bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Ferroelectric and Electrical Properties of Sol-Gel deposited Bi4Ti3Oi2 Thin Films by Multiple Rapid Thermal Annealing Techniques
Authors: Wang Hua. , Ren Minfang
Published: April 2011

Ferroelectric Bi4Ti3O12 thin films were fabricated by sol-gel method with multiple rapid thermal annealing (MRTA) techniques on Pt/Ti/SiO2/p-Si substrates. The effect of annealing temperature on crystallinity, ferroelectric and electrical properties of Bi4Ti3O12 films derived by MRTA and by normal RTA were investigated. The results reveal that the grain size and the roughness of surface increase with the annealing temperature increase, but the maximal remnant polarization of Bi4Ti3O12
Thin Ferroelectric Film between Double Schottky Barriers
Authors: Delimova Lyuba A. , Grekhov Igor V. , Mashovets Dmitri V. , Shin Sangmin , Koo June-Mo , Kim Suk-Pil , Park Youngsoo
Published: April 2011

Thin-film uniform metal-ferroelectric-metal (M/F/M) structure between back-to-back Schottky barriers (SBs) is considered. The ferroelectric is assumed to be a p-type semiconductor, and the film thickness is far less than the depletion layer induced by the S.B. Numerical integration of the Poisson equation is used to analyze the influence of double Shottky barriers on the distributions of the electric field, potential, and polarization across the film thickness as functions of external bias and the film electrical history. The range of structure parameters is determined, where the Poisson equation for M/F/M structure can be solved analytically providing an obvious and easy-to-interpret representation of the M/F/M behavior. Electric fields induced by back-to-back SBs under zero external bias compensate each other to a great extent. As a result, the potential across the ferroelectric film remains virtually unchanged providing the flat-band condition in the energy diagram of zero-biased M/F/M structure; in fact, the external bias applied to M/F/M structure exerts influence only on the reverse-biased barrier.
Switching Properties of PST Ferroelectric Films for Memory Applications using Conductive Oxide LSCO Electrodes
Authors: Martínez E. , Blanco O. , Siqueiros J. M.
Published: April 2011

We have investigated the switching properties of ferroelectric lead strontium titanate (Pbx Sr1-x)TiO3 (PST) capacitors using epitaxial and polycrystalline La0.5Sr0.5CoO3 (LSCO) electrodes to evaluate its potential for non-volatile memory applications (FRAM'S). The electrical performance of the PST based capacitors grown on epitaxial and polycrystalline LSCO substrates were evaluated through Polarization-Voltage (P-V) and Fatigue measurements. The [001] preferentially oriented PST ferroelectric capacitor did not show a decrease in polarization up to 108 switching cycles at an applied voltage of 4 volts and a frequency of 100 kHz. Polycrystalline PST films, on the other hand were severely fatigued. It is proposed that the good performance of the PST capacitors can be attributed to the high degree of orientation of the PST films in the [001] direction induced by the epitaxial LSCO film. However, after 1010 switching cycles in the fatigue tests, the decay of the non-volatile polarization of these films was about 18% of its initial value. We use a simple model to describe two major microscopic scenarios for the suppression of polarization at the electrodes interfaces. This model is supported by Auger Electron Spectroscopy to determine the bulk and interfacial characteristics. The depth distribution of the elements of the PST film is nearly uniform throughout the volume of the film; however the relative concentrations of Pb and O were abnormally distributed on the surface. It is concluded that, in spite of the good performance due to the favorable conditions for the growth of the PST films provided by the textured LSCO, higher quality interfaces and better control of composition is necessary to improve on fatigue.
Characterization of Number Fluctuations in Gate-last Metal Nanocrystal Nonvolatile Memory Array beyond 90nm CMOS Technology
Authors: Lee Chungho , Ganguly Udayan , Kan Edwin C.
Published: April 2011

Experimental characterization of nanocrystal formation in gate trenches were performed, which includes the analyses of number fluctuation, the size distribution, and the correlation of the size and number density in gate patterns with various feature sizes from 50nm to 150nm. The gate regions with 51nm oxide wall are defined by e-beam lithography and reactive ion etching (RIE). By using direct-deposit self-assembly (i.e., evaporation and post-annealing), Au, Ag, and Pt nanocrystals are formed on the gate tunneling oxide. From the statistical evaluation by scanning electron microscopy (SEM) observation, the number fluctuation of nanocrystals in a gate trench could be always controlled under 12%, while it follows the Poisson distribution in the unconstrained self-assembly. This is mainly due to the confinement effect by the trench sidewalls, corners, and edges. The current study demonstrated that the direct-deposit self-assembly process could be successfully adapted beyond 90nm metal nanocrystal memory technology with satisfactory parametric yield in the nanocrystal number density.
Local Self-Order Observed During Chemical Vapor Deposition of Silicon Quantum Dots for Application in Nanocrystal Memories
Authors: Puglisi Rosaria A. , Nicotra Giuseppe , Lombardo Salvatore , Salvo Barbara De , Gerardi Cosimo
Published: April 2011

A systematic study on the Si dot formation after chemical vapor deposition on silicon oxide substrates is presented. The process has been followed from the early stages of the dot formation up to 25% of coverages. Structural characterization has been performed by means of energy filtered transmission electron microscopy, which allowed us to observe dot sizes down to 0.5 nm in radius. The nanodots are shown to be surrounded by a depleted zone, where no new Si dots are observed to nucleate. This has been attributed to the adatoms capture mechanism by pre-existing dots, during the deposition. The dot radius and the capture size are shown to collapse onto the same curve, thus indicating the scaling behavior of the process. The adatom diffusion process is shown to restrict the number of nucleation sites, the final dot size and the dot position, thus driving the process toward partial self-order.
Polymer electrical bistable device and memory cells
Authors: Ouyang Jianyong , Chu Chih-Wei , Prakash Ankita , Yang Yang
Published: April 2011

Electrical bistable states with the conductivity different by more than four orders in magnitude were observed in a polymer film sandwiched between two metal electrodes. This polymer film was composed of gold nanoparticles, 8-hydroxyquinoline and polystyrene, and was formed by a solution process. The film can be programmed between the two electrical states by an electric field. The as-prepared device, which was in a low conductivity state, exhibited an abrupt increase of current when the device was scanned up to 2.8 volt (V). The high conductivity state can be returned to the low conductivity state at a voltage of –1.8 V in the reverse direction. The device has a good stability in both the states. The transitions are nonvolatile, and the transition from the low to the high conductivity state takes place in nanoseconds, so that the device can be used as a low-cost, high-density, high-speed, and nonvolatile memory. The switching mechanism was studied by investigating the current-voltage characteristics, the temperature dependence of the current, the surface potential atomic force microscopy and the energy levels of the materials. The electronic transition is attributed to the electric-field induced charge transfer between the gold nanoparticles and 8-hydroxyquinoline molecules.
Non-Volatile Giant Resistance Switching in Metal-Insulator-Manganite Junctions
Authors: Fors Rickard , Khartsev Sergey I. , Grishin Alexander M.
Published: April 2011

Heteroepitaxial CeO2(80nm)/L0.67Ca0.33MnO3(400nm) film structures have been pulsed laser deposited on LaAlO3(001) single crystals to fabricate two terminal resistance switching devices. Ag/CeO2/L0.67Ca0.33MnO3 junctions exhibit reproducible switching between a high resistance state (HRS) with insulating properties and a semiconducting or metallic low resistance state (LRS) with resistance ratios up to 105. Reversible electrical switching is a polar effect achievable both in continuous sweeping mode and in the pulse regime.
Microwave Materials with High Q and Low Dielectric Constant for Wireless Communications.
Authors: Ohsato Hitoshi
Published: April 2011

Microwave dielectrics with high Q and low εr are expected for millimeterwave applications. In this paper the preparation and properties of some candidates for microwave dielectrics such as forsterite, willemite, alumina, corundum-type compounds, green phase of Y2BaCuO5 are presented. High purity forsterite has low εr of 7.0 high Q·f of 270000 GHz and τf of -65ppm/°C. Willemite also has low εr of 6.5, and high Q·f of 160000 GHz. Alumina has ultra high Q·f of 680000GHz with εr of 10.05, and τf of -60 ppm/°C. Mg4(Nb2-x Tax)O9 which belongs to corundum group has εr of 11.5, Q·f of 350000 GHz, and τf of -70ppm/°C. Y2Ba(Cu1/4Zn3/4)O5 which belongs to green phase group has εr of 15.4, Q·f of 220000 GHz. The τf’s of these materials, which are an important property for millimeterwave applications, have been adjusted to zero ppm/°C by the addition of rutile, or adjustment of solid solution composition.
MIM Capacitors Using ALD Al2O3 for RF IC and DRAM Applications
Authors: Ko Sung Yong , Oh Jung Ik , Choi Joung Cheul , Lee Kang Hee , Bae Young Ho , Jung Young Chul , Lee Yong Hyun
Published: April 2011

Metal-insulator-metal (MIM) capacitors were fabricated in a coplanar waveguide type using the Al2O3 thin film. The Al2O3 film was grown by atomic layer deposition(ALD) using Methyl-Pyrolidine-Tri-Methyl-Aluminum (MPTMA) and H2O on Ti. The capacitance per unit area of the fabricated MIM capacitor was 0.229 μF/cm2. And it had lower voltage coefficient of capacitance (VCC) and lower leakage current than that of Al2O3 MIM capacitor prepared by Al oxidation and Si3N4 MIM capacitor prepared by PECVD respectively. The fabricated Al2O3 MIM capacitors prepared by ALD exhibited low VCC, low leakage current, small frequency-dependent capacitance reduction, low temperature coefficient of capacitance (TCC) and good reliability. The characteristics of the device were suitable for RF ICs and DRAM.
A Study on Thin Film Microstructure and Its Effects on Acoustic Film Velocity Through Picosecond Ultrasonics Technique
Authors: Li Ta-Ching , Pu Nen-Wen , Lwo Ben-Je , Kao Chin-Hsing , Hu Long-Jang
Published: April 2011

In acoustic devices such as film bulk acoustic resonators (FBAR), it is most essential to accurately determine the thin-film sound velocities in situ. In this work, we analyzed the microstructure properties of the zirconia thin films deposited by RF magnetron reactive sputtering with various oxygen partial pressures, and measured the longitudinal film velocity with picosecond ultrasonic technique. The picosecond ultrasonic waves were produced by irradiating the testing samples with an ultrafast laser pulse generated by a self-made mode-locked Ti: Sapphire laser, and detected by a delayed probe laser pulse. The acoustic velocities of the thin films were next determined from the echo times of the ultrasonic waves. To derive more accurate and reliable velocity, three different reflective layers were employed so that the echo shapes and intensities of ultrasonic wave can be compared. It was found in this work that the thin film velocities we measured were less than the bulk value, which can be calculated from Young's modulus and the density. Meanwhile, with the measurement results, it is also found that the measured acoustic velocity and the microstructure of films have strong dependence on the growth conditions. Consequently, accurate thin film velocity will be obtained for an SMR designer through better controlling on deposition conditions during manufacturing process.
Width and Gap Dependent Performance of Ferroelectric Coplanar Waveguide Phase Shifter Based on Ba1-xSrxTiO3 Thin Films
Authors: Moon Seung Eon , Kim Eun-Kyoung , Kwak Min Hwan , Kim Young-Tae , Ryu Han-Cheol , Lee Su-Jae , Kang Kwang-Y ong , Kim Won-Jeong
Published: April 2011

(001) oriented (Ba, Sr)TiO3 (BST) thin films were deposited on MgO (001) single crystal substrates by the pulsed laser deposition method. Structural properties of BST films were investigated using X-ray diffractometer. Coplanar waveguide (CPW) device based on BST/MgO layer structure was fabricated by dc sputtering deposition, photolithography and etching process. To study the geometrical factor dependent microwave performance of the CPW phase shifter based on (001) oriented BST film, the CPW devices having various gap and width were fabricated. The microwave dielectric properties of BST CPW phase shifter devices were examined by calculating the scattering parameter obtained using a HP 8510C vector network analyzer with the frequency range 0.5 ∼ 20 GHz at room temperature under the dc bias field of 0 ∼ 40V. The measured return loss and insertion loss at 10 GHz with no dc bias were about -12 ∼ -4 dB and -14 ∼ -3 dB, respectively, which mainly depended on the impedances of the CPW transmission lines. The measured differential phase shift values were about 20 ° ∼ 140 ° at 10 GHz with 40 V dc bias variations, which depended on the gap size.
Optimization of Passive Isolator Based On Barium Ferrite Sputtered Films
Authors: Le Berre M. , Capraro S. , Chatelon J. P. , Rouiller T. , Bayard B. , Barbier D. , Rousseau J. J.
Published: April 2011

Ferrites have magnetic properties suitable for electronic applications, especially in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which have a large resistivity and high permeability at high frequencies are of great interest for microwave device applications.

This contribution deals with BaM films, 1 to 36 microns thick, which were deposited under optimized conditions by RF magnetron sputtering. The films were then crystallized using a 800°C thermal annealing. Isolators were then realized using patterning of coplanar wave guides with standard lift-off technique. The slots and the central width were 300 μm wide, gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate) and the CPW metallic thickness. As standard design, the CPW were deposited on the top of the magnetic film. For the first design, transmission coefficients showed a non reciprocal effect, which reaches 7 dB per cm of line length at 50 GHz for a 26.5 μm thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate, the BaM film was selectively wet etched prior to the metal deposition everywhere except between the conductors. In that case we measured that the non reciprocal effect reached high values for lower BaM thicknesses than in comparison to design # 1 and that the insertion losses also decreased. Moreover for the design # 2, also in relation with the localization of the BaM between the conductors, the non reciprocal effect improved with increasing conductor thickness as the interaction between the field lines created by the conductors and the magnetic film is then favored.
Recent Advances in Microwave Applications of Thin Ferroelectric Films at the NASA Glenn Research Center
Authors: Romanofsky Robert R. , Miranda Felix A. , Van Keuls Fred W. , Valerio Matthew D.
Published: April 2011

We report on recent developments in microwave applications and understanding of thin Ba50Sr50TiO3films. Most of our recent efforts have focused on developing low loss, wide band phase shifters from X-band (8.4 GHz) to Ka-Band (26.5 GHz) for scanning reflectarray antennas. Attempts to reduce tanδ by Mn-doping Ba50Sr50TiO3films are briefly discussed. We have demonstrated a hybrid device at X-band that produces in excess of 300 degrees of phase shift with about 3.5 dB insertion loss and greater that 10% bandwidth. Preliminary results are presented here. The effects of mild (600 rad Si) proton radiation on device performance will also be discussed. Preliminary results on optical phase shifters will be included.
Novel nonreciprocal materials based on magnetic photonic crystals
Authors: Figotin A. , Vitebskiy I.
Published: April 2011

Magnetic photonic crystals are spatially periodic dielectric composites with at least one of the constitutive components being a magnetically polarized material. Magnetic polarization, either spontaneous or induced, is always associated with nonreciprocal circular birefringence (Faraday rotation), which can bring qualitatively new features to the electrodynamics of photonic crystals. If the geometry of the periodic array meets certain symmetry criterion, the electromagnetic properties of the composite appear similar to those of a hypothetical bianisotropic medium with gigantic linear magnetoelectric effect. In particular, such a photonic crystal can display sptrong spectral asymmetry, which implies that electromagnetic waves propagate from left to right significantly faster or slower than from right to left. The strong spectral asymmetry can result in the phenomenon of electromagnetic unidirectionality. A lossless unidirectional medium, being perfectly transmissive for electromagnetic wave of certain frequency, “freezes” the radiation of the same frequency propagating in the opposite direction. The frozen mode is a coherent Bloch wave with nearly zero group velocity and drastically enhanced amplitude. The phenomenon of electromagnetic unidirectionality is essentially nonreciprocal and unique to gyrotropic photonic crystals. Physical conditions for the phenomenon include (i) significant Faraday rotation in the magnetic component of the composite structure at the frequency range of interest and (ii) the proper spatial arangement of the constituents. Unidirectional photonic crystals can be very attractive for a variety of applications.
Magneto-optical response of a one-dimensional all-garnet photonic crystal in transmission and reflection
Authors: Kahl S. , Grishin A. M.
Published: April 2011

We present spectra of transmittance, reflectance, and Faraday rotation of transmitted and reflected light for a periodic garnet multilayer structure with a central defect layer. The multilayer consists of alternating layers of bismuth and yttrium iron garnet, is 1.5 μm thick, and was prepared by pulsed laser deposition. For the reflection measurements, a silver mirror was evaporated on top of the multilayer. Faraday rotation is strongly enhanced at resonances in transmission and reflection. The peak value obtained at 748 nm in transmission is 5.3 deg and at 733 nm in reflection is 18 deg. A single layer BIG film of equivalent thickness shows 2.2 deg Faraday rotation at 748 nm. We find rather good agreement between measured and calculated spectra. Using calculations of the distributions of light intensities at different wavelengths inside the multilayer, we are able to give consistent qualitative explanations for the enhancement of Faraday rotation. We also find numerically that - at moderate strengths of the optical resonances - a linear relation exists between Faraday rotation and the intensity integrated over all magneto-optically active layers, if absorption is neglected.

We suggest to modify the usual sensor film for magneto-optical imaging by introducing a Bragg mirror consisting of heteroepitaxial garnet layers between the substrate and sensor film. For one example situation, we show by calculation that the quality factors of image contrast and optical efficiency can be higher for heteroepitaxial garnet multilayers than for single-layer iron garnet films currently in use as sensor films.
Electro-Optic and Magneto-Optic Photonic Bandgap Materials Kevin
Authors: Zou Y. , Wang Yanyun , Li Kewen , Jiang Hua , Mondal Samir K. , Hills Bethanie J.
Published: April 2011

This work presents a study of electro-optic and magneto-optic films made by a Metal-Organic Chemical Liquid Deposition (MOCLD) method. Electro-optic thin film, La-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PLMNT) and magneto-optic thin film, rare earth doped yittrium iron garnet (YIG) have been grown at different conditions. Low temperature growth on buffered semiconductor substrates has been studied for semiconductor device integration. High quality PLMNT film with EO coefficient of 1x10-16 (m/V)2 was obtained with MOCLD. Doped and undoped YIG onto MgO and glass substrates and also onto buffered semiconductors were successfully deposited using MOCLD method. Several of these films had successful rotations that were of device quality. Based on these high quality functional films, two dimensional photonic bandgap waveguide structures were designed and simulated.
Superprism effect in magneto-photonic crystals
Authors: Vinogradov A. P. , Merzlikin A. M. , Granovsky A. B. , Inoue M. , Khanikaev A. B.
Published: April 2011

In frame of computer simulation we study for the first time the magnetic superprism effect. We employ a simple square lattice model and restrict ourselves to lossless case. The photonic band structure for 2D PC built up of magneto-optical matrix with square holes is calculated. It is shown that an external magnetic field applied perpendicularly to the holes changes 2D PC band structure and thus propagation of light through PC.The effect exists even for a weak magneto-optical activity of the matrix but only for the definite set of model parameters. Thus, it makes possible to deflect a light beam by applying magnetic field without variation of frequency or initial angle of incidence.
Three-Dimensional Magneto-Optical Recording
Authors: Itoh Akiyoshi
Published: April 2011

In this report, the newly developed three-dimensional magneto-optical (MO) recording scheme and the experimental results are reported. A part of this work has been done as the national project of 3D-MO (3-dimensional MO) project. It started at September 1998 and ended March 2002 as a part of the national project “Nanometer-Scale Optical High Density Disk Storage System” and aimed at achieving 100 Gb/in2 in storage density. Three-dimensional MO recording is one of the prosperous candidates of next generation ultra high density recording. Magnetic amplifying MO system (MAMMOS) is employed for achieving the novel three-dimensional MO recording. Double-MAMMOS scheme consists of 2-recording layers of differing compensation temperature (Tcomp ) and one readout layer was proposed and discussed.

With write/read test it is succeeded to show the results corresponding to a 100 Gb/in2 (50 Gb/in2 × 2) recording density. We also proposed and showed results of simulations of a new type of Double-MAMMOS in which the recording layers can hold quadri-valued information by single writing process.
Temperature Dependence Free Magneto-Optical (Tb,Bi)Fe Garnet Films Grown By LPE Method
Authors: Imaizumi Nobuo , Fukuhara Takashi , Kuwano Yasuhiko , Shiroki Kenichi
Published: April 2011

Bi-substituted TbFe Garnet films grown by Liquid-Phase Epitaxial (LPE) method are demonstrated as a candidate for the temperature dependence free Faraday rotator in the telecom devices or the optical sensors applications. Several types of substituted GdGaGarnet (SGGG) substrates are applied in the tests. At X=0.48 o 0.56 in the Tb(3-X)BiXFe5O12, a series of very low temperature dependence garnet films are fabricated on the lattice constant of 12.465Å (GdCa)3(GaZrMg)5O12 substrates through the LPE-grown processing with optimized flux compositions. A couple of device applications are also demonstrated using these suppressed temperature dependence garnet films.
Experiments Towards the Realisation of a Monolithically-Integrated Optical Isolator Incorporating Quasi-Phase Matched Magneto-Optical Effects
Authors: Holmes Barry. M. , Hutchings David. C. , Bregenzer Josef. J.
Published: April 2011

Experiments towards the realisation of the necessary components for future integrated waveguide optical isolators have been conducted. The design, fabrication and characterisation of GaAs/AlGaAs reciprocal mode converters, realised through the use of three novel approaches, is reported. These devices have been tested at λ=0.9m and 1.3m, producing TE-TM conversion efficiencies up to 70%. Initial investigations into the inclusion of magneto optic materials with III-V semiconductor structures for non-reciprocal mode conversion are also discussed.
Cd1-xMnxTe Magneto-Optical Waveguide for Monolithical Integration of Optical Isolator into Optoelectronics Circuits
Authors: Zayets Vadym
Published: April 2011

Diluted magnetic semiconductor Cd1-xMnxTe was proposed as a magneto-optic material for waveguide optical isolator. Waveguide propagation loss below 1 dB/cm, complete magneto-optical mode conversion and optical isolation of 20 dB were demonstrated with Cd1-xMnxTe waveguides grown on GaAs substrate. The high isolation ratio, high magneto-optic effect and low propagation loss achieved in the magneto-optical waveguide grown on the semiconductor substrate shows the feasibility of monolithical integration of an optical isolator with semiconductor optoelectronic devices.
Hybrid semiconductor-ferromagnetic-metal active optical isolator.
Authors: Zayets Vadym , Ando Koji
Published: April 2011

The effect of non-reciprocal loss/gain in semiconductor-ferromagnetic-metal hybrid was studied. It is shown that the optical loss/gain of this semiconductor-ferromagnetic-metal hybrid differs for the forward and backward propagation when the magnetization is perpendicular to the light propagation and lies in the film plane. Using this effect a new design of optical isolator is proposed, which is beneficial for monolithic integration of optical isolator with laser diode. The non-reciprocal loss was experimentally observed in Ga1-xAlxAs waveguide covered by Co for the first time.
Fabrication of a TE Mode InGaAsP Active Waveguide Optical Isolator Based on the Nonreciprocal Loss shift
Authors: Shimizu Hiromasa , Nakano Yoshiaki
Published: April 2011

We have fabricated a TE mode InGaAsP active waveguide optical isolator based on the nonreciprocal loss shift in an optical fiber telecommunication wavelength of 1550nm. We demonstrated a TE mode nonreciprocal loss shift of 9.3dB/mm under a magnetic field of +/-1kG in the facricated InGaAsP active waveguide with Fe on an InP substrate at a wavelength of 1560nm. This result opens a way to the monolithic integration of semiconductor-waveguide-type optical isolators with edge emitting semiconductor lasers.
Application of Magnetic Garnet Films for Magnetooptical Imaging of Magnetic Field Distributions
Authors: Dötsch H. , Holthaus C. , Trifonov A. , Klank M. , Hagedorn O. , Shamonin M. , Schützmann J.
Published: April 2011

Rare-earth iron garnet films of high quality can be grown by liquid phase epitaxy on paramagnetic substrates of gadolinium galliumgarnet. Such films are currently used for imaging of the spatial distribution of magnetic fields. This application is based on the Faraday rotation which can strongly be enhanced by bismuth incorporation.

The physical properties of the films can be controlled by the chemical composition, the growth conditions and the crystallographic orientation. The sensor properties like sensitivity, dynamic range, signal linearity and unambiguity must be optimized according to the application desired. These properties, however, are not independent of each other. In addition, they strongly depend on the optical wavelength. Thus, it is necessary to find compromises.

The influence of Faraday rotation, Faraday ellipticity, optical absorption, magnetic anisotropies and film thickness on the performance of a magnetooptical indicator film is investigated. Based on the swing of the photoresponse, a new optimization process is introduced. The process is experimentally verified and application examples are demonstrated.

Furthermore, two methods are presented to enhance the sensitivity of magnetooptical sensors. Using specific crystallographic orientations, an easy plane of magnetization can be induced which is inclined with respect to the film plane. If the magnetization lies in this plane a very high sensitivity is achieved. The dependence of the geometrical orientation of the easy plane on the growth direction is calculated and the sensitivity and dynamic range are derived. Experimental results of a [112] oriented garnet film are in good agreement with calculations.

Garnet films which are magnetized along the film normal due to a strong induced uniaxial anisotropy support magnetic domains. If the collapse field perpendicular to the film plane is small, such films can be used as very sensitive indicator films. Such films are easier to prepare than sensitive in-plane films. However, the spatial resolution is limited by the size of the domains. This disadvantage can be avoided by applying a bias field in the film plane. Directly at the in-plane collapse field the sensor film is in-plane magnetized yielding high spatial resolution at still high sensitivity. The variation of magnetooptical images with in-plane induction is demonstrated. Experimental results are in agreement with calculations.
Growth and Characterization of Magnetooptic Garnet Films with Planar Uniaxial Anisotropy
Authors: Fratello Vincent J. , Mnushkina Irina , Licht Steven J. , Abbott Robert R.
Published: April 2011

Thick film garnet Faraday rotators with perpendicular anisotropy have limited utility for variable polarization rotation applications because multi-domain effects result in large effective insertion losses in device applications. Thick film growth of (BiGdLu)3(FeGaAl)5O12 on (100) substrates yields growth-induced anisotropies ranging from positive anisotropy perpendicular domains to negative anisotropy in-plane domains. Planar domains show variable magnetization by domain rotation with a uniform projection of magnetization along the axis of light propagation. This can produce low-loss devices when operated in sub-saturation applications such as magnetic field sensors, variable optical attenuators and polarization controllers.
Clamped Ferroelectric and Magnetic Domain Walls and their Application to Memory Engineering
Authors: Hanamura Eiichi , Tanabe Yukito
Published: April 2011

A family of rare-earth metal manganites are antiferromagnetic (AFM) ferroelectrics and some of these may show also weak ferromagnetism. First we will show how to observe the ferroelectric (FEL) and AFM domain structures by the interference effects of second harmonic generation (SHG). Second, the observed clamping of the AFM domain wall (DW) to the FEL domain boundary (DB) is intuitively explained by the group theoretical consideration of the magnetic anisotropy energy depending upon the sign of the FEL polarization. Third, the application of these clamped DW-DB to the memory engineering will be briefly discussed.
Characterization of Li insertion mechanisms in negative electrode materials for Li-ion batteries by Mössbauer spectroscopy and first-principles calculations
Authors: Lippens P.E. , Aldon L. , Ionica C.M. , Robert F. , Olivier-Fourcade J. , Jumas J.C.
Published: April 2011

The Mössbauer spectroscopy is an efficient experimental tool to study lithium insertion mechanisms in negative electrodes of Li-ion batteries at the atomic scale. However, a quantitative interpretation of the experimental data is often difficult due to the complexity of the spectra and we propose to use first-principle calculations of the hyperfine parameters. Three different types of negative electrode materials are considered. First, the experimental 119Sn Mössbauer spectrum obtained for the insertion of 3.5 Li into SnO is compared to the theoretical spectrum, which clearly establishes the existence of Li-Sn stable phases. Then, the analysis of the 121Sb Mössbauer spectra for metal antimonides at the end of the first discharge shows different behaviours depending on the lithium rate. Finally, tin and iron doped titanates are considered to study changes in Ti local environments during lithium insertion.
Reversible electrochemical extrusion of copper by lithium. Role of the initial structure
Authors: Morcrette M. , Leriche J.B. , Chevalier F. , Rozier P. , Dupont L. , Poizot P. , Laffont L. , Tarascon J.M.
Published: April 2011

The reversible Li-driven copper extrusion/insertion mechanism into Cu2.33V4O11 electrode has been studied and a new ion-exchanged assisted electrochemical process was unravelled. This process, entails during the charging of “Lix V4O11 + Cu0” composite electrodes vs. Li, the oxidation of Cu metal into copper ions that concomitantly exchanged for lithium ions to produce back Cu2.33V4O11. The electrochemical performances of such cells, namely in terms of capacity retention and power rates, are explained on the basis of the electrochemically generated Cu ions that can either being ion-exchanged with Li within the Li-V-O host or released in the solution. When the former does occur we show, owing to excellent kinetic of both, the ion-exchanged reaction between Cu2+ and Li+ together with a fast charge transfer between Cu0 and Cu2+, that high rate performances electrodes can be achieved whereas when the latter prevails the cells rapidly fail. It appears then that Cu+ ions should be removed. Thus, a new copper vanadate Cu1.1V4O11 phase has been isolated by both chemical and electrochemical removal of Cu from the mother Cu2.33V4O11 phase, and its electrochemical performance in Li cells studied. The removal of copper was shown to occur in a topotactic manner resulting in a stacking of [V4O11]n layers linked by differently coordinated copper ions. This new phase reversibly reacts with 5 Li, leading to a capacity of about 260 mAh/g, through a process involving a reversible displacement reaction entailing to the growth/disappearance of Cu dendrites.
Synthesis, Characterization and Properties of New Vanadia-Alumina and Vanadia-Silica Composites Prepared by Interpenetrating Polymer Network Approach
Authors: Zampronio Elaine C. , Barbosa Glauciane N. , Graeff Carlos F.O. , Lassali Tânia A.F. , Oliveira Herenilton P.
Published: April 2011

In this study, we incorporated vanadium pentoxide xerogel into an alumina matrix and into a silica matrix in order to improve the structural stability by incorporating the electroactive material into an inert matrix which provides structural stability to the electrode. The novel materials were characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, cyclic voltammetry and impedance spectroscopy. V2O5/SiO2 and V2O5/Al2O3 xerogel composites prepared by soft chemistry present conductivity almost five orders of magnitude higher than other related systems. The electrochemical behavior is quite similar to that found for V2O5 xerogel. In addition, the cyclic voltammetric and electrochemical impedance spectroscopy studies demonstrated that the alumina and silica matrices provide an improvement of the electrochemical properties mainly in relation to the kinetics of the lithium electroinsertion into the oxide matrix with little decrease of total charge during successive redox cycles. Overall, the synthetic approach applied in this study is extremely attractive due to its simplicity and can provide new strategies for tailoring new materials and future family members for electrochromic devices, batteries and chemical sensing.
Co-Sintering of Dense Electrophoretically Deposited YSZ Films on Porous NiO-YSZ Substrates for SOFC Applications
Authors: Savo Giuseppe , Rainer Alberto , D'Epifanio Alessandra , Licoccia Silvia , Traversa Enrico
Published: April 2011

An original process for the preparation of YSZ dense films with a thickness lower than 10 μm over NiO-YSZ substrates is presented. This process involves the preparation of a green membrane of NiO-YSZ and subsequent electrophoretic deposition (EPD) of commercial YSZ powder on this polymer-rich membrane. A single thermal treatment allowed removal of the organic compounds, sintering of the layers and full densification of the electrolyte.
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.
Composite Inorganic Filler Based Electrolyte Membranes for Fuel Cells Applications
Authors: Aricò Antonino S. , Baglio Vincenzo , Blasi Alessandra Di , Antonucci Vincenzo
Published: April 2011

Various recast Nafion® composite membranes containing ceramic oxide fillers with different surface characteristics (SiO2, SiO2-PWA, Al2O3, ZrO2) have been investigated for application in high temperature direct methanol fuel cells (DMFCs). Cell resistance at 145 °C increases as a function of the pH of slurry of the inorganic filler indicating a strong influence of the acid-base characteristics on the electrolyte conductivity. This effect has been attributed to the different water retention capabilities of the various membranes. Fuel cell performance at 145 °C, expressed as both maximum power density and current density at 0.5 V cell potential, increases almost linearly as the pH of slurry of the oxide materials decreases. Appropriate selection of the surface properties for the inorganic fillers allows to enhance the proton conductivity and extends the operating temperature range of composite membranes. An infrared spectroscopic investigation of inorganic fillers employed in composite membranes has been carried out. The surface acidity of the fillers appears to influence the bending and stretching vibrational frequencies of the water physically adsorbed on the filler surface. Inorganic fillers characterised by acidic properties undergo a strong interaction with water and enhance the DMFC performance at high temperature.
Influence of the grain boundaries on conductivity of yttrium stabilized zirconia
Authors: Petrovsky V. , Jasinski P. , Anderson H.U. , Petrovsky T.
Published: April 2011

The influence of the grain boundaries on the ionic conductivity of yttrium stabilized zirconia (YSZ) was investigated. The initially nanocrystalline samples were prepared using a tape casting process. The samples were annealed at different temperatures in the range from 1000 to 1400°C to overlap the grain size from 100nm to ∼10μm and investigated using impedance spectroscopy. Two distinct semicircles were found on all YSZ samples corresponding to the influence of the grain and grain boundary on the resistance. The activation energies for both resistances are very close (1.00 and 1.03eV correspondingly). The grain resistance does not change significantly during the annealing process, but the grain boundary resistance decreases after high temperature annealing which causes a decrease in the overall resistance of the material. The calculations show that the decrease in the grain boundary resistance is connected only with the increase in the grain size and the specific grain boundary resistance (per unit surface area of grain boundary) does not change with annealing.
Preparation and characterization of lead ruthenate based composite cathodes for SOFC applications
Authors: Esposito Vincenzo , Traversa Enrico , Wachsman Eric D.
Published: April 2011

Nanometric pyrochlore lead ruthenate (Pb2Ru2O6.5) powders were prepared using a new chemical route as a possible candidate for cathode materials in solid oxide fuel cells (SOFCs). Pb2Ru2O6.5 was mixed with yttria-stabilized zirconia (YSZ) and erbia-stabilized bismuth oxide (ESB) to fabricate porous composite electrodes. Pure pyrochlore or composite electrodes were deposited as thick films onto YSZ and ESB electrolytes. Powders and films were analyzed using X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). Electrochemical features of the electrodes were investigated using electrochemical impedance spectroscopy (EIS) measurements at different temperatures in air for symmetric cells. The composite electrodes were compared to single Pb2Ru2O6.5 phase electrodes to evaluate the effect on polarization of the addition of the pure ionic conductor phase in the electrodes.
Synthesis, spectroscopic and electrochemical characterization of hybrid membranes for Polymer Electrolyte Membrane Fuel Cells.
Authors: Vona Maria Luisa Di , Marani Debora , D'Epifanio Alessandra , Traversa Enrico , Trombetta Marcella , Licoccia Silvia , Caldarelli Stefano , Knauth Philippe
Published: April 2011

Commercial polyether-etherketone was sulfonated and reacted with SiCl4 to obtain a hybrid polymer. Polymers having different inorganic content were characterized by 29Si NMR, ATR/FTIR spectroscopies and mass spectrometry (FAB-MS) demonstrating the formation of covalent bonds between the organic and inorganic components and the absence of dispersed inorganic silicon. The physicochemical properties of the hybrids were suitable for the preparation of membranes which showed sufficiently high conductivity values to make them promising candidates for application in PEMFCs.
Progress in Producing Large Area Flexible Dye Sensitized Solar Cells
Authors: Mandal Krishna C. , Choi Michael , Noblitt Caleb , David Rauh R.
Published: April 2011

Dye sensitized nanocrystalline TiO2 solar cells have been reported with over 11% efficiency and are extremely promising as very low cost and lightweight photovoltaic sources. However, most reports are for cells of low area fabricated on glass, which withstands processing temperatures of ∼450°C. In this paper, we describe the fabrication and performance of cells made on flexible ITO-coated polyethylene terephthalate (PET) substrates with 6” × 3” dimensions. To improve the efficiency in the cells, we enhanced the ITO current collection efficiency with metallization fingers. The fingers resulted in a >10 fold increase in short-circuit current under normal solar illumination compared to cells without metallization. Further improvements were realized by passivating the metallization fingers at the metal/polymer electrolyte interface.
Time Evolution of Photoconductivity in TiO2 Electrodes Fabricated by a Sol Gel Method
Authors: Xie Zhibin , Burlakov Victor M , Henry Bernard M. , Kirov Kiril R. , Grovenor Christopher R. M. , Assender Hazel E. , Andrew G. , Briggs D. , Kano Mitsuru , Tsukahara Yusuke
Published: April 2011

We report here on the time evolution of photoconductivity under continuous illumination in nanocrystalline TiO2 samples prepared by a sol gel method, and also on the conductivity decay once the illumination is switched off. We observe strong dependence of the photoconductivity on the illumination intensity for both processes. It is found that the conductivity decay after high-intensity illumination is slower than after low-intensity illumination, and we have attempted to explain these experimental results using a model involving hole trapping-detrapping processes.
Quantum Dot-Single Wall Carbon Nanotube Complexes for Polymeric Photovoltaics
Authors: Landi Brian J. , Castro Stephanie L. , Evans Chris M. , Ruf Herbert J. , Bailey Sheila G. , Raffaelle Ryne P.
Published: April 2011

The ability to dissociate the photo-generated excitons and transport the resulting charge carriers are the major impediments in improving the efficiency of polymeric solar cells. In order to simultaneously address both of these issues, we have investigated the use of quantum dotsingle wall carbon nanotube (QD-SWNT) complexes as a suitable nanomaterial dopant in these devices. The formation of CdSe-SWNT complexes occurred through covalent attachment of carboxylic acid-functionalized SWNTs with CdSe-aminoethanethiol (AET) quantum dots. An additional synthetic approach was evaluated using both electrostatic and covalent attachment schemes for CuInS2-mercaptoacetic acid (MA) quantum dots and amine terminated SWNTs. The efficacy of each approach is discussed, including the necessary transmission electron microscopy (TEM) and optical absorption spectroscopy data to probe the interactions between nanomaterials. The potential effects of charge transfer between components may have important implications in the efficiency of these materials for polymeric photovoltaic devices.
High Efficiency P3HT/PCBM Solar Cell
Authors: Inoue Kanzan , Ulbricht Ross , Madakasira Pallavi C. , Zhou Miaoxin , Lee Sergey B. , Ferraris John , Zakhidov Anvar A.
Published: April 2011

We report a nearly twofold increase of short circuit current: from Isc ∼ 10 mA/cm2 to Isc = 16–20 mA/cm2 in P3HT/PCBM solar cells (SC) employing freshly prepared regio-regular poly(3-hexylthiophene) (RR-P3HT) without special purification. The power conversion efficiency is enhanced to η≥ 4% as compared to our best η=3.8% in SC with commercial polymer despite the decreased filling factor (FF= 0.42, as compared to best FF = 0.59). We used our earlier found [1] procedures with optimal post heat treatment temperatures and time for our polymer SC. We also discovered a strong correlation between the device preparation procedures and performance. The optimal phase separation of PCBM and RR-P3HT into a bi-continuous network structure occurs after quite long solution stirring times (enhanced homogenization) and surprisingly very short annealing time at optimal temperature. We also found that the optimal concentration of PCBM in a RR-P3HT matrix is rather low, only c∼35 wt%, contrary to high c∼80 wt% in PPV based SC.
Novel Strategies for the Preparation of TiO2 Nanofibers
Authors: Balkus Kenneth J. , Xiong Chunrong , Macias-Guzman Minedys
Published: April 2011

The various polymorphs of titanium oxide (TiO2) are probably the most widely studied materials for photovoltaic applications. It is well known that composition and particles size can have a profound effect on photoactivity. It is thought that high surface to volume nanostructures such as nanofibers and nanorods may possess the optimal properties. We have developed technology for the preparation of TiO2 nanofibers in a variety of forms including core shell structures, papers and films. The formation of mesoporous TiO2 fibers as spider webs and papers has been achieved by electrostatic deposition. The mesoporous fibers and other forms such as shaped particles and films have been employed as templates to grow TiO2 nanofibers in various configurations. The proposed research below will address the synthesis and characterization of the TiO2 fibers developed by these techniques