bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameterization of Transient Models of Defect Dynamics in Czochralski Silicion Crystal Growth
Authors: Sinno Talid , Frewen Thomas , Dornberger Erich , Hoelzl Robert , Hoess Christian
Published: April 2011

A transient model for point defect dynamics during Czochralski silicon crystal growth is parameterized using detailed experimental data generated under varying crystal growth conditions. Simulated Annealing is used to perform the model parameterization because of the complex nature of the defined objective functions. It is shown that the method is robust and despite the computational expense associated with a large number of function evaluations, can be readily used in multiple dataset, multiple objective function environments.
Going Through Rough Times: from Non-Equilibrium Surface Growth to Algorithmic Scalability
Authors: Korniss G. , Novotny M.A. , Rikvold P.A. , Guclu H. , Toroczkai Z.
Published: April 2011

Efficient and faithful parallel simulation of large asynchronous systems is a challenging computational problem. It requires using the concept of local simulated times and a synchronization scheme. We study the scalability of massively parallel algorithms for discrete-event simulations which employ conservative synchronization to enforce causality. We do this by looking at the simulated time horizon as a complex evolving system, and we identify its universal characteristics. We find that the time horizon for the conservative parallel discrete-event simulation scheme exhibits Kardar-Parisi-Zhang-like kinetic roughening. This implies that the algorithm is asymptotically scalable in the sense that the average progress rate of the simulation approaches a non-zero constant. It also implies, however, that there are diverging memory requirements associated with such schemes.
Statistical Modeling of a Dislocation Phase-Field in Ductile Single Crystals
Authors: Koslowski M. , Ortiz M. , Cuitino A.M.
Published: April 2011

A model for the description of strain hardening and hysteresis at different temperatures and strain rates in ductile single crystals is introduced. The theory accounts for: and arbitrary number and arrangement of dislocation lines over a slip plane; the long-range elastic interactions between dislocation lines; the core structure of the dislocations; the interaction between the dislocations and applied resolved shear stress field; and the dissipative in teractions with short-range obstacles and lattice friction, resulting in hardening, path dependency and hysteresis. We introduce a variational formulation for the statistical mechanics of dissipative systems. The influence of finite temperature as well as the mechanics are modeled with Metropolis Monte Carlo simulations and a mean field approximation. The theory predicts a range of behaviors which are in qualitative agreement with observation, including: hardening and dislocation multiplication under monotonic loading and hysteresis loops under under cyclic loading. The flow stress was found to be dependent on the temperature and on the strain rate only at finite temperature.
An Extended Cahn-Hilliard Model for Interfaces with Cubic Anisotropy
Authors: Abinandanan T.A. , Haider F.
Published: April 2011

For studying systems with a cubic anisotropy in interfacial energy σ, we extend the Cahn-Hilliard model by including in it a fourth rank term, which leads to an additional linear term in the evolution equation for the compositioneld. It also leads to an orientation-dependent effective fourth rank coeffcient γ(hkl) in the governing equation for the one-dimensional composition prole across a planar interface. The main effect of a non-negative γ(hkl) is to increase both σ and interfacial width w, each of which, upon suitable scaling, is related to γ(hkl) through a universal scaling function. The anisotropy in the interfacial energy can be large enough to give rise to corners in the Wul. shapes in two dimensions. In particles of finite sizes, the corners get rounded, and their shapes tend towards the Wul. shape with increasing particle size. In the study of unmixing of concentrated alloys, the anisotropy not only leads to non-spherical particle shapes, but also to strongly elongated morphologies.
Engineering Properties of Spider Silk
Authors: Ko Frank K. , Kawabata Sueo , Inoue Mari , Niwa Masako , Fossey Stephen , Song John W.
Published: April 2011

Motivated by the high level of strength and toughness of spider silk and its multifunctional nature, this paper reports on the engineering properties of individual fibers from Nephila Clavipes spider drag line under uniaxial tension, transverse compression and torsional deformation. The tensile properties were compared to the Argiope Aurentia spider silk and show different ultimate strength but similar traits of the unusual combination of strength and toughness characterized by a sigmoidal stress-strain curve. A high level of torsional stability is demonstrated. comparing favorably to other aramid fibers (including Kevlar fibers).
Composites of Carbon Filaments Made from Methane
Authors: Shui Xiaoping , Fu Xuli , Segiet Martin , Chung D.D.L.
Published: April 2011

Polymer-matrix and cement-matrix structural composites containing discontinuous carbon filaments (diameter = 0.1 μm) that were made catalytically from methane were developed for structural and electromagnetic functions. The composites were particularly attractive for electromagnetic interference shielding and radio wave reflection, due to the skin effect and the small diameter of the filaments. Coating the filaments with nickel by electroplating further enhanced the electromagnetic performance. However, the composites were not attractive for structural functions other than vibration damping, due to the large amount of interface between the filaments and the matrix. An effective configuration for the damping function involved using the filaments as an additive between the laminae of continuous conventional carbon fibers in a polymer-matrix structural composite.
Some Aspects on Preparation and Properties of Alginate and Chitosan Fibres
Authors: Struszczyk Henryk
Published: April 2011

Demand for special fibres produced from natural polymers such as alginate, chitin or chitosan, starch, keratin or biosynthesised cellulose is a function of their unique properties and growing areas of application. Two types of fibres made from chitosan and alginate are discussed in this paper. The wet-spinning method was applied for their manufacture using modified spinning solutions of the polymers. The properties and some of the application areas of chitosan and alginate fibres are discussed.
Processing and Optical Properties of YAG- and Rare-Earth-Aluminum Oxide-composition Glass Fibers
Authors: Weber Richard , Abadie Johan , Key Thomas , Hixson April , Nordine Paul , Feillens Yannick , Noguchi Hiroshi , Kurz Jonathan , Wood Brandon , Digonnet Michel , Fejer Martin
Published: April 2011

Rare-earth-aluminum oxide-composition glass fibers 5-50 μm in diameter and containing up to 50 mole % rare-earth oxide were drawn from undercooled liquids 550-650 K below the equilibrium melting point. The fibers have tensile strengths of ∼6 GPa, glass transition temperatures of ∼1150 K, and infrared transmission up to ∼5500 nm. The optical properties of erbium-doped fibers containing up to 12.5 mole % Er2O3 were investigated. The 1/e lifetime of the 4I13/2 excited state was 0.8-7 ms, decreasing with increasing Er concentration. Amplified spontaneous emission measurements indicate extremely broadband spectra, up to 135 nm (3-dB width) in 0.5 mole % fibers. Although this result is encouraging, the gain bandwidth, which has not been measured, is likely narrower. Glass fibers were crystallized by heat treatment under tension at temperatures of 1300-1900 K to form flexible, creep resistant polycrystalline monofilaments with tensile strengths up to 2.4 GPa.
Novel Multi-Layer Melt Blown Microfiber Webs
Authors: Joseph Eugene G.
Published: April 2011

Melt blowing is a melt extrusion process that allows us to start with a material in resin form and obtain a final web product in one step. The fine fibers that are characteristic of this process are in the 0.1 to 15 micron range in diameter. This process was first described in the literature by Wente of the Naval Research Laboratory in 1956 [1] and the purpose of the work was to investigate the feasibility of making ultrafine fibers for evaluation as a filtermedia. Since then melt blowing has been one of the fastest growing technologies in the non-wovens area as evidenced by the numerous articles in the literature and the number of issued patents. For example, an article by McCulloch and Graham [2] illustrated the diverse use of melt blown webs which are also referred to as Blown Micro Fiber(BMF) webs.
Bulk Microstructure and Local Elastic Properties of Laminate Composites Studied by the Microacoustical Technique
Authors: Levin Vadim M. , Liu Songping , Guo Enming
Published: April 2011

The focused ultrasonic beam technique has been employed for imaging of bulk microstructure of fiber-reinforced composites, for measuring local elastic properties and mapping their distribution over the composite body. Ultrashort probe pulses (operation frequency of 50 MHz) provide resolution of 100 μm. The technique has been employed for nondestructive layer-by-layer imaging of microstructure of CFR laminate composites. Series of acoustic images in planes parallel to the specimen face (C-scans) or perpendicular to it (B-scans) enable to reconstruct of bulk microstructure of compound unidirectional CFR laminates. Different types microdefects, including failures in interply adhesion, buckling of single prepreg plies, internal defoliations and disbonds, have been observed. The method has been applied to measure local values of elastic wave velocities in laminates within area of 100 - 150 μm diameter.

Quality of acoustic images depends on kind and density of fiber packing and on depth of position of the imaging plane. Experience shows that specimens 2-10 mm thick are appropriate for visualization of their bulk microstructure and measuring local values of sonic velocities. The technique is promising for NDE of different composites, not only for carbon-based ones.
Crystallization Mechanism of Amorphous Mullite and the Al2O3-SiO2Phase Diagram
Authors: Kriven Waltraud M.
Published: April 2011

Recent progress in the crystallization of amorphous mullite (3Al2O3•2SiO2) and yttrium aluminate (Y3Al5O12, 5Al2O3•3Y2O3or “YAG”) beads and fibers is reviewed. Studies were made by differential thermal analyses, (DTA, DSC), synchrotron X-ray diffraction and Rietveld profile fitting, HREM, EDS and SEM. Crystallization kinetics, activation energies and microstructures were determined, leading to temperature-time-transformation (T-T-T) curves. The crystallization of mullite from the solid state proceeds by formation of large-grained, pseudo-tetragonal mullite of composition 70 mol% Al2O3, which is highly strained and which contains <10 nm silica-containing inclusions. During further heat treatments, the inclusions react with the first-formed mullite yielding single phase, orthorhombic mullite of 60 mol% Al2O3. Recrystallization also occurs on further heating with a significant reduction of grain size, in a manner similar to recrystallization in brass. These observations (using more modern and sensitive characterization techniques) suggest the presence of a peritectic-like, syntectic or syntectoidal invariant reaction in the Al2O3-SiO2phase diagram. Further work needs to be done to ascertain whether the reaction is an equilibrium or non-equilibrium phenomenon.
Optical Characterization and Modeling of Sulfur Incorporated Nanocrystalline Carbon Thin Films Deposited By Hot Filament CVD
Authors: Gupta S. , Weiner B. R. , Morell G.
Published: April 2011

Sulfur incorporated nanocrystalline carbon (n-C:S) thin films grown on molybdenum substrates by hot-filament chemical vapor deposition (HFCVD) using gas mixtures of methane, hydrogen and a range of hydrogen sulfide (H2S) concentrations are optically examined using Raman spectroscopy (RS) and ex situ spectroscopic phase modulated ellipsometry (SPME) from near IR to near UV (1.5-5.0 eV) obtaining their vibrational frequencies and pseudodielectric function, respectively. The ellipsometry data (<εr(E)>, <εi(E)>) were modeled using Bruggeman effective-medium theory (BEMT) and five parameters Forouhi and Bloomer (FB) dispersion Model. A simplified two-layer model consisting of a top layer comprising an aggregate mixture of sp3C+sp2C+void and a bulk layer (L2), defined as a dense amorphized FB-modeled material was found to simulate the data reasonably well. Through these simulations, it was possible to estimate the dielectric function of our n-C: S material, along with the optical bandgap (Eg), film thickness (d), and roughness layer (σ) as a function of [H2S]. The physical interpretation(s) of the modeling parameters obtained were discussed. The Raman and ellipsometry results indicate that the average size of nanocrystallites in the sulfur-incorporated carbon thin films becomes smaller with increasing H2S concentration, consistent with AFM measurements. The bandgap was found to decrease systematically with increasing H2S concentration, indicating the enhancement of midgap states and sp2 C network, in agreement with RS results. These results are compared to those obtained for the films grown without sulfur (n-C), in order to study the influence of sulfur addition to the CVD process. This analysis led to a correlation between the film microstructure and its electronic properties.
Structure of Zirconia Nanoparticles used for Pillaring of Clay
Authors: Sadykov V. A. , Kuznetsova T. G. , Doronin V. P. , Sorokina T. P. , Kochubei D. I. , Novgorodov B. N. , Kolomiichuk V. N. , Moroz E. M. , Zyuzin D. A. , Paukshtis E. A. , Fenelonov V. B. , Derevyankin A. Ya. , Beloshapkin S. A. , Matyshak V. A. , Konin G. A. , Ross J. R. H.
Published: April 2011

SAXS and EXAFS were applied to study genesis of polynuclear zirconium hydroxyspecies in pillaring solutions as dependent upon the zirconium concentration, addition of alkaline-earth chlorides and aging. After the montmorillonite clay pillaring, the structure of zirconium nanopillars was characterized by applying X-ray structural analysis, UV-Vis, FTIRS of adsorbed CO and nitrogen adsorption isotherms. Main pillaring species appear to be nanorods comprised of several Zr4 tetramers. Basic structural features of the tetramers are preserved in zirconia nanoparticles fixed between alumosilicate layers in pillared clays. In calcined samples, those nanoparticles contain only bridging hydroxyls and/or oxygen anions responsible for bonding within pillars and between pillars and clay sheets.
Fabrication of Metal Nanostructures in Mesoporous Silicas
Authors: Chao Kuei Jung , Yang Chia Min
Published: April 2011

Mesoporous silicas were used as hosts for fabrication of nanostructured metals. Due to the confinement effect, densely packed metal nanowire bundles and nano-networks or highly dispersed metal nanoparticles were prepared inside the channels of mesoporous silicas by metal incorporation/reduction processes. The structure of nanostructured metals was analyzed by TEM and PXRD, and the composition was investigated by ICP-AES, EDX and EELS.
Formation of Ordered Silica-Organic Hybrids by Self-Assembly of Hydrolyzed Organoalkoxysilanes with Long Organic Chains
Authors: Kuroda Kazuyuki , Shimojima Atsushi
Published: April 2011

Various layered hybrid films prepared from organoalkoxysilanes with long organic chains, based on the self-assembly of the hydrolyzed species, are reviewed. Morphological control of transparent and oriented films was achieved by cohydrolysis and polycondensation with tetraalkoxysilanes, followed by dip- or spin-coating. In addition to alkyltrialkoxysilanes, alkyldimethylmonoalkoxy- and alkylmethyldialkoxy-silanes were also used as the structural units, implying that the inorganic-organic interface can be designed at a molecular level. In these cases, co-condensation in the precursor solution plays an essential role in the formation of homogeneous and ordered films. Alkenyltriethoxysilanes with terminal C=C bonds were also employed to prepare layered hybrid films. Interlayer chains were polymerized upon UV irradiation, and the resulting films exhibited a significant increase in the hardness if compared with the films before polymerization. Hybrid films thus obtained are a new class of materials and of great interest for a wide range of materials chemistry.
Grain Size Dependent Magnetic Properties of Nanocrystalline Sm [BE]Co [BD][BJ]/Cu
Authors: Bessais L. , Djéga-Mariadassou C. , Zhang J. , Lalanne V. , Percheron-Guégan A.
Published: April 2011

The evolution of both micro structural and magnetic properties of the Sm[BE]Co[BD][BJ] Cu powder, is studied as a function of soft co-milling time. The average grain size in the range 20 - 50 nm was determined by transmission electron microscopy coupled with x-ray diffraction using the Rietveld method. The particle shape and chemical distribution were investigated by elemental mapping, using wavelength dispersive x-ray analysis with electron microprobe analysis. The coercivity evolution shows that an optimum value of 6 kOe is obtained after 5 h co-milling. The microstructure analysis indicates that both materials are well mixed in nanometer scale. This technique appears as a potential route to synthesize nanocrystalline Sm[BE]Co[BD][BJ] isolated by non-magnetic metal Cu.
Fluorescence from Coated Oxide Nanoparticles
Authors: Vollath D. , Lamparth I. , Szabó D. V.
Published: April 2011

In many cases, coated nanoparticles behave like isolated ones. Using the microwave plasma process, it is possible to produce oxide nanoparticles with ceramic or polymer coating. Coating the particles has the additional advantage that by proper selection of the coating it is possible to suspend the particles in distilled water without using any colloid stabilizer. From quantum dots made of sulfides or selenides, it is well known from literature that fluorescence depends strongly on the coating of the kernels. In the case of CdSe, the kernels are coated with CdS. Within this study, similar phenomena are found with coated oxide nanoparticles having sizes of ca. 6 nm exhibiting a very narrow particle size distribution. The coating consists of a second ceramic phase or a polymer one, each one influencing fluorescence differently. Obviously, the type of coating is a tool to modify fluorescence. This behavior is demonstrated on kernels made of Al2O3, ZrO2, HfO2, ZnO etc. PMMA, PTFE, or Al2O3were used as coating material. In most cases, the fluorescence spectra showed broad bands. In some cases, such as ZnO, additionally, a sharp emission line in the UV appears. It is interesting to note that coatings made of fluorine containing polymer materials did not lead to fluorescence intensities comparable with PMMA coatings. The observed spectra are equivalent whether the powder is in aqueous suspensions or dry on a quartz glass carrier. The experimental results in this study indicate that the combination of non-fluorescent oxide core with a non-fluorescent polymer coating may lead to a nanocomposite with strong fluorescence. This is a phenomenon not described in literature until now.
Nanocomposite Electrodes for Advanced Lithium Batteries: The LiFePO4 Cathode
Authors: Yang Shoufeng , Song Yanning , Zavalij Peter Y. , Whittingham M. Stanley
Published: April 2011

LiFePO4 was successfully synthesized by high temperature and hydrothermal synthesis. A nanocomposite was formed by carbon coating this material; initial electrochemical results showed that up to 70% capacity could be obtained at 1.0 mA/cm2 current density. In contrast, the hydrothermally prepared LiFePO4 showed a lower capacity even at lower discharge rates due to a partial occupation of lithium sites by iron. This occupation, identified by Rietveld X-ray refinement, decreased both the rate and degree of intercalation and de-intercalation of lithium; chemical reaction with butyl lithium and bromine confirmed the electrochemical behavior. This investigation showed that the cathode could be prepared by high temperature synthesis, followed by a carbon black coating to achieve high capacity at high current density.
Single-Wall Carbon Nanotubes Synthesis by Means of UV Laser Vaporization: Effects of the Furnace Temperature and the Laser Intensity Processing Parameters
Authors: Braidy N. , Khakani M.A. El , Botton G.A.
Published: April 2011

Carbon single-wall nanotubes (SWNTs) have been successfully synthesized by means of KrF laser vaporization of a Co-Ni-doped graphite pellet in a flowing argon atmosphere. The effects of two key processing parameters, namely the furnace temperature (in the 25-1150 °C range) and the laser intensity (in the 0.8-4.4 x 108 W/cm2 range), on the yield and the structural characteristics of the carbon SWNTs were investigated. By characterizing the obtained deposits by means of transmission electron microscopy and micro-Raman spectroscopy techniques, we were able to identify a threshold temperature as low as ∼550 °C, below which no carbon SWNTs can be grown. The increase of the furnace temperature from 550 to 1150 °C was found to lead not only to a significant increase in the SWNTs yield but also to the formation of larger SWNTs bundles. Raman analysis have also revealed that the diameter distribution peak shifts from ∼1.05 to ∼1.22 nm as the temperature is raised from 550 to 1150 °C. At the highest furnace temperature of 1150 °C, we also found that a minimum laser intensity of about 1.6 x 108 W/cm2 is required to grow carbon SWNTs by means of the KrF laser. Higher laser intensities have resulted in a higher yield of SWNTs with relatively thicker bundles. Moreover, the increase of the laser intensity was found to promote the growth of 1.22 nm-diameter nanotubes to the detriment of thinner carbon nanotubes (1.05 and 1.13 nm-diameters).
Controlling the Microstructure and Magnetic Properties of Ferromagnetic Nanocrystals Produced by Ion Implantation
Authors: Beaty K.S. , Meldrum A. , Franck J.P. , Sorge K. , Thompson J. R. , White C.W. , Zuhr R.A. , Boatner L.A. , Honda S.
Published: April 2011

Ion implantation coupled with annealing is a versatile and flexible approach to creating ferromagnetic near-surface nanocomposites that represent a wide range of particle/host combinations. We have used ion implantation and thermal processing to create a layer of Co nanoparticles in a sapphire host that was subsequently irradiated with Xe, Pt, or Pb in order to systematically modify the magnetic properties of the composite. Transmission electron microscopy (reported in an accompanying paper in this volume) was used to carry out a detailed characterization of the microstructure of the resulting near-surface composites whose magnetic properties were determined using SQUID magnetometry or magnetic circular dichroism. These composites exhibit magnetic hysteresis with coercivities ranging from near zero (i.e., superparamagnetism) up to 1.2 kG - depending on the composition and microstructure. We also present the results of preliminary experiments in which we attempt to control the spatial distribution of magnetic elements within ion-implanted ferromagnetic nanocomposites. The results demonstrate methods for tailoring the magnetic properties of nanocomposites produced by ion implantation for specific applications.
Surface Modification of Superparamagnetic Nanoparticles for in-vivo Bio-medical Applications
Authors: Kim D. K. , Toprak M. , Mikhailova M. , Zhang Y. , Bjelke B. , Kehr J. , Muhammed M.
Published: April 2011

Chemical modifications of Superparamagnetic Iron Oxide Nanoparticles (SPION) surfaces by attachment of functional groups and further covalent coupling with biodegradable substances have been studied. Based on computer-assisted chemical equilibrium calculations, several optimum operation conditions for a coprecipitation process of magnetite nanoparticles were predicted. These particles were immobilized by ultra-thin films of PVA, Dextran, Dextrin, PEG and MPEG to obtain a biocompatible particle surface for further functionalization purposes. The effect of surface modification of the superparamagnetic nanoparticles in terms of chemical and physical properties of the samples was investigated with several techniques, including microelectrophoresis measurement. The feasibility of using SPION in biomedical applications was investigated by in-vivo treatment in rat brains.
Electron Field Emission from Nano-Diamond Films
Authors: Wang S.G. , Zhang Q. , Yoon S.F. , Ahn J. , Wang Q. , Yang D.J. , Huang Q.F.
Published: April 2011

In this paper, the field emission properties of nano-diamond films were investigated by measuring the curves of emission current density (J) versus applied electric field (E). The nano-diamond films were prepared on n-type (100) silicon substrate by microwave plasma enhanced chemical vapor deposition (MPECVD) technique using a gas mixture of nitrogen-methane-hydrogen. Field emission results show that, with increasing hydrogen gas flow ratio of [H2]/[N2+CH4+H2] from 0 to 10 %, diamond grain size increases from 5 to 60 nm, threshold electric field for electron field emission increases from 1.2 to 5.75 V/μm, and emission current density decreases from 820 to 560 μA/cm2, demonstrating that small grain size nano-diamond films are promising as a cathode material for low-field electron emitters.
Nanoparticles Synthesis by Air-Assisted Ultrasonic Spray Pyrolysis
Authors: Tsai Shirley C. , Song Yu L. , Chen C.Y. , Tseng T. Kuan , Tsai Chen S. , Lin Hong M.
Published: April 2011

This paper presents new findings regarding the effects of precursor drop size and concentration on product particle size and morphology in ultrasonic spray pyrolysis. Large precursor drops (diameter >30 μm) generated by ultrasonic atomization at 120kHz yielded particles with holes. Precursor drops 6-9 μm in diameter, generated by an ultrasonic nebulizer at 1.65MHz and 23.5W electric drive power, yielded uniform spherical particles 150nm in diameter under proper control of heating rate and precursor concentration. Moreover, air-assisted ultrasonic spray pyrolysis at 120kHz and 2.3W yielded spherical particles of which nearly half were smaller than those produced by the ultrasonic spray pyrolysis of the 6-9 μm precursor drops, despite the much larger precursor drop sizes (28 μm peak diameter versus 7 μm mean diameter). These particles are much smaller than those predicted by the conventional one particle per drop mechanism, suggesting that a vapor condensation mechanism may also be involved in spray pyrolysis. It may be concluded that through this new mechanism air-assisted ultrasonic spray pyrolysis can become a viable process for mass production of nanoparticles.
Multiply Twinned Structures in Gas-Phase Sintered Stoichiometric FePt Nanoparticles
Authors: Stappert Sonja , Rellinghaus Bernd , Acet Mehmet , Wassermann Eberhard F.
Published: April 2011

Stoichiometric FePt nanoparticles with sizes in the range 3 – 6 nm were prepared in the gas-phase and thermally sintered prior to deposition. Whereas unsintered particles exhibit irregular shapes and a low degree of crystallinity, the majority of the sintered particles are multiply twinned and have predominantly icosahedral structure. There is no indication for the occurance of L10 ordering in the gas-phase sintered particles, although previous post-deposition annealing experiments of unsintered particles had shown the occurrence of partial formation of the L10 FePt intermetallic phase. On the other hand, analysis of the structural data obtained from (high resolution) electron microscopy shows that the relative amount of icosahedral particles increases with increasing sintering temperature. This result is discussed on the basis of a structure model of an irregular icosahedron, which is built up from distorted tetrahedral building blocks. The distortion in each tetrahedron is in accordance with the tetragonally compressed unit cell of the L10-phase.
Nanowire Formation by Electrodeposition in Modified Nanoporous Polycrystalline Anodic Alumina Templates
Authors: Mikhaylova M. , Toprak M. , Kim D. K. , Zhang Y. , Muhammed M.
Published: April 2011

Template-assisted metallic nanowires, or hollow nanotubes, were synthesized by controlled electrodeposition of a metal salt under a controlled ac frequency in an anodic alumina membrane (AAM). Homogeneous large dimension AAM (D=5cm) was prepared by a modified two step anodization, using a specially designed reaction vessel that holds the sample perpendicular during the anodization. A ripping process, i.e. applying an opposite current after the anodization, easily separated the AAM from the Al substrate. TEM, SEM, and AFM were used to investigate the AAM structure, pore density and size, and distribution. Large aspect ratio metallic nanoparticles were prepared in an AAM within hexagonally close packed (hcp) alumina nanochannels.
Nano-Encapsulated ZnS:Ag Phosphors for Field Emission Flat Panel Display Applications
Authors: Ollinger Michael , Craciun Valentin , Singh Rajiv K.
Published: April 2011

ZnS:Ag phosphor particles were encapsulated with nano-meter thick films of indium tin oxide (ITO) in order to slow the degradation process of the phosphor as well as to reduce the amount of sulfur species out-gassing from the phosphor. Cathodoluminescent (CL) degradation measurements were performed at two different vacuum conditions (6.1–10-7 Torr and 1–10-5 Torr). The CL degradation curves showed that the ITO coating improved the brightness lifetime. X-ray photoelectron spectroscopy was used to determine the chemical changes on the coated and uncoated degraded particle surfaces. CL images were used to show the loss of brightness from the surface of the phosphor particles. Then energy dispersive x-ray spectroscopy was used to measure the ratio of the area under the zinc and sulfur peaks on an atomic weight %, which showed a loss in sulfur during the degradation experiments.
First-Principles Simulations of Atomic Structure and Magnetism in Fe Nanoparticles
Authors: Postnikov A. V. , Entel P. , Soler José M.
Published: April 2011

The properties of small clusters Fe3 and Fe5, in which the non-collinearity of magnetic density is expected to be important, and of larger nanoparticles (consisting of up to 62 atoms) are studied from first principles making use of density functional theory, norm-conserving pseudopotential and numerical local orbitals method, as implemented in the SIESTA code. We concentrate on the interplay of lattice relaxation, mostly pronounced near the surface of particles, and the particles' magnetic characteristics. Previously obtained theoretical findings of enhanced magnetic moments in outer shells of nanoparticles are confirmed. These results are refined by taking structure relaxation into account and by considering more representative bcc- and fcc-related particles; moreover, we allowed antiferromagnetic ordering along with ferromagnetic one.
Boron Nitride Nanotube, Nanocable and Nanocone
Authors: Golberg Dmitri , Bando Yoshio , Bourgeois Laure , Ma Renzhi , Ogawa Kazuhiko , Kurashima Keiji , Sato Tadao
Published: April 2011

Boron nitride nanotubes, nanocones and nanocables were prepared and their atomic structures were identified by using a 300 kV field emission transmission electron microscope equipped with an electron energy loss spectrometer and energy dispersion X-ray detector. Multiwalled BN nanotubes and nanocones were synthesized by reacting C nanotube templates and boron oxide under nitrogen atmosphere at 1723-2023 K. Additions of metal oxide promoters, e.g. MoO3, CuO, and PbO, significantly improved BN-rich nanotube yield at the expense of B-C-N nanotubes. It was shown that BN nanotubes had preferential “zigzag” chirality and exhibited either hexagonal or rhombohedral stacking between shells. An efficient synthetic route for bulk quantities of BN tube production was also developed, where a B-N-O precursor was used during a CVD process. Nanocones of BN were mostly found to have 240° disclinations which ensure the presence of B-N bonds only. One case was observed of a cone constituted of 300° disclination implying that structures may contain line defects of non B-N bonds. The first synthesis of insulating BN nanocables was carried out, where BN nanotubes were entirely filled with Invar Fe-Ni nanorods. The filled nanotube diameters ranged between 30 to 300 nm, whereas the length of filling reached several microns.
Processing of single wall carbon nanotubes and implications for filling experiments
Authors: Chikkannanavar Satishkumar B. , Smith Brian W. , Russo Richard M. , Stercel Ferenc , Luzzi David E.
Published: April 2011

Single wall carbon nanotubes (SWNTs) have been processed in different schemes to get clean material for use in various filling experiments. The SWNTs synthesized by different methods require different processing schemes, and this is presumably due to heterogeneous nature of the various contaminants present along with the carbon nanotubes. For the pulsed laser synthesized SWNTs, a combination of nitric acid, hydrogen peroxide and hydrochloric acid treatment gives best results and the purified SWNTs give best ever filling fraction for fullerene, C60 of ~90%. The processing improves the surface cleanliness of SWNTs, in turn giving greater access for the target molecules, and hence the higher filling fraction. For the carbon arc produced SWNTs, air oxidation followed by treatment with nitric acid has been found to work best and the processed SWNTs have been used for filling experiments with metal chlorides. Both these processing schemes still leave a small fraction of catalyst impurities in the final material, thus the material quality of filled material and hence its properties depend on the processed material used for the filling experiments.
Purification of SWNTs Using Microwave Heating
Authors: Harutyunyan Avetik R. , Pradhan Bhabendra K. , Sumanasekera Gamini U. , Chang Jiping , Chen Gugang , Goto H. , Fujiwara J. , Eklund Peter C.
Published: April 2011

A new method for purifying single wall carbon nanotubes (SWNTs) using microwave heating is developed. The microwaves couple to the residual metal catalyst, raising significantly the local temperature leading to both the oxidation and rupturing of the carbon passivation layer over the metal catalyst particles and sintering. With this protective carbon coating weakened or removed, a mild acid treatment in HCl is then sufficient to remove most of the metal in the sample, leaving the nanotubes in tact. Results from transmission and scanning electron microscopy (TEM & SEM), Raman spectroscopy and thermo-gravimetric studies are discussed.
Carbon Networks Synthesized using Microwave Plasma Enhanced Chemical Vapor Deposition
Authors: Yang D. J. , Zhang Qing , Yoon S.F. , Ahn J. , Wang S.G. , Wang Q.
Published: April 2011

A new carbon network is prepared using microwave plasma enhanced chemical vapor deposition(MPCVD) under the plasma of a mixture of methane, hydrogen and nitrogen at 720 °C. The Field Emission Scanning Electronic Microscopy(FESEM) images show that the carbon nanotubes are self-organized into carbon networks, which is different from the previously reported carbon nanotube ropes or nanofibers. The carbon networks are about 1 micron in diameter, more than 10 microns in length and composed of hundreds of carbon nanotubes with the diameter from 20 to 100 nm. Energy Dispersive X-Ray(EDX) results confirm that the network is carbon in nature, with a small amount of Ni which was used as catalyst.
Dispersion and Alignment of Carbon Nanotubes in Polycarbonate
Authors: Sennett Michael , Welsh Elizabeth , Wright J. B. , Li W. Z. , Wen J. G. , Ren Z. F.
Published: April 2011

Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber spinning apparatus. The effects of mixing time and fiber draw ratios on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw ratio was greater than 7. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties.
The Role of Adsorbates on the Field Emission Properties of Single-Walled Carbon Nanotubes
Authors: Collazo R. , Liang M. , Schlesser R. , Sitar Z.
Published: April 2011

Two field-emission states of single-walled carbon nanotubes were identified according to their respective emission current levels. The state yielding increased emission current was attributed to the presence of adsorbates on the nanotubes as confirmed by electron emission measurements at different background pressures. Application of high electric fields induced large emission currents and a transition between the two states. During this transition, a current drop to 10% of the original value was observed. Under a constant applied electric field, the current took around 1000 s to recover its original level at a background pressure of 10-10 Torr, while it took half that time at 10-6 Torr. For the high current state, field-emitted electrons originated from states located up to 1 eV below the Fermi level, as was determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tunneling probability of electrons. The adsorbed states are removed at high applied electric fields, presumably due to ohmic heating caused by large emission currents. This adsorption/desorption process is completely reversible.
Field Emission Properties of Vertically Aligned Carbon Nanotubes Driven by Polar and Non-Polar Gas Adsorption
Authors: Song Youngsik , Usner Brian , Choi Jaewu , Lim Seong-Chu , Lee Young Hee
Published: April 2011

We studied the gas adsorption effects on the field emission properties of vertically aligned multiwalled carbon nanotube films by exposing them to polar (H2O) and non-polar (N2O) gas molecules. The charge transfer between adsorbates and carbon nanotubes plays an important role in the field emission properties. With bias voltage ~ 1.2V/μm, the field emission properties of the carbon nanotubes are improved by exposing the nitrous oxide while the bias effect with water exposure is less significant. The improvement of the field emission properties by gas exposure is attributed not only to the change in the work function of the carbon nanotubes caused by a charge transfer, but also to the reactivity of the adsorbate gas with localized-cap states.
Single-Wall Carbon Nanotube Electron Emitters Produced by Electrophoresis
Authors: Obraztsova Elena D. , Pozharov Anatoly S. , Terekhov Sergey V. , Osadchy Alexander V. , Pimenov Sergey M. , Konov Vitaly I. , Kononenko T.V. , Skaballanovich Tatiana A. , Ivanova Svetlana R. , Volkov Alexander P. , Obraztsov Alexander N.
Published: April 2011

Single-wall carbon nanotubes have been synthesized, purified, attested with a high resolution electron microscopy and Raman scattering and deposited by liquid electrophoresis onto different substrates (including a metallized glass) to produce the effective and homogeneous film cathodes for low-field electron emitters. The emission properties (a threshold of the emission switching on, a current value, a time-stability) of the SWNT cathodes have been investigated. A prototype of a phosphorescent lamp with a nanotube cathode has been designed. The Raman spectra of the SWNT cathode registered in situ from the shining lamp have shown no temperature increase and time-degradation of the nanotube material during the emission process.
Raman Spectra from One Carbon Nanotube
Authors: Dresselhaus M. S. , Jorio A. , Filho A. G. Souza , Dresselhaus G. , Saito R. , Pimenta M. A.
Published: April 2011

The use of Raman spectroscopy as a characterization tool for individual single wall carbon nanotubes is briefly reviewed. New physical phenomena occurring at the single nanotube level are discussed, with special emphasis given to the use of resonance Raman scattering for the structural determination of (n, m) for individual nanotubes, based on diameter and chirality dependent phenomena associated with the radial breathing mode, the G-band and the G[prime]-band features. Examples are given to show how single nanotube spectroscopy provides insight into the use of Raman spectroscopy for the characterization of nanotube bundles and for the study of new physical phenomena occurring at the single nanotube level.
Quantum Transport in Nanotube-Based Structures
Authors: Nardelli M. Buongiorno , Fattebert J.-L. , Bernholc J.
Published: April 2011

Using state of the art quantum calculations, we have studied the electronic and transport properties of a variety of nanotube-based structures relevant for the design of nanoscale electronic devices. We have investigated the conductance of carbon nanotubes under mechanica distortions such as bending, defects and tube-tube contacts, and analyzed the behavior of carbon nanotube-metal contacts with the aim of explaining the anomalously large contact resistance observed in nanotube devices. Our results provide a clear interpretation of recent experimenta findings and suggest avenues for the use of carbon nanotubes in electromechanical systems.
Carbon Nanotubes under Bending Strain
Authors: Huhtala M. , Kuronen A. , Kaski K.
Published: April 2011

Bending induced deformations in single walled carbon nanotubes with zigzag and armchair chirality have been studied computationally using a classical molecular dynamics simulation method. In this the interatomic forces have been described with Brenner's empirical model potential. The results given by this classical model have been assessed by letting the most critical, i.e. the most deformed part, of the nanotube further relax by using a dynamical tight binding simulation method. We find that the empirical potential based approach and the tight binding method reproduce similar deformation patterns when the deformation remains relatively small but at higher levels of deformation the results differ significantly. These comparative simulations indicate that graphene interlayer interaction is an important factor in the behavior of deformed nanotubes.
Fabrication of Two- and Three-Dimensional Structures of Nanoparticles Using LB Method and DNA Hybridization
Authors: Takahagi Takayuki , Huang Shujuan , Tsutsui Gen , Sakaue Hiroyuki , Shingubara Shoso
Published: April 2011

In this paper we describe fabrication methods for two types of nanostructures, two- and three-dimensional arrays of gold nanoparticles. Large-scale and high-ordered monolayers of alkanethiol-encapsulated gold particles were fabricated by using Langmuir-Blodgett (LB) method. Three-dimensional nanoparticle arrays composed of gold nanoparticles of two different sizes, which were encapsulated by complementary thiol-capped DNA oligonucleotides, were fabricated by using DNA hybridization. DNA hybridization occurred upon mixing these particles, which resulted in the assembly of three-dimensional nanostructure of gold particles. Scanning electron microscopy observations and UV spectroscopy measurement were performed to confirm the construction of the nanostructures.
Self-Assembling of Nanoparticles in the form of Double Linear Chains and Superlattices on their Basis
Authors: Malkhasyan R.T. , Karakhanyan R.K. , Nazaryan M.N. , Sung C.
Published: April 2011

The self-assembling systems in nanoscale powders of crystalline MoO3 are disclosed. For the first time, the double linear chain aggregates of the MoO3 nanoparticles were revealed in nanoscale powders of MoO3, treated by vibrationally excited molecules of hydrogen. Double linear chain aggregates form a linear and an orthogonal supperlattices. Both the double linear chain aggregates and the supperlattices formed are being considered as self-assembling systems. The treatment of the powders by the molecules of hydrogen is a method of obtaining long self-assembling chains of inorganic materials and supperlattices on their basis.
Planar Molecular and Macromolecular Gradients: Preparation and Properties
Authors: Genzer J. , Wu T. , Efimenko K.
Published: April 2011

We present a method for fabricating polymer brushes with a gradual variation of grafting density on solid substrates. The technique for generating such structures consists of: i) deposition of a molecular gradient of polymerization initiator on the solid substrate, and ii) polymerization from the substrate bound initiator centers (“grafting from”). In this publication we describe the preparation of gradient polymer brushes of poly(acryl amide) on silica-covered substrates. We show that the polymer density within the gradient polymer brush can be varied by controlling the polymerization time.
Morphologies of Self-Assembled Quantum Dots: A Variational Approach
Authors: Budiman R. Arief , Ruda Harry E.
Published: April 2011

We construct a 3D model for coherent island formation by (i) using a novel 3D strain tensor to account for bulk strains and (ii) representing adatom diffusion as an external field that perturbs an otherwise flat strained layer. Equilibrium shapes of coherent islands and wetting layer thickness are obtained. Coherently compressed layers are typically unstable, but become stable in tension. Comparisons with Si1-xGex/Si(001) and Si0.5Ge0.5/Si1-xGex(001) layers are discussed.
Formation of Ordered Silica–Organic Hybrids by Self-Assembly of Hydrolyzed Organoalkoxysilanes with Long Organic Chains
Authors: Kuroda Kazuyuki , Shimojima Atsushi
Published: April 2011

Various layered hybrid films prepared from organoalkoxysilanes with long organic chains, based on the self-assembly of the hydrolyzed species, are reviewed. Morphological control of transparent and oriented films was achieved by cohydrolysis and polycondensation with tetraalkoxysilanes, followed by dip- or spin-coating. In addition to alkyltrialkoxysilanes, alkyldimethylmonoalkoxy- and alkylmethyldialkoxy-silanes were also used as the structural units, implying that the inorganic–organic interface can be designed at a molecular level. In these cases, co-condensation in the precursor solution plays an essential role in the formation of homogeneous and ordered films. Alkenyltriethoxysilanes with terminal C=C bonds were also employed to prepare layered hybrid films. Interlayer chains were polymerized upon UV irradiation, and the resulting films exhibited a significant increase in the hardness if compared with the films before polymerization. Hybrid films thus obtained are a new class of materials and of great interest for a wide range of materials chemistry.
Fabrications and Electron Transport Properties of One Dimensional Arrays of Gold and Sulfur Containing Fullerene Nanoparticles
Authors: Shih Sheng-Ming , Su Wei-Fang , Lin Yuh-Jiuan , Wu Cen-Shawn , Chen Chii-Dong
Published: April 2011

Novel arrays of gold nanoparticles with sulfur containing fullerene nanoparticles were self-assembled through the formation of Au-S covalent bonds. Disulfide functional groups were introduced into C60 molecule by reacting propyl 2-aminoethyl disulfide with C60. The two dimensional(2D) arrays were formed at the interface of aqueous phase of gold particles and organic phase of fullerene particles as a blue transparent film. TEM images showed that the fullerene spacing between adjacent Au(∼10 nm) particles was about 2.1±0.4 nm, which was consistent with the result of 2.18 nm by molecular molding calculations(MM+). The arrays were deposited on the top of pairs of gold electrodes to form 2D colloidal single electron devices. The electrode pairs were made by electron beam lithography techniques, and the separation between tips of the two electrodes in a pair was less then 100 nm. Transport measurements at low temperatures exhibited Coulomb-Blockade type current-voltage characteristics, the lower the temperature the more pronounced the Coulomb gap. Also, step-by-step method was used to assemble one-dimensional(1D) array of gold nanoparticles with fullerene derivative between two electrodes spaced with 15 nm. The Coulomb blockade behavior of 1D arrays was clearer than that of 2D arrays.