bluuebunny/crossref_metadata_2025 huggingface dataset:
Overview of U.S. Department of Energy Superconductivity Program for Electric Power
Authors: Hawsey Robert A.
Published: April 2011

A top priority of the U.S. government is to improve the energy delivery infrastructure. According to the report issued May 2001 by the National Energy Policy Development (NEPD) Group, “For the electricity we need, we must be ambitious. Transmission grids stand in need of repair, upgrading, and expansion…if we put these connections in place, we'll go a long way to avoiding future blackouts.” Superconductivity is such an important aspect of our nation's energy future that we should “…expand the Department's research and development on transmission reliability and superconductivity.” Prototype superconducting power cables that will help upgrade our power grid when commercialized later this decade are being demonstrated today in Carrollton, Georgia and Detroit, Michigan. Much research remains, however, if the superconducting wires are to have the electrical performance and low-cost features necessary for U.S. companies to fully commercialize new transmission cables that will help eliminate the bottlenecks in urban areas. The U.S. Department of Energy (DOE) leads the U.S. national effort to develop high-temperature superconducting (HTS) wires and to demonstrate prototype electric power applications using the best wires available today. The industry-led Second Generation Wire Initiative is exploiting breakthroughs at the national laboratories that promise unprecedented current carrying capacity in HTS wires at lower cost than first-generation “BSCCO” wires. Some of the recent progress in the U.S. development of HTS “coated conductors” and in fielding prototype applications is presented
Thermomechanical Characterization of Bismuth Telluride Based Thermoelectric Materials
Authors: Brostow Witold , Menard Kevin P. , White John B.
Published: April 2011

The thermoelectric properties of bismuth telluride based thermoelectric (TE) materials are well-characterized, but comparatively little has been published on the mechanical and thermomechanical properties of these materials. In this paper, we present the initial dynamic mechanical analysis (DMA) data for n-type and p-type bismuth telluride based TE materials. The materials' tan δ values, indicative of viscoelastic energy dissipation modes, approach that of glassy or crystalline polymers and are greater than ten times the tan delta of structural metals. TE samples measured perpendicular to the van der Waals planes have higher tan δ values. Thermal scans in the DMA compressive mode showed changes in mechanical properties versus temperature with clear hysteresis effects. These changes were correlated to differential scanning calorimetry (DSC) thermal transitions. The expected anisotropy was shown in flexural 3-point bending results for one n-type material that showed a storage modulus of 0.10 to 0.45 GPa in the direction parallel to the van der Waals planes and 0.07 to 0.2 GPa in the perpendicular direction.
Nuclear Density Analysis in Solids. The Case of Ba8Ga16Si30
Authors: Iversen B. B. , Bentien A. , Palmqvist A. E. C. , Bryan D. , Stucky G. D. , Schultz A. J. , Henning R. W.
Published: April 2011

Multi-temperature (15, 100, 150, 200, 300, 450, 600, 900 K) single crystal neutron diffraction data on the type I clathrate Ba8Ga16Si30are analyzed with the maximum entropy method to obtain direct space nuclear densities. The nuclear densities suggest that the guest atoms are structurally disordered, and the disorder appears to be temperature dependent with increased host-guest interaction at high temperatures.
Cross-Plane Thermoelectric Properties in Si/Ge Superlattices
Authors: Yang Bao , Liu Jian L. , Wang Kang L. , Chen Gang
Published: April 2011

In this paper, a set of methods is developed to measure the Seebeck coefficient, electrical conductivity, and thermal conductivity in the cross-plane direction of thin films. The method employs microfabricated heaters, voltage and temperature sensors, and phase-lock amplifiers to determine the temperature and Seebeck voltage oscillation in the cross-plane direction of the samples, from which the thermal conductivity and Seebeck coefficient of thin films are determined simultaneously. The cross-plane electrical conductivity is also measured by a modified transmission line model. These methods are applied to Si/Ge superlattices grown by molecular beam epitaxy.
Thermoelectric structural composites and thermocouples using them
Authors: Wang Shoukai , Wen Sihai , Guerrero Victor H. , Chung D.D.L.
Published: April 2011

The tailoring of the sign and magnitude of the absolute thermoelectric power was achieved in structural composites by the choice of the reinforcing fibers and of the particulate filler between laminae. The resulting thermoelectric structural composites included continuous carbon fiber polymer-matrix composites and short fiber cement-matrix composites. In addition, it resulted in thermocouples in the form of structural composites. The fibers and interlaminar filler impacted the thermoelectric behavior in the longitudinal and through-thickness directions respectively.
Classical Size Effect on In-plane Thermoelectric Transport at Low Dimension
Authors: Liu W. L. , Chen G.
Published: April 2011

Previous models on low-dimensional thermoelectric investigation deal with the quasi twodimensional electron transport due to quantum confinement effect. The formation of sub-bands in quantum well requires that electron wave reflections or transmissions at the interface are strictly in the specular direction and the superimposed wave function keeps phase coherence. However, due to the interface non-ideality or roughness, electrons can lose coherence such that their transport will deviate from that described by two-dimensional quantum well limit theories. In this paper, we report a theoretical approach to investigate the classical size effect on in-plane thermoelectric transport at low dimensions. A theoretical model based on Boltzmann equation is established with interface scattering treated as partial specular and partial diffuse scattering boundary condition. With the infinite quantum well assumption, the classical size effect in the quantum-classical mixed regime is quantitatively demonstrated. Factors that affecting classical size effect, such as quantum well width and relaxation length, are discussed.
Nano Indentations Studies of WC/C and TiN/(Ti,Al)N Multilayer PVD Coatings Combined with Cross-sectional Electron Microscopy Observations
Authors: Carvalho N.J.M. , Hosson J.Th.M. De
Published: April 2011

Multilayers of tungsten carbide/carbon (WC/C) with an amorphous structure and multilayers of titanium nitride/titanium-aluminum nitride (TiN/(Ti,Al)N) with a polycrystalline structure, prepared by physical vapor deposition, have been subjected to nanoindentation testing. The investigation has been aimed at establishing whether the load-displacement responses provides accurate information on the fracture mechanisms and whether such mechanisms can be characterized using a new technique for cross-sectional electron microscopy of the nanoindentations. Analysis of the load-displacement curves showed that they can be used to identify the cracking mechanisms occurring in the multilayers and that cross-sectioning of the nanoindentations is necessary if a more complete understanding of the multilayer coatings behavior is required.
High Quality Optical Film Formation with O2 Cluster Ion Assisted Deposition
Authors: Toyoda Noriaki , Shirai Kenichi , Terasawa Mititaka , Matsui Shinji , Yamada Isao
Published: April 2011

High-quality Ta2O5/SiO2 were deposited with oxygen gas cluster ion assisted deposition at low-temperature for advanced optical filters. With gas cluster ion assisted deposition, high refractive index and very smooth surface of Ta2O5 films were realized. The optimum cluster ion energy and cluster ion current density for Ta2O5 films were found to be 7keV and 0.5μA/cm2, respectively. The structure of film was very uniform and no porous or columnar structures were observed. The surface or interfaces of Ta2O5/SiO2 films were also very flat by surface smoothing effect of cluster ion beams. Very smooth surface can be realized even though the bottom surface was rough. There was no significant wavelength shift after an environmental test, which indicates that dense oxide films were formed at low-temperature with O2 cluster ion assisted deposition.
Surface Phases of Metals on Silicon as Material for Surface Engineering
Authors: Saranin Alexander A. , Rizhkov Sergey V. , Tsukanov Dmitriy A. , Lifshits Victor G. , Zotov Andrey V. , Oura Kenjiro , Hasegawa Shuji
Published: April 2011

To study structural and transport properties of the surface phases on silicon, a number of adsorbate/silicon systems on Si(100) and Si(111) surfaces has been investigated using scanning tunneling microscopy (STM), reflection-high-energy-electron diffraction (RHEED) and in-situ electrical resistance measurements. Results of investigations of formation and electrical properties of Si-Al, Si-Na, Si-Ag and Si-In surface structure are presented.
CVD Diamond Synthesis on WC-Co Cutting Tool via Electrophoretic Seeding Process
Authors: Tsubota Toshiki , Okada Naoki , Ida Shintaro , Nagata Masanori , Matsumoto Yasumichi , Yatsushiro Nobumitsu
Published: April 2011

Electrophoretic deposition was effective for the synthesis of the film type CVD diamond on the WC cutting tool without removing cobalt on the surface, although the adhesion force of CVD diamond was insufficient for the application to a cutting tool. Heat treatment after electrophoretic deposition improved the adhesion force.
The Effects of Substrate Temperature and Bias on the Structural, Mechanical and Tribological Properties of TiC films deposited by Magnetron Assisted Pulsed Laser Deposition
Authors: Phani A.R. , Krzanowski J.E. , Nainaparampil J.J.
Published: April 2011

Titanium carbide films have been deposited using a hybrid magnetron sputtering/ pulsed laser deposition technique. One set of films was deposited at substrate temperatures ranging from room temperature to 600oC with no substrate bias, and a second set was deposited at 400°C bias voltages up to -150V. X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy were employed for structural and compositional characterization of the films, and nano-indentation hardness testing and pin-on-disc wear tests were used to evaluate the mechanical and tribological properties. All the TiC films deposited without substrate bias were highly crystalline. The films deposited with bias had significantly reduced crystallinity and non-stoichiometric film compositions. The hardness of the TiC films increased with substrate temperature from 8 GPa at room temperature to 18 GPa at 600oC, whereas the biased films had a maximum hardness of 12 GPa. The wear test data showed significantly lower friction and longer wear life for the -150V biased film.
Polyoxometallate Containing Polymeric Materials for Nanolithography and Molecular Devices
Authors: Glezos N. , Argitis P. , Velessiotis D. , Koutsolelos P. , Diakoumakos C.D. , Tserepi A. , Beltsios K.
Published: April 2011

In this paper, molecular compounds that come from the class of tungsten or molybdenum polyoxometallates (POM) are examined as components of polymeric materials with potential use in nanolithography and molecular devices. In the past, POMs have been used as components of DUV resists with promising results, but the metallic compound presence and their unconventional processing demands discouraged their further use in microlithography. In this paper routes for the use of these compounds in e-beam nanolithography are investigated. Different resist formulations, where poly (vinyl alcohol) and poly (methyl methacrylate) are used as host polymers, will be discussed along with the related process issues.

First results from the use of polyoxometallate compounds as active elements, or components, of molecular electronic nanodevices will be also presented. The electronic transport properties of the composite materials have been tested using planar devices with contact distances of 40μm, 5μm, 50nm and 25nm. Contacts were fabricated using electron beam lithography and a lift–off process. Even at room temperature conditions conductivity peaks appear in the case of distances smaller than 25nm. These peaks are related to the energy distance of the HOMO – LUMO levels of the active molecules and the work function of the electrode used. The position and the size of the peaks depend upon the mean distance of the molecules as well as the electrode distance. On the other hand when the contact is illuminated, conductivity increases even by two orders of magnitude. This is attributed to the photon excitation of electrons from the HOMO.
Novel Approaches to Nanopatterning: From Surface Monolayer Initiated Polymerization to Hybrid Organometallic-Organic Bilayers
Authors: Henderson Clifford L. , Barstow Sean , Jeyakumar Augustin , McCoy Kendra , Hess Dennis W. , Tolbert Laren M.
Published: April 2011

The extendability of conventional subtractive lithographic processing using spin-coated polymeric single layer resists (SLR) faces many challenges as feature sizes in microelectronics push below 100 nm. In addition, the opacity of the polymeric materials traditionally used as SLR resins to future exposure sources presents new challenges as the radiation penetration depth decreases (e.g. 157 nm, EUVL, low keV e-beam). One solution to these problems is the use of surface imaging materials and processes. In such surface imaging methods, exposure in only a thin surface layer is used to create a pattern in a substantially thicker etch barrier layer. Conventional surface imaging approaches have mainly focused on silylation techniques which have experienced a variety of problems. This paper presents an update on two novel surface imaging methods under investigation: (1) surface monolayer initiated polymerization (SMIP) and (2) organometallic-organic bilayer resists.

The SMIP process involves using a monolayer that contains a polymerization initiator functionality. Exposure of the monolayer to radiation can deactivate the initiators in selected areas and the remaining initiators can subsequently be used to directly grow patterned polymer structures. This process allows complete decoupling of the imaging properties of the monolayer from the etch properties of the polymer etch barrier. In essence, the polymerization process is used to amplify the pattern initially formed in the monolayer. Recent results are presented that demonstrate the use of x-ray photoelectron spectroscopy in conjunction with dose array experiments to analyze the sensitivity of the initiators used for this process.

The other novel surface imaging method presented in this work uses organometallic-organic bilayers. In these systems, thin films of radiation sensitive organometallic precursors are used as an imaging layer in conjunction with thick organic etch barrier layers. Upon exposure, the organometallic precursor film is selectively converted to metal oxide. After exposure, the unexposed regions of the film can be developed away. Subsequent dry pattern transfer in an oxygen plasma can be used to transfer the pattern defined in the thin oxide layer through the organic etch barrier layer. Organometallic precursor films with sensitivities on the order of 70 μC/cm2 are demonstrated which result in oxide films that possess an etch selectivity of 100:1 with respect to novolac in oxygen plasmas. 500 nm line-space patterns are demonstrated as a first lithographic imaging proof-of-concept.
Nanometric Surface Patterns for Tissue Engineering: Fabrication and Biocompatibility in Vitro
Authors: Riehle M , Dalby M , Johnstone H , Gallagher J , Wood M A , Casey B , McGhee K , Affrossman S , Wilkinson C D W , Curtis A S G
Published: April 2011

Three fundamentally different methods were used to fabricate nanometric surface features on polymers or fused silica. Phase separation of binary polymer mixes resulted in randomly distributed features whose depth and shape could be tightly controlled over large areas. Colloidal resist patterned large areas randomly and uniformly with very fine spikes. In contrast e-beam and reactive ion etching were used to create a set of regular spaced pillars on an orthogonal pattern. Some of the surfaces were replicated by in situ polymerization, solvent casting, embossing or melt molding onto polystyrene (PS) or ε–poly caprolactone (ε–PCL). Nanometric features down to 60nm were imprinted onto the polymers with high fidelity. Cells were seeded onto the nanometric surfaces and adhesion, morphology and cytoskeleton investigated. Cells respond to regular features of 170/80nm (width/depth) with reduced adhesion and changes in overall morphology and cytoskeleton. Small nanofeatures (13nm, 35nm depth) made by phase separation on the other hand increased adhesion and promoted cytoskeletal differentiation. The responses of the cells are indicative that nanometric surface features are useful modifications on scaffolds for tissue engineering or on medical implants.
Surface Functionalization of Ceramic Nanoparticles: Application to Ion-Sensing and Gas-Sensing Devices
Authors: Baraton Marie-Isabelle
Published: April 2011

The consequences of surface functionalization by grafting molecules like hydroxysilane, chlorosilane, and hexamethyldisilazane (HMDS) are reviewed for different types of nanoparticles including Si3N4, TiO2, and SnO2. Fourier transform infrared spectrometry is used as primary investigation tool. In terms of physical properties, these surface chemical modifications lead to improvements of the ion-sensitive FET and gas sensors characteristics. The beneficial effect of hydroxy- and chlorosilane grafted on Si3N4 used as ion sensitive membranes will be demonstrated. Then, the reduction of humidity effects on HMDS-grafted TiO2 and SnO2 nanosized powders used for screen-printed CO sensors will be reported.
AFM Studies of Fracture Surfaces of Composition B Energetic Materials
Authors: Lanzerotti Y. D. , Sharma J.
Published: April 2011

The characteristics of TNT (trinitrotoluene) crystals in Composition B have been studied using atomic force microscopy (AFM). The size of TNT crystals has been examined by analyzing the surface structure that is exhibited after mechanical failure of the Composition B. The mechanical failure occurs when the material is subjected to high acceleration (highg)inan ultracentrifuge and. the shear or tensile strength is exceeded. AFM examination of the topography of the Composition B fracture surface reveals fracture across columnar grains of the TNT. The width of the columnar TNT grains ranges in size from ~ 1 μm to~2 μm. Their height ranges in size from ~ 50 nm to ~ 300 nm.
Electric Field Induced Patterning of Polymer Films
Authors: Bucknall David G. , Andrew G. , Briggs D.
Published: April 2011

By confining a polymer film between two electrodes one of which is solid but thin enough to be flexible, a characteristic lateral morphology is produced when a strong electric field is applied across the film. A simple model to describe the observed behaviour is presented which accounts for the length scales of the observed morphology. This model demonstrates that feature sizes ranging from microns to nanometers can be obtained through selective choice of key parameters.
New organic nonlinear optical materials: dithienylethylenes
Authors: Sahraoui B. , Pluciński K.J. , Kityk I. V. , Paci B. , Baldeck P. , Nunzi J-M. , Frère P. , Roncali J.
Published: April 2011

Measurements of the third-order susceptibilities of new dithienylethylenes in solutions using a degenerate four wave mixing technique at λ=532 nm in picosecond regime were made. From these measurements we deduced the second order hyperpolarizabilities. Optical power limiting properties of the mentioned compounds using nanosecond laser pulses in the visible range are evaluated. The dispersion of nonlinear absorption coefficients is obtained. The appropriate quantum chemical calculations are carried out.
Surface Structure and Electrochemical Polymerization of Mixed, Thiophene-Capped Monolayers
Authors: Kang Jung F. , Harrison Katherine , Kilbey S. Michael
Published: April 2011

We have investigated the growth of polythiophene from self-assembled monolayers (SAMs) that contain pendant thiophene groups using electrochemistry and atomic force microscopy. The SAMs are formed on indium tin-oxide (ITO) by coadsorption of 11-(3-thienyl)undecyltrichlorosilane (3TUTS) and undecyltrichlorosilane (UTS). By altering the composition of the underlying monolayers we can manipulate the onset of electrochemical polymerization and affect the surface topography of the resultant polythiophene layer. Films made on SAMs that have high loadings of 3TUTS have small, distinct grains, but as the monolayers become enriched in UTS, the grain size increases; however, these films are neither as rough nor as diffuse as films formed on ITO without an underlying SAM. These experiments suggest that the electrochemical growth and structure of the polythiophene layer can be manipulated by tuning the underlying SAM.
Time-Resolved Spectral Measurement of Dendrimer Molecular Films with Rhodamine B Core
Authors: Zhou M. , Otomo A. , Yokoyama S. , Mashiko S.
Published: April 2011

We investigated molecular thin films fabricated using novel organic materials, such as dendrimers with a rhodamine B (Rh-B) core, by a pump-probe measurement for ultrafast time-resolved spectroscopy with a time resolution of approximately 160 fs. The photon energy transfer caused by the interaction of the dendrimer molecules was measured in terms of absorbance. The wavelength of the pump light was 550 nm and a white continuum light spanning from 450 nm to 750 nm was used as a probe light. A spin-coated molecular film made of dendrimer molecules with Rh-B core has a relatively high molecular density. We measured a strong stimulated emission at a wavelength of 612 nm, whose fast decay was assumed to be caused by intermolecular interactions between the dendrimer molecules with Rh-B core. The lifetime of the molecules in the excited state was measured to be as short as 10 ps. Several types of molecular films with different molecular densities were compared, and cases with different pump energies were also discussed.
Light pulse propagation in three-dimensional photonic crystals
Authors: Kitano H. , Minami F. , Sawada T. , Yamaguchi S. , Ohtaka K.
Published: April 2011

The phase characteristics of transmitted optical pulses in three-dimensional photonic crystals were investigated in the frequency and time domain by using the spectrally resolved cross-correlation technique. The temporal evolution of femtosecond pulses passing through polystyrene colloidal crystals exhibits a large phase distortion near the stop bands. The phase discontinuity around the band gap was observed in the frequency-domain. The phase of the transmitted pulses is found to change by φ across the band gap. The dispersion curve estimated from the phase shift shows good correspondence with those calculated from a photonic band calculation. The group velocity significantly slows down near the stop bands. A large change of the group velocity dispersion is also observed near the band edges. These results are in good agreement with the band theory.
Waste Package Environment for the Yucca Mountain Site Characterization Project
Authors: Gdowski G.E. , Wolery T.J. , Rosenberg N.D.
Published: April 2011

Environmental parameters that would affect the degradation of engineered materials, including waste packages and drip shields, in the potential high level nuclear waste repository at Yucca Mountain, Nevada are being characterized as part of the Yucca Mountain Project. These parameters include: temperature, relative humidity, range of water chemistry, deliquescence of salts, pH, and electrochemical potential (Eh). The likelihood of various brine compositions forming on the engineered components under repository conditions, and the implications, is discussed. Relative humidity controls the ionic strength and composition of the aqueous solutions, and hence strongly influences the corrosion processes that could occur. Studies are underway to more fully characterize the redox state of aqueous solutions in contact with engineered system components.
Gas Contaminant Mobility at Subsurface Disposal Area
Authors: Downs Wayne C. , Oh Chang H. , Housley Todd , Sondup Jeff
Published: April 2011

Beginning in 1952, waste materials, including volatile organic compounds (VOCs)contaminated with transuranic radionuclides, were generated during the fabrication, assembly, and processing of nuclear weapons components in the US Department of Energy (DOE) weapons productions complex at the Rocky Flats Plant (RFP). Following processing and containerization, drums were shipped to the Subsurface Disposal Area (SDA) at the Idaho National Engineering and Environmental Laboratory (INEEL). During 1968 approximately 9,691 drums were buried there.

In subsequent years, observations made during drum retrieval studies indicated that many of the drums were compromised on impact or suffered physical damage by compaction equipment shortly after burial. Corrosion also appears significant on drums buried for a few years. A large vadose-zone contaminant plume composed of solvents buried in the drums has been found beneath the burial area.

Phase partitioning calculations show it unlikely that separate-phase solvent has leaked from the compromised drums deep into the soil profile or that solvents have dissolved into infiltrating water. Rather, it appears that the solvents are evaporating out of the barrels into the air phase and further partitioning from there throughout the subsurface.

This paper describes the history of mixed wastes buried at the SDA, phase partitioning, and preliminary computer simulation results on gas contaminant mobility in the vadose zone.
Effect of ZrO2 on the glass durability
Authors: Lobanova M. , Ledieu A. , Barboux P. , Devreux F. , Spalla O. , Lambard J.
Published: April 2011

Borosilicate glasses were prepared with the molar composition 70 SiO2-15 Na2O-15B2O3-n ZrO2 with n ranging from 0 to 10. The glasses were studied by conventional static dissolution tests of powders at 90°C in pure water and in buffered solutions for long times (months) and short times (minutes). During the first minutes of alteration in a buffered solution, sodium is rapidly leached until its loss becomes controlled by the silicon hydrolysis. The experimental data show that the introduction of zirconium drastically reduces the initial dissolution rate (Vo) of the glass. Zirconium strengthens the silica network but also strongly modifies the porous layer morphology. In the case of glasses with small Zr contents (less than 2%), the silica dissolution rate decreases but the formation of a passivating alteration layer is also delayed. As a result, small amounts of zirconium paradoxically decrease the loss of silica but increase the final loss of sodium and boron in the static leaching tests. Larger zirconium contents (above 5%) increase the durability of the glass regarding the initial dissolution rate and the final concentration of all elements.
Radionuclide Incorporation in Secondary Crystalline Minerals from Chemical Weathering of Waste Glasses
Authors: Mattigod Shas V. , Serne R. Jeff. , McGrail Bernard P. , LeGore Virginia L.
Published: April 2011

Data from corrosion and radionuclide sequestration studies on two waste glasses indicated chemical weathering resulted in the formation of zeolite minerals such as herschelite and analcime. We also found that these minerals incorporated ∼8 – 22%, ∼1- 13% and ∼8 – 25% of spiked 125I, 99Tc, and 75Se respectively. Increasing concentrations of radionuclides in spike solution resulted in higher degree of sequestration as observed by significantly higher proportion of stable isotopes (∼70 – 95% I, ∼58 – 100% Re, and ∼100% Se) in secondary minerals. The radionuclide incorporation mechanisms for these minerals appear to be mainly isomorphic substitution of Se and Re in tetrahedral sites and iodide substitution for framework oxygen.
Fracture and Fatigue Behavior of a Self-Healing Polymer Composite
Authors: Brown Eric N. , Moore Jeffrey S. , White Scott R. , Sottos Nancy R.
Published: April 2011

Inspired by biological systems, in which damage triggers an autonomous healing response, a polymer composite material that can heal itself when cracked has been developed. The material consists of an epoxy matrix composite, which utilizes embedded microcapsules to store a healing agent and an embedded catalyst. This paper investigates issues of fracture and fatigue consequential to the development and optimization of this new class of materials. When damage occurs, the propagating crack ruptures the microcapsules, which releases healing agent into the crack plane. Polymerization of the healing agent is triggered by contact with exposed catalyst, which bonds the crack faces closed. The efficiency of crack healing is defined as the ability of a healed sample to recover fracture toughness. Healing efficiencies of over 90% have been achieved. Embedded microcapsules significantly increase the fracture toughness and reduce the fatigue crack propagation rate of epoxy. Fracture mechanisms for neat epoxy and epoxy with embedded microcapsules are presented.
Structure and Properties of Poly(α-hydroxyl acids)/Nano Hydroxyapatite Composite Scaffolds
Authors: Wei Guobao , Ma Peter X.
Published: April 2011

Tissue losses and organ failures resulting from injuries or diseases remain frequent and serious health problems despite great advances in medical technologies. Transplantation and reconstructive surgeries are seriously challenged by donor tissue shortage. We take a tissue engineering approach to design 3D scaffolds for cells to grow and synthesize new tissues. The scaffolds are biodegradable and will be absorbed after fulfilling the purpose as 3D templates, leaving nothing foreign in the body. To better mimic natural bone structurally, mechanically and biologically, nano-sized hydroxyapatite particles (N-HAP) were formulated with biodegradable poly(α-hydroxyl acids) to form composite scaffolds with well-controlled pore structures using thermally induced phase separation (TIPS) in this work. The pore structure and mechanical properties of the scaffolds were optimized by the use of multiple solvent systems, different quenching rates and quenching depths. The fabricated scaffolds possessed porosities higher than 90% and average pore sizes ranging from 50 to 500 μm. The scaffolds containing N-HAP maintained open and regular 3D pore structure similar to those of plain polymer scaffolds, implying that N-HAP particles were dispersed within the polymer pore walls of the scaffolds. The addition of N-HAP increased the compressive modulus by 20∼80% over that of plain polymer scaffolds. These results indicate that poly(α-hydroxyl acids)/N-HAP scaffolds may provide excellent 3D substrates for bone tissue engineering.
Solubility Properties of Hydroxyapatite Doped with Divalent and Trivalent Ions
Authors: Smith Jennifer L. , Massa-Schlueter Elizabeth A. , Webster Thomas J.
Published: April 2011

Hydroxyapatite (HA) is a bone-like ceramic with good cytocompatibility properties and, consequently, has been used as coatings for dental and orthopedic implants. However, the main limitation of using HA as a coating material is its high calcium dissolution rate. The present study investigated an assortment of dopants in order to lower the calcium dissolution rate of HA. The HA dopants used in the present study were divalent (magnesium and zinc) and trivalent (yttrium, lanthanum, indium, and bismuth) cations. In a 21 day study, undoped HA and HA doped with magnesium (Mg), lanthanum (La), and bismuth (Bi) were found to increase in mass while formulations doped with zinc (Zn), indium (In), and yttrium (Y) were found to decrease in mass. Decreased mass may be due to loss of a number of chemical groups (such as calcium, phosphorous, and hydroxyl groups). Studies were also performed to specifically evaluate calcium dissolution. The divalent and trivalent-doped HA averaged samples had calcium concentrations in the supernatant consistently below the undoped HA samples suggesting lower calcium dissolution rate for all doped formulations. The results of the present study demonstrated that of those dopants tested that increased in mass, HA doped with Bi had the lowest amount of calcium released into the supernatant media. Since calcium has been shown to increase adsorption of proteins important for new bone growth, the present study provided evidence that to decrease the calcium dissolution rate of HA, dopants should be used, particularly Bi.
Deposition, Recrystallization, and Epitaxy of Silicon, Germanium, and GaAs on Fibers and Metal Wires for Optoelectronic Device Applications
Authors: Mauk Michael G. , Feyock Bryan W. , Balliet Jeremy R. , Ruffins Todd R.
Published: April 2011

Semiconductor p-n junctions formed in a cylindrical geometry as concentric cladding layers surrounding a wire or fiber ‘substrate’ could have significant advantages for optoelectronic devices such as LEDs and solar cells, especially with regard to optical coupling efficiency and high-throughput manufacturing. Fiber-based semiconductor device components may also prove useful in conformable electronics or electrotextiles, and for giant -area flexible circuits. We describe techniques and results for chemical vapor deposition and melt coating to form 2- to 50-micron thick cladding layers of silicon or germanium on various types of fibers and refractory metals. These Ge or Si cladding layers can be recrystallized to achieve large (several millimeters or greater) grains oriented along the axis of the fiber. Additional GaAs cladding layers are grown on the recrystallized Ge or Si by vapor-phase epitaxy or metallic solution growth. p-n junctions are formed by diffusion or epitaxy. Light-sensitive diodes have been fabricated in these structures.
Biomimetic Synthesis of Water Soluble Conductive Polypyrrole and Poly (3,4 ethylenedioxythiophene).
Authors: Bruno Ferdinando F. , Fortier Jacqueline M. , Nagarajan Ramaswamy , Roy Sucharita , Kumar Jayant , Samuelson Lynne A.
Published: April 2011

A novel biomimetic method for the synthesis of a conducting molecular complex of polypyrrole and of Poly(3,4 ethylenedioxythiophene) (PEDOT) in the presence of a polyelectrolyte, such as polystyrene sulfonate (SPS) is presented. A poly(ethylene glycol) modified hematin (PEG-Hematin) was used to catalyze the polymerization of pyrrole and of 3,4 ethylenedioxythiophene in the presence of SPS to form a Polypyrrole/SPS and PEDOT/SPS complex. UV-vis, FTIR, electrical conductivity and TGA studies for all complexes indicate the presence of a thermally stable and electrically conductive form of these polymers. Furthermore the presence of SPS in this complex provides a unique combination of properties such as processability and water-solubility. Water-soluble polypyrrole opens new avenues for the fabrication of novel biosensors.
Synthesis and Characterization of 2,5-bis[(3,4-ethylenedioxy)thien-2-yl]-3-Substituted Thiophenes
Authors: Pepitone Michael F. , Eaiprasertsak Kalya , Hardaker Stephen S. , Gregory Richard V.
Published: April 2011

Synthesis and functionalization of 3-bromothiophene afforded novel 2,5-bis[(3,4-ethylenedioxy)thien-2-yl]-)-3-substituted thiopehene monomers with blue emission characteristics and having a quantum yield of 3–5%. Cyclic voltammetry was employed to investigate the electrochemical behavior of the four monomers reported here. Polymer films were deposited by repeated potential cycling. These materials are considered for use in tailoring properties in opto-electronic device applications.
Binary and Ternary Mercury Chalcogenide Quantum Dots and Clusters
Authors: Kuno Masaru , Higginson Keith A. , Qadri Syed B. , Yousuf Mohammad , Davis Benjamin L. , Mattoussi Hedi
Published: April 2011

This paper describes the synthesis, characterization and optical properties of binary and ternary mercury chalcogenide quantum dots and clusters. Such materials were made by applying a synthetic strategy involving the simultaneous use of strong Hg(II) coordinating ligands and the explicit phase separation of both metal and chalcogen precursors. High quality QDs and clusters are obtained in this manner with sharply structured absorption and band edge emission covering the visible to near infrared.
semiconductor nanocrystal based saturable absorbers for optical switching applications
Authors: Raynolds James E. , LoCascio Michael
Published: April 2011

This document presents experimental and theoretical results of an effort to develop semiconductor nanocrystal doped thin films for optical switching applications. Films doped with high quality PbS and PbSe nanocrystals have been fabricated. Measurements of the absorption spectra are compared with theoretical predictions. A general theoretical framework for treating the optical properties of multi-layer dielectric structures containing thin nanocrystal doped layers is used. A simple model (the particle-in-a-sphere) is used as a starting point, however, more sophisticated models (such as those based on k.p theory, or fits to experiment) can easily be incorporated. A prototypical micron-scale Fabry-Perot optical cavity has been constructed and is discussed. Theoretical predictions for the switching behavior of such a structure, upon introduction of the semiconductor nanocrystal material into the optical cavity, are presented. A full-length version of this paper is available at Evident Technologies' web site.
Isolated and Embedded Silicon Based Nanodots: the Role of Surface Oxygen
Authors: Luppi Marcello , Ossicini Stefano
Published: April 2011

We have extensively studied the effects of oxygen on the optoelectronics properties of various types of isolated silicon nanodots, through ab initio total energy calculations within the density functional theory. Varying the cluster size we have considered different Si/O bonding geometries and different levels of oxidation. We provide strong evidences that the role of the interface region surrounding the silicon nanostructures have to be carefully taken into account in order to understand the striking optical properties of these systems. Moreover the multiple presence of silanone Si=O bonds at the nanodots surface is shown to provide a consistent interpretation of the photoluminescence red-shift observed in oxidized porous silicon samples. Finally for the first time we have performed ab initio calculations on small silicon nanodots embedded in a SiO2 matrix stressing the strong interplay between the nanodot and the surrounding host environment and the active role of the interface region between them.
Photon, Electron and Utlrasonic Emission from Nanocrystalline Porous Silicon Devices
Authors: Koshida N. , Gelloz B. , Kojima A. , Migita T. , Nakajima Y. , Kihara T. , Ichihara T. , Watabe Y. , Komoda T.
Published: April 2011

For quantum-sized nanocrystalline silicon (nc-Si), various optical and electronic effects have been clarified in addition to a significant band gap widening. As typical examples of these induced effects, some emission properties of nanocrystalline porous silicon (PS) are described in this paper including the present status of application studies. The first one is electroluminescence (EL) of PS diodes. It is shown that following a drastic improvement in the external quantum and power efficiencies, stability has been significantly enhanced by the formation of covalent termination nc-Si surfaces. Next topic is the cold electron emission from PS diodes. When the nanostructure of the PS drift layer is appropriately controlled, injected electrons are accelerated ballistically toward the outer surface and emitted via tunneling through a thin-film top electrode perpendicular to the device surface as energetic electrons. As an efficient surface-emitting electron source, there are many advantages in this emitter over the conventional cold cathodes. The applicability of this emitter to either vacuum-type or solid-state flat-panel display is demonstrated. Finally, the usefulness of a PS device as a thermally induced ultrasonic emitter is presented on a basis of its fundamental characterizations. Technological potential of this emitter for functional acoustic devices is also discussed.
Tuning of the electroluminescence from Si nanocrystals through the control of their structural properties
Authors: Irrera A. , Iacona F. , Pacifici D. , Miritello M. , Franzò G. , Sanfilippo D. , Di G. , Fallica P.G. , Priolo F.
Published: April 2011

We have studied the structural, optical and electrical properties of MOS devices, where the dielectric layer consists of a substoichiometric SiOx (x < 2) thin film deposited by plasma enhanced chemical vapor deposition. After deposition the SiOx samples were annealed at high temperature (> 1000°C) to induce the separation of the Si and SiO2 phases with the formation of Si nanocrystals embedded in the insulating matrix. The effects of the Si concentration in the SiOx layer and of the annealing temperature on the electrical and optical properties of these devices are reported and discussed. It is shown that by increasing the Si content in the SiOx layers the operating voltage of the device decreases and the total efficiency of emission increases. In fact, devices having an active layer with high Si concentration (46 at.%) annealed at 1100 °C, exhibit the best performances (i.e. the highest electroluminescence intensity and the lowest operating voltage). Furthermore, we have observed that by decreasing the thickness of the SiOx layer from 75 to 25 nm it is possible to strongly reduce the operating voltage down to 4 V.
Clausius-Mossotti Approximation for Nonlinear Composites with Coated Ellipsoidal Particles
Authors: Pinchuk Anatoliy O.
Published: April 2011

ABSRTACT:An effective nonlinear dielectric permittivity of a heterogeneous composite structure consisting of coated ellipsoidal nonlinear nanoparticles embedded in a linear host medium has been theoretically studied. An expression for the effective dielectric permittivity tensor of such a system has been derived following the Clausius-Mossotti approximation. The conditions for the existence of electromagnetic bistability phenomenon in a single coated ellipsoidal particle with a nonlinear core and a metallic shell have been obtained. The numerical results show more prominent bistability phenomenon in more dense suspensions of nonlinear heterogeneous ellipsoids.
Periodic Two-dimensional Arrays of Silicon Quantum Dots for Nanoscale Device Applications
Authors: Striemer Christopher C. , Krishnan Rishikesh , Xie Qianghua , Tsybeskov Leonid , Fauchet Philippe M.
Published: April 2011

We report a successful unification of standard lithographic approaches (top down), anisotropic etching of atomically smooth surfaces, and controlled crystallization of silicon quantum dots (bottom up) to produce silicon nanoclusters at desired locations. These results complement our previous demonstration of silicon nanocrystal uniformity in size, shape, and crystalline orientation in nanocrystalline silicon (nc-Si)/SiO2 superlattices, and could lead to practical applications of silicon nanocrystals in electronic devices. The goal of this study was to induce silicon nanocrystal nucleation at specific lateral sites in a continuous amorphous silicon (a-Si) film. Nearly all previous studies of silicon nanocrystals are based on films containing isolated nanocrystals with random lateral position and spacing. The ability to define precise two-dimensional arrays of quantum dots would allow each quantum dot to be contacted using standard photolithographic techniques, leading to practical device applications like high-density memories. In this work, a template substrate consisting of an array of pyramid-shaped holes in a (100) silicon wafer was formed using standard microfabrication techniques. The geometry of this substrate then influenced the crystallization of an a-Si/SiO2 superlattice that was deposited on it, resulting in preferential nucleation of silicon nanoclusters near the bottom of the pyramid holes. These clusters are clearly visible in transmission electron microscopy (TEM) images, while no clusters have been observed on the planar surface areas of the template. Possible explanations for this selective nucleation and future device structures will be discussed.
Optical Properties of Silicon Nanoparticles in Silica Gel Monoliths
Authors: Posada Y. , San Miguel L. , Fonseca L. F. , Resto O. , Weisz S. Z.
Published: April 2011

We have synthesized highly photoluminescent monoliths by incorporating nanocrystalline Silicon (nc-Si) from Porous Silicon (PSi) into a Sol Gel Silica matrix. The optically transparent samples are the result of mixing an acid catalyzed solution of Sol-Gel and nc-Si that forms a solution of Si-nanoclusters (Si-n) that eventually after condensation for three days produces the final luminescent material. Photoluminescence (PL) basic studies show a very high orange emission band with a maximum peak that ranges between 600 nm and 750 nm. The PL emission intensity was increased up to ten times the luminescence of the native nano material PSi, the mechanical and thermal stability properties were also greatly improved. The PL corresponds to different concentrations or preparations of Sol-Gel with Si-n (Sol-Si) with a broad size distribution that produces orange and blue emissions, and for this reason we take as our future work to tailor samples with very high Si-n densities for semiconducting and photonic applications.
Exploiting Silicon Porosity Gradients for Superior Antireflective Films
Authors: Striemer Christopher C. , Fauchet Philippe M.
Published: April 2011

An electrochemical etching technique has been developed that provides continuous control over the porosity of a porous silicon (PSi) layer as a function of etching depth. Thin films with engineered porosity gradients, and thus a controllable refractive index gradient, have been used to demonstrate broadband antireflection (AR) properties on silicon wafers and solar cell substrates. This low broadband reflectivity is a direct result of the formation of a refractive index gradient at the substrate surface, where the transition between air and silicon occurs continuously throughout the thickness of a PSi film. These graded index films are formed by applying a continuously changing current function to the electrochemical cell during the PSi etch. The application of these films as solar cell AR coatings is of particular interest, where their broadband nature is a critical advantage. For this application, graded index PSi films must not only offer superior AR properties, but must also prove minimally disruptive to the electrical properties of the underlying solar cell. This requirement limits the total thickness of these films to approximately 120 nm, creating several challenges for this process. However, the simplicity and highly reproducible nature of this technique, in combination with its short duration (less than 10 seconds), make it a strong alternative to current vacuum deposited AR coating technology.