bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silver Nanodisk: Synthesis, Characterization and Self-Assembly
Authors: Chen Sihai , Fan Zhiyong , Carroll David L. 
Published: April 2011

ABSTRACTA new form of silver nanostructured materials, a silver nanodisk, is generated by a solution-phase approach. In this method, two main steps are applied: the first is the generation of the truncated triangular silver nanoplates, which are obtained by seed-mediated growth of silver particles using cetyltrimethylammonium bromide (CTAB) as the soft templates. The second is the mild aging of the above triangular silver nanoplate solution at 40 °C to get the desired silver nanodisks. Transmission electron microscopy and atomic force microscopy studies show that the nanodisk has a thickness of the order of 20 – 30 nm, and a diameter around 60 nm. X-ray and electron diffraction analysis reveal that the nanodisk is single crystal and with its basal plane as (111) lattice plane. These nanodisks display a strong surface plasmon absorption band at 475 nm; this band can be continuously tuned within 420 nm to 560 nm through adjusting the aging time. The formation of self-assembled monolayer of CTAB on the basal plane is suggested to account for both the anisotropic growth from triangular nanoplates to nanodisks, and the formation of large-scale necklace-like structures.
Simulation of Carbon Nanotube Pull-outWhen Bonded to a Polymer Matrix
Authors: Frankland S. J. V. , Harik V. M. 
Published: April 2011

ABSTRACTA carbon nanotube pulling through a polyethylene matrix was simulated using molecular dynamics. The interfacial sliding was characterized in terms of a nanoscale friction model, which is parametrized from the molecular dynamics simulation, and involves determining the critical pull-out force on the nanotube and the effective viscosity at the nanotube/polymer interface. Comparison was made of the pull-out behavior of non-bonded and functionalized nanotube composites. Chemical bonds between the polymer and the nanotube increased the critical pullout force, the resistance to interfacial sliding, and the interfacial viscosity.
Nanocomposite Fibers
Authors: Kim Yong K. , Lewis Armand F. , Patra Prabir K. , Warner Steven B. , Mhetre Shamal K. , Shah Mithun A. , Nam Daejin 
Published: April 2011

ABSTRACTNanocomposite fibers involve the concept of integrally dispersing nanosized particles of the second phase inorganic material into fiber forming polymers such as nylon or polyester. The material goal involves obtaining bi-phasic fibers with high mechanical stiffness and strength, electrical conductivity and/or enhanced other features such as thermal stability. Thus far, the main difficulties toward achieving nanocomposite fibers are: (1) the inability of obtaining large quantities of nanoparticles in a pure, un-agglomerated state and (2) obtaining a uniform, intimate dispersion of single entity nanoparticles in a fiber polymer matrix. These problems have been approached in the context of studying the properties of experimentally prepared nano-silica reinforced fibers and attempts to prepare carbon nanotube, CNT, containing fiber material. Modulus and tenacity tests on experimentally prepared nanosilica filled PET (polyethyleneterephthalate) fibers showed the silica nanoparticles reduced the modulus and tenacity (tensile strength) of the filled PET fiber materials. DSC and shrinkage studies on nano-silica/PET fiber show that polymer crystallinity is influenced by the presence of the silica nano-particles. Heats of melting are found to increase as the filler loading increases. In further shrinkage studies, the “shrinkage modulus” of these nanosilica/PET fibers was found to increase by the addition of silica nanoparticles. Attempts to prepare nylon reinforced CNTs (multi-wall) from a commercially available CNT/nylon resin “concentrate” failed due to the poor melt dispersion processing of the blended polymer. Only very weak CNT reinforced nylon fibers could be prepared.
Plastic Relaxation Mechanics in Systems with a Twist-Bonded Layer
Authors: Priester Catherine , Grenet Geneviève 
Published: April 2011

ABSTRACTWith a view to investigating how a thin film twist-bonded to a host substrate can have compliant behavior from a plasticity point of view, the onset and spread of edge dislocations throughout a mesa are studied. The discussion focuses on the energy relaxed by such dislocations in a mesa made from two coherently bonded lattice-mismatched layers twist-bonded onto a host substrate and patterned down to the film/host substrate interface. Our theoretical results show that the confinement of threading dislocations into a thin twist-bonded film is energetically favorable allowing the overgrowth of a mismatched layer exempt of any threading dislocation at least as far as mesas are concerned.
Electrodeposition of Ni Catalyst on Tungsten Substrates and Its Effect on the Formation of Carbon Nano- and Micro-coils
Authors: Einarsson Erik , Jiao Jun , Prado Josie , Coia George M. , Petty Jeremy , Love Logan 
Published: April 2011

ABSTRACTCarbon micro-coils and nano-coils were produced in high yield from nickel catalyst particles electrochemically deposited onto tungsten substrates. Various electrochemical deposition techniques were used to produce the nickel catalyst particles. These particles catalyzed the chemical vapor deposition (CVD) of acetylene at 800°C, resulting in growth of carbon microand nano-coils. Linear-sweep (cyclic) voltammetry produced catalyst particles which resulted in single- filament coils intermixed with thin nanotubes over most of the substrate surface. Passing the same amount of charge by constant current electrolysis produced nickel particles that decomposed carbon but did not grow coils. Catalyst particles deposited by constant current electrolysis grew nanocoils similar to linear-sweep voltammetry but in small, localized, high-yield patches. The coils produced were either spring- like micro-coils of low pitch and large diameter or rope- like nano-coils of higher pitch and smaller diameter. High-resolution transmission electron microscopy (HRTEM) showed typical graphite fringes in the filaments, but did not reveal an internal tubular structure. Catalyst particles were often detected at the ends of the coils.
Nucleation Induced Nanostructures
Authors: ten Bosch A. 
Published: April 2011

ABSTRACTNumerical simulations in films and aggregates have repeatedly shown the presence of vibrations during a phase transition and/or the appearance of periodic structures. A phase transition could be controlled and novel nanostructures created by astute manipulation of such phenomena. In order to study the occurrence and effect of wave-like phenomena, the dynamics of a first order phase transition is described using kinetic theory. At a first order phase transition, the initial phase is replaced in time by the new phase on propagation of a density front through the sample. The dynamic stability analysis studies the transition to the uniform phase by propagation of the front and provides the conditions for the formation of transient periodic structures by a local increase of density. The results apply also to spherical geometry and a discussion of cluster dynamics follows the planar case.
Nanophase Alumina/Poly(L-Lactic Acid) Composite Scaffolds for Biomedical Applications
Authors: Dulgar Tulloch Aaron J. , Bizios Rena , Siegel Richard W. 
Published: April 2011

ABSTRACTThree-dimensional composites of nanophase alumina and poly(L-lactic acid) with an interconnected porous network and an overall porosity in excess of 90% are cytocompatible. Osteoblast proliferation on the nanophase ceramic/polymer composites is a function of time of cell culture and of nanoceramic loading in the biomaterial substrates.
Synthesis of Aerogel-Metal Cluster Composites by Gamma Radiolysis
Authors: Bertino Massimo F. , Hund Jared F. , Zhang Guohui , Sotiriou-Leventis Chariklia , Leventis Nicholas , Tokuhiro Akira T. , Farmer John 
Published: April 2011

ABSTRACTNoble metal clusters (Ag, Au) were formed in a silica aerogel matrix by gamma irradiation of hydrogel precursors loaded with aqueous solutions containing Ag+ or [AuCl4]- ions. Hydrogels exposed to gamma rays assumed the color expected for colloidal suspensions of Ag (respectively Au) clusters. The hydrogels were subsequently washed and supercritically dried, without any evident change in color, indicating that the metal clusters were not removed during drying. Typical gamma ray doses were between 3 and 3.5 kGy, and achieved complete reduction of hydrogels containing metal ion concentrations in the 10-4-10-3 M range. Metal clusters in the aerogel monoliths were characterized with optical absorption, transmission electron microscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. These techniques have shown that the clusters have a crystalline fcc structure. Au clusters consist of pure Au, while surface oxidation of Ag clusters was observed with XPS.
Molecular Dynamics Simulations on Nanocomposites Formed by Intermetallic Dispersoids of L12 Type and Aluminum Matrices
Authors: Namkung Min , Paik Sun Mok , Wincheski Buzz 
Published: April 2011

ABSTRACTMolecular dynamics simulations were performed to characterize the lattice morphology in the region adjacent to the interfaces in nanocomposite systems of a Ni3Al dispersoid embedded in Al matrix (Ni3Al/Al) and an Al3Nb dispersoid embedded in aluminum matrix (Al3Nb/Al). A nearly perfect coherent interface is obtained in the Al3Nb/Al system with the lattice planes of dispersoid and matrix aligned parallel in all directions. The simulation results show the presence of the matrix atom-depleted regions near the dispersoid boundary for most cases. Detailed analysis revealed that certain sites immediately next to the dispersoid are energetically favored for the matrix atoms to occupy. The matrix atoms occupying these sites attract other atoms producing the depleted regions. In certain specific situations of Al3Nb/Al system, however, the wetting of a rotated dispersoid is overwhelmingly complete prompting the need of further study for better understanding. The order parameters of dispersoids calculated for Ni3Al in aluminum is nearly constant while that for Al3Nb in aluminum is rapidly decreasing function of temperature in the range of 300 to 1800K.
Condensation of Carbon Vapour in the Microwave Oven
Authors: Kharissova Oxana V. , Lopez Israel Nieto , Méndez Ubaldo Ortiz , Aguilar Juan A. , Rivera Moisés Hinojosa 
Published: April 2011

ABSTRACTThis work is devoted to microwave heating of graphite for studying the processing of carbon nanotubes (CNTs) by graphite vaporization. We have applied heating by microwaves (MW) (power 800W, frequency 2.45 GHz) in air at 20–90 min. The oven temperature was approximately 1200°C. The condensed material was collected on a fused silica target. After deposition, the morphology of carbon nanotubes was studied by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM). The samples were found to contain nanotubes, nanoparticles and fibers (at 1.30–2.80 micrometers to 6–11 micrometers) which appeared to be highly graphitized. It was observed that multi-walled nanotubes (MWNT's) were produced by this method.
Deformation-induced crystallization and amorphization of Al-based metallic glasses
Authors: Hebert Rainer J. , Perepezko John H. 
Published: April 2011

ABSTRACTA main requirement for the application of nanostructured materials for structural applications is their thermal stability. Structural materials are often exposed to mechanically-induced stress states. Nanomaterials for structural applications should therefore retain their microstructure not only within a defined temperature range but also under applied load. Cold-rolling experiments with melt-spun Al87Ni10Ce3ribbons containing a dispersion of nanocrystallites in an amorphous matrix demonstrate that during the continued deformation through repeated rolling and folding crystallization as well as amorphization reactions could be induced. The results indicate that in addition to the microstructure control through annealing of precursor materials, deformation processing represents an effective approach to the synthesis of amorphous and nanophase composite materials.
Densification and Sintering of a Microwave-Plasma-Synthesized Iron Nanopowder
Authors: Kecskes L. J. , Woodman R. H. , Klotz B. R. 
Published: April 2011

ABSTRACTPowder compacts made from microwave-plasma-synthesized iron (Fe) nanopowder (Materials Modification Inc., Fairfax, VA) were sintered under hydrogen (H2). Results showed that without the application of pressure, the powder could not be sintered to full density. In subsequent experiments, the powder was consolidated to final densities near 80% of the theoretical full density, using plasma pressure compaction (P2C). To provide an explanation for the difficulty in attaining full densification, the precursor powder and compacted pellet characteristics were examined by several methods. These included residual porosity by mercury pycnometry, surface area measurement by Brunauer, Emmett, and Teller (BET) analysis, and structural change by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It was observed that the nanosized primary particles were aggregated into micrometer-sized dendritic structures, with the appearance of tumbleweeds. The observed limitations in the densification and associated porous microstructures of the pressureless-sintered and P2C-densified compacts were rationalized in terms of the behavior of the dendritic aggregate structures rather than that of the nanosized primary particles.
Continuum Mechanics-Discrete Defect Modeling and Bubble Raft Simulation of Cracked Specimen Response in Nanoscale Geometries
Authors: Starr Michael J. , Drugan Walter J. , Lopez-Garcia Maria d. C. , Stone Donald S. 
Published: April 2011

ABSTRACTIn a continuation of prior work, a new group of Bragg bubble model experiments have been performed to explore the effects of nanoscale crack size and nanoscale structural geometry on atomically-sharp crack tip dislocation emission behavior. The experiments have been designed to correspond to the theoretical limits that bound the expected crack tip response. Continuum elasticity analyses of these situations have also been carried out, in which the leading-order terms in the Williams expansion (the K and T terms) are determined, and the predictions of these continuum analyses coupled with discrete dislocation theory are compared with the experimental results. The experiments exhibit fascinating changes in crack tip dislocation emission direction with changing crack and structural size, crack location and loading conditions, as well as substantial changes in the magnitude of the resolved shear stress that drives dislocation emission. These changes are predicted well by the continuum elasticity-discrete dislocation model down to extremely small dimensions, on the order of a few atomic spacings. Preliminary experiments were performed with layered and two-atom basis rafts to establish crucial comparisons between theory and experiment that validate the applicability of continuum elasticity theory to make predictions directly related to nanoscale fracture behavior.
Structure and Characterization of Sol-gel and Aerogel Materials and Oxidation Products from the Reaction of (CH3O)4Si and C16H33Si(OCH3)3
Authors: Tillotson Thomas M. , Reynolds John G. 
Published: April 2011

ABSTRACTReactions of (CH3O)4Si and C16H33Si(OCH3)3 at various mole ratios were performed in methanol using base and acid catalysis. Sol-gel materials were formed that have low surface areas (∼10 m2/g). Subsequent supercritical drying using CO2 at 40 °C produced materials that are very different than traditional aerogels, with surface areas around the same values as the corresponding sol-gels, as well as no detectable meso-pore features. In some cases, the aerogels even melted upon heating. Spectroscopic characterization, using IR, 29Si and 13C NMR revealed normal Si-O substitution as well as incorporation of the carbon chain into the Si framework.Heating of the stable forms of the materials in air at different temperatures yielded, depending upon oxidation conditions, several materials with much higher surface areas, typical of aerogels. Pore size distribution measurements revealed meso-pore features with a narrow distribution around 35Å. Spectroscopic characterization revealed the disappearance of the R-Si substitution and the appearance of an oxidized intermediate.This paper will describe the chemistry and characterization of these unusual sol-gels, aerogels, and oxidation products, as well as potential applications.
Nanomechanical Characterization on Zinc and Tin Oxides Nanobelts
Authors: Zhao Minhua , Mao Scott , Wang Zhong Lin , Xu Fengting , Barnard John A 
Published: April 2011

ABSTRACTNanobelts are a group of materials that have a rectangle-like cross section with typical widths of several hundred nanometers, width-to-thickness ratios of 5 to 10, and lengths of hundreds of micron meters. In this paper, nanoindentations were made on individual ZnO, SnO2 nanobelts and (0001) bulk ZnO by using AFM and Hysitron Triboscope indenters. It was shown that the indentation size effect was still obvious for the indentation depth under 50 nm. It is also demonstrated that nanomaching is possible on nanobelt using AFM tip.
Interfacial Effects on the Premature Failure of Polycrystalline Silicon Structural Films
Authors: Muhlstein C.L. , Stach E.A. , Ritchie R.O. 
Published: April 2011

ABSTRACTAlthough bulk silicon is not known to be susceptible to cyclic fatigue, micron-scale structures made from mono and polycrystalline silicon films are vulnerable to degradation by fatigue in ambient air environments. Such silicon thin films are used in small-scale structural applications, including microelectromechanical systems (MEMS), and display “metal-like” stress-life (S/N) fatigue behavior in room temperature air environments. Previously, the authors have observed fatigue lives in excess of 1011 cycles at high frequency (∼40 kHz), fully-reversed stress amplitudes as low as half the fracture strength using a surface micromachined, resonant-loaded, fatigue characterization structures. Stress-life fatigue, transmission electron microscopy, infrared microscopy, and numerical models were used to establish that the mechanism of the fatigue failure of thin-film silicon involves the sequential oxidation and environmentally-assisted crack growth solely within the native silica layer, a process that we term “reaction-layer fatigue”. Only thin films are susceptible to such a failure mechanism because the critical crack size for catastrophic failure of the entire silicon structure can be exceeded by a crack solely within the native oxide layer. The importance of the interfacial geometry on the mechanics of the reaction-layer fatigue mechanism is described.
Controlling Casimir Forces in Mems and Nems
Authors: Esquivel-Sirvent R. , Villarreal C. 
Published: April 2011

ABSTRACTWe present a theoretical study of vacuum effects in systems of length scales of micrometers and nanometers. In particular, we calculate the Casimir force between dielectric plates with different compositions. We show that by an appropriate choice and configurations of materials, the Casimir forces develop noticeable changes than could be used to inhibit or modulate the action of vacuum fluctuations in MEMS and NEMS.
Tailoring of Stress Development in MEMS Packaging Systems
Authors: Walwadkar Satyajit S. , Cho Junghyun , Farrell P.W. , Felton Lawrence E. 
Published: April 2011

ABSTRACTA better understanding of the origin and evolution of the stresses is a crucial step in improving reliability of packaging systems for microelectromechanical systems (MEMS). Given its importance, we examine the stresses developed in hermetically packaged MEMS inertial sensors. For this purpose, an optical surface profilometer is employed to assess the stresses by measuring the curvature of dummy silicon dies (3.5×3.5 mm2) assembled in different types of packages and die attach adhesives. We also explore a temporal evolution of stresses during thermal exposure of the test packages in an effort to emulate actual packaging processes and device operation conditions. The result shows different levels of stresses generated from various adhesives and package types, and also a stress evolution during packaging processes. The mechanical stress data also show a good agreement with MEMS performance data obtained from actual accelerometers. Therefore, the stress data will not only be useful in better understanding performance of MEMS packages, but the testing protocol can also provide a diagnostic tool for very small packaging systems.
Defect-Induced Shifts in the Elastic Constants of Silicon
Authors: Allred Clark L. , Borenstein Jeffrey T. , Weinberg Marc S. , Yuan Xianglong , Bazant Martin Z. , Hobbs Linn W. 
Published: April 2011

ABSTRACTAs MEMS devices become ever more sensitive, even slight shifts in materials properties can be detrimental to device performance. Radiation-induced defects can change both the dimensions and mechanical properties of MEMS materials, which will be of concern to designers of MEMS for applications involving radiation exposure, such as those in a reactor environment or in space. We have performed atomistic simulations of the effect that defects and amorphous regions, such as could be produced by radiation damage, have on the elastic constants of silicon. We have then applied the results of the elastic constant shift calculations to a hypothetical MEMS device, and calculated the difference that would be generated by this effect.
Design and Performance of a Microengine Realized with Arrays of Asymmetrical Electrothermal Polysilicon Surface Micromachined Microactuators
Authors: Kolesar Edward S. , Ruff Matthew D. , Odom William E. , Jayachandran Joseph A. , McAllister Justin B. , Ko Simon Y. , Howard Jeffery T. , Allen Peter B. , Wilken Josh M. , Boydston Noah C. , Bosch Jorge E. , Wilks Richard J. 
Published: April 2011

ABSTRACTThis research focuses on the design and experimental characterization of two types of MEMS asymmetrical electrothermal microactuators. Both microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. Deflection and force measurements of both microactuators as a function of applied electrical power are presented. Also described is the practical integration of the electrothermal microactuators in a monolithic microengine that is capable of rotating a set of gears.
Manufacturing of 3-D Microstructures Using Novel Upsams Process for Mems Applications
Authors: Sharon André , Bilsing Axel , Lewis Gordon , Zhang Xin 
Published: April 2011

ABSTRACTThis paper introduces a new microfabrication technique, Ultraprecision Manufacturing of Self-Assembled Micro-Systems (UPSAMS), which combines ultraprecision micromachining (milling/turning/drilling/grinding) with sacrificial/structural multi-layer manufacturing processes to produce self-assembled, 3-D microsystems and associated mesoscale interfaces from a variety of materials for MEMS applications. With this process, a new class of microsystems can be developed that is highly three dimensional, precisely machined, and automatically assembled.