Cody Friesen Arizona State University
Robert C. Cammarata Johns Hopkins University
Andrea Hodge University of Southern California-Los Angeles
Oden L. Warren Hysitron, Inc.
Johns Hopkins University, Dept. of MS&
Lawrence Livermore National Laboratory, CMLS Division
U1: Polymers and Composites
Tuesday PM, March 25, 2008
Room 3007 (Moscone West)
9:30 AM - U1.1
Strengthening of Polyolefins by Bottom-up Self-assembly of POSS Nanoparticles.
Byoung Jo Lee 1 , Sadhan Jana 1 Show Abstract
1 Polymer Engineering, University of Akron, Akron, Ohio, United States
9:45 AM - U1.2
High-Performance Metal/Epoxysilane Sol-Gel Coupling Layers.
Mark Oliver 1 , Asmita Kumar 1 , Kay Blohowiak 2 , Reinhold Dauskardt 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 , The Boeing Company, Seattle, Washington, United States
Metal oxide/epoxy resin adhesion is critical to many emerging technologies ranging from fiber metal laminates for aerospace structures to a variety of micro-scale devices. These technologies require nanoscale, high-performance coupling layers that are easily processed and possess resistance to harsh environmental conditions. To date, epoxysilane molecules have been used extensively as coupling agents but it has recently been found that the incorporation of metal species via metal alkoxide precursors can improve the adhesion-promoting properties of some silane-based layers. The optimal composition and structure of these hybrid organic-inorganic layers are those that provide a balance between strong adhesion to both oxide and resin, high cohesive toughness, and resistance to attack by environmental chemical species. Therefore, the design of thinner, better-performing metal/epoxysilane coupling layers requires a fundamental understanding of how the layer composition and nanostructure influence the ability of the layer to meet these various, often competing, requirements. This research has focused on experimentally measuring the adhesive and cohesive fracture properties of sol-gel coupling layers processed from 3-glycidoxypropyltrimethoxysilane and a variety of metal alkoxide precursors including alkoxides of Si, Ti, and Zr. Both critical and environmentally assisted subcritical cracking were investigated. Sol-gel layers were deposited onto flat (RMS ~ 1nm) oxidized surfaces including Si, Al, and Ti by dip coating. Linear elastic fracture mechanics test methods were used to measure the fracture properties of the layers. X-ray photoelectron spectroscopy and atomic force microscopy have been used to analyze the composition and morphology of the fracture surfaces, respectively. Experimental results showing the dependence of the resistance to fracture and location of fracture within these layers on composition and processing variables will be presented and the mechanisms responsible for the observed behavior will be discussed.
10:00 AM - U1.3
Adhesion of Transparent Hard Coatings on Polymer Substrates.
Ani Kamer 1 , Vasan Sundaram 2 , Kjersta Larson 2 , Reinhold Dauskardt 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Boeing Phantom Works, The Boeing Company, Tukwila, Washington, United States
Polymers are replacing silica-based glasses in a range of optical and structural applications such as windows, eyeglass lenses and displays. The advantage of polymers over conventional glass is their higher toughness/weight ratio, better light transmission and formability at lower temperatures. An important drawback is the low polymer resistance to scratching and water absorption/desorption. A solution is to coat the polymer with a hard transparent polysiloxane-based coating that preserves optical clarity and provides a highly scratch resistant surface during service. Little is currently understood, however, regarding the adhesion of the coating to the polymer substrate, and common problems associated with the progressive degradation of the coating adhesion during exposure to periodic cleaning and terrestrial environmental conditions during service have not been quantified. Adhesion of hard coatings is currently assessed with semi-quantitative methods such as the “cross-cut tape test.” In the present study, we employ thin-film fracture mechanics based techniques to quantitatively study the adhesion of polysiloxane-based hard coatings on polymethylmethacrylate (PMMA) thermoplastic substrates used for commercial aerospace passenger windows. Modifications of these techniques involving the application of an asymmetric double cantilever specimen to ensure the appropriate loading mode mixity, or ratio of shear to normal stresses, are described to ensure clean debonding of the coating and prevent crazing and cracking of the underlying substrate. We report relatively low coating adhesion values of ~ 7 J/m2 that were found to depend on surface preparation and polysiloxane formulation. After 5 years of service, coating adhesion was found to decrease to ~ 5 J/m2. In subcritical debonding experiments we observed the kinetics of the delamination process, which was found to be surprisingly insensitive to changes in moisture content of the testing environment. The effects of simulated solar radiation on coating adhesion was studied following exposure to a Xenon arc lamp for increasing durations. The fundamental processes of photochemical degradation and its effects on the coating integrity are described.
10:15 AM - **U1.4
Nature-Inspired Hybrid Structural Materials.
D. Alsem 1 2 , M. Launey 1 2 , E. Munch 1 2 , E. Saiz 1 2 , A. Tomsia 1 2 , Robert Ritchie 1 2 Show Abstract
1 Materials Science & Engineering, University of California, Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
The structure of materials invariably defines the mechanical behavior. However, in most materials, specific mechanical properties are controlled by structure at widely differing length scales. Nowhere is this more apparent than with biological materials, which are invariably sophisticated composites whose unique combination of mechanical properties derives from an architectural design that spans nanoscale to macroscopic dimensions. Moreover, they are generally able to defeat the “law of mixtures” by devising such hierarchical structures with weak constituents into strong/tough hybrid materials that display superior properties to their individual constituents. The fracture resistance of such materials originates from toughening mechanisms at each dimension; few engineering composites have such a hierarchy of structure. However, the biomimetic approach has not been that successful because of the difficulty of synthesizing such materials. In this presentation we describe attempts to develop a range of bone- and nacre-like structural materials using a new freeze-casting technique, which utilizes the intricate structure of ice to create hybrid materials with complex lamellar and/or mortar and brick structures modeled across several length-scales. Our initial results show ceramic-polymer and ceramic-metal hybrid materials with toughness well in excess of those expected from a rule of mixtures construction. The architecture and properties of the synthetic materials are compared to their natural counterparts in order to identify the mechanisms that control mechanical behavior over multiple dimensions and propose new design concepts to guide the synthesis of hybrid/hierarchical structural materials with unique mechanical responses.
10:45 AM - U1.5
Nano-Cavitation in Self-Assembled Amphiphilic Block Copolymer-Modified Epoxy.
Jia (Daniel) Liu 1 , Hung-Jue Sue 1 , Zach Thompson 2 , Frank Bates 2 , Marv Dettloff 3 , George Jacob 3 , Nikhil Verghese 3 , Ha Pham 3 Show Abstract
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 3 Thermosets R&D, The Dow Chemical Company, Freeport, Texas, United States
Tuesday, March 25Transfer Poster U8.45 to U1.5 @ 9:45 AMNano-Cavitation in Self-Assembled Amphiphilic Block Copolymer-Modified Epoxy. Jia (Daniel) Liu
11:00 AM - U1:Poly/Comp
11:30 AM - U1.6
A Metric for Measurement of Finite Elasticity in Asymmetric Polymer Nanocomposites.
Korin Kohen 1 , Briana Hecht 1 , James Ferri 1 2 Show Abstract
1 , Lafayette College , Easton, Pennsylvania, United States, 2 , Max Planck Institute for Colloids and Interfaces, Golm-Potsdam Germany
11:45 AM - U1.7
Mechanical and Wetting Properties of Hydrothermally Reinforced Layer-by-Layer Nanoparticle Thin Films.
Zekeriyya Gemici 1 , Hiroomi Shimomura 2 , Robert Cohen 1 , Michael Rubner 2 Show Abstract
1 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Nanoparticle-containing thin films have been studied extensively for their optical, catalytic, and wetting properties. Many such films owe their functionalities to delicately designed nanoparticle (NP) assemblies held together by weak secondary interactions. For example, conformal coatings can be assembled layer-by-layer (LbL), where layers of positively and negatively charged polymers, NPs, or polyvalent ions can be electrostatically adsorbed on flat or textured surfaces. Such delicate assemblies can rarely endure mild rubbing with even soft cloths and readily delaminate from their underlying substrates. A few studies have addressed this problem and suggested either high-temperature calcination, which is incompatible with plastic substrates, or imbibition of polymerizable species into the NP assemblies by sol-gel or CVD.Owing to their enhanced solubilities, NPs can be stitched together in situ upon exposure to steam, without grossly altering film structure or porosity. We reinforced nanoporous all-NP and polymer-NP LbL assemblies (80-150nm) by in situ hydrothermal (HT) treatment (124-134°C) on both glass and plastic substrates. This versatile and unintrusive method can make NP-containing multilayer thin films withstand shear abrasion similar to what consumer products would experience in everyday use.Optical properties of nanoporous antireflection films were exploited in an abrasion test (25-100kPa normal stress) to quantify the extent of abrasive wear observed qualitatively by SEM. Marginal damage was observed under optimal reinforcement conditions. Polymer-NP films were more durable than all-NP films after HT treatment. Untreated films not only delaminated from surfaces completely, but also damaged their underlying glass and polycarbonate substrates during testing. The nature of the substrate played an important role in determining abrasion resistance, regardless of the level of particle fusion in the film.We document two types of wear: abrasive and tribochemical (TC). While abrasive wear involves scratching under the influence of third bodies, TC wear acts to flatten nanoscale surface texture by dissolving the topmost layer of oxide NP films (e.g.SiO2) and polishing the surface. Surface roughness and morphology are critical for both superhydrophilic and superhydrophobic surfaces; preservation of surface nanotexture is a major bottleneck in developing practical applications. While much emphasis has been placed on improving hardness and/or scratch-resistance, we point out the critical importance of avoiding tribochemical wear.To our knowledge, this is the first study describing HT reinforcement of NP-containing LbL films and identifying TC wear as a major suspect in loss of surface nanotexture during abrasion. Current efforts are focused on identifying nanoscale features that can support interesting metastable states (e.g.superoleophobicity) and on the preservation of surface nanotexture to achieve “durable” extreme wetting properties.
12:00 PM - U1.8
Mechanical Behavior of Al Based Nanocomposites.
Tapas Laha 1 , Rustin Vogt 1 , Zhihui Zhang 1 , Enrique Lavernia 1 , Julie Schoenung 1 Show Abstract
1 , University of California, Davis, Davis, California, United States
An appreciable improvement in mechanical strength has been documented in ultrafine grained Al based nanocomposites with coarse grains distributed in the matrix. In this study, micromechanics models are invited to rationalize the mechanical behavior of the nanocomposite. The Al-based nanocomposites were synthesized by a two-stage powder metallurgy route. Cryomilling of Al alloys and B4C powder was carried out to synthesize a nanocrystalline composite powder. This cryomilled powder was blended with unmilled powder, followed by consolidation, to fabricate nanocomposites. The B4C content in the cryomilled powder was maintained at a constant value for all of the bulk nanocomposite samples. Mechanics-based analytical models are used to estimate the strength response and elastic modulus of the nanocomposites and compared with experimental data. The load transfer mechanism has been elucidated with TEM at the interfaces of the nanocomposites.
12:15 PM - U1.9
Quenching and Annealing Effects in Ultrafine-grained Al-B4C Composites.
Rustin Vogt 1 , Zhihui Zhang 1 , Tapas Laha 1 , Enrique Lavernia 1 , Julie Schoenung 1 Show Abstract
1 Chemical Engineering and Materials Science, UC Davis, Davis, California, United States
12:30 PM - U1.10
Damage Mechanisms in Trimetallic Nanocomposites.
Ioannis Mastorakos 1 , Hussein Zbib 2 Show Abstract
1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Nano-Metallic Material (NMM) composites represent a novel class of advanced engineering materials whose scientific significance and technological potential as high performance materials is just beginning to be explored. Besides their near-theoretical strength, high ductility and morphological stability, NMM composites are also found to exhibit high fatigue and radiation damage resistance making them uniquely multifunctional materials. Presently, NMM composites are made of bimetallic systems and are typically classified into coherent (the two metals having the same crystal structure and a small lattice parameter mismatch) and incoherent systems (the two metals having different crystal structure and a large lattice parameter mismatch). While coherent systems are more ductile, incoherent systems are generally stronger. The purpose of this work is to expand our understanding on the behavior of NMM by performing atomistic simulations on trimetallic systems. The simulated composite material consists of alternating layers of Ni/Cu/Nb, thus creating a combination of coherent/incoherent interfaces. The deformation behavior as well as the damage mechanisms of the trimetallic system are investigated under uniaxial and biaxial loading conditions. The propagation of dislocations is examined and compared with the bi-layer systems. Finally, systems with different thicknesses are considered and the interfacial energies are investigated as a function of the layer thickness.
12:45 PM - U1.11
Mechanics of a Novel Shear-activated Microfiber Array Adhesive.
Carmel Majidi 1 2 , Ronald Fearing 2 Show Abstract
1 Mechanical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Electrical Engineering and Computer Sciences, University of Califronia, Berkeley, California, United States
Motivated by principles of rod theory and contact mechanics, scientists and engineers are developing a new class of microfiber array adhesives. Still in its early stages, this emerging field aims to introduce adhesives that are pressure-sensitive, directional, reusable, biocompatible, temperature resistance, and self-cleaning. A recent example is an array of polypropylene (PP) microfibers with radius 0.3 microns, length 20 microns, and a density of 42 million fibers per square centimeter on a 35 microns thick PP backing. On smooth glass, a 4 square centimeter patch can support more than 200 grams in pure shear – a factor of 1000 greater than with a smooth PP sheet of similar size and thickness. However, unlike a conventional Pressure Sensitive Adhesive (PSA), this adhesive is composed entirely of a stiff, glassy polymer (PP, elastic modulus E = 1 GPa). High elastic modulus correlates with high wear resistance and low tack and so may be essential for reusability and self-cleaning. Interestingly, attachment of the microfiber patch to the glass substrate requires an applied shear load. Once this shear load is removed, the patch spontaneously delaminates from the substrate and can be easily removed. The reason is that in the absence of a shear load, the fibers are naturally vertical and thus stiff in tension (though compliant in compression by buckling). Thus, any interfacial gaps (resulting from substrate roughness, fiber length variation, backing curvature, surface defects, contaminant particles, etc.) will drastically reduce load sharing among the bonds formed between the fiber tips and glass substrate. However, when shear is applied, the fibers deform into a non-singular configuration that admits compliance in the compressive and tensile directions through fiber bending. Treating the fiber tips as hemispherical, the maximum allowable forces that can be supported at each contact is approximated by Johnson-Kendall-Roberts (JKR) theory. Our model couples JKR and elastic rod theory to furnish two closed-form equations that relate microfiber geometry, mechanical properties, and interfacial properties with total interfacial shear strength and the maximum allowable amplitude of the interfacial gaps. These design criteria will allow engineers to determine the appropriate microfiber geometry for shear-activated adhesion with any selected material.
Cody Friesen Arizona State University
Robert C. Cammarata Johns Hopkins University
Andrea Hodge University of Southern California-Los Angeles
Oden L. Warren Hysitron, Inc.
U5: New Findings in Nanoindentation
Thursday AM, March 27, 2008
Room 3007 (Moscone West)
9:00 AM - **U5.1
Deformation of Thin Amorphous Metallic Films and Multilayers.
Frans Spaepen 1 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States
Thursday, March 27Transferred *G6.1 @ 8:00 AM to *U5.1 @ 8:00 AMDeformation of Thin Amorphous Metallic Films and Multilayers. Frans Spaepen
9:30 AM - U5.2
Study of Incipient Plasticity of Stepped Gold Surfaces at the Atomic Scale.
Arantzazu Mascaraque 1 , Violeta Navarro 1 , Oscar Rodriguez de la Fuente 1 , Juan Rojo 1 Show Abstract
1 Dpto. Fisica de Materiales , Universidad Complutense Madrid, Madrid, Madrid, Spain
9:45 AM - U5.3
Nanoscale Deformation in Tantalum Single Crystals.
Andrea Hodge 1 , Monika Biener 2 , Juergen Biener 2 , Alex Hamza 2 Show Abstract
1 Aerospace and Mechanical Engineering, USC, Los Angeles, California, United States, 2 Nanoscale Synthesis and Characterization Lab, LLNL, Livermore, California, United States
The study of dislocations nucleation by nanoindentation is a very interesting subject for which only a few studies have been performed on BCC metals. Here we report on the deformation behavior of BCC single crystal Ta(100), (111) and (110) studied by a combination of nanoindentation and atomic force microscopy. For all three crystal orientations the onset of plasticity is marked by a discontinuity in the load displacement curve, which is most pronounced on the (100) surface. In the subcritical load range residual impressions were not observed. At higher loads, in the plastic deformation regime, a positive strain rate effect was observed, and the pile-up pattern around the indents reflects the symmetry of the crystal surface. We will discuss the origin of the "pop-in" event as well as the atomistic mechanism of the deformation process during nanoindentation.Prepared by LLNL under Contract DE-AC52-07NA27344
10:00 AM - U5.4
Crystal Plasticity Finite Element Analysis of Spherical Indentation.
Daniel Esque-de los Ojos 1 , Jan Ocenasek 2 , Jorge Alcala 1 Show Abstract
1 GRICCA, E.U.E.T.I.B, Universitat Politècnica de Catalunya, Barcelona Spain, 2 Christian Doppler Laboratory of Material Mechanics of High Performance Alloys, Technische Universität München, Garching b. München Germany
10:15 AM - U5.5
Comparing Viscoelastic Functions Measured by Nanoindentation and Transformations from the Frequency Domain to the Time Domain.
Erik Herbert 1 2 , Warren Oliver 1 2 , George Pharr 2 3 Show Abstract
1 , MTS Nano Instruments, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 3 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
10:30 AM - U5.6
Characterization of Pressure-Induced Phases of Silicon by Indentation at the Nanoscale.
Bianca Haberl 1 , Naoki Fujisawa 1 , Simon Ruffell 1 , Jodie Bradby 1 , Jim Williams 1 Show Abstract
1 Department of Electronic Material Engineering, Research School of Physcial Sciences and Engineering, Australian National University, Canberra, Australian Capital Territory, Australia
It is well known that crystalline silicon undergoes a phase transformation to a metallic silicon phase, Si-II, on loading during nanoindentation. Depending on the conditions of the pressure release this phase either transforms to high-pressure polycrystalline phases of silicon (Si-III and Si-XII) or to amorphous silicon. Little is known about the structural properties of the high pressure phases and the exact form of pressure-induced amorphous silicon and this study addresses these issues.Nanoindentation itself (by reindentation within a previously indented region) is one way to determine the mechanical properties of these various phases of silicon. A relatively large volume (9 μm diameter extending approximately 500 nm below the surface) of the high pressure phases (and indeed the pressure-induced amorphous silicon) can be created in a crystalline/amorphous substrate by indentation using a microscale tip. This material can be probed further by indentation using a nanometer scaled Berkovich tip allowing sampling of the top 150 nm.In this presentation, characteristic indentation load-displacement curves from pressure-induced amorphous silicon both before and after annealing at 450C will be reported. These indentation results are correlated with Raman microspectroscopy and transmission electron microscopy studies. We find that annealing changes the deformation behavior of pressure-induced amorphous silicon significantly in that the as-indented pressure-induced amorphous silicon deforms via plastic flow, whereas annealed pressure-induced amorphous silicon phase transforms in a similar way to crystalline silicon. This behavior is compared with the indentation behavior of relaxed and unrelaxed ion-implanted amorphous silicon that we have reported previously. In addition, nanoindentation data from the high pressure phases will be presented, which reveal a hardness for these mixed phases greater than that of the diamond cubic Si-I phase.
10:45 AM - U5.7
Mechanical Characterization of High Aspect Ratio Silicon Nanolines.
Bin Li 1 , Huai Huang 1 , Qiu Zhao 1 , Zhiquan Luo 1 , Jang-Hi Im 1 , Paul Ho 1 , Min Kang 2 , Rui Huang 2 , Richard Allen 3 , Michael Cresswell 3 Show Abstract
1 Laboratory for Interconnect and Packaging, Microelectronics Research Center, The University of Texas at Austin, Austin, Texas, United States, 2 Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, Texas, United States, 3 Semiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
11:30 AM - U5.8
An Improvement of the Doener-Nix Analytical Model for Substrate Effects in Ultrathin Films.
Bo Zhou 1 , Bart Prorok 1 Show Abstract
1 Materials Engineering, Auburn University, Auburn, Alabama, United States
11:45 AM - U5.9
Estimation of Dislocation Nucleation Stresses During Nanoindentation by Combined Finite-element Analysis and Experiment.
Dylan Morris 1 , Li Ma 1 , Lyle Levine 1 , David Bahr 2 Show Abstract
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
12:00 PM - U5.10
High Resolution Sub-50 nm Indentation of Polymeric Surfaces Using a Quartz Crystal Resonator-Based Atomic Force Microscope.
Yen Peng Kong 1 , Albert Yee 1 Show Abstract
1 Chemical Engineering and Materials Science, University of California Irvine, Irvine, California, United States
Polymeric structures manufactured on the scale of several tens of nanometers are being considered for electronic storage devices and sensors. Some of these polymeric nanostructures might be used to perform a mechanical function and so it is important to know their mechanical properties. As nanostructures shrink in size, the surface to volume ratio increases and the surface mechanical properties dominate its mechanical behavior. Knowledge of the mechanical properties of polymeric surfaces might allow its use to predict the mechanical behavior of nanostructures.Atomic Force Microscope (AFM) based nanoindentation has recently been used to measure the mechanical properties of polymers. The advantage of using AFM nanoindentation is the instrument’s high spatial and force resolution. To measure the very small forces related to extremely small indentations, the laser light lever-based force measurement configuration requires the use of very compliant AFM cantilevers, which unfortunately precludes it from indenting the surface and measuring the force accurately, and this eventually leads to erroneous measurements of the Young’s modulus of surfaces. We propose to solve this conundrum with the use of a quartz crystal resonator-based force sensor AFM(QCR-AFM). With the QCR-AFM we have a low compliance indenting probe coupled with high spatial and force resolution measurement capabilities.Nanoindentation measurements on monodisperse polystyrene (Mw=220.9 kg/mol, Mw/Mn=1.03) reveal a Young’s modulus that is an order of magnitude lower than that of the bulk material for sub-50 nm indents. Experiments on free standing thin polymer films (20–80 nm thick) have revealed large reductions in the glass transition temperature. Our results are consistent with the thin film results and suggest that the surface of the polymer has chains that are much more mobile than those in the bulk, which would result in a lower Young’s modulus at the surface. Our nanoindentations were carried out with relatively fast loading and unloading rates and at shallow indents, thus resulting in loading and unloading curves that appear to be well-described as indentation into an elastic material. The method proposed by Cheng and Cheng was used to extract the Young’s modulus. We believe that further refinement of the method and analysis is needed for very small indentations where molecular-level inhomogeneities are likely to be present. Also an inexplicable increase in the modulus for 5 nm deep indents possibly indicates that for very shallow indentations, a correction to the contact area term in classical contact mechanics model is needed.The QCR-AFM is a unique tool that can also be used to measure the mechanical properties of very thin interfaces and free standing nanostructures.This work is supported by NSF grant CMMI-0728352.References: E. Dalnoki-Veress et al., Phys. Rev. E 6303(3), 2001 Y.T. Cheng & C.M. Cheng, Mater. Sci. Eng., A 409(1-2), 2005
12:15 PM - U5.11
On Obtaining Local Mechanical Properties at the Grain Scale in Metals by Spherical Nanoindentation.
Siddhartha Pathak 1 , Dejan Stojakovic 1 , Surya Kalidindi 1 , Roger Doherty 1 , Brendan Donohue 1 Show Abstract
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Nanoindentation shows tremendous promise for interrogating the local mechanical response of individual crystals in a polycrystalline sample. It has been proposed that with appropriate models, the instrumented nanoindentation test data can be analyzed to yield the stress-strain behavior of the test material. However, most of the analysis techniques in literature are limited to obtaining the elastic properties and the final hardness of the test material. In order to address this problem, we have developed and validated techniques which can translate the load-displacement curves generated in spherical nanoindentation into indentation stress-strain (ISS) curves for a better representation of the material deformation behavior. Such an analyses enables us to follow the entire evolution of the stress-strain response of the material from initial elasticity through the initiation of plasticity at a critical load (yield behavior), to finite plastic strains. More importantly, the ISS curves allow us to obtain the indentation modulus from the initial loading segment itself, where the spherical indenter is pressed on to a flat, undeformed material surface. The resulting modulus is therefore more accurate than the modulus calculated using unloading curves, which would reflect a surface altered by prior indentation. In addition, the ISS curves are also very helpful in studying the yield and post-yield behavior of the sample in indentation-type deformation modes.In this work we show the analyses procedures for such an approach which have been extensively validated for isotropic metals like tungsten and aluminum. We outline a stepwise procedure to accurately determine of the point of first contact between the sample and the indenter (the ‘zero’ point for both the load and the displacement) – a critical step in obtaining correct ISS curves. Once the zero point has been satisfactorily determined, the procedure can then be used to determine the indentation modulus and indentation yield strength of the sample. In the case of anisotropic metals like steel (Fe-3%Si), this analyses is able to differentiate between grains of different orientations (namely the ,  and the  orientations) in terms of their indentation modulus and indentation yield stress. The  orientation in steel is found to have a higher indentation modulus (~202 GPa) than the  orientation (~170 GPa). The indentation yield point also is also found to vary (by ~0.3 GPa) in between these two orientations. A higher variation in the yield stresses is expected upon deformation of the material. In addition, this technique is currently being used to explore the constitutive response of grain boundaries under contact loading. As such this study constitutes a crucial first step in the formulation of a rigorous mechanical framework for the analysis of the local mechanical properties for metals at the submicron scale.
12:30 PM - U5.12
Nanoscale Stress and Toughness Measurement using Confocal Raman Spectroscopy.
Robert Cook 1 , Yvonne Gerbig 1 , Mark Vaudin 1 , Jeroen Schoenmaker 2 , Stephan Stranick 2 Show Abstract
1 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Among the three modes of accommodating deformation—elastic, plastic, and fracture—quantifying material or structural resistance to these at the nanoscale is least advanced for fracture. This is in spite of the fact that most materials used in microelectronic, photonic, and microelectromechanical devices are still brittle at this length scale and fracture is one of the leading detractors of device yield and reliability. In addition, determining the state of deformation at the nanoscale is also difficult. Optimizing the yield and reliability of devices that depend on nano-scale “strain engineering” is thus made difficult as is the identification of the “stress signatures” of plastic and fracture defects that control device performance and reliability. Here we present a confocal Raman spectroscopy technique that allows stress measurement at the nanoscale, which in turn enables measurement of stress-intensity factors (SIF) at crack tips and thus toughness to be estimated at the nanoscale. The technique is based on hyperspectral Raman measurements (typically 128 x 128 spectra over a field). Both large-area (150 μm x 150 μm) and high-resolution (10 μm x 10 μm) scans are demonstrated on micro- and nano-indentations in Si. Peak-fitting and super-resolution techniques enable stress resolution of approximately 20 MPa at nanoscale lateral spatial resolution and depth resolution of approximately 300 nm. Indentation and crack field stress distributions are measured and compared with both analytical expressions and strain measurements from electron back-scattered diffraction. The SIF for microindentation cracks in Si is shown to be in the range 0.3 MPa m1/2 to 0.7 MPa m1/2, consistent with chipping-induced indentation stress relief and the toughness of Si (approximately 0.7 MPa m1/2). The effects of indentation load for both spherical and pyramidal indentation and crystal orientation are demonstrated, as are strain-engineered surfaces using arrays of nanoindentations and the ability of the technique to estimate sub-surface stress distributions beneath films.
U8: Poster Session
Friday AM, March 28, 2008
Salon Level (Marriott)
9:00 PM - U8.1
The Growth and Mechanical Properties of Gold Nanowires.
Rui Dou 1 , Brian Derby 1 Show Abstract
1 Material Science Centre, University of Manchester, Manchester United Kingdom
It is well documented in the literature that many loading configurations show a distinct size effect for the measured strength, which is particularly evident at sub-micron length scales. Many of these observations can be explained by phenomena such as the presence of grain boundaries or strain gradient plasticity. However, recent experiments by Greer and Nix  found a size effect in the uniaxial compression strength of small single crystal gold rods with diameters in the range 300 – 900 nm. This strengthening was explained by a dislocation starvation model where the absence of dislocation sources within the columns led to rapid exhaustion of deformation and a rapid hardening to strengths 50 times greater than bulk gold. Here we investigate the mechanical properties of gold nanowires of smaller diameters.Highly ordered anodic aluminum oxide films containing regular pore arrays, with diameters < 100 nm, have been used as templates for the fabrication of metal nanowires by electrodeposition. Gold and nickel nanowires have been successfully grown in the pores. The diameters of the nanowires range between 30 nm and 80 nm. The mechanical properties of the gold wires have been measured using an MTS Nanoindenter XP system with a flat punch diamond tip. The diameter of the nanowires and the nanowire separation are significantly smaller than the flat punch diameter, thus the deformation experiments sample a number of nanowires and compress them in parallel. In the stress – strain curves, clear yield points before the onset of plastic deformation can be defined. The measured yield strengths are diameter – dependent and increase from 650 MPa to 1.4 GPa as the nanowire diameter decreases from 70 nm to 30 nm. Our results are consistent with the trends observed with previous uniaxial compression test results on larger, focused ion beam machined, gold columns by Nix  and Volkert . Furthermore, the yield stress of the finest nanowires in this study is very close to the yield strength value 1.5 GPa measured in nanoporous gold column with 15 nm diameter ligaments . Our compression experiments are conducted without strain gradient and avoid the sample surface damage caused by focused ion beam, demonstrating that the dislocation starvation model is still operative in these smaller diameter nanowires.  J.R. Greer and W.D. Nix, Phys. Rev. B 73 Art. No. 245410 (2006). C.A. Volkert and E.T. Lilleoddon, Philos. Mag. Vol. 86, Nos. 33-35, 5567-5579 (2005). C.A. Volkert and E.T. Lilleoddon, Appl. Phys. Lett. 89, 061920 (2006).
9:00 PM - U8.10
WITHDRAWN 02/21/08 Theoretical Investigation of a Half-loop Dislocation Formation from a Surface Step by Atomistic Calculations.
Pierre Hirel 1 , Sandrine Brochard 1 , Laurent Pizzagalli 1 , Pierre Beauchamp 1 Show Abstract
1 , LMP - CNRS, Futuroscope Chasseneuil France
Thursday, March 27WithdrawnPosterU8.10
9:00 PM - U8.11
Mechanical Properties of WS2 Nanotubes.
Ifat Kaplan-Ashiri 1 , Sidney Cohen 2 , Konstantin Gartsman 3 , Thomas Heine 4 , Viktoria Ivanovskaya 4 , Yuekui Wang 4 , Gotthard Seifert 4 , H. Wagner 1 , Reshef Tenne 1 Show Abstract
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel, 2 Surface Analysis Laboratory, Weizmann Institute of Science, Rehovot Israel, 3 Electron Microscopy Unit, Weizmann Institute of Science, Rehovot Israel, 4 Institut für Physikalische Chemie, Technische Universität Dresden, Dresden Germany
9:00 PM - U8.12
Mechanodynamic Penetration of Helium Atoms into Nanocrystalline Metals.
Vitaly Shpeizman 1 , Oleg Klyavin 1 , Vladimir Nikolaev 1 , Boris Smirnov 1 , Lev Khabarin 1 , Yurii Chernov 1 Show Abstract
1 Russian Academy of Sciences, Ioffe Physicotechnical Institute, Saint-Petersburg Russian Federation
9:00 PM - U8.13
Nanoscale Mapping of Elastic Modulus on Granular Topographies by Contact-resonance Atomic Force Microscopy.
Gheorghe Stan 1 , Robert Cook 1 Show Abstract
1 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
9:00 PM - U8.14
Coupled Nanoscratch and 4-Point Bending Evaluations of Adhesion and Cohesion in SiCN/Cu/Ta,/TaN/SiO2/Si Stacked Layers.
Kouji Yoneda 1 , Satoshi Shimizu 1 , Nobuo Kojima 1 , Chikai Sato 1 , Jiping Ye 1 Show Abstract
1 Research Department, NISSAN ARC, LTD., Yokosuka Japan
9:00 PM - U8.15
Elastic Constants of Strained Cu Thin Films Studied by Acoustic-Phonon Resonance Spectroscopy.
Nobutomo Nakamura 1 , Hirotsugu Ogi 1 , Tomohiro Shagawa 1 , Masahiko Hirao 1 Show Abstract
1 Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
Thin films are used in many devices, and their quality highly affects the reliability and performance of the devices. Thin films often include weak bonding regions and residual stress, which degrade the devices’ reliability. Considering that elastic constants change depending on the internal structure, we can nondestructively evaluate them by measuring the thin films’ elastic constants. For this task, accurate measurement of the thin-film elastic constants is indispensable. We propose the acoustic-phonon resonance spectroscopy for studying the elastic property of thin films. When ultra-short pulse laser, duration time of ~100 fs, irradiates a film surface, electric field of the laser beam generates acoustic phonons in the thin film. Although most of the phonons attenuate rapidly and disappear, a part of them remains and a longitudinal standing wave occurs along the thickness direction. Resonance frequency of the standing wave is closely related with the mass density, film thickness, and elastic constant concerning to the longitudinal acoustic wave propagating along the thickness direction. Therefore, we can determine the elastic constant by measuring the resonance frequency. When film surface is strained, reflectivity of laser beam changes. Therefore, by measuring the amplitude of reflected probe beam changing the delay time, we can detect the acoustic-phonon oscillation. Acoustic-phonon oscillation was observed in Cu thin films of 12-100 nm thickness. In the determination of thin film’s elastic constants, measurement error of the film thickness highly affects the resultant elastic constants. We determine the film thickness by X-ray reflectivity measurements. When the incident angle of X-ray is small, reflected X-ray from the film surface and from the interface between the film and substrate interfere, and oscillation pattern appears in the X-ray diffraction spectrum. Film thickness was determined from the oscillation period within the error of 5 %. We investigated the elastic constants of Cu thin films deposited on monocrystal (001) Si substrates. Si substrate is usually covered with the oxide, and Cu film becomes polycrystalline on it. However, hydro-fluoric treatment removes the oxide, and pure Si (001) plane appears, on which Cu film grows epitaxially with <001> direction perpendicular to the film surface. Interatomic distance in Cu (001) plane is smaller than that in Si (001) plane, and Cu film is extended along the in-plane directions near the interface. Although large elastic strain changes the elastic constants because of the anharmonic interatomic potential, elastic constants of epitaxial Cu thin films were comparable to that of bulk Cu, and significant strain dependence was not observed. We confirmed that this unexpected strain-independent elastic constant is specific characteristics observed in only (001) Cu film by calculating the strain-dependence of bulk Cu’s elastic constants assuming several strain states.
9:00 PM - U8.16
Temperature-dependent Mechanical Behavior by Nanoindentation.
Holger Pfaff 1 , Wolfgang Stein 1 Show Abstract
1 Nanolab, Surface , Hueckelhoven Germany
9:00 PM - U8.17
Calculation of Nanoscale Elastic, Shear, and Bending Modulus of Sheet Silicates Using Molecular Dynamics Simulation.
Greg Zartman 1 , Hendrik Heinz 2 Show Abstract
1 Department of Physics and Department of Polymer Engineering, University of Akron, Akron, Ohio, United States, 2 Department of Polymer Engineering, University of Akron, Akron, Ohio, United States
9:00 PM - U8.18
Fractal Dimensions of Soy Protein Nanoparticle Aggregates determined by Dynamic Mechanical Method.
Lei Jong 1 Show Abstract
1 National Center for Agricultural Utilization Research, United States Department of Agriculture, Peoria, Illinois, United States
Soy protein isolate (SPI) is obtained from soybean by removing soybean oil and soy carbohydrates. Soy protein nanoparticle aggregates were prepared by alkali hydrolysis of SPI and followed by centrifugation at acidic pH. Structurally, SPI is a globular protein and its aggregates in water consist of sphere-like protein particles, which further consist of nano-sized aggregates of subunits. Light scattering measurements of hydrolyzed SPI (HSPI) indicate a narrow size distribution of dispersed aggregates. In swollen state, the volume and number weighted mean aggregate size are 260 and 210 nm respectively. The hydrolysis has significantly reduced the aggregate size from ~4 μm to ~0.2 μm. The dry aggregate size is ~150 nm by correcting the swelling effect. The fractal dimension of the protein aggregates can be estimated by dynamic mechanical methods when the particle aggregates are imbedded in a polymer matrix. Nanocomposites were formed by mixing HSPI nanoparticle aggregates with elastomeric styrene-butadiene (SB) latex, followed by freeze-drying and compression molding process. The dynamic shear moduli of the elastomeric composites containing 20, 30, and 40% particle fractions were measured over a temperature range from -70 to 140 oC at 0.16 Hz. A logarithmic plot of shear modulus vs. particle fraction in rubber plateau region at 140 oC can be fitted with a linear line. From the slope of the fitted line, the fractal dimension of the particle aggregates was estimated using the Cluster-Cluster Aggregation (CCA) model developed by Kluppel and Heinrich. The CCA model can also be used to extract fractal dimension from dynamic strain sweep experiments. In this study, the strain sweep experiments were carried out on the composite samples repeatedly for 8 times at 140 oC with a dynamic frequency of 1 Hz over a strain sweep range of 0.01% to 15%. The strain cycles generated a stress softening effect in the composites and eventually reached a reversible equilibrium state. The reversible strain sweep data was then fitted with a CCA model expression developed by Huber and Vilgis to yield the fractal dimension of the particle aggregates. Although these two types of experiments are quite different, the results show that the fractal dimensions extracted from both linear and non-linear viscoelastic data have a reasonably good agreement with each other. The model fitting indicates HSPI has a greater fractal dimension and therefore a more compact structure than the un-hydrolyzed soy protein aggregates.
9:00 PM - U8.19
Improved Load Transfer between Single Wall Carbon Nanotube and Polyvinyl Alcohol (PVA) within a SWNT -Collagen-PVA Composite.
Debdulal Roy 1 , Sanjib Bhattacharyya 2 , Aikaterini Plati 3 , Aron Rachamim 4 , Marie-Louise Saboungi 5 Show Abstract
1 , National Physical Laboratory, Teddington United Kingdom, 2 2Centre de Recherche sur la Matière Divisée, CNRS, Orleans France, 3 Department of Materials Science, University of Cambridge, Cambridge United Kingdom, 4 Engineering Department, University of Cambridge, Cambridge United Kingdom, 5 2Centre de Recherche sur la Matière Divisée, CNRS, Orleans France
9:00 PM - U8.2
Detection of Organophosphate Gases and Biological Molecules using Embedded Piezoresistive Microcantilever Sensors.
Tim Porter 1 , Tim Vail 2 , Amanda Wooley 2 , Rick Vendam 3 Show Abstract
1 Physics, Northern Arizona University, Flagstaff, Arizona, United States, 2 Chemistry, Northern Arizona University, Flagstaff, Arizona, United States, 3 , National Secutity Technologies, LLC, Las Vegas, Nevada, United States
Embedded piezoresistive microcantilever (EPM) sensors have been used in the detection of a variety of analyte species, including volatile organic compounds, carbon monoxide, hydrogen cyanige gas, hydrogen fluoride, single strand DNA, proteins, and certain viral particles. EPM sensors utilize a tiny piezoresistive microcantilever partially embedded into a sensing material to produce a sensing instrument that is compact, simple, resistant to movement and shock, and suitable for remote sensing applications. Support electronics for EPM sensors are simple and compact, as the sensing elements require only a resistance measurement. Sensors may be deployed as small units tethered to a computer via USB connection, or as battery powered motes that comminicate through a radio-frequency mesh network of battery powered motes. In the current project, we have used novel, composite sensing materials comprised of an immobilizing polymer functionalized with either target enzymes or antibodies to detect two biological agents, bacillus globigi (BG) and diisopropyl fluorophosphate (DFP). DFP is an organophosphate used as a simulant for many organophosphate nerve agents such as sarin, while BG is a large bacterial spore used as a simulant for other bacterial spores such as bacillus anthracis. Sensing results are presented for both types of EPM sensors.
9:00 PM - U8.20
Effects of Ion Irradiation on Microstructure and Mechanical Properties of Sputtered Cu/V Nanolayers.
Engang Fu 1 , Jesse Carter 2 , Michael Martin 2 , Greg Swadener 3 , Amit Misra 3 , Nan Li 1 , Lin Shao 2 , Haiyan Wang 4 , Xinghang Zhang 1 Show Abstract
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Nuclear Engineering, Texas A&M University, College Station, Texas, United States, 3 Mater. Sci. Tech. Div., Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Electrical Engineering, Texas A&M University, College Station, Texas, United States
9:00 PM - U8.21
Quantitative Study of Nano-scratch and Indentation Behavior for Polymer Hybrid Materials.
Keehae Kwon 1 , Il-Jin Kim 1 Show Abstract
1 Chemical R&D Center, Cheil Industries Inc., Gyeonggi-Do Korea (the Republic of)
9:00 PM - U8.22
A Unique Probe for Tip Enhanced Raman Scattering and Shadow NSOM.
Judy Ernstoff 1 , Hesham Taha 1 , Rimma Dekhter 1 , Galia Zinoviev 1 , Galina Fish 1 , Aaron Lewis 2 Show Abstract
1 , Nanonics Imaging Ltd., Jerusalem Israel, 2 Applied Physics, Hebrew University , Jerusalem Israel
We present a unique atomic force microscope [AFM] probe for tip enhanced Raman scattering [TERS] and a new form of near-field microscopy called Shadow Near-field Scanning Optical Microscopy. The probe consists of growing a single gold nanoparticle at the tip of a cantilevered nanopipette and the single gold particle is exposed to the optical axis of either an upright or inverted optical microscope. When such probes are used in combination with a Nanonics MV 2000 AFM/NSOM system, that has a completely free axis from above and below, full integration into all forms of optical microscopy are allowed and a complete integration of the AFM and Raman functions with either tip and/or sample scanning is permitted. With such a system we show that a protocol for the independent motion of the probe and the sample can either produce enhancement or a shadow effect. Both of these effects are enhanced by the ability to effect difference Raman spectra with the tip in and out of contact while independently scanning the sample. With such a protocol and the high sensitivity of difference Raman spectroscopy we have analyzed the Raman signals of a thin nanometric strained silicon layer deposited on bulk silicon. This sample can readily be studied with these probes since the probes are not produced from silicon and thus do not produce any silicon background signal or for that matter any Raman background. With such a sample we have developed an understanding of the optical mechanisms of enhancement, scattering and shadowing. Our results show that different optical mechanisms occur as a result of tip and sample interactions. These include the TERS effect obtained by the near-field interaction of the probe with the top layer of strained silicon which occurs when the probe is held off-axis. Under such conditions large enhancements of at least 4 orders of magnitude are seen. At other appropriate positions of the probe an analysis of the relative intensities of the bulk and strained silicon Raman peaks indicate either an increase in the light scattered by the bulk or an effective shadowing of the surface. Recording these phenomena with the aid of difference Raman spectroscopy highlights the nanometric interactions of the probe and the sample and offers new nanometric imaging possibilities.
9:00 PM - U8.23
Nanostructured Fe/W Multilayers Subjected to Helium ion-irradiation.
Nan Li 1 , Engang Fu 1 , Haiyan Wang 2 , Amit Misra 4 , Richard Hoagland 5 , Jesse Carter 3 , Michael Martin 3 , Lin Shao 3 , Xinghang Zhang 1 Show Abstract
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, 4 Materials Physics and Application Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 5 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Department of Nuclear Engineering, Texas A&M University, College Station, Texas, United States
9:00 PM - U8.24
Mechanical Measurements in 3D on III-V Nanowires with AFM.
Christian Kallesoe 1 , Kristian Molhave 1 , Martin Larsen 1 , Peter Boggild 1 Show Abstract
1 MIC - Department of Micro- and Nanotechnology, Technical University of Denmark, Kgs. Lyngby Denmark
Nanowires are rod-like structures with diameters of tens up to a few hundred nanometers, which can be grown epitaxially from substrates. Due to their small size, they can show peculiar mechanical and electrical properties. Furthermore, epitaxial growth of heterostructures allows for the formation of very precise transitions between two semiconductor materials, and definition of very narrow sections with a specific composition . As such 1D hetereo-nanowires offer a unique possibility for tuning the structure, examining the consequences for the mechanical properties are of great importance for applications. Such investigations could involve Youngs Modulus for narrow structures, the influence of defects in the nanowires, the influence of heterostructures in the nanowires, the strength of the interface to the substrate is for a lattice mismatched epitaxial nanowire grown on silicon., as well as the piezoelectric behaviour.For multiwalled and singlewalled CNTs, several techniques on measuring Young’s Modulus have been established [2-5]. For example, a scanning electron microscope (SEM) equipped with deformation and manipulation stages , scanning tunneling microscope (STM)  and atomic force microscopes (AFM) [4,5] setups have been employed to measure plastic and elastic deformation parameters of CNTs. However not many experimental tests on mechanical properties have been performed for III-V nanowires.In this work a simple method to characterize the mechanically properties of nanostructures grown on a planar substrate has been developed. An AFM style cantilever probe is used to deflect a vertically aligned nanowire repeatedly at different positions along the nanowire, which enables accurate determination of the spring constant and Youngs Modulus to be found on many individual nanowires in short time. This method has good clamping at the base compared to previous published mechanical measurements on suspended nanostructures . Furthermore it is possible to contact individual nanowires and to map the mechanical properties in 3D with nanometer resolution along the nanowire, while the force resolution will be determined by the AFM. Additionally, by electrically contacting the nanowire sample and the AFM cantilever, the piezoelectricity of the nanowires can be mapped out simultaneously.Based on this method the spring constant and Youngs Modulus of several epitaxial grown III-V nanowires, with different geometrical and material structures, has been determined and also an examination of their piezoelectricity has been performed. These structures cover a wide range of spring constants from below 0.01 N/m to 10 N/m. W. Seifert et. al., Journal of Crystal Growth 272(1-4), 211-220, (2004). M. F. Yu et. al., Science 287(5453), 637-640, (2000). M. Wang et. al., Advanced functional materials 15(11), 1825-1831, (2005). E. Wong et al., Science 277(5334), 1971-1975, (1997). J. Song et. al. Nano Letters 5(10), 1954-1958, (2005).
9:00 PM - U8.25
Molecular Dynamics Study of Nanoindentation of Thin Films.
Arun Nair 2 , Diana Farkas 1 Show Abstract
2 Engineering Science and Mechanics, Virginia Tech, Blacksburg, Virginia, United States, 1 Materials Science, Virginia Tech, Blacksburg, Virginia, United States
9:00 PM - U8.27
Nanomechanics of Self-Assembled Monolayers on Nanoscale Gold Films.
Milca Aponte-Roman 1 , Adrian Mann 1 Show Abstract
1 Materials Sci & Eng, Rutgers University, Piscataway, New Jersey, United States
9:00 PM - U8.28
Structure-Property Relationships of Mg(OH)2 Filled Poly(methyl methacrylate) Composites.
Cathie Condron 1 , Stefanie Gravano 2 , Mark Ellsworth 2 , Mike Toney 1 Show Abstract
1 , Stanford Synchrotron Radiation Laboratory, Menlo Park, California, United States, 2 , Tyco Electronics Technology Division, Menlo Park, California, United States
Mg(OH)2 is an interesting alternative to brominated flame retardants for halogen free formulations. When dispersed in a PMMA matrix, the composite has excellent weatherability and good chemical resistance. However the elongation suffers as a function of increased elastic modulus. We have evaluated Mg(OH)2 filled polymer samples of varying Mg(OH)2 loadings under different conditions such as elongation and shear using small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). Each formulation has a critical loading point where the elastic modulus is maximized and elongation is maintained. Above this loading, preferred polymer orientation becomes distorted which in turn effects the mechanical properties. Structure analysis utilizing SAXS and WAXS will be presented and correlated to the mechanical properties.
9:00 PM - U8.29
Simulations of an Interface Crack Nucleation During Nanoindentaion : Molecular Dynamics and Finite Element Coupling Approach.
Shotaro Hara 1 , Satoshi Izumi 2 , Shinsuke Sakai 3 , Yoshiyuki Eguchi 4 , Tomio Iwasaki 5 Show Abstract
1 , the university of Tokyo, Tokyo Japan, 2 , the university of Tokyo, Tokyo Japan, 3 , the university of Tokyo, Tokyo Japan, 4 , Hitachi East Japan Solutions, Ltd, Ibaraki Japan, 5 , Hitach, Ltd, Ibaraki Japan
9:00 PM - U8.3
Mechanical Behavior Associated with Heterogeneous Grain-boundary Diffusion and Sliding in Nanocrystals.
Yujie Wei 1 , Allan Bower 1 , Huajian Gao 1 Show Abstract
1 Engineering, Brown University, Providence, Rhode Island, United States
9:00 PM - U8.30
Threading and Interlocking: A Mechanism for the Simultaneous Enhancement of Polymer Stiffness, Strength, and Ductility.
Lokman Torun 1 , Nicholas Tsui 2 , Alex Paraskos 3 , Timothy Swager 3 , Edwin Thomas 2 Show Abstract
1 Materials Institute, Marmara Research Center, Gebze, , Kocaeli, Turkey, 2 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 3 Department of Chemistry, MIT, Cambridge, Massachusetts, United States
— We have synthesized polyester systems containing pendant iptycene units and compared their mechanical/structural properties to a homologues reference polymer wherein benzene replaces iptycene units. Iptycenes have unique structural properties called internal molecular free volume (IMFV). The incorporation of iptycene into polyesters backbone results in a polymer chain contour resembling “molecular barbed wire.” The contribution of iptycene to the mechanical properties of polyesters is significant and robust across concentration and processing conditions. The triptycene polyester films displayed a nearly 3-fold increase in Young’s modulus, an approximately 3-fold increase in strength, and a more than 20-fold increase in strain to failure. We proposed that the presence of triptycene introduces two mechanisms for the enhancement of tensile mechanical properties: molecular threading and molecular interlocking.
9:00 PM - U8.31
Mechanical Dissipation in Ultrananocrystalline and Nanocrystalline Diamond Resonators.
Vivekananda Adiga 1 , Anirudha Sumant 2 , Sampath Suresh 5 , Chris Gudeman 5 , Orlando Auciello 4 , John Carlisle 3 , Robert Carpick 6 1 Show Abstract
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 5 , Innovative Microtechnology, Santa barbara, California, United States, 4 Materials Science Divsion, Argonne National Laboratory, Argonne, Illinois, United States, 3 , Advanced Diamond Technologies, Inc, Romeoville, Illinois, United States, 6 Mechanical Engineering & Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
9:00 PM - U8.32
Modeling of Dislocations and Mismatched Layers in Pentagonal Nanorods.
Anna Kolesnikova 1 , Alexei Romanov 2 Show Abstract
1 , Institute of Problems of Mechanical Engineering, St.Petersburg Russian Federation, 2 , Ioffe Physico-Technical Institute RAS, St.Petersburg Russian Federation
9:00 PM - U8.34
Role of Local Electronic Structures in the Size-dependent Mechanics of Silicon Nanowires.
Byeongchan Lee 1 , Robert Rudd 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Mechanical properties, from general considerations, are understood with local electronic structures: the strong binding of silicon due to the covalent nature of bonding, surface stresses and the corresponding surface lattice constants are typical examples. A better understanding of nanomechanics, therefore, entails the detailed understanding of electronic structures. In this talk, I will present the recent first-principles density functional theory calculations of the mechanical properties of silicon <001> nanowires including the Young's modulus and residual stress, and discuss the relationship between the local electronic structure and nanomechanics.The local electronic environment is often captured in terms of the bond order, which in turn is used to explain structural and mechanical properties of a system, i.e. bond order-bond length-bond strength relationship. The complication arises at the nanometer scale when two different driving forces of the local environment change come into the picture: the increased surface effect and the reduced dimensionality of silicon nanowires. Interestingly, these two driving forces have opposite contributions, if not conflicting, to the net electronic structure change. The surface states increasingly dominate the electronic structure of silicon nanowires and tend to decrease the band gap as the wire size is decreased. On the other hand, the fundamental quantum size effecrt, or quantum confinement, drives the increase in the band gap. The interplay between the two size dependences generates a range of different electronic structures for silicon nanowires, but the resulting changes in structural as well as mechanical properties are not well understood.The mechanics of nanowires from various combinations of size, shape, and surface conditions have been obtained from first principles density functional calculations, and the role of the underlying electronic structures is portrayed with qualitative and quantitative approaches including the bond order. The understanding of the role of the local electronic structures in the change of mechanical properties will help us improve the development of computationally more attractive empirical potentials for large-scale, mixed metallic-semiconducting systems, in which the local environment is not necessarily confined to the bulk-like condition.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.UCRL-ABS-235994.
9:00 PM - U8.35
Brittle and Ductile Failure Behavior of Silicon Nanowires.
Keonwook Kang 1 , Wei Cai 1 Show Abstract
1 Mechanical Engineering Department, Stanford University, Stanford, California, United States
9:00 PM - U8.36
Is Small Perfect ? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts.
Varlei Rodrigues 1 , Fernando Sato 1 , Douglas Galvao 1 , Daniel Ugarte 1 2 Show Abstract
1 Applied Physics Department, State University of Campinas, Campinas, Sao Paulo, Brazil, 2 , LNLS, Campinas, Sao Paulo, Brazil
The structural and mechanical properties of nanometric wires represent a fundamental issue for the understanding of different phenomena such as friction, fracture, adhesion, etc. There is a renewed interest in such systems motivated by the growing demand on nanotechnology miniaturization, new functionalities and less power consuming systems. Components such as diodes, switches, and electronic mixers have been built with simple molecules as active units. In spite of these technological advances, important aspects on device integration (ex. how to connect them in a stable and reproducible way) are still open issues. In order to build functional nanodevices, electrical contacts of nanometric dimensions are needed. In this context, it is necessary to understand the influence of lead properties in the device characteristics and also the role played by structural defects since they can compromise the device functionality and reliability.We report high resolution transmission electron microscopy and ab initio calculation results (LDA and GGA calculations using the SIESTA code) for defect formation in sharp pyramidal Pt nanocontacts (NCs). Our results  show that the elongation of Pt NCs induces the formation of twins located a few planes away from the apex, where the atomic arrangement of the atomically sharp Pt pyramid remains close to the ideal one. This means that it is possible to produce NC with a well defined structure. Many models in molecular electronics have assumed defect free pyramidal NC as leads, which has been object of criticism as being unrealistic. Our results showed that this is in fact a reasonable approximation. On the other hand, an extended defect will always be present beyond the 4th atomic plane counting from the tip and will work as a scattering plane. Thus, it is expected that full electron transmission coefficients are not longer possible, at least for Pt NCs. These aspects should be taken into account when modeling the typical two point electrical measurement on molecular electronic devices. Similar results were also obtained for Au and Ag, suggesting that this is a general behavior of fcc metals. Nevertheless they should be observed only at lower temperates (few Kelvin). The twin planes with areas approximately corresponding to the 4th/5th atomic planes of the Pt pyramid may be considered as a lower size limit for defect generation. V. Rodrigues, F. Sato, D. S. Galvao, and D. Ugarte, Physical Review Letters - in press.
9:00 PM - U8.37
Additivity of Hardenings by Nanolamellar Structure and Antiphase Domain in Ti-39at%Al Single Crystals.
Yuichiro Koizumi 1 , Yoritoshi Minamino 1 , Kazuki Iwamoto 1 , Takayuki Tanaka 1 Show Abstract
1 Department of Adaptive Machine Systems, Osaka University, Suita, Osaka, Japan
9:00 PM - U8.38
Novel Precipitation in Nanocrystalline and Ultrafine-grained 7075 Al.
Yonghao Zhao 1 , Steven Dalleck 2 , Peter Liddicoat 3 , Xiaozhou Liao 4 , Yuntian Zhu 5 , Simon Ringer 3 , Ruslan Valiev 6 , Yizhang Zhou 1 , Enrique Lavernia 1 Show Abstract
1 Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States, 2 Carderock Division, Naval Surface Warfare Center, West Bethesda, Maryland, United States, 3 Australian Key Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales, Australia, 4 School of Aerospace, Mechanical & Mechatronic Engineering, University of Sydney, Sydney, New South Wales, Australia, 5 Department of Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina, United States, 6 Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa Russian Federation
9:00 PM - U8.39
Ultrahigh Tensile Ductility and High Strength in Nickel via Cryo-milling and Quasi-isostatic Forging.
Yonghao Zhao 1 , Troy Topping 1 , Andrea Dangelewicz 2 , Yuntian Zhu 2 , Yizhang Zhou 1 , Enrique Lavernia 1 Show Abstract
1 Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States, 2 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, California, United States
9:00 PM - U8.4
In situ Mechanical Testing in a Scanning Electron Microscope.
Robert Peters 1 , Warren Oliver 1 , Julia Greer 2 Show Abstract
1 Research&Development, MTS Nano Instruments, Oak Ridge, Tennessee, United States, 2 Materials Science, California Institute of Technology, Pasadena, California, United States
9:00 PM - U8.41
Mechanical and Wear Properties of Gold Thin Films.
Alex Volinsky 1 , Du Ke 1 , Xiaolu Pang 2 Show Abstract
1 Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 2 Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing China
Gold thin films are used in many applications, ranging from microelectronics and MEMS to protective coatings, and require high electrical conductivity, thermal and mechanical stability, corrosion and wear resistance. Mechanical properties of electroplated and sputtered gold films were measured by means of nanoindentation and scratch testing. Correlations between gold mechanical properties and thin film microstructure are made.
9:00 PM - U8.42
Effects of Ion Beam Current on the Microstructure, Surface Morphology, and Hardness of TiAlN Films Grown by Ion Beam Assisted Magnetron Sputtering.
Chao-Te Lee 1 , Chi-Chung Kei 1 , Chien-Ying Su 1 Show Abstract
1 Vacuum Technology Division, Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu Taiwan
9:00 PM - U8.43
Measuring the Elastic Modulus and Residual Stress of Free-standing Thin Film Bridges by Nanoindentation.
Erik Herbert 1 2 , Warren Oliver 1 2 , Maarten de Boer 3 4 , George Pharr 2 5 Show Abstract
1 , MTS Nano Instruments, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 3 Mechanical Engineering, Carnegie Mellon, Pittsburgh, Pennsylvania, United States, 4 , Sandia National Laboratory, Sandia, New Mexico, United States, 5 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
9:00 PM - U8.44
Morphological Evolution in Polycrystalline Films.
Ramanathan Krishnamurthy 1 , Mikko Haataja 2 Show Abstract
1 Materials Modeling Group , Technical Center, Caterpillar Inc.,, Mossville, Illinois, United States, 2 Department of Mechanical Engineering, Princeton University, Princeton, New Jersey, United States
9:00 PM - U8.46
Mechanics of High-density Nanocrystalline Ceramic Composites.
Beril Kavukcuoglu 1 , Jafar Al-Sharab 1 , Bernard Kear 1 , Rajendra Sadangi 1 , Vijay Shukla 1 , Adrian Mann 1 Show Abstract
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Tuesday, March 25Transferred Oral Talk U1.5 @ 9:45 AM to Poster U8.46Mechanics of High-density Nanocrystalline Ceramic Composites. Beril Kavukcuoglu
9:00 PM - U8.5
Nanoindentation Testing of Nanoporous Metal Foams.
Reed Doucette 1 , Andrea Hodge 1 , Juergen Biener 2 , Alex Hamza 2 Show Abstract
1 Aerospace and Mechanical Engineering, USC, Los Angeles, California, United States, 2 Nanoscale Synthesis and Characterization Lab, LLNL, Livermore, California, United States
Testing of macro-porous materials (< 30% relative density) by indentation has been shown to follow the relationship H ~ σy, where H is the hardness and σy is the yield strength. However, as we approach the nano-regime is this approximation still valid? In this study, we present the mechanical behavior of nanoporous foams with relative densities between 20 to 40% and cell ligament sizes ranging from 10nm to 1 micron, investigated by nanoindentation tests. We demonstrate that during nanoindentation, foam deformation underneath the indenter is mostly plastic, and thus mostly compressible for which sample areas outside the indentation area remain undeformed. Additionally, we analyze the normalized indenter size to cell size and demonstrate an exponential decay in hardness as a function of indentation depth, which appears to plateau after indentation depths larger than 500 nm. Overall, this study presents nanoindentation as a valid testing technique for nanoporous foams as long as the proper parameter space is used. Prepared by LLNL under Contract DE-AC52-07NA27344
9:00 PM - U8.6
Atomistic Mechanism of Ion Beam Deposition Induced Curvature Formation in Thin Films.
Sachin Terdalkar 1 , Sulin Zhang 2 , Joseph Rencis 1 Show Abstract
1 Mechanical Engineering Department, University of Arkansas, Fayetteville, Arkansas, United States, 2 Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, United States
9:00 PM - U8.7
Relation Between the Elastic Modulus of ZnO Nanowires and its Size: Surface Stress Effect.
Guofeng Wang 1 , Xiaodong Li 2 Show Abstract
1 Department of Mechanical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, United States, 2 Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States