bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dispersion and Alignment of Carbon Nanotubes in Polycarbonate
Authors: Sennett Michael , Welsh Elizabeth , Wright J. B. , Li W. Z. , Wen J. G. , Ren Z. F. 
Published: April 2011

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

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

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

AbstractSingle-wall carbon nanotubes have been synthesized, purified, attested with a high resolution electron microscopy and Raman scattering and deposited by liquid electrophoresis onto different substrates (including a metallized glass) to produce the effective and homogeneous film cathodes for low-field electron emitters. The emission properties (a threshold of the emission switching on, a current value, a time-stability) of the SWNT cathodes have been investigated. A prototype of a phosphorescent lamp with a nanotube cathode has been designed. The Raman spectra of the SWNT cathode registered in situ from the shining lamp have shown no temperature increase and time-degradation of the nanotube material during the emission process.
Quantum Transport in Nanotube-Based Structures
Authors: Nardelli M. Buongiorno , Fattebert J.-L. , Bernholc J. 
Published: April 2011

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

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

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

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

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

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

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.
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.
Orientation of Ferroelectric Liquid Crystals by Self-Assembled Bilayer Molecular Assembly
Authors: Jain Sukhmal C. , Dixit Vivechana , Tanwar Vinod K. , Shivaprasad S. M. 
Published: April 2011

ABSTRACTMolecular films of amino propyl triethoxy silane (APTES) attached with cinnamoyl moieties were deposited on indium tin oxide (ITO) coated glass and quartz substrates by self-assembly technique. The deposition of the monolayer films resulted in a large change in the wettability of the substrates. X-ray photoelectron spectroscopy (XPS) and UV-spectroscopy were used to study the structure and properties of the grown films. The molecular assembly was photodimerized by irradiating it with a linearly polarized UV-light. Thus created polymer-solid interface has been shown to produce good, stable planar orientation of ferroelectric liquid crystal mixtures. The electro-optical and switching properties of the ferroelectric liquid crystal cells have been investigated and found to be quite similar to those prepared in conventional manner.
Light-Controllable Chiral Photochromic Multifunctional Liquid Crystal Polymers
Authors: Shibaev Valery P. , Bobrovsky Alexey Yu. , Boiko Natalia I. 
Published: April 2011

ABSTRACTA new family of light-controllable chiral photochromic multifunctional liquid crystalline (LC) side-chain acrylic polymers consisting of nematogenic, chiral and photochromic monomer units was obtained. The new principle of photoregulation of the helical supramolecular structure and optical properties of the binary and ternary chiral photochromic LC polymers based on the change of helical twisting power of the chiral photochromic monomer units was developed. The features of photooptical behaviour of LC polymers possessing the dual photochromism and the peculiarities of optical data recording based on the photochemical spectral gap burning were presented and discussed. The synthesized polymers are shown to be promising candidates for colour data recording and storage.
A Molecular Dynamics Simulation Study of the Nonlinear Optical Response of Liquid Crystalline Systems
Authors: Kiyohara Kenji , Ohta Koji , Shimizu Yo 
Published: April 2011

ABSTRACTWe investigated the third-order nonlinear optical response of a Gay-Berne system at the isotropic, nematic, and smectic phases by molecular dynamics simulation. The components of the optical response were calculated for the three different axes with respect to the director of the system, separately. In the nematic phase, in particular, we observed that the response function does not vanish at long times. This means that the orientation of the director of the system is permanently changed by an instant irradiation of polarized light, as a result of third-order nonlinear optical response. In the smectic phase, however, all the components of the response function decay quickly. Our results give a theoretical background at molecular level on the interpretation of the reported experimental observations of peculiar dynamics of liquid crystalline systems at irradiation of laser lights.
Investigation of Polymer Stabilized Liquid Crystal Formation Using Fluorinated and Aliphatic Monoacrylates
Authors: McCormick Demetrius , Guymon C. Allan 
Published: April 2011

ABSTRACTThis study focuses on the photo-polymerization of a fluorinated monoacrylate monomer and aliphatic analog within a room temperature smectic liquid crystal (LC) in an effort to understand how factors such as LC order, monomer segregation, and monomer chemical structure affects the polymerization mechanism in polymer stabilized liquid crystalline systems (PSLC). Specifically, a fluorinated monoacrylate exhibits significantly enhanced polymerization rates when compared to an aliphatic monoacrylate. Moreover, this rate enhancement is particularly pronounced in the smectic phase of the LC, where the fluorinated monoacrylate displays a polymerization rate in the smectic phase that is over three times faster than the aliphatic monoacrylate in the smectic phase. Also the fluorinated monoacrylate exhibits enhanced segregation between the smectic layers of the LC both before and after polymerization, whereas the aliphatic monoacrylate phase separates during polymerization. The results of this study demonstrate how changes in the monomer chemical structure (i.e. fluorination) can significantly impact the polymerization mechanism and segregation in polymer stabilized systems. This study also offers the potential to further the understanding of tailoring these unique systems for display applications.
Structure properties Relationships of Dendritic and Multipodal Liquid Crystal Materials based on Carbosilazane Cores
Authors: Elsäßer R. , Martin D. Rodriguez , Richardson R. M. , Photinos D. J. , Goodby J. W. , Veith M. , Mehl G. H. 
Published: April 2011

ABSTRACTThe synthesis of the first inorganic-organic hybrid liquid crystal dendrimers based on carbosilazane cores, which exhibit enantiotropic nematic and smectic C and columnar phase behaviour is presented and the liquid-crystalline phase properties and the phase structures are discussed.
Semifluorinated Polymeric Liquid Crystals as A Mechanistic Tool to Study The Effects of Interfacial Energies on The Orientation of Liquid Crystals
Authors: Perahia Dvora , Traiphol Rakchart , Smith Dennis W. 
Published: April 2011

ABSTRACTObtaining spontaneous orientation and fast collective response of ultra thin liquid crystalline (LC) layers to external stimuli without memory effects, is one of the major challenges in achieving the next generation of LC devices. The relationship between interfacial energies, structure and dynamics of support layers and their effects on surface orientation of liquid crystals has been investigated. A model polymeric system, containing a mesognic group, α- methylstilbene as anchoring group, bridged by an energy controlling moiety, fluorocyclobutyl, has been used to obtain substrates with controlled surface energy and structure. Neutron reflectivity was used to study the surface structure of the polymer. The orientation of a well characterized liquid crystal, 8CB that exhibits both nematic and Smectic phases, was studied by optical microscopy and small angle X-ray scattering. Correlation between the surface structure of the polymeric layer and the orientation of the Smectic phase indicated direct correlation between the surface orientation and the concentration of fluorine at the interface.
Characterization of Thin Polymer Blend Films using ESEM – No Charging, No Staining.
Authors: Bache Ian C. , Ramsdale Catherine M. , Thomas D. Steve , Arias Ana-Claudia , MacKenzie J. Devin , Friend Richard H. , Greenham Neil C. , Donald Athene M. 
Published: April 2011

ABSTRACTCharacterising the morphology of thin films for use in device applications requires the ability to study both the structure within the plane of the film, and also through its thickness. Environmental scanning electron microscopy has proved to be a fruitful technique for the study of such films both because contrast can be seen within the film without the need for staining (as is conventionally done for electron microscopy), and because cross-sectional images can be obtained without charging artefacts. The application of ESEM to a particular blend of relevance to photovoltaics is described.
The Use of Aqueous Enzymatic Polymerization of Amphyphilic Alkyl Tyrosine Derivatives as Environmentally Benign Coatings in the Microelectronics Industry
Authors: Angelopoulos Anastasios P. , Marx Kenneth A. , Oh Kyoung S. 
Published: April 2011

ABSTRACTThe surface coating properties of enzymatically polymerized decyl esters of d-tyrosine from aqueous solutions onto gold surfaces have been investigated utilizing the complementary techniques of Potentiometeric Titration, UV-VIS Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). The aqueous-based coatings are of interest as environmentally friendly and cost-effective replacements for epoxy-based coatings currently employed in the microelectronics industry for both chemical protection and electrical insulation of gold-covered metallic conductors. Experimental results with respect to polymerization pH, immersion pH, and immersion time are presented and compared to the ionization behavior of the monomers in solution. Optimum processing conditions have been established, which yield uniform aqueous-based polymeric coatings on gold conductor surfaces.
Secondary Ion Mass Spectroscopy Study of Failure Mechanism in Organic Light Emitting Devices
Authors: Ke Lin , Zhang Keran , Kumar Ramadas Senthil , Chua Soo Jin , Yakovlev Nikolai 
Published: April 2011

ABSTRACTSecondary ion mass spectroscopy is used to examine the dark, non-emissive defects on the organic light-emitting device. Boundary movements are originated from electrode imperfection. Due to flexibility and movability of polymer layer, distribution variations and a more severe Indium and Calcium overlapping are detected in dark spot defect area. Boundary movements are not in good agreement between different layers. Interfaces became undulate. The closeness and proximity between the In sharp spikes and cathode metal protrusion leads to the initial point of dark spot. We demonstrate that the presence of cathode imperfection and interface roughness of different layers correlated to the device dark spot formation.
Molecular Dynamics Studies on the Effects of Water Speciation on Interfacial Structure and Dynamics in Silica-Filled PDMS Composites
Authors: Gee Richard H. , Maxwell Robert S. , Dinh Long N. , Balazs Bryan 
Published: April 2011

ABSTRACTSignificant changes in materials properties of siloxane based polymers can be obtained by the addition of inorganic fillers. In silica-filled polydimethylsiloxane (PDMS) based composites the mechanism of this reinforcing behavior is presumably hydrogen bonding between surface hydroxyls and backbone siloxane species. We have chosen to investigate in detail the effect of chemisorbed (hydroxyls) and physisorbed water on the interfacial structure and dynamics in silica-filled PDMS based composites. Toward this end, we have combined molecular dynamics simulations and experimental studies employing DMA and NMR analysis. Our results suggest that the polymer-silica contact distance and the mobility of interfacial polymer chains significantly decreased as the hydration (hydroxyl and/or physisorbed water) level at the interface was reduced. The reduced mobility of the PDMS chains in the interfacial domain reduced the overall motional properties of the polymer, thus causing an effective "stiffening" of the polymer matrix. The role of the long-ranged Coulombic interactions on the structural features and chain dynamics of the polymer were also examined. Both are found to be strongly influenced by the electrostatic interactions as identified by the bond orientation time correlation function and local density distribution functions. These results have important implications for the design of nanocomposite silica-siloxane materials.