, which remains a disadvantage in cases in which a thinner drive apparatus is required.

We have therefore also made the bias magnets unnecessary by introducing a device to generate a magnetic field as a magnetic film included inside the medium.
Condenser-Transducer Configuration for Improving Radiation Efficiency of Near-Field Optical Transducers
Authors: Sendur Kursat , Peng Chubing , Challener William
Published: April 2011

Near-field radiation efficiency of the ridge waveguide transducer is investigated in the vicinity of a recording magnetic medium. Near-field radiation from a ridge waveguide transducer is expressed in terms of power density quantities. This allows us to quantify the near-field radiation efficiency from the near-field transducer with respect to the input optical power. Finite element method (FEM), which is capable of modeling focused beams, is used to simulate various geometries involving ridge waveguides. The incident electric field near the focal region is determined using a Gaussian beam expression and Richards-Wolf vector field equations for low NA and high NA beams, respectively. First, the ridge waveguide transducer is placed at the focal point of an optical lens system. The maximum value of the absorbed optical power in the recording medium is 1.6*10-4 mW/nm3 for a 100 mW input optical power. Finally, the ridge waveguide is placed adjacent to a solid immersion lens but separated by a low-index dielectric layer. For this case, the maximum value of the absorbed optical power in the recording medium is 7.5*10-4 mW/nm3 for a 100 mW input optical power. The improvement in the transmission efficiency is a result of two factors: 1. Increased incident electric field over the transducer surface due to increased NA of the optical system, 2. Surface plasmon enhancement obtained by placing a low-index dielectric material between the solid immersion lens and ridge waveguide.
The Dependence of the Magnetic Properties of GaMnN on Codoping by Mg and Si
Authors: Reed Mason J. , Oliver Luen M. , Reed Meredith L. , Bedair Salah M. , Arkun Fevzi Erdem , Berkman Erkan Acar , Elmasry Nadia A. , Zavada John
Published: April 2011

The magnetic properties of GaMnN, grown by metalorganic chemical vapor deposition, depend on the addition of dopants; where undoped materials are ferromagnetic, and n -type (Si-doped) and p -type (Mg-doped) films are either ferromagnetic or paramagnetic depending on dopant concentration. The ferromagnetism of this material system seems correlated to Fermi level position, and is observed only when the Fermi level is within or close to the Mn energy band. This allows ferromagnetism-mediating carriers to be present in the Mn energy band. The current results exclude precipitates or clusters as the origin of room temperature ferromagnetism in GaMnN.
Neutron diffraction and electrochemical studies of LixNi1/3Mn1/3Co1/3O2
Authors: Yin Shih-Chieh , Rho Young-Ho , Swainson Ian , Nazar Linda F.
Published: April 2011

Amongst solid solutions of the Li-Ni-Mn-Co-O series, LiNi1/3Mn1/3Co1/3O2 has received much attention owing to its high capacity and thermal stability. A major issue in these ordered rock salt structures is the irreversibility on the first cycle, and degree of Li+/Ni2+ cation disorder which inhibits the rate capability. To examine these factors, different synthesis methods were employed which led to LiNi1/3Mn1/3Co1/3O2 that exhibited varying degrees of cation disorder. Neutron diffraction studies were carried out on samples (LixNi1/3Mn1/3Co1/3O2, x = 1.00 → 0.04) prepared by chemical oxidation. The studies reveal that the extent of Ni2+/Li+ disorder between the 3b and 3a sites was preserved on Li extraction and re-insertion. Complete extraction of lithium to form the O1 phase was achieved in some materials. However, reformation of the O3 phase on chemical relithiation does not occur in these cases, whereas materials that only partly convert to the Ol phase exhibit complete conversion back to the O3 phase on relithiation. The differences are attributed to lithium site occupancy/stoichiometry and crystallite size effects.
Fe/Mn-based Perovskite-Type Oxides with Excellent Oxygen Permeability and Reduction Tolerance
Authors: Teraoka Yasutake , Shimokawa Hironobu , Kusaba Hajime , Sasaki Kazunari
Published: April 2011

A family of Co-free, Fe/Mn-based perovskite-type oxides, (Sr, A')(Fe, Mn)O3-δ (A'=La, Ba, Ca), was synthesized, and their oxygen permeability and phase stability in reducing atmosphere were investigated. The substitution of Mn at B site caused the decrease in oxygen permeability. As for the effect of A-site substitution, prominent promotion was observed by the substitution of Ba for 30% of Sr, and Ba0.3Sr0.7FeO3-δ was found to be one of most excellent oxygen permeable materials with the permeation flux of 3.0 cm3(STP) cm−2 min−1 at 900 °C. Reduction tolerance was evaluated by TG measurements in a 5%H2/N2 stream up to 1000 °C. After the TG measurements, crystal structures of La-Sr-Co-Fe-O and Sr-Fe-(Mn)-O perovskites were decomposed or transformed into low oxygen permeable phases, but the perovskite-type structure of Ba-Sr-Fe-(Mn)-O survived. The Fe/Mn-based perovskites with high oxygen permeability and exceeding reduction tolerance could be used as stable membrane materials for membrane reactors catalyzing NO-CH4 reaction and the partial oxidation of CH4 into synthesis gas.
Metastable Phase Evolution in TiO2-YO3/2-ZrO2
Authors: Schaedler Tobias , Girma Solome , Gandhi Ashutosh S. , Sampath Sanjay , Levi Carlos G.
Published: April 2011

The metastable-to-equilibrium phase evolution over a wide range of compositions in the TiO2-YO3/2-ZrO2 system was investigated. The competing phases are all derivatives of the fluorite structure and compositions within the fluorite and pyrochlore fields exhibit technologically interesting ionic and mixed ionic-electronic conductivity. Powders of various compositions were synthesized by precursor routes, pyrolyzed and subsequently heat-treated in a stepwise manner at progressively higher temperatures to explore the sequence of phase evolution. Extended solid solutions with amorphous, fluorite and ordered pyrochlore structures were produced over significant composition ranges within the ternary. The study also sheds new light on the correct form of the phase equilibria at 1300°C.
Development and characterization of thin-film perovskite membranes with oxygen permeability.
Authors: Muydinov R. , Popova M. , Kaul A. , Stiens D. , Wahl G.
Published: April 2011

Two conceptions of oxygen selective membrane's development, ceramic and thin film ones were considered using perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ(BSCF) with mixed oxygen ionic and electronic conductivity. The films of BSCF (2–3mkm thick) were deposited by a MOCVD technique on the porous substrates (YSZ, Al2O3). Gas tightness, selective oxygen flux at 750–950°C and stability of the asymmetric film membranes in working conditions were investigated in comparison with ceramic ones. Sufficiently gas tight films can be directly obtained only on the substrates with submicron pores and at Tdep< 600°C. New alternative approach of large-pore substrates modification for obtaining gas-tight oxygen selectively permeable membranes was developed. To avoid the chemical interaction between BSCF and YSZ or Al2O3the intermediate layer of BaO was pre-deposited. Resulting permeation through asymmetric membranes was thought to be dependent on oxygen exchange surface reaction and gas permeability of the porous supports.
Profiling of Anode Surface Cycled in LiBOB-based Electrolyte of Li Ion Batteries
Authors: Lee Unchul , Xu Kang , Zhang Sheng S. , Richard T.
Published: April 2011

As the youngest battery chemistry, Li ion technology was made possible by the formation of stable electrode/electrolyte interfaces. The correlation between the electrochemistry and the surface profile of the graphitic anode was studied in this work with a new salt lithium bis (oxalate) borate (LiBOB).

In an attempt to depict a dynamic picture of the formation of graphite/electrolyte interface during the initial forming cycle, we employed X-ray photoelectron spectroscopy in combination with the “pre-formation” technique to establish the dependence of the surface chemistry on the forming potential of the anode. A progressive transition in the 1s electron binding energies of the major elements was observed as the lithiation proceeds; however, the surface chemical species as well as their abundances seemed to stabilize around 0.55 V and remained constant during the subsequent delithiation process, indicating that a stable solid electrolyte interface (SEI) exists thereafter. Integrating the information revealed by different analyses, we believe that the reductive decomposition of BOB−-anion starts at ca. 1.00 V, while the effective protection of graphene surface by SEI is available after the anode is lithiated below the potential of 0.55 V.
Anode Hosts for Lithium Batteries: Revisiting Tin and Aluminum
Authors: Fan Quan , Zavalij Peter , Stanley Whittingham M.
Published: April 2011

Pure tin reacts readily with four lithium atoms, and so is a prime candidate as the host for the anode of lithium batteries. Tin foil and an expanded tin grid (microporous tin) have a capacity of >600 mAh/g over more than 10 deep reaction cycles, indicating the inherent reversibility of tin anode. The microporous tin showed superior chemical capacity retention. Different phases are observed during the intercalation of lithium. Capacity loss was observed after 10 cycles though, consistent with the significant increase of the cell impedance. For comparison aluminum expanded grids were also examined as hosts, where LiAl is formed. Capacities approaching 1 Ah/g were obtained. LiBOB (lithium bis(oxalato)borate) was also studied as the electrolyte salt for comparison with the reactive and high cost LiPF6 salt.
Density-Functional Theoretical Study on the Intercalation Properties of Layered LiMO2 (M = Zr, Nb, Rh, Mo, and Ru)
Authors: Singh S. P. , Tomar M. , Ishikawa Yasuyuki , Majumder S. B. , Katiyar R. S.
Published: April 2011

Average Li intercalation potentials were calculated for lithium-4d-transition-metal-oxides. The effect on the intercalation voltage of metal substitution was systematically studied by altering the 4d transitional metals M (M= Mo, Nb, Rh, Zr, Ru) in LiMO2 in the α-NaFeO2 structure. Lattice parameters in the layered α-NaFeO2 structure computed in the GGA approximation are in reasonable agreement with experiment. The intercalation potentials and relative formation energies of the fully lithiated LiNi1/3Mn1/3Mo1/3O2, fully delithiated Ni1/3Mn1/3Mo1/3O2 and the intermediate phases, Li1/3Ni1/3Mn1/3Mo1/3O2 and Li2/3Ni1/3Mn1/3Mo1/3O2, were computed by employing a generalized alloy theory. A minute substitution of cationic Mo in LiNiMnO2 was experimentally investigated to examine the effect of the Mo substitution on the electrochemical properties.
Nanostructured PEFC Electrode Catalysts Prepared via In-situ Colloidal Impregnation
Authors: Sasaki Kazunari , Shinya Kenji , Tanaka Shuhei , Kawazoe Yuudai , Kuroki Takashi , Takata Kouhei , Kusaba Hajime , Teraoka Yasutake
Published: April 2011

Nanostructured Platinum-based electrode catalysts were prepared via in-situ colloidal impregnation for polymer electrolyte fuel cells. Crystallite size, grain size, and distribution of Pt nanoparticles on carbon support materials were characterized by XRD, TEM, high-resolution FESEM, and STEM. Effective surface area and kinetically-controlled current density of Pt electrode catalysts were analyzed by cyclic and hydrodynamic voltammetry using rotating disk electrodes. PEFCs with these electrode catalysts were also prepared and their I-V characteristics were examined at 80°C.

We have succeeded to develop Pt electrode catalysts with a diameter of a few nm, supported on carbon nanofibers with different structures (including herringbone-type fibers, platelet-type fibers, and highly-conductive vapor-grown fibers), carbon nanotubes, as well as carbon black. The dependencies of nanostructure and electrochemical properties on crystallographic structure of carbon support materials and preparation conditions of electrode catalysts are analyzed and discussed. Nanostructural design of PEFC electrode catalyst layers using carbon nanofibers as catalyst supports and electrode fillers is also discussed.
Investigation of Imidazole-Based Lithium Conducting Materials
Authors: Czardybon A. R. , Sivasubramaniam K. , Goward G.R.
Published: April 2011

This study aims to develop novel polyelectrolytes including lithiated imidazole heterocycles for use in lithium ion rechargeable batteries. Lithium ion local mobility in these materials is characterized by 6, 7Li solid-state NMR. By comparing these results with macroscopic ionic conductivity, measured by impedance spectroscopy, we will be able to develop a picture of the ionic conductivity at the microscopic level. Multinuclear solid state NMR provides information on microscopic interactions including ionic mobility and ring reorientations which govern the efficiency of conductivity. Our research includes 6, 7Li variable MAS NMR studies at intermediate spinning speeds, relaxation investigations to determine spin-lattice relaxation times (T1) of lithium ion hopping, and 2D exchange spectroscopy to determine possible chemical exchange processes. A very long T1 (135 s at ambient temperature) and an activation energy Ea = 17.2 kJ/mol suggests rigid molecule structure and the absence of the ring reorientation of the model compound, lithium imidazolium (LiIm). We compare this to the behavior of LiIm doped with lithium methanesulfonate, which we show to form a new ionic complex with lower T1 and corresponding lower activation energy. With the goal of creating new polyelectrolytes, we have synthesized electrolytes incorporating lithiated imidazole rings, where lithium transport may be independent of polymer-backbone flexibility, and thus polymers with high Tg may be viable. Such materials are highly desirable for secondary lithium polymer battery applications.
Amphiphilic Dye for Solid-State Dye-Sensitized Solar Cells
Authors: Schmidt-Mende Lukas , Zakeeruddin Shaik M. , Grätzel Michael
Published: April 2011

We report a solid-state dye-sensitized solar cell with a record efficiency of 4% under simulated sunlight (AM1.5global, 100mW/cm2). This was made possible by using a new amphiphilic dye with hydrophobic spacers in combination with spiro-OMeTAD. We attribute the significant improvement in the device performance to the self-assembly of the dye to form a compact layer on the TiO2 surface and to the hydrophobic chains working as blocking layer between spiro-OMeTAD and TiO2 to reduce the back electron transfer. In addition, we studied the influence of nanoporous TiO2 film thickness on the performance of the device. These results demonstrate the high potential for solid state dye sensitized solar cells to compete with amorphous silicon cells as low cost alternative.
Plasticized conjugated polymers: a possible route to higher voltage solar cells
Authors: Wentzel Paul , Pasquier Aurelien Du
Published: April 2011

The introduction of propylene carbonate (PC) into the poly (3-alkyl)thiophenes (P3AT) poly(octyl)thiophene (P3OT) and poly(hexyl)thiophene) (P3HT) is studied. In both cases, we observe a diminution of their melting temperature, which demonstrates a plasticizing effect. We also observe an increase of photovoltage and photocurrent in sandwich devices M//P3AT+PC//ITO-PET where M=Al, Mg and ITO-PET is Indium thin oxide coated on polyester. We attribute this effect to the introduction of oxygen from the PC. When mixed with an electron acceptor PCBM, the photocurrents only slightly increase and the photovoltages are similar. In this case, the presence of oxygen is detrimental to the system.
Star-shaped heptamers of discotic dyes as new materials for photovoltaic devices
Authors: Holger Eichhorn S. , Fox Nicholas , Bornais Bryan
Published: April 2011

Potentially n-type and p-type semi-conducting discotic liquid crystal dyes are linked together to star-shaped heptamers, which might self-organize into super-columns of separated p-type and n-type columnar stacks. Their synthesis, mesomorphism, and electronic properties will be discussed along with their potential use in photovoltaic devices.
Structural studies of chloride-treated RF sputtered Cd1-xMnxTe films
Authors: Wang S. L. , Lee S. H. , Gupta A. , Compaan A. D.
Published: April 2011

Cd1-xMnxTe alloy films with band gaps of 1.6 ∼ 1.8 eV have been deposited by RF magnetron sputtering for solar-cell applications. The films have been treated by chloride vapors to improve the photovoltaic performance. These as-deposited and chloride-treated CdMnTe films have been investigated by Raman spectroscopy, x-ray diffraction (XRD) and scanning electron microscopy (SEM). Raman results indicate that Te and/or TeO2 exists in the annealed samples depending on anneal conditions.