bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractNanoparticles 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

AbstractCu-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

AbstractCarbon 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

AbstractNovel 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

AbstractNovel 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

AbstractApplicability 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

AbstractThis 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

AbstractUsing 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

AbstractTwo 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

AbstractWe 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

AbstractWe 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

AbstractWe 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

AbstractCarbon 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

AbstractPolymer-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

AbstractWe 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

AbstractWe 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

AbstractOur 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

AbstractNanowires 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

AbstractA 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

AbstractCarbon 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.