bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model Narrow Nanotubes Related to C36, C32 and C20: Computationa Insight
Authors: Slanina Zdeněk , Uhlík Filip 
Published: April 2011

AbstractVery 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

AbstractThe 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

ABSTRACTIn 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

ABSTRACTSelf-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

ABSTRACTIonically 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

ABSTRACTThree 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

ABSTRACTThermodynamic 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

ABSTRACTWe 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

ABSTRACTBeamsteering 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

ABSTRACTLinear 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

ABSTRACTOptical 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.
A Novel Polymer Patterning Method based on Pattern Forming States of Liquid Crystals as Templates
Authors: Kang Shin-Woong , Sprunt Samuel , Chien Liang-Chy 
Published: April 2011

ABSTRACTWe describe a new polymer patterning technique that produces controllable morphological and optical anisotropy in a polymer network. This technique is based on the use of pattern-forming states of nematic and cholesteric liquid crystals as templates for forming ordered polymer networks. One and two-dimensional optical patterns are induced by applying an electric field across a narrow gap of an electro-optical cell. These field-induced optical patterns are then stabilized by UV-induced polymerization of a typically 5 wt% reactive monomer in liquid crystal host. Depending on specific conditions (e.g., thickness to pitch ratio of a cholesteric, applied electric field, and wavelength of UV illumination), the polymer captures various degrees of the orientational order and spatial periodicity of the pattern-forming states of liquid crystals. The fidelity of the templating effect is explored using polarizing optical microscopy and SEM. We also describe the effect of UV wavelength on the network morphology and the morphological control over the”third” dimension (normal to the cell substrates).
Holographic Polymer Dispersed Liquid Crystals: Effect of Partial Matrix Fluorination on Electro-Optical and Morphological Properties
Authors: Schulte Michael D. , Clarson Stephen J. , Natarajan Lalgudi V. , Guymon C. Allan , Bunning Timothy J. 
Published: April 2011

ABSTRACTHolographic polymer dispersed liquid crystal (H-PDLC) films with partially fluorinated matrices were investigated. Electro-optical and morphological studies revealed that fluorinated composites were substantially different from non-fluorinated analogues. The addition of a fluorinated monofunctional acrylate monomer to a pentaacrylate-derived polymer matrix resulted in improved diffraction efficiency. These findings suggest that the partial fluorination of the host polymer decreases the compatibility between the matrix and liquid crystal phase. Morphological differences between fluorinated films and non-fluorinated control specimens were verified using low-voltage, high-resolution scanning electron microscopy (LVHRSEM).
Theory and Simulation of Fiber Texture Formation and Rheology of Carbonaceous Mesophase Fibers
Authors: Rey A. D. 
Published: April 2011

ABSTRACTCarbonaceous mesophases are discotic nematic liquid crystals that are spun into high performance carbon fibers using the melt spinning process. The spinning process produces a wide range of different fiber textures and cross-sectional shapes. Circular planar polar (PP), circular planar radial (PR) textures, ribbon planar radial (RPR), and ribbon planar line (RPL) textures are ubiquitous ones. This paper presents, solves, and validates a model of mesophase fiber texture formation based on the classical Landau-de Gennes theory of liquid crystals, adapted here to carbonaceous mesophases. The effects of fiber cross-sectional shape and elongational flow on texture formation are characterized. Emphasis is on qualitative model validation using existing experimental data [1, 2]. The results provide additional knowledge on how to optimize and control mesophase fiber textures.
Film Thickness Effects on Interfacial Fracture of Epoxy Bonds
Authors: Moody N. R. , Bahr D. F. , Kent M. S. , Emerson J. A. , Reedy E. D. 
Published: April 2011

ABSTRACTNanoindentation test techniques were combined with deposition of highly stressed overlayers to study the interfacial fracture susceptibility of spin coated Epon 828/T403 on aluminized glass substrates as a function of film thickness. The test techniques required to induce fracture differed between samples. Nevertheless, the resulting interfacial fracture energies decreased monotonically with film thickness to a value near 0.5 J/m2. This value is higher than the ‘true work of adhesion' for uncured epoxy oliogomers on a methyl-terminated aluminum surface. However, it may indicate that we have irreversible specific interactions such as hydrogen bonding. Then 0.5 J/m2 may be near the fundamental value for such an interaction, or the ‘practical work of adhesion’.
Application of Self Assembled Monolayer Approach to Probe Fiber Matrix-Adhesion
Authors: Feresenbet E. , Raghavan D. , Holmes G. A. 
Published: April 2011

ABSTRACTAdhesion at the fiber-matrix interface of composites is often related to a combination of factors such as mechanical interlocking, physico-chemical interactions, and chemical bonding of the fiber-matrix interphase region. We demonstrate the use of self-assembled monolayer (SAMs) approach for depositing silane coupling agent on glass fiber and studying the impact of the individual interactions on the adhesion process. Through some unique chemistry, functionalized and non-functionalized C11 chlorosilanes were deposited on to E-glass fiber and modified. The adhesion of diglycidyl ether of bisphenol-A (DGEBA) cured with meta-phenylene diamine (m-PDA) to SAM layer on E-glass fibers was measured by performing single fiber fragmentation tests (SFFT). The extent of adhesion between the fiber and matrix was found to be dependent on carbon chain length of coupling agents, and the functional group at the end of the SAMs layer. Furthermore, the contributions to adhesion by physico-chemical interaction and covalent bonding has been individually assessed.
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. , Guimarães Francisco E. G. 
Published: April 2011

ABSTRACTIn this work we report on the influence of interfaces (metal/film, ITO/film) on the optical properties of ultrathin layers of poly(p-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.
Emission Light from Prism/Silver/Molecular Ultrathin Films and Excitations of Multiple Surface Plasmons in ATR Kretschmann Configuration
Authors: Kaneko Futao , Nakano Takayuki , Sato Toshiharu , Shinbo Kazunari , Kato Keizo , Kawakami Takahiro , Wakamatsu Takashi 
Published: April 2011

ABSTRACTEmission light through the prism has been investigated from the Kretschmann configuration of the prism/ Ag thin film/ rhodamine-B (RB) LB film in the resonant excitation of the attenuated total reflection (ATR) measurement. The emission light and the spectra strongly depended upon the emission angles where the light was observed. The emission properties corresponded to the dispersion relation of the resonant excitations of surface plasmons (SPs) in the ATR configuration. It was concluded that the emission light was caused by multiple excitations of SPs in the ATR configuration. It is thought that the phenomenon will be used as a new sensing device.
Dielectric Properties of Multi-Layer High-K Polymer Composite Films
Authors: Sakai Wataru , Chiang C. K. 
Published: April 2011

ABSTRACTThe electrical properties of thin polymer films are key parameters in the design of both smaller and faster circuit devices in the microelectronics industry. In this study, we made a three-layer film structure, ABA', to investigate the dielectric interaction between two high-K dielectric polymer thin films, A and A', as a function of the thickness of the middle B layer. The Cole-Cole plot showed clear changes with the thickness of the middle B layer. The total capacitances were evaluated with a simple serial three capacitances model. This ABA' structure is thought to be very useful for studying mechanical and thermal properties of thin polymer film system.
Modelling of the Thin Organic Film/Carbon Steel Interface
Authors: Popa Mihai V. , Drob Paula , Vasilescu Ecaterina , Anghel Maria , Rosca Iulia Mirza , Lopez Agustin Santana 
Published: April 2011

ABSTRACTThe electrochemical impedance spectroscopy (EIS) has been used for the modelling of the alkyd organic film/carbon steel interface in 3% NaCl solution. Both the dielectric properties of the organic film and the corrosion processes of the metallic substrate were investigated with this method. Analysis of the impedance spectra (Nyquist and Bode plots) and the interpretation with the fitting software developed by Boukamp, established the presence of two time constants in the first 250 immersion hours. One time constant concerning the organic layer describes the electrical and barrier properties of film. The second time constant concerning the substrate represents the corrosion reactions at the film/metal interface. For long immersion periods, after the formation of the conductive pathways in the film and the development of the diffusion processes, are necessary another two time constants concerning these phenomenons. The error magnitude between the measured and calculated data with these electric equivalent circuits is satisfactory. The physical properties obtained from the principal elements of the equivalent electric circuits are in concordance with those obtained from others testing methods.