bluuebunny/crossref_metadata_2025 huggingface dataset:
Doping and Electrochemical Capacitance of Carbon Nanotube-Polypyrrole Composite Films
Authors: Hughes Mark , Chen George Z. , Shaffer Milo S. P. , Fray Derek J. , Windle Alan H.
Published: April 2011

Composite films were electrochemically synthesised via the simultaneous deposition of multiwalled nanotubes and polypyrrole, a conducting polymer. Negatively charged functional groups attached to the surface of the acid treated nanotubes enables the tubes to act as a dopant for the PPy in these films. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy revealed that the nano-porous three-dimensional arrangement of PPy coated MWNTs in these films produced specific capacitances per mass and geometric area as high as 192 F g-1 and 1.0 F cm-2, respectively. This value of specific capacitance per geometric area exceeds that of both component materials and other carbon nanotube-conducting polymer composites. The composite films described in this report were also able to charge and discharge more than an order of magnitude faster than similarly prepared pure PPy films. The nano-porosity and small diffusion distances within the composite films, crucial to achieving the superior capacitive performance, were found to be dependent on the concentration of nanotubes and additional dopant anions in the polymerisation electrolyte, offering possibilities for tailoring of the composite structure.
Nano-Cylinder Structure Studied by X-ray Diffraction
Authors: Xu Gu , Feng Zhechuan , Popovic Zoran , Lin Jianyi , Vittal Jagadese. J.
Published: April 2011

The study of nano-cylinder structure has attracted much attention due to the application of multi-wall carbon nanotubes (MWCNTs). While some TEM observations indicate that they are formed by seamless concentric cylinders, other TEM and high pressure X-ray diffraction studies suggest that they look like scrolls of graphite sheets. Although many people now accept the concentric cylinder model, there has been no confirmation reported. On the other hand, this structural difference of MWCNTs plays a crucial role in determining the properties and suitability for future applications. For example, the periodical boundary condition can only be imposed for cylinders, but not for scrolls. To resolve this issue, we employed high-resolution X-ray diffraction to measure detailed profiles of the Bragg peaks for high-purity MWCNTs. We then identified some unusual observations unique to the nano-cylinder structure, followed by the analysis of the structural difference in the Fourier transform between nanotubes formed by scrolls and concentric cylinders. The simulation results are then compared with the experimental data to reveal the structural details.
A Non-Traditional Vapor-Liquid-Solid Method for Bulk Synthesis of Semiconductor Nanowires
Authors: Sharma Shashank , Sunkara Mahendra K. , Lian Guoda , Dickey Elizabeth C.
Published: April 2011

Multiple silicon nanowires were synthesized using large gallium pools and microwave plasma. Results showed that nanowires growing out of different sized large gallium drops show little variation in diameters, suggesting that our non-traditional technique can be used to synthesize bulk amounts of monodispersed nanowires out of thin films of molten gallium.
Optical, Electrical and Microstructural Properties of Tin Doped Indium Oxide Films made from Sintered Nanoparticles
Authors: Hultåker Annette , Hoel Anders , Granqvist Claes-Göran , Doorn Arie van , Jongerius Michel J. , Burgard Detlef
Published: April 2011

Thin transparent and electrically conductive films of tin doped indium oxide (ITO) were made by sintering of nanoparticle dispersions. The resistivity decreased to 1–10-2 μcm upon treatment at 800°C, while the luminous transmittance remained high. The property evolution was connected with sintering and densification as studied by Scanning Electron Microscopy, X-ray Diffraction, X-ray Fluorescence and Elastic Recoil Detection Analysis.
Grain-Size-Dependent Thermal Transport Properties in Nanocrystalline Yttria-Stabilized Zirconia
Authors: Yang Ho-Soon , Eastman J.A. , Thompson L.J. , Bai G.-R.
Published: April 2011

Understanding the role of grain boundaries in controlling heat flow is critical to the success of many envisioned applications of nanocrystalline materials. This study focuses on the effect of grain boundaries on thermal transport behavior in nanocrystalline yttria-stabilized zirconia (YSZ) coatings prepared by metal-organic chemical vapor deposition.
Supersonic Nanocrystal Deposition for Nanostructured Materials
Authors: Nichols W.T. , O'Brien D.T. , Malyavanatham G. , Becker M.F. , Keto J.W.
Published: April 2011

We experimentally demonstrate the large scale production and controlled collection of metal and semiconductor nanocrystals by laser ablation of microparticles entrained at high density in a flowing aerosol. For silver, produced nanocrystals exhibit bimodal, log-normal size distributions. Mean particle sizes are controlled from 3-16 nm by varying the type and pressure of carrier gas as well as laser fluence. For collection, a micronozzle orifice (d = 200 [.mu]m) accelerates nanocrystals through a sonic jet into a vacuum chamber for deposition onto a room temperature substrate. We describe two regimes of deposition that depend on the nanocrystal's energy per atom on impact. Soft landings ( E << 1 eV/ atom) preserve the individual particle properties such as size and shape. Low energy impaction is demonstrated for CdSe in an argon carrier gas. The CdSe nanoclusters remain crystalline upon deposition and display visible photoluminescence. At higher particle impaction velocities (E ∼ 0.3 eV/atom) nanocrystals exhibit the onset of self sintering upon impact. At high number densities, adherent, conductive lines are formed from deposited silver nanocrystals. Line widths of 33 [.mu]m FWHM are directly written onto substrates using a 200 [.mu]m diameter nozzle.
Processing Effects on The Morphology of Hydrothermally Derived Nanocrystalline Lead Titanate
Authors: Ye Zhiyuan , Slamovich Elliott B. , King Alexander H.
Published: April 2011

Nanocrystalline lead titanate was synthesized by reacting nanocrystalline titanium oxide in aqueous solutions of potassium hydroxide and lead acetate at 200 degrees C. X-ray diffraction (XRD) and TEM studies suggest that the initial KOH concentration influenced the nucleation and growth behavior of the lead titanate nanoparticles. Powders were processed in aqueous solutions containing 0.10 M lead acetate and a Pb:Ti ratio of 1, with varying concentrations of KOH. Powders processed in 0.01 M KOH were composed of irregularly shaped particles with 50-100 nm in size, processing in 0.10 M KOH produced particles with finger-like morphology and broader particle size distribution, and processing in 1.0 M KOH resulted in anisometric plates with (001) facets, and 100-200 nm in size. XRD studies have shown systematic variations in the position and symmetry of reflections with a l component as a function of particle size. This indicates that the c/a ratio of lead titanate increases with decreasing nanoparticle size
Nanocomposite based on semiconductor oxides SnO2/WO3
Authors: Rumyntseva M.N. , Boulova M.N. , Chareev D.A. , Ryabova L.I. , Akimov B.A. , Gaskov A.M.
Published: April 2011

Nanocrystalline SnO2 and WO3 and nanocomposite with Sn:W ratio 1:9, 1:1, 9:1 were prepared by co-precipitation of α-stannic and tungstic acids. Phase composition and average crystallite size were determined from XRD data. Presence of the second component results in the reduction of the crystallites growth rate, giving rise to the enhancement of thermal stability of nano-scaled system. TGA data allowed to estimate the concentration νH2O of water adsorbed on nanocomposite effective surface. Maximal νH2O value and the highest resistance were observed for nanocomposite with Sn:W = 1:1. The temperature dependence of resistance R reveals its activation character. The current-voltage curves are interpreted in terms of electrochemical capacitor recharge.
Dispersion of Functionalized Nanoclay Platelets in an Amine-Cured Epoxy Resin System
Authors: Raghavan D. , Feresenbet E. , Yebassa D. , Emekalam A. , Holmes G.
Published: April 2011

Nanocomposites are a relatively new class of materials obtained by dispersing montmorillonite clay in a polymer matrix. Evidences from literature suggest that clay platelet dispersion during nanocomposite preparation and clay-matrix adhesion are major technical issues that need to be addressed in order to achieve the desired property enhancements in polymer-clay hybrid nanocomposites. We have studied the interaction of the organically functionalized clay with the epoxy resin by including along the chain structure functional groups that will facilitate interaction with the resin. Through conventional routes, functional molecules have been synthesized and deposited on to the clay surface. Both the functionalized and nonfunctionalized clay has been analyzed using thermal gravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). The exfoliation of nanoclay platelets in amine cured epoxy system has been studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM).
Innovative And Cost-Effective Microfabrication Of Nanoceramic Components
Authors: Nair Balakrishnan G.
Published: April 2011

An innovative and cost-effective processing technique has been developed at Ceramatec Inc for the microfabrication of ceramic components requiring very high dimensional tolerance. The materials system is a proprietary nanophase composition called CERCANAM (CERamatec CAstable NAno Material). Scanning electron microscopy revealed that CERCANAM components can be fabricated with dimensional tolerance as high as ± 2 [.proportional]m for surface features on the die that have dimensions about 1 mm. The process can also be modified to fabricate nanoporous ceramic components with very high surface areas. Components with retained surface areas as high as 67-82% of the starting powder were fabricated. The fabrication process does not involve a high-temperature sintering step, which eliminates the loss of surface area from high temperature sintering. It is anticipated that microcomponents fabricated with specific microstructures and properties will have applications in the optical fiber industry as interconnects, in the electronic packaging industry and the chemical industry.
3D Highly Oriented Nanoparticulate and Microparticulate Array of Metal Oxide Materials
Authors: Vayssieres Lionel , Guo Jinghua , Nordgren Joseph
Published: April 2011

Advanced nano and micro particulate thin films of 3d transition and post-transition metal oxides consisting of nanorods and microrods with parallel and perpendicular orientation with respect to the substrate normal, have been successfully grown onto various substrates by heteronucleation, without template and/or surfactant, from the aqueous condensation of solution of metal salts or metal complexes (aqueous chemical growth). Three-dimensional arrays of iron oxide nanorods and zinc oxide nanorods with parallel and perpendicular orientation are presented as well as the oxygen K-edge polarization dependent x-ray absorption spectroscopy (XAS) study of anisotropic perpendicularly oriented microrod array of ZnO performed at synchrotron radiation source facility.
Control of Nucleation to Realize High Density Si Nanoparticles on SiO2 Thin Films
Authors: Zhu Jian-hong , Leach W. Thomas , Ekerdt John G.
Published: April 2011

A non-thermal method to facilitate nucleation for subsequent thermal chemical vapor deposition of Si nanoparticles on SiO2/Si(001) with high density and uniform size is demonstrated. Submonolayers of Si adatoms are predeposited on SiO2/Si(001) substrates by hot-wire chemical vapor deposition with disilane in an UHV chamber. The nanoparticles are grown with a disilane pressure of 1×10-4 Torr at 550 °C. The Si nanoparticles density is increased and size distribution is narrowed by predeposition of Si adatoms when compared to thermal growth on bare SiO2/Si(001). The nanoparticles density can be controlled by the amount of Si adatom predeposition. 1.2×1012 cm-2 density and 5.5 nm size are demonstrated on SiO2/Si(001) under UHV-CVD conditions.
Indium Tin Oxide Nanoparticles Prepared by Chemical Vapor Synthesis
Authors: Brehm Joachim U. , Winterer Markus , Hahn Horst , Michael Günther , Gutsch Andreas
Published: April 2011

Nanoparticles of indium oxide, tin oxide and indium oxide doped with tin oxide (ITO) have been prepared by Chemical Vapor Synthesis, CVS (a modified CVD process), starting with In- (tmhd)3 as precursor. A modification of the CVS process using a novel radio-frequency reaction zone has been developed in order to avoid the rapid decomposition of the nanocrystalline indium oxide particles at high temperatures. These oxides are candidates for applications as transparent conducting oxides, catalysts and gas sensors. Structural characterization by high resolution scanning and transmission electron microscopy and X-ray-diffraction has been used to determine the phase, grain size, grain size distribution and crystallinity of the nanoparticles. The specific surface area, and particle or agglomerate size of the powders have been measured by nitrogen sorption. Agglomerate sizes in aqueous dispersions have been determined by photon correlation spectroscopy. Zeta-potentials were measured. As well CVS powders exhibit a narrow size distribution with an average size of about 5 nm.
Cu-Nanoclusters Produced on AuCu-Alloys with an Electrochemical Scanning Tunneling Microscope
Authors: Maupai S. , Dakkouri A.S. , Stratmann M. , Schmuki P.
Published: April 2011

Cu-nanoclusters can be produced in an electrochemical environment by tip-induced metal deposition using an electrochemical scanning tunneling microscope (EC-STM). These clusters, consisting of 100-1000 atoms only, show a surprising stability against anodic oxidation. The clusters, which are 2-3 atomic layers in height dissolve slowly when the applied potential is increased step by step to 200 mV positive of the reversible Nernst potential for “normal” copper dissolution. The presented work gives evidence that the unusual stability of the clusters could be a consequence of interfacial alloying between the cluster and the underlying substrate. In order to study these effects Cu-nanoclusters have been produced on pure gold substrates and on carefully prepared Au3Cu(111)-substrates. This work compares the results obtained on both substrates.
Microstructure of Carbon Encapsulated Superparamagnetic Co Nanoparticles
Authors: Sun Xiang-Cheng , Reyes-Gasga J. , Dong X. L.
Published: April 2011

Carbon encapsulated magnetic Co nanoparticles have been synthesized by modified arc-discharge method. Both high-resolution transmission electron microscopy (HREM) and powder x-ray diffraction (XRD) profiles reveal the presence of 8-15nm diameter crystallites coated with 1-3 carbon layers. Specially, HREM images indicate that the intimate and contiguous carbon fringe around those Co nanoparticles is good evidence for complete encapsulation by carbon shell layers. The encapsulated phases are identified as hcp (α)-Co, fcc (β)-Co and cobalt carbide (Co3C) nanocrystals by using x-ray diffraction, electron diffraction and energy dispersive x-ray analysis. However, some fcc (β)-Co particles with a significant fraction of stacking faults are observed by HREM and confirmed by means of numerical Fourier transform (FFT) of HREM lattice images. In particular, the carbon encapsulation formation and growth mechanism are also reviewed.
Encapsulation of Magnetic Particles in Metallic Hollow Nanospheres
Authors: Toprak M. , Kim D. K. , Mikhailova M. , Zhang Y. , Jeong Y. K. , Muhammed M.
Published: April 2011

Novel metallic capsules containing magnetite with given size in the sub-micron range have been produced. These nanocapsules are prepared in several steps through a colloidal templating approach. The first step is the synthesis of size-selected SiO2 nanospheres. The second step is coating the SiO2nanospheres by electroless deposition with gold, in order to form a porous gold shell around the silica. Electroless deposition is controlled by the concentration of gold in the coating solution. Subsequently, the core (SiO2) was removed to obtain gold capsules. The final step is the inclusion of magnetite nanoparticles inside these nanocapsules and recoating the capsules with gold in order to have continuous encapsulation. The nanocapsule and core-shell structure have been characterized by TEM and DSC
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.
Monitoring of Silicon Nano-Crystal Dots Formation on SiO2 and on Si3N4 in an UHV-CVD System
Authors: Kawashima Takayuki , Mashiro Supika , Sakai Junro , Rao Rajesh , Muralidhar R. , Nguyen Bich-Yen , White Bruce
Published: April 2011

Applicability of SPA (Surface Photo Absorption) as an in-situ monitor of Si nanocrystal formation was comparatively studied to a monitoring with pyrometer.

Although both SPA and pyrometer provide a signature of the Si nanocrystals nucleation and growth process as a function of irradiation time, SPA was found to be more sensitive to detect formation of desired nanocrystals on both SiO2 and Si3N4 surfaces. By using SPA as an in-situ monitor of nanocrystal formation, good repeatability of both nanocrystals' density and size was obtained on SiO2 and Si3N4 surfaces.
Role of Clay-Solvent Inter and Intraparticle Interactions on Swelling Characteristics of Montmorillonite Nano-Meso-Micro Scale Particulate Systems
Authors: Katti Dinesh R. , Katti Kalpana S. , Shanmugasundaram Vijayakumar
Published: April 2011

This paper deals with fundamental molecular issues related to macroscopic mechanical properties of nano-meso-microscale montmorillonite clay particulate systems. Molecular interaction of high aspect montmorillonite particles with solvents has large influence on resulting swelling characteristics in clays consisting of montmorillonite. A new controlled uniaxial swelling (CUS) cell is designed which allows a simultaneous measurement of swelling and swelling pressure in addition to ease of removal of undisturbed samples for electron microscopic and fourier transform infrared spectroscopic investigations. Our work shows that the swelling behavior of montmorillonite directly results from breakdown of large particles to smaller nano and meso scale particles with increased water incorporation in the interlayers. The Si-O vibration band regions of the montmorillonite spectra obtained at controlled amounts of swelling from 0-100% (where 0% swelling is defined as fully saturated samples under no volume change) show changes in band shape, intensity, and positions resulting from increased H-bonding in the interlayers and surface of montmorillonite particles. In addition, orientation dependant micro-attenuated total reflectance (ATR) spectroscopic investigations are also conducted on the controlled swelled samples. Our results indicate that the reduced particle size with increased swelling is related to increased misorientation of the montmorillonite platelets. The relationship between molecular interactions microstructure and macroscopic response (swelling and swelling pressure) is the key to development of novel nanocomposite systems based on montmorillonite with tailored properties.
Light Scattering by Isolated Nanoparticles with Arbitrary Shapes
Authors: Noguez Cecilia , Sosa Iván O. , Barrera Rubén G.
Published: April 2011

Using the Discrete Dipole Approximation we have studied the optical properties of different isolated nanoparticles with arbitrary shapes. We have investigated the main features in the optical spectra, depending of the geometry and size of such nanoparticles. We present and discuss our results in terms of the scattering, extinction and absorption optical coefficients, which can be directly compared with experiments. The results are discussed in terms of the optical signature of each nanoparticle depending of its size and shape.
Sensing Characteristics of Cubic and Rhombohedral Nanocrystalline ITO Thick Films
Authors: Huh Jeung-Soo , Kim Bong-Chull , Kim Jae-Yeol , Lim Jeong-Ok
Published: April 2011

Two kinds of nanocrystalline Tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) powders with different crystal structures – rhombohedral and cubic – were prepared using a coprecipitation method through the control of pH of a mixing solution and aging time after coprecipitation. The two powders have the same particle size of 15 nm in diameter but different morphologies (spherical for rhomboheral and rectangular for cubic). The gaseous ethanol sensing characteristics of the sensors prepared by the two ITO powders were quite different. The sensitivity of rhombohedral ITO sensor was high compared to that of the cubic ITO sensor across all temperatures. The reason for this is explained through the viewpoint of the binding energy of XPS and the surface structure relating to the crystal structure.
Fibers of Carbon Nanotubes
Authors: Vigolo Brigitte , Launois Pascale , Lucas Marcel , Badaire Stéphane , Bernier Patrick , Poulin Philippe
Published: April 2011

We briefly review some methods recently proposed to make films and fibers of preferentially oriented carbon nanotubes. We discuss in more detail a simple spinning process which consists in dispersing the nanotubes in a surfactant solution, re-condensing the nanotubes in the flow of a coagulating polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. We measure the mechanical properties of the obtained fibers and characterize the nanotube alignment along the fiber axis by X-ray scattering experiments. We show that the alignment can be improved by stretching the fibers under well-defined conditions. This allows the Young's modulus to be increased by a factor 4, leading thereby to materials forty times stronger than high-quality buckypaper. We believe that these improved fibers can already be potentially useful as functional materials. A simple example of electromechanical actuation is shown.
Large Cryogenic Storage of Hydrogen in Carbon Nanotubes at Low Pressures
Authors: Pradhan B. K. , Harutyunyan A. , Stojkovic D. , Zhang P. , Cole M. W. , Crespi V. , Goto H. , Fujiwara J. , Eklund P. C.
Published: April 2011

We report (6 wt %) storage of H2 at T=77 K in processed bundles of single-walled carbon nanotubes at P=2 atmospheres. The hydrogen storage isotherms are completely reversible. D2 isotherms confirm this anomalous low-pressure adsorption and further reveal the effects of quantum mechanical zero point motion. We propose that our post-synthesis treatment of the sample not only improves access for hydrogen to the central pores within individual nanotubes, but also may create a roughened tube surface with an enhanced binding energy for hydrogen. Such an enhancement is needed to understand the strong adsorption at low pressure. We obtain an experimental isosteric heat qst=125 ± 5 meV for processed SWNT materials.
Imaging Schottky Barriers at Carbon Nanotube Contacts
Authors: Freitag Marcus , Johnson A. T.
Published: April 2011

We use scanning gate microscopy to precisely locate the gating response in single-wall nanotube devices. Junctions of metallic and semiconducting nanotubes show a dramatic increase in transport current when they are electrostatically doped with holes at the junction. We ascribe this behavior to the turn-on of a reverse biased Schottky barrier. A similar effect is seen in field-effect transistors made from an individual semiconducting single-wall carbon nanotube. In this case, there are two Schottky barriers at the metal contacts, one of which is forward, and one of which is reverse biased. The gating action is only observed at the reverse biased Schottky barrier at the positive electrode. By positioning the gate near one of the contacts, we convert the nanotube field-effect transistor into a rectifying nanotube diode. These experiments both clarify the gating mechanism for nanotube devices and indicate a strategy for diode fabrication based on controlled placement of acceptor impurities at a nanotube field-effect transistor.
Electric Transport Properties and Percolation in Carbon Nanotubes / PMMA Composites
Authors: Benoit Jean-Michel , Corraze Benoit , Lefrant Serge , Bernier Patrick , Chauvet Olivier
Published: April 2011

Carbon nanotubes (CNT) possess remarkable physical properties. However, because of their size, they are difficult to handle. Making composites with them gives an alternative way to handle these objects and to make use of their properties at a macroscopic scale. Here, we present a comparative study of the transport properties of PMMA / nanotubes composite films with both SWNTs and MWNTs. At room temperature, the conductivity of the composites follows a pure percolation behavior when increasing the nanotube content. The universal scaling law for random site percolation with a very low percolation threshold (0.3 weight %) is obeyed over two orders of magnitude in CNT content. At low temperature, SWNTs and MWNTs based composites behave differently. While MWNTs composites still obey the percolation law, deviations are observed for SWNTs. The transport properties are discussed in terms of tube-tube contact and charging energy of the tubes.
Polymer-Single Wall Carbon Nanotube Composites for Potential Spacecraft Applications
Authors: Park Cheol , Ounaies Zoubeida , Watson Kent A. , Pawlowski Kristin , Lowther Sharon E. , Connell John W. , Siochi Emilie J. , Harrison Joycelyn S. , Clair Terry L. St.
Published: April 2011

Polymer-single wall carbon nanotube (SWNT) composite films were prepared and characterized as part of an effort to develop polymeric materials with improved combinations of properties for potential use on future spacecraft. Next generation spacecraft will require ultra-lightweight materials that possess specific and unique combinations of properties such as radiation and atomic oxygen resistance, low solar absorptivity, high thermal emissitivity, electrical conductivity, tear resistance, ability to be folded and seamed, and good mechanical properties. The objective of this work is to incorporate sufficient electrical conductivity into space durable polyimides to mitigate static charge build-up. The challenge is to obtain this level of conductivity (10-8 S/cm) without degrading other properties of importance, particularly optical transparency. Several different approaches were attempted to fully disperse the SWNTs into the polymer matrix. These included high shear mixing, sonication, and synthesizing the polymers in the presence of pre-dispersed SWNTs. Acceptable levels of conductivity were obtained at loading levels less than one tenth weight percent SWNT without significantly sacrificing optical properties. Characterization of the nanocomposite films and the effect of SWNT concentration and dispersion on the conductivity, solar absorptivity, thermal emissivity, mechanical and thermal properties were discussed. Fibers and non-woven porous mats of SWNT reinforced polymer nanocomposite were produced using electrospinning.
Interference of Electron Waves on Carbon Nanotubes at Room Temperature
Authors: Hassanien A. , Umek P. , Vrbanic D. , Mozetic M. , Venturini P. , Tokumoto M. , Mihailovic D. , Pejovnik S.
Published: April 2011

We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. At low bias voltage, topographic STM images show standing wave pattern of the charge density in the vicinity of nanotube ends. The patterns originate from constructive interference between the electronic states and its reflection on the nanotube tips. The modulations extend along 6-8 nm away from the cap. Atomically resolved images show asymmetry in the charge density that smears out as the bias voltage increases. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.
G-band Raman Spectra of Isolated Single Wal Carbon Nanotubes: Diameter and Chiraity Dependence
Authors: Jorio A. , Filho A. G. Souza , Dresselhaus G. , Dresselhaus M. S. , Swan A. K. , Ünlü M. S. , Goldberg B. B. , Pimenta M. A. , Hafner J. H. , Lieber C. M. , Saito R.
Published: April 2011

We present results from resonant Raman spectroscopy on the graphite-like G band by measuring Raman spectra on isolated single wal carbon nanotubes (SWNTs). We discuss the G-band lineshape dependence on nanotube diameter and chirality, as well as polarization studies related to the antenna effect. Symmetry selection rules, dipolar and multipolar antenna behaviors are discussed. Spectra at the single nanotube level are related to spectra observed from SWNT bundles.
Structure and Properties of C60@SWNT
Authors: Smith Brian W. , Russo Richard M. , Chikkannanavar S.B. , Stercel Ferenc , Luzzi David E.
Published: April 2011

Our recent achievement of high-yield C60@SWNT synthesis facilitates characterization by various techniques, including selected area electron diffraction (SAD) and Raman spectroscopy. The obtained SAD patterns show that interior C60 molecules sit on a simple 1-D lattice having a parameter of 1.00 nm. Simulated SAD patterns and real-space measurements both support this determination and do not indicate a lattice with a more complex basis, e.g. a dimer basis. Empty and bulk-filled SWNTs (22%, 56%, and 90% yields), each subjected to identical processing steps, were examined by room temperature Raman spectroscopy. Systematic differences are seen between the spectra of filled and unfilled SWNTs, particularly with respect to the G- and RBM-bands of the nanotubes. We present a possible explanation for this behavior.
Filling Single Wall Carbon Nanotubes with Metal Chloride and Metal Nanowires and Imaging with Scanning Transmission Electron Microscopy
Authors: Chikkannanavar Satishkumar B. , Taubert Andreas , Luzzi David E.
Published: April 2011

Nanowires of magnetic metals (Ho, Gd) have been synthesized inside the hollow interior of single wall carbon nanotubes by the sealed-tube reaction. Amongst the d- and f-series metal chlorides investigated in this study, HoCl3 and GdCl3 fill the SWNTs to a significantly higher extent than FeCl2 and CoCl2. HoCl3 and GdCl3 nanowires have been transformed into the respective metal nanowires via the reduction of the chloride nanowires. The nanowires have been imaged using high-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM). X-ray energy dispersive spectroscopy carried out in conjunction with STEM confirmed the presence of metal chloride and metal nanowires.
A Novel Class of Carbon Nanocones
Authors: Dimovski Svetlana , Libera Joseph A. , Gogotsi Yury
Published: April 2011

A new class of low-angle conical carbon crystals has been described and their characteristics are reported here. These carbon nanocones were found in pores of a glassy carbon (GC) along with cylindrical multiwall nanotubes and graphite polyhedral crystals. The largest cones reach 2 to 3 microns in length, although most are in the submicron range. Scanning Electron Microscopy (SEM) reveals cones protruding from the inner pore surfaces with the tips oriented toward the inside of the pores. Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) show that cones are made of thick (up to several hundred layers), highly-ordered graphitic walls. Their tips are graphitic as well, and exhibit a dome-like morphology. These cones also differ from any carbon cones observed earlier in that they have a much smaller apex angle, sometimes less than 3°. Small angle carbon nanocones can potentially be used for probes and field emission elements.
Li Uptake in Carbon Nanotube Systems: A First Principles Investigation
Authors: Meunier Vincent , Kephart Jeremy , Roland Christopher , Bernholc Jerry
Published: April 2011

Carbon nanotube systems can substantially increase their capacity for Li ion uptake, provided that the nanotube interiors become accessible to the ions. We examine theoretically, with ab initio simulations, the ability of Li ions to enter a nanotube interior. While our calculations show that it is quite unlikely for the ions to pass through pristine nanotubes, they are much more likely to enter via large-sized topological defects consisting of at least 9- or more membered rings. It is unlikely that such defects are formed spontaneously, but it may be possible to induce such topological defects by violent non-equilibrium means such as ball milling, chemical means and/or ion bombardment. Indeed, recent experiments on ball milled nanotube samples do report an important increase in the Li ion uptake.
Model Narrow Nanotubes Related to C36, C32 and C20: Computationa Insight
Authors: Slanina Zdeněk , Uhlík Filip
Published: April 2011

Very recently, narrow nanotubes have been observed with a diameter of 5 Å and even with a diameter of 4 Å. It has been supposed that the narrow nanotubes are closed by fragments of C36 and C20 fullerenes. The contribution reports computations on related model nanotubes with stoichiometries like C84, C96 or C80. Computations are carried out at the PM3 (Parametric Method 3), SaM1 (Semi-Ab-Initio Model 1), HF/4-31G (Hartree-Fock SCF approach with the standard 4-31G basis set), and B3LYP/6-31G* (Becke's three parameter functional with the non-local Lee-Yang-Parr correlation functional using the standard 6-31G* basis set) levels, though the geometry optimizations are performed only at the semiempirical levels. Two C36 fullerenes are considered, D6h and D2d, and, for example, at the PM3 level and with the C84 nanotube stoichiometry the D2d cage closure gives a lower energy (by 185 kcal/mol and diameter of 5.42 Å). There is another possible candidate, C32 cage with a D4d symmetry. At the PM3 level and with the C96 nanotube stoichiometry the D4d closure has the nanotube enrgy lower by 210 kca/mol (with the nanotube diameter of 5.43 Å) compared to the D6h nanotube closure. On the other hand, four-membered rings should not play a significant role in the narrow nanotubes with the diameter of 4 Å, where the dodecahedron-related closure should be exclusive as a four-membered ring containing structure is located already much higher in energy.
D-band Raman Spectra of Graphite and Single Wall Carbon Nanotubes
Authors: Saito R. , Grueneis A. , Cançcado L. G. , Pimenta M. A. , Jorio A. , Filho A. G. Souza , Dresselhaus G. , Dresselhaus M. S.
Published: April 2011

The double resonance Raman spectra of the disorder-induced D-band and some other non-zone-center phonon modes are discussed for two-dimensional (2D) graphite and to some extent for single wall carbon nanotubes (SWNTs). The phonon dispersion relations of graphite can be determined using Raman spectroscopy b y measuring the non-zone center Raman phonon frequencies in combination with theoretically determined phonon q-vectors. We report a t of the phonon dispersion relations to experimental Raman spectra which were previously observed but have not y et been assigned to speci c phonon branches. We found that the D-band and the G0-band of 2D graphite consist of, respectively, two and one Raman Lorentzian peaks, while 3D graphite shows two G0-band Lorentzian peaks. The appearance of two G0 peaks in the resonance Raman spectra of SWNTs may come from resonances of one laser line with two di erent van Hov e singularities.
Surface and Interfacial Properties in Thin Poly(p-Phenylene vinylene) Multilayers Prepared by Self-Assembly Method
Authors: Borges Célio A. M. , Marletta Alexandre , Faria Roberto M. , Guimarãaes Francisco E. G.
Published: April 2011

In this work we report on the influence of interfaces (metal/film, ITO/film) on the optical properties of ultrathin layers of poly(-phenylene vinylene), PPV, adsorbed by self-assembly. PPV films were prepared exploiting the self-assembly method (SA) in addition to a low temperature conversion process for PPV. Using atomic force microscopy we show that 0.5 nm thick PPV layers can be homogeneously deposited on different metals (50% transmission Au, Cu, Pt, Ag, Cr films), glass and ITO surfaces. Absorption measurements reveal that the transitions involving φ-φ conjugated states are blue shifted to different extents depending on the interface and on the film thickness. This indicates different extensions of interfacial disorder in the PPV layers. The ITO/PPV interface has the highest extension for disorder (∼16 nm) and highest surface roughness (RMS∼2.5 nm) while the lowest values (∼5 nm and 0.6 nm, respectively) were found for the quartz/PPV interface. The metal interface induces significant luminescence quenching and spectral shifts, which depend on the type of metal used. The effect from incorporation of carbonyl and from chemical modifications of the ITO/organic interface during PPV thermal conversion is discussed.
Hole Transport in Self-Organized Oligosilane Thin Films with Highly Ordered Hopping Sites
Authors: Okumoto H. , Yatabe T. , Richter A. , Shimomura M. , Kaito A. , Minami N.
Published: April 2011

Self-organized oligosilane thin films possess molecular orientation normal to substrates with multilayered structure. This unique order of σ-conjugated molecules results in good hole transport properties. In the present work, carrier transport properties at low temperature are studied for 1,10-diethyldecamethylsilane polycrystalline films. Even at a temperature as low as 173 K, a time-of-flight transient photocurrent waveform showed a clear plateau and a sharp decay, whose shape is similar to that at room temperature. Their hole mobility followed Arrhe-nius type temperature dependence with a small activation energy of 0.09 eV. The hole mobility of 6.3×10-5cm-2/Vs at 193 K was more than 2 orders of magnitude higher than that of typical polysilanes, which inevitably contain disordered structures hindering smooth carrier transport.
In Situ Measurement of the Second Harmonic Signal of Adsorbing Nonlinear Optical Ionically Self-Assembled Monolayers.
Authors: Brands C. , Neyman P.J. , Guzy M.T. , Shah S. , Van Cott K.E , Davis R.M. , Wang H. , Gibson H.W. , Heflin J.R.
Published: April 2011

Ionically self-assembled monolayers (ISAMs) have recently been shown to spontaneously exhibit a polar ordering that gives rise to substantial second order nonlinear optical response. The deposition of ISAMs has been studied in situ via second harmonic generation. This is a particularly sensitive probe of the growth of nanometer-thick films since the centrosymmetry of the immersion solutions, the substrate, and the container yields no SHG contribution from these bulk components. Upon immersion in the NLO-active polyelectrolyte solution, the SHG rises sharply over the first minute. When a film is immersed into salt water, the SHG decreases significantly only to be restored when the salt solution is replaced with deionized water.
Enhanced Photoluminescence from Long Wavelength InAs Quantum Dots Embedded in a Graded (In,Ga)As Quantum Well
Authors: Chen L. , Stoleru V. G. , Pan D. , Towe E.
Published: April 2011

Three sets of self-organized InAs quantum dots (QDs) embedded in an external InGaAs quantum well samples were grown by solid source molecular beam epitaxy (MBE). By modifying Indium composition profile within quantum well (QW) region, it's found the photoluminescence emission from quantum dots can be greatly enhanced when employing a graded quantum well to surround QDs. This quantum dots in a graded quantum well structure also preserves the long wavelength (1.3 μm) spectrum requirement for the future use in optoelectronics devices.
Atomic Self-Ordering in Heteroepitaxially Grown Semiconductor Quantum Dots Due to Relaxation of External Lattice Mismatch Strains
Authors: Möck Peter , Topuria Teya , Browning Nigel D. , Nicholas Robin J. , Booker Roger G.
Published: April 2011

Thermodynamic arguments are presented for the formation of atomic order in heteroepitaxially grown semiconductor quantum dots. From thermodynamics several significant properties of these systems can be derived, such as an enhanced critical temperature of the disorder-order transition, the possible co-existence of differently ordered domains of varying size and orientation, the possible existence of structures that have not been observed before in semiconductors, the occurrence of atomic order over time, and the occurrence of short range order when the growth proceeds at low temperatures. Transmission electron microscopy results support these predictions. Finally, we speculate on the cause for the observed increase in life time of (In,Ga)As/GaAs quantum dot lasers [H-Y. Liu et al., Appl. Phys. Lett. 79, 2868 (2001)].
Self-Assembled Structures of Gas-Phase Prepared FePt Nanoparticles
Authors: Rellinghaus Bernd , Stappert Sonja , Acet Mehmet , Wassermann Eberhard F.
Published: April 2011

We report on a non-lithographic method for the preparation of self-assembled FePt nanoparticles via inert-gas condensation. Prior to deposition the particles can be sintered in flight at temperatures as high as TS = 1273 K. Whereas un-sintered particles have irregular shapes, particles sintered at elevated temperatures TS ≤ 793 K show a regular faceting. (High resolution) transmission electron microscopy ((HR)TEM) shows that these regularly faceted particles are of icosahedral structure. When being deposited onto amorphous carbon films, the gas-phase sintered particles are found to have a high mobility. In particular, for the high-temperature sintered FePt nanoparticles, we observe that this mobility leads to the formation of particle arrays with hexagonal close-packed arrangements. Within these ordered patches, the particles are separated from one another. Analytical investigations using energy filtered TEM (EFTEM) show that a carbon layer is formed between the particles. Magnetization analyses give results showing that the gas-phase sintered particles are superparamagnetic at room temperature with a blocking temperature of TB = 49K.
Liquid Crystal Optical Phase Modulators for Beam Steering
Authors: Stockley Jay , Xia Xiaowei , Ewing Teresa , Serati Steve
Published: April 2011

Beamsteering using liquid crystals can be achieved with refractive or diffractive implementations. The common thread in these various structures is that the liquid crystal is employed as an optical phase modulator. Either nematic or smectic liquid crystal phases can be used to shift the phase of light and steer an optical beam. Various liquid crystal optical phase modulating schemes will be described. Examples include polarization independent and quasi-achromatic modulators. Model predictions and experimental results demonstrating the optical phase modulation and beamsteering made possible using different liquid crystal based designs will be presented.
Capillary Instabilities in a Thin Nematic Liquid Crystalline Fiber Embedded in a Viscous Matrix
Authors: Cheong Ae-Gyeong , Rey Alejandro D.
Published: April 2011

Linear stability analysis of capillary instabilities in a thin nematic liquid crystalline cylindrical fiber embedded in an immiscible viscous matrix is performed by formulating and solving the governing nemato-capillary equations, that include the effect of interfacial viscous shear forces due to flow in the viscous matrix. A representative axial nematic orientation texture is studied. The surface disturbance is expressed in normal modes, which include the azimuthal wavenumber m to take into account non-axisymmetric modes. Capillary instabilities in nematic fibers reflect the anisotropic nature of liquid crystals, including the orientation contribution to the surface elasticity and surface bending stresses. Surface gradients of bending stresses provide additional anisotropic contributions to the capillary pressure that may renormalize the classical displacement and curvature forces that exist in any fluid fiber. The exact nature (stabilizing and destabilizing) and magnitude of the renormalization of the displacement and curvature forces depend on the nematic orientation and the anisotropic contribution to the surface energy, and accordingly capillary instabilities may be axisymmetric or non-axisymmetric, with finite or unbounded wavelengths. Thus, the classical fiber-to-droplet transformation is one of several possible instability pathways while others include surface fibrillation. The contribution of the viscosity ratio to the capillary instabilities of a thin nematic fiber in a viscous matrix is analyzed by two parameters, the fiber and matrix Ohnesorge numbers, which represent the ratio between viscous and surface forces in each phase. The capillary instabilities of a thin nematic fiber in a viscous matrix are suppressed by increasing either the fiber or matrix Ohnesorge number, but estimated droplet sizes after fiber breakup in axisymmetric instabilities decrease with increasing matrix Ohnesorge number.
Photorefractive Effect in Nematic Liquid Crystal Cell with Sandwiched Structure
Authors: Kim Hyun-Wuk , Kim Jong-Duk
Published: April 2011

Optical responses and orientational photorefractivities of nematic liquid crystal cells doped with fullerene were investigated with a sandwiched structure. The photorefractive effect was attributed to the reorientation and switching of liquid crystals using a photoalignment layer for vertical alignment. When nematic liquid crystals were injected at a nematic phase, a better cell texture could be obtained due to the capillary flow-induced orientation effect. Samples with this method showed the higher photorefractive effects than those injected at an isotropic phase. Therefore, the state of molecular ordering is important for the orientational photorefractive effects.