bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTData 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

ABSTRACTInspired 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

ABSTRACTTissue 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

ABSTRACTHydroxyapatite (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

ABSTRACTSemiconductor 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

ABSTRACTA 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

ABSTRACTSynthesis 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

ABSTRACTThis 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

ABSTRACTThis 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

ABSTRACTWe 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

ABSTRACTFor 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

ABSTRACTWe 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.
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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTAn 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.
Optical Amplification In Nanocrystalline Silicon Superlattices
Authors: Ruan J. , Chen H. , Fauchet Philippe M. 
Published: April 2011

ABSTRACTToday, the overall performance of a multi-chip computing system is limited by the interconnection delay between chips. Conventional interconnects based on metal lines are expected to cause unmanageable problems with speed and power dissipation. Optical interconnects provide a solution to these problems. However, the low quantum efficiency associated with radiative recombination in silicon has so far prevented the demonstration of a practical laser. Recently stimulated emission has been demonstrated in Si nanocrystals prepared by ion-implantation. The reported material gain is high enough to realize a practical Si based laser. However, the optical filling factor in these samples was less than 10% due to the poor wave guiding nature of these structures.In this work, we explore a possible way to achieve optical gain in nanocrystalline silicon superlattices. The samples are produced by growing alternating layers of amorphous silicon and SiO2 and then using a two step crystallization method to transform each amorphous silicon layer into a high density array of silicon nanocrystals having identical size. The waveguide structure is formed by sandwiching the superlattice between cladding layers. To measure optical gain we use the variable stripe length method where the amplified spontaneous emission emitted from the edge is measured as a function of the excitation length. Tuning from loss to gain was observed by just varying the pump power.
Graphyne nanotubes: New Families of Carbon Nanotubes
Authors: Coluci Vitor R. , Braga Scheila F. , Legoas Sergio B. , Galvão Douglas S. , Baughman Ray H. 
Published: April 2011

ABSTRACTFundamentally new families of carbon single walled nanotubes are proposed. These nanotubes, called graphynes, result from the elongation of covalent interconnections of graphite-based nanotubes by the introduction of yne groups. Similarly to ordinary nanotubes, armchair, zig-zag, and chiral graphyne nanotubes are possible. We present here results for the electronic properties of graphyne based tubes obtained from tight-binding and ab initio density functional methods.
Evolution of Carbon Self-Assembly in Colloidal Phase Diagram
Authors: Bouda V. 
Published: April 2011

ABSTRACTThe growth of the self-assembled structure of carbon colloidal particles has been studied [1]. The system of carbon particles was processed in electrical field in polymer melt with controlled ionic concentration. The interpretation of the complex evolution of the self-assembled structure of carbon particles was given in terms of phase transitions of colloidal systems of carbon particles.Interactions between doublets of carbon black (CB) particles are interpreted in terms of DLVO approximation of interaction energy as multiples of average thermal fluctuation kT. Plots of the sum of energy of electrostatic repulsion and energy of van der Waals attraction versus separation between the doublets show the energy barriers to coagulation of high B and the energy wells with the secondary minima of depth W. The colloidal phase transitions appear at critical conjuncture of the concentration of ions in the medium and surface potential on the colloids. Six transition lines determine five phases of the assembly of carbon colloids in the proposed colloidal phase diagram: lateral vapor + axial vapor (vapor), lateral liquid + axial vapor (columnar liquid crystal), lateral liquid + axial liquid (smectic LC), lateral liquid + axial solid (nematic LC), and lateral solid + axial solid (solid).The diagram provides a tool to control the evolution of carbon self-assembly. The eventual morphology depends on the route of the steps of the processing. During the time elapsed in the LC state, the structure can reorganize and the eventual coagulation produces various crystals. On the contrary, the route outside the LC state can produce glass.
Dramatic Effect of Temperature on Metal-oxide Nanostructures: Oxidation of Cu Films by In situ UHV-TEM
Authors: Zhou Guangwen , Yang Judith C. 
Published: April 2011

ABSTRACTWe investigated the temperature effect on the Cu2O morphology by oxidizing Cu(100) thin films at the temperature ranging from 350°C to 1000°C. We demonstrated that dramatically different morphologies of oxide nanostructures can be achieved by modifying the oxidation temperature. Quasi-one-dimensional Cu2O structures with aspect ratios as large as 40:1 were formed at the oxidation temperature of 600°C. The in situ observation data on the elongation of Cu2O islands agree with the energetic calculations based on the balance between surface and interface energies and the elastic stress relaxation in the three dimensional islands.