bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTSulfur 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

ABSTRACTSAXS 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

ABSTRACTMesoporous 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

ABSTRACTVarious 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

ABSTRACTThe 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

ABSTRACTIn 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

ABSTRACTLiFePO4 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

ABSTRACTCarbon 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

ABSTRACTIon 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

AbstractChemical 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

AbstractIn 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

AbstractThis 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

AbstractStoichiometric 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

AbstractTemplate-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

AbstractZnS: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

AbstractThe 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

AbstractBoron 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

AbstractSingle 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

AbstractA 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

AbstractA 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.