bluuebunny/crossref_metadata_2025 huggingface dataset:
RF Microwave Switches Based on Reversible Metal-Semiconductor Transition Properties of VO2Thin Films: An Attractive Way To Realise Simple RF Microelectronic Devices
Authors: Dumas-Bouchiat Frédéric , Champeaux Corinne , Catherinot Alain , Givernaud Julien , Crunteanu Aurelian , Blondy Pierre
Published: August 2010

Microwave switches in both shunt and series configurations are developped using semiconductor to metal (SC-M) transition of vanadium dioxide (VO2) thin films deposited byin situpulsed laser deposition on C-plane sapphire and SiO2/Si substrates. The influence of geometrical parameters such as the length of the switch is shown. The VO2-based switches exhibit up to 30-40 dB average isolation of the radio-frequency (RF) signal on a very wide frequency band (500 MHz-35 GHz) with weak insertion losses, when thermally activated. Furthermore, they can be electrically activated. Finally these VO2-based switches are integrated in the fabrication of innovative tunable band-stop filters which consist in a transmission line coupled with four U-shaped resonators and operate in 9-11 GHz frequency range. Its tunability is demonstrated using electrical activation of each VO2-based switch.
Modeling of Nanoimprinting of Metals by Nanotube Arrays
Authors: Li Lili , Xia Zhenhai , Yang Yanqing
Published: August 2010

Molecular dynamics (MD) simulations are reported for buckling and interfacial friction of single- and multi-wall carbon nanotubes (CNT) with interwall sp3 bonds imprinted on copper substrates. A small perturbation of mechanical vibration is applied to the systems in the nanoimprinting. The imprinting capabilities of multi-wall CNTs are much better than single-wall CNTs. While the single-wall CNT is insensitive to the vibration, the indentation force and buckling of multi-wall CNTs with interwall sp3 bonding is dependent on the amplitude of the perturbation, providing a way to controlling the interfacial friction. There is an optimal amplitude, at which the buckling and friction force of the CNTs are minimized in nanoimprinting.
X-ray Micro Laue Diffraction and Neutron Diffraction Analysis of Residual Elastic Strains in a 1% Uniaxial Tensile Tested Nickel Alloy 600 Sample
Authors: Chao Jing , Mark Alison , Suominen Fuller Marina Lynn , Barabash Rozaliya , McIntyre N. Stewart , Holt Richard A. , Klassen Robert J. , Liu Wenjun
Published: August 2010

The magnitude and distribution of elastic strain for a nickel alloy 600 (A600) sample that had been subjected to uniaxial tensile stress were measured by micro Laue diffraction (MLD) and neutron diffraction techniques. For a sample that had been dimensionally strained by 1%, both MLD and neutron diffraction data indicated that the global residual elastic strain was on the order of 10−4, however the micro-diffraction data indicated considerable grain-to-grain variability amongst individual components of the residual strain tensor. A more precise comparison was done by finding those grains in the MLD map that had appropriate  oriented in the specific directions matching those used in the neutron measurements and the strains were found to agree within the uncertainty. Large variations in strain values across the grains were noted during the MLD measurements which are reflected in the uncertainties. This is a possible explanation for the large uncertainty in the average strains measured from multiple grains during neutron diffraction.
Nanocrystalline Diamond Coatings: Creation of Proper Surface Topography for Orthopedic Applications
Authors: Yang Lei , Webster Thomas J. , Sheldon Brian W.
Published: August 2010

The idea of using nanocrystalline diamond (NCD) as a coating on orthopedic implants originates back to the last century since NCD possesses superior mechanical and tribological properties as well as chemical stability. However, it has only been within recent years that the interactions between NCD and osteoblasts (OB, bone forming cells) have been investigated. In this study, the impact of NCD surface topography on OB functions including proliferation (24 hrs to 48 hrs) and differentiation (7 to 21 days) was studied. NCD of varied grain sizes (from less than 100 nm to approximately 600 nm) were fabricated by microwave plasma enhanced chemical-vapor-deposition and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Surface topography of the NCD changed dramatically as grain size grew. OB proliferation on these coatings was studied by SEM after incubation for 24 hrs and 48hrs, respectively. OB differentiation on diamond coatings after incubation from 1 to 3 weeks was investigated by alkaline phosphatase activity and calcium deposition. Results demonstrated that OB proliferation and differentiation were dependent on topography with NCD grain sizes less than 100 nm exhibiting the best OB responses. To explain this enhancement, OB filopodia protrusions on different NCD were observed by SEM and the results revealed that surface topography of NCD played a crucial role in OB filopodia extensions. In summary, these findings provided important design criteria for creating proper NCD surfaces for orthopedic coatings and also provided cues on promoting interactions between nanostructured surfaces and cell responses.
Hole Drift Mobility Measurements on a-Si:H using Surface and Uniformly Absorbed Illumination
Authors: Dinca Steluta Adriana , Schiff Eric A , Guha Subhendu , Yan Baojie , Yang Jeff
Published: August 2010

The standard, time-of-flight method for measuring drift mobilities in semiconductors uses strongly absorbed illumination to create a sheet of photocarriers near an electrode interface. This method is problematic for solar cells deposited onto opaque substrates, and in particular cannot be used for hole photocarriers in hydrogenated amorphous silicon (a Si:H) solar cells using stainless steel substrates. In this paper we report on the extension of the time-of-flight method that uses weakly absorbed illumination. We measured hole drift-mobilities on seven a Si:H nip solar cells using strongly and weakly absorbed illumination incident through the n-layer. For thinner devices from two laboratories, the drift-mobilities agreed with each other to within our random error of about 15%. For thicker devices from United Solar, the drift-mobilities were about twice as large when measured using strongly absorbed illumination. We propose that this effect is due to a mobility profile in the intrinsic absorber layer in which the mobility decreases for increasing distance from the substrate.
Environmental Effects on the Single Molecule Conductance of bis(thiahexyl)oligothiophenes
Authors: Leary Edmund , Höbenreich Horst , Higgins Simon J. , van Zalinge Harm , Haiss Wolfgang , Nichols Richard J. , Finch Christopher , Grace Iain , Lambert Colin J.
Published: August 2010

Simple alkanedithiols exhibit the same molecular conductance whether measured in air, under vacuum or under liquids of different polarity. Here, we show that the presence of water ‘gates’ the conductance of a family of oligothiophene–containing molecular wires, and that the longer the oligothiophene, the larger is the effect; for the longest example studied, the molecular conductance is over two orders of magnitude larger in the presence of water, an unprecedented result suggesting that ambient water is a crucial factor to be taken into account when measuring single molecule conductances (SMC), or in the design of future molecular electronic devices. Theoretical investigation of electron transport through the molecules, using the ab initio non-equilibrium Green's function (SMEAGOL) method, shows that water molecules interact with the thiophene rings, shifting the transport resonances enough to increase greatly the SMC of the longer, more conjugated examples.
Comparison of Molecular Monolayer Interface Treatments in Organic-inorganic Photovoltaic Devices
Authors: Albin Jamie M. , Baker Darick J. , Allen Cary G. , Furtak Thomas E. , Collins Reuben T. , Olson Dana C. , Ginley David S. , Weigand Christian C. , Vardoy Astrid-Sofie , Ladam Cecile
Published: August 2010

In this study, we explore the effects of alkyl surface terminations on ZnO for inverted, planar ZnO/poly(3-hexylthiophene) (P3HT) solar cells using two different attachment chemistries. Octadecylthiol (ODT) and octadecyltriethoxysilane (OTES) molecules were used to create 18-carbon alkyl surface molecular layers on sol gel-derived ZnO surfaces. Molecular layer formation was confirmed and characterized using water contact angle measurements, infrared (IR) transmission measurements, and X-ray photoelectron spectroscopy (XPS). The performances of the ZnO/P3HT photovoltaic cells made from ODT- and OTES-functionalized ZnO were compared. The ODT-modified devices had higher efficiencies than OTES-modified devices, suggesting that differences in the attachment scheme affect the efficiency of charge transfer through the molecular layers at the treated ZnO surface.
Tools for Aggregating, Analyzing and Mining Combinatorial Data
Authors: Jones Wesley , Suh Changwon , Graf Peter A , Korytina Daniel , Swank Craig , Perkins Christopher
Published: August 2010

We demonstrate how data mining techniques can be applied to complex combinatorial data sets and how data from multiple sources can be aggregated via the developed scientific data management system. An example is shown for the case of aggregated combinatorial data for the study of composition, processing, structure, and property relationships of transparent conducting oxides by applying data mining techniques such as principal component analysis. Data mappings of mined results are shown to effectively enable visualization of data trends, identification of anomalies in Fourier transform infrared spectroscopy patterns, and scientifically interesting libraries and spectral regions.
High Throughput Screening of Waterbased Coating Formulations
Authors: Roper John , Johnson Michael , Keefe Melinda , Mecca Jodi , Cesaretti Richard
Published: August 2010

Since 1998, Dow has been actively developing and applying high throughput research (HTR) methodologies to increase the speed to market and the probability of successful product introductions. Initially Dow implemented this approach in the area of homogeneous catalysis. Based upon the success in this area, high throughput methods have been expanded into other research areas such as waterborne coatings. Paint formulations offer an excellent opportunity to use the strengths of high throughput research to understand how complex interactions between many components affect final properties. High throughput tools enable the rapid and reproducible development of paints, preparation of coating on substrates, and evaluation of performance. Rapid formulation and testing allows the interactions between formulation variables to be investigated in much more depth and breadth than has been possible in the past. Finally, statistical anaylsis and data mining tools can be used to optimize a desired balance of properties within customer defined constraints. This paper presents an example of using Dow's HTR coatings workflow to improve properties for low VOC / low odor architectural coatings.
Mechanical Characterization of Interfacial Adhesion in Elastomeric Material for Microelectronic Device through JKR Model Combined with Micro-to-Nano IIT
Authors: Lee Gyujei , Oh Jae-sung , Byun Kwang-yoo , Kang Seung-kyun , Kwon Dongil
Published: August 2010

Instrumented indentation testing (IIT) is a very useful technology for the mechanical characterization of materials. However, existing IIT techniques, which are based on the Hertz model and were developed for hard materials with negligible surface adhesion such as metals and ceramics, are difficult to directly apply to compliant materials such as elastomeric polymers which have viscoelastic hysteresis due to infinitesimal surface/interfacial adhesion. Here we employed some modified model to evaluate the work of adhesion in elastomeric polymer from our previous work, and reinforced our theory and algorithm through empirical approaches so as to consider the time-dependency of viscoelastic material as testing parameter. To do these all, we combined analytic JKR theory and conventional IIT technology to analyze the physical meaning of the theory and then verified our ideas experimentally with elastomeric polymer, PDMS (poly(dimethyl-siloxane)), of various compositions. Our algorithm was developed and verified on a microinstrumented indentation basis and extended even into the nanoinstrumented testing for the micro/nano-scaled applications.
Lattice and electronic effects in rutile TiO2containing charged oxygen defects fromab initiocalculations
Authors: Park Seong-Geon , Magyari-Köpe Blanka , Nishi Yoshio
Published: August 2010

We performed first-principle simulation for the study of oxygen vacancy defect in rutile TiO2based on density functional theory. The effects of a vacancy on the electronic structure of rutile TiO2were studied. Here we have employed neutral and charged oxygen vacancy in the supercell to address the resistance switching mechanism. Neutral vacancy induces the band gap states at deep level, ∼0.7 eV below the conduction band minimum, which is occupied by highly localized electrons. The calculation results of positively charged oxygen vacancy show that larger atomic relaxation surrounding oxygen vacancy results in the stretching of Ti-O bond around vacancy, thus band gap states are formed near the conduction band minimum.
Spectral Control of Thermal Radiation by Metallic Surface Relief Gratings
Authors: Sai Hitoshi , Kanamori Yoshiaki , Watanabe Kengo , Yugami Hiroo
Published: August 2010

The microcavity effect of two-dimensional W surface-relief gratings has been investigated by means of the finite-difference time-domain simulation. The peak structure of the spectral emissivity of W gratings with a number of microcavities is in good agreement with the spectral features of a single microcavity. This result shows that the emissivity enhancement by W gratings with microcavities is mainly attributable to the microcavity effect that arises from each microcavity. It is that the spectral emissivity can be controlled by a combination of several microcavities with different parameters, and that not only a rectangular but a cylindrical microcavity also shows the microcavity effect according to its cavity modes.
Solvothermal Preparation, Processing, and Characterization of Nanocrystalline CuIn1-xAlxSe2 Materials
Authors: Exstrom Christopher L. , Olejníček Jiří , Darveau Scott A. , Mirasano Anatole , Paprocki David S. , Schliefert Megan L , Ingersoll Matt A. , Slaymaker Laura E. , Soukup Rodney J. , Ianno Natale J. , Kamler Chad A.
Published: August 2010

We report solvothermal preparations of nanocrystalline CuIn1-xAlxSe2 materials prepared from the reaction of Se, CuX2 (X = Cl− or stearate), InCl3, and Al(oleate)3 in refluxing oleylamine for 30 minutes to 3 hours. Scanning electron microscopy (SEM) images reveal morphologies consisting of hexagonal plates (100-400 nm diameter) with smaller isomorphic nodules. Micro-Raman spectroscopy, x-ray diffraction, and optical bandgap data are consistent with Al3+ incorporation into the chalcopyrite structure. For aluminum-containing reactions, product Al/(In+Al) ratios are estimated to be between 0.15 and 0.35 regardless of the indium-aluminum stoichiometry employed in the reaction. When Se is added to the reaction last, the reaction pathway involves an early-formed Cu2-xSe(s) intermediate that appears to react with In- and Al-containing species simultaneously. This intermediate is avoided when heating InCl3, Al(oleate)3, and Se together prior to Cu addition, but the final product includes Se contamination that must be removed or reacted by annealing.
New Structural Investigations in the Cu2Se(S)-In2Se3(S)/Cu2Se(S)-Ga2Se3(S) Phase Diagrams
Authors: Stephan Christiane , Schorr Susan , Schock H.W.
Published: August 2010

Non-stoichiometry is a characteristic feature of ternary chalcopyrites like Cu-III-VI2 (III=In,Ga; VI=S,Se). The results of a comparative study of structural trends within the homogeneity region of the chalcopyrite type α-phase of the Cu2Se(S)-In2Se3(S) and Cu2Se(S)-Ga2Se3(S) quasibinary phase diagrams are presented. Powder samples of Cu-rich and Cu-poor [Cu2Se(S)]1-y-[In2Se3(S)]y as well as [Cu2Se(S)]1-y-[Ga2Se3(S)]y alloys were prepared (0.4<y<0.6) by solid state reaction of the elements (T=850°C) and investigated by X-ray powder diffraction and electron microprobe analysis. It was shown that the grain size depends on composition and structural parameters. The tetragonal distortion η=c/2a has been determined for the different trivalent cations and influences the microstructure in Cu-poor Cu1-xIII1+x/3VI2 samples. In Cu-rich samples the Cu-content is in all cases the driving force for the formation of the homogeneous microstructure observed.
Growth by Molecular Beam Epitaxy of GaNAs Alloys with High As Content for Potential Photoanode Applications in Hydrogen Production
Authors: Novikov Sergey V , Staddon Chris R , Akimov Andrey V , Campion Richard , Zainal Norzaini , Kent Anthony J , Foxon Tom , Chen Chien H , Yu Kin M , Walukiewicz Wladek
Published: August 2010

We have studied the low-temperature growth of GaNAs layers on sapphire substrates by plasma-assisted molecular beam epitaxy. We have succeeded in achieving GaN1-xAsx alloys over a large composition range by growing the films at temperature much below the normal GaN growth temperatures with increasing the As2 flux as well as Ga:N flux ratio. We found that the alloys with high As content x>0.1 are amorphous. Optical absorption measurements reveal a continuous gradual decrease of band gap from ˜3.4 eV to ˜1.4 eV with increasing As content. The energy gap reaches its minimum of ˜1.4 eV at the x˜0.6-0.7. For amorphous GaAsN alloys with x<0.3 the composition dependence of the band gap follows the prediction of the band anticrossing model developed for dilute alloys. This suggests that the amorphous GaN1-xAsx alloys have short-range ordering that resembles random crystalline GaN1-xAsx alloys. Such amorphous GaN1-xAsx alloys with tunable electronic structure may be useful as photoanodes in photo-electrochemical cells for hydrogen production.
1.2 kV AlGaN/GaN Schottky Barrier Diode Employing As+ Ion Implantation on SiO2 Passivation Layer
Authors: Lim Jiyong , Choi Young-Hwan , Kim Youngshil Kim , Kim Min-Ki , Han Min-Koo
Published: August 2010

Considerable amount of works have been reported to achieve a high breakdown voltage of AlGaN/GaN heterostructure devices by employing additional process such as SiO2 passivation1,2, floating metal rings and Ni/Au Oxidation3. However, it should be point out that treatment of passivation layer of AlGaN/GaN heterostructure devices has been reported scarcely. As+ ion implantation on SiO2 passivation layer may be a simple and effective to reduce electric field strength to increase breakdown voltages.
The cross-sectional view of the proposed AlGaN/GaN Schottky barrier diode is shown in Fig. 1. We fabricated conventional AlGaN/GaN Schottky barrier diode and passivated the device with SiO2 layer of 350 nm thick. Finally As+ ions were implanted on the SiO2 passivation layer. We measured the surface potential of the test samples with electric force microscopy (EFM) in order to verify that implanted As+ ions remained as positively charged ions in SiO2 layer after ion implantation. After ion implantation, 2 dimensional electron gas (2DEG) concentration was increased slightly from 8.28E12 /cm2 to 8.38E12 /cm2 so that the forward current was also increased slightly. Table shows the breakdown voltages of the SBDs before and after As+ ion implantation. After As+ 80 keV 1 × 1E14 atoms/cm2 implantation, the breakdown voltage increased considerably from 604 V to 1204 V due to the edge termination by implanted As+ ions. The reverse leakage current decreased from 80.3 uA/mm to 21.2 nA/mm due to the relaxation of electric field concentration by As+ ion implantation. We verified the electric field relaxation through 2D simulation. After As+ ion implantation, the depletion region curvature under the reverse biased condition became moderate so that the maximum electric field strength was decreased.
As+ ion implantation method may be a simple and effective edge termination method for improving the breakdown voltage as well as the leakage current of the proposed AlGaN/GaN SBDs. Proposed AlGaN/GaN SBDs showed high breakdown voltage of 1204 V and low leakage current of 21.2 nA/mm without any considerable decrease of forward characteristics while that of conventional device was 604 V and 80.3 uA/mm, respectively.
Effects of Synthesis Conditions on the Crystalline Phases and Photocatalytic Activities of Silver Vanadates via Hydrothermal Method
Authors: Huang Chao-Ming , Pan Guan T. , Chen Lung C. , Yang C.K. Thomas , Chang Wen S.
Published: August 2010

Visible-light-driven Ag3VO4 photocatalysts were successfully synthesized using low-temperature hydrothermal synthesis method. Under various hydrothermal conditions, the structures of silver vanadates were tuned by manipulating the hydrothermal time and the ratio of silver to vanadium. X-ray diffraction (XRD) results reveal that the powders prepared in a stoichiometric ratio consisted of pure α-Ag3VO4 or mixed phases of Ag4V2O7 and α-Ag3VO4. With increasing the Ag-to-V mole ratio to 6:1, the resulting samples were identified as pure monoclinic structure α-Ag3VO4. UV-vis spectroscopy indicated that silver vanadate particles had strong visible light absorption with associated band gaps in the range of 2.2-2.5 eV. The sample synthesized in the excess silver exhibited higher photocatalytic activity than that synthesized in a stoichiometric ratio. The powder synthesized at silver-rich at 140℃ for 4 h (SHT4) exhibited the highest photocatalytic activity among all samples. The reactivity of SHT4 (surface area, 3.52 m2 g-1) on the decomposition of gaseous benzene was about 16 times higher than that of P25 (surface area, 49.04 m2 g-1) under visible light irradiation. A well developed crystallinity of Ag3VO4 of SHT 4 was considered to enhance the photocatalytic efficiency.
Photocatalysis of nano-perovskites
Authors: Chen Yen-Hua , Chen Yu-De
Published: August 2010

In this study, we can successfully synthesize nano-perovskites, including nano-CaTiO3, nano-SrTiO3, and nano-BaTiO3, by a co-precipitation method. The band gap of the nano-perovskites are 3.65 eV, 3.44 eV, and 3.35 eV, for nano-CaTiO3, nano-SrTiO3, and nano- BaTiO3, respectively. The ability of photocatalysis for nano-BaTiO3 is a little bit better than other nano-perovskites. It is also observed the photocatalytic activity increases with the increasing amount of photocatalysts. Moreover, the ability of photocatalysis using a higher energy UV-light is not promoted with the low energy UV-light.
Low-Energy Ion Beam Synthesis as a New Route toward Plasmonic Nanostructures
Authors: Carles Robert , Farcau Cosmin , Campos Julien , Bonafos Caroline , BenAssayag Gérard , Zwick Antoine
Published: August 2010

Single δ-layers of dispersed silver (Ag) nanoparticles are obtained by low-energy ion beam implantation in a silica thin film. TEM microscopy reveals that the obtained Ag particles are spherical, crystalline, and the particles layer is located at only few nanometers below the free silica surface. We use reflectivity measurements to probe the optical/plasmonic response of the fabricated structures and exploit plasmon resonance and optical interference effects in the silica film to record the Raman scattering by quadrupolar vibrations of the spherical particles.
Strong Exciton Polariton Dispersion in Multimode GaN Microcavity
Authors: Liu Mei-Chun , Cheng Yuh-Jen , Hsu Shih-Hsin , Kuo Hao-Chung , Lu Tien-Chang , Wang Shing-Chung
Published: August 2010

We report the experimental observation of a very strong cavity polariton dispersion in a multi-axial mode GaN microcavity. The linewidth of photoluminescent (PL) spectrum covers a few cavity axial modes. The resonant photoluminescent peaks have a strong dispersion. The frequency spacing between adjacent peaks decreases by almost a factor of five from 470nm to 370nm. The strong dispersion can be well described by cavity polariton dispersion, but not by the dispersion of the refractive index of GaN. The measured exciton-photon interaction constant is 260 meV. It is an order of magnitude higher than the typically reported values for GaN microcavities
Large area light propagation in quasi-zero average refractive index materials
Authors: Dardano Principia , Mocella Vito , Cabrini Stefano , Chang Allan S. , Moretti Luigi , Rendina Ivo , Olynick Deindre , Harteneck Bruce , Dhuey Scott
Published: August 2010

In this paper the experimental results show near-infrared light collimation through large area (2 x 2 mm) nanopatterned material with refractive index quasi-zero on the average. This quasi-zero refractive index is obtained alternating photonic crystals strips with effective refractive index neff = –1 and air strips (n = 1). Layers optically annihilate each other, verifying the optical antimatter concept theoretically proposed by Pendry et al [J. Phys.: Condens. Matter 15, 6345 (2003)].
Automated diffraction tomography combined with electron precession: a new tool forab initionanostructure analysis
Authors: Kolb Ute , Gorelik Tatiana , Mugnaioli Enrico
Published: August 2010

Three-dimensional electron diffraction data was collected with our recently developed module for automated diffraction tomography and used to solve inorganic as well as organic crystal structuresab initio. The diffraction data, which covers nearly the full relevant reciprocal space, was collected in the standard nano electron diffraction mode as well as in combination with the precession technique and was subsequently processed with a newly developed automated diffraction analysis and processing software package. Non-precessed data turned out to be sufficient forab initiostructure solution by direct methods for simple crystal structures only, while precessed data allowed structure solution and refinement in all of the studied cases.
Reflection High-energy Electron Diffraction Study of Nanostructures: From Diffraction Patterns to Surface Pole Figure
Authors: Tang Fu , Lu Toh-Ming , Wang Gwo Ching
Published: August 2010

In this report we present a brief overview of the growth of nanostructures by the oblique angle deposition where the nanostructures possess both out-of-plane and in-plane preferred orientations or a biaxial texture. The degree of preferred crystal orientations can be quantitatively determined from a method called “RHEED surface pole figure analysis” that we developed recently.
High Energy X-ray Diffraction Measurement of Load Transfer between Hydroxyapatite and Collagen in Bovine Dentin
Authors: Deymier Alix C. , Almer Jonathan D. , Stock Stuart R. , Haeffner Dean R. , Dunand David C.
Published: August 2010

Dentin is a load bearing multiphase composite composed of a ceramic phase, hydroxyapatite (HAP), a polymeric phase, collagen, and fluid filled porosity. In order to create better dentin replacements it is important to understand how applied load is naturally transferred between the phases during chewing and other stresses. To determine the apparent elastic modulus of HAP in dentin, applied stress over lattice strain in HAP, high energy wide angle x-ray diffraction measurements were performed on in situ loaded bovine dentin samples. It was determined that the average longitudinal apparent elastic modulus of HAP in dentin was 18.3±2.19GPa. This value is much lower than values predicted by the Voigt model when combined with volume fractions determined for the sample by thermo-gravimetric and chemical analysis. It has been determined that the decrease in apparent elastic modulus is most likely due to a decrease in the “bulk” elastic modulus of HAP due to nanometric effects.
Design and Realization of Biomedical Devices Based on Shape Memory Polymers
Authors: Maitland Duncan J , Small IV Ward , Singhal Pooja , Hwang Wonjun , Rodriguez Jennifer N , Clubb Fred , Wilson Thomas S
Published: August 2010

Our experience with shape memory polymers (SMP) began with a project to develop an embolic coil release actuator in 1996. This was the first known SMP device to enter human trials. Recent progress with the SMP devices include multiple device applications (stroke treatments, stents, other interventional devices), functional animal studies, synthesis and characterization of new SMP materials, in vivo and in vitro biocompatibility studies and device-tissue interactions for the laser, resistive, or magnetic-field activated actuators. We describe several of our applied SMP devices.
Multilayer Polymer Films for Photonic Applications
Authors: Zhou Juefei , Singer Kenneth , Song Hyunmin , Wu Yeheng , Lott Joseph , Andrews James , Hiltner Anne , Baer Eric , Weder Christoph
Published: August 2010

Polymers are receiving considerable attention as components in novel optical systems because of the tailored functionality, easy manufacturing, and relatively low cost. The processing of layered polymeric systems by coextrusion is a method to produce films comprising hundreds to thousands of alternating layers with thickness spanning the nanoscale to microscale in a single, one-step roll-to-roll process. Several layered polymer optical systems have been fabricated by coextrusion, including tunable refractive index elastomers, photonic crystals, and mechanically tunable photonic crystals. Layered polymeric optical systems made by coextrusion can also incorporate active components such as laser dyes for all-polymer laser systems.
Structural and Magneto-Electric Properties of Pulsed Laser Deposited Ferroelectric/Ferromagnetic Heterostructure
Authors: Martinez Ricardo , Kumar Ashok , Palai Ratnakar , Katiyar Ram S.
Published: August 2010

Asymmetric superlattices (SLs) with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) as constitutive layers were fabricated on conducting LaNiO3 (LNO) coated (001) oriented MgO substrates using pulsed laser deposition (PLD). The crystallinity, ferroelectric and magnetic properties of the SLs were studied over a wide range of temperatures and frequencies. The structure exhibited ferromagnetic behavior at 300K, and ferroelectric behavior over a range of temperatures between 100K and 300K. The dielectric response as a function of frequency obeys normal behavior below 300 K, whereas it follows Maxwell–Wagner model at elevated temperatures. The effect of ferromagnetic LSMO layers on ferroelectric properties of the SL indicated strong influence of the interfaces. The asymmetric behavior of ferroelectric loop and the capacitance-voltage relationship suggest development of a built field in the SLs due to high strain across the interfaces.
Structural, Magnetic, and Electrical Properties of BiFe1-xMnxO3 Thin Films
Authors: Barrionuevo Danilo G , Singh Surinder P , Tomar Maharaj S.
Published: August 2010

We synthesized BiFe1-xMnxO3 (BFMO) for various compositions by sol gel process and thin films were deposited by spin coating on platinum Pt/Ti/SiO2/Si substrates. X-ray diffraction shows all the diffraction planes corresponding to rhombohedrally distorted perovskite BiFeO3 structure. The absence of any impurity phase in the films suggests the incorporation Mn ion preferentially to Fe site in the structure for low concentration. Magnetic measurements reveal the formation of ferromagnetic phase at room temperature with increased Mn substitution. On the other hand, ferroelectric polarization decreases with increasing Mn ion concentration. Raman studies suggest the dopant induced structural distortion.
A New Method to Increase the Magnetoelectric Voltage Coefficients of Metglas/PVDF Laminate Composites
Authors: Fang Zhao , Lu David Sheng-Guo , Mokhariwale Ninad , El Tahchi Mario Remond , Zhang Qiming
Published: August 2010

The magnetic flux density inside a Metglas sheet is much higher than that of the applied external magnetic field due to its high magnetic permeability, which is known as the magnetic flux concentration effect. Magnetic flux concentration of Metglas as a function of its sheet aspect ratio (width/length) was investigated for Metglas/Polyvinylidene fluoride (PVDF) laminar composites. Both the simulations and experimental results suggest that the magnetic flux concentration effect is markedly enhanced when the aspect ratio of a Metglas sheet is reduced. Consequently the magnetostriction of Metglas and the magnetoelectric (ME) voltage coefficients of the laminar composites are enhanced. The ME voltage coefficient for a laminar composite with a 1 mm wide and 30 mm long Metglas sheet (25 μm thick) is 21.46 V/cm•Oe, which is much higher than those reported earlier in similar laminar composites without making use of the flux concentration effect. The results demonstrate an effective means to significantly enhance the sensitivity of the magnetostrictive/piezoelectric composites as weak magnetic field sensors.
High Temperature Phase Transitions in BiFeO3
Authors: Arnold Donna , Kavanagh Christopher M , Lightfoot Philip , Morrison Finlay Doogan
Published: August 2010

The high temperature phases of BiFeO3 have courted much controversy with many conflicting structural models reported, in particular for the paraelectric β-phase. High temperature powder neutron diffraction (PND) experiments indicate that the ferroelectric (R3c) α-phase transforms to the paraelectric β-phase at approximately 820 °C via a first order phase transition. We demonstrate that this phase is unambiguously orthorhombic, adopting the GdFeO3 structure-type with a space group Pbnm. On further heating BiFeO3 undergoes another first order phase transition (β-γ) at approximately 930 °C which is marked by a discontinuous decrease in cell volume consistent with an insulator-metal transition. Close inspection of the PND data show no evidence of any symmetry change, with the postulated γ-phase remaining orthorhombic Pbnm. In addition we present PND and impedance spectroscopy data for BiFeO3 which suggest that the so-called ‘Połomska’ transition observed by some authors at approximately 185 °C is not intrinsic.
Recent Development of the Magnetic Shape Memory Materials Research in Finland
Authors: Söderberg Outi , Aaltio Ilkka , Ge Yanling , Soroka Alexandr , Niemi Raisa , Liu Xuwen , Hannula Simo-Pekka
Published: August 2010

Ni-Mn-Ga based magnetic shape memory (MSM) materials have been studied since 1998 in Finland at the Helsinki University of Technology (TKK, previously HUT). The large HUT-MSM-project resulted in MSM-alloys with high service temperature, 10 % field-induced-strain, as well as circumstances when and how a Ni-Mn-Ga alloy exhibits this phenomenon. The understanding of the structure and behavior of twin boundaries, and their role, for example, in the vibration damping and long-term actuation has been enhanced in the recent projects. Twin boundaries have been studied by XRD, by high-resolution transmission electron microscopy (HRTEM), and by in-situ straining in TEM, the last one in co-operation with the Institute of Physics in Prague (ASCR-IP), Czech Republic. The results obtained by neutron diffraction in co-operation with Hahn-Meitner-Institut Berlin, Institute for Metal Physics (IMP), Kiev, and Institut Laue-Langevin (ILL), Grenoble, have given new crystallographic information. Damping of Ni-Mn-Ga polymer composites has been proved to be excellent at high stiffness levels with the loss factor = 0.6 at E ≈ 1 GPa. This research was carried out in co-operation with the University of California Los Angeles (UCLA), USA. In the long-term actuation, a fatigue life of 2×109 has been recorded for a five-layered modulated Ni-Mn-Ga structure in mechanical cycling. The evolution of the MSM parameters during the long-term use is recorded and used as an input data for the models developed in the European MAFESMA co-operation. The search for alloys with wide stable thermal property range showing MSM effect has continued and alloys that are stable down to 4 K have been established. Modeling based on Ginsburg-Landau theory has been applied to evaluate aging and thermal fluctuations in the modulated Ni-Mn-Ga structures. As a commercial target, AdaptaMat Ltd. develops technology to produce Ni-Mn-Ga magnetic shape memory material with improved quality, lower twinning stress, longer fatigue life as well as lower cost and better availability for use in research and development.
First-principles study of static displacements in Fe-Pd magnetic shape-memory alloys
Authors: Gruner Markus E.
Published: August 2010

This contribution reports static ionic displacements in ferromagnetic disordered Fe70Pd30 alloys obtained by relaxation of the ionic positions of a 108-atom supercell within the framework of density functional theory. Comparison with a simple statistical model based on Lennard-Jones pair interactions reveals that these displacements are significantly larger than can be explained by the different sizes of the elemental constituents. The discrepancies are presumably related to collective displacements of the Fe atoms. Corresponding distortions are experimentally observed for ordered Fe3Pt and predicted by first-principles calculations for all ordered Fe-rich L12 alloys with Ni group elements and originate from details of the electronic structure at the Fermi level.
Lateral uniformity of the transport properties of graphene/4H-SiC (0001) interface by nanoscale current measurements
Authors: Giannazzo Filippo , Sonde Sushant , Huntzinger Jean-Roch , Tiberj Antoine , Yakimova Rositza , Raineri Vito , Camassel Jean
Published: August 2010

Conductive Atomic Force Microscopy was applied to study the lateral uniformity of current transport at the interface between graphene and 4H-SiC, both in the case of epitaxial graphene (EG) grown on the Si face of 4H-SiC and in the case of graphene exfoliated from HOPG and deposited (DG) on the same substrate. This comparison is aimed to investigate the role played by the C-rich buffer layer present at EG/4H-SiC interface and absent in the case of DG/4H-SiC. The distribution of the local Schottky barrier heights at EG/4H-SiC interface (ΦEG) was compared with the distribution measured at DG/4H-SiC interface (ΦDG), showing that ΦEG (0.36±0.1eV ) is ˜0.49eV lower than ΦDG (0.85 ± 0.06eV). This difference is explained in terms of the Fermi level pinning ˜0.49eV above the Dirac point in EG, due to the presence of positively charged states at the interface between the Si face of 4H-SiC and the buffer layer.
Layer-by-Layer Assembly of Nanotube-Polymer Thin Films with High Electrical Conductivity and Transparency
Authors: Park Yong Tae , Ham Aaron Y. , Grunlan Jaime C.
Published: August 2010

Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Three different types of carbon nanotubes (CNTs) were used: (1) multi-walled carbon nanotubes (MWNTs), (2) a mixture of single, di- and tri-walled nanotubes (XM grade) and (3) purified HiPCO single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (> 85 %T across visible spectrum) and electrically conductive (˜ 150 S/cm) 20-bilayer films with 42 nm thickness. Moreover, optoelectronic performance of SWNT-based thin films was improved with heat treatment due to the removal of PDDA. A 20-bilayer SWNT LbL film achieved a conductivity of 369 S/cm with a 5 min exposure to 400 °C. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films, which may be useful for a variety of large area electronics applications.
Effect of O2 on thickness uniformity of CdTe thin film deposited using CSS
Authors: Vora Nirav D , Dhere Ramesh
Published: August 2010

Incorporating O2 in the closed space sublimation (CSS) of CdTe thin film has resulted in improved cell efficiencies. Many studies have been undertaken to understand this effect on cell efficiency. In this work we study the effect of oxygen on lateral uniformity of the deposited CdTe film. A finite element model has been developed to represent the mass and heat transfers involved in the CSS process. The model takes into consideration the effect of O2 by modeling its reaction with Cd vapors in the space between the source and the substrates and with the CdTe source. So a gradient of O2 from the edges to the center of the substrate can result in non-uniform oxidation of the source and subsequently a laterally non-uniform film. A steady state model solved at various temperatures, pressures, and separation distances. O2 concentration gradient was found to depend on the oxidation rate of Cd vapors and thus on temperature, total pressure, and oxygen partial pressure in the system.
High rate deposition of cluster-suppressed amorphous silicon films deposited using a multi-hollow discharge plasma CVD
Authors: Koga Kazunori , Sato Hiroshi , Kawashima Yuuki , Nakamura William Makoto , Shiratani Masaharu
Published: August 2010

We have examined effects of gas velocity and gas pressure on a deposition rate of hydrogenated amorphous silicon (a-Si:H) films and on a volume fraction of clusters in the films using a multi-hollow discharge plasma CVD method. The maximum deposition rate realized for each pressure exponentially increases with decreasing the pressure from 1.0 Torr to 0.1 Torr, whereas the volume fraction of clusters very slightly increases with increasing the deposition rate. Based on the results, we have succeeded in depositing highly stable a-Si:H films of 4.9×1015cm-3 in a stabilized defect density at a rate of 3.0nm/s using the method.
Reduction of Porous Silica Pellets by Electrodeoxidation in Molten Salts
Authors: Ergul Emre , Karakaya Ishak , Erdogan Metehan
Published: August 2010

Direct electrochemical reduction of porous SiO2 pellets in molten CaCl2 salt and CaCl2-NaCl salt mixture were investigated by applying 2.8 V potential. The study focused on the effects of temperature, powder size and cathode contacting materials. Starting materials and electrolysis products were characterized by X-ray diffraction analysis and scanning electron microscopy. Due to reactive nature of silicon, different cathode contacting materials were used to test the extent of reactions between silicon produced at the cathode and the contacting materials. X-ray diffraction patterns showed that silicon produced at the cathode reacted with nickel, and iron in stainless steel to form Ni-Si and Fe-Si compounds respectively. Besides, studies revealed that higher temperature and smaller particle size had positive effects in increasing reduction rate. The results were interpreted from variation of current versus time graphs under different conditions, microstructures and compositions of the reduced pellets.
Electrical Properties of Silicon with Bistable Impurity Complexes
Authors: Karazhanov Smagul Zh. , Nærland Tine U , Mayandi Jeyanthinath , Søndenå Rune , Holt Arve
Published: August 2010

Many impurity complexes in silicon such as boron-oxygen and iron-boron complexes are found to be bistable. Commonly bistable recombinative complexes in silicon are studied through carrier lifetime experiments and are analysed by use of Shockley-Read-Hall (SRH) recombination theory. SRH recombination theory is valid for stable defects with one configuration and one energy level in the band gap, however, the theory might fail upon considering the recombination centers through bistable defects, which can be in two different configurations separated by a potential barrier. This work presents a study of electrical properties of silicon with bistable impurity complexes. The analysis has been performed for statistics of free electrons and holes, their recombination rate and lifetime. The results have been compared with those obtained from the Shockley-Read-Hall recombination theory.
Novel Nanostructured Photoelectrodes - Electrodeposition of Metal Oxides onto Transparent Conducting Oxide Nanofibers
Authors: Ostermann Rainer , Rudolph Melanie , Schlettwein Derck , Smarsly Bernd M
Published: August 2010

Nanostructured metal oxides with high surface areas have been shown to be efficient photoelectrodes for light-to-energy conversion in dye-sensitized solar cells (DSCs). In this work we demonstrate the use of nanofibrous mats of transparent conducting oxides (TCOs) as nanostructured electrodes, especially for DSCs. The nanofibers have been obtained by electrospinning suitable inorganic precursors and polymers, followed by calcination to remove the polymer. Afterwards, TiO2 layers were generated on our 3D-electrodes by electrodeposition. An improved performance as DSC was found compared to flat electrodes of similar thickness, validating our approach.
Electrodeposition of Mesoporous Silica on 3-D Scaffolds as Templates for 3-D Porous Metal Electrodes
Authors: Cordes Nikolas , Bakker Martin
Published: August 2010

Supercapacitors and advanced batteries capable of rapid charge and discharge need conductive three dimensional porous electrodes. The high conductivities of porous metal electrodes are attractive. However, the surface areas of such electrodes are still well short of those achievable in carbon. One approach to formation of high surface area porous metal electrodes is to electrodeposit metal into nanostructured templates on 3-D scaffolds such as nickel foam. By careful control of composition and voltage thin films of mesoporous silica can be deposited onto these 3-D templates. Removal of the templating surfactant produces a very high surface area mesoporous coating. Metal can then be plated into the mesoporous silica, which, after removal of the silica, leaves a high surface area 3-D porous electrode.
Multiscale Modeling of Helium-Vacancy Cluster Nucleation under Irradiation: A Kinetic Monte-Carlo Approach
Authors: Suzudo Tomoaki , Yamaguchi Masatake , Kaburaki Hideo , Ebihara Ken-ichi
Published: August 2010

We applied ab initio calculation and an object kinetic Monte Carlo modeling to the study of He-vacancy cluster nucleation under irradiation in bcc and fcc Fe, which are surrogate materials for ferritic/martensitic and austenitic steels, respectively. The ab initio calculations provided parameters for the object kinetic Monte Carlo model, such as the migration energies of point defects and the dissociation energies of He and vacancy to He-vacancy clusters. We specially focused on the simulation of high He/dpa irradiation such as He-implantation into the materials and tracked the nucleation of clusters and the fate of point defects such as SIAs, vacancies, and He atoms. We found no major difference of He-vacancy cluster nucleation between bcc and fcc Fe when we ignore the intracascade clustering even if the migration energies of point defects are significantly different between the two crystals.
Production of Layered Double Hydroxides for Anion Capture and Storage
Authors: Phillips Jonathan , Vandeperre Luc
Published: August 2010

Technetium has a long half life of up to 2.13×105 years. It is separated from liquid waste streams with tetraphenylphosphonium bromide [1], which upon degradation releases Tc as the pertechnetate anion, TcO4−. Pertechnetate is highly mobile in groundwater and it is therefore highly desirable to capture and immobilise this anion within a solid for interim and ultimately long term storage. Layered Double Hydroxide (LDH) materials are known to possess excellent anion sorption capabilities due to their structure which consists of ordered positively charged sheets intercalated with interchangeable hydrated anions. The composition can be tailored to produce suitable precursors for ceramic phases by varying the divalent and trivalent cations and the anions. LDHs with the general formula Ca1-x (Fe1-y, Aly)x (OH)2 (NO3)x . nH2O were produced by a co-precipitation method from a solution of mixed nitrates. Calcination leads to the formation of Brownmillerite Ca2(Al,Fe)2O5 like compounds for temperatures as low as 400°C, this is close to the lowest temperature at which Tc is known to volatilise (310.6 °C Tc2O7). It was shown that after calcining up to 600°C, the LDH structure is recovered in water allowing rapid ion capture to occur. This suggests that these materials have potential for both capture and as a storage medium for Tc.