bluuebunny/crossref_metadata_2025 huggingface dataset:
The density factor in the synthesis of carbon nanotube forest by injection chemical vapor deposition
Authors: Call R. W. , Read C. G. , Mart C. , Shen T.-C.
Published: December 2012

Beneath the seeming straight-forwardness of growing carbon nanotube (CNT) forests by the injection chemical vapor deposition (CVD) method, control of the forest morphology on various substrates is yet to be achieved. Using ferrocene dissolved in xylene as the precursor, we demonstrate that the concentration of ferrocene and the injection rate of the precursor dictate the CNT density of these forests. However, CNT density will also be affected by the substrates and the growth temperature which determine the diffusion of the catalyst adatoms. The CNT growth rate is controlled by the temperature and chemical composition of the gases in the CVD reactor. We show that the final height of the forest is diffusion limited, at least in the conditions of our experiments. Because of the proximity and entanglement of the CNTs in a forest, the growing CNTs can lift-up the inactive CNTs resulting in reduced density toward the base of the forest unless the nucleation rate of the new catalyst particles is sufficiently high to replenish the inactive catalyst particles. Significant loss of CNT attachment by the lift-up effect reduces the adhesion of the forest to the substrate. Optimizing the ferrocene concentration in the precursor, precursor injection rate, gas mixture, substrate, and temperature is necessary to achieve desired forest morphology for specific applications.
Rigid C*-tensor categories of bimodules over interpolated free group factors
Authors: Brothier Arnaud , Hartglass Michael , Penneys David
Published: December 2012

Given a countably generated rigid C*-tensor category ${\sf C}$C, we construct a planar algebra P• whose category of projections ${\sf Pro}$Pro is equivalent to ${\sf C}$C. From P•, we use methods of Guionnet-Jones-Shlyakhtenko-Walker to construct a rigid C*-tensor category ${\sf Bim}$Bim whose objects are bifinite bimodules over an interpolated free group factor, and we show ${\sf Bim}$Bim is equivalent to ${\sf Pro}$Pro. We use these constructions to show ${\sf C}$C is equivalent to a category of bifinite bimodules over $L(\mathbb {F}_\infty )$L(F∞).
Selective nucleation induced by defect nanostructures: A way to control cobalt disilicide precipitation during ion implantation
Authors: Fortuna F. , Nguyen M.-A. , Ruault M.-O. , Kirk M. A. , Borodin V. A. , Ganchenkova M. G.
Published: December 2012

In this paper, we show a way to control cobalt disilicide precipitation during Co ion implantation at high temperatures (650 °C) by affecting radiation defects involved in precipitate nucleation and growth. We demonstrate that the relative shares of different precipitate types nucleated by implantation are strongly affected by defect microstructures deliberately created in investigated samples prior to cobalt implantation. Especially interesting is the effect of a dense ensemble of extremely small (1-3 nm) cavities, which promotes the formation of a relatively uniform layer of coherent cobalt disilicide precipitates with a narrow size distribution. In order to better understand the mechanism of the microstructural influence on the precipitate nucleation modes during Co implantation, we investigate the disilicide precipitation using different implantation setups and compare the results with those for cavity-free Si specimens implanted in similar conditions.
Ruby pressure scale in a low-temperature diamond anvil cell
Authors: Yamaoka Hitoshi , Zekko Yumiko , Jarrige Ignace , Lin Jung-Fu , Hiraoka Nozomu , Ishii Hirofumi , Tsuei Ku-Ding , Mizuki Jun'ichiro
Published: December 2012

Laser-excited N and R fluorescence lines of heavily doped ruby have been studied up to 26 GPa at low temperatures. While the intensity of the R lines at ambient pressure significantly decreases with decreasing temperature, the intensity of N lines originating from exchange-coupled Cr ion pairs is enhanced at low temperatures. The pressure induced wavelength shift of the N lines at 19 K is well fitted with an empirical formula similar to the equation for the R1 line, showing that the intense N line could be used as an alternative pressure scale at low temperatures. We also observe continuous increase in non-hydrostaticity with increasing pressure at low temperatures when silicone oil and 4:1 mixture of methanol and ethanol are used as pressure media.
Spontaneous electromagnetic fluctuations in unmagnetized plasmas. III. Generalized Kappa distributions
Authors: Lazar M. , Yoon P. H. , Schlickeiser R.
Published: December 2012

In the first two papers of this series, the general expressions for the spontaneous fluctuations spectra (electric and magnetic field, charge and current densities) from uncorrelated plasma particles are derived and illustrated for a Maxwellian (relativistic or nonrelativistic) plasma close to thermal equilibrium. In this paper, the results are illustrated for the nonideal case of a plasma out of thermal equilibrium and described by the generalized Kappa (power-law) particle distribution function in the nonrelativistic limit. The suprathermal fluctuations of weakly amplified modes and aperiodic modes are provided. Thus, it is shown for the first time the existing finite level of noncollective fluctuations, which are particularly important in the context of plasma fluctuations (collective or noncollective) as the best agent in the energy dissipation and transfer to suprathermal populations. The results obtained in the first paper for an equilibrium plasma are recovered only in the limit of a very large power index κ→∞.
Effect of a change in thickness on the structural and perpendicular magnetic properties of L1 ordered FePd ultra-thin films with (001) texture
Authors: Ko Jungho , Bae Taejin , Hong Jongill
Published: December 2012

Ultra-thin FePd films were prepared by the sputter-deposition of Fe and Pd layers. After annealing at 500 °C, they transformed to a (001) oriented L10 ordered phase from an A1 disordered phase and changed their anisotropy to perpendicular magnetic anisotropy from in-plane. The ordered parameter was about 0.7 for all thicknesses of the FePd films. The 20 nm-thick FePd film exhibited the squareness of 0.3 because both the disordered phase with in-plane magnetic anisotropy and ordered phase with perpendicular magnetic anisotropy existed in the FePd film. The disordered phase was reduced, and the L10 phase became predominated as the thickness of the FePd films decreased. In particular, when the FePd films were 3 and 5 nm thick, the squareness became unity while maintaining a thermal stability factor of over 60. The uniaxial magnetic anisotropy constant Ku was over 1 × 107 erg/cm3. Those characters make ultra-thin L10 FePd films suitable for use in nano-devices for magnetic applications.
Effect of silicon/crucible interfacial energy on orientation of multicrystalline silicon ingot in unidirectional growth
Authors: Fujiwara K. , Maeda K. , Koizumi H. , Nozawa J. , Uda S.
Published: December 2012

We investigated the effects of the Si crystal/crucible and Si melt/crucible interfacial energies on the orientation of the nucleus of multicrystalline Si during unidirectional growth. We calculated the Gibbs free energy upon nucleation on the crucible by considering the shape of the nucleus of the Si crystal and found that the nucleus with the 〈111〉 or 〈100〉 upper direction is stable. It was experimentally shown that {111} planes are dominant at the bottom of a multicrystalline Si ingot grown at a low rate, which was explained by the difference between the Si crystal/crucible and Si melt/crucible interfacial energies at nucleation.
Electronic and magnetic properties of oxygen patterned graphene superlattice
Authors: Huang Haiming , Li Zhibing , Wang Weiliang
Published: December 2012

Graphene superlattices formed by adsorbing oxygen lines on graphene are studied using spin-polarized density functional theory calculations. It is found that separating zigzag chains (armchair dimer lines) with one oxygen adsorbate on each periodic segment of the chain (line) are sufficient to divide the graphene sheet into series of graphene nanoribbons. The energy band gap of the graphene with armchair (zigzag) oxidation lines (chains) is modulated with line (chain) separation as the width modulation of the freestanding graphene ribbon. The magnetic properties of superlattices with different oxidized line width for both zigzag and armchair oxidized lines are also investigated. Magnetism is found in oxygen-patterned graphene superlattice with zigzag interface and is enhanced with the increasing width of separating oxidation chains.
Particle-in-cell simulations of the runaway breakdown of nitrogen
Authors: Levko D. , Krasik Ya. E.
Published: December 2012

The runaway breakdown initiated by a mono-energetic beam of runaway electrons propagating through a cathode-anode gap filled with nitrogen at atmospheric pressure is studied using the one-dimensional particle-in-cell numerical model. It is shown that the breakdown is strongly influenced by the amplitude of the beam, its duration, and the electric field in the vicinity of the cathode. In addition, the simulation results showed that, in spite of the formation of rather dense plasma inside the cathode-anode gap by runaway electrons, the electric field is not screened because of frequent electron–neutral collisions.
Ballistic impact behavior of carbon nanotube and nanosilica dispersed resin and composites
Authors: Pandya K. S. , Akella K. , Joshi M. , Naik N. K.
Published: December 2012

Experimental studies are presented on the ballistic impact behavior of nanoparticle dispersed materials viz. symmetric balanced cross-ply laminates made using unidirectional E-glass fabric with epoxy resin and neat epoxy resin. The nanoparticles used are nanosilica and multi-walled carbon nanotube for polymer matrix composites and nanosilica for epoxy resin. For comparison, studies are carried out on symmetric balanced cross-ply E-glass/epoxy and neat epoxy resin without nanoparticles. Effect of nanoparticle dispersion on ballistic limit velocity, V50 and energy absorbed has been studied. It is observed that V50 can be enhanced up to 6.3% for polymer matrix composites and up to 7.3% for neat resin on addition of nanoparticles. Also, energy absorbed can be increased up to 13.0% for polymer matrix composites and up to 15.2% for neat resin on addition of nanoparticles. Damage and energy absorbing mechanisms for different types of materials studied is also presented. Further, it is observed that the damage size on the target around the point of impact decreases on addition of nanoparticles. Quantitative data are given for high velocity impact behavior of the five types of specimens studied.
A random rotor molecule: Vibrational analysis and molecular dynamics simulations
Authors: Li Yu , Zhang Rui-Qin , Shi Xing-Qiang , Lin Zijing , Van Hove Michel A.
Published: December 2012

Molecular structures that permit intramolecular rotational motion have the potential to function as molecular rotors. We have employed density functional theory and vibrational frequency analysis to study the characteristic structure and vibrational behavior of the molecule (4′,4″″-(bicyclo[2,2,2]octane-1,4-diyldi-4,1-phenylene)-bis-2,2′:6′,2″-terpyridine. IR active vibrational modes were found that favor intramolecular rotation. To demonstrate the rotor behavior of the isolated single molecule, ab initio molecular dynamics simulations at various temperatures were carried out. This molecular rotor is expected to be thermally triggered via excitation of specific vibrational modes, which implies randomness in its direction of rotation.
Effect of H and OH desorption and diffusion on electronic structure in amorphous In-Ga-Zn-O metal-oxide-semiconductor diodes with various gate insulators
Authors: Hino Aya , Morita Shinya , Yasuno Satoshi , Kishi Tomoya , Hayashi Kazushi , Kugimiya Toshihiro
Published: December 2012

Metal-oxide-semiconductor (MOS) diodes with various gate insulators (G/Is) were characterized by capacitance–voltage characteristics and isothermal capacitance transient spectroscopy (ICTS) to evaluate the effect of H and OH desorption and diffusion on the electronic structures in amorphous In–Ga–Zn–O (a-IGZO) thin films. The density and the distribution of the space charge were found to be varied depending on the nature of the G/I. In the case of thermally grown SiO2 (thermal SiO2) G/Is, a high space-charge region was observed near the a-IGZO and G/I interface. After thermal annealing, the space-charge density in the deeper region of the film decreased, whereas remained unchanged near the interface region. The ICTS spectra obtained from the MOS diodes with the thermal SiO2 G/Is consisted of two broad peaks at around 5 × 10−4 and 3 × 10−2 s before annealing, while one broad peak was observed at around 1 × 10−4 s at the interface and at around 1 × 10−3 s in the bulk after annealing. Further, the trap density was considerably high near the interface. In contrast, the space-charge density was high throughout the bulk region of the MOS diode when the G/I was deposited by chemical vapor deposition (CVD). The ICTS spectra from the MOS diodes with the CVD G/Is revealed the existence of continuously distributed trap states, suggesting formations of high-density tail states below the conduction band minimum. According to secondary ion mass spectroscopy analyses, desorption and outdiffusion of H and OH were clearly observed in the CVD G/I sample. These phenomena could introduce structural fluctuations in the a-IGZO films, resulting in the formation of the conduction band tail states. Thin-film transistors (TFTs) with the same gate structure as the MOS diodes were fabricated to correlate the electronic properties with the TFT performance, and it was found that TFTs with the CVD G/I showed a reduced saturation mobility. These results indicate that the electronic structures in the a-IGZO films were strongly influenced by the nature of the G/Is as well as the process conditions. It is concluded that controlling of the natures of the G/I such as film density and hydrogen content in the films is critical to obtain high-performance electronic devices using a-IGZO.
Clustering and mobility of hard rods in a quasicrystalline substrate potential
Authors: Kählitz Philipp , Schoen Martin , Stark Holger
Published: December 2012

Recently, we have studied the self-assembly of hard needles in a quasicrystalline substrate potential with decagonal symmetry [P. Kählitz and H. Stark, J. Chem. Phys. 136, 174705 (2012)10.1063/1.4711086]. We have identified new structure formation using Monte Carlo simulations. However, hard needles have a zero width. To investigate how the excluded volume of rod-shaped particles influences their phase ordering, we extend here our studies to spherocylinders. We determine phase diagrams and plot them in the relevant variables, strength of substrate potential versus area fraction. At increasing area fraction η short rods form clusters that ultimately destroy directional ordering along the decagonal symmetry directions while surface-induced positional order exists for all η. In contrast, long rods show directional order in the whole density range. However, at high area fractions they assemble into compact clusters which destroy positional ordering. Finally, we also study the rod mobility using the kinetic Monte Carlo method and discuss an unexpected mobility enhancement with increasing density. All these features crucially depend on the non-zero excluded volume of the spherocylinders.
The tension of a curved surface from simulation
Authors: Sodt Alexander J. , Pastor Richard W.
Published: December 2012

This paper demonstrates a method for calculating the tension of a system with a curved interface from a molecular dynamics simulation. To do so, the pressure of a subset of the system is determined by applying a local (virtual) mechanical deformation, fitting the response to that of a bulk fluid, and then using the Young-Laplace equation to infer the tension of the interface. The accuracy of the method is tested by calculating the local pressure of a series of water simulations at various external pressures. The tension of a simulated curved octane-water interface is computed with the method and compares well with the planar tension (≈ 46.7 dyn/cm). Finally, an ambiguity is resolved between the Harasima and Irving-Kirkwood methods of calculating the local pressure as a means for computing the tension.
Vapor-liquid coexistence in 2D square-well fluid with variable range of attraction: Monte Carlo simulation study
Authors: Rżysko Wojciech , Trokhymchuk Andrij
Published: December 2012

Monte Carlo simulation study of the vapor-liquid coexistence in two-dimensional square-well fluid with 12 different values of the attraction shell width are reported. The densities of coexisting vapor and liquid phases as well as the coexisting chemical potentials for each simulated system are determined by means of hyperparallel tempering and histogram reweighting technique, while the location of critical point was tuned by means of the finite size scaling analysis. By studying dependence of the critical point parameters on the attraction shell width, we found that critical point temperature and critical point chemical potential both are changing monotonically while the critical point density oscillates, exhibiting higher or lower values depending on the particular width of the attraction shell.
Completion of Hankel partial contractions of extremal type
Authors: Curto Raúl E. , Lee Sang Hoon , Yoon Jasang
Published: December 2012

We find concrete necessary and sufficient conditions for the existence of contractive completions of Hankel partial contractions of size 4 × 4 in the extremal case. Along the way we introduce a new approach that allows us to solve, algorithmically, the contractive completion problem for 4 × 4 Hankel matrices. As an application, we obtain a concrete example of a partially contractive 4 × 4 Hankel matrix, which does not admit a contractive completion.
Information geometric characterization of the complexity of fractional Brownian motions
Authors: Peng Linyu , Sun Huafei , Xu Guoquan
Published: December 2012

The complexity of the fractional Brownian motions is investigated from the viewpoint of information geometry. By introducing a Riemannian metric on the space of their power spectral densities, the geometric structure is achieved. Based on the general construction, for an example, whose power spectral density is obtained by use of the normalized Mexican hat wavelet, we show its information geometric structures, e.g., the dual connections, the curvatures, and the geodesics. Furthermore, the instability of the geodesic spreads on this manifold is analyzed via the behaviors of the length between two neighboring geodesics, the average volume element as well as the divergence (or instability) of the Jacobi vector field. Finally, the Lyapunov exponent is obtained.
Formulation of quantized Hamiltonian dynamics in terms of natural variables
Authors: Akimov Alexey V. , Prezhdo Oleg V.
Published: December 2012

We present a formulation of quantized Hamiltonian dynamics (QHD) using variables that arise naturally from the Heisenberg equation of motion. The QHD equations are obtained and solved either directly in terms of these generalized variables, or by employing a wavefunction ansatz. The approach avoids a Taylor expansion and other approximations to the potential, leading to more stable dynamics and a higher precision of the calculated quantities. The proposed formulation is also amenable to for analytic and numerical implementations, thus facilitating its use in molecular dynamics simulation.
HOMO-LUMO transitions in solvated and crystalline picene
Authors: Fanetti Samuele , Citroni Margherita , Bini Roberto , Malavasi Lorenzo , Artioli Gianluca A. , Postorino Paolo
Published: December 2012

The optical properties of picene at ambient conditions have been investigated through the measurement of UV/Vis absorption and fluorescence spectra and of excitation profiles, using one- and two-photon excitation, in solution and in the crystal phase. For solvated picene an assignment of the vibronic structure of the transitions to the four lowest-energy excited singlet states (S1–S4) has been obtained from the absorption data, and the vibronic structure of the fluorescence spectra has been assigned. The absorption and fluorescence spectra of the solid phase can be interpreted according to the single molecule analysis. Nevertheless, the strong increase of the optical density in the spectral region of the lowest HOMO–LUMO transitions and the frequency shift of absorption and fluorescence bands may be explained by a mixing of the states of adjacent molecules in the crystal. Moreover, peculiar emission features depending on the crystal dimensions (10−1 to 102 μm) are observed.
Continuous diffraction patterns from circular arrays of carbon nanotubes
Authors: Butt Haider , Butler Tim , Montelongo Yunuen , Rajesekharan Ranjith , Wilkinson Timothy D. , Amaratunga Gehan A. J.
Published: December 2012

We report the remarkable diffraction effects produced from circular patterned arrays of multiwalled carbon nanotubes (MWCNTs). Highly ordered circular arrays of multiwalled carbon nanotubes (with inter-nanotube spacings of 633 nm) display optical dispersion effects similar to compact discs. These arrays display remarkable diffraction patterns in the far field which are spatially continuous. High quality diffraction patterns were obtained experimentally which are in excellent agreement with the theoretical calculations. The achieved continuous diffraction patterns pave the way towards the utilization of engineered carbon nanotube arrays in applications like three dimensional holograms.
Novel biaxial nematic phases of side-chain liquid crystalline polymers
Authors: Matsuyama Akihiko
Published: December 2012

We present a mean field theory to describe biaxial nematic phases of side-chain liquid crystalline polymers, in which rigid side-chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. Taking into account both excluded volume and attractive interactions between rigid rods, novel biaxial nematic phases are theoretically predicted. We calculate uniaxial and biaxial orientational order parameters as a function of temperature and the length of backbone chains. We find a first-order biaxial-biaxial phase transition and a first (or second)-order uniaxial-biaxial one, depending on the length of mesogens and backbone chains.
Potential energy surface and rovibrational energy levels of the H2-CS van der Waals complex
Authors: Denis-Alpizar Otoniel , Stoecklin Thierry , Halvick Philippe , Dubernet Marie-Lise , Marinakis Sarantos
Published: December 2012

Owing to its large dipole, astrophysicists use carbon monosulfide (CS) as a tracer of molecular gas in the interstellar medium, often in regions where H2 is the most abundant collider. Predictions of the rovibrational energy levels of the weakly bound complex CS-H2 (not yet observed) and also of rate coefficients for rotational transitions of CS in collision with H2 should help to interpret the observed spectra. This paper deals with the first goal, i.e., the calculation of the rovibrational energy levels. A new four-dimensional intermolecular potential energy surface for the H2-CS complex is presented. Ab initio potential energy calculations were carried out at the coupled-cluster level with single and double excitations and a perturbative treatment of triple excitations, using a quadruple-zeta basis set and midbond functions. The potential energy surface was obtained by an analytic fit of the ab initio data. The equilibrium structure of the H2-CS complex is found to be linear with the carbon pointing toward H2 at the intermolecular separation of 8.6 ao. The corresponding well depth is −173 cm−1. The potential was used to calculate the rovibrational energy levels of the para-H2-CS and ortho-H2-CS complexes. The present work provides the first theoretical predictions of these levels. The calculated dissociation energies are found to be 35.9 cm−1 and 49.9 cm−1, respectively, for the para and ortho complexes. The second virial coefficient for the H2-CS pair has also been calculated for a large range of temperature. These results could be used to assign future experimental spectra and to check the accuracy of the potential energy surface.
Reactive and internal contributions to the thermal conductivity of local thermodynamic equilibrium nitrogen plasma: The effect of electronically excited states
Authors: Bruno D. , Colonna G. , Laricchiuta A. , Capitelli M.
Published: December 2012

Internal and reactive contributions to the thermal conductivity of a local thermodynamic equilibrium nitrogen plasma have been calculated using the Chapman-Enskog method. Low-lying (LL) electronically excited states (i.e., states with the same principal quantum number of the ground state) and high-lying (HL) ones (i.e., states with principal quantum number n> 2) have been considered. Several models have been developed, the most accurate being a model that treats the LL states as separate species while disregarding the presence of HL states, on account of their enormous transport cross sections.
Modelling charge transport lengths in heterojunction solar cells
Authors: Musselman K. P. , Ievskaya Y. , MacManus-Driscoll J. L.
Published: December 2012

A drift-diffusion model is used to estimate the minority carrier transport length and depletion width in heterojunction solar cells from measured external quantum efficiency (EQE) data. The model is applied to Cu2O-ZnO heterojunctions synthesized by electrodeposition and thermal oxidation, and the electron drift and diffusion lengths are estimated: Ldrift ≈ 110 nm for electrodeposited Cu2O and Ldrift ≈ 2790 nm and Ldiff ≈ 310 nm for thermally oxidized Cu2O. Better fitting of EQE data is obtained than with traditional models that neglect recombination in the depletion region.
Culturing photosynthetic bacteria through surface plasmon resonance
Authors: Ooms Matthew D. , Bajin Lauren , Sinton David
Published: December 2012

In this work, cultivation of photosynthetic microbes in surface plasmon enhanced evanescent fields is demonstrated. Proliferation of Synechococcus elongatus was obtained on gold surfaces excited with surface plasmons. Excitation over three days resulted in 10 μm thick biofilms with maximum cell volume density of 20% vol/vol (2% more total accumulation than control experiments with direct light). Collectively, these results indicate the ability to (1) excite surface-bound cells using plasmonic light fields, and (2) subsequently grow thick biofilms by coupling light from the surface. Plasmonic light delivery presents opportunities for high-density optofluidic photobioreactors for microalgal analysis and solar fuel production.
Three-dimensional localization of fluorescent targets in turbid media using time reversal optical tomography
Authors: Wu Binlin , Cai W. , Gayen S. K.
Published: December 2012

An optical tomography approach for locating fluorescent targets embedded inside a turbid medium is introduced. It uses multi-source probing and multi-detector signal acquisition to collect diffuse fluorescence signal, and time reversal matrix formalism with subspace based signal processing for image reconstruction. It could provide three-dimensional position co-ordinates of two small fluorescent targets embedded in Intralipid-20% suspension of thickness ∼60 times the transport mean free path with an accuracy of ∼1 mm. Fast reconstruction and high spatial resolution make the approach potentially suited for detecting and locating contrast-enhanced breast tumor at early stages of growth.
Characterization and manipulation of the “saturation” effect by changing the surface temperature of a dielectric barrier discharge actuator
Authors: Durscher Ryan , Stanfield Scott , Roy Subrata
Published: December 2012

The thrust produced by a sinusoidally driven dielectric barrier discharge actuator in quiescent air is known to increase with a power law of the applied voltage. For voltages greater than a threshold, the exponent of the power law reduces limiting the thrust increase and the actuator is said to have “saturated,” limiting the actuator's usefulness. The onset of saturation is visually correlated by the inception of filamentary discharge events. In this letter, the flow transition to the saturation condition is characterized. Furthermore, the saturation effect can be manipulated by changing the local surface temperature of the dielectric.
TiO2 nanoparticles and silicon nanowires hybrid device: Role of interface on electrical, dielectric, and photodetection properties
Authors: Rasool Kamran , Rafiq M. A. , Ahmad Mushtaq , Imran Z. , Hasan M. M.
Published: December 2012

We report ∼12, 5, 12, 100, and 70 times enhancement of external quantum efficiency, detectivity, responsivity, AC conductivity, and overall dielectric constant (ε′), respectively of hybrid silicon nanowires (SiNWs) and titania (TiO2) nanoparticles (NPs) device as compared to SiNWs only device. Devices show persistent photoconductivity. Metal assisted chemical etching and co-precipitation method were used to prepare SiNWs (length ∼40 μm, diameter ∼30–400 nm) and TiO2 NPs (diameter ∼50 nm), respectively. Formation of acceptor like states at NPs and SiNWs interface improves electrical properties. Presence of low refractive index TiO2 around SiNWs causing funneling of photon energy into SiNWs improves photodetection.
Extend the omnidirectional electronic gap of Thue-Morse aperiodic gapped graphene superlattices
Authors: Zhang Zhengren , Li Hongqiang , Gong Zhijie , Fan Yuancheng , Zhang Tianqi , Chen Hong
Published: December 2012

An effective way used to extend omnidirectional electronic gap (OEG) by using Thue-Morse gapped graphene superlattice (GSL) heterostructure is proposed. The heterostructure consists of different Thue-Morse gapped graphene superlattices with different width ratios of potentials. The optimal potential width ratios of constituent Thue-Morse gapped graphene superlattices are easy to be established owing to the lower and upper energy edges of omnidirectional electronic gap depend on the width ratio of potentials. Furthermore, the omnidirectional electronic gap is independence of structure order, thus we can use different optimal Thue-Morse gapped graphene superlattices of any structure order to form a heterostructure to extend this gap as desired.
Note: Radiofrequency scanning probe microscopy using vertically oriented cantilevers
Authors: Valdrè G. , Moro D.
Published: December 2012

We present a simple method, based on the modification of a widespread atomic force microscope, that allows the simultaneous acquisition of the sample topography and RF spectra at the nanoscale minimizing the parasitic capacitance of the cantilever. We used a microcantilever set with its long axis perpendicular to the specimen surface and connected to a vector network analyzer (RF range 100 kHz–8.5 GHz) to measure RF impedance signal variations at the cantilever apex-sample interface. The RF impedance signal was found highly sensitive to very short probe-to-sample distances (<50 nm) and to material properties at the interface.
Three-dimensional micro electromechanical system piezoelectric ultrasound transducer
Authors: Hajati Arman , Latev Dimitre , Gardner Deane , Hajati Azadeh , Imai Darren , Torrey Marc , Schoeppler Martin
Published: December 2012

Here we present the design and experimental acoustic test data for an ultrasound transducer technology based on a combination of micromachined dome-shaped piezoelectric resonators arranged in a flexible architecture. Our high performance niobium-doped lead zirconate titanate film is implemented in three-dimensional dome-shaped structures, which form the basic resonating cells. Adjustable frequency response is realized by mixing these basic cells and modifying their dimensions by lithography. Improved characteristics such as high sensitivity, adjustable wide-bandwidth frequency response, low transmit voltage compatible with ordinary integrated circuitry, low electrical impedance well matched to coaxial cabling, and intrinsic acoustic impedance match to water are demonstrated.
Fatigue properties of atomic-layer-deposited alumina ultra-barriers and their implications for the reliability of flexible organic electronics
Authors: Baumert E. K. , Pierron O. N.
Published: December 2012

The fatigue degradation properties of atomic-layer-deposited alumina, with thickness ranging from 4.2 to 50 nm, were investigated using a silicon micro-resonator on which the coatings were deposited and strained in a static or cyclic manner, with strain amplitudes up to 2.2%, in controlled environments. Based on the measured resonant frequency evolution, post-test scanning electron microscopy observations, and finite element models, it is shown that cracks in the alumina nucleate and propagate under cyclic loading, and that the crack growth rates scale with the strain energy release rates for crack channeling. The implications for the reliability of flexible electronics are discussed.
Influence of the surface structure on the magnetic properties of Zn1−xCoxO
Authors: Ciatto G. , Di Trolio A. , Fonda E. , Amidani L. , Boscherini F. , Thomasset M. , Alippi P. , Amore Bonapasta A.
Published: December 2012

The surface of ferromagnetic Zn1−xCoxO wurtzite epilayers has been studied by coupling atomic force microscopy and advanced x-ray spectroscopy. We found that, even in high-quality epilayers, the formation of Co clusters and iso-space-group Co-rich regions can take place at the sample surface while the bulk maintains random Co distribution. Comparing structural characterization with magnetometry, we show that these surface modifications are not at the origin of the magnetic properties of the material. Quite the reverse, ferromagnetic behavior is enhanced in the sample characterized by the less defective surface.
Strain relaxation in GaN nanopillars
Authors: Tseng W. J. , Gonzalez M. , Dillemans L. , Cheng K. , Jiang S. J. , Vereecken P. M. , Borghs G. , Lieten R. R.
Published: December 2012

In this work, we demonstrate the direct measurement of the strain state at the surface of nanostructures by in-plane X-ray diffraction. GaN tapered nanopillars have been fabricated by dry etching of a highly strained epilayer. The strain of the surface as function of pillar height shows an exponential relaxation which can be described by a single relaxation parameter. Additionally, we have simulated the strain relaxation and distribution of nanopillars. The impact of the pillar geometry on the strain relaxation has been discussed. In agreement with the measurements, an exponential relaxation of the strain is observed.
Flicker noise in n-channel nanoscale tri-gate fin-shaped field-effect transistors
Authors: Theodorou C. G. , Fasarakis N. , Hoffman T. , Chiarella T. , Ghibaudo G. , Dimitriadis C. A.
Published: December 2012

In n-channel nanoscale tri-gate fin-shaped field-effect transistors with high-k gate dielectric stack, the 1/f noise is investigated, ascribed to the carrier number fluctuations with correlated mobility fluctuations. The overall results show that the gate dielectric trap density is uniform in both top-gate and side-gates and the product Ω=αscμeffCox of the Coulomb scattering coefficient αsc, the effective carrier mobility μeff and the gate oxide capacitance per unit area Cox increase with decreasing the fin thickness due to enhancement of side-gates interface roughness effects.
Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes
Authors: Kennedy Matthew J. , Ladouceur Harold D. , Moeller Tiffany , Kirui Dickson , Batt Carl A.
Published: December 2012

The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125 × 125-μm2 cross-section. Use of the device produces liposomes in the size range of 100–300 nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein.
Electrochromic switchable mirror glass fabricated using adhesive electrolyte layer
Authors: Tajima Kazuki , Hotta Hiromi , Yamada Yasusei , Okada Masahisa , Yoshimura Kazuki
Published: December 2012

We have developed a simple process for fabricating electrochromic switchable mirror glass using an adhesive electrolyte layer. The adhesive electrolyte layer was a mixture of polyethyleneimine electrolyte and polyvinyl butyral adhesive dissolved in gamma-butyrolactone. The device was formed from two substrates; the adhesive electrolyte layer was applied to one of the substrates before they were stuck together. The applied voltage required to change the state of the device was smaller than that of a conventional device with a solid electrolyte layer deposited by sputtering. Our method is simple, fast, and efficient and can be used to fabricate large devices.
Influence of isothermal hot pressing-doping treatment on the electrical and mechanical properties of bulk Bi-Sr-Ca-Cu-O
Authors: Khalil S. M.
Published: December 2012

The influences of (isothermal hot pressing-doping) treatment on the microstructure, electrical and mechanical properties of Bi2Sr3-xCaxCu2O8+δ (BSCCO), x ranging from 0.0 to 2 are assessed. BSCCO pellets were prepared by isothermal hot pressing (IHP) technique. The experimental works in this study consists of dc electrical resistivity measurements for electrical and superconducting properties, microhardness tests for mechanical characteristics, powder x-ray diffraction (XRD) for phase analyses (phase ratio), differential thermal analysis (DTA) for melting behaviour and scanning electron microscopy (SEM) for microstructure investigations. The results indicated that the Ca2+ doping and isothermal hot pressing increased significantly the superconducting transition temperature (Toc), which promotes the formation of high-Tc phase. Additionally, Vickers microhardness (VHN), Young's modulus, fracture toughness, brittleness index and elastic stiffness coefficient were also improved. Moreover, IHP-Doping improved the microstructure and the density of the BSCCO studied samples. Microhardness was found to be load dependent. Otherwise, we evaluated the load independent hardness, Young's modulus, fracture toughness and brittleness index of BSCCO samples. The possible reasons for the observed enhancement in electrical and mechanical properties due to (i) the homogeneity of grain region distribution (ii) the enhancement of superconducting phases.
The inquiry of liquids and glass transition by heat capacity
Authors: Ke Hai Bo , Wen Ping , Wang Wei Hua
Published: December 2012

Reconsidering the intrinsic connection between simple liquids and the glass transition, we attempt to understand them with an explicit liquid model. Liquids are defined to the mixture composed of tiny particles restricted in non-identical potential energy wells, where translational motions of tiny particles in statistical equilibrium, as well as vibrations and rotations, are distinguished. The liquid model offers an opportunity to build up a quantitative correlation between heat capacity and the basic motions appearing in liquids. Agreements between theoretical prediction and experimental data on heat capacities of typical simple liquids are reached. A serial of experimental data confirm that the glass transition originates from the falling out-of-equilibrium of the translational motions in liquids. The work might provide a novel and intuitive way to uncover a shady corner of the mysterious liquids and the glass transition.
Characterization of Dispersion Effects on Reaction Optimization and Scale-Up for a Packed Bed Flow Hydrogenation Reactor
Authors: Eschelbach John W. , Wernick David , Bryan Marian C. , Doherty Elizabeth M.
Published: December 2012

A well known advantage of flow chemistry reactors in chemical synthesis is the ability to screen multiple catalysts and reaction parameters with optimal conditions scaled accordingly. This approach, however, consumes significant quantities of material as the reactor must be equilibrated with the reactants in a continuous, steady-state mode before the start of the reaction. In this work we explore a screening and reaction approach using bolus injections, which is more conducive to the lower material consumption that may be required in a drug discovery setting. A commercially available ThalesNano H-Cube® was evaluated to determine the practicality of this approach for heterogeneous hydrogenations. When working with boluses in flow systems, one of the biggest limitations can be the inherent dispersion of the reactant stream caused by the reactor. The dispersion on the H-Cube® was characterized to determine the minimum volume for the reactor to reach a steady-state. The H-Cube® fluidics and heating coil were found to generate significantly more dispersion than the reaction cartridge (CatCart®) itself, increasing the minimum volume of injection required to achieve steady-state. A 2 mL injection was found as a good compromise between maximizing material conservation and sufficient volume of reaction at steady-state condition. Conditions optimized at 2 mL screening scale were successfully scaled five-fold, while lower volume bolus injections were shown to be less predictable. A stacked injection protocol using lower volume boluses was found to be a reliable alternative to scale reactions while efficiently conserving material. This application of small bolus injections to flow reaction screening and scale-up provides a desirable alternative to traditional continuous flow approaches in the material-limited discovery setting.
Computational Evaluation of the Sulfonyl Radical as a Universal Leaving Group for RAFT Polymerisation
Authors: Gryn'ova Ganna , Guliashvili Tamaz , Matyjaszewski Krzysztof , Coote Michelle L.
Published: December 2012

The present study investigates the performance of the sulfonyl radical, i.e. •SO2Ph, as a universal leaving group in reversible addition–fragmentation chain-transfer (RAFT) polymerisation. The sulfonyl radical is widely used as a radical initiator and has already been proved successful as a leaving group in an atom-transfer radical polymerisation. Our results, obtained using high-level ab initio computational methodology under relevant experimental conditions, indicate superior performance of the sulfonyl compared with a reference cyanoisopropyl group in controlling RAFT of a wide range of monomers. Importantly, the presence of sulfonyl chain ends in the polymers so formed opens attractive possibilities for further functionalisation. Potential synthetic routes to the R-sulfonyl RAFT agents are discussed.
Analysis of early vigour in twenty modern cultivars of bread wheat (Triticum aestivum L.)
Authors: Maydup M. L. , Graciano C. , Guiamet J. J. , Tambussi E. A.
Published: December 2012

Fast development of seedling leaf area is a relevant trait in order to increase early resource acquisition. The use of semi-dwarf genotypes of wheat has decreased early vigour of modern cultivars. We studied early vigour of 20 cultivars cropped in Argentina, and our main objectives were: (i) to analyse the genotypic variability in early vigour; (ii) to study morphological traits that can be good indicators of early vigour, such as seed mass, leaf width, and specific leaf area; and (iii) to determine whether increased dry mass allocation to roots impacts negatively on early vigour. Experiments with non-size-selected and size-selected seeds were carried out in a greenhouse. A field trial was also conducted in order to test the reliability of the greenhouse results. Seeds mass was the main parameter related to early vigour. However, results from the experiment with seeds selected by size (45–50 mg seed–1) showed that seed mass per se only partially explains early vigour, since a significant coefficient of determination was observed between the seedling leaf area of each cultivar in both experiments (i.e. with randomly chosen or size-selected seeds).
We observed a high coefficient of determination between net assimilation rate and changes in the ranking of early vigour of the cultivars with time after transplant. Root biomass was positively correlated with leaf area, indicating that the traits were not mutually exclusive. We built simple models by multiple regression to predict early vigour, including some parameters that were easy to measure. Seed mass and leaf width taken together showed better fit than seed mass or leaf width alone. We found a significant coefficient of determination between early vigour in greenhouse and field experiments; thus, screening for early vigour under semi-controlled conditions may be feasible.
Effects of growth differentiation factor-9 and FSH on in vitro development, viability and mRNA expression in bovine preantral follicles
Authors: Vasconcelos G. L. , Saraiva M. V. A. , Costa J. J. N. , Passos M. J. , Silva A. W. B. , Rossi R. O. D. S. , Portela A. M. L. R. , Duarte A. B. G. , Magalhães-Padilha D. M. , Campelo C. C. , Figueiredo J. R. , van den Hurk R. , Silva J. R. V.
Published: December 2012

The present study investigated the role of growth differentiation factor (GDF)-9 and FSH, alone or in combination, on the growth, viability and mRNA expression of FSH receptor, proliferating cell nuclear antigen (PCNA) and proteoglycan-related factors (i.e. hyaluronan synthase (HAS) 1, HAS2, versican, perlecan) in bovine secondary follicles before and after in vitro culture. After 12 days culture, sequential FSH (100 ng mL–1 from Days 0 to 6 and 500 ng mL–1 from Days 7 to 12) increased follicular diameter and resulted in increased antrum formation (P < 0.05). Alone, 200 ng mL–1 GDF-9 significantly reduced HAS1 mRNA levels, but increased versican and perlecan mRNA levels in whole follicles, which included the oocyte, theca and granulosa cells. Together, FSH and GDF-9 increased HAS2 and versican (VCAN) mRNA levels, but decreased PCNA mRNA expression, compared with levels in follicles cultured in α-minimum essential medium supplemented with 3.0 mg mL–1 bovine serum albumin, 10 µg mL–1 insulin, 5.5 µg mL–1 transferrin, 5 ng mL–1 selenium, 2 mM glutamine, 2 mM hypoxanthine and 50 μg mL–1 ascorbic acid (α-MEM+). Comparisons of uncultured (0.2 mm) and α-MEM+ cultured follicles revealed that HAS1 mRNA expression was higher, whereas VCAN expression was lower, in cultured follicles (P < 0.05). Expression of HAS1, VCAN and perlecan (HSPG2) was higher in cultured than in vivo-grown (0.3 mm) follicles. In conclusion, FSH and/or GDF-9 promote follicular growth and antrum formation. Moreover, GDF-9 stimulates expression of versican and perlecan and interacts positively with FSH to increase HAS2 expression.