bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid-crystals-plasmonics for ultrafast broadband all-optical switching
Authors: Khoo I. C. , Huang J. , Zhou S. , Liou J. , Hong K. L. , Ma Yi 
Published: September 2011

ABSTRACTWe present the results and critical analyses of recent studies of ultrafast optical nonlinearities of liquid crystals in the isotropic and ordered phases for time scales spanning femtoseconds – microseconds. Pure undoped liquid crystals as well as liquid crystals containing plasmonic nano-particles have been investigated. Individual molecular electronic optical nonlinearities are found to be useful for femtoseconds – nanoseconds nonlinear transmission clamping applications. On the other hand, laser induced order parameter and birefringence modification in aligned nematic cells allow very rapid transmission switching of visible as well as near infrared lasers with response times in the sub-microseconds - few nanoseconds regime.
π-π Stacking Molecular Interactions Between Carbon Nanotubes and 5CB Liquid Crystal
Authors: Georgiev Georgi Y. , Gombos Erin A. , McIntyre Michael B. , Cebe Peggy 
Published: September 2011

ABSTRACTMultiwall Carbon Nanotubes (MWCNT) align by coupling to the liquid crystals’ (LC) nematic director in LC/MWCNT dispersions. This coupling is so strong that the LC molecules act as molecular motors to reorient the MWCNTs when an electric field is applied across oriented electro optic cells. On the other hand, MWCNTs also improve the LC order and modify the crystal phase of LCs. We investigate the physical reasons for those strong effects by studying the molecular interactions between a host LC and MWCNTs. It has been predicted theoretically that the aromatic rings could stack with their π orbitals in 4-Cyano-4’-pentylbiphenyl (5CB) and MWCNT nanocomposites. Experimentally 5CB modifies the MWCNTs Raman breathing modes in the same nanocomposites. In turn, we look for evidence of this interaction between MWCNTs and LCs at the 5CB molecules. Using FTIR spectroscopy we found that the modes corresponding to 5CB aromatic rings vibrations are affected in the presence of MWCNTs which confirms that π-π stacking of 5CB’s biphenyl rigid core to the carbon rings on the MWCNTs’ surface may indeed be major mechanism for MWCNT/LC nematic coupling. It shows also that the Raman breathing mode effects on MWCNTs can be due to this π-π stacking interaction with 5CB. Further investigations of the MWCNTs interactions with 5CB can lead to developing of a complete model of this phenomenon and help applications for electro optic cells, nanoswitches, new crystal forms for optics, communication technology and others.
Atomic structure of metal-free and catalyzed Si nanowires
Authors: Nicotra Giuseppe , Bongiorno Corrado , Convertino Annalisa , Cuscunà Massimo , Martelli Faustino , Spinella Corrado 
Published: September 2011

ABSTRACTMetal-free and Au-catalyzed silicon nanowires (Si-NWs) grown at low temperatures have been analyzed through transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and their crystalline phase studied. All the observed nanowires are crystalline, grow along two different directions, <110> or <112>, and contain high density of planar defects, such as stacking faults (SFs) and twins. The defect size is comparable to the wire diameter for the metal-free process whilst it is much larger than the wire diameter for the Aucatalyzed Si-NWs. In this latter case parallel SFs may re-arrange and transform in a metastable rhombohedral 9R polytype structure whose formation mechanism is discussed.
Electrical Characterization of Ge Nanocrystals in Oxide Matrix
Authors: Capan Ivana , Buljan Maja , Misic-Radic Tea , Pivac Branko , Radic Nikola , Grenzer Joerg , Holy Vaclav , Levichev S. , Bernstorff Sigrid 
Published: September 2011

ABSTRACTWe report on electrical properties in [(Ge+SiO2)/SiO2]×2 films deposited by magnetron sputtering on a periodically corrugated-rippled substrate and annealed in vacuum and forming gas. The rippled substrate caused a self-ordered growth of Ge quantum dots, while annealing in different environments enabled us to separate charge trapping in quantum dots from the trapping at the dot-matrix and matrix-substrate interfaces. We show that the charge trapping occurs mainly in Ge quantum dots in the films annealed in the forming gas, while Si–SiO2 interface trapping is dominant for the vacuum annealed films.
RHEED Pole Figure Measurements of Biaxial Thin Film Growth Front Evolution
Authors: Wang Gwo-Ching , Liu Yu , Gaire Churamani , Yuan Wen , Lu Toh-Ming 
Published: September 2011

ABSTRACTThe most frequently used characterization technique for biaxial texture formation in thin films is x-ray pole figure analysis. However, x-rays interact weakly with matter and can penetrate a few microns deep into the film. The texture obtained by x-rays is therefore an average texture from the entire thickness of the film. As the texture of a film often changes during growth, information on the basic mechanisms that control the final texture is often lost. In contrast electrons interact strongly with matter and they have very limited penetration and escape depths of a few nm. In this paper we will show how we can use our newly developed reflection high energy electron diffraction (RHEED) surface pole figure technique to probe the surface texture evolution of the growth front from the initial stage (nm thick) to the later stage. The RHEED pole figure technique is a surface-sensitive technique that allows us to obtain information on the dynamic behavior of texture evolution of the growth front during film deposition. We shall explain the principle, measurement, and construction of such RHEED surface pole figures. An example of the biaxial texture evolution of CaF2 due to the atomic shadowing effect during oblique angle deposition is described.
Enhanced CO Oxidation Catalysis of Pt0.1Cu0.9/Fe2O3 Synthesized by Radiolytic Process
Authors: Yamamoto Takao A. , Kitagawa Ryota , Seino Satoshi , Nakagawa Takashi 
Published: September 2011

ABSTRACTCatalysts in which Pt and Cu are immobilized on support particles of γ-Fe2O3 were synthesized by the radiolytic process and were evaluated for CO oxidation in a gas flow mixture (1% CO, 0.5% O2, 67.2% H2 and N2 balance) by measuring the CO concentration in the outlet gas. The Pt/Cu atomic ratios of the as-synthesized catalysts were determined to be 100:0, 90:10, 78:22, 50:50, 21:79, and 11:89, and the total metal loadings determined by chemical analyses were 10 wt%. Material characterization was performed using X-ray diffraction, X-ray absorption near edge structure, and transmission electron microscopy, and it was indicated that the composite catalysts consist of Pt-Cu bimetallic grains immobilized on the support at higher Pt-loading, while CuO with poor crystallinity is also observed at lower Pt-loading. The catalytic activity decreased as the Pt-loading was decreased to 50 at%, and also with increasing temperature. However, as the Pt-loading was further decreased, the activity contrariwise increased, and increased with increasing temperature up to 100 °C. The sample containing only 11 at% Pt exhibited the highest activity at 100 °C, which is higher than that of the commercial catalyst measured for comparison, and given at a lower temperature than that for the commercial catalyst. This enhanced activity, despite the low Pt-loading, could be attributed to oxygen supply via CuO from the O2-poor atmosphere to PtCu bimetallic grains trapping CO molecules. This new material is promising for use as a catalyst to purify hydrogen gas fed to a polymer electrolyte fuel cell.
Effects of Al3Ti Addition on the Sintering of TiB2
Authors: Yoshida Masashi 
Published: September 2011

ABSTRACTTitanium diboride (TiB2) has been sintered using spark plasma sintering (SPS). With the addition of Al3Ti, the Vickers hardness, Hv, of TiB2 increases up to as high as 2100 by the sintering at 1273K, while that of the sample sintered without Al3Ti is as low as 20. Such a remarkable improvement is caused by the formation of rigid direct contacts between TiB2 grains in addition to the effect that Al3Ti fills in the space between TiB2 grains and acts as a binder.
Synthesis and Comparison of Boron Nitride Nanostructure Prepared on Silicon and Molybdenum Substrates by Laser Plasma Deposition Technique
Authors: Sajjad M. , Zhang H. X. , Feng P. X. 
Published: September 2011

ABSTRACTThe synthesis of boron nitride nanowires on silicon (Si) and nanorods on molybdenum (Mo) substrates at the same experimental conditions was composed. Fine tip nanowires with diameters around 50 nm were produced on Si substrates, whereas, nanorods with diameter around 100 nm were formed on Mo substrates. The change in length from 5 μm to 100 μm for nanowires and 0.2 μm to 0.8μm for nanorods following variation of substrate temperature were studied systematically.Scanning Electron Microscopy was used to analyze the surface images of BN nanowires and nanorods. Energy Dispersive X-Ray spectroscopy (EDS) was used to analyze boron and nitrogen concentration in the samples. The crystal structures of BN samples were investigated using Raman spectroscopy and x-ray diffraction. The experimental results showed that the nanorods are hexagonal mixed with cubic, whereas the nanowires are hexagonal.
Sonosensitive nanoparticle formulations for cavitation-mediated ultrasonic enhancement of local drug delivery
Authors: Wagstaffe Sarah J. , Arora Manish , Coussios Constantin-C , Schiffter Heiko A. 
Published: September 2011

ABSTRACTInertial cavitation, namely the rapid expansion and subsequent violent collapse of micron-sized cavities under the effect of ultrasound-induced pressure variations, has widely been considered as an undesirable phenomenon forin-vivobiomedical applications. This is mainly because of its highly stochastic nature and difficulties in its reliable initiationin vivousing moderate ultrasound pressure levels. Methods of lowering the pressure required to initiate cavitation, which is known as the cavitation threshold, has been previously addressed with the use of ultrasound contrast agents in form of encapsulated stabilized micron sized bubbles. However, such agents do not readily extravasate into tumours and other target tissues due to their relatively large size. This paper investigates the engineering of core-shell nanoparticles and examines their ability to initiate inertial cavitation in the context of ultrasound-enhanced local drug delivery. The nanoparticulate formulations are size-engineered to target tumour vasculature whilst presenting high surface roughness, facilitating surface air entrapment upon drying. The core-shell nanoparticles have been demonstrated to substantially lower the cavitation threshold in aqueous solution, allowing the initiation of inertial cavitation with moderate ultrasound amplitudes and the low energy levels typically deployed by diagnostic systems. The peak focal pressure where the probability of cavitation is greater than 0.5 was found to decrease by factors of five to ten fold, dependant on particle size, total surface area and surface morphology.
Formation of dense and aligned planar arrangements of Pb nanoparticles at silica/silicon interfaces
Authors: Luce Flavia P. , Kremer Felipe , Sanchez Dario F. , Fabrim Zacarias E. , Reboh Shay , Zawislak Fernando C. , Fichtner Paulo F. P. 
Published: September 2011

ABSTRACTThe ion beam synthesis of Pb nanoparticles (NPs) in silica/silicon films is studied in terms of the combination of a two-step annealing process consisting of a low temperature long time aging treatment followed by a high temperature short time furnace annealing. The samples are analyzed through Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. The aging process leads to the suppression of the classical homogeneous nucleation of metallic Pb NPs in the silica, thus promoting Pb redistribution during the high temperature annealing. This causes the formation of dense bi-dimensional NP arrays located at the silica-silicon interface, presenting small size dispersion.
Tuning Electronic and Structural Properties of Triple Layers of Intercalated Graphene and Hexagonal Boron Nitride: An Ab-initio Study.
Authors: Coutinho Samir S. , Azevedo David L. , Galvão Douglas S. 
Published: September 2011

ABSTRACTRecently, several experiments and theoretical studies demonstrated the possibility of tuning or modulating band gap values of nanostructures composed of bi-layer graphene, bi-layer hexagonal boron-nitride (BN) and hetero-layer combinations. These triple layers systems present several possibilities of stacking. In this work we report an ab initio (within the formalism of density functional theory (DFT)) study of structural and electronic properties of some of these stacked configurations. We observe that an applied external electric field can alter the electronic and structural properties of these systems. With the same value of the applied electric field the band gap values can be increased or decreased, depending on the layer stacking sequences. Strong geometrical deformations were observed. These results show that the application of an external electric field perpendicular to the stacked layers can effectively be used to modulate their inter-layer distances and/or their band gap values.
Biodegradable Microfluidic Scaffolds with Tunable Degradation Properties from Amino Alcohol-based Poly(ester amide) Elastomers
Authors: Wang Jane , Kniazeva Tatiana , Campbell Carly F. , Langer Robert , Ustin Jeffrey S. , Borenstein Jeffrey T. 
Published: September 2011

ABSTRACTBiodegradable polymers with high mechanical strength, flexibility and optical transparency, optimal degradation properties and biocompatibility are critical to the success of tissue engineered devices and drug delivery systems. In this work, microfluidic devices have been fabricated from elastomeric scaffolds with tunable degradation properties for applications in tissue engineering and regenerative medicine. Most biodegradable polymers suffer from short half life resulting from rapid and poorly controlled degradation upon implantation, exceedingly high stiffness, and limited compatibility with chemical functionalization. Here we report the first microfluidic devices constructed from a recently developed class of biodegradable elastomeric poly(ester amide)s, poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)s (APS), showing a much longer and highly tunable in vivo degradation half-life comparing to many other commonly used biodegradable polymers. The device is molded in a similar approach to that reported previously for conventional biodegradable polymers, and the bonded microfluidic channels are shown to be capable of supporting physiologic levels of flow and pressure. The device has been tested for degradation rate and gas permeation properties in order to predict performance in the implantation environment. This device is high resolution and fully biodegradable; the fabrication process is fast, inexpensive, reproducible, and scalable, making it the approach ideal for both rapid prototyping and manufacturing of tissue engineering scaffolds and vasculature and tissue and organ replacements.
Polyimide-Silica Hybrid Aerogels with High Mechanical Strength for Thermal Insulation Applications
Authors: Dong Wenting , Rhine Wendell , White Shannon 
Published: September 2011

ABSTRACTHigh performance polyimides have been widely investigated as materials with excellent thermal, mechanical, and electronic properties due to their highly rigid structures. Aspen has developed an approach to prepare polyimide aerogels which have applications as low dielectric constant materials, separation membranes, catalyst supports and insulation materials. In this paper, we will discuss the preparation of polyimide-silica hybrid aerogel materials with good mechanical strengths and low thermal conductivities. The polyimide-silica hybrid aerogels were made by a two-step process and the materials were characterized to determine thermal conductivity and compressive strength. Results show that compressive moduli of the polyimide-silica hybrid aerogels increase dramatically with density (power law relationship). Thermal conductivity of the aerogels is dependent on the aging conditions and density, with the lowest value achieved so far being ~12 mW/m-K at ambient conditions. The relationship between aerogel density and surface area, thermal stability, porosity and morphology of the nanostructure of the polyimide-silica hybrid aerogels are also described in this paper.
Evaluation of the Adsorption Potential of Synthesized Anatase Nanoparticles for Arsenic Removal
Authors: Kocabaş Z. Özlem , Yürüm Yuda 
Published: September 2011

ABSTRACTTitanium dioxide has been extensively tested in environmental applications, especially in separation technologies. In the present study, anatase nanoparticles were synthesized by using a sol-gel method, and batch adsorption experiments were carried out to analyze arsenic removal capacity of the anatase nanoparticles from water. The maximum arsenic removal percentages were found ~ 84 % for As(III) at pH 8 and ~98% for As(V) at pH 3, respectively, when 5 g/l anatase nanoparticles were used at an initial arsenic concentration of 1 mg/l. The results of the sorption experiments, which take into consideration the effects of equilibrium concentration on adsorption capacity, were analyzed with two popular adsorption models, Langmuir and Freundlich models. From the comparison of R2 values, the adsorption isotherm for As(III) was fitted satisfactorily well to the Langmuir equation (R2 > 0.996) while the adsorption behavior of As(V) on anatase nanoparticles was described better with Freundlich equation (R2 > 0.991). This study proposes the potential adsorbent material for water which is contaminated with arsenic species.
Site Dependence of Electronic Structure of Gd Impurities in GaN
Authors: Cheiwchanchamnangij Tawinan , Punya Atchara , Lambrecht Walter R. L. 
Published: September 2011

ABSTRACTElectronic structure calculations are reported for Gd in GaN on Ga as well as on N site and for pairs of Gd on neighboring Ga and N sites, using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The energy of formation for the N site is found to be much higher than for the Ga site even after relaxations are included. The GdN configuration is found to be at best metastable (in ZB). In WZ and in the pair configurations, the Gd is found to move toward an interstitial site leaving a nitrogen vacancy behind. The electronic structure of these structures and their magnetic moments are discussed.
First-principles Study of Nitrogen Vacancies in GdN
Authors: Punya Atchara , Cheiwchanchamnangij Tawinan , Thiess Alexander , Lambrecht Walter R. L. 
Published: September 2011

ABSTRACTThe electronic structure of nitrogen vacancies in gadolinium nitride are studied using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The vacancy is found to have two localized defect levels in the gap, one of each spin. The third electron of each vacancy in the neutral state dopes the conduction band. The single positive state is found to be the ground state for Fermi levels located anywhere within the band gap. The vacancy has a net magnetic moment of 1 μB in the neutral charge state. The presence of the vacancy is found to increase the average exchange interactions between Gd atoms and hence the Curie temperature but only by about a factor 2 compared to GdN without vacancies.
Solid Bridging during Pattern Collapse (Stiction) Studied on Silicon Nanoparticles
Authors: Peter Daniel , Dalmer Michael , Lotnyk Andriy , Kienle Lorenz , Lechner Alfred , Bensch Wolfgang 
Published: September 2011

ABSTRACTThe high surface to volume ratio of nanoparticles allows a detailed experimental study of the surface phenomena associated with solid bridging. Besides bulk analyses, the local view on the structure and composition via HRTEM is particularly essential. 50 nm core shell particles consisting of a silicon (Si) core and a SiO2 shell were used as model system to understand surface phenomena appearing for Si-based nanostructures. Evaporative drying from de-ionized water shows the most significant bridging effect based on SiO2. There is only a localized deposition of oxides between the particles during the drying process and no overall oxidation. For the deposition material, silicates are the most likely candidates.
Preparation of Nanoporous MgAl2O4 by Combined Utilization of Sol-Gel Process and Combustion of Biorenewable Oil
Authors: Hörtz Christian , Ladd Danielle M. , Seo Dong-Kyun 
Published: September 2011

ABSTRACTNanoporous MgAl2O4 particulates with high porosities were successfully prepared from sol-gel reactions, solvent exchange with castor oil and subsequent combustion and calcination at 700 °C. The products were crystalline and semitransparent. Changes in the metal precursor concentrations allowed control of pore volumes from 0.7 to 1.1 cm3/g and average pore sizes from 14 to 19 nm. The specific surface areas are about 200 m2/g regardless of the precursor concentrations. After heating at 1000 °C for 10 hours, the products kept about 70% of their original pore volume and about 60% of the original surface area. Heating at 1100 °C caused a drastic reduction of pore volume and surface area to 40 and 36%, respectively, as the average particle size increased to 23 nm.
The Adsorption and Chemistry of Tripropyl phosphate (TPP) into Microporous and Mesoporous NaX Zeolites
Authors: Meng Qingguo , Doetschman David C. , Rizos Apostolos K. , Lee Min-Hong , Schulte Jürgen T. , Spyros Apostolos , Kanyi Charles W. 
Published: September 2011

ABSTRACTAdsorption and chemistry of tripropylphosphate (TPP) in mesoporous NaX zeolite, which was templated by cationic templated polymer (polydiallyldimethylammonium chloride, PDADMAC) with two different length chains, was investigated. The structural properties of the zeolites were characterized by X-ray diffraction (XRD) and nitrogen adsorption analysis. The chemical activities of different zeolites toward the decomposition of TPP were determined with solid state 31P NMR spectra. After exposure of zeolites to TPP was sufficient and equilibrium was reached, a stoichiometric amount of water was also adsorbed and hydrolysis was observed. The TPP decomposition yields in different NaX zeolites were compared.
Mechanical Performance of Tubular Microtruss Materials Reinforced With Nanocrystalline Sleeves
Authors: Bele Eral , Azhar Mishaal , Hibbard Glenn D. 
Published: September 2011

ABSTRACTMicrotruss cellular materials are assemblies of struts with characteristic features in the μm to mm scale, arranged in a periodic, three-dimensional architecture. Compared to conventional cellular architectures (e.g. stochastic foams and honeycombs), they can possess improved structural efficiency, because externally applied loads are resolved axially along the constituent struts. We have recently fabricated composite microtruss materials by electrodepositing reinforcing nanocrystalline sleeves on tubular polymeric scaffolds. These materials can offer enhanced structural performance by exploiting advantageous properties along three length scales: the inherent strength of the electrodeposited material (grain size reduction to the nm scale), its location away from the bending axis of the struts (cross-sectional efficiency in the μm scale), and the spatial arrangement of the struts (architectural efficiency in the mm scale). This study uses finite element analysis and experimental methods to characterize the mechanical properties of these composite materials.