bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence of bayerite clusters within the AAO amorphous bulk alumina. Consequence for AAO SANS matching properties.
Authors: Lagrené Karine , Zanotti Jean-Marc
Published: April 2011

Small Angle Neutron Scattering (SANS) and neutron diffraction are used to probe the structure of Anodized Aluminium Oxide (AAO) in an extended Q range, from 7.10−3 to 16 Å−1. In the small angle region [7. 10−3 Å−1 − 7. 10−2 Å−1], impregnation of a D2O/H2O mixture within the AAO porous structure, leads to a dramatic decrease of the coherent SANS signal by two orders of magnitude, but perfect matching of the membrane cannot be reached. We explain such an imperfect matching by the presence of 1 nm in size Bayerite domains within the bulk of the amorphous Al2O3 matrix, as detected by Neutron diffraction in the [0.3 Å−1 − 4 Å−1] Q range. Traces of sulfur, probably incorporated during the anodic synthesis process in a H2SO4 solution, are also detected by Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX). We estimate the AAO neutron scattering length to be 4.22 1010 cm−2. This value is an important input, when taking advantage of neutron contrast matching to probe the large scale filling homogeneity (adsorption of a liquid or deposition of a solid) within the porous structure of AAO membranes.
Tunable Thin Film Integrated Material Characterizations for Microwave Applications
Authors: Al Ahmad Mahmoud , Payan Sandrine , Michau Dominique , Maglione Mario , Plana Robert
Published: April 2011

In this work, a simple, fast and repeatable technique is proposed for tunable integrated thin film material characterizations. The technique does not depend on the type of material development method or special thin film processing. Moreover, additional structures or calibrations are not required. The proposed method can be used to determine the loss of a thin film material using radio frequency capacitance measurements in both parallel plate and interdigital topologies. An analytical formulation is given for the computation of the film loss based on its measured input impedance which is extracted from the measured scattering parameters. This technique is used for barium strontium titanate (BST) thin film material characterizations.
Stacked Boron Doped Poly-Crystalline Silicon-Germanium Layers: an Excellent MEMS Structural Material
Authors: Claes Gert , Van Barel Gregory , Van Hoof Rita , Du Bois Bert , Gromova Maria , Verbist Agnes , Van der Donck Tom , Decoutere Stefaan , Celis Jean-Pierre , Witvrouw Ann
Published: April 2011

In this work stacked boron doped poly-crystalline Silicon-Germanium (poly-SiGe) layers, which can be applied as structural MEMS layers, were studied. A standard 1 µm base layer, deposited at 480 ºC chuck temperature, is stacked until the required thickness (e.g. 10 x for a 10 µm thick layer). This 1 µm base layer consists of a PECVD seed layer (+/− 75 nm), a CVD crystallization layer (+/− 135 nm) and a PECVD layer to achieve the required thickness with a high growth-rate. The top part of this PECVD layer can optionally be used for optimizing the stress gradient by a stress compensation layer. This approach resulted in 4 µm thick poly-SiGe MEMS structural layers with low tensile stress (50 MPa), low resistivity (2 mΩcm) and a low strain gradient (< 1*10−5/µm).
Dispersive Evaluation and Self-Sensing of Single Carbon Fiber/CNT-Epoxy Composites using Electro-Micromechanical Techniques
Authors: Park Joung-Man , Jang Jung-Hoon , Wang Zuojia , Kim Pyung-Gee , Lee Woo-Il , Park Jong-Kyoo , DeVries Lawrence K.
Published: April 2011

Self-sensing and interfacial evaluation were investigated with different dispersion solvents for single carbon fiber/carbon nanotube (CNT)-epoxy composites by electro-micromechanical technique and acoustic emission (AE) under loading/subsequent unloading. Optimized dispersion procedure was set up to obtain improved mechanical and electrical properties. Apparent modulus and electrical contact resistivity for CNT-epoxy composites were correlated with different dispersion solvents for CNT. CNT-epoxy composites using good dispersion solvent showed higher apparent modulus because of better stress transferring effect due to relatively uniform dispersion of CNT in epoxy and enhanced interfacial adhesion between CNT and epoxy matrix. However, good solvent showed high apparent modulus but low thermodynamic work of adhesion, Wa for single carbon microfiber/CNT-epoxy composite. It is because hydrophobic high advanced contact angle was shown in good solvent, which can not be compatible with carbon microfiber well. Damage sensing was also detected simultaneously by AE combined with electrical resistance measurement. Electrical resistivity increased stepwise with progressing fiber fracture due to the maintaining numerous electrical contact by CNT.
Dielectric Charging in Low Temperature Silicon Nitride for RF-MEMS Capacitive Switches
Authors: Daigler Richard , Papaioannou George , Papandreou Eleni , Papapolymerou John
Published: April 2011

The paper presents a systematic investigation of dielectric charging in low temperature silicon nitride for RF-MEMS capacitive switches. The investigation takes includes both the effect of dielectric film thickness as well as the effect of metal contacts. The investigation demonstrates that the charging process is asymmetric. It is shown that the amount of stored charge depends significantly on the dielectric film thickness, which is caused from the contribution of the space charge polarization mechanism. Finally, the results are compared with those of higher temperature silicon nitride.
Thick Film Capacitors with Variable Tc on Cu Foils
Authors: Kim Byeong Kon , Shin Dong Joo , Song Jun Kwang , Cho Yong Soo
Published: April 2011

High k dielectric thick films, consisting of BaTiO3, a low softening glass and fluoride compounds, were studied to apply them as potential low temperature N2-fireable capacitors on commercially-available Cu foils. Different additive combinations of LiF, ZnF2 and BaF2 were specifically compared in terms of dielectric constant, dielectric loss and Curie temperature (Tc) for the purpose of optimizing dielectric performance. The thick film consisting of 95BaTiO3-1.5LiF-1.5ZnF2-2 bismuth borosilicate glass exhibited the best performance, i.e., a dielectric constant of 2,382 and a dissipation factor of 0.021 at Tc of 27°C at the firing temperature of 950°C. This result can be regarded as one of the best performance, compared to literature reported on embedded capacitors in Cu-PCB applications. No apparent Cu-diffusion was detected across the Cu-thick film-Cu foil structure.
Linear FMCW Laser Radar for Precision Range and Vector Velocity Measurements
Authors: Pierrottet Diego , Amzajerdian Farzin , Petway Larry , Barnes Bruce , Lockard George , Rubio Manuel
Published: April 2011

An all fiber linear frequency modulated continuous wave (FMCW) coherent laser radar system is under development with a goal to aide NASA's new Space Exploration initiative for manned and robotic missions to the Moon and Mars. Linear FMCW lidar has the capability of high resolution range measurements, and when configured into a multi-channel receiver system it has the capability of obtaining high precision vector velocity measurements. Precision range and vector velocity data are beneficial to navigating planetary landing pods to the pre-selected site and achieving autonomous, safe soft-landing. This paper discusses the design of a second generation prototype system under development at NASA Langley Research Center and presents preliminary performance data obtained from field experiments.
All-Optical Active Plasmonics Based on Ordered Au Nanodisk Array Embedded in Photoresponsive Liquid Crystals
Authors: Zheng Yue Bing , Hsiao Vincent K. S. , Huang Tony Jun
Published: April 2011

We propose a new approach towards all-optical active plasmonics based on ordered Au nanodisk arrays embedded in azobenzene-doped liquid crystals (LCs). Upon photoirradiation, the doped LCs went through phase transition induced by trans-cis photoisomerization of the azobenzene molecules. The phase transition led to the change in the refractive index of the LCs experienced by incident light, and enabled reversible tuning of the localized surface plasmon resonance (LSPR) of the embedded Au nanodisks. The tuning utilized the sensitivity of the LSPR of the Au nanodisks to the change in the surroundings' refractive index. Experimental observations on both peak shift and intensity change of the LSPR matched those from discrete dipole approximation (DDA) calculations.
Optimization of Plasmonic Nano-Antennas
Authors: Sendur Ibrahim Kursat , Karabasoglu Orkun , Baran Eray Abdurrahman , Kiziltas Gullu
Published: April 2011

Interaction of light with plasmonic nano-antennas is investigated. First, an extensive parametric study is performed on the material and geometrical effects on dipole and bow-tie nano-antennas. The transmission efficiency is studied for various parameters including length, thickness, width, and composition of the antenna as well as the wavelength of incident light. The modeling and simulation of these structures is done using 3-D finite element method based full-wave solutions of Maxwell's equations. Next, a modeling-based automated design optimization framework is developed to optimize nano-antennas. The electromagnetic model is integrated with optimization solvers such as gradient-based optimization tools and genetic algorithms.
Silicon-compatible Ultra-long-range Surface Plasmon Modes
Authors: Sabbah Ali , Durfee C. G. , Collins R. T. , Furtak T. E. , Hollingsworth R. E. , Flammer P. D.
Published: April 2011

Surface plasmon waveguides show promise as sub-wavelength signal elements in integrated optoelectronic devices. Modulation of these signals requires designs that are compatible with existing semiconductor fabrication technologies, such as MOS structures. We show that waveguides of this type are not only practical, but offer distinct advantages. In particular, an asymmetric geometry is shown to support very long-range modes. In preliminary experimental results we report the observation of these modes in an visible wavelength analog structure. Our models predict that these characteristics can be maintained while shifting the operating conditions to the fiber communications band in waveguides constructed in silicon.
From Process Assumptions to Development to Manufacturing
Authors: Standaert Theo , Gabor Allen , Simon Andrew , Lisi Anthony , Peters Carsten , Child Craig , Kioussis Dimitri , Engbrecht Edward , Chen Fen , Baumann Frieder , Lembach Gerhard , Wendt Hermann , Choi Jihong , Linville Joseph , Chanda Kaushik , Kumar Kaushik , Davis Kenneth , Economikos Laertis , Nicholson Lee , Chae Moosung , Lustig Naftali , Bravo Oscar , McLaughlin Paul , Srivastava Ravi Prakash , Filippi Ronald , Sankaran Sujatha , Bolom Tibor , Menon Vinayan , McGahay Vincent , Li Wai-Kin , Tseng Wei-Tsu , Landers William , Choi Youngjin , Biery Glenn , Gow Thom
Published: April 2011

A tool has been developed that can be used to characterize or validate a BEOL interconnect technology. It connects various process assumptions directly to electrical parameters including resistance. The resistance of narrow copper lines is becoming a challenging parameter, not only in terms of controlling its value but also understanding the underlying mechanisms. The resistance was measured for 45nm-node interconnects and compared to the theory of electron scattering. This work will demonstrate how valuable it is to directly link the electrical models to the physical on-wafer dimensions and in turn to the process assumptions. For example, one can generate a tolerance pareto for physical and or electrical parameters that immediately identifies those process sectors that have the largest contribution to the overall tolerance. It also can be used to easily generate resistance versus capacitance plots which provide a good BEOL performance gauge. Several examples for 45nm BEOL will be given to demonstrate the value of these tools.
Effects of Plasma Surface Treatment on the Self-forming Barrier Process in Porous SiOCH
Authors: Koike Junichi , Koike Junichi , Tökei Zsolt
Published: April 2011

Self-forming barrier process was carried out on a porous low-k material with the Cu-Mn alloys. The effects of various surface treatments were investigated in the sample having a pore size of 0.9 nm and a porosity of 25%. Before and after annealing, samples were analyzed in cross section with transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). Concentration profile was also analyzed with time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicated the penetration of Cu into the low-k interior during deposition, followed by the segregation of Cu at the low-k/Si interface during subsequent annealing. Although a diffusion barrier layer was formed and no further Cu penetration was not observed during annealing, initial Cu penetration in the deposition process was detrimental and should be prevented by restoring the plasma damage on the low-k surface.
Growth and Integration of High-Density CNT for BEOL Interconnects
Authors: Negreira Ainhoa Romo , Cott Daire J. , Verhulst Anne S. , Esconjauregui Santiago , Chiodarelli Nicolo′ , Ek Weis Johan , Whelan Caroline M. , Groeseneken Guido , Heyns Marc , De Gendt Stefan , Vereecken Philippe M.
Published: April 2011

The integration of high-density CNT bundles as via interconnects in a CNT/Cu-hybrid BEOL stack is evaluated. CNT via-conduits may greatly improve heat dissipation and as such lower interconnect resistance and improve electromigration resistance. Each carbon shell of the nanotube contributes to electrical and thermal conduction and densities as high as 5×1013 shells per cm2 are estimated necessary. CNT growth processes on BEOL compatible metals are presented with tube densities up to 1012cm−2 and shell densities approaching 1013 cm−2 on blanket substrates. Selective growth of CNT bundles with carbon shell densities around 1012cm−2 is demonstrated with high yield. Ohmic behavior of TiN/CNT/Ti contacts is shown with a CNT via resistivity of 1.2 mΩ cm.
Electrical Characterisation of a Low-Density Layer of SnO Nanowires Deposited on a Set of Parallel Pt Electrodes
Authors: Kiselev Ilia , Kiselev Ilia , Sysoev Victor , Schneider Thomas
Published: April 2011

Low-density layers of SnO2 nanowires were produced using the vapor solid method and dry-pressed onto surface-oxidized Si-substrates equipped with a set of 39 parallel Pt-electrodes. Current-Voltage (I-V) characteristics of the segments between the electrodes were measured in ambient air at a substrate temperature of 300°C. Statistical analysis of the 38 I-V characteristics allows drawing conclusions, that only Schottky contacts between large nanowires and electrodes are significant for conductometry, and that they have very similar barrier characteristics. The statistical approach and its advantages are demonstrated. The clarity obtained concerning the roles of different resistivity mechanisms involved enables predictions of the nanowire net device behavior in applications, which is demonstrated on an instance of long-term stability examination of gas sensor arrays.
Nanowire Solar Cell Sensitized with II-VI Quantum Dot Layer
Authors: Nadarajah Athavan , Word Robert C. , VanSant Kaitlyn , Könenkamp Rolf
Published: April 2011

We report first results on a new solar cell consisting of a p-i-n hetero-junction formed between n-type transparent nanowires, undoped semiconductor quantum dots and a wide bandgap p-type polymer layer. The overall structure is SnO2/ZnO/CdSe/MEH-PPV with MEH-PPV standing for poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]. Microscopic studies on the structure of the quantum dot layer before and after anneal indicates a morphology change from a quantum dot assembly to a continuous polycrystalline thin film. The charge transfer between the absorber layer and the adjacent layers is improved as the layer is converted from the quantum dot assembly towards a polycrystalline thin film structure. In optimized devices the spectral photocurrent response shows contributions from the ZnO, the CdSe and the MEHPPV, covering the spectral range from 300 to 700nm with an external quantum efficiency between 30 and 40%. The overall energy conversion efficiency approaches 1%.
The Electronic Structures of Fullerene/Transition-Metal Hybrid Material
Authors: Matsumoto Yoshihiro , Sakai Seiji , Naramoto Hiroshi , Hirao Norie , Baba Yuji , Sugai Isamu , Takanashi Koki , Shimada Toshihiro , Maeda Yoshihito
Published: April 2011

Local electronic structures of C60-Co hybrid films have been studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. XPS spectra of C 1s main and satellite peaks for the C60-Co films show binding-energy shifts and also line-broadening compared to those in a pure C60 film. In addition, XPS spectra in valence band region suggest an appearance of three new components at near Fermi level and HOMO level in the C60-Co film. These results are attributed to hybridizations between Co 3d band and C60 LUMO. The same effects have been observed in NEAXFS spectra at C 1s excitations.
Bimetallic Nanoparticles as Catalysts in Ionic Liquids
Authors: Scott Robert William James , Dash Priyabrat
Published: April 2011

We will show that metallic and bimetallic nanoparticles solubilized in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquids (IL) can be used as catalysts for a variety of oxidation and hydrogenation reactions. Nanoparticles were either directly synthesized in the IL or transferred to the IL from other solvents. Characterization was carried out by UV-Vis spectroscopy and transmission electron microscopy. Both the activity and selectivity of the hydrogenation reactions could be tuned by varying the composition of AuPd bimetallic nanoparticles. We will also show that the nanoparticle/IL catalysts can be recycled and then reused for further catalytic reactions with minimal loss in activity. In addition, new insights into the stabilization of nanoparticles in ionic liquids will be presented.
Threading and Interlocking: A Mechanism for the Simultaneous Enhancement of Polymer Stiffness, Strength, and Ductility
Authors: Torun Lokman , Paraskos Alex J. , Tsui Nicholas T. , Swager Timothy M. , Thomas Edwin L.
Published: April 2011

We have synthesized polyester systems containing pendant iptycene units and compared their mechanical/structural properties to a homologous reference polymer wherein benzene replaces iptycene units. Iptycenes have unique structural properties called internal molecular free volume (IMFV). The incorporation of iptycene into polyester backbones results in a polymer chain contour resembling “molecular barbed wire.” The contribution of iptycene to the mechanical properties of polyesters is significant and robust across concentration and processing conditions. The triptycene polyester films displayed a nearly 3-fold increase in Young's modulus, an approximately 3-fold increase in strength, and a more than 20-fold increase in strain to failure. We proposed that the presence of triptycene introduces two mechanisms for the enhancement of tensile mechanical properties: molecular threading and molecular interlocking.
LEEM / PEEM Study of Anisotropic Diffusion Fields in the Ag/Si(001) System
Authors: Wall Dirk , Roos Kelly Ryan , Horn-von Hoegen Michael , Meyer zu Heringdorf Frank-Joachim
Published: April 2011

We used direct imaging of diffusion fields in photoemission electron microscopy to study the diffusion (an)isotropy of Ag on flat and vicinal Si(001) surfaces with miscut angles between 0.2° and 4° in the [110] direction. While the diffusion field, represented by its iso-coverage zone, is isotropic on flat Si(001), it becomes elongated on the vicinal surface. The aspect ratio of the iso-coverage zone is used as a measure of the effective diffusion anisotropy on the surface. The aspect ratio of the iso-coverage zone increases continuously with the miscut angle, up to the maximum miscut that was studied. For the 4° miscut surface we find that the shape of the diffusion field is independent of the kink density of the substrate. From the temperature dependence of the aspect ratio, we determine an effective energy of ΔEani ∼ 0.7 eV for the activation energy responsible for the anisotropy.
Versatile Core-Sheath Biofibers using Coaxial Electrospinning
Authors: Han Daewoo , Boyce Steven T. , Steckl Andrew J.
Published: April 2011

We have investigated coaxial electrospinning to produce core-sheath fibers for tissue engineering. We have successfully produced core-sheath structured fibers of poly(ε-caprolactone) (PCL) and gelatin using the coaxial electrospinning technique. The core-sheath scaffold exhibits better mechanical properties compared to gelatin scaffold. We have characterized the resulting core and core-sheath fiber diameters and the scaffold porosity, etc.
Biomorphic Mesoporous Ce1−xZrxO2 Nanostructures Fabricated from Paper Templates
Authors: Ng Dickon H. L. , Li Jia
Published: April 2011

A simple and versatile procedure was developed for synthesizing biomorphic mesoporous Ce1-xZrxO2. Aqueous cerium nitrate and zirconium nitrate solutions, and paper were used as the starting materials. Under the structure-directed effect offered by the active hydroxyl radicals of the cellulose in the paper templates, porous and fibrous structures of paper were replicated by the self-assembly of Ce1-xZrxO2 nanocrystallites after the paper underwent chemical infiltration and calcinations. The product, composing of interwoven network of fibers with diameter ranging from 10 to 20 m, was a replica of the original paper structure only that each fiber was assembled by Ce1-xZrxO2 nanocrystallites with grain size of 3-10 nm. The templating function of cellulose and the mechanism in the formation of nanocrystallites were proposed.
Site-selective immobilization of streptavidin on enzymatically biotinylated bacterial magnetic particles
Authors: Maeda Yoshiaki , Yoshino Tomoko , Takeyama Haruko , Takahashi Masaaki , Ginya Harumi , Asahina Junko , Tajima Hideji , Matsunaga Tadashi
Published: April 2011

Biotinylated magnetic nanoparticles were constructed by displaying biotin acceptor peptide (BAP) on the surfaces of bacterial magnetic particles (BacMPs) synthesized by Magnetospirillum magneticum AMB-1. Both BAP and green fluorescent protein (GFP) were fused to Mms13 that was isolated from BacMP membranes. The localization of the fusion protein, BAP-Mms13-GFP, was confirmed by fluorescence analysis. BacMPs that expressed BAP-Mms13-GFP (BAP/GFP-BacMPs) were extracted from bacterial cells and incubated with biotin and Escherichia coli biotin ligase. The in vitro biotinylation of BAP/GFP-BacMPs was confirmed using alkaline phosphatase (ALP)-streptavidin detection. The conjugation system developed in this study provides a method for producing biotin- or streptavidin-labeled magnetic nanoparticles without the use of a crosslinker reagent. Various functional materials can be immobilized site-selectively onto these uniquely designed BacMPs. By combining this site-selective biotinylation technology and protein display methodology, increasingly innovative and attractive magnetic nano-materials can be constructed.
Incorporating Azo-group-functionalized Molecular-Junctions between Metal Nanoelectrodes to produce High-Rectification-Memory Nanodevices
Authors: Jasuja Kabeer , Berry Vikas
Published: April 2011

This report presents the functioning of a molecular memory device with azo-group-functionalized molecular-junctions between metal nanoelectrodes. These junctions are fabricated by a novel electrostatic-assembly process to incorporate azo-group containing polyelectrolyte (AP) between oppositely charged gold nanoparticles (GNP), functioning as nanoelectrodes. The device exhibits a bistable electronic memory effect induced by charge-transfer between AP and GNP, which can be controlled by photo-excitation of the AP. The ON and OFF memory states were found to have a rectification in the range of ∼5000 – 10000. This study will open avenues for development of next-generation molecular systems and devices to produce novel optoelectronic properties.
Microstructure and Hydrogen Absorption/Desorption Behavior of Nanoporous Pd Thin Films
Authors: Li Wen-Chung , Schendel Simone C. , Balk T. John
Published: April 2011

Nanoporous Pd (np-Pd) prepared from Pd-Ni alloy films on Si substrates was studied to understand hydriding/dehydriding processes in nanoscale Pd. Porous structures of the np-Pd thin films can be changed under different dealloying conditions. Stress measurement of the np-Pd showed that the np-Pd thin films can survive hydrogen pressures from 0 to 1 atm with no blistering, although this problem often occurs in dense Pd films in actual, high-pressure hydrogen environments. These tests indicated that hydrogen atoms can be stored in the np-Pd for much longer times than in fully dense Pd films subjected to ambient conditions. It is proposed that the stress distribution in np-Pd and the small pore size (<10 nm) inhibit hydrogen diffusion to free surfaces and thus prevent hydrogen degassing from the nanoporous structure. Moreover, phase transformation of Pd hydrides and effect of hydrogen trapping are also considered as possible reasons for the slow release of hydrogen.
Studies on Proton Conductivity and Methanol Permeability of Poly(ether sulfone)/Sulfonated Poly(ether ether ketone) Blend Membranes
Authors: Zhu Hong , Yang Wein-Duo , Wei Yong-sheng , Yang Wu-bin , Yu Xue-qing , Cao Xu-dong
Published: April 2011

Partially Sulfonated Poly(ether ether ketone) (SPEEK) samples were prepared by modification of corresponding poly(ether ether ketone) (PEEK) with concentrated sulfuric acid. Poly(ether sulfone)(PES) was blended into SPEEK to prepare PES/SPEEK blend membranes by solution casting. The glass transition temperature of blend membranes indicated the molecular miscibility between PES and SPEEK. Characteristics of the blend membranes, including water uptake, thermal stability, methanol permeability, swelling degree, proton conductivity, etc, were investigated. PES played an important role in the blend membranes. Though the proton conductivity of PES/SPEEK blend membranes decreased to some extent, their performance for barrier methanol and swelling had remarkably enhanced, showing the feasibility for direct methanol fuel cell.
Thermodynamics of Gaseous Hydrogen and Hydrogen Transport in Metals
Authors: San Marchi Chris , Somerday Brian P
Published: April 2011

The thermodynamics and kinetics of hydrogen dissolved in structural metals is often not addressed when assessing phenomena associated with hydrogen-assisted fracture. Understanding the behavior of hydrogen atoms in a metal lattice, however, is important for interpreting materials properties measured in hydrogen environments, and for designing structurally efficient components with extended lifecycles. The assessment of equilibrium hydrogen contents and hydrogen transport in steels is motivated by questions raised in the safety, codes and standards community about mixtures of gases containing hydrogen as well as the effects of stress and hydrogen trapping on the transport of hydrogen in metals. More broadly, these questions are important for enabling a comprehensive understanding of hydrogen-assisted fracture. We start by providing a framework for understanding the thermodynamics of pure gaseous hydrogen and then we extend this to treat mixtures of gases containing hydrogen. An understanding of the thermodynamics of gas mixtures is necessary for analyzing concepts for transitioning to a hydrogen-based economy that incorporate the addition of gaseous hydrogen to existing energy carrier systems such as natural gas distribution. We show that, at equilibrium, a mixture of gases containing hydrogen will increase the fugacity of the hydrogen gas, but that this increase is small for practical systems and will generally be insufficient to substantially impact hydrogen-assisted fracture. Further, the effects of stress and hydrogen trapping on the transport of atomic hydrogen in metals are considered. Tensile stress increases the amount of hydrogen dissolved in a metal and slightly increases hydrogen diffusivity. In some materials, hydrogen trapping has very little impact on hydrogen content and transport, while other materials show orders of magnitude increases of hydrogen content and reductions of hydrogen diffusivity.
Properties of MgB2 Fabricated by Sintering Mg and B Sandwich Structures
Authors: Yeung Andrew , Ng Dickon H. L.
Published: April 2011

Magnesium diboride (MgB2) was successfully produced in a pellet with sandwich-like structure. The sample was prepared by embedding a layer of Mg powder in between layers of boron powder before they were cold-pressed and sintered in argon atmosphere at different temperatures. After sintering, the interfacial regions between the Mg and B layers were examined and hexagonal platelets were observed lying along the interfacial regions in samples sintered at temperatures above 700°C. These hexagonal platelets were confirmed as MgB2. When samples were sintered at higher temperatures, the lateral size of the platelets increased. At 700°C, the average size of the platelets was 0.5 μgm, and it increased to 1.5 μgm in sample sintered at 900°C. In addition, the critical temperature (TC) and the magnetization (M) were also changed from 35.4 K to 37.1 K and −0.7 to −1.8 emu/g, respectively.
Requirements for TCO Substrate in Si-based Thin Film Solar Cells -Toward Tandem
Authors: Oyama Takuji , Kambe Mika , Taneda Naoki , Masumo Kunio
Published: April 2011

Newly developed SnO2:F films having “double–texture (W-texture)” were evaluated in terms of optical and electrical properties and compared with Asahi type-U substrate. “W-textured” transparent conductive oxide (TCO) film was composed of a combination of 300-500nm large hills and small pyramidal texture covering them. “W-textured” TCO could show a large haze value exceeding 80% even at 800nm. Microcrystalline Si (μc-Si:H) thin film solar cells were fabricated on these TCOs and characterized. The result showed that a quantum efficiency of μc-Si:H solar cells was improved with “W-textured” TCOs significantly in longer wavelength region.
Design and Numerical Simulation on the Optical and Electrical Behavior of a ZnO:Al Nanowire Array a-Si pin Solar Cell
Authors: Liu Chang-Wei , Pei Zingway , Chang Shu-Tong , Ho Ren-Yui , Ho Min-Wei , Chen Yi-Chan , Chen Chi-Lin
Published: April 2011

One of the parameters that limit the efficiency of a thin film solar cell, especially the a-Si and the nc-Si solar cell is the cell thickness. Although thicker film can absorb most of the sun light, the optical generated carriers will recombination through the numerous gap states in the film that obtained lower short circuit current and fill factor. In the controversy, thinner film could not absorb enough sun light that also limit the short circuit current. In this works, we utilize nanowire structure to solve the conflict between the light absorption and the carrier transport. The designed structure has ZnO:Al nanowire array on the substrate. The p-i-n a-Si solar cell structure is grown along the surface of each ZnO: Al nanowire sequentially. Under sunlight illumination, the light is absorbed in the axis direction of the nanowire. However, the carrier transport is along the radial direction of the solar cell. Therefore, the long nanowire could absorb most of the solar light. In the mean time, the thickness of the solar cell still is thin enough for photo-generated carrier transport. The dependence of short circuit current, open circuit voltage and fill factor to the length, diameter and density of ZnO:Al nanowires were simulated.
Light Trapping in Thin Film Silicon n-i-p Solar Cells - Gains and Losses
Authors: Schropp Ruud E.I. , Li Hongbo , Rath Jatin K. , Franken Ronald H.
Published: April 2011

Thin film silicon solar cell technology frequently makes use of rough or textured surfaces in order to enhance light absorption within the thin absorber layers by scattering and total internal reflection (“light trapping”). The rough morphology of the optically functional internal surfaces both in superstrate and substrate cells however, not only has a beneficial effect on light scattering properties, but on the other hand may also have deleterious effects on the microscopic structure of the deposited layers, in particular if these layers are nanocrystalline. The narrow valleys in the surface morphology may lead to structural defects, such as cavities and pinholes. By adjusting the morphology, these defects can be avoided.

However, even when structural defects in layers directly deposited on rough interfaces are avoided, the obtained optically defined maximum current density is still much lower than expected. For instance, in n-i-p structures the rough interface (the textured back reflector consisting of nanostructured Ag coated with ZnO) is located at the back of the cell, where only long wavelength light is present. The natively textured Ag film is sputtered at elevated temperature and optimized for diffusely reflecting this long wavelength light. From experiments we infer that the nanostructured metallic surface also gives rise to plasmon absorption in the red and near IR, and that this leads to a parasitic absorption, i.e. at least part of the absorbed energy is not re-emitted to the active layers.
Periodic Structures for Improved Light Management in Thin-film Silicon Solar Cells
Authors: Krc Janez , Campa Andrej , Luxembourg Stefan L. , Zeman Miro , Topic Marko
Published: April 2011

Advanced light management in thin-film solar cells is important in order to improve the photo-current and, thus, to raise up the conversion efficiencies of the solar cells. In this article two types of periodic structures ¡V one-dimensional diffraction gratings and photonic crystals,are analyzed in the direction of showing their potential for improved light trapping in thin-film silicon solar cells. The anti-reflective effects and enhanced scattering at the gratings with the triangular and rectangular features are studied by means of two-dimensional optical simulations. Simulations of the complete microcrystalline solar cell incorporating the gratings at all interfaces are presented. Critical optical issues to be overcome for achieving the performances of the cells with the optimized randomly textured interfaces are pointed out. Reflectance measurements for the designed 12 layer photonic crystal stack consisting of amorphous silicon nitride and amorphous silicon layers are presented and compared with the simulations. High reflectance (up to 99 %) of the stack is measured for a broad wavelength spectrum. By means of optical simulations the potential for using a simple photonic crystal structure as a back reflector in an amorphous silicon solar cell is demonstrated.
Harvesting Photons in Thin Film Solar Cells with Photonic Crystals
Authors: Zhoue Dayu , Biswas Rana
Published: April 2011

Enhanced light absorption and improved photon harvesting is a major avenue to improving solar cell performance. We simulate and design photonic crystal based loss-less back reflectors. The photonic crystal is a 2-dimensional photonic crystal combined with a distributed Bragg reflector. We have designed and simulated a thin film a-Si:H solar cell with the photonic crystal reflector and an antireflection coating. The photonic crystal has square lattice symmetry and generates strong diffraction of near band edge photons in the absorber layer. The absorption of red and near-IR photons is increased by more than an order of magnitude by the photonic crystal. The photonic crystals are composed of ITO and can easily serve as a conducting back contact. This scheme can be easily extended to other solar absorber layers. We have optimized the geometry of the photonic crystal to maximize absorption using rigorous scattering matrix simulations. The optical path length with the photonic crystal can improve over the limit for a random roughened scattering surface.
Influence of Radiation Damage and Isochronal Annealing on the Magnetic Susceptibility of Pu1-xAmx Alloys
Authors: McCall Scott K , Fluss Michael J , Chung Brandon W. , Haire Richard G.
Published: April 2011

Results of radiation damage in Pu and Pu1-xAmx alloys studied with magnetic susceptibility, χ(T), and resistivity are presented. Damage accumulated at low temperatures increases χ(T) for all measured alloys, with the trend generally enhanced as the lattice expands. There is a trend towards saturation observable in the damage induced magnetic susceptibility data. that is not evident in similar damage induced resistivity data taken on the same specimen. A comparison of isochronal annealing curves measured by both resistivity and magnetic susceptibility on a 4.3at% Ga stabilized δ-Pu specimen show that Stage I annealing, where interstitials begin to move, is largely transparent to the magnetic measurement. This indicates that interstitials have little impact on the damage induced increase in the magnetic susceptibility. The isochronal annealing curves of the Pu1-xAmx alloys do not show distinct annealing stages as expected for alloys. However, samples near 20% Am concentration show an unexpected increase in magnetization beginning when specimens are annealed to 35K. This behavior is also reflected in a time dependent increase in the magnetic susceptibility of damaged specimens indicative of first order kinetics. These results suggest there may be a metastable phase induced by radiation damage and annealing in Pu1-xAmx alloys.
First-principles Study of the Electronic Structure and Local Moment Interactions in PuAm Alloy
Authors: Han Myung Joon , Wan Xiangang , Savrasov Sergej Y
Published: April 2011

Expected to provide a clue about the origin of zero moment in the bulk phase of Plutonium, Pu1-xAmx alloys have attracted a great attention, in which upon doping the system transforms from the Kondo lattice to the diluted impurity limit. To understand the electronic structure and the magnetic properties of Pu in different crystal environments, we performed fully self-consistent first-principles calculations of the PuAm system based on the local density approximation (LDA) combined with static (LDA+U) and dynamic corrections (LDA+DMFT) for on-site electron correlations. The electronic structure strongly depends on the level of approximation for correlation effects. The exchange interactions between Pu 5f electrons and the Kondo screening strength were estimated and compared, which provide a new insight to Pu magnetism.
Zirconia Inert Matrix Fuel for Plutonium and Minor Actinides Management in Reactors and as an Ultimate Waste Form
Authors: Degueldre Claude , Wiesenack Wolfgang
Published: April 2011

A plutonia stabilised zirconia doped with yttria and erbia has been selected as inert matrix fuel (IMF) at PSI. The results of experimental irradiation tests on yttria-stabilised zirconia doped with plutonia and erbia pellets in the Halden research reactor as well as a study of zirconia solubility are presented. Zirconia must be stabilised by yttria to form a solid solution such as MAz(Y,Er)yPuxZr1-yO2-ζ where minor actinides (MA) oxides are also soluble. (Er,Y,Pu,Zr)O2-ζ (with Pu containing 5% Am) was successfully prepared at PSI and irradiated in the Halden reactor. Emphasis is given on the zirconia-IMF properties under in-pile irradiation, on the fuel material centre temperatures and on the fission gas release. The retention of fission products in zirconia may be stronger at similar temperature, compared to UO2. The outstanding behaviour of plutonia-zirconia inert matrix fuel is compared to the classical (U,Pu)O2 fuels. The properties of the spent fuel pellets are presented focusing on the once through strategy. For this strategy, low solubility of the inert matrix is required for geological disposal. This parameter was studied in detail for a range of solutions corresponding to groundwater under near field conditions. Under these conditions the IMF solubility is about 109 times smaller than glass, several orders of magnitude lower than UO2 in oxidising conditions (Yucca Mountain) and comparable in reducing conditions, which makes the zirconia material very attractive for deep geological disposal. The behaviour of plutonia-zirconia inert matrix fuel is discussed within a burn and bury strategy.
Pu-Bearing Materials - From Fundamental Science To Storage Standards
Authors: Tam Shiu-Wing , Liu Yung
Published: April 2011

The behavior of plutonium (Pu) oxides in the presence of water/moisture in a confined space and the associated issues of hydrogen and oxygen generation due to radiolysis have important implications for the storage and transportation of Pu-bearing materials. This paper reviews the results of recent studies of gas generation in the Pu-O-H system, including the determination of release rates via engineering-scale measurement. The observations of the significant differences in gas generation behavior between “pure” Pu-bearing materials and those that contain salt impurities are addressed. In conjunction with the discussion of these empirical observations, the work also addresses recent scientific advances in the investigations of the Pu-O-H system using state-of-the-art ab initio electronic structure calculations, as well as advanced synchrotron techniques to determine the electronic structure of the various Pu-containing phases. The role of oxidizing species such as the hydroxyl radical from the radiolysis of water is examined. Discussed also is the challenge in the predictive ab-initio calculations of the electronic structure of the Pu-H-O system, due to the nature of the 5f valence electrons in Pu. Coupled with the continuing material surveillance program, it is anticipated that this work may help determine the electronic structure of the various Pu-containing phases and the role of impurity salts on gas generation and the long-term stability of oxygen/hydrogen-containing plutonium oxides beyond PuO2.
Dialogue-Based Public Engagement with Nanotechnology
Authors: Aggelopoulou Argiri , Kramer Victoria , Reynolds J. Ryan , Townsend Colin , Toumey Chris
Published: April 2011

Theory and experience emphasize that science communications between experts and nonexperts should be dialogue, not monologue. This principle guides a program of public engagement with nanotechnology at the University of South Carolina. It enables the participants to express their values and concerns to experts, and to question them. It is intended that the knowledge and confidence generated by this program will enhance the participants' ability to have active and constructive roles in nanotech policy.
Education and Outreach Program on Materials at the University of Puerto Rico - Mayaguez
Authors: Suárez Oscar Marcelo , Dika Sandra , Santos Jeannette , Marrero Eddie
Published: April 2011

The University of Puerto Rico-Mayaguez and University of Wisconsin-Madison Partnership for Research and Education in Materials (UPRM-UW PREM) aims to create richer educational and research opportunities for Hispanic students in Materials Science and Engineering (MSE) and increase their representation in the Materials Science community. The educational and outreach (E&O) components for the UPRM-UW PREM include interventions for high school students and teachers, and undergraduate and graduate students at UPRM. The present report focuses on activities conducted with high school and university students during the third year of the program (2006-07). Results of surveys with student participants indicate that their participation contributes positively to their learning and development in laboratory, research and professional skills, as well as increases student interest in pursuing graduate studies in MSE.
Green Nanotechnologies for Responsible Manufacturing
Authors: Vaseashta Ashok , Reisfeld Renata , Mihailescu Ion N.
Published: April 2011

A perpetual increase in population and thus consumption of fossil fuels has led to increased pollution worldwide. Pollution in large metropolitan cities has reached an alarming level and is widely believed to be the leading contributor to chronic and deadly health disorders and diseases affecting millions of people each year. Although correlation between environmental pollution and global warming is debatable, the effects of pollution and its impact on human health are irrefutable and highly observable. Use of nanomaterials to generate energy, in an attempt to reduce environmental pollution, is in its preliminary stages and requires urgent and detailed investigation. This investigation focuses on three aspects of sustainability, (a): use of nanomaterials to monitor, detect, and remediate the environmental pollution, (b): responsible manufacturing of nanomaterials by employing principles of “green chemistry”, and (c): to drastically reduce waste and emission by-products employing use of nanomaterials as catalysts for enhanced efficiency. The synthesis of nanomaterials is accomplished by processes employing processes such as electrospinning, sol-gel, and MAPLE to drastically reduce and isolate emission and waste by-products. An exhaustive overview of the scope of our investigation and some specific applications relating to the use of nanomaterials in environmental friendly investigations, viz.; applications of nanomaterials as catalysts for enhanced efficiency, materials in CO2 sequestration, remediation of toxic metals in water streams, efficient thin film photovoltaic devices, fuel cells, and biodegradable consumable products is described. Fate and transport of nanomaterials in air, water, and soil; life-cycle analysis, and methodologies to conduct risk-assessment in the context of source reduction and conservation is discussed as a step towards sustainability.
Durability of a Cementitious Wasteform for Intermediate Level Waste
Authors: McGlinn Peter J. , Brew Daniel R.M. , Aldridge Laurence P. , Payne Timothy E. , Olufson Kylie P. , Prince Kathryn E. , Kelly Ian J.
Published: April 2011

Cementitious material is the most commonly used encapsulation medium for low and intermediate level radioactive waste. This paper focuses on the aqueous durability of a Materials Testing Reactor (MTR) cementitious wasteform – a possible candidate for the proposed intermediate level waste management facility in Australia. A series of medium term (up to 92 months) durability tests, without leachate replacement, were conducted on samples of this wasteform.

The wasteform was made from cement, ground granulated blast furnace slag and a simulated waste liquor. The compressive strength (39 MPa) was typical of MTR cement wasteforms and well above that required for handling or storage. The wasteform was an inhomogeneous mixture containing calcite, a calcium silicate hydrate phase, hydrotalcite and unreacted slag particles. After leaching for 92 months the crystallinity of the calcium silicate hydrate phase increased.

The majority of the releases of Ca, Si, Al, Sr, S, Na and K was reached within 4 days of leaching, with the maxima ie. the highest concentrations in the leachates, occurring at 3 months for Ca, Al, Sr, S, Na and K, and at 1 month for Si. For the longer leach periods (6 months and 3 months respectively) there was a slight reduction in concentration in the leachates, and these levels were similar to those for the longest period of 92 months, suggesting steady-state conditions prevailing after 3 to 6 months of leaching. The highest releases of matrix elements were for Na (37%), K (40%) and S (16%). Releases for elements such as Ca, Na, Al and Sr were similar in magnitude to those reported by the UKAEA in earlier MTR studies.

After leaching for 92 months there was an alteration layer about 80 ∞m deep where calcium has been depleted. Na, K and Sr showed signs of diffusion towards the outer part of the cement samples.