bluuebunny/crossref_metadata_2025_split huggingface dataset:
CoPt3 nanoparticles adsorbed on SiO2: a GISAXS and SEM study
Authors: Flege Jan I. , Schmidt Thomas , Alexe Gabriela , Clausen Torben , Bernstorff Sigrid , Randjelovic Igor , Aleksandrovic Vesna , Kornowski Andreas , Weller Horst , Falta Jens 
Published: April 2011

ABSTRACTUltra-thin CoPt3 nanoparticle films have been prepared on SiO2 surfaces using a Langmuir-Blodgett (LB) deposition technique. The structural properties of the overlayers have been investigated by grazing-incidence small-angle x-ray scattering (GISAXS) and high-resolution scanning electron microscopy (SEM) for the first time. Self-assembly of the nanoparticles is found and with GISAXS an average particle-particle distance of (8.23 ± 0.06) nm is determined, in good agreement with the SEM results. A particle correlation length of (22.3 ± 1.2) nm was derived which is shown to be independent of the surface coverage. The latter quantity may be controlled by choice of a suitable retraction speed during the LB step.
Internal Strain Measurements and X-ray Imaging in Interpenetrating-Phase Al2O3/Al Composites
Authors: Young Marcus L. , Almer Jon D. , Lienert Ulrich , Fezzaa Kamel , Lee Wah-Keat , Haeffner Dean R. , Dunand David C. 
Published: April 2011

ABSTRACTInterpenetrating Al2O3/Al composites were created by liquid-metal infiltration of alumina preforms with three-dimensional periodicity produced by a robotic deposition method. Volume-averaged lattice strains in the alumina phase were measured by synchrotron x-ray diffraction at various uniaxial compression stresses up to 350 MPa. Load transfer, which is experimentally found to occur between the aluminum and the alumina phase, is in agreement with simple rule of mixtures models. Spatially resolved measurements showed variations in load transfer at different positions within the composite for the elastic-, plastic-, and damage-deformation regimes. Using phase-enhanced imaging, the extent of damage within the composites was observed.
X-ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals
Authors: Magid K. R. , Lilleodden E. T. , Tamura N. , Florando J. N. , Lassila D. H. , LeBlanc M. M. , Barabash R. I. , Morris J. W. 
Published: April 2011

ABSTRACTThe deformation behavior of BCC metals is being investigated by x-ray microdiffraction measurements (μXRD) for the purpose of characterizing the dislocation structure that results from uniaxial compression experiments. The high brilliance synchrotron source at the Advanced Light Source (Lawrence Berkeley National Lab) and the micron resolution of the focusing optics allow for the mapping of Laue diffraction patterns across a sample. These measurements are then analyzed in order to map the distribution of residual stresses in the crystal. An important finding is the observation of Laue spot “streaking”, which indicates localized rotations in the lattice. These may represent an accumulation of same-sign dislocations. Theoretical modeling of the diffraction response for various slip systems is presented, and compared to experimental data. Preliminary results include orientation maps from a highly strained Ta bicrystal and a less highly strained Mo single crystal. The orientation maps of the bicrystal indicate a cell-like structure of dense dislocation walls. This deformation structure is consistent with previous OIM studies of the same crystal. The results suggest that μXRD may be a particularly useful tool for microscale studies of deformation patterns in a multi-scale investigation of the mechanisms of deformation that ranges from macroscopic deformation tests to high resolution TEM studies of dislocation structures.
Measurement of Residual Strains with High Depth Resolution by Energy-Variable Diffraction on Synchrotron Beam Lines
Authors: Zolotoyabko E. , Pokroy B. , Quintana J. P. 
Published: April 2011

ABSTRACTAn energy-variable synchrotron diffraction technique is established as a novel method for depth-resolved measurements of d-spacings and residual strains in polycrystalline structures. The depth sensitivity is achieved by the controlled changing the x-ray energy and, hence, the x-ray penetration into the sample. Quasi-parallel synchrotron radiation being diffracted at different depths deviates differently from the detector axis. As a result, the maximum diffraction intensity recorded in the detector is coming from a certain depth, which is energy dependent. This finding opens a way for strain measurements with high depth resolution by changing the x-ray energy in small enough steps. The developed technique is applied to characterize the electrodeposited Cu/Ni multilayers.
Measurement of Crystal Lattice Rotations under Nanoindents in Copper
Authors: McLaughlin Kirsten K. , Stelmashenko Nadia A. , Lloyd Stephen J. , Vandeperre Luc J. , Clegg William J. 
Published: April 2011

ABSTRACTA technique is described to measure the rotations of the crystal lattice in the deformed region around a nanoindent from volumes smaller than 3 × 10−5 μm3. To demonstrate this method, a copper crystal has been indented on its (001) face to depths of 500 and 1300 nm. Cross-sections of nanoindents were prepared for transmission electron microscopy by focused ion beam milling, and rotations were measured about the [001], [010] and [100] axes using convergent beam electron diffraction.
The Mechanics of Nanoimprint Forming
Authors: Cross Graham L. W. , Langford Richard M. , O'Connell Barry S. , Pethica John B. 
Published: April 2011

ABSTRACTNanoimprint and a number of other related techniques are a collection of surface patterning technologies that involve direct contact of a master template with the target surface. As such, they are governed by the laws of contacting bodies, and the mechanics involved can readily be investigated by existing indentation methods or close variants thereof. Among the many demonstrated applications of nanoimprint, lithographic resist processing has generated considerable interest due to its combination of high resolution with rapid throughput over wide areas. Pattern transfer can be achieved by the application of heat and pressure to the stamp (hot embossing), or solely by the generation of shear stress at the contact (cold forming.) In both cases we have found that elastic and viscoplastic strains are present during the forming process, the former of which can considerably alter the characteristics of the pattern transfer. The use of depth sensing instrumented indentation in conjunction with specially designed stamps and a variety of microscopy techniques has allowed us to isolate, control, and measure many of the stresses and strains directly during the imprint process. Further, in a more standard role, the indenter can be used to characterize the mechanical properties of imprinted structures. In this paper we summarize our experimental findings and conclusions on the role of important factors influencing the fidelity of the imprint process including elastic stresses, plastic deformation mechanisms, complexities in the confined deformation rheology, and choices in the form of applied stress. These are illustrated by a series of idealized experiments ranging from the squeeze flow of prepared coupons to the flat punch indentation of thin films and back extrusion into isolated cavities. A connection between these more localized experiments and the established findings and requirements of applications such as wide area lithography and functional polymer patterning will be made to establish the concept of “instrumented imprint”.
A Nanoindentation Study of Thermally-Grown-Oxide Films on Silicon
Authors: Helvaci Fatih , Cho Junghyun 
Published: April 2011

ABSTRACTWe explore the effect of the substrate on mechanical behavior of thin films using a depth-sensing indentation. For this purpose, nanoindentation has been performed on thermally grown silicon oxide films on the silicon substrate. One primary goal of this study is to extract ‘film-only’ mechanical properties from the nanoindentation data by subtracting the substrate effect. It is also shown that elastic modulus of the film is more influenced by the substrate than hardness due to a larger elastic extension beyond a plastically deformed region, as well as a larger elastic mismatch between the SiO2 film and the Si substrate. Further, an inverse analysis of indentation data is proposed to estimate a thickness of thin films. Consequently, this study provides a fundamental understanding in mechanical phenomena of thin films occurring at nanoscales.
Nanoindentation of Bone in a Physiological Environment
Authors: Akhtar R. , Morse S. , Mummery P. M. 
Published: April 2011

ABSTRACTNanoindentation has been established as an effective method to measure the mechanical properties of bone tissue at the micron and sub-micron length scale. Although it is well-documented that the mechanical properties of macroscopic bone specimens vary depending on whether the samples are tested dry or wet, nanoindentation is generally conducted on dehydrated bone tissue at room temperature, primarily because nanoindentation systems are extremely sensitive to changes in environmental conditions such as humidity and temperature. In this study, these problems were overcome by using a specially constructed liquid cell with an extension piece that allowed the indenter tip to be submerged under 5 mm of liquid. The custom setup was used to test cortical bovine bone and cancellous human bone specimens in three distinct conditions – dehydrated, rehydrated in simulated body fluid (SBF) at 20°C, and rehydrated in SBF at 37.5°C. A heating element with a temperature control unit was used to test at 37.5°C. The hardness and elastic modulus of the bone samples were found to decrease when dry specimens were rehydrated and tested in physiological conditions. It is suggested that nanoindentation in physiological conditions gives a better estimate of the mechanical properties of the microstructural components of bone in vivo rather than nanoindentation under conventional conditions.
Multiple-Frequency Nanoindentation Testing
Authors: Fischer-Cripps A. C. 
Published: April 2011

ABSTRACTThis paper describes a new method of dynamic nanoindentation testing whereby, instead of the imposition of a single sinusoidal modulation onto the driving force signal, a multiple-frequency modulation is applied and a Fourier analysis used to extract frequency-dependent mechanical properties. The instrument response is cancelled by the use of a reference transfer function using an equalization process. The present work gives details of the method and presents some example measurements.
Molecular Mobility and Confined Plasticity in NEMS Applications
Authors: Overney René M. , Sills Scott 
Published: April 2011

ABSTRACTMany modern and future technological applications involve ultrathin polymer films with a thickness below the 100-nanometer scale, where statistical bulk averaging is jeopardized and interfacial constraints dictate transport properties. In such confined polymeric systems, transport properties strongly depend on molecular relaxation and structural phases that deviate from the bulk. This is particularly relevant in applications involving nano-electromechanical systems (NEMS). In this paper, we address the correspondence between bulk deviating local glass transition values with the non-monotonic plastic deformation properties in ultrathin polystyrene films. Polystyrene serves as a model material in a NEMS application designed to circumvent the superparamagnetic limit associated with magnetic data storage. The application involves data bit writing via an ultrahigh density thermomechanical indentation process. An elaborate friction-velocity analysis is introduced as a material characterization tool. It provides fundamental insight into the glass forming process, and consequently, the glass transition value in ultrathin spin coated polymer films. The glass transition value is thereby discussed as a phenomenological limit, not unlike an asymptote, to a diverging size of cooperative rearranging regions upon cooling. Unexpected large cooperative clusters up to 40 nm were observed – a dimension that is noticeable at the 100-nanometer length scale. In the light of MD simulations and their good correspondence with the presented intrinsic friction analysis, the importance of angular and torsional intramolecular motions are particularly emphasized for nanotechnological applications.
Indentation Creep and Relaxation Measurements of Polymers
Authors: VanLandingham Mark R. , Drzal Peter L. , White Christopher C. 
Published: April 2011

ABSTRACTInstrumented indentation was used to characterize the mechanical response of polymeric materials. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for creep compliance and stress relaxation modulus for epoxy, poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison to the indentation creep and stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than rheometry values. Additional study of the deformation remaining in epoxy after creep testing revealed that a large portion of the creep displacement measured was due to post-yield flow. Indentation creep measurements of the epoxy using a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the PDMS were mainly linear elastic, but the filled PDMS exhibited some time-dependence and nonlinearity in both rheometry and indentation measurements.
Spherical Load Indentation in Submicron NiTiCu Shape Memory Thin Films
Authors: Hassdorf R. , Feydt J. , Thienhaus S. , Buforn L. , Conté N. , Pykhteev O. , Kružík M. , Botkin N. , Moske M. 
Published: April 2011

ABSTRACTNanoindentation with spherical tipped indenters provides a powerful technique to explore surface and thin film mechanical properties through the application of Hertzian contact mechanics. The full range of mechanical response can be obtained from elastic, through the yield point, to permanent deformation. In this study spherical indentation has been used for probing MBE-grown NiTiCu alloy thin films into superelasticity or stress-induced martensitic transformation. By this way, obstacles typically occurring related to the fabrication of freestanding films (film thickness < 1 μm) are avoided. The indentation measurements were performed starting from the parent austenite state. Notably, for loads as small as 0.5 mN, deformation appears to be completely reversible. As loading is increased (up to 5 mN) the indent becomes irreversible following local plastic deformation within the tip-specimen contact area. Using finite-element simulations the indentation data were converted into a stress-strain diagram aimed at simulating uniaxial tension load. Therefrom, the superelastic strain is estimated to be around 3%.
Effect of Alloying Elements (Ga, Ge, Si) on Pseudoelasticity in Fe3Al Single Crystals
Authors: Yasuda Hiroyuki Y. , Kase Takashi , Umakoshi Yukichi 
Published: April 2011

ABSTRACTPseudoelasticity in Fe3Al single crystals doped with a small amount of Ga, Ge and Si was investigated focusing on the antiphase boundary (APB) energy and the ordered domain structure. Single crystals of Fe-23at%Al and Fe-21at%Al-2at%X (X=Ga, Ge, Si) were grown by a floating zone method. In Fe-23at%Al single crystals, superpartial dislocations with Burgers vector (b) of 1/4<111> moved dragging APB during loading, while APB pulled back the superpartials during unloading. This resulted in giant pseudoelasticity regardless of martensitic transformation and the recoverable strain was about 5%. Ga addition was found to be effective in increasing the recovery strain compared with Fe-23at%Al crystals. In contrast, both Ge and Si additions decreased the amount of shape recovery. Stress at which the shape recovery started, was increased by Ga, Ge and Si additions. This means the APB energy increased by the additions, since the surface tension of APB pulling back the superpartials increases with increasing the energy. On the other hand, the frictional stress of the superpartials with b=1/4<111> increased significantly by Ge or Si doping due to solid solution hardening, though the stress of Ga-doped crystals was almost the same as that of the binary crystals. Higher frictional stress of Ge- and Si-doped crystals made the reversible motion of the superpartials difficult, resulting in the small recovery ratio. Ordered domains with displacement vector (R) of 1/4<111> in Fe-23at%Al and Fe-Al-Ga alloys were observed to be small, less than 100nm. In contrast, Ge and Si additions increased the domain size to more than 500nm. Since the domain boundaries with R=1/4<111> played an important role in the individual motion of the superpartials with b=1/4<111>, the fine domain structure was found to be favorable for giant pseudoelasticity in Fe3Al single crystals. Ga addition increased the APB energy following the superpartials and kept the domain size small, resulting in the increase in recovery strain.
First-Principles Study of Structural and Defect Properties in FeCo Intermetallics
Authors: Krcmar M. , Fu C. L. , Morris J. R. 
Published: April 2011

ABSTRACTEmploying ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the <111> slip on both {110} and {112} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stresses near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.
Development of high temperature creep resistance in Fe-Al alloys
Authors: Morris D. G. , Muñoz-Morris M. A. , Baudin C. 
Published: April 2011

ABSTRACTMost of the studies aimed at the development of creep-resisting Fe-Al intermetallics have been oriented at application temperatures of the order of 500–650°C, where these materials may compete with conventional stainless steels. The Fe-Al intermetallics are, however, particularly excellent in their oxidation and corrosion resistances at temperatures of the order of 1000°C, where Chromium-Nickel steels are no longer able to withstand the aggressive environments. This presentation is part of a study aimed at the development of good creep resistance at such high temperatures.Studies of a variety of cast Fe3Al-base alloys, strengthened by solution or precipitate/dispersoid-forming alloying additions, are reported. The alloys show good strength from room temperature to about 500°C, but thereafter strength falls rapidly as thermally-activated deformation processes become operative. Solution additions are capable of producing good low temperature strength, but do not contribute significantly to creep strength at very high temperatures (above 700°C). Precipitation hardening has been examined in Nb-containing alloys, where Fe2Nb Laves precipitates form at intermediate temperatures. These materials show good strength up to about 700°C, but at higher temperatures the fine precipitates coarsen excessively. Strengthening in the intermediate temperature range varies depending on whether the solute is precipitated prior to high temperature testing or concurrent with this.
Microstructures and Mechanical Properties in Ni3Si-Ni3Ti-Ni3Nb-Based Multi-Intermetallic Alloys
Authors: Takasugi T. , Ohira K. , Kaneno Y. 
Published: April 2011

ABSTRACTMicrostructure, high-temperature tensile deformation and oxidation property of Ni3Si-Ni3Ti-Ni3Nb multi-phase intermetallic alloys with a microstructure consisting of L12, D024 and D0a phases were investigated. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L12 phase in the wide range of test temperatures. 50-ppm boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. The multi-phase intermetallic alloy with a high Si content had good oxidation resistance, and also the boron addition to this alloy resulted in enhanced oxidation resistance. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy, which has a high Si content and is composed of L12 matrix dispersed by D024 and D0a phases, had the most favorable properties as high-temperature mechanical and chemical materials.
A Bond-Order Potential Incorporating Analytic Screening Functions for the Molybdenum Silicides
Authors: Cawkwell Marc J. , Mrovec Matous , Nguyen-Manh Duc , Pettifor David G. , Vitek Vaclav 
Published: April 2011

ABSTRACTThe intermetallic compound MoSi2, which adopts the C11b crystal structure, and related alloys exhibit an excellent corrosion resistance at high temperatures but tend to be brittle at room and even relatively high temperatures. The limited ductility of MoSi2 in ambient conditions along with the anomalous temperature dependence of the critical resolved shear stress (CRSS) of the {110)<111], {011)<100] and {010)<100] slip systems and departure from Schmid law behavior of the {013)<331] slip system can all be attributed to complex dislocation core structures. We have therefore developed a Bond-Order Potential (BOP) for MoSi2 for use in the atomistic simulation of dislocations and other extended defects. BOPs are a real-space, O(N), two-center orthogonal tight-binding formalism that are naturally able to describe systems with mixed metallic and covalent bonding. In this development novel analytic screening functions have been adopted to properly describe the environmental dependence of bond integrals in the open, bcc-based C11b crystal structure. A many-body repulsive term is included in the model that allows us to fit the elastic constants and negative Cauchy pressures of MoSi2. Due to the internal degree of freedom in the position of the Si atoms in the C11b structure which is a function of volume, it was necessary to adopt a self-consistent procedure in the fitting of the BOP. The constructed BOP is found to be an excellent description of cohesion in C11b MoSi2 and we have carefully assessed its transferability to other crystal structures and stoichiometries, notably C 40, C 49 and C 54 MoSi2, A15 and D03 Mo3Si and D8m Mo5Si3 by comparing with ab initio structural optimizations.
Coarsening Behavior and Coercivity in L10-Ordered Intermetallic Fe-Pd Ferromagnets with Equiaxed Grain Morphology
Authors: Wiezorek Jörg M.K. , Deshpande Anirudha R. 
Published: April 2011

ABSTRACTThermo mechanical processing of equiatomic FePd has been used to establish a nearly equiaxed microstructure that consists of mono-variant L10 ordered grains. The technically important hard magnetic properties, e.g. coercivity, of the uniaxial ferromagnetic L10-FePd with equiaxed microstructure depend on the grain size. Thus, here, the evolution of grain size during the later stages of annealing has been studied using SEM and computer assisted image analysis with the goal to determine the activation parameters for the relevant coarsening processes. Using a classical grain growth analysis the activation parameter for coarsening of the 5% largest grains in the populations of L10-ordered grains in FePd has been determined as approximately 30kcal/mol.