bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomistic Modeling of Elasticity and Fracture of a (10,10) Single Wall Carbon Nanotube
Authors: King Ryan , Buehler Markus J 
Published: April 2011

ABSTRACTWe use the ReaxFF reactive force field to model extreme tensile deformation of a (10,10) armchair carbon nanotube. The ReaxFF force field has been developed based on DFT quantum mechanical calculations without any empirical parameters (Duin et al., 2001). We report an analysis of the stress-strain relationship for the elastic and plastic regime, including a description of the microscopic fracture mechanisms. We find Young's modulus to be around 1 TPa, close to experimental values. Our modeling yields a fracture tensile strain of approximately 30%, with a maximum tensile stress of approximately 300 GPa. Fracture of the CNT originates from formation of 5-7 Stone-Wales-like defects, leading to formation of micro-cracks.
Air Bridge and Vertical Carbon Nanotube Switches for High Performance Switching Applications
Authors: Kaul Anupama B , Wong Eric W , Epp Larry , Bronikowski Michael J. , Hunt Brian D 
Published: April 2011

ABSTRACTCarbon nanotubes are attractive for switching applications since electrostatically-actuated CNT switches have low actuation voltages and power requirements, while allowing GHz switching speeds that stem from the inherently high elastic modulus and low mass of the CNT. Our first NEM structure, the air-bridge switch, consists of suspended single-walled nanotubes (SWNTs) that lie above a sputtered Nb electrode. Electrical measurements of these air-bridge devices show well-defined ON and OFF states as a dc bias of a few volts is applied. The switches were measured to have switching times down to a few nanoseconds. Our second NEM structure, the vertical CNT switch, consists of nanotubes grown perpendicular to the substrate. Vertical multi-walled nanotubes (MWNTs) are grown directly on a heavily doped Si substrate, from 200 − 300 nm wide, ∼ 1 μm deep nano-pockets, with Nb metal electrodes to result in the formation of a vertical single-pole-double-throw CNT switch architecture.
Elastodynamic Characterization of Imprinted Nanolines
Authors: Johnson Ward L. , Flannery Colm M. , Kim Sudook A. , Geiss Roy , Heyliger Paul R. , Soles Chris L. , Hu Walter , Pang Stella W. 
Published: April 2011

ABSTRACTThe advancement of imprint lithography as a method for fabricating nanostructures is impeded by a lack of effective tools for characterizing mechanical properties and geometry at the nanoscale. In this report, we describe the development of methods for determining elastic moduli and cross sectional dimensions of imprinted nanolines from Brillouin light scattering (BLS) measurements using finite-element (FE) and Farnell-Adler models for the vibrational modes. An array of parallel nanoimprinted lines of polymethyl methacrylate (PMMA) with widths of ∼65 nm and heights of ∼140 nm served as a model specimen. Several acoustic modes were observed with BLS in the low-gigahertz frequency range, and the forms of the vibrational displacements were identified through correlation with calculations using measured bulk-PMMA moduli and density as input. The acoustic modes include several flexural, Rayleigh-like, and Sezawa-like modes. Fitting of Farnell-Adler calculations to the measured dispersion curves was explored as a means of extracting elastic moduli and nanoline dimensions from the data. Some values obtained from this inversion analysis were unrealistic, which suggests that geometric approximations in the model introduce significant systematic errors. In forward calculations, the frequencies determined with the FE method are found to more closely match measured frequencies. This suggests that the FE approach may be more accurate for inversion analysis. Initial estimates of uncertainties in the FE calculations support this conclusion.
Calcium Phosphate Bioceramics with Tailored Crystallographic Texture for Controlling Cell Adhesion
Authors: Kim Hyunbin , Camata Renato P. , Lee Sukbin , Rohrer Gregory S. , Rollett Anthony D. , Hennessy Kristin M. , Bellis Susan L. , Vohra Yogesh K. 
Published: April 2011

ABSTRACTThe orientation distribution of crystalline grains in calcium phosphate coatings produced by pulsed laser deposition was investigated using an X-ray pole-figure diffractometer. Increased laser energy density of a KrF excimer laser in the 4–7 J/cm2 range leads to the formation of hydroxyapatite grains with the c-axis preferentially aligned perpendicularly to the substrates. This preferred orientation is most pronounced when the plume direction of incidence is normal to the substrate. This crystallographic texture of hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups, and dehydroxylation effects during deposition all seem to play important roles in texture development. Studies of cell adsorption using human Mesenchymal stem cells reveal that hydroxyapatite coatings with strong texture and random orientation show different cell adsorption behavior, which is consistent with the notion that protein attach differently on different faces of hydroxyapatite crystals. Cells seeded on textured coatings exhibit better spreading and adhesion compared to those placed on randomly oriented coatings.
Biphasic Polymeric Shell-Core 3D Fiber Deposited Scaffolds Enhance Chondrocyte Differentiation
Authors: Moroni Lorenzo , Hendriks Jeanine A.A. , Schotel Roka , de Wijn Joost R. , van Blitterswijk Clemens A. 
Published: April 2011

ABSTRACT3D fibrous scaffolds with shell-core fiber architecture offer the possibility to create multifunctional structures. In this study, a construct that combines mechanical stability with the core polymer and optimal surface properties for cell-material interactions with the shell polymer is discussed. Scaffolds were fabricated by a rapid prototyped technique known as 3D Fiber Deposition (3DF) and used for cartilage tissue engineering. Cells maintained the typical rounded morphology of cartilage in the shell-core scaffolds, while they spread into a spindle-like shape in scaffolds fabricated with the core polymer only. Extracellular matrix production and an increase in the dynamic stiffness of the engineered construct revealed a progressive maturation of the formed tissue, suggesting that shell-core 3D scaffolds could be optimal for cartilage tissue engineering.
Sequential Bone Response to Immediately Loaded Mini-Implants, in vivo Study
Authors: Guimarães Glaucio Serra , de Morais Liliane Siqueira , Elias Carlos Nelson , Meyers Marc Andre 
Published: April 2011

ABSTRACTThe use of osseointegrated titanium implants has been related like an excellent alternative to traditional orthodontic anchorage methodologies, and they are a necessity when dental elements lack quantity or quality, when extraoral devices are impractical, or when noncompliance during treatment is likely. In orthodontics, the implants can be use to anchor different movements. However, conventional dental implants can only be placed in limited areas such as the retromolar or the edentulous areas. Another limitation has been the direction of the force application and conventional dental implants are troublesome for patients because of the severity of the surgery, the discomfort of the initial healing, and the difficulty of oral hygiene. Due to these factors, mini-implants became widely used. They have little limitations related to the local of implantation, the surgical procedure of insertion is relatively simple and the control of direction and quantify of the force is simple to be done. These improvements were obtained due to decrease of the size, but these changes could result on significant changes to the bone-implant interface. Since, the orthodontic treatment has to be done as fast as possible. The purpose of this work is to analyze the bone healing reactions to immediately loaded mini-implant of titanium alloy grade 4 by histological, fluorescent and SEM observation, by histomorphometric analysis and by removal torque test. Material and method: Seventy two mini-implants were inserted in eighteen New Zealand rabbits. Four mini-implants were put in the right tibiae of each rabbit and two of then were loaded immediately with 100 gf. Subcutaneous injections of fluorescent labels were administrated in defined periods. The animals were euthanized after 1, 4 and 12 weeks, performing three time analysis and the tibias were dissected and prepared to microcopy analysis and to removal torque test. Results: The results indicated that all the mini-implants remained stable during experimental time. The SEM findings indicated no differences between load and unload group in one and four weeks period, although, the 12 weeks loaded group demonstrated more mature bone formation than the unload group in the same time. These findings suggest that the force can be applied after insertion of the mini-implant without compromises their stability.
Nano Monitors for Identification of Vulnerable Cardio-vascular Plaque
Authors: Prasad Shalini , Barrett Thomas , Carruthers John 
Published: April 2011

AbstractWe describe highly sensitive, non–invasive, label-free, electrical detection of protein biomarkers using nanoporous alumina membrane based electrochemical conductance based devices. The principle of operation of these sensors are based on electrochemical conductance varitions associated with the binding of antibody-antigen complexes to a metallic substrate.In these devices distinct pore clusters are selectively surface functionalized with specific antibodies, that are in turn are incorporated into micro scale arrays. Protein markers were routinely detected at nanomolar concentrations. This opens the potential for developing highly sensitive and selective biomarker detection assays in clinically relevant samples for diagnosis of complex disease state like vulnerable coronary plaque rupture that results in poor post surgical outcomes and other complex diseases.
A polymer-based Chronic Nerve Interface Microelectrode Array
Authors: Farrell Brian , Jauniskis Linas , Phely-Bobin Thomas , Streeter Richard , Edell David , Dean Robert 
Published: April 2011

ABSTRACTThis paper will present ongoing work in the development of a thin, flexible, photolithographically-defined polymer-based electrode array based on Liquid Crystal Polymer (LCP) films and substrates. The goal of the effort is to develop and qualify a new platform technology that would allow accurate positioning of large numbers of electrode contacts in neural tissue for chronic applications. LCP films are a far greater match to the density of neural tissue than the competing wire and silicon arrays and thus will match the bending and flexing as the neural tissues change dimension. This flexibility would cause less neural damage and will maintain a more constant relationship with local neurons. Technology development activities include thin film metallization, interconnect insulation and device microfabrication.
Cold Neutron Prompt Gamma-Ray Activation Analysis for Characterization of Hydrogen Storage and Related Materials
Authors: Paul Rick 
Published: April 2011

ABSTRACTPrompt gamma-ray activation analysis (PGAA) is an important technique for analyzing materials that may impact the hydrogen economy. An instrument for cold neutron PGAA, located at the NIST Center for Neutron Research (NCNR), has proven useful for the measurement of hydrogen and other elements in a variety of such materials. The detection limit for hydrogen is less than 10 mg/kg for most materials. PGAA has been used to characterize materials with potential for hydrogen storage (e.g. single wall carbon nanohorns, lithium magnesium imides, and zirconium beryllium hydrides), to measure hydrogen uptake by solid proton conductors, and to characterize stoichiometries of Nafion films used as membranes in fuel cells. Future upgrades to the instrument will improve detection limits, applicability, and user interface.
Advantages of high surface area niobium oxide catalysts on MgH2 sorption properties
Authors: Bhat Vinay V , Rougier Aline , Aymard Luc , Nazri Gholam A , Tarascon Jean-Marie 
Published: April 2011

ABSTRACTWe report the synthesis by ‘chimie douce’ route of high surface area (200 m2/g) nano crystalline Nb2O5 (so called p-Nb2O5) and the importance of its addition to enhance the hydrogen sorption properties of MgH2. All of the prepared Nb2O5 catalysts induce faster kinetics, up to twice the desorption rate, than commonly used commercial Nb2O5. Among them, both p-Nb2O5 and Nb2O5:350 (p-Nb2O5 heated to 350 °C) exhibit the best catalytic activity, since a 5.2 wt% hydrogen desorption was achieved at 300 °C for (MgH2)p−Nb2O5, as compared to less than 4 wt.% for commercial Nb2O5 added MgH2, (MgH2)c−Nb2O5, within 12 min. Furthermore, due to the addition of high surface area Nb2O5, the desorption temperature was successfully lowered down to 200 °C, with a significant amount of desorbed hydrogen (4.5 wt%). In contrast at this “low” temperature, (MgH2)c−Nb2O5 shows no desorption.
Capillary Densification of Hydrogen in Nanoporous, Amorphous Carbons
Authors: Lustig Steven R. , Shiflett Mark , Corbin David , Gai Pratibha , Kourtakis Konstantinos 
Published: April 2011

ABSTRACTWe have studied the effect of synthesis conditions on the nanostructure of advanced carbons that show moderate to high hydrogen storage. We have performed in situ studies of the dynamic pyrolysis of palladium catalyzed multifunctional polymers (MFP) in nitrogen environments, to understand the effect of process parameters and to utilize the results in the development of optimum nanostructures to meet the storage requirements. Carbon sorbents have been synthesized from polysaccharides including chitosan, chitin, and cellulose. Pyrolysis in a hydrogen atmosphere at 1373 K and 24 h has lead to microporous carbons with an optimum surface area and pore volume exceeding 2000 m2 g−1 and 2.0 cc g−1, respectively. Gravimetric microbalance studies indicate that these materials physically absorb hydrogen and store between 7 to 10 mass percent at 10 bar and 100 K. TEM micrographs indicate that the amorphous carbon shows additional ordering with prolonged hydrogen treatment from 2 to 24 h which has proven beneficial in increasing hydrogen storage. X-ray diffraction, TEM analysis, and porosimetry measurements also indicate that extending hydrogen exposure beyond 24 h leads to decreasing hydrogen storage due to the continuation of a loss in carbon relative to metal contaminants (P, Ca, Na) in the starting materials and increased crystallinity. Comparison of the results have shown that for advanced carbons derived from polymers or natural products treated with hydrogen at high temperatures, the optimum nanostructure is substantially disordered (turbostratic) graphite, whereas for materials derived from MFP, it is primarily amorphous carbon. The experiments have also revealed the optimum temperature region for storage where sorption/desorption curves show evidence of capillary condensation/densification.
The Inclusion of Hydrogen in Clathrate Hydrates of the Various Guests and Tuning of the tert-Butylamine Hydrate
Authors: Lee Huen , Lee Jong-won , Kim Do Youn , Park Jeasung 
Published: April 2011

ABSTRACTClathrate hydrates of structure II with organic cyclic oxides were identified to have the ability to include molecular hydrogen into their empty small cages at near-ambient temperature and moderate pressure. Solid-state NMR and Raman spectroscopy of the included hydrogen molecules indicate that the small cavities are both singly and doubly occupied by hydrogen molecules in the mixed hydrates. The inclusion mechanism can be derived from the critical progression of the cage occupancies as determined from in-situ kinetic experiments on formation and decomposition. The inclusion ability of hydrogen molecules was observed for several organic clathrate hydrate formers such as THF (tetrahydrofuran) and 1,4-dioxane, suggesting this to be a general property. A structural transition of the simple amine hydrate was suggested to produce a novel double CH4 + t-BuNH2 hydrate as confirmed by using microscopic analytical methods. The corresponding hydrate compositions were determined by using NMR spectroscopy to describe a tuning mechanism to increase the storage capacity.
Phonon modes, dielectric constants, and exciton mass parameters in ternary MgxZn1−xO
Authors: Bundesmann Carsten , Lorenz Michael , Grundmann Marius , Schubert Mathias 
Published: April 2011

ABSTRACTThe long-wavelength optical phonons and dielectric constants of PLD-grown MgxZn1−xO films are studied by combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The ternary alloy MgxZn1−xO exhibits a phase transition with change of coordination number from four-fold coordinated, hexagonal wurtzite structure (ZnO) to six-fold coordinated, cubic rocksalt structure (MgO). It is found that both phonon mode frequencies and dielectric constants change abruptly upon phase transition, which is assigned to the change of coordination number. The change of dielectric constants can be related to the change of electronic properties, for instance, the exciton binding energy. In a simple approach, the exciton binding energy depends on the reduced exciton mass and the static dielectric constant. By comparison with experimental values of the exciton binding energies it is found that the reduced exciton mass must increase by a factor of about two upon face transition from wurtzite to rocksalt structure.
Vapor-Phase Functionalization of Nanostructured Gradient-Index Titanium Dioxide Thin Films
Authors: van Popta Andy C. , Steele John J. , Tsoi Shufen , Fok Enrico , Veinot Jonathan G. C. , Brett Michael J. , Sit Jeremy C. 
Published: April 2011

ABSTRACTChemical treatments, when applied to nanostructured oxide thin films, can be used to generate added functionality in many devices. In this study, a nanostructured defect-mode optical filter was prepared by glancing angle deposition of titanium dioxide and functionalized with 3,3,3-trifluoropropyl-trichlorosilane to render the thin film insensitive to variable humidity conditions. Electrical characterization and contact angle measurements demonstrate that the hydrophilic thin film becomes hydrophobic when functionalized, and transmission measurements clearly show that the wavelength shift of the defect-mode becomes strongly inhibited for a wide range of humidity levels.
Structuring of Low Firing Temperature PZT Thick Films by Photolithography
Authors: Schimpf Stefan , Schmidt Bertram 
Published: April 2011

ABSTRACTStructured piezoelectric PZT thick films were fabricated on silicon wafers. Different supplements, like lead oxide and glasses, were added to the PZT to enhance the sintering. The films were structured by doctor blading on an epoxy based photoresist mask. This allows very accurate micro patterns of high quality piezoelectric material. A firing process was developed to gain PZT structures with 200 μm in lateral size and a 200 μm pitch. The structures were electrically contacted, poled and characterized.
Studies of Interfacial Optical and Electrical Properties on Transparent Dielectrics/ZnO Systems
Authors: Wang Ran Shi , An Jin , Ong H.C. 
Published: April 2011

ABSTRACTTransparent conducting oxides (TCOs) have recently attracted considerable attention due to their potential in making "invisible electronic circuits". Among different TCOs, ZnO is probably one of the most promising candidates due to its desirable optical and electrical properties. In the transistor, metal and metal-dielectric in general are used as the gate on the active channel layer to control the flow of carriers. In order to obtain high mobility, the interface between the gate and ZnO must be well controlled so that the unwanted surface recombination can be minimized. Although studies of metal/ZnO have been well documented, only a few are seen on metal/dielectric/ZnO. Here, we report a systematic study on AlOx/ZnO and MgOx/ZnO interfaces for the potential use on transistor. From previous optical measurements, both the photoluminescence (PL) and cathodoluminescence (CL) show that the cap layers improves the emission characteristics of ZnO by enhancing the band-edge emission while at the same time reducing the unwanted deep-level emissions [K.C. Hui, H.C. Ong, P.F. Lee, J.Y. Dai, Appl. Phys. Lett. 86, 152116 (2005)]. On the contrary, in this study, we find post-thermal annealing of AlOx/ZnO and MgOx/ZnO gradually degrades the emission as well as charge transport properties, which indicates defects evolve upon annealing. By using secondary ion mass spectroscopy (SIMS), we elucidate out-diffusion of Zn into the oxide layer is the root cause of degrading the optical and electrical properties of oxide/ZnO.
Preparation and Characterization of Solid Oxide Fuel Cells Cathode Films
Authors: Baqué Laura , Serquis Adriana , Grunbaum Nicolás , Prado Fernando , Caneiro Alberto 
Published: April 2011

ABSTRACTPerovskite oxide cobaltites with composition La0.4Sr0.6Co0.8Fe0.2O3 have been prepared by an acetic acid-based gel route. Then, cathodes were deposited onto porous ceramic substrates, like the usual electrolytes Cerium Gadolinium Oxide (CGO), by spray, spin coating and dip-coating. The structure and morphology of the layers were characterized by XRD and SEM, respectively. Electrical properties are characterized by complex impedance measurements. Finally, the correlation between structural characteristics and electrical properties is discussed.
The Mexican Cactus as a New Environmentally Benign Material for the Removal of Contaminants in Drinking Water
Authors: Young Kevin Andrew , Anzalone Alessandro , Pichler Thomas , Picquart Michel , Alcantar Norma A. 
Published: April 2011

ABSTRACTThe use of natural environmentally benign agents in the treatment of drinking water is rapidly gaining interest due to their inherently renewable character and low toxicity. We show that the common Mexican cactus produces a gum-like substance, cactus mucilage, which shows excellent flocculating abilities and is an economically viable alternative for low-income communities. Cactus mucilage is a neutral mixture of approximately 55 high-molecular weight sugar residues composed basically of arabinose, galactose, rhamnose, xylose, and galacturonic acid. We show how this natural product was characterized for its use as a flocculating agent. Our results show the mucilage efficiency for reducing arsenic and particulates from drinking water as determined by light scattering, Atomic Absorption and Hydride Generation-Atomic Fluorescence Spectroscopy. Flocculation studies proved the mucilage to be a much faster flocculating agent when compared to Al2(SO4)3 with the efficiency increasing with mucilage concentration. Jar tests revealed that lower concentrations of mucilage provided the optimal effectiveness for supernatant clarity, an important factor in determining the potability of water. Initial filter results with the mucilage embedded in a silica matrix prove the feasibility of applying this technology as a method for heavy metal removal. This project provides fundamental, quantitative insights into the necessary and minimum requirements for natural flocculating agents that are innovative, environmentally benign, and cost-effective.
Adsorption of Heavy Metals and Organic Contaminants on Functionalized Periodic Mesoporous Organosilicates
Authors: Ding Fengling , Ingram Conrad 
Published: April 2011

ABSTRACTMesoporous organosilicates containing an ethylene bridge within the otherwise silicate pore walls and an additional organic functionality extended within the pore showed varying adsorption capacities for mercury and dimethylphenol. Thiol and imidazole functionalized organic-inorganic materials were effective for the adsorption of mercury, whereas the purely siliceous mesoporous MCM-41 was more effective for dimethylphenol adsorption than its organosilicate counterparts.