bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Relaxations of Aluminum Simulated by Bond Order Potentials
Authors: Nishitani S. R. , Ohgushi S. , Adachi H. , Aoki M. 
Published: April 2011

AbstractAn interatomic potential for aluminum was developed, which is based on empirical tight binding approximations. The model successfully reproduced the shear constants, structure energy differences, and phonon dispersion curves. This transferable potential was applied on static surface relaxations, and shows good agreements with experimental results on the oscillatory damped behavior of the multilayer relaxations and the expansion of the (111) surface.
A Discrete Dislocation Analysis of Crack Growth under Cyclic Loading
Authors: Cleveringa H.H.M. , Van Der Giessen E. , Needleman A. 
Published: April 2011

AbstractCyclic loading of a plane strain mode I crack under small scale yielding is analyzed using discrete dislocation dynamics. The dislocations are all of edge character, and are modeled as line singularities in an elastic solid. At each stage of loading, superposition is used to represent the solution in terms of solutions for edge dislocations in a half-space and a nonsingular complementary solution that enforces the boundary conditions, which is obtained from a linear elastic, finite element solution. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated into the formulation through a set of constitutive rules. An elastic relation between the opening traction and the displacement jump across a cohesive surface ahead of the initial crack tip is also specified, which permits crack initiation and crack growth to emerge naturally. It is found that crack growth can occur under cyclic loading conditions even when the peak stress intensity factor is smaller than the stress intensity required for crack growth under monotonic loading conditions.
A Multiple Slip Plane Model for Crack-Tip Plasticity
Authors: Noronha S. J. , Roberts S. G. , Wilkinson A. J. 
Published: April 2011

AbstractA single slip plane dislocation dynamics based model for the brittle to ductile transition has been extended to have multiple slip planes around the crack-tip. The crack-tip plastic behaviour is studied for a variety of dislocation source configurations. The results are presented for the case of iron. The effect of modelling the plastic-zone as a single slip plane and as an array of parallel slip planes are compared.
The Effect of Material Inhomogeneity on Serrated Plastic Flows
Authors: Li X. , Tong W. 
Published: April 2011

AbstractSerrated plastic flows or propagating Portevin-Le Chatelier (PLC) bands in uniaxial tensile aluminum alloy sheet samples were analyzed by a 3D finite element model. A local dynamic strain aging viscoplasticity model motivated by dislocation dynamics was implemented in an ABAQUS user material subroutine. When the sheet metal was assumed to be spatially homogeneous, individual plastic deformation bands inclined about 50° with regard to the axial tensile loading were predicted by the model to propagate along the thin sheet sample, similar to the experimentally observed behavior of the solid solution strengthened alloy AA5182-0. When the sheet metal was assumed to be inhomogeneous by making a few material elements slightly harder or softer, the model predicted a propagating single neck formed by double shear bands, similar to the behavior of the precipitation strengthened alloy AA6111-T4.
Self-Affine Fractal Characterization of a TNT Fracture Surface
Authors: Meisel L. V. , Scanlon R. D. , Johnson M. A. , Lanzerotti Y. D. 
Published: April 2011

AbstractA trinitrotoluene (TNT) fracture surface image is characterized in terms of a self-affine fractal structure. The fracture surface was produced by high acceleration in an ultracentrifuge when the TNT strength was exceeded. An atomic force microscope (AFM) captured the topography of a 4 micron square region on the fracture surface. The present analysis supports a self-affine description of the TNT fracture surface (wavelengths of 0.016 micron to 4.0 micron) and provides a new prespective on fracture processes in TNT. An essential step in self-affine fractal characterization of surfaces is the determination of reference surfaces. A self-affine fracture surface can be described in terms of a single-valued height function. In the TNT fracture surface, single-valued height functions, which describe surface texture can only be defined with respect to curved reference surfaces. By employing curved reference surfaces, we have demonstrated that self-affine fractal scaling can be used to characterize the TNT fracture surface. This provides important information that is not evident in the analysis of individual surface scans.
Dislocation Interactions with Lamellar Grain Boundaries in Titanium Aluminum Intermetallics
Authors: Wiezorek Jörg M. K. , Zhang Xiao-Dong , Fraser Hamish L. 
Published: April 2011

AbstractThe interactions of dislocations asscociated with deformation modes active in hard orientation compressed polysynthetically-twinned (PST) TiAl with lamellar boundaries have been studied by transmission electron microscopy (TEM). The deformation modes observed in the γ-phase involved soft superdislocation and hard ordinary dislocation slip, and hard twin systems. The transfer of these latter hard twin shears occurred across all types of lamellar (γ/γ)- and frequently across (γ/α2)-boundaries. Slip of superdislocations in the minority U2-phase lamellae has been shown to be associated with both direct transfer of piled-up twinning dislocation shears across the lamellar boundaries and the activation of interfacial sources due to pile-up stresses. The active deformation modes were consistent with macroscopic shape changes of the PST-TiAI when the various defect interactions with the lamellar boundaries and the proposed shear trasnfer processes were considered.
Atomistic Modeling of Interfacial Diffusion in the Lamellar Li0 TiAl
Authors: Nomura M. , Luzzi D. E. , Vitek V. 
Published: April 2011

AbstractAtomistic simulation employing many-body central-force potentials was performed to elucidate the diffusion mechanisms in the bulk and at lamellar interfaces assuming a vacancy mechanism. First the self- diffusion of Ti and Al in stoichiometric structures was studied. It was found that the diffusion was faster along lamellar interfaces than in the bulk; the effective activation energy for the diffusion coefficient is about ∼15% lower. The simulations were then extended to investigate diffusion along lamellar boundaries with segregated Ti which is likely in Ti rich alloys. The surprising result is that diffusion remains practically unchanged when compared with the stoichiometric case. The reason is that while the path controlling the diffusion is different, the corresponding effective formation and migration energies are practically the same as in the stoichiometric case.
A Model for Predicting Weld Metal Grain Refinement in G-V Space
Authors: Grong Ø. , Cross C.E. 
Published: April 2011

AbstractA model has been developed which allows for the graphical representation of undercooling and nucleation site density in G-V space (i.e. temperature gradient G versus growth rate V). This model is used to explain a unique grain structure in weldments where equiaxed grains may be found both at the fusion boundary and along the center of the weld metal. Details of this model will be given and discussed in relation to grain refinement predictions in G- V space.
Modeling the Effect of Noise on Multiscale Dislocation Cell Structures
Authors: Miodownik M. A. , Holm E. A. , Browne D.J. 
Published: April 2011

AbstractPlastic flow in metals occurs by a dislocation mechanism in which strain is accommodated by a dislocation flux. This results in tangled networks of dislocations which self-organize into stable cell structures with two characteristic length scales. These structures have a number of remarkable properties not least of which is that they exhibit scaling. We examine the idea that the evolution of geometrically necessary boundaries is dominated byrandom fluctuations, construct a simple model of cell orientations and show that scaling of misorientation distributions emerges a direct result of Gaussian white noise. We investigate whether hierachical microstructures containing both incidental dislocation boundaries and geometrically necessary boundaries can be studied using the same model. The results are compared with the experimental measurements and show good agreement.
Synchroshear Versus Conventional Shear Mechanisms in Transitionmetal Disilicides with the C40 Structure
Authors: Inui H. , Yamaguchi M. 
Published: April 2011

AbstractThe deformation behavior of (0001) <1210> basal slip in single crystals of five different transitionmetal disilicides with the C40 structure has been investigated in the temperature range from room temperature to 1500°C in compression. These disilicides are found to be classified into two groups depending on the onset temperature for plastic flow. The low-temperature group, which consists of VSi2, NbSi2 and TaSi2, exhibits the onset temperature for plastic flow around 0.3 T/Tm (melting temperature) and deforms by a conventional shear mechanism. In contrast, the high temperature group, which consists of CrSi2 and Mo(Si,Al)2, exhibits the onset temperature around 0.6T/Tm and deforms by a synchroshear mechanism. Factors affecting the deformation mechanism in these C40 disilicides are discussed in terms of directionality of atomic bonding and the relative stability of the C40 phase with respect to the C11b phase.
Solution-Processed Inorganic Transistors and Sub-Micron Non-Lithographic Patterning using Nanoparticle Inks
Authors: Ridley Brent A. , Nivi Babak , Hubert Brian N. , Bulthaup Colin A. , Wilhelm Eric J. , Jacobson Joseph M. 
Published: April 2011

ABSTRACTPyridine solutions of CdSe nanocrystals were solution-deposited in the fabrication of thin film transistors (TFTs). A peak mobility of 1 cm2V−1s−1 and an ON/OFF ratio of 3×104 were observed for TFTs processed at 350 °C. The nanocrystals acted as a precursor to the bulk material, coalescing to form a semiconductor thin film when heated at plastic-compatible temperatures. Single crystalline regions several hundred times the size of the original semiconductor nanocrystals were observed for films processed at 350 °C. We also report a process for direct liquid phase deposition and patterning of nanoparticle inks at sub-micron resolutions by elastomeric embossing and AFM nanospotting. These results suggest that microelectronic devices produced from nanoparticle-based inks can enjoy the processing advantages usually associated with organic materials while retaining the performance advantages typically associated with inorganic materials.
Synthesis of Self-Capped Metal Sulfide Nanoparticles
Authors: Lazell Mike , O'Brien Paul 
Published: April 2011

ABSTRACTIn this paper we report the synthesis of metal sulfide nanocrystals, (CdS and ZnS), from the thermolysis, between 150 – 300 °C, in a dynamic vacuum, of the novel long chain asymmetric metal dithiocarbamates, bis(N-methyloctadecyldithiocarbamato) cadmium(II) or zinc(lI), [M {S2CN(C18H37)(CH3)}2].These nanoparticles ‘self-cap’ during preparation. Different size nanocrystals were synthesised, at different temperatures and there was a change in phase from cubic to hexagonal CdS at a decomposition temperature greater than 300 °C.
Controlled Growth of Amorphous Silicon Nanowires Via a Solid-Liquid-Solid (SLS) Mechanism
Authors: Yan H. F. , Xing Y. J. , Hang Q. L. , Yu D. P. , Xu J. , Zhang H. Z. , Xi Z. H. , Feng S. Q. 
Published: April 2011

ABSTRACTAmorphous silicon nanowires (a-SiNW's) with average diameter around 20 nm were synthesized at about 950° C under an Ar/H2 atmosphere on large area of a (11) Si substrate without supplying any gaseous or liquid Si sources. The Si substrate, deposited with a layer of Ni of about 40 nm thick, served itself as a silicon source for the growth of the a-SiNWs. Different from the well-known vapor-liquid-solid (VLS) for conventional whisker growth, it was found that growth of the a-SiNWs was controlled by a solid-liquid-solid mechanism, which is analogous to the VLS model.
Structural, Magnetic Properties of the Electrochemically Deposited Arrays of Nickel Nanowires
Authors: Khan H.R. , Petrikowski K. 
Published: April 2011

ABSTRACTThe room temperature structural, magnetization and magnetoresistive properties of Ni-nanowires of diameters 18, 30 and 78 nm and various lengths, fabricated by electrochemical deposition of Ni in the nanopores of anodic alumina, are investigated. The crystallographic orientation depends on the diameter of nanowires. Nanowires show perpendicular magnetic anisotropy and enhanced coercivity (Hc) and remanent magnetization (Mr) values of up to 500 Oe and 50% respectively. An electrodeposited Ni-layer (5 μm) on copper substrate shows in plane magnetic anisotropy and the Hc and Mr values are 97 Oe and 37%. Ni-nanowires and Ni-layer show an anisotropic magnetoresistive behaviour.
Crack Healing in an Alumina/Silicon Carbide Nanocomposite After Grinding and Annealing
Authors: Wu H.Z. , Titchmarsh J.M. , Roberts S.G. , Derby B. 
Published: April 2011

ABSTRACTAlumina/silicon carbide nanocomposites are known to show their highest strength levels after surface grinding followed by annealing. After annealing in flowing argon, nanocomposites with very coarsely ground surfaces have strengths exceeding those with a finely polished surface. Specimens with lapped surfaces also show a small improvement in strength on annealing. TEM investigations of annealed cross-sections show that the annealing process leads to surface crack healing. The chemical composition of the subsurface region has been studied, and reactive products on and close to the nanocomposite surface after annealing have been investigated by energy dispersive X-ray analysis in the STEM.
Transparent Monolithic Metal Ion Containing Nanophase Aerogels
Authors: Risen William M. , Hu Xiangjun , Ji Shuang , Littrell Kenneth 
Published: April 2011

ABSTRACTThe formation of monolithic and transparent transition metal containing aerogels has been achieved through cooperative interactions of high molecular weight functionalized carbohydrates and silica precursors, which strongly influence the kinetics of gelation. After initial gelation, subsequent modification of the ligating character of the system, coordination of the group VIII metal ions, and supercritical extraction afford the aerogels. The structures at the nanophase level have been probed by photon and electron transmission and neutron scattering techniques to help elucidate the basis for structural integrity together with the small entity sizes that permit transparency in the visible range. They also help with understanding the chemical reactivities of the metal-containing sites in these very high surface area materials. These results are discussed in connection with new reaction studies.
Preparation of Submicron and Micron Size Cr (IV) Optical Composites
Authors: Isaacs L.L. , Petricevic V. , Wang BaoPing , Ying Jinpin , Alfano R.R. 
Published: April 2011

ABSTRACTSol - gel technology is used to prepare sub-micron to micron size particles of Chromium (IV) doped materials. These materials show strong luminescence, as single crystals, in the 1-2 μm range. Such materials include; Cr (IV): (Ca2GeO4, Mg2SiO4, LiScGeO4). The optically active particles are dispersed into glassy matrixes to form optical composites. Ongoing research is aimed at, a) reducing the size and the size distribution of the optically active particles, and b) finding suitable matrix materials.
Quantum Confined Gallium Nitride in a Mesoporous Matrix of Mcm-41
Authors: Winkler H. , Fischer R. A. , Schmechel R. , von Seggern H. 
Published: April 2011

ABSTRACTWe report the synthesis of a nanocomposite materials consisting of gallium nitride (GaN) confined in the well ordered mesoporous transparent matrix MCM-41 with the help of the metalorganic single source precursor triazido(trimethylamine)gallium using solution impregnation technique. The loading of the pores of MCM-41 with GaN was confirmed by chemical analysis, XRD, TEM, BET, NMR and optical spectroscopy (PL and PL-excitation spectroscopy). The composites exhibit a blue shift of the bandgap of GaN due to quantum confinement.
Soft Chemical Design of Transition-Metal-Oxide/Clay Layered Nanocomposites
Authors: Fuda Kiyitali , Narita Shuji , Kudo Shuji , Murakami Kenji , Matsunaga Toshiaki 
Published: April 2011

ABSTRACTRoom-temperature synthesis of transition metal ( TM = Co, Ni and Mn ) oxide intercalated clays has been developed, which extends the potentiality of clay based materials for the design of electroactive nanophase. The structure was examined by using powder XRD - one-dimensional Fourier analysis, magnetic susceptibility measurement as well as conventional analytical methods. From the results, it was revealed that the oxidation by using NaClO as the oxidative reagent affords a new expanded layer structure with a basal spacing of about 1.96 nm wherein a conductive TM oxide sheetadjacent to two hydrated sodium ion layers resides in the gallery of the clay. The resultant sodium cobaltate interlayered smectite bears multi-functionality; an apparent bulk conductivity in the order of 10−5 Scm−1 and a cation exchange ability.
Catalytic Activity and Surface Characterization Study of Pd Supported on Nanocrystalline and Polycrystalline CeO2
Authors: Hoflund Gar B. , Li Zhenhua , Campbell Timothy J. , Epling William S. , Hahn Horst W. 
Published: April 2011

ABSTRACTThe catalytic activity of polycrystalline and nanocrystalline CeO2-supported Pd (Pd/pCeO2 and Pd/nCeO2) has been determined as a function of temperature and Pd loading. While the untreated nCeO2 support gives 50% methane conversion at 420°C, the untreated pCeO2 support exhibits little activity under the conditions examined due to its low surface area. A Pd loading of 5 wt% increases the activity of pCeO2 to 50% conversion at 260°C, while a 40 wt% Pd loading on nCeO2 exhibits a relatively smaller activity increase, yielding 50% conversion at 240°C. On a mass basis the 40 wt% Pd/nCeO2 catalyst is the most active tested in this study, but it is less active than the 5 wt% Pd/pCeO2 catalyst on a surface-area basis. Furthermore, the activity of the 40 wt% Pd/nCeO2 catalyst does not decrease during 100 hrs of exposure to CH4 and O2 at 250°C.X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) have been used to characterize the surfaces of both bare supports and Pd-containing catalysts before and after exposure to reactor conditions. The XPS results reveal that the Pd surface concentration is more than an order of magnitude higher for 5 wt% Pd/pCeO2 than for 5 wt% Pd/nCeO2 due to the larger surface area of nCeO2 and that the 40 wt% Pd/nCeO2 catalyst has a lower Pd loading on a surface-area basis than the 5 wt% Pd/pCeO2 catalyst. Most of the supported Pd is in the form of PdO, but higher PdO2/PdO ratios are observed for both CeO2 supports compared to Pd supported on ZrO2 or CO3O4. Furthermore, a significant amount of metallic Pd forms on Pd/nCeO2 but not on Pd/pCeO2 during reaction. The nanocrystalline and polycrystalline CeO2 behave differently chemically which is consistent with the fact that the nanocrystalline catalysts are less active on a surface-area basis. Accumulation of H20 on the Pd/pCeO2 surface during reaction is significant but not on the Pd/nCeO2 surface. This suggests that the rate limiting step may be H2O desorption on Pd/pCeO2 while for Pd on nCeO2 adsorption of methane appears to be the slow step. The ISS data indicate that the outermost atomic layer of Pd/nCeO2 consists mostly of O and C, which is not the case for Pd/pCeO2. Site blockage by these species may also contribute to the lower activity on a surface-area basis of Pd/nCeO2 compared to Pd/pCeO2.
Electrical Resistivity as a Characterization Tool for Nanocrystalline Metals
Authors: McCrea J.L. , Aust K.T. , Palumbo G. , Erb U. 
Published: April 2011

ABSTRACTThe electrical resistivity as a function of temperature (4K to 673K) of several electrodeposited nanocrystalline materials (Ni, Ni-Fe, Co) has been examined. The contribution of the grain boundaries to the electrical resistivity was quantified in terms of a specific grain boundary resistivity, which was found to be similar to previously reported values of specific grain boundary resistivity for copper and aluminum obtained from studies involving polycrystalline materials. In the high temperature range, the resistivity of the nanocrystalline samples was monitored as a function of time. The observed time dependence of the resistivity at elevated temperatures was correlated to microstructural changes in the material. The study has shown that electrical resistivity is an excellent characterization tool for nanocrystalline materials giving useful information regarding grain size and degree of thermal stability, as well as some insight into the grain growth kinetics at various temperatures.
Synthesis and Characterization of Manganese Vanadium Oxides as Cathodes in Lithium Batteries
Authors: Zhang Fan , Zavalij Peter , Whittingham M. Stanley 
Published: April 2011

ABSTRACTOur research on new cathode nano-materials for advanced lithium batteries has focused on the hydrothermal method for synthesis. We have synthesized two novel manganese vanadium oxides using the hydrothermal reactions of vanadium (V) pentoxide, [N(CH3)4]MnO4, and MnSO4 with an organic templating cation at 165°C. The 6-type [N(CH3)4]zMnyV2O5*nH2O has a monoclinic structure, a= 11.66(2)Å, b=3.610(9)Å, c= 13.91(4)Å, β= 108.8(2)°. It has a disordered V2O5 double layer and the Mn and N(CH3)4 ions reside between the layers. The γ-type MnV2O5 is orthorhombic, belongs to the space group Pnma, a=9.7585(2) Å, b=3.5825(l)Å, c= 11.2653(2) Å. These compounds were also characterized by electron microprobe, FTIR and TGA. They reacted readily with lithium, and their electrochemical behavior in lithium cells was determined.
Nanoporous Alumina Coatings for Medical Implants and Stents - Radiotherapy, Drug Delivery, Biological Compatibility
Authors: Sawitowski T. , Brandau W. , Fischer A. , Heilmann A. , Schmid G. 
Published: April 2011

ABSTRACTThe body implant interaction is strongly affected by the implant surface structure and chemistry [1,2]. Thus by applying a nanoporous coating to metallic implants the implant surface can be adjusted to different needs. Compared to biological molecules the size of the pores is so small (between 5 nm and 250 nm) that the cellular response to this surface modification is not affected by the structure itself. Nevertheless by loading the pores with bioactive molecules it is possible to achieve a new kind of active implants surfaces for soft and hard tissue implants. With this coating it is possible to irreversibly bind radioactive isotopes like 99mTc, 186/188Re, 103Pd, and many more for local radiotherapy onto soft tissue implants like stents or seeds.
Microstructural and Magnetic Properties on Graphitic Encapsulated Ni Nanocrystals and Pure Ni Nanoparticles with NiO Layer
Authors: Suns Xiangcheng , Yacamana M. Jose , Morales F. 
Published: April 2011

ABSTRACTTwo kinds of different nickel nanoparticles with distinct morphological properties, Ni(C) and Ni(O), are studied. Magnetization measurements for the assembly of two kinds of Ni nanoparticles show, a larger coercivity and remanence as well as the deviation between the zero field cooling (ZFC) and the field cooling (FC) magnetization have been observed in the Ni(O) particles. This deviation may be explained as a typical cluster glass-like behavior due to ferromagnetic interaction among the assembly of Ni(O) particles. However, Ni(C) particles exhibit superparamagnetism at room temperature. The average blocking temperature (TB) is determined to around 115K. We also observe gradual decrease in saturation magnetization, which is attributed to the nanocrystalline nature of the encapsulated particles.