Symposium Organizers
Peter Anderson Ohio State University
Neville Moody Sandia National Laboratories
David Bahr Washington State University
Ralph Spolenak ETH Zurich
SS1: Mechanical Behavior of Nanoporous Materials
Session Chairs
Monday PM, November 28, 2011
Constitution A (Sheraton)
9:30 AM - **SS1.1
Tensile and Compressive Mechanical Behavior of Nanoporous Gold.
Nicolas Briot 1 , Tobias Kennerknecht 2 , Daniel Gianola 2 3 , Christoph Eberl 2 , T. John Balk 1
1 Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States, 2 Institute for Applied Materials, Karlsruhe Institute of Technology, Karlsruhe Germany, 3 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractNanoporous metals with nanoscale ligaments offer a unique opportunity to explore the deformation behavior of highly confined metallic volumes and understand the mechanisms that govern mechanical behavior at the nanometer length scale. The narrow ligaments, with widths of 5 to 15 nm, provide an extreme constraint on the motion of dislocations, which must traverse very small volumes. Hardness testing of nanoporous Au (np-Au) suggests equivalent strength values (calculated with scaling equations) that may approach the theoretical strength level. Tensile testing of np-Au is difficult, due to its macroscopically brittle nature. By combining a fabrication approach that minimizes cracking in bulk np-Au and a microspecimen test technique that permits small testing volumes, both tension and compression tests were performed on sub-millimeter gage thicknesses of np-Au. Compressive strength was slightly higher than tensile strength, as would be expected for a brittle material, but all strength values were significantly lower than literature values for nanoindentation testing. Measured elastic modulus was nearly the same in tension and compression, and was much lower than Gibson-Ashby scaling relations would predict for porous gold with this density.
10:00 AM - SS1.2
In Situ Nanoindentation of Nanoporous Au during Electrochemical Cycling.
Eike Epler 1 , Afrooz Barnoush 2 , Jan Boekenkroeger 1 , Holger Pfaff 3 , Cynthia Volkert 1
1 Institute for Materials Physics, University of Goettingen, Goettingen Germany, 2 , Saarland University, Saarbruecken Germany, 3 , Agilent Technologies Sales and Services GmbH Campus Kronberg, Kronberg Germany
Show AbstractIn the past few years, numerous studies on the mechanical properties of nanoporous gold with different relative densities and ligament sizes have been published. They all show an increase in flow stress with decreasing ligament diameter. Given the presumed absence of surface layers and lack of defect structures, this high strength has been difficult to explain. In an effort to understand the strength of nanoporous Au and the effect of possible surface layers, as well as to complement our recent studies on polymer infiltrated nanoporous Au composites, we study the effect of reversible electrochemical induced surface oxidation of nanoporous Au in a nanoindenter. Studies by microcompression testing and Berkovich indentation allow us to investigate the effect of oxidation on the elastic modulus, flow stress, hardness and ductility of micron sized volumes of nanoporous Au. It is observed that the presence of an oxide layer does not change the modulus, but leads to an increase in flow stress as well as the qualitative observation of reduced ductility. These effects revert to the initial behavior on removing the oxide layer. Our results compare well with the modulus and flow stress obtained in a recent similar study on bulk nanoporous Au. The mechanical behavior can be explained by an oxide layer that is thin and compliant enough to negligibly contribute to load sharing, but adhesive and strong enough to hinder the egress of dislocations from the gold. A comparison of the effect of the oxide film with that of the polymer infiltration on the composite mechanical properties will be used to gain insights into design rules for high strength and high ductility nanocomposites.
10:15 AM - **SS1.3
Design and Properties of Novel Functional Nanoporous Architectures.
Jeff De Hosson 1 , Eric Detsi 1 , Patrick Onck 1
1 Applied Physics, Un. of Groningen, Groningen Netherlands
Show AbstractNanoporous metals have attracted considerable attention in recent years due to their potential for various applications, including catalysts, sensors, actuators, supercapacitors, nano-filters and drug delivery platforms. In recent years, various alternatives for achieving large displacements in actuation materials have been investigated and several designs and techniques were proposed for the displacement amplification including cantilever systems, hydraulic-piston devices and piezoelectric motors. These techniques however are not always appropriate for micro-scale applications. This paper concentrates on a novel design and properties of nanoporous metals with a layered structure and show that the size of these layers can be tailored via the grain size of the alloy precursor. The morphology was designed to enhance the functional properties of nanoporous materials and we have scrutinized the charge-induced strain response associated to this structure. One advantage of the actuation mechanism associated to these novel layered structures is the possibility to achieve comparable large relative displacements at smaller scales. This approach is suitable for the current technological trends dictated by miniaturization of devices. Giant strain amplitudes up to 6% are measured, which are roughly two orders of magnitude larger than in conventional nanoporous gold. A model is presented to explain these phenomena.
SS2: Size Effects - Deformation and Fracture
Session Chairs
Monday PM, November 28, 2011
Constitution A (Sheraton)
11:15 AM - **SS2.1
Influence of Dislocation Density on the Indentation Size Effect in Self-Irradiated Fe-Cr Alloys.
Andy Bushby 1 , Steve Roberts 2 , Chris Hardie 2
1 School of Engineering and Materials Science, Queen Mary University of London, London United Kingdom, 2 Department of Materials, University of Oxford, Oxford United Kingdom
Show AbstractMaterials for nuclear fusion reactors have to be able to withstand high doses of neutron radiation without degrading their properties or creating high activity radio isotopes. Fe-Cr alloys are candidate materials for structural components that are plasma facing. High energy (14MeV) neutron radiation causes displacement of atoms from their lattice sites and the generation of Frenkel pairs and associated dislocation loops, voids and clusters. These damage mechanisms can be simulated through self-implantation from a beam of Fe ions in a linear accelerator. However, implantation depths are limited by the beam energy (3MeV) to the order of a micron, creating a damage layer at the surface. The mechanical properties of such a layer are ripe for investigation by nanoindentation, treating the damage layer as a coating with only the defect density differing from the substrate material. By protecting some parts of the surface from radiation, these materials provide the unusual possibility to compare high and low dislocation density within the same crystal grain. Using spherical indenters, the differences in the indentation stress-stain behaviour of irradiated and un-irradiated material can be determined while highlighting many of the metrological issues inherent with indentation testing. These materials also present a unique opportunity to investigate the influence of dislocation density on the indentation size effect at both first yield and flow.
11:45 AM - SS2.2
Size Dependent Fracture of Silicon Nanoparticles during Lithiation: Implication to Lithium Ion Batteries.
Jianyu Huang 1 , Xiaohua Liu 1 , Li Zhong 2 , Shan Huang 3 , Ting Zhu 3 , Scott Mao 2
1 , Sandia National Laboratories, Albuqerque, New Mexico, United States, 2 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractLithiation of single silicon nanoparticles was observed in real time in a transmission electron microscope for the first time. A strong size dependent fracture behavior was discovered, i.e., there exists a critical particle diameter of ~ 150 nm, below which the particles neither cracked nor fractured upon lithiation, above which the particles first formed surface cracks and then fractured due to lithiation induced swelling. The unexpected surface fracture arose owing to the buildup of large tensile hoop stress in the surface layer that reversed the initial compression, and the small-sized nanoparticles averted fracture because of insufficient mechanical energy to drive crack propagation during the electrochemical energy storage, as revealed by the non-linear fracture mechanics analysis of J-integral. These results provide direct evidence of the mechanical robustness of small silicon nanoparticles for their applications in lithium ion batteries.
12:00 PM - SS2.3
Probing the Mechanisms Underlying Plasticity Size Effects by Varying Indenter Geometry.
Xiaodong Hou 1 , Nigel Jennett 1 , Andy Bushby 2
1 Materials Division, National Physical Laboratory, Teddington, Middlesex, United Kingdom, 2 School of Engineering & Materials Science, Queen Mary, University of London, London United Kingdom
Show AbstractIt has long been known (and exploited) that materials show strength size effects due to microstructure size and defect density. More recently it has been shown that free standing structures (uniaxial compression of micro pillars) and mechanical contacts (indentation size effect) also follow a Hall-Petch like inverse square root law of strength vs. size. Conrad’s slip distance theory (SDT) requires only a limiting dimension to explain size effects; including those found in the absence of constraint or strain gradient. Jennett et al. (2009 Applied Phys. Lett. 95:123102) compressed wall-like structures to show that the smallest dimension determined the yield strength of Tungsten, with only SDT able to fit the data. SDT suggests that different critical lengths can be superposed, and we have previously shown that Cu yield strength follows a Hall-Petch-like relationship in which the critical length is the reciprocal sum of the indentation size (ISE) and the structure size (SSE) multiplied by suitable scalars k1 & k2 (2008 J. Phys. D: Applied Physics 41(7):074006). Taking this idea further, work hardening can be included as a scaled function, (kp√ρs), of the pinning defect density, ρs. By using Spherical, Berkovich, 90° sphero-cone and 90° tapered wedge indenter geometries, we compare the effects of different stress distributions, indentation strains and indent symmetry on the scaling parameters in the SDT fits to indentation of single crystals of Copper and Aluminium. As expected, we find that the kp√ρs term follows the increase in pinning dislocation density as a material work hardens. Comparing Spherical vs. Berkovich indentation of Cu (a change in stress distribution) results in a k1 difference of only a factor of 2. All self-similar indenter geometries produce the same k1 parameter in Al but the absolute value indicates that the ISE critical dimension in Al is 20 times that of Cu for the same contact size. This is useful information for the safe spacing of indentations. Now, the difference in modulus, Burgers vector and bulk yield stress for Al and Cu are small. However, we note that Al has a much larger stacking fault energy than Cu (200 mJ/m2 and 78 mJ/m2 respectively) and a lower melting point; both indicating easier mobility of dislocations. This suggests that, after normalising for the smaller differences in material properties, SDT analysis may provide a rapid and quantitative means to compare the mobility and mean free path of dislocations in materials. Direct characterisation is needed to investigate this further.
12:15 PM - SS2.4
The Role of Stacking Fault Energy on the Indentation Size Effect of FCC Pure Metals and Alloys.
David Stegall 1 , A. Elmustafa 1
1 Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia, United States
Show AbstractThe effect of different interfacial energies, such as stacking fault free energy (SFE), on the magnitude of indentation size effect of several pure FCC metals has been investigated using nanoindentation. The metals chosen were 99.999% Aluminum, 99.95% Nickel, 99.95% Silver, and 70/30 Copper Zinc (alpha-brass). Aluminum has a high SFE of about 200 mJ/m2, whereas alpha-brass has a low SFE of less than 10 mJ/m2. Nickel and Silver have intermediate SFE of about 150 mJ/m2 and 22 mJ/m2 respectively. The SFE is an important interfacial characteristic and plays a significant role in the deformation of FCC metals due to its influence on dislocation movement and morphology. The SFE is a measure of the distance between partial dislocations and has a direct impact on the ability of dislocations to cross slip during plastic deformation. The lower the SFE the larger the separation between partial dislocations and thus cross slip and dynamic recovery are inhibited. The SFE impacts pure metals differently from alloys. It was discovered that the characteristic ISE behavior for the pure metals was different when compared to the alpha-brass which is an alloy. Several additional alloys were chosen for comparison including 7075 Aluminum, 70/30 Nickel Copper, and 90/10 Platinum Rhodium. To further articulate possible differences in the SFE on the magnitude of ISE in these metals electron backscattered diffraction (EBSD) will be used to examine the micro-structural misorientation of the lattice around the nanoindentation sites.
12:30 PM - **SS2.5
Strain Hardening and Brittle Fracture at the Nanoscale.
William Gerberich 1 , N. Tymiak 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractStrain hardening is known to be beneficial to increased ductile fracture toughness. Both prior experimental and theoretical models have shown that preventing local necking instabilities with high-strain hardening leads to improved fracture resistance. But what about cleavage and brittle fracture? Some plastically-induced cleavage models (e.g. Suo, et al circa 1993) demonstrated that increased hardening exponents might decrease the cleavage fracture toughness by a factor of four. While this was a theoretical concept, recent experimental evidence suggests that length scale in the vicinity of 50 to 200 nm has a large effect on both strain-hardening capacity as well as yield strength and fracture toughness. In single crystal silicon, both pillars and spheres demonstrate that toughness and strength increase as diameter decreases. However, strain hardening exponents decrease resulting in an opposite trend. With an order of magnitude increase in strength and fracture toughness but a corresponding factor of four decrease in strain-hardening exponents, the global versus atomistic basis for the size effect is presented. Some elastic-plastic finite element modeling is presented to qualitatively assess the suggested approaches.
SS3: Polymers and Fibers
Session Chairs
Asa Barber
Michelle Dickenson
Monday PM, November 28, 2011
Constitution A (Sheraton)
2:30 PM - SS3.1
Low-Modulus Standards for Nanoindentation and Their Application to Testing Low-k Materials.
Bryan Crawford 1 , Erik Herbert 2
1 Analytical Services Laboratory, Nanomechanics, Inc., Oak Ridge, Tennessee, United States, 2 Material Science and Engineering, Univ. of Tennessee, Knoxville, Tennessee, United States
Show AbstractWhen conducted under appropriate conditions, the Continuous Stiffness Measurement (CSM) technique provides the evolution of mechanical properties as the indenter penetrates the surface of a sample. However, when conducted under inappropriate conditions the resulting data from the technique can be misleading. The condition of tapping, where the applied harmonic oscillation is too large to be supported by the material at shallow penetration depths, has been presented by Pharr et al [1]. Another condition arises when the oscillation size becomes too small and the controlling electronics react to recover the oscillation size that is commanded; this commonly occurs when testing low-modulus, low-hardness materials and the data causes a “skin-effect” to appear in the results.In this presentation, data using the Continuous Stiffness Measurement (CSM) technique are analyzed on fused silica and a new low-modulus reference material showing the skin-effect that appears when the oscillation size is too small and not at steady-state. These data show that performance of the instrument is excellent - even at very shallow penetration depths - on the fused silica sample, but discrepancies appear for the data on the low-modulus sample. If the experiment is incorrectly controlled, one could easily interpret the results on the low-modulus sample as being a skin-effect caused by processing. Results from low-k films are used to highlight the influence of the harmonic displacement during these measurements which can lead to the appearance of a skin-effect and significant errors in the measured mechanical properties – even when fused silica data is accurate. Data from new test techniques that provide superior CSM control are presented along with a new low-modulus reference material. [1] Pharr, G.M., Strader, J.H., Oliver, W.C. Critical issues in making small-depth mechanical property measurements by nanoindentation with continuous stiffness measurement. J. Mater.Res. 24, 653 (2009).
2:45 PM - SS3.2
In Situ Compression Behavior of Polymer-Micropillar Using Force Measurement System in FIB.
Jiyeong Lee 1 2 , Won-Kyung Seong 1 , In-Suk Choi 1 , Ashkan Vaziri 3 , Kwang-Ryeol Lee 1 , Cheol-Woong Yang 2 , Myung-Woon Moon 1
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 , Sungkyunkwan University, Suwon Korea (the Republic of), 3 , Northeastern University, Boston, Massachusetts, United States
Show AbstractWe measured the adhesion strength and observed deformation behavior to identify the benefit of the surface modification of fibrils head by in-situ force measurement system (FMS) equipped in focused ion beam (FIB). We fabricated straight micropillars on the surface of the polydimethylsiloxane (PDMS) using soft lithography. The micropillars have diameter of 9.3 μm, height of 30 μm and spacing of 10 μm, where spacing is defined as the distance between the edges of the adjacent micropillars. After fabrication of the straight pillars, ion beam irradiation was employed to modify the surface and to tailor the shape of fibrils such as wrinkle and hairy structure. It has been shown recently that ion beam bombardment at low ion energy of 1 keV on Polydimethylsiloxane (PDMS) results in instability and undulation of the polymeric surface. This observation suggests that ion beam bombardment induces a compressive strain in the surface layer of the polymer. The ion beam irradiation causes surface modification of the PDMS and induces a stiff skin, which is 70-100 times stiffer than PDMS. Ion beam irradiation also causes shrinkage of the surface, resulting in a strain mismatch between the induced stiff skin and soft polymer and thus, instability of the surface skin in the form of wrinkles. Furthermore, it was found that high energy ion beam bombardment of 5 ~ 30 keV expands pillar’s top head, resulting in mushroom structure.In this study, we investigated the deformation behavior of a single micropillar with various head geometry using force-measurement sensor in the FIB. The pull-off strength was increased proportional to the number of micropillar. The pull-off force for various surface of fibril head is shown continuously as a function of the compressive preload. Potential applications of the created structures are vast and range from non-wetting painting and smart adhesives to bioinspired machines such as nano- and micro- robots with climbing abilities.
3:00 PM - SS3.3
Nanostructural Evidence of Mechanical Aging and Performance Loss in Aromatic Polyamines.
John Howarter 1 , Jae Hyun Kim 1 , Haruki Kobayashi 1 , Walter McDonough 1 , Gale Holmes 1
1 Polymers Division, NIST, Gaithersburg, Maryland, United States
Show Abstract Ballistic performance of aromatic polyamine fibers is related to the fiber’s ultimate tensile strength, strain-to-failure, and Young’s modulus. Ideal high-performance ballistic materials maximize these material properties while minimizing material density. Equally important is long-term mechanical and chemical stability; the fibers should not exhibit performance loss over a conventional material lifetime. To anticipate the design limitation of vests that utilize the next generation high performance ballistic fibers, methods of rapidly probing the potential aging and degradation behavior of the fibers are critical to ensure the fidelity of the woven fibers. Multiple variations of next generation high-performance fibers were investigated under accelerated aging conditions; performance loss was correlated with chemical and nanostructural changes as a result of aging.Homogenous, single component high performance fibers of poly(paraphenylene terephthalamide) (PPTA) and poly[(benzo-[1,2-d:5,4-d’]-benzoxazole-2,6-diyl)-1,4-phenylene] (PBO) were subjected to repeated folding up to 80,000 cycles to simulate damage caused by wear. Likewise, fibers were exposed to simulated environmental conditions to mimic chemically induced degradation. Similar experiments were performed on block-copolymer fibers comprised of PPTA and 5-amino-2-(p-aminophenyl)-benzimidazole (APAB). Fracture behavior of the aged samples varied based on fiber type indicating that lifetime fidelity of high-performance fibers is affected by chemical and nanostructural composition of the fibers. Chemical degradation at the fiber surface was characterized with x-ray photoelectron spectroscopy (XPS). Fiber nanostructure was characterized with small angle x-ray scattering (SAXS) and positron annihilation lifetime spectroscopy (PALS) to measure the onset of changes in free volume and void formation.
3:15 PM - SS3.4
Measuring Size Dependent Mechanics of Electrospun Polymer Nanofibers Using In Situ SEM-AFM.
Russell Bailey 1 , Beatriz Cortes-Ballesteros 1 , Asa Barber 1
1 Department of Materials, Queen Mary University of London, London United Kingdom
Show AbstractPolystyrene (PS) is typically a brittle polymer in tension and exhibits low toughness. However, experimental and theoretical considerations have shown that heterogeneous deformation compromises PS toughness and results in localized failure [1]. The promotion of homogeneous deformation in tension is achievable when structural heterogeneities are removed and can exist when reducing the length scale of the PS [2]. Processing of polymers using electrospinning is advantageous in order to study potential size dependent toughening of PS as resultant fibers can be produced with diameters ranging from many microns to nanometers length scales. This paper therefore explores the mechanical properties of electrospun PS fibers in order to examine potential enhancement of fiber ductility at relatively small length scales. Mechanical testing of individual electrospun PS fibers are performed directly using an novel atomic force microscopy (AFM) setup inside a scanning electron microscope (SEM), which allows both manipulation and visualization of mechanical deformation of PS fibers while recording accurate force information. References1.R. J. M. Smit, ‘Toughness of heterogeneous polymeric systems: A modeling approach’. PhD Thesis. Technische Universiteit Eindhoven (1998)2.M. C. M. van der Sanden, ‘Ultimate toughness of amorphous polymers’. PhD Thesis. Technische Universiteit Eindhoven (1993)
3:30 PM - SS3.5
A Nano-Cheese-Cutter to Directly Measure Adhesion of Freestanding Polymer Nanofibers.
Xin Wang 1 , Johnny Najem 2 , Shing-Chung Wong 2 , Kai-tak Wan 1
1 Mechanical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Mechanical Engineering, University of Akron, Akron, Ohio, United States
Show AbstractElectrospun fibers in the micro- and nano-scale are used in filters, protective clothing, ultrahigh strength composite coatings, biomedical scaffolds, drug delivery, and wound dressing, because of its high aspect ratio and large surface area. Since the mechanical integrity of fiber mesh membranes is closely related to the stiffness of the constituting fibers, extensive investigations in single fiber characterization in the micro Newton range are present in the literature. One by and large ignored but essential factor influencing the mesh performance is the inter-fiber adhesion at the cross-links, without which the membrane cannot stay intact upon external loads. In this paper, a nano-cheese-cutter is fabricated to characterize freestanding electrospun nano-fibers for their elastic modulus, adhesion, and intersurface forces, which can be readily adapted for other nano-structures. Sample fibers were produced by the standard electrospun technique. A nano-cheese-cutter is fabricated by attaching a single freestanding nano-fiber to two microspheres readily glued to the tip of an atomic force microscope (AFM) cantilever. Another freestanding fiber is similarly prepared on a mica substrate. The fibers are arranged in orthogonal crossed-cylinder geometry. External compressive / tensile loads are applied to the AFM cantilever deforming the two fibers into complementary V-shapes. At a critical tensile “pull-off” force, the adhering fibers spontaneously detach from each other. Repeated loading-unloading are also performed to investigate fiber degradation and repeated adhesion-detachment. Mechanical deformation of the fibers as a result of coupled bending-stretching and surface forces, and the external load at the critical “pull-off”, are analyzed using linear elasticity and the Derjaguin-Muller-Toporov (DMT) model. Simultaneous measurements of load and vertical displacement allows one to deduce (i) intersurface force range and magnitude, (ii) adhesion energy of the fiber-fiber interface, (iii) elastic modulus and bending rigidity of fiber.
3:45 PM - SS3.6
Monitoring Multi-Scale Mechanics in Electrospun Fibers Using In Situ AFM Synchrotron.
Urszula Stachewicz 1 , Ilker Peker 2 , Wei Tu 1 , Himadri Gupta 2 , Mark Frogley 3 , Gianfelice Cinque 3 , Asa Barber 2
1 , Nanoforce Technology/Queen Mary University of London, London United Kingdom, 2 Department of Materials, Queen Mary University of London, London United Kingdom, 3 , Diamond Light Source Ltd, Didcot United Kingdom
Show AbstractNanofibrous arrays are produced both synthetically, for example in filtration devices, and in nature such as silk assemblies. Polymeric nanofibres are now being routinely produced cheaply and in large quantities using electrospinning manufacturing methods. Our recent studies showed that the electrospun nanofiber networks, and potentially other fibrous networks, present an inherent toughening ability due to stress delocalization around cracks that are large relative to the fiber components of the network. Electrospun nanofibres are expected to deform through nanoscale fibers deformation and strain to failure at the larger scale together with a reorientation of fibers network in the direction of the applied forces. We study the structural deformation of single nanofibres and deformation of nanofibres network itself by using in-situ AFM synchrotron. Since the polymer chain organization during the tensile testing defines the mechanical properties of the nanofibre, structural investigations during the deformation behavior can elucidate the origin of the improved electrospun fibers mechanical performance. Based on in-situ AFM synchrotron studies of electrospun mats we are able to show how powerful this technique is, allowing understanding of structural changes in materials at multi-scale.
SS4/OO3: Joint Session: Living Systems III: Nano and Submicron Mechanical Testing
Session Chairs
Monday PM, November 28, 2011
Constitution A (Sheraton)
4:30 PM - **SS4.1/OO3.1
New Techniques Using Nanoindentation of Biological Tissues in Fluid Environments.
Michelle Dickinson 1
1 Chemical and Materials Engineering, Univeristy of Auckland, Auckland New Zealand
Show AbstractNanoindentation has become a common and useful technique for measuring the mechanical properties of heterogeneous and microscale materials. Recently there has been a trend to use this technique for testing biological tissues, however the standard preparation methods of dehydrating, mounting and polishing specimens combined with the Oliver and Pharr technique for data analysis are not best suited for such delicate and visco-elastic materials. This study will introduce some of the key challenges for obtaining realistic mechanical properties of biological tissues using nanoindentation including the immersion of samples in fluid, mounting and preparation techniques, contact area error, substrate effects and appropriate data analysis models. Results showing a new nanoindentation test technique for measuring the elastic properties of elastin modified epithelial tissue layers ranging from 7-20μm (3 to 5 cell layers) in thickness will be given. Although previous measurement attempts on these films using tensile testing have failed due to their compliant nature leading to gripping and aligning difficulties, this study will introduce a new drumhead indentation technique. Using this technique, the membrane can be grown and floated over the drum mounting device without removal from the incubation fluid thus removing the need for sample fixation or storage. The membrane is gently held down along the periphery to create a drum-like skin upon which indentation tests are carried out. The indentation loads ranging from 1-5μN result in load-displacement curves where both the linear and non-linear deflection responses can be analysed. This study will show the first results measured for this type of thin biological film displaying modulus values ranging from 200-1000kPa. To highlight the issues related to hard biological tissues, SEM images showing indentation crack propagation and deflection paths in dehydrated mineralized tissues from E. chloroticus sea urchins will be compared to those tested without sample preservation emphasizing the importance of appropriate fluid immersion and testing for biological composites.
5:00 PM - SS4.2/OO3.2
Determination of Mechanical Properties in Escherichia Coli by Nanoindentation.
Cody Wright 1
1 Department of Mechanical Engineering, Old Dominion University, Suffolk, Virginia, United States
Show AbstractEscherichia coli, like other gram-negative bacteria, is protected from the surrounding harsh environment by a cell wall consisting of the peptidoglycan and outer membrane. Whereas the cytoplasmic membrane is the selective barrier, the cell wall provides mechanical strength for the cell. As bacteria navigate various environments, osmotic pressure can change dramatically. The peptidoglycan together with cellular proteins mitigate the osmotic stress that would otherwise cause lysis. The mechanical properties of E. coli cells and its individual layers have been largely indeterminable until the recent development of probe-based measurement tools. Since their invention, scientists have reported significant data measuring elasticity, modulus, and stiffness using atomic force microscopy (AFM). Fundamentally, in order to determine these mechanical properties through probe-based techniques the contact area and load should be well defined. The load can be precisely calculated through the AFM cantilever spring constant. However, the silicon tip contact area can only be estimated, potentially leading to compounding uncertainties. Therefore, we propose a methodology to determine nanomechanical properties of E. coli using a nanoindenter. The mechanical properties of the live bacteria will be tested in liquid.
5:15 PM - SS4.3/OO3.3
Linking Nano- and Micromechanical Measurements of the Bone-Cartilage Interface.
Sara Campbell 1 , Virginia Ferguson 2 , Donna Hurley 1
1 , NIST, Boulder, Colorado, United States, 2 2.Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, United States
Show AbstractA thin (~10 to 100 µm) region of articular calcified cartilage (ACC) anchors stiff (~20 GPa) bone to the significantly more compliant (~100’s of MPa) hyaline articular cartilage (HAC). Although this bone-cartilage, or osteochrondal, interface resists remarkably high shear stresses and rarely fails, its mechanical properties are largely unknown. In this hierarchical study, we combine nanoindentation and atomic force microsopy (AFM) methods to elucidate the mechanisms that facilitate load transmission across the ostetochondral interface. A rabbit femoral head embedded in PMMA was sectioned in the coronal plane and ultramicrotomed to provide a flat surface for testing. Nanoindentation tests (maximum load of 2 mN) were placed in an array traversing the interface region from the ACC into the HAC with 3 µm spacing. Nanoindentation measurements revealed a transition zone in mechanical properties between the calcified and uncalcified region approximately 9 µm wide. Contact resonance force microscopy (CR-FM) measures the frequency and quality factor of the AFM cantilever’s vibrational resonance in contact mode. With this technique, measurements of relative storage modulus E' and loss modulus E'' with 300 nm spacing were possible. CR-FM measurements indicated a substantially narrower (~3 µm) interface, demonstrating the importance of multiscale testing. The inherent nanoscale heterogeneity of ACC was evidenced by significantly higher coefficients of variation than those for HAC for E' values measured by both nanoindentation and CR-FM. This nanoscale heterogeneity is likely to contribute to energy dissipation and the functionality of the bone-cartilage interface at the macroscale. Complimentary measurements with quantitative backscatter electron imaging indicated a decrease in mineral content across the transition zone that corresponded with the increase in E' values. Understanding the functionality of the osteochondral interface will further aid in the development of biomimic interfaces.
5:30 PM - SS4.4/OO3.4
Spherical Nanoindentation Applied to Biomimetic Composites.
Mohammed Abba 1 2 , Surya Kalidindi 1 , Ulrike Wegst 2
1 Mechanical Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractOver time, scientists and engineers all over the world have used nature as a template to design and fabricate materials with varying functionality. While there have been considerable advances made in replicating and improving on naturally occurring materials, man has yet to fully understand the science behind some of them. One of the most widely studied fields is that of biological composites and their multifunctionality. Usually made of biopolymers and some minerals these composites have been found to have a resistance to fracture that is orders of magnitude greater than their constituent materials. With the increasing demand for “green” materials, these composites can serve as a useful template as they are made from safe, biodegradable and readily available materials. This study will focus on how hierarchical structures, such as those found in nacre, can be replicated using a fast and repeatable method. Using chitosan and alumina platelets, we will design films by casting and by smearing the solution. The smeared solution will show more aligned layers and higher mechanical properties. Mechanical properties will be measured in tension as well as using spherical nanoindentation to better understand properties and interfaces at the nanoscale level.
5:45 PM - SS4.5/OO3.5
Failure of Bone at the Sub-Lamellar Level Using In Situ AFM-SEM Investigations.
Ines Jimenez-Palomar 1 , Asa Barber 1
1 Department of Materials, School of Engineering and Materials Science, Queen Mary University of London, London, London, United Kingdom
Show AbstractBone is a fibrous biological nanocomposite material, which is optimized to avoid catastrophic failure [1, 2]. The fracture behavior of bone is expected to be controlled by the various structural features present across the many existing hierarchical length scales [3]. However, micron sized lamellae in bone present the simplest composite unit in bone consisting of mineralized collagen fibrils within a protein matrix, with some work suggesting that this length scale dominates the fracture of whole bone [2]. In this paper we examine the mechanical properties of individual lamellae using novel atomic force microscopy (AFM)-scanning electron microscopy (SEM) techniques [4]. Individual lamellar beams are selected from bone using focussed ion beam (FIB) microscopy and mechanically deformed with the AFM while observing failure modes using SEM. Both the elastic and fracture behavior of the bone lamellae are determined using these techniques. Composite analysis is used to evaluate the mechanical behavior of lamellae and results at micron and sub-micron length scales related to the overall toughness of bone material. Thus, the contribution of micron and sub-micron toughening mechanisms to the fracture of whole bone is considered. References1.Fratzl, P. and R. Weinkamer. Nature's hierarchical materials. Progress in Materials Science. 528 (2007) p. 1263-1334.2.Peterlik, H., et al. From brittle to ductile fracture of bone. Nature Materials. 5 (2006) p. 52-55.3.Gupta, H. S. and P. Zioupos. Fracture of bone tissue: The ‘hows’ and the ‘whys’. Medical Engineering and Physics. 30 (2008) p. 1209-1226.4.Hang, F. and A.H. Barber. Nano-mechanical properties of individual mineralized collagen fibrils from bone tissue. J. R. Soc. Interface. 857 (2011) p. 500-505.
Symposium Organizers
Peter Anderson Ohio State University
Neville Moody Sandia National Laboratories
David Bahr Washington State University
Ralph Spolenak ETH Zurich
SS7: Poster Session: Properties and Processes at the Nanoscale I
Session Chairs
Tuesday PM, November 29, 2011
Exhibition Hall C (Hynes)
SS5: Micromachined Structures for Nanoscale Property Measurements
Session Chairs
Tuesday PM, November 29, 2011
Constitution A (Sheraton)
9:30 AM - SS5.1
Dislocation Entrapment and Plasticity in Nano-Sized Cu Pillars Coated with Atomic Layer Deposited (ALD) TiO2.
Cameron Gross 1 , Andrew Jennings 1 , Frank Greer 3 , Zachary Aitken 1 , Christopher Weinberger 2 , Julia Greer 1
1 Engineering and Applied Sciences, Caltech, Pasadena, California, United States, 3 Microdevices Laboratory, Jet Propulsion Lab, Pasadena, California, United States, 2 , Sandia National Lab, Albuquerque, New Mexico, United States
Show AbstractInvestigations into the size-dependent strength of single-crystalline nano-pillars suggest that free surfaces play an important role by serving as dislocation annihilation sites and by enabling nucleation of new dislocations. Here we study the effect of ~5-15 nm-thick, ALD-deposited conformal Al2O3/TiO2 coatings on the mechanical response of single crystalline Cu nano-pillars and the related, fundamental problem of dislocation confinement at the nano-scale. We observe that passivated pillars show an increased failure strength, smoother stress-strain curves, and Bauschinger effect-like hysteresis upon unloading/reloading as compared with the uncoated samples. In contrast to as-fabricated pillars, TEM images of post-mortem coated pillars reveal distinct dislocation patterns confirming the coating’s role in confining dislocations and causing them to pile-up at the interface. We present a fundamental model, based on classical dislocation theory that suggests a possible mechanism whereby these dislocation pileups account for the observed increased strength.
9:45 AM - SS5.2
Mechanical Properties of Interface-Containing Cu-Fe Nano-Pillars.
Qiang Guo 1 , Andrew Jennings 1 , Julia Greer 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractUnderstanding origins of size-dependent mechanical behavior in small-scale crystals has recently garnered significant scientific interest. We report mechanical response and a novel fabrication route for producing 100nm-diameter bi-material nano-pillars comprised of single crystalline Cu (fcc) and Fe (bcc). Transmission electron microscopic (TEM) analysis shows that the orientation of Cu is ~<111> while that of Fe is ~<110>, forming heterogeneous interfaces with orientation relationship close to Kurdjumov-Sachs. We find that these interfaces exhibit very high, > 1GPa shear strengths, as revealed by uniaxial nano-compression tests. These bi-material pillars represent a prototyped metal-matrix nano-composite with highly controllable microstructure, high strengths, as well as strong metal-metal interfaces. The isolation and subsequent engineering of a single interface in a pillar allows for fundamental insights gained into their deformation mechanisms, leading to more intelligent design of the interfaces.
10:00 AM - SS5.3
A New Regime for Mechanical Annealing and Strong Sample-Size Strengthening in BCC Molybdenum.
Ling Huang 1 , Qingjie Li 1 , Zhiwei Shan 1 , Ju Li 1 2 , Jun Sun 1 , Evan Ma 1 3
1 Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano) & Hysitron Applied Research Center in China (HARCC), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, Shaanxi, China, 2 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractDue to the crystal symmetry, body centered cubic (BCC) metals lack stable one-layer stacking faults and planar screw dislocation cores, have large differences in lattice friction between screw and edge dislocations, and manifest generally different mechanical behaviors from face centered cubic (FCC) metals. While mechanical annealing (significant drop in stored dislocation density in response to applied stress) has been observed in FCC metals, it has not been observed in BCC metals so far. By in situ compression of nanopillars inside a transmission electron microscope, we demonstrate that with the pillar diameter decreasing to hundreds of nanometers, significant mechanical annealing does occur in BCC Mo. In addition, there exists a critical size (DC ~ 200 nm for Mo at room-temperature) below which the strengthening exponent α in Hall-Petch like regression σ~D-α increases dramatically, from α≈0.3 to α≈1. Thus, a new regime for size effects in BCC is discovered that converges to that of FCC, revealing deep connection in the dislocation dynamics of the two systems. We attribute the observed phenomena to the diminishing mobility difference between screw and edge dislocations at high stresses.
10:15 AM - SS5.4
Microstructure–Properties Relation in Submicron Cu Investigated by In Situ TEM.
Daniel Kiener 1 3 , Zaoli Zhang 2 , Andrew Minor 3 4
1 Department of Materials Physics, University of Leoben, Leoben Austria, 3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben Austria, 4 Department of Materials Science and Engineering, University of California in Berkeley, Berkeley, California, United States
Show AbstractIn recent years significant advances in fabrication and testing of small scale structures were achieved (Uchic MD, et al. Science 2004;305:986). A key technology for this advance was the focused ion beam (FIB), which offers the versatility to fabricate various sample geometries down to the 100 nm regime out of nearly any material. However, as most machining techniques, the FIB modifies the near surface structure of the material under consideration. This was shown to have significant influence on the mechanical response, in particular for initially defect free materials (Shim S, et al. Acta Mater. 2009;57:503).In this work, we investigate the mechanical response of sub-micron single crystal copper samples containing various kinds of defects. In detail, we compare the response of FIB prepared specimens, FIB damage free annealed material with contains a significant dislocation density, and FIB prepared samples with a high density of irradiation defects. Quantitative tensile and compression tests were performed in-situ in a transmission electron microscope (TEM) to get further insight into the acting deformation mechanisms. This was complemented by advanced TEM characterization techniques.We consistently observe that plastic deformation in all three cases is governed by the operation of spiral dislocation sources as reported earlier (Oh SH, et al. Nat. Mater. 2009;8:95.). However, there are significant differences in the size-dependent strength characteristic for the different material conditions. In detail, the FIB prepared specimens show the common size dependent yield behavior as reported earlier (Kiener D, Minor AM. Acta Mater. 2011;59:1328). In comparison, the FIB damage free material depicts significantly higher strengths in the same size regime. Even more interesting, the irradiated material containing dispersed radiation defects exhibits a transient behavior from size-dependent to size-independent strength with increasing specimen dimension.These results will be discussed with respect to the question whether size affected microstructure interactions in sub-micron samples can be used to derive bulk-like properties from nano-scale tests.
10:30 AM - SS5.5
Mechanical Properties of Crystalline/Amorphous Nanoscale Multilayers.
Inga Knorr 1 , Susanne Seyffarth 1 , Tobias Liese 1 , Nicolas Cordero 3 , Erica Lilleodden 2 , Hans Krebs 1 , Cynthia Volkert 1
1 Institute for Materials Physics, Georg-August-University of Göttingen, Göttingen Germany, 3 Centre des Matériaux, MINES ParisTech, Evry Cedex France, 2 Institute of Materials Research, GKSS Research Center, Geesthacht Germany
Show AbstractIn this work, the mechanical behavior of three different multilayer film systems composed of alternating polycrystalline metal and amorphous layers is investigated. The specific films consist of Cu/Polycarbonate, Ti/amorphous ZrO2, or Cu/amorphous Pd78Si22 layers with individual layer thicknesses between 10 and 300 nm. The amorphous layers typically deform homogeneously so that they constrain the deformation of the adjacent crystal layers to an extent determined by the relative elastic moduli and flow stresses. Thus the goal of this study is to investigate the effect of length scale and constraint on deformation of nanoscale metals by systematically varying layer thickness and surrounding materials.Mechanical characterization of the multilayer films is performed using nanoindentation and micro-compression tests and shows that the multilayer elastic moduli and flow stresses can be explained by rule-of-mixture behavior, so long as the flow stress of the metal layers is assumed to be layer thickness dependent. The inferred Cu layer flow stresses are consistent with extrapolations of literature values and show a constant value of 2 GPa below a layer thickness of 100 nm, indicating that the theoretical strength has been reached. The Ti layer flow stresses continue to increase with decreasing size even down to layer thicknesses of 10 nm. Investigations with SEM and TEM show that all multilayer systems show similar deformation and failure modes. The multilayer microcompression pillars fail via double barreling and eventual formation of a catastrophic shear band at high strains. Moreover, strain softening is observed which may be attributed to shear induced disordering in the amorphous layers and to layer rotation near the edges of the pillars, which results in a geometrical reduction of the flow stress. Failure modes and flow stresses are directly correlated with the shear strength of the individual layers which can be measured using a novel nanoindenter-based micromechanical method. Based on the observations of the three different multilayer systems and on considerations of crack propagation and strain localization, optimum design and performance of crystalline/amorphous multilayers will be discussed.
10:45 AM - SS5.6
Effect of Lattice Anisotropy on Plasticity Mechanisms in Ti2AlN Studied by In Situ Compression of Micro-Pillars under Synchrotron Micro-Beam.
Ludovic Thilly 1 , Joan J. Roa 1 , Antoine Guitton 1 , Christophe Tromas 1 , Anne Joulain 1 , Cécile Marichal 2 , Steven Van Petegem 2 , Helena Van Swygenhoven 2
1 Pprime Institute, University of Poitiers, Futuroscope France, 2 , Paul Scherrer Institut, Villigen Switzerland
Show AbstractTi2AlN is a ternary nitride belonging to a class of materials called MAX phases with general formula Mn+1AXn phases (M is a transition metal, A belongs to group A of the periodic table of elements, X is carbon or nitrogen): it exhibits a complex nano-layered hexagonal lattice with very high c/a ratio (∼4.5). In general, MAX phases combine some of the best properties of metals (machinability, damage tolerance, electrical and thermal conductivities) and ceramics (high specific stiffness, low thermal expansion coefficients, high temperature resistance). Their deformation mode consists of kink and shear bands as well as grain delamination which are attributed to the very anisotropic nano-layered structure where basal dislocation slip is mostly operative leading to kinking nonlinear elastic (KNE) properties. The micro-mechanism suggested to explain KNE properties is the incipient kink band (IKB) composed of parallel basal dislocation loops, stacked on top of another. The geometry of IKBs is such that they only remain extended if a load is applied; removal of the load resulting in their total annihilation. To date, direct evidence for the existence of IKBs, is lacking, bearing witness to our incomplete knowledge of this elementary deformation mechanism.The purpose of the present work is therefore to study the elementary deformation mechanisms of MAX phases and more generally the effect of lattice anisotropy: polycrystalline Ti2AlN samples have been characterized by EBSD to obtain full knowledge of the crystalline orientation of the individual grains, in particular the orientation of the (0001) basal plane with respect to the sample surface. Specific grains have been selected for having the basal plane parallel, perpendicular or close to 45° to the surface: Several single crystalline micro-pillars have been fabricated from these grains by focused ion beam (FIB) milling and in-situ compressed under micro-focused x-ray beam at the MicroXAS beamline of the Swiss Light Source at Paul Scherrer Institute. The compression of the micro-pillars, associated with in situ micro-diffraction, shed light on the intrinsic deformation mechanisms: the simultaneous recording of the applied compressive stress-strain curve and of the Laue patterns allows associating the onset of micro- and macro-plasticity and/or non-linear elasticity, with the local lattice characteristics, taking advantage both of the diffraction and the micrometer size of the beam.
11:30 AM - SS5.7
Structure and Mechanical Properties of Nanoscale Metal–Ceramic Multilayers.
Dhriti Bhattacharyya 1 , Amit Misra 1
1 , Los Alamos national lab, Los Alamos, New Mexico, United States
Show AbstractThe unique structures and mechanical properties of Al-TiN nanoscale multilayers will be overviewed. First, the Al layers in an alternating Al/TiN composite grow in a twin relationship to both the TiN and the underlying Al layers but only when the TiN layers are less than a critical thickness of approximately 2 nm. Density functional theory based calculations are used to interpret these observations. Second, micro-pillar compression experiments revealed that at extremely small layer thicknesses (< 5nm), the nano-scale multilayers exhibit unusually high flow strengths (~ 4.5 GPa maximum) significantly higher than hardness divided by a factor of 3, high compressive deformability (5-7% plastic strain) and high strain hardening rates in the Al layers, which are on the order of 16-35 GPa (~E/4 – E/2). Nanoscale metal-ceramic multilayers allow the design of nano-composite materials with both flow strength and work hardening rates approaching the theoretical limits.
11:45 AM - SS5.8
Influence of Bulk Pre-Straining on the Size Effect in Nickel Compression Pillars.
Andreas Schneider 1 , Daniel Kiener 2 , Patric Gruber 3 , Hans Maier 4 , Christopher Yakacki 5 6 , Carl Frick 7
1 Metallic Microstructures, INM Leibniz-Institut für Neue Materialien, Saarbrücken Germany, 2 Department of Materials Physics, University of Leoben, Leoben Austria, 3 Institut für Zuverlässigkeit von Bauteilen und Systemen, Karlsruhe Institute of Technology, Karlsruhe Germany, 4 Lehrstuhl für Werkstoffkunde, Universität Paderborn, Paderborn Germany, 5 Department of Research & Development, MedShape Solutions, Inc, Atlanta, Georgia, United States, 6 School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 7 Department of Mechanical Engineering, University of Wyoming, Laramie, Wyoming, United States
Show AbstractMicrocompression tests were performed on pre-strained nickel (Ni) single crystals in order to investigate the influence of the initial dislocation structure on the size dependence of small-scale metal structures. A bulk Ni sample was grown using the Czochralski method and sectioned into four compression samples which were pre-strained to nominal strains of 5, 10, 15 and 20%. Bulk samples were then characterized using transmission electron microscopy (TEM), Laue diffraction, and electron backscatter detection. Small-scale pillars with diameters of 200 nm to 5 µm were focused ion beam microscope (FIB) machined from each of the four deformed samples and further compressed via a nanoindenter equipped with a flat punch. Results definitively show that bulk pre-straining inhibits the size effect. Pillars in the micron range cut from heavily pre-strained bulk samples demonstrate elevated strength values, however, deformation history does not play a role in stress-strain behavior as diameter decreases below 1 μm. In situ TEM and micro-Laue diffraction measurements of pillars show little change in dislocation density during pillar compression.
12:00 PM - SS5.9
Plasticity in BCC Pillars Observed In Situ by Laue Diffraction.
Helena Van Swygenhoven 1 2 , Julien Zimmermann 1 2 , Cecile Marichal 1 2 , Steven Van Petegem 1
1 NUM/ASQ, Paul Scherrer Institut, Villigen Switzerland, 2 Institute of Materials, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne Switzerland
Show AbstractMicro-compression testing is widely used to investigate the deformation behavior of micron sized volumes. The micro-compression technique has revealed a “smaller is stronger” trend in single crystal pillars with diameters below 10 microns. This size effect, often represented by a power law between pillar diameter and strength, is observed to be different for fcc and bcc metals. In-situ Laue diffraction during micro-compression was developed to explore the activation of slip systems and determine the onset of slip. It has been demonstrated that the use of focused ion beam (FIB) methods to synthesize the pillars can induce a strain gradient [Scripta Mat. 62 (2010) 746] and that for fcc metals a pre-existing strain gradient encourages non-Schmid behavior [Acta Mat 57(2009) 5996]. In this talk in-situ Laue diffraction is applied to study bcc pillars, with the aim to understand the difference in size effect between bcc and fcc single crystal pillars and to explore the possible influence of the critical temperature Tc. The role of Tc in bulk bcc plasticity is well documented in the literature. It is generally believed that, at temperatures well below Tc, the flow stress and plastic deformation mechanisms in bcc metals are primarily controlled by the glide of ½<1 1 1> screw dislocations on {110} planes. This has been ascribed to the non-planar dislocation core of the screw dislocation which results in high lattice friction and thus a lower mobility compared to the edge dislocation, features that have been extensively supported by atomistic simulations The first series of pillars compressed during in-situ Laue diffraction are performed on single crystal Mo pillars obtained from a directionally solidified (DS) NiAl-Mo eutectic (Bei and George, Acta Mat. 53 (2005) 69), a metal for which Tc lies above RT. These Mo pillars were investigated in the as-grown and in the 11% pre-strained conditions, as well as after FIB milling. Continuous and load unload experiments have been performed. Careful analysis of the diffraction patterns show that the diffraction peaks move initially along a rotation direction corresponding to slip on {1 1 2} plane with streaking along a <1 1 1> direction,. Inspection in SEM of the pillar surfaces after deformation until large strains, confirm the presence of bursts along a {1 1 2} plane. TEM analysis shows the presence of dislocations of mixed character, i.e. with screw and edge component. A similar analysis is performed on W single crystal pillars, a material with a much higher Tc temperature. For this material all pillars are made by using FIB. The slip behavior of single crystal bcc pillars is discussed in terms of Tc, the role of the FIB damage and the initial presence of dislocations due to pre-straining.
12:15 PM - SS5.10
Plasticity of Indium Nanostructures as Revealed by Synchrotron X-Ray Microdiffraction.
Arief Budiman 1 , Gyuhyon Lee 2 , Michael Burek 2 , Dongchan Jang 3 , SeungMin Han 4 , Nobumichi Tamura 5 , Martin Kunz 5 , Julia Greer 3 , Ting Tsui 2
1 Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory (LANL), Los Alamos, New Mexico, United States, 2 Waterloo Institute of Technology, Universityof Waterloo, Waterloo, Ontario, Canada, 3 DIvision of Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States, 4 Graduate School of EEWS, Korea Advanced Institute of Science & Technology, Daejeon Korea (the Republic of), 5 Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractIndium is a key material in advanced lead-free solder applications for the microelectronics industry due to its extended ductility, excellent wetting properties and high electrical conductivity. With the size of electronic devices continuing to shrink and the promise of indium-based nanotechnologies, it is important to develop a fundamental understanding of this material’s small-scale mechanical properties and reliability. Studying how the dislocation configurations and densities evolve in particular during deformation will be crucial in understanding the mechanical behaviors of indium nanostructures and this is enabled by the synchrotron Laue X-ray microdiffraction (µSXRD) technique. Using this approach, we found significant Laue peak broadening of indium after the deformation which indicates accumulation of dislocations much like in bulk metals during deformation. These observations, coupled with post-compression scanning electron microscopy as well as in situ uniaxial compression tests, suggest thermally activated deformation processes in low-melting temperature indium such as diffusion and dislocation climbs act to suppress the size effect commonly reported in other metal nanostructures.
12:30 PM - SS5.11
Microcompression of Ceramics – Advantages and Difficulties.
Sandra Korte 1 , Martin Ritter 1 , Robert Stearn 1 , Paul Midgley 1 , William Clegg 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractMicrocompression is used predominately to locally study plasticity in metals and the associated strong effects of size. However, the technique is also very well suited to the investigation of plasticity in ceramics, due to the possibility to suppress cracking in uniaxial tests on brittle materials, a much reduced effect of size on the yield stress in intrinsically strong materials and the availability of high temperature experiments to study the often thermally activated deformation mechanisms in hard materials. In exploring these advantages of testing ceramics at small scales, several challenges need to be overcome, such as the increased scatter in the onset of plasticity, the pronounced effect of misalignment on the extracted mechanical properties and the need for additional characterisation techniques, such as 3D-EBSD presented here as an example, to observe the often limited plastic deformation.
12:45 PM - SS5.12
Small Scale Plasticity of Silicon as a Function of Electronic Doping.
Rudy Ghisleni 1 , Jacques Rabier 2 , Jean-Luc Demenet 2 , Johann Michler 1
1 Laboratory for Mechanics of Materials and Nanostructures, EMPA, Thun Switzerland, 2 Département de Physique et Mécanique des Matériaux, Institut P' - CNRS - Université de Poitiers – ENSMA, Chasseneuil-Futuroscope Cedex France
Show AbstractThere are two ways to lower the brittle ductile transition temperature (BDTT) of brittle materials: by applying a hydrostatic pressure superimposed to the stress required for plastic deformation or by reducing drastically the sample dimensions. Rabier et al. have contributed to explore the original and somehow unexpected plasticity mechanisms of materials below the BDTT by using deformation under confining pressure. In particular, in silicon, a high stress regime has been evidenced which is controlled by movement of perfect shuffle dislocations [J. Rabier et al. (2010), DOI: 10.1016/S1572-4859(09)01602-7]. On the other hand, the study of silicon nanopillars plasticity under uniaxial compression at room temperature (and a strain rate of 1-5 x 10-3) has shown that pillars having a diameter larger than a critical one are brittle whereas those having a smaller diameter exhibit a ductility which compares to that of metallic materials. The critical diameter has been found to be between 310 and 400nm [F. Östlund et al. (2009), DOI: 10.1002/adfm.200900418].At these temperature and stress levels, effects which have been neglected or considered as “academic” can become relevant such as the electronic effects on dislocation movements and plastic deformation.The aim of this work is: 1) to confirm that perfect shuffle dislocations control the plasticity of silicon nanopillars at high stress; 2) to determine the effect of doping on the yield stress and on the brittle to ductile transition diameter of silicon nanopillars (doping affects the Fermi level position and thus the staking fault energy). The mechanical tests are conducted on <123> oriented silicon single crystal nanopillars with diameters ranging from 500 nm to 2 μm obtained by focused ion beam machining. Wafers with different electronic doping are tested: intrinsic (P doped, Nn <= 1014 cm-3); n type (P doped, Nn = 6*1018 cm-3), and p type (B doped, Np = 1*1018 cm-3). Lowering the strain rate at 6.7 x 10-4 s-1 and orienting the pillar for single slip deformation allowed increasing the critical diameter for the intrinsic Si wafer to 850 nm at room temperature, at a yield strength measured in 7 GPa. The doped pillar presented a 10% increase in the yield strength, more statistic (more experiments will be conducted before this work will be presented at the end of november 2011) is needed before drawing any conclusion on the effect of the electronic doping on the plastic deformation.
SS6: One Dimensional Structures: Single and Aggregate Properties
Session Chairs
Dan Gianola
Alan Needleman
Tuesday PM, November 29, 2011
Constitution A (Sheraton)
2:30 PM - **SS6.1
Modeling Deformation of Vertically Aligned Carbon Nanotubes.
Alan Needleman 1
1 Materials Science and Engineering, University of North Texas, Denton, Texas, United States
Show AbstractVertically aligned carbon nanotubes (VACNTs) have promising mechanical properties for use in a variety applications including, for example, as energy absorbers and as compliant thermal interfaces. A fundamental understanding of their mechanical behavior is needed to provide the basis for design in such applications as well as in applications where mechanical performance may not be the primary objective. A compressible elastic-viscoplastic constitutive relation is developed to model the inelastic behavior of VACNTs. This constitutive model is then used in finite deformation, finite element analyses to model the response of VACNTs under various imposed loadings, including modeling experiments on uniaxial compression of pillars composed of VACNTs carried out by Hutchens and Greer at Caltech. The effects of material parameter variations on the mechanical response are also considered. Results of the analyses are compared with experimental observations. This is joint work with Shelby B. Hutchens and Professor Julia R. Greer of Caltech.
3:00 PM - SS6.2
Catastrophic vs. Gradual Collapse of Thin-Walled Nanocrystalline Ni Cylinders as Building Blocks of Micro-Lattice Structures.
Jie Lian 1 , Lorenzo Valdevit 2 , Tobias Schaedler 3 , Alan Jacobsen 3 , William Carter 3 , Julia Greer 1
1 Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, United States, 2 Department of Mechanical and Aerospace Engineering, University of California, Irvine, California, United States, 3 Sensors and Materials Laboratory, HRL Laboratories LLC, Malibu, California, United States
Show AbstractOrdered cellular structures - lattice materials - exhibit good thermal, mechanical and energy absorbing properties, and particularly, display enhanced stiffness and strength per unit mass. These attributes make lattice materials ideal for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. In lattice-type structures, as the truss member thickness is reduced to micron- and sub-micron levels, the interactions between the external dimensional parameter, film thickness and the microstructural parameter, grain size can drastically alter the material’s mechanical strength. To capitalize on such size-dependent mechanical properties in a 3-dimensional lattice structure, in this work, we show that hollow nanocrystalline Ni cylinders with wall thicknesses of 500 nm and 150 nm exhibit strikingly different collapse modes: the 500 nm sample collapses in brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than the predicted values by shell buckling theory, likely due to localized buckling and fracture events observed from in situ compression experiments. These results are further interpreted by elastic shell buckling theory and Finite Element analyses.
3:15 PM - SS6.3
Mechanics of Whisker Formation in Sn-Based Coatings.
Fei Pei 1 , Nitin Jadhav 1 , Eric Chason 1
1 School of Engineering, brown university, Providence, Rhode Island, United States
Show AbstractSn-based coatings on Cu are known to form thin filaments (whiskers) that grow out of their surface and can lead to short circuits in electronic components. The whiskers are believed to grow in response to stress induced by the formation of a Sn-Cu intermetallic compound at the interface between the layers. Therefore, understanding the atomic-scale mechanics in Sn is critical to understanding how the whiskers form. The problem has become more severe in recent years due to the removal of Pb as an alloying element (for environmental reasons) which prevents whisker formation. However, it is still not understood what makes the whiskers form at specific sites on the surface and how Pb-alloying suppresses whiskering. In this work, we will discuss real-time studies of Sn/Cu and Sn-Pb/Cu samples by means of EBSD to understand the correlation between the microstructure, local stress evolution and whisker nucleation. Simultaneous measurements of surface morphology and the underlying grain structure will be shown to describe how they change before and during whisker growth. The role of different kinetic processes, such as nucleation or recrystallization, on whisker formation will be discussed on the basis of our experiment results.
3:30 PM - SS6.4
In Situ Mechanical Property Measurements of Amorphous Carbon-Welded Boron Nitride Nanotubes.
Jae-Woo Kim 1 , Jennifer Carpena Nunez 2 , Emilie Siochi 2 , Kristopher Wise 2 , Yi Lin 1 , John Connell 2 , Michael Smith 2
1 , National Institute of Aerospace, Hampton, Virginia, United States, 2 , NASA LaRC, Hampton, Virginia, United States
Show AbstractRecently, boron nitride nanotubes (BNNTs) were successfully synthesized and found to have substantial crystalline morphology, high strength-to-weight ratio, and elevated temperature stability, about 800 oC in air. The mechanical, chemical, thermal, and radiation shielding properties of BNNTs make them applicable for many uses in aerospace applications. For example, an elastic modulus of BNNTs (~ 0.9 TPa, theoretically) make them potential candidates for structural reinforcement applications. However, carbon nanotube (CNT) reinforced structural composites have shown that the composite properties are much lower than the intrinsic properties of the CNTs. This is caused by poor intertube load transfer and physical defects created during processing and fabrication. Also, damage occurring during the service life of the CNT composites lead to a decrease in properties. One approach to overcome these shortcomings involves creating cross-links between tubes, either chemically or by electron beam ‘welding’ of adjacent tubes. In this study, we have taken the latter approach by physically connecting BNNTs together with amorphous carbon (a-C) deposited using electron beam irradiation. Here, we present a method for measuring the mechanical properties of individual BNNTs and pairs of BNNTs joined with a-C inside a transmission electron microscope equipped with an integrated atomic force microscope system. In-situ tensile testing of a-C-bonded BNNT hybrid structures was performed. The failed and broken specimens were subsequently repaired between tests by deposition of additional a-C, and re-evaluated. Here, we present the mechanical properties of various a-C-modified BNNT hybrid structures.
3:45 PM - SS6.5
Crack-Interface Interaction in Carbon Nanotube-Reinforced Amorphous Carbon Matrix Composites.
Jianbing Niu 1 , Zhenhai Xia 1
1 , University of North Texas, Denton, Texas, United States
Show Abstract Amorphous carbon (a-C) composites incorporating nanosized reinforcements are being actively pursued as next-generation super-hard/super-tough and wear-resistance coatings. The a-C based composites with carbon nanotubes (CNT), nano-diamond and TiC nano-particles were fabricated and reported to have high hardness, very low friction coefficient and high elastic recovery. One of the key issues in the development of the a-C based composites is the a-C/reinforcement interface that plays a major role in determining the mechanical properties and chemical behavior of the system. Fracture toughness could be improved through interface design by introducing toughening mechanism similar to those in microscale composites. Wear resistance is also related to interfacial behavior of the composites. Moreover, nanocomposites could exhibit novel toughening mechanisms because of their unique reinforcement and interface structures. Here, the mechanics of crack-interface interactions have been addressed via molecular dynamics simulations. We revealed a new mechanism of nanofiber premature failure under the high interfacial friction when matrix crack deflects along the interface. We show that the structure of the CNT reinforcement – single vs. ideal multi-wall vs. multi-wall with interwall sp3 bonding – influences the interfacial sliding and crack penetration. With increasing the sp3 bond fraction, the bridging strength of the CNTs increases to a plateau. Since sp3 bond in multi-walled CNTs can be controlled by several techniques, our results thus suggest that a-C matrix composites reinforced by the multi-walled CNTs with interwall bonding represent a viable ceramic matrix composite that can be engineered for higher toughness.
4:30 PM - **SS6.6
Probing Deformation Mechanisms in Single Crystalline Nanowires.
Daniel Gianola 1 , Lisa Chen 1 , Kathryn Murphy 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show Abstract Emerging applications for which inorganic nanowires are used as the fundamental building block are numerous and growing, largely due to the promise of new size-dependent physical phenomena offering superior device performance such as high efficiencies, faster response, and good sensitivity. Despite the alleged advantages over conventional materials, nanowires are often subjected to extreme duress, often manifesting in the form of coupled fields (e.g. thermomechanical, electromechanical) where the materials response is unknown at these length scales. Full predictive capability for optimal and reliable use demands experiments that are able to accurately measure such properties using relevant testing modalities. We show in situ tensile experiments on individual single crystalline nanowires to attempt identification of strength- and rate-controlling deformation mechanisms. A suite of in situ mechanical testing tools is employed to quantify mechanical response and correlate measured behavior with deformation morphology. Electrical behavior is measured concurrently with tensile testing, which is used as a signature of microstructural change during plastic deformation. Transient and elevated temperature nanomechanical experiments are employed to extract activation parameters for plastic deformation. These results will be discussed in the context of thermal activation of nanoscale plastic deformation, which has recently been predicted to be important in ultra-strength materials.
5:00 PM - SS6.7
Ultrahigh Fracture Strength of Si Nanowires under Bending.
Gheorghe Stan 1 , Sergiy Krylyuk 2 , Albert Davydov 2 , Igor Levin 1 , Robert Cook 1
1 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThe shrinking features of today's nanoscale devices and systems lead to challenging requirements for new tests and procedures for reliable measurements of the nanoscale mechanical properties of Si. Readily fabricated in top-down and bottom-up systems, Si nanowires are one-dimensional single crystals that provide excellent specimens for testing the mechanical properties of Si at the nanoscale. In this work, the ultimate bending strength of Si nanowires with radii in the 20 nm to 60 nm range[1, 2] were investigated by using a new bending atomic force microscopy (AFM)–based protocol. Si nanowires dispersed on Si substrates were bent into hook and loop configurations by AFM manipulation. The bending states prior to failure were analyzed in great detail to observe the bending dynamics and the ultimate fracture strength of the investigated nanowires. An increase in the fracture strength from 12 GPa to 18 GPa was measured as the radius of nanowires decreased from 60 nm to 20 nm. The large values of the fracture strength of these nanowires, although comparable with the ideal strength of Si, are explained in terms of the coupled effects of crystal defects and surface morphology of the nanowires.[1] S. Krylyuk, A. V. Davydov, I. Levin, A. Motayed, and M. D. Vaudin, Appl. Phys. Lett. 94, 063113 (2009).[2] G. Stan, S. Krylyuk, A. V. Davydov, and R. F. Cook, Nano Lett. 10, 2031 (2010).
5:15 PM - SS6.8
Temperature- and Strain-Rate-Dependent Incipient Plasticity in FCC Nanowhiskers.
Lisa Chen 1 , Gunther Richter 2 , John Sullivan 3 , Daniel Gianola 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Max Planck Institute for Intelligent Systems, Stuttgart Germany, 3 CINT Science Dept., Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractSmall-scale crystalline materials have demonstrated strength levels near their theoretical limits, provided sufficiently high crystalline quality. This ultra-strength behavior has been attributed to low to zero defect densities, resulting in a dearth of productive dislocation sources, coupled with facile dislocation losses at nearby free surfaces. The instigation of plastic deformation then relies on the nucleation of defects, which is predicted to be thermally activated. Simulations and calculations have shown that the probability of dislocation nucleation increases at lower strain rates and higher temperatures, but concrete, quantitative relationships between these parameters have yet to be experimentally confirmed. To elucidate the energetic and kinetic barriers for deformation mechanisms in nanoscale metals, we have measured the tensile behavior of nominally defect-free Au and Pd nanowhiskers as a function of temperature over a range of 25– 250°C and strain rate. We employ a MEMs-based tensile-testing setup adapted to a temperature-controlled heating stage to apply a nominally uniform temperature to the nanowhisker during testing. The data we obtain from these experiments allows us to systematically monitor not only the deformation behavior, but also the competition and transition between different deformation modes (e.g. propagation of full dislocations vs. twinning), as a function of size, strain rate, and temperature. High resolution electron microscopy is used to identify vestiges of plastic deformation following mechanical testing. We compare our results with theoretical data to gain further insight into the relevant factors and governing mechanisms for incipient plasticity at the nanoscale.This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Basic Energy Sciences user facility at Los Alamos National Laboratory (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-AC04-94AL85000).
5:30 PM - SS6.9
Controlling the Lithiation-Induced Strain and Charging Rate in Nanowire Electrodes by Coating.
Xiaohua Liu 1 , Li Qiang Zhang 2 , Yang Liu 1 , Shan Huang 3 , Ting Zhu 3 , Scott Mao 2 , John Sullivan 1 , Jian Yu Huang 1
1 Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractLithiation-induced strain (LIS) can result in high stress, fracture, and capacity loss of the electrodes in lithium ion batteries (LIBs). Previously methods, such as using elastomeric binders, were used to accommodate the mechanical strain and mitigate these adverse mechanical effects. Here we demonstrate that the intrinsic LIS of a SnO2 nanowire during charging can be dramatically altered by applying a carbon, aluminum, or copper coating [Ref: ACS Nano, DOI: 10.1021/nn200770p (2011)]. Revealed by direct, real-time observations with advanced in situ TEM, the radial expansion of the coated nanowires was completely suppressed, resulting in enormously reduced tensile stress at the reaction front, as evidenced by the lack of formation of dislocations. Furthermore, the SnO2 nanowires coated with carbon, aluminum, or copper can be charged about 10 times faster than the non-coated ones. These improvements are attributed to the effective electronic conduction and mechanical confinement of the coatings. Our work demonstrates that nanoengineering the coating enables the simultaneous control of electrical and mechanical behaviors of electrodes, pointing to a promising route for building better LIBs.
5:45 PM - SS6.10
Investigating the Size Effect of Ultra Strong and Ductile Single Crystalline Metallic Nanowires Using In Situ Tensile Test.
In-suk Choi 1 , Jong Hyun Seo 2 4 , Tae-Yeon Seong 4 , Bongsoo Kim 3 , Jae-Pyoung Ahn 2
1 High Temperature Energy Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Nano-Materials Analysis Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 4 Department of Materials Science and Engineering, Korea Unversity, Seoul Korea (the Republic of), 3 Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractA series of uniaxial tensile tests were performed for dislocation free single crystalline Pd nanowires with diameter ranging from 30 nm to 256 nm to study the fundamental questions of the intrinsic size effect on mechanical response of metallic materials. Using the In-situ tensile tests in FEI DualBeam system, we could quantitatively visualize the deformation mechanism of single crystalline Pd nanowires. The <110> single crystalline Pd nanowires showed ultra-strong and ductile deformation behavior resulting from deformation twinning process. For the diameter of 105 nm, the yield stress of a <110> rhombic Pd nanowire reaches up to 2.4 GPa at 4% elastic strain with subsequent load drop down to 150 MPa due to twin nucleation. Then, twin migration occurs at the constant stress of 150 MPa with structural reorientation of the <110> rhombic nanowires into the <100> square nanowires resulting in ductile elongation at about 45 %. The Pd nanowires with different diameters also showed high strength and ductile behavior through deformation twinning. The size effects in yield strength and twin migration stress manifest as the yield stress decreases from 4 GPa to 1 GPa and the twin migration stress from 860 MPa to 70 MPa. While the size scaling exponent lies in the range of the values reported for FCC metals, the exponent value for twin migration stress is notably higher than that of yield stress even if both twin nucleation and twin migration are associated with the surface emission of leading partial dislocations.
SS7: Poster Session: Properties and Processes at the Nanoscale I
Session Chairs
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - SS7.1
Blast Wave Mitigation Using Nanoporous-Materials-Functionalized Liquids.
Yu Qiao 1 1 , Weiyi Lu 1 , Taewan Kim 1
1 Dept of Struct. Eng., UCSD, La Jolla, California, United States, 1 Program of Mater. Sci. Eng., UCSD, La Jolla, California, United States
Show AbstractThe use of bombs and blasts was a major threat to the U.S. troops in Iraq and Afghanistan. Recently, we developed a novel, nanoporous-materials-functionalized (NMF) liquid, that can react within microseconds to sufficiently reduce shock fronts. A NMF liquid is formed by suspending nanoporous particles in a liquid phase. The inner nanopore surface is specially treated so that it is nonwettable to the liquid. Under ambient condition, due to the capillary effect, the nanopores remain empty. At a blast wave front, the local high pressure can rapidly compress the liquid into the nanopores, converting a significant amount of energy into heat as well as interfacial tension. Moreover, the small ligament length and the effective multilayer structure of large impedance mismatch of the nanoporous phase enable the high-efficiency energy capture, as the wave energy transmission paths are interrupted. Our quasi-static, drop-tower, gas gun, blast chamber, small-scale blast, and live blast experiments have shown encouraging results. The unique pressurized nanofluidic behaviors are also investigated via molecular dynamics simulation.
9:00 PM - SS7.10
Rapid Shear Modulus Switching of Ambient Temperature Range Photo-Responsive Azobenzene Side Chain Liquid Crystal Polymer.
Michael Petr 1 , Matt Helgeson 1 2 , Johannes Soulages 2 , Sarah Bates 2 , Gareth McKinley 2 , Paula Hammond 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe shear modulus of a new azobenzene side chain liquid crystal polymer (SCLCP) was shown to be photo-responsive from 0-50°C using oscillatory shear rheometry (OSR) with in-situ UV irradiation. After annealing, the SCLCP forms a metastable nematic phase from its Tiso at 72°C all the way down to its Tg around -7°C. At a frequency of 10 rad/s and at strains within the linear visco-elastic regime (LVE), as characterized by constant value moduli strain sweeps and elliptical Lissajous plots, the UV light was cycled off and on, and, when the UV light was turned on, the shear loss modulus (G”) dropped about 30% at 5°C, 20% at 25°C, and 5% at 50°C and the shear storage modulus (G’) dropped 30% at 0°C, all due to disruption of the nematic phase caused by the azobenzene’s trans to cis isomerization. At temperatures above 0°C, G” is higher than G’, but at 0°C, G’ is higher signifying a transition to a glassy phase. This glassy transition was further characterized by temperature and frequency sweeps because higher oscillation frequencies increase the apparent stiffness of the material. Demonstration of rapid and reversible photo-responsiveness for this SCLCP in the normal living temperatures of humans is significant because it is a step towards its application as an actuator material.
9:00 PM - SS7.11
Nanoscale Dynamic Viscoelastic Measurements at Elevated Temperature.
Jiping Ye 1 , Satoshi Shimizu 1
1 Cutting-edge Technology Department, Nissan ARC, Ltd., Yokosuka, Kanagawa, Japan
Show AbstractAs a technique for estimating small scale mechanical properties, nanoindentation measurement has been widely used to evaluate the hardness and modulus of thin film and small volume materials. However, the traditional indentation method for hardness and modulus measurement is of limited effectiveness for characterizing time-dependent and temperature-dependent mechanical behaviors of viscoelastic materials. Viscoelastic materials exhibit viscous behavior at glass-transition (Tg) temperature and this Tg state is sensitive to environments such as moisture and the surrounding air. It is necessary to develop a method (so-called nano-Dynamic Mechanical Analysis, nano-DMA) for accurately measuring time-dependent mechanical material properties over a range of non-ambient temperatures at the nanoscale. Meanwhile, nanoindentation measurement method applies a load in the micro Newton range by pressing a diamond stylus on the specimen surface and then detects the penetration depth at a nanometer scale. The rigorous accuracy required for loading and displacing the stylus has made it difficult to apply nanoindentation measurement at high temperature. Up to now nanoindentation measurement for evaluating the mechanical properties has been restricted to room temperature (RT) and in ambient air. In this work, an attempt was made to apply nanoindentation measurement over a temperatures range from -120oC up to 500oC under environmental control for evaluating the temperature and frequency dependence of elastic modulus of small scale polymer materials. An insulation cooling system was incorporated in a Hysitron nanoindentation system to protect the transducer, used for loading and detecting the displacement of the stylus, against heat convection from the heating stage. To avoid moisture effect, an environment-controlled system was applied for the indentation measurements. Measurement reliability was examined by using a homogeneous and isotropic PET sample. No significant difference was observed in temperature dispersions of storage elastic modulus, loss elastic modulus and loss tangent between nanoindentation measurement data and bulk data measured by DMA. A practical application on surface-deteriorated PE tubes was used to demonstrate the validity and usefulness of this nano-DMA method. Infrared spectroscopic imaging revealed the surface layer of PE tube was oxidized to carbonyl O=C<. The storage elastic modulus and Tg of the surface layer became much higher than its interior layer. These data give us a reason why the PE tube surface was deteriorated to form brittle cracks. The results of this study indicate this nano-DMA measurement method has been successfully developed for use in evaluating the nanoscale dynamic viscoelastic properties of small scale polymer materials over a range of non-ambient temperatures from -120oC up to 500oC.
9:00 PM - SS7.14
Adhesion in Organic and Hybrid Organic/Inorganic Solar Cells.
Deying Yu 1 3 , Tiffany Tong 2 3 , David Kwabi 1 3 , Onobu Akogwu 1 3 , Wole Soboyejo 1 3 4
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 3 , Princeton Institute of Science and Technology of Materials, Princeton, New York, United States, 2 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 4 Theoretical Physics, African University of Science and Technology (AUST), Abuja Nigeria
Show AbstractThe results of experimental studies of adhesion between bi-material pairs that are relevant to organic and hybrid organic/inorganic solar cells are presented. Adhesion between the possible bi-material pairs is measured using force microscopy techniques. These include interfaces that are relevant to bulk heterojunction solar cells, and hybrid combinations of titanium dioxide (TiO2) and poly(3-hexylthiophene) (P3HT). The adhesion to rigid indium tin oxide (ITO)-coated glass substrates is also compared to that on flexible/stretchable PDMS substrates with Cr interlayers. The implications of the results are discussed for the design of robust organic electronic and hybrid organic/inorganic solar cell devices.
9:00 PM - SS7.15
Size Effects and Multiscale Mechanics of Semiflexible Random Fiber Networks.
Ali Shahsavari 1 , Catalin Picu 1
1 Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractRandom fiber networks are structural elements in many biological and non-biological materials and systems. For example, their elasticity plays an important role in the multifunctionality of the cytoskeleton of eukaryotic cells and of connective tissue. In this work we show that networks composed of semiflexible fibers are highly heterogeneous bodies with multiscale character, and that their mechanics is affected by strong size effects. Their effective elastic moduli are controlled by the level of non-affinity in the structure which, in turn, depends on the size of the system, the geometry of the network and the fiber persistence length. These effects are studied and quantified. A master curve predicting the elasticity of the network in terms of system parameters is established. A size effect affecting the non-linear range of the deformation is also discussed.
9:00 PM - SS7.16
Understanding Interfaces in Cellulose Nanowhisker Nanocomposites.
Stephen Eichhorn 1 2
1 , University of Manchester, Manchester United Kingdom, 2 Physics, University of Exeter, Exeter United Kingdom
Show AbstractThe interfaces between cellulose nanofibers made using a variety of processes and polymeric resins are presented; namely cellulose nanowhiskers (nanocrystals) prepared by acid hydrolysis of plants, bacterial cellulose and microfibrillated cellulose. It is shown how interfacial micromechanics can be obtained using Raman spectroscopy by monitoring a shift in the peak position of a band emanating from nanocellulose reinforcements in the composites. The approach allows the effect of water and surface modification of the cellulose nanofibers to be probed in detail, and acts as a valuable processing tool to optimise performance.
9:00 PM - SS7.19
SiO2/Si Nanotowers Fracture on the Scanning Force Microscope.
Dariusz Jarzabek 1 2 , Thomas Jung 1 , Zygmunt Rymuza 2
1 , Paul Scherrer Institut, Villigen PSI Switzerland, 2 Insititue of Micromechanics and Photonics, Warsaw University of Technology, Warsaw Poland
Show AbstractA tool and a method for investigating mechanical properties of interface between two materials in nanoscale is presented. Micro-structured nanotowers, made of silicon (Si) and silicon dioxide (SiO2), are mapped and modified with an Atomic Force Microscope (AFM). The AFM is operated in the contact mode and serves as a measuring instrument (topography, lateral force). By using different normal forces, the lateral force, which acts on the interface between Si and SiO2, can be changed. In combination with a statistical analysis of the fracture incidents observed at certain experimental conditions e.g. the perpendicular or lateral force exerted by the tip, this experiment allows the quantitative assessment of the threshold conditions for fracture. Nanotowers can be manufactured with lithography for example by using an electron beam to write structures directly into resist materials. One class of nanotowers which have such been prepared consists of amorphous SiO2 on Si with dimensions of a few nanometers. The interface height can be adjusted by controlling the duration of the etch process and co-detemines the initiation of fracture of the towers. If tower dimensions reach below the distance between defects characteristic to the material, the majority of nanotowers will be defect free, thus allowing the analysis of the defects' influence on the fracture behaviour. Results show that the nanotowers not only may be fractured at the interface but also at the base. The way of fracture depends on a height of the interface, the radius of the cantilever's tip used in an experiment, the tip's velocity and many more. By combining these parameters, it is possible to measure and compare the adhesion force between Si and SiO2, and the cohesion force in silicon. The main goal is to establish this technology as an alternative to conventional adhesion tests e.g. Scotch-tape test, Peel test and micro tensile test.
9:00 PM - SS7.20
Plastic Deformation in Micropillar Compression of Silicon Carbide at Room Temperature.
Chansun Shin 1 , Hyung-ha Jin 1 , Junhyun Kwon 1 , Dong Jin Kim 1
1 , Korea Atomic Energy Research Institute, Daejeon Korea (the Republic of)
Show AbstractSilicon carbide (SiC) has excellent thermal, mechanical and electronic properties that make it a promising material for next-generation electronic devices and for structural components in fusion reactors. We have experimentally investigated the compressive strength of SiC micropillars by uniaxial compression tests. The material used in this study is chemically vapor-deposited polycrystalline beta-SiC, which exhibits a columnar grain structure with a strong {110} fiber texture and a grain size of 2 to 10 μm.The diameters of SiC micropillars range from 5.4 down to 0.7 μm. The micropillars were fabricated by mask and inductively coupled plasma etching technique. A few hundred micropillars could be fabricated under an identical fabrication condition, which is advantageous for the statistical analysis of the fracture properties of brittle ceramic materials. The aspect ratio of micropillars was set to two to three, and taper angle is approximately 4°. Uniaxial compression tests have been conducted using flat punch nanoindentation at room temperature. Engineering stress/strain curves were estimated from measured load/displacement data by correcting the displacement considering sink-in of the pillar and load frame displacement. The engineering stress/strain curves showed an initial elastic portion, followed by a rapid burst of displacement. SEM observations of pillars after deformation showed that brittle fracture occurred in micropillars with a diameter larger than 1 μm. We found, however, that fracture preceded by a large plastic deformation (~18% strain) in smaller pillars. Slip bands were clearly visible on the surface of the deformed pillar from SEM images. TEM observation of a lamella prepared from the pillar by using FIB showed that slip occurred in {111} slip planes. No twins could be observed, so the plastic deformation of SiC is induced by glide of perfect dislocations. Compressive fracture strength showed a clear specimen size effect. The strength varied from 6.5 GPa up to 18 GPa as the diameter decreased. Present results are found to be in agreement with the values reported in literature, i.e. compressive strength of 2.5 GPa for bulk SiC sample and 19~24 GPa converted from nano-hardness measured by nanoindentation.
9:00 PM - SS7.21
Atomistic Simulation Study of Size Effects during Compression of Nanoscale Cu Pillars Containing High-Density Dislocation Networks.
Frederic Sansoz 1
1 School of Engineering, The University of Vermont, Burlington, Vermont, United States
Show AbstractStudying the interaction mechanisms between preexisting dislocations and free surfaces during deformation at the atomic scale is critical for a fundamental understanding of size effects on strength in nanoscale crystals. However, the dislocation processes controlling flow stress scaling in face-centered cubic (fcc) crystals less than 100 nm in size have remained an open question due to limited knowledge on microstructural evolution during deformation in such small volumes. This talk presents some recent advances using a new atomistic simulation technique to generate nanoscale Cu crystals containing random networks of dislocations, and study their evolution during compression as a function of pillar diameter. This technique is shown to enable the simulation of key mechanisms of nanoscale plasticity observed in the past in nanopillars with different methods, such as in-situ nanocompression experiments or DDD simulations. Remarkably, the present simulations reveal that <111> Cu pillars less than 75 nm in diameter with a high initial dislocation density exhibit the same flow stress scaling in compression, as a function of pillar diameter, than that observed experimentally in Cu crystals with larger diameters and smaller densities. A deformation mechanism map is presented for Cu crystals with different diameters, and used to elucidate the origin of size-dependent plasticity in nanoscale fcc crystals. Also, particular focus will be placed in this presentation on strain-hardening processes and temperature effects.
9:00 PM - SS7.22
Interface Shear Strength-Controlled Plasticity in Nanoscale Multilayered Materials.
Youbin Kim 2 , Arief Budiman 1 , Amit Misra 1 , Seung Min Han 2
2 Graduate School of EEWS, Korea Advanced Institute of Science & Technology (KAIST), Daejeon Korea (the Republic of), 1 Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory (LANL), Los Alamos, New Mexico, United States
Show AbstractMicrocompression tests were performed on the incoherent interface Al-Nb multilayers with bi-layer thicknesses of 5nm and 50nm. The Al-Nb multilayers showed increase in strength as the bi-layer thickness was reduced; the average 5% flow stress from the 5nm and 50nm bi-layer spacing Al-Nb specimens were determined to be 2.1GPa and 1.4GPa, respectively. The results from our microcompression study were compared with the previous report on Cu-Nb multilayer microcompression results that indicated that the flow stresses of the Al-Nb multilayer are lower than those of Cu-Nb of the same bi-layer spacing. The observed difference in strength was attributed to a potential difference in the interfacial strength of the two incoherent multilayer systems.
9:00 PM - SS7.23
On the Role of Dislocation Nucleation in the Brittle-to-Ductile Transition in InSb Semi-Conductor Micro-Pillars.
Ludovic Thilly 1 , Rudy Ghisleni 2 , Johann Michler 2
1 Pprime Institute, University of Poitiers, Futuroscope France, 2 , EMPA - Swiss Federal Laboratories for Materials Testing and Research, Thun Switzerland
Show AbstractAt ambient temperature and pressure, most of the semiconductor (SC) materials are brittle: this is the case of the III-V compound SC indium antimonide, InSb. In general, the brittle-to-ductile-transition (BDT) temperature is situated around 0.6Tm where Tm is the absolute melting temperature: for InSb, TBDT is around 150°C. The evolution, with temperature, of the elementary plasticity mechanisms (dislocations) in InSb has been studied by compression of macroscopic samples under hydrostatic pressure and subsequent transmission electron microscopy (TEM) analysis: in the ductile regime (above TBDT), perfect dislocations are observed while at low temperature only partial dislocations are observed. This change of deformation mechanism may explain the occurrence of the BDT: after the emission of the leading partial dislocation, the sources are shut off and crystal plasticity is restricted [Acta Mat, 58, 2010, 1418-1440].To study the role of dislocation nucleation, InSb micro-pillars have been fabricated by FIB and in-situ compressed at room temperature in a SEM, in order to correlate the observation of slip traces at the pillars surface and features of the stress-strain curve. TEM thin foils have been cut out of the pillars to study the deformation microstructure.Surprisingly, InSb pillars can be plastically deformed up to strains of 20% for diameters up to ~20µm. At larger diameters, the pillars become brittle without plasticity. Moreover, the yield stress increases when reducing the pillar diameter.The TEM study and the observation of slip traces at free surfaces during cyclic compression show that increasing the surface-to-volume ratio of the pillars modifies the dislocation nucleation conditions and favours plasticity even at room temperature. The role of dislocation nucleation from free surfaces is thus discussed within the larger context of the micro-pillar compression technique and extrinsic size effects.
9:00 PM - SS7.25
Nanomechanical Properties of Teflon-MWCNT Bilayer Films.
R. Schoeppner 1 , A. Qiu 1 , D. Stauffer 2 , R. Major 3 , J. Skinner 4 , T. Zifer 4 , G. O'Bryan 4 , A. Vance 4 , W. Gerberich 2 , D. Bahr 1 , N. Moody 4
1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 3 , Hysitron Inc., Minneapolis, Minnesota, United States, 4 , Sandia National Laboratories, Livermore, California, United States
Show AbstractCarbon nanotubes have attracted considerable attention in the fabrication of conductive dispersions owing to their unique combination of mechanical, electrical, and magnetic properties and good processability. Ofparticular interest is the potential for creating conductive coatings on insulating polymer films for static dissipation while maintaining the chemical and physical properties of the polymer. The amorphous fluoropolymer Teflon AF (TAF) was chosen for its limited solubility, low dielectric constant and high chemical resistance and multi-walled carbon nanotubes (MWCNTs) for their high conductivity, high aspect ratios, and relatively low cost compared to single-walled nanotubes. There are few studies on polymer MWCNT suspension properties and even fewer that use Teflon. To define mechanical and electrical property relationships in this film system, bilayers of Teflon AF MWCNT films were created with differing concentrations of functionalized and nonfunctionalized MWCNTs. Nanoindentation revealed that addition of 8 weight percent MWCNTs increased modulus by about 25% and hardness by about 15%. Conducting indentation showed that films with 8 weight percent MWCNT exhibited uniform stable conductance once indentation depth exceeded several hundred nanometers. Films with lower concentrations of MWCNTs were insulating. In this presentation, the results will be used to show that the two techniques provide a unique description of structure property relationships in this suspension film system. This work is supported by Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - SS7.26
Effects of Grain Size and Frequency on Internal Friction in Nanocrystalline Thin Films and Nanowires of Aluminum.
Kaushik Das 1 , Dorothee Almecija 1 , Guruprasad Sosale 1 , Srikar Vengallatore 1
1 , McGill University, Montreal, Quebec, Canada
Show AbstractMeasuring internal friction in ultrathin films and nanowires can provide useful insight into the effects of scale on mechanical behavior and guide the design of high-Q micro- and nanomechanical resonators for sensing and communications. To this end, we have developed a MEMS-based silicon microcantilever platform to measure internal friction in nanostructured materials. The silicon microcantilevers are designed so as to have low damping approaching the fundamental limits of thermoelastic dissipation. Thus, these structures enable accurate measurement of internal friction in nanomaterials by using thermoelastic damping for calibration [1]. Using this platform, we have measured the effects of grain size and frequency on internal friction at room temperature in sputtered thin films of aluminum with thickness of 60 nm and 100 nm. The microstructure of the as-deposited and annealed films was extensively characterized using transmission electron microscopy and atomic force microscopy. Internal friction in these ultrathin films is a strong function of grain size but only weakly dependent on frequency. Thus, internal friction in 100 nm thick films reduced by a factor of five when the average grain size was increased from 90 nm to 390 nm by annealing. This result suggests that grain-boundary sliding contributes significantly to dissipation in these films. However, for constant film thickness and grain size, the internal friction reduced monotonically only by a factor of two when the frequency was increased from 50 Hz to 50 kHz. Using the same platform, we also measured internal friction in nanowires of aluminum that were patterned at the root of the microcantilevers using e-beam lithography. The thickness of these polycrystalline nanowires ranged from 50 nm to 100 nm, and their width from 118 nm to 396 nm. These nanowires were patterned in arrays with center-to-center spacing of 1 micrometer. An analytical model was developed to extract the internal friction in the nanowires from the damping of the composite microcantilever. The internal friction in the nanowires was essentially the same as in the thin films for frequencies ranging from 6.5 kHz to 24.5 kHz, suggesting that lateral confinement does not significantly affect dissipation in aluminum. The details of these measurements, and their implications for the mechanisms of internal friction in nanostructured aluminum, will be presented.[1] G. Sosale, S. Prabhakar, L. Frechette and S. Vengallatore, Journal of Microelectromechanical Systems, vol. 20, pp. 764-773 (2011)
9:00 PM - SS7.28
Two-Phase Model of Plasticity in Polycrystalline Nanostructures.
Fabrizio Cleri 1
1 IEMN, University of Lille I, Lille France
Show AbstractWe present a continuum model to describe the extreme plastic behavior of nanostructured materials. We take inspiration from both experiments on Si nanowires [1], and recent MD simulation results [2], where it was observed that deformation in a nanostructure made of nanocrystals embedded in an amorphous network proceeds by transferring the deformation energy to and from three distinct regions: a crystalline phase, corresponding to the interior of each nano grain; a constrained amorphous phase, the connecting network between different nano grains; a ’defect process’ zone, a thin shell surrounding each nano grain. We obtain equations for the strain and stress which are solved numerically to follow the evolution of the material phases, and the overall mechanical response. The P zone is considered as a sub-part of the crystal, therefore its evolution is accounted implicitly. Surface diffusion is also included in the model, to account for stress-assisted diffusion leading to non constant volume of the nanostructure during the mechanical deformation. A remarkable agreement with experiments on Si nanowires is obtained.[1] T. Ishida, F. Cleri et al., Nanotechnology (2011) in press[2] F. Cleri et al., Applied Physics Letters, 97, 153106 (2010)
9:00 PM - SS7.29
Using Atomic Force Microscopy for Property Evaluation of Nanowires and Their Adhesion with Metallic Electrodes.
Manish Tiwari 1 , Simone Schuerle 1 , Bradley Nelson 1 , Dimos Poulikakos 1
1 Mechanical and Process Engineering, ETH Zurich, Zurich Switzerland
Show AbstractIn atomic force microscopy (AFM) the force feedback can also be used for high sensitivity force measurements provided an accurate force calibration is employed. In the current work, we present such accurately calibrated force-deflection measurements on single walled carbon nanotubes and silicon nanowires (referred simply as NWs) suspended on a trench between two metal electrodes. We also measure the mechanical properties of the NWs and characterize the mechanical contact between the NWs and the electrodes. These measurements are particularly relevant in nanoelectronic devices such as ultra-high frequency filters and resonators for high sensitivity gas/mass detection.Fluidics assisted dielectrophoresis (DEP) has been recently proposed as a means to assemble NWs in nanolectronic devices with high yield. Our device was fabricated using standard photolithography/lift-off to form of metal electrodes on silicon wafers with thermally grown SiO2, followed by fluidic dielectrophoretic assembly of NWs. The NWs are then suspended by HF etching of the SiO2 layer. Low pressure chemical vapor deposition synthesized NWs were dispersed in DI water and used for DEP. Both capacitively coupled and direct contact modes of DEP were used. Either palladium or gold were used as electrode materials to test the contact quality between NWs and metal electrodes. Optionally, E-beam lithography is used to cover the NWs from the top with metal as a means to enhance the clamp quality. AFM tips are used to deflect the NWs laterally as well as normally in order to determine the NW properties and their adhesion with the electrode metals. The lateral force constant of the tip was determined using a diamagnetic system with a levitated pyrolytic graphite sheet. First the spring constant of the levitated graphite was determined using a laser vibrometer based setup, which could then be used to calibrate the lateral force constant of the AFM tip. Force calibration was repeated by altering the weight of the graphite sheets to check the accuracy. Following this accurate calibration, repeatable deflection forces as high as 2700 nN were recorded for SWCNTs suspended on palladium electrodes with ~1.5 microns spacing, indicating a strong mechanical bonding between Pd and SWCNT. The measurements also provide a very repeatable and accurate way to measure NW mechanical properties such as Young’s modulus and ultimate strength. The normal mode measurements were performed using focused ion beam milled tips with sharp nanocavities in order to ensure easy location of the ~nm size NWs. The normal and lateral measurements are compared. Unclamped tubes invariably show signs of slippage on the electrodes, which can be a source of detrimental energy loss in nanoelectronic applications. Therefore, our study underscores the importance of top side clamping for high quality factor resonators as well as provides a reliable means to determine mechanical properties of NWs.
9:00 PM - SS7.31
Deformation of Al Nanowires in an Oxygen Environment.
Fatih Sen 1 , Yue Qi 2 , Adri C.T. van Duin 3 , Ahmet T. Alpas 1
1 Department of Mechanical, Automotive and Materials Engineering, University of Windsor, Windsor, Ontario, Canada, 2 Chemical Sciences and Materials Systems Laboratory, General Motors R&D Center, Warren, Michigan, United States, 3 Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractAs the surface to volume ratio increases at nanoscale, the surface oxidation can significantly alter the deformation mechanisms of Al. To simulate deformation of Al nanowire (NW) in a non-vacuum environment, we first simulated the oxidation of a single crystal Al NW, then deformed it in an oxygen environment using molecular dynamics (MD) simulations with reactive force field (ReaxFF). The amorphous oxide shell with a thickness of 1 nm formed on the Al NW with a 2 nm radius. We found that pure aluminum NW deformed in vacuum, yielded by nucleation of partial dislocations at the surface. The oxide shell acted as defect nucleation sites and the partial dislocations nucleated from the aluminum/aluminum oxide interface in the oxide covered Al NW. Thus, the presence of an oxide shell was found to decrease the yield strain compared to pure Al NW. Single crystal aluminum NW showed brittle fracture in vacuum, however the thin oxide shell can deform plastically by opening up of Al-O rings and eventually forming one atom thick Al-O chains. In vacuum, when the aluminum NW covered by the oxide shell, the total elongation increases with slower strain rate when it deforms in oxygen. When the strain rate is slow enough, the oxide shell showed an interesting super-plastic deformation behaviour that was attributed to continuous surface oxidation. The tensile deformation at different strain rates and oxidation rates were used to depict a kinetic model for the aluminum deformation under an oxygen environment.
9:00 PM - SS7.32
In Situ Transmission Electron Microscopy Observation of Discrete Hopping Lithiation in ZnO Nanowire.
Akihiro Kushima 1 , Xiao Liu 2 , Guang Zhu 3 , Ju Li 1 4 , Zhong Wang 3 , Jian Huang 2
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 , Georgia Institute of Technology, Atlanta, Georgia, United States, 4 , Xi'an Jiaotong University, Xi'an China
Show AbstractThe lithiation processes of individual ZnO NW electrodes in a lithium ion battery configuration were observed by in-situ transmission electron microscopy (TEM) using a unique nano-battery setup inside the TEM [Jian Yu Huang, et al, Science, 463 (2010) 335] developed recently for observing the electrochemistry processes in real time. The nano-battery consisted of a single ZnO NW as an anode, an ionic-liquid electrolyte (ILE), and LiCoO2 particles as cathode. In the lithiation of the ZnO NW, the solid-state reaction front propagated along the longitudinal direction of the NW away from the ILE by initiating discrete cracks before the reaction front. The lithiation then propagated laterally along its two side. The new crack grew in a similar fashion to the old crack, and this process repeated until the entire nanowire was lithiated. From the above observations, the lithiation of the ZnO NW consists of three steps. 1) The Li+ adsorbs on the NW surface initiating the lithiation. 2) The reaction leads to crack formation in the NW making path from the surface inward the bulk. 3) Li+ penetrates into the NW from the crack and reacts with the NW. The crack formation during the lithiation process caused the ZnO NW to break into multiple segments. The fracture of the NW is considered to cause poor cyclability of the battery when ZnO is used as the LIB electrode. Our observations provide important insight for developing battery with higher performance and longer lifetime by providing the failure mechanism of the electrode material.
9:00 PM - SS7.33
Nanofluidic Flow on a Solid Nanowire.
Yu Chieh Lo 1 2 , Jian Yu Huang 3 , Ju Li 1 2
1 Department of Mechanical Engineering and Materials Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Nuclear Science and Engineering and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractForming tiny liquid droplets and guiding their movement is important for nanotechnology, with wide-ranging applications in printing/patterning, chemical reactions and bio assays. According to the theory of solid-liquid interactions, if the liquid is non-volatile, a liquid film of molecular thickness (1 to 10nm) called the precursor film can creep up the nanowire surfaces with certain spatial-temporal features, in the complete wetting scenario. Such flow can develop alternating thin film (precursor film) - discrete beads riding on the precursor film, rapidly moving the liquid beads to the other end of the nanowires. The simulations confirm that the driving force of liquid drops occurred during the transport process was due to the friction between the circumstance of wire surface and fluid, like the traffic jam problem. Once the pressures balance before and after the drop was broken due to the accumulation of molecular concentration gradient, the liquid bullet was trigged.
9:00 PM - SS7.34
Effect of Stacking Fault Energy on the Twin Deformation of Single Crystalline Metallic Nanowires.
Seo Jong-Hyun 1 3 , Youngdong Yoo 2 , Sang Won Yoon 1 3 , Tae-Yeon Seong 3 , Bongsoo Kim 2 , In-Suk Choi 4 , Jae-Pyoung Ahn 1
1 Nano Analysis Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 3 Department of Materials Science and Engineering, Korea University, Seoul Korea (the Republic of), 2 Department of Chemistry, KAIST, Seoul Korea (the Republic of), 4 High-Temperature Energy Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractWhile various ingenious methods such as nanosize grain generation and nano-twin thickness optimization have successfully achieved high strength and favorable ductility in crystalline materials, they are still constrained by mutually exclusive attributes of strength and ductility. Since preexisting defects stimulate nucleation and multiplication of dislocations, and strongly influence their propagation, the creation and subsequent reaction of dislocations in a purely single-crystalline material would follow quite different paths from those in conventional materials. The recent molecular dynamics works have predicted strong but ductile behavior of face centered cubic (fcc) metal nanowires achieved by deformation twinning. However both properties have been not experimentally proven by the tensile test of metallic nanowires. Unfortunately, previous experiments only observed high strength but brittle fracture in nanowires. In addition, we experimentally observed ultra-strong but ductile deformation behavior of single crystalline Au, Pd and PdAu nanowires with different stacking fault energy (SFE), which decides on the nucleation and propagation of deformation twinning. In-situ tensile tests of nanowires were performed using Nanomanipulator and AFM force measurement equipped in FEI DualBeam system. The twin nucleation and propagation of nanowires was observed with quantitative stress-strain measurements. The yield stress of a <110> rhombic Au nanowire reaches up to 1.54 GPa at 4% elastic strain and then twin nucleation occurs with a sudden load drop down to 200 MPa. Followed by twin migration, structural reorientation of the <110> rhombic nanowires into the <100> square nanowires results in ductile elongation at about 41% at the constant stress of 200 MPa. Pd and PdAu nanowires with different SFE possess much higher yield strength than Au, while the twinning stress is recorded as same value of about 200 MPa. Here, we decipher the effect of SFE on the nucleation and propagation of twin in fcc metal nanowires.
9:00 PM - SS7.35
Experimental-Computational Characterization of the Elastic Modulus of GaN Nanowires.
Rodrigo Bernal 1 , Ravi Agrawal 1 , Bei Peng 1 , Kristine Bertness 2 , Norman Sanford 2 , Albert Davydov 3 , Horacio Espinosa 1
1 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 2 Optoelectronics Division, National Institute for Standards and Technology, Boulder, Colorado, United States, 3 Metallurgy Division, National Institute for Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractGallium Nitride (GaN) is an important semiconductor material because of its direct, wide band-gap and its piezoelectric properties, making it relevant for photonics and power electronic applications. In particular, GaN nanowires have shown promise toward greater functionality in all these areas. Their piezoelectric properties —which link mechanical deformation with generation of charge— make them attractive for sensors, actuators and energy harvesting applications [1]. Because some of the aforementioned applications require mechanical movement of the nanowires in order to achieve functionality, precise characterization of their mechanical properties, such as elastic modulus and fracture strain and strength are important for designing optimal and failure-resistant devices. Furthermore, it is desirable that this characterization is performed at the individual-nanowire level, in order to establish the morphologic, structural and synthesis characteristics that optimize device performance.In this vein, we have carried out studies on the elastic modulus of individual GaN nanowires in the three major growth axes reported in the literature, namely, [0001] or c-axis, [1-100] or m-axis and [1-210] or a-axis, using a combined computational-experimental approach [2]. We performed atomistic modeling utilizing quantum-mechanical density functional theory (DFT) and molecular dynamics (MD) calculations with the Stilinger-Weber potential. Experiments were conducted in-situ TEM using a Micro-Electromechanical-System (MEMS) that allows uniaxial tensile testing with measurement of strain and stress. Similar-diameter NWs were investigated by both approaches. Characterized diameters ranged from 2.4nm to 20nm in the computational studies and from 44nm to 225nm in the experiments.The experiments and computations present a consistent picture. For all the axes, there is an elasticity size-effect where the modulus increases as the diameter decrease. However, for diameters greater than ~20nm this size-effect becomes irrelevant and therefore the elastic modulus is the same as bulk GaN crystals. In particular, we find that the elastic modulus is 300 GPa for c-axis nanowires and 266.7 GPa for a- and m-axis nanowires. We assert that the size effect is too small to be observed experimentally under the current techniques and therefore, for realistic GaN nanowire sizes, bulk elastic properties can be used for device design.References1.Wang, X., J. Song, F. Zhang, C. He, Z. Hu, and Z. Wang, "Electricity Generation based on One-Dimensional Group-III Nitride Nanomaterials", Advanced Materials, 2010. 22(19): p. 2155-2158.2.Bernal, R.A., R. Agrawal, B. Peng, K.A. Bertness, N.A. Sanford, A.V. Davydov, and H.D. Espinosa, "Effect of Growth Orientation and Diameter on the Elasticity of GaN Nanowires. A Combined in Situ TEM and Atomistic Modeling Investigation", Nano Letters, 2010. 11(2): p. 548-555.
9:00 PM - SS7.36
Testing the Limits of Small Scale Plasticity with Thin Wires in Torsion.
Andy Bushby 1 , Nicola Schmitt 1 3 , Julien Feuvrier 2 , David Dunstan 2 , Oliver Kraft 3
1 School of Engineering and Materials Science, Queen Mary University of London, London United Kingdom, 3 Institute for Advanced Materials, Karlsruher Institute of Technology, Karlsruhe Germany, 2 School of Physics, Queen Mary University of London, London United Kingdom
Show AbstractThe plasticity of materials and structures in the micron and submicron range is of great interest at the present time. Methods of lithography and focus ion beam milling allow structures to be formed with structural dimensions of the order of a micron. Similarly, the same techniques can be used to construct testing systems small enough to fit in the electron microscope. However, few of these methods have the sensitivity to detect the elastic limit and the very early stages of plasticity. Here we report experimental data on the torsional loading of long thin wires with micro-strain resolution. Copper and gold wires with diameters ranging from 10 microns to 150 microns were tested using a load-unload method, twisting the wire to a give angle and then untwisting and noting the angle at which the wire hangs freely. Reversal of the loading direction was possible through rotation of the wire in the opposite direction. Passing an electric current through the wire allowed experiments to be conducted at elevated temperatures. These experiments allow a range of key issues in nanomechanics to be explored and theories of nano-scale plasticity to be tested. Size effects in the elastic limit, the Hall-Petch effect, the influence of surface oxide and the Bauschinger effect could all be determined.
9:00 PM - SS7.37
Dislocation Dynamics Simulator for Hexagonal Close-Packed Crystals.
Chi-Chin Wu 1 3 , Sylvie Aubry 2 , Peter Chung 3 , Athanasios Arsenlis 2
1 , Oak Ridge Affiliated Universities, Belcamp, Maryland, United States, 3 Computational and Information Sciences Directorate, US Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States, 2 High Performance Computational Materials Science and Chemistry Group Condensed Mater and Materials Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractPlastic deformation mechanisms in hexagonal close-packed (HCP) crystals are more complex than those in cubic systems such as face-centered cubic (FCC) and body-centered cubic (BCC) crystals due to the reduced crystal symmetry and limited available slip systems in HCP. Instead of unanimously gliding on the close-packed basal planes, as all dislocations do in FCC and BCC, depending on the c/a ratio, dislocations in HCP also glide on different combinations of non-basal families with more complicated Burgers vectors such as 1/3<1 1 -2 -3>. Microscopic experiments have also found that dislocation characters in HCP-based crystals are not only material dependent but also change with experimental conditions. For instance, some cases reported varying slip systems with temperature, film thickness, and the substrate. Such complexities of dislocation-related deformations make dislocation dynamics simulations challenging for HCP crystals although scattered studies have been reported.This paper presents a modified dislocation dynamics simulator, Parallel Dislocation Dynamics Simulator (ParaDiS) for HCP materials. In order to model for HCP, all possible slip systems as well as cross-slip planes are included in the code. A cubic coordinate system is chosen for treating the HCP structure and simplifying the use of periodic boundary conditions (PBC). Simulations of several dislocation mechanisms are performed in the bulk to verify and validate the accuracy of our code. Careful comparisons with the orientation-dependent line tension model are done. In particular, we will present simulations of Frank-Read sources, loop shape relaxation, cross-slip as well as binary junction maps. A careful study of the unzipping stress of a junction will also be presented.
9:00 PM - SS7.38
Dislocation Emission from the Transformed Crack Tip of BCC Iron Bulk Nanocrystal - Molecular Dynamics Simulations.
Hideo Kaburaki 1 , Tomoko Kadoyoshi 1 , Mitsuhiro Itakura 1 , Masatake Yamaguchi 1
1 Center for Computational Science and e-Systems, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan
Show AbstractEmission of dislocations from the crack tip of bcc iron has long been studied atomistically in terms of brittle and/or ductile behavior of bcc materials. However, the criterion of dislocation emission and fracture at the crack tip of bcc iron has not been clearly verified by the atomistic method due to the limitation of the system size, strain rate, and the empirical potential. With the molecular dynamics method, a wide range of parameters, such as temperature and strain rate, have been varied on quasi-two dimensional and bulk three-dimensional systems to find the bcc-fcc transformation phase at the crack tip, and emission of dislocations and propagation of a crack are largely influenced by this phase. The presence of this transformed phase under the uniaxial tension at the crack tip has been noted for quite a while although the effect of this phase on the dislocation emission and crack propagation has not been fully discussed. The results of the simulation show that crack propagation and dislocation emission are largely influenced by the presence of the transformed fcc phase at the crack tip on both the quasi-two dimensional and bulk three dimensional systems, but the behavior, in particular, of the emission of dislocations is quite different on two and three dimensional systems. In the low temperature (50K) region on the bulk three dimensional system, we find the wavy crack front under mode I tension consisting of the transformed phase, which was previously predicted by the elasticity theory. In the high temperature (500K) region, we find the emission of dislocations from the interface of the transformed phase in front of the crack tip on the quasi-two dimensional system, and a half-loop dislocation is emanated from the tip of the transformed phase and the advancement of a crack is retarded where the dislocation is generated. The effects of system size, temperature, and strain rate on the emission of dislocations at the crack tip are discussed in terms of the transformed phase.
9:00 PM - SS7.39
Comprehensive Analysis Techniques for Crystalline Materials in Atomistic Computer Simulations.
Alexander Stukowski 1 , Athanasios Arsenlis 1
1 Condensed Matter and Materials Division, Lawrence Livemore National Laboratory, Livermore, California, United States
Show AbstractAtomistic simulation methods such as molecular dynamics (MD) are routinely used to study crystalline materials at the atomic scale. Since crystal defects play a critical role for the understanding of most materials properties, they are the subject of many simulation studies. Interpreting simulation data and extracting quantitative information from it, however, have become a challenge as system sizes increase and the interaction of crystal defects gets richer and more complex in large-scale computer simulations.In this contribution we present a set of sophisticated computational analysis techniques that allow to extract and characterize structural defects in atomistic simulations of crystalline materials in a fully automated way. The newly developed methods cover defects such as stacking faults, grain boundaries, interphase interfaces, dislocations, point defects, and defect clusters in a wide range of crystal lattices.To exemplify the range of applications of our crystal analysis techniques, we describe how they enable the identification of grain boundary dislocations in molecular dynamics simulations. This allows us to directly visualize their interaction and/or reaction with lattice dislocations. We also show how the atomic trajectories obtained from MD simulations can be used to calculate the deformation tensor field, and how this field can be decomposed into elastic and plastic components to quantify the contribution of dislocations to total strain.
9:00 PM - SS7.4
Size Effects in Molding Replication of Aluminum-Based Micro-/Nano- Scale Structures.
Ke Chen 1 , Wen Meng 1 , Glenn Sinclair 1
1 Mechanical Engineering, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractAt the present time, a bottleneck for efficient and economical construction of metal-based micro/nano devices is the lack of suitable technologies capable of high fidelity and high throughput manufacturing of micro-/nano- scale metallic structures. Compression molding with inserts containing micro-/nano- scale patterns promises to replicate micro/nano features in metals accurately and quickly.We have previously shown that compression molding of simple metals with stress-strain curves approximating that of an elastic - perfectly plastic material, such as Al at relevant molding temperatures, can be understood from a simple continuum mechanics model if the characteristic length scale is ~100 microns [1]. At such a length scale, conclusions derived from continuum mechanics, such as a one-parameter scaling relationship, can be extended to materials exhibiting significant strain hardening and even oscillatory stress-strain behavior [2].When single crystal Al was molded by a long rectangular punch, we have shown that the characteristic contact pressure exhibits a significant dependence on the punch width, as it decreases from micron to submicron scales. Structural characterization of molded Al underneath the punch, combining focused ion beam (FIB) sectioning and transmission electron microscopy (TEM), showed nanoscale grain formation as a result of the large strain plastic deformation. Importantly, this size effect is distinctly different from the conventionally observed indentation size effect (ISE) with a Berkovich indenter [3]. This last observation provides a clear example for the influence of indenter geometry on the manifestation of ISE. Alternatively stated, the characteristic material length appears to be dependent on the indenter geometry, and not a unique function of the indented material.The present submission follows the work described above, and studies the dependence of contact pressure on the characteristic contact length when a single crystal Al specimen is molded by a long wedge-shaped diamond. Molding force – displacement data are obtained and analyzed. The dependence of contact pressure on the characteristic contact length is studied as a function of the included wedge angle. Additional structural investigations of Al underneath the wedge indenter are carried out by combining FIB and TEM. The implication of the present results will be discussed.References:[1] J. Jiang, W. J. Meng, G. B. Sinclair, E. Lara-Curzio, J. Mater. Res. 22, 1839 (2007).[2] Fanghua Mei, Ke Chen, J. Jiang, W. J. Meng, Acta Mater. 58, 2638 (2010).[3] Ke Chen, W. J. Meng, Fanghua Mei, J. Hiller, D. J. Miller, Acta Mater. 59, 1112 (2011).
9:00 PM - SS7.42
Homogeneous versus Heterogeneous Dislocation Nucleation: A Comparative Study.
Hasan Saeed 1 , Satoshi Izumi 2 , Shotaro Hara 2 , Shinsuke Sakai 2
1 Department of Mechanical Engineering, National University of Sciences & Technology, College of Electrical & Mechanical Engineering, Rawalpindi Pakistan, 2 Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan
Show AbstractIn crystalline solids, the fundamental mechanical properties of ductility and strength are governed by dislocations. Dislocation nucleation is a stress mediated thermally activated transition, which, being an atomistic phenomenon, can be best approached by atomistic tools. To date, most of the atomistic level simulation work done on dislocation nucleation has been done on heterogeneous systems. However, the fact that there is an infinite number of configurations of heterogeneous systems, each with its own peculiar complexities, makes it difficult to organize the subject of dislocation nucleation in a coherent manner. The transition of dislocation nucleation, therefore, cannot be studied at a fundamental level while focusing on heterogeneous systems because the results are subject to influence by complex effects originating from heterogeneities such as stress fields, surfaces, interfaces, and other defects, which distort the physical picture. In this study, we seek to link homogeneous and heterogeneous dislocation nucleation in order to deepen insight into the phenomenon of dislocation nucleation. Two common scenarios of heterogeneous dislocation nucleation—from a sharp corner in a Si crystal under shear, and from a corner of a Cu nanotube under compression—are compared with corresponding results for homogeneous dislocation nucleation. Both sets of results are based on the Nudged Elastic Band (NEB) algorithm and extended schemes. The comparison is made in terms of activation energy, activation volume, and the mechanics of the saddle-point configurations. The quantitative effect of heterogeneities in terms of lowering of the strength of the material—from the reference ideal strength of the homogeneous crystal—is also discussed.
9:00 PM - SS7.43
Screw Dislocation Kink Dynamics Model in BCC Iron Based on First-Principles and Molecular Dynamics Calculations.
Mitsuhiro Itakura 1 , Hideo Kaburaki 1 , Masatake Yamaguchi 1
1 , JAEA, Kashiwa Japan
Show AbstractNucleation and migration of kinks of screw dislocation in BCC iron is simulated using Langevin dynamics. Static parameters such as Peierls potential and line tension coefficient are derived from first-principles calculations, while dynamic parameters such as effective mass and viscosity coefficient are derived from molecular dynamics. The most important result of numerical simulation is that this model can reproduce the jerky motion of screw dislocations observed in low-temperature in-situ observation experiments.
9:00 PM - SS7.44
Activation Parameters for Plastic Deformation in Zr-Cu-Al Metallic Glasses by Broadband Nanoindentation Creep.
Zenon Melgarejo 1 , Jinwoo Hwang 1 , Chuang Zhang 1 , Joseph Jakes 2 , Eren Kalay 3 , Matthew Kramer 3 , Paul Voyles 1 4 , Donald Stone 1 4
1 Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 , Performance Enhanced Biopolymers, United States Forest Service, Forest Products Laboratory, Madison, Wisconsin, United States, 3 , Iowa State University/Ames Laboratory , Ames, Iowa, United States, 4 Materials Science and Engineering Dept., University of Wisconsin-Madison , Madison, Wisconsin, United States
Show AbstractModels of low-temperature plastic deformation in metallic glasses theorize as the elementary unit of plastic deformation the concept of the shear transformation zone (STZ), which consists of clusters of 10’s or 100’s of atoms. Shear of the STZ is thermally activated, with the activation energy depending on stress. Activation parameters should vary systematically with atomic structure including short and medium range order and should therefore be sensitive to composition, quenching rate, and annealing. In the present work we apply broadband nanoindentation creep, or BNC, to measure hardness across 5-6 decades of deformation rate in Zr-Cu-Al metallic glasses. BNC generates the high quality data necessary to characterize activation volume as a function of stress. From BNC it is possible to assess the form of the activation energy function and STZ size. Bulk and ribbon Zr54Cu38Al8 (Tg = 676K) and Zr50Cu45Al5 ribbon (Tg = 667K) are studied. Annealing treatments are performed in a differential scanning calorimeter (DSC) at 573°K and at slightly above the glass transition temperature. The degree of structural relaxation is characterized by measuring heat evolution during subsequent thermal cycling. BNC results suggest that not only does annealing increase the hardness, but it changes STZ size.
9:00 PM - SS7.46
Deformation and Fracture of Pulsed Laser Oxides on 304L Stainless Steel.
S. Lawrence 1 5 , D. Stauffer 4 2 , R. Major 2 , D. Adams 3 , W. Gerberich 4 , D. Bahr 1 , N. Moody 5
1 Mechanical and Materials Engineering, Washington State Univeristy, Pullman, Washington, United States, 5 , Sandia National Laboratories, Livermore, California, United States, 4 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 , Hysitron Inc., Minneapolis, Minnesota, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractLocalized heating from a focused laser beam of oxidizing metals in ambient atmosphere produces dielectric phases, creating unique, metastable, layers that have characteristic optical appearances, resulting in varying colors of films. Little research has focused on pulsed laser colorized films and none have studied their mechanical behavior. We have investigated the mechanical behavior of color-patterned oxides, with thicknesses of approximately 400nm, on polished 304L stainless steel where film and substrate properties control macroscopic wear and fracture processes. Quasi-static and dynamic nanoindentation probed oxide deformation and fracture, resulting in modulus and hardness values of approximately 160GPa and 12GPa, respectively for films formed under a variety of processing conditions. Microstructure of the films was determined using a combination of microscopy and x-ray diffraction, and shows a variety of oxides form in these systems. Conductive nanoindentation measured electrical contact resistance (ECR) for colored oxides indicating a correlation exists between laser exposure, conductance during loading, I-V behavior at constant load, and indentation response. In this presentation we will show that combining techniques provides a unique approach for defining mechanical behavior and processes and the resulting performance of the films in conditions that cause wear. This work was supported by DTRA Basic Research Award #IACRO 10-4257, NSF Grant NSF/DMR-0946337, and Sandia National Laboratories, a Lockheed Martin Company for USDOE NNSA under contract DE-AC04-94AL85000.
9:00 PM - SS7.47
In Situ High Resolution Imaging and Chemical Analysis of Liquids and Hydrated Materials.
Katherine Jungjohann 1 , James Evans 2 , Ilke Arslan 1 , Nigel Browning 1 2 3
1 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 2 Molecular and Cellular Biology, University of California Davis, Davis, California, United States, 3 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractThe goal of many in-situ analysis methods is to obtain structural and chemical information from materials on the nanoscale. However, in many cases the resolution of the method is reduced by the need to create the environmental conditions around the sample. In (scanning) transmission electron microscopy (S/TEM) imaging capabilities start from the sub-angstrom level for conventional imaging modes, meaning that a slight degradation in resolution by an in-situ cell does not significantly impact the ability to study nanoscale systems. The recent commercial availability of in-situ windowed cells for TEMs has propelled the analysis of samples in liquid into new areas where the environmental conditions can now be completely removed from the vacuum within the microscope. Such cells operate based upon a sandwich design encasing the solution between two thin-film membrane windows. In-situ TEM can now be coupled with all the usual analytical methods for elemental identification and electronic structural analysis, thereby providing the ideal platform for investigations of hydrated materials. In this presentation we demonstrate the multiple applications of this method through studies of nanoparticle growth, electron beam induced damage, and structural imaging of nano- and biological materials within an aqueous environment. Atomic resolution imaging of nanomaterials within the liquid cell will be presented along with electron energy loss spectra from water and nanoparticle suspensions. One main obstacle for liquid TEM experiments is the dose of the electron beam on the liquid cell can cause significant radiolysis damage to the fluid causing gas formation and evacuation of the windowed cell. This type of damage effect can be mitigated by the implementation of the dynamic transmission electron microscope (DTEM), which provides low dose imaging conditions and high temporal resolution. These conditions are ideally suited for liquid cell experiments to decrease radiolysis damage to the liquid as well as acquire unperturbed images from the dynamic system. Current results of this low dose technique will be presented to display the spatial and temporal resolution of the DTEM used in combination with the in-situ liquid stage. Overall, we expect liquid TEM methods to provide real-time structural information that can impact the fields of colloids, energy storage, biological structure characterization and nanomaterial synthesis and dynamics.
9:00 PM - SS7.48
Ferromagnetic Nano-Wire in Undoped Antiferromagnetic NiO Thin Film.
Issei Sugiyama 1 , Syunsuke Kobayashi 1 , Yukio Sato 2 , Teruyasu Mizoguchi 4 , Naoya Shibata 2 , Yuichi Ikuhara 2 3 , Takahisa Yamamoto 2
1 Advanced Materials Science, University of Tokyo, Chiba Japan, 2 Engineering Innovation, University of Tokyo, Tokyo Japan, 4 Industrial Science, University of Tokyo, Tokyo Japan, 3 , Japan Fine Ceramics Center, Nagoya Japan
Show AbstractOne dimensional materials are exciting system which shows anomalous properties, such as superconductivity, optical property, and so on. However, the variety of properties was limited because one dimensional materials has the intrinsically one dimensional structures. To break through the limitation, we have proposed a new concept to build up such structures inside bulks using dislocations.For example, we doped Ti ions only at dislocations by pipe-diffusion to obtain one-dimensional structure inside a sapphire [1]. Obtained Ti nano-wire exhibits electrical conductivity at very localized area. As for other example, conductive nano-wire is also successfully made by pipe-diffused Mn ions in threading dislocations of AlN thin film [2]. However, the structure in dislocations is difficult to control. In this study, we applied the technique to threading dislocations in NiO thin films grown by PLD method. The purpose is to make ferromagnetic nano-wire in antiferromagnetic NiO thin film, and to reveal the relationship between structure and property.NiO thin films were grown on the SrTiO3 single crystal by pulsed laser deposition (PLD). The film thickness was controlled to be 150nm. The lattice mismatch between substrate and thin film is expected to be 150nm. After deposition, the sample was annealed at 1100 degree Celsius in Air for 0.5 hour. The film was analyzed by X-ray diffraction (XRD, ATX-G, Rigaku), transmission electron microscopy (TEM, JEM-2010HC, JEOL) and atomic force microscopy (AFM, JSPM-5200, JEOL) and magnetic property is measured by magnetic force microscopy (MFM). The NiO thin films was confirmed to be a single crystal, and the lattice mismatch between the NiO thin film and SrTiO3 is 6.75% by XRD measurement. To reveal the morphology of dislocations in obtained films, TEM observation was carried out in plan-view and cross-sectional direction. By defining the [001] as growth direction of thin film, the Burgers vector is determined to be α[001], where α is a lattice constant of NiO. The dislocation line is parallel to [001], which means they are screw dislocations. Some dislocations include [110] Burgers vector component which implies edge dislocation component. AFM observation at the surface of the thin film revealed that there are some dips. The density of the dips corresponds to that of the dislocations observed by TEM, indicating the dips are formed by thermal etching around the dislocations. Around the dips, local magnetic field is observed by MFM. Hence, ferromagnetic nano-wire is made successfully in anti-ferromagnetic thin film by introducing threading dislocations.[1] A. Nakamura, et al., Nature Mater., 357 (2003) 453[2] Y. Tokumoto, et al., J. Appl. Phys., 106 (2009) 124307
9:00 PM - SS7.49
Modeling of Electron and Phonon Transport in Multiperiod Nanolayer Film Structures.
John Chacha 1 3 , Jonathan Lassiter 2 3 , Claudiu Muntele 3
1 Electrical engineering, Alabama A&M University, Huntsville, Alabama, United States, 3 Center for Irradiation of Materials, Alabama A&M University, Normal, Alabama, United States, 2 Department of Physics, Alabama A&M University, Normal, Alabama, United States
Show AbstractHigh energy ion beams are used to modify co-deposited nanolayer films of alternated materials (i.e. insulator and metal, two different semiconductors, even more complex arrangements), to form nanodots through localized nucleation. The particular application being considered is for high efficiency thermoelectric conversion systems. The performance of a thermoelectric converter is generally given by the figure of merit, ZT, which is a function of the Seebeck coefficient, electrical conductivity, and thermal conductivity. A performant device would have a maximized electrical conductivity and a minimized thermal conductivity (maximum electron transport, minimal phonon transport). The current models of electron and phonon transportation through 1D, 2D, 3D quantum regimented structures assume an infinitely repetitive perfect structural “cell”, with complicated algorithms requiring intensive computing power. The main focus for this modeling effort is to reduce the three-dimensional problem to a single dimensional approximation without sacrificing the quality of the result. While the nanostructure being investigated could have nanoscale features arranged with perfect periodicity in all three Cartesian directions, of interest are the heat and electricity flow in one particular direction (cross-plane as initially layered). Non-Equilibrium Green Functions Formalism (NEGF) is the mode for calculating the transport of electrons and phonons assuming a one-dimensional quantum well arrangement in the z-direction (with finite or infinite boundaries in the x and y directions), with a tight binding model for electrons and a valence force field for phonons. The results are to be compared with experimental measurements on such structures.
9:00 PM - SS7.5
Alzheimer’s β-Amyloid All-D-Enantiomers and All-L-Enantiomers Exhibit Similar Nanoscale Structural Properties: Atomic Force Microscopy and MD Simulation Studies.
Laura Connelly 1 , Fernando Teran Arce 1 , Hyunbum Jang 2 , Ricardo Capone 1 , Samuel Kotler 1 , Ruth Nussinov 2 3 , Ratnesh Lal 1
1 Materials Science & Engineering, University of California San Diego, La Jolla, California, United States, 2 SAIC-Frederick Center for Cancer Research Nanobiology Program, NCI, Frederick, Maryland, United States, 3 Sackler School of Medicine, TAU, Tel Aviv Israel
Show AbstractAlzheimer’s disease (AD) is a protein misfolding disease characterized by a build-up of β-amyloid (Aβ) peptide as senile plaques, uncontrolled neurodegeneration, and memory loss. The prevailing hypothesis for the AD pathology is the disruption of cell ionic homeostasis by interaction of globular Aβ with cell membranes. The Aβ peptide inserts into cell membranes creating ion conductive pores that destabilize intracellular calcium ion homeostasis. Aβ may also destabilize ionic homeostasis by its action via cell membrane receptors. We have investigated these two differing mechanisms by taking advantage of the biochemical tenet that ligand-receptor interactions are stereospecific; all-L-proteins but not all-D-proteins bind to cell membrane receptors. Using all-D-enantiomer and all-L-enantiomer of the full length Aβ(1-42), we probed the nanoscale structural features of the peptide with respect to pore and fiber formation using atomic force microscopy (AFM). We report similar properties for both stereoisomers. Both form ion channel-like structures in AFM imaging and both show similar fiber formations. The structural and functional results are supported by molecular dynamics (MD) simulation studies. Mechanically, both isomers appear to interact with artificial membrane in similar fashion. Our results suggest that amyloid-mediated disruption of ionic homeostasis occurs by a direct pathway through its own ion channel and may not rely on its interaction with membrane receptors. Understanding the mechanism of peptide-membrane interaction and insertion at the nanoscale is essential to therapeutic design aiming to control and prevent pore formation.
9:00 PM - SS7.50
Nano Scale Physical Property Measurement of Carbon Fibers and Polymers with Electron Energy Loss Spectroscopy (EELS).
Sabyasachi Ganguli 1 2 , Ajit Roy 2
1 , UDRI, Dayton, Ohio, United States, 2 , AFRL/RXBT, Dayton, Ohio, United States
Show AbstractThe need of measurement of the physical properties of materials with nano-constituents is usually associated with making multiple large form factor specimens. Practically this is not a viable option. Predicting the physical properties of the nano-engineered composite from EELS as established in this study is an enabling technique that can lead to rapid prototyping of the different interface tailoring of the nano-constituent and predicting the final properties. Plasmon energy originates due to the excitation of valence electrons in a material. Since the availability of valence electrons in carbon fibers is different from that in thermoplastics, the plasmon model should be different between the two. This is evident from our study.
9:00 PM - SS7.51
Nanostructural Alterations and Rheological Aging of Clay Dispersions in Response to Heating.
Elisabeth Hansen 1 , Henrik Hemmen 1 , Davi Fonseca 1 , Christophe Coutant 1 , Tomás Plivelic 3 , Kenneth Knudsen 2 , Jon Otto Fossum 1
1 Physics, NTNU, Trondheim Norway, 3 , MAXlab, Lund Sweden, 2 Physics, IFE, Oslo Norway
Show AbstractThe fact that aqueous clay dispersions can form colloidal gels and glasses even at very low solid fractions has inspired several investigations on the emergence of arrested states in these systems. In studies conducted in particular on suspensions of synthetic Laponite RD it is argued that complex aging dynamics promote either the formation of gelled states, whose dynamics are characterized by the growing in size with time of percolated particle clusters, or glassy states dominated by the cooperative electrostatic trapping of particles in the potential ‘cages’ formed by their neighbors [1]. It is observed that the volume fraction of particles as well as the strength and sign of interparticle interactions strongly influence whether and which jammed states develop [2]. In the present study, we focus on aqueous dispersions of high-charge synthetic Na-fluorohectorite clay platelets, similar to natural hectorites, and investigate how heating affects the nanoscale structure of the dispersions and their rheological properties. Our recent X-ray scattering results [3] show that during heating to temperatures above about 40 deg. C, particles that are stacked structures at room temperature delaminate to form much thinner particles. Subsequently, we show that the increased particle number density occurring as a result of this delamination leads to a rapid growth of the suspension viscosity . We furthermore investigate with rheology the structural regrowth of samples after preshear, and how this regrowth depends upon whether the suspensions have undergone heating, giving insight into the emergence of structural arrest in clay systems.
9:00 PM - SS7.53
Activation Energy and Blistering Rate in Hydrogen Implanted Semiconductors.
Daniel Pyke 1 , Robert Elliman 1 , Jeffrey McCallum 2
1 Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory, Australia, 2 MicroAnalytical Research Centre, School of Physics, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractSilicon-on-insulator (SOI) structures are routinely used for the fabrication of integrated electronic circuits, photonic devices and structures and micro-electro-mechanical systems (MEMS), and are most commonly fabricated by a hydrogen-induced cleavage technique in which ion-implanted hydrogen is employed to initiate and propagate cracks in a plane parallel to the silicon surface. Considerable research effort has been devoted to understanding and optimising this cleavage technique in (100) silicon but several fundamental issues remain to be understood, including the role of stress on hydrogen platelet alignment, and the details of the bond-breaking processes associated with crack propagation (i.e. stress induced or hydrogen-mediated). There is also keen interest in extending the technique to other silicon orientations (i.e. (110) and (111) orientations) and semiconductor materials (e.g. Ge, GaAs). To this end, the present work compares blister rates in Si (100), Si (111) and Ge (100) substrates as a function of annealing temperature and time, for a range of implant energies and fluences.Samples were implanted at room-temperature and annealed at temperatures in the range 300-650°C until blister formation occurred, from which the blistering rate and activation energy were determined. Elastic recoil detection and Rutherford backscattering spectroscopy were used to study the evolution of hydrogen profiles and implant damage respectively; optical profilometry was used to examine the blister depths and the roughness of the cleaved surface and transmission electron microscopy was used to study the sample microstructure. For each material, the rate of blister formation was found to exhibit Arrhenius behaviour and to be characterised by a single activation energy over the temperature range examined. The extracted activation energies were 2.28±0.03 eV, 2.17±0.06 eV and 1.4±0.03 eV for (100) Si; (111) Si and (100) Ge, respectively. These results are compared with reported measurements and discussed in relation to proposed models of hydrogen blistering.
9:00 PM - SS7.54
The Effect of Substrate and Film Thickness on Phase Transition Temperatures of GST Thin Films.
Kadir Cil 1 , Yu Zhu 2 , Chung Lam 2 , Helena Silva 1
1 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 T. J. Watson Research Center, IBM, Yorktown, New York, United States
Show AbstractPhase change memory (PCM) is a promising non-volatile memory technology that offers fast speed, high endurance and low programming energy [1, 2]. These devices utilize materials that can repeatedly and rapidly switch between amorphous and crystalline phases. GST (GeSbTe) is the most commonly used material for PCM devices. In this work, we investigate the crystallization behavior of amorphous GST thin films with thicknesses of 100, 50, 20, and 10 nm through resistance characterization (R-T) from 30 to 375 C. The thin films were deposited on oxidized Si and Si3N4 substrates by co-sputtering. The films were encapsulated by 10 nm SiO2 to prevent evaporation of the phase change material at high temperatures. The measurements are performed in a probe station chamber without light and under high vacuum (~10-5 Torr). The resistances of the GST films are measured with a semiconductor parameter analyzer using four-point probe method. Both phase transition (amorphous-fcc and fcc-hcp) temperatures depend on film thickness and underlying film [3]. References[1] S. Lai, "Current status of the phase change memory and its future," in Electron Devices Meeting, 2003. IEDM'03 Technical Digest. IEEE International, 2004, pp. 10.1. [2] S. Raoux, G. W. Burr, M. J. Breitwisch, C. T. Rettner, Y. C. Chen, R. M. Shelby, M. Salinga, D. Krebs, S. H. Chen, H. L. Lung and C. H. Lam, "Phase-change random access memory: A scalable technology," IBM Journal of Research and Development, vol. 52, pp. 465-480, 2008. [3] N. Ohshima, “ Crystallization of germanium-antimony-tellurium amorphous thin film sandwiched between various dielectric protective films,” J. Appl. Phys. 79, 8357 (1996).
9:00 PM - SS7.55
An Examination of the Indentation Size Effect and Bi-Linear Behavior of FCC Metals.
David Stegall 1 , Abdelmageed Elmustafa 1 , Bryan Crawford 2
1 Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia, United States, 2 , Nanomechanics Inc, Oak Ridge, Tennessee, United States
Show AbstractWe investigated pure FCC metals including Aluminum, Nickel, Silver, and 70/30 Copper Zinc ((alpha-brass) alloy for the indentation size effect (ISE) and bilinear behavior using a single Berkovich indenter tip in a single test machine. The results were consistent with those reported by Elmustafa and Stone, 2003 of the ISE and the bilinear behavior using two separate indenter tips (Berkovich and Vickers) from two separate machines. This behavior is mechanistic in nature and is observed regardless of the type of the self similar indenter tip employed. Furthermore, the research presented in this paper would seem to also validate the conclusions that Elmustafa et al (2004) articulate that the Strain Gradient Plasticity collapses at small scales and that the bilinear behavior of these FCC metals is attributed to the presence of long range shear stresses induced by geometrically necessary dislocations. Also, we observed what has been defined as a “tapping” issue for materials with high E/H ratios when using the CSM. The CSM protocol results in erroneous hardness readings at very shallow depths for high E/H ratio soft metals due to the so called “tapping” of the stylus as articulated by Pharr et al. (2009). This method should only be used as a secondary technique to the load control protocol when examining the ISE effect.
9:00 PM - SS7.56
Nanoengineered Surfaces and Coating Technologies for Scale Remediation.
Ghazal Azimi 1 , Yuehua Cui 1 , Jonathan Smith 1 , Kripa Varanasi 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIn this work, durable coatings and innovative surfaces with significantly improved scale nucleation and adhesion properties were engineered and fabricated. To this end, a fundamental understating of the surface chemistry effect on the scale adhesion strength was established, which then made it possible to design the surfaces with reduced scale-surface interactions by manipulating both the surface chemistry and morphology (heterogeneity and texture). A number of self-assembling organic silane coatings with various surface energies were deposited on glass substrates to investigate the effect of passive material coatings on the scale nucleation and adhesion. Subsequently, a number of innovative nanoengineered surfaces with a systematic variation in surface energy were developed. The new coatings and surfaces were tested in-situ to examine the adhesion and growth of mineral scales of sodium chloride and calcium sulfate. The results showed significant improvement in “scale-phobicity” of the surfaces; about 10-fold reduction in both growth rate and adhesion strength between bare steel and coated surfaces was observed. The advancing and receding contact angles of three liquids (water, ethylene glycol, and diiodomethane) on the substrates were measured and used to quantify the surface energies utilizing the van Oss-Chaudhury-Good analysis. The results of this work would provide a pathway to explore and exploit durable nanoengineered designs with controlled scale nucleation and adhesion properties. Despite the perseverance of the scaling problems, no previous studies has been undertaken to investigate practical solutions for scale prevention or mitigation by reducing the adhesion forces between scale and the surface. Successful deployment of the developed surfaces and coatings would reduce costs involved in scale inhibition and remediation and would improve process reliability by preventing catastrophic failures in various industrial sectors.
9:00 PM - SS7.57
Tuning Oxygen Vacancies in Heteroepitaxial SrMnO3-δ Thin Films Grown by Pulsed Laser Deposition.
Shunsuke Kobayashi 1 , Teruyasu Mizoguchi 2 , Naoya Shibata 3 , Yukio Sato 3 , Yuichi Ikuhara 3 , Takahisa Yamamoto 1
1 Department of Advanced Materials Science, University of Tokyo, Kashiwa Japan, 2 Institute of Industrial Science, University of Tokyo, Tokyo Japan, 3 Institute of Engineering Innovation, University of Tokyo, Tokyo Japan
Show AbstractThe oxygen vacancies (Vo) in perovskite-type oxide ABO3-δ thin films have large influences on various physical properties due to causing the electron doping and the structural change around Vo. Therefore, controlling the amount of the Vo in perovskite-type oxides is very important to obtain objective properties. In general, as-grown thin films have a possibility for including many Vo under some growth conditions. Therefore, to recover the residual Vo, post-annealed treatment is carried out after the film growth. Here, the important point is that Vo gives some strains in the films due to the electrostatic repulsion. So, recovering Vo is possibly related to the strain in the thin films, which is given by the lattice mismatch between the films and the substrates. Thus, in this study, we investigated the relationship between the recovery of Vo and the strain induced by lattice mismatch in the films. Among various perovskite-type oxides, we focused on SrMnO3-δ (0≦δ≦0.5, a=0.3805 nm:δ=0) (SMO), which has attractive possibilities due to Mn3+/Mn4+ mixed valence state induced by Vo.SMO films prepared on atomically flat single crystal SrTiO3 (STO) (001) (a=0.3905 nm) and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (001) (a=0.3868 nm) substrates by pulsed laser deposition (PLD). The atomic structure of the obtained films was investigated by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) using an aberration corrector, both of which were operated at 200 kV. In addition, electron energy loss spectroscopy (EELS) attached to a STEM was used to estimate the amount of oxygen vacancies by analysis of the Mn valence state in the film [1]. Lattice parameters were measured by X-ray diffractometry. X-ray reciprocal space mapping was performed around 114 Bragg reflections from the substrates. The reciprocal space mapping showed that the in-plane lattice parameter of SMO thin film coincided with that of the STO substrate. The plan view observation and EELS analysis were clarified that the oxygen amount of SMO film grown on STO substrate was δ=0.5 (SrMnO2.5). After annealing as-grown films at 400 °C for 12 h in air to remove Vo, the c-axis lattice parameter in post-annealed SMO film showed the lattice expansion from an ideal lattice parameter, which is calculated by using Passion ratio. This result implies that Vo in SMO film could not be removed even after annealing. In fact, the amount of residual Vo estimated from EELS analysis was δ=0.14 (SrMnO2.86). On the other hand, when SMO film was grown on LSAT substrates with a different lattice parameter, it was found that the amount of the residual Vo in the film decreased from the film grown on STO substrate due to decreeing the lattice mismatch. Consequently, the Vo in SMO films are closely related to the strain from lattice mismatch with substrates. [1] S. Kobayashi et al., J. Appl. Phys. 108, 124903 (2010).
9:00 PM - SS7.58
CMP Pad Wear Characterization Using Novel Non Destructive Techniques for Patterned Media Fabrication.
Joseph Bonivel 1 2 , Justin Hinson 1
1 Mechanical Engineering, University of South Florida, Tampa , Florida, United States, 2 Nanomaterials Research and Education Center, University of South Florida, Tampa, Florida, United States
Show AbstractA stable and predictable CMP process requires full control of the consumable parameters. The polishing pad is arguably the most important component of the CMP system and has substantial economic impact. The surface of the polishing pad, with its pores, grooves, and compressibility play an important role in the mechanical removal of the reaction products from the wafer surface at the nano and micron scale. The surface morphology evolution of three commercially available CMP pads were characterized using a novel non destructive ultrasound technique (UTS) and SEM to optimize CMP for patterned media. The UTS readings are crucial indicators of the pad life and provide critical insight into the evolution of the morphology through a cost effective means. The UTS characterization and SEM characterization were able to detect that the pad material properties are inversely proportional to the porosity of the pad which relates directly to the functionality of the pad. A statistical wafer to wafer non-uniformity (WTWNU) measurement is calculated to indicate how repeatable the polish parameters are for each pad and polish set. The Rodel dual layer IC-1000 Suba-V, k-groove pad provides superior material removal, resulting surface roughness, and pad life for polishing with the commercially available slurries tested.
9:00 PM - SS7.59
Room Temperature ASE from Multiexcitonic States in Colloidal CdSe/CdS Tetrapods.
Yile Liao 1 , Guichuan Xing 2 , Yin Thai Chan 1 , Tze Chien Sum 2
1 Chemistry, National University of Singapore, Singapore Singapore, 2 , Nanyang Technological University , Singapore Singapore
Show AbstractColloidal core-shell CdSe/CdS nanoheterostructures are promising optical gain materials due to their high quantum yields, large absorption cross-sections and reduced non-radiative Auger recombination rates relative to bare CdSe nanoparticles. We present our efforts in incorporating monodisperse CdSe seeded CdS nanotetrapods into sol-gel derived films, which provided us with a robust platform in which to systematically investigate the effects of the CdS arm width/length and CdSe core diameter on the biexcitonic amplified spontaneous emission (ASE) threshold. Varying the physical dimensions of the tetrapods allowed for room temperature biexcitonic ASE at wavelengths corresponding to either the CdS arms or CdSe core, where ASE thresholds could be reconciled with Variable Stripe Length (VSL) optical gain measurements. The achievement of ASE in either the tetrapod core or its arms may be understood from their respective Auger lifetimes, volume fraction and band alignment. We show that room temperature ASE from multiexcitonic states in these tetrapods can be readily achieved, yielding surprisingly high optical gain values as determined by VSL measurements. Our findings collectively indicate a good potential for such structures to achieve tunable, multiple wavelength lasing from a single gain material.
9:00 PM - SS7.6
Improvement of Adhesive Strength of Polyacetal by Irradiation of Vacuum Ultra-Violet Light and Deposition of Nanometer-Sized Particles Simultaneously Using Laser Ablation.
Akihiro Takeichi 1 , Yasushi Okamoto 2 , Hirozumi Azuma 1
1 , TOYOTA Central Research and Development Laboratories Incorporated, Nagakute, Aichi 480-1192 Japan, 2 , DENSO CORPORATION, Kariya, Aichi 448-8661 Japan
Show Abstract Polyacetal is a resin which has excellent property, such as formability, mechanical property, electrical property, heat resistance, chemical resistance, and abrasion resistance. However, polyacetal has a poor adherence property using adhesive material, and the improvement of adhesive strength is strongly demanded. Therefore, for the improvement of the adhesive strength, simultaneous surface treatments of polyacetal by irradiation of vacuum ultra-violet (VUV) light and deposition of nanometer-sized particles using laser ablation with C, Si, and Ti targets were carried out. The surface treatments were carried out with different wavelengths, energies, and processing times. The targets were irradiated with a pulsed laser of a pulse duration of 8 ns, and a repetition rate of 10 Hz from Nd-YAG laser. Two different wavelengths of 532 nm (SHG) and 355 nm (THG) were used. Energy conditions of 850 mJ/pulse and 430 mJ/pulse were used in the case of 532 nm. And, energy conditions of 530 mJ/pulse and 270 mJ/pulse were used in the case of 355 nm. Focus size was an ellipse of 2.2 mm × 1.8 mm (energy density of 9-27 J/cm^2, irradiation intensity of 1.1-3.4 GW/cm^2). Processing times (irradiation times) were from 15-sec to 60-sec. Polyacetal tensile test pieces were used as substrates. The distance between target and substrate was 87 mm. Substrates were located from 3 to 33 degrees from normal direction of targets. The degree of vacuum of the chamber was under 10^-3 Pa. After surface treatments, polyacetal tensile test pieces were bonded by epoxide-based adhesive. And, longitudinal shear strengths were measured. As a result, after surface treatment of polyacetal using C target with a wavelength of 532 nm, energy of 850 mJ, and processing time of 60-sec, the highest shear bond strength of 5.6 MPa for polyacetal was measured, which is 8 times higher than that of non-surface treated sample. The improvement of the adhesive strength of the polymer, simultaneously surface-treated with VUV light and nanometer-sized particles deposition, is caused by the new-creation of the dangling-bonds on the polymer surface by VUV irradiation and preservation of each dangling-bonds from recombination of them by a separation effect of deposited nanometer-sized particles. These survived dangling-bonds probably increase adhesive strength. And, it was also found that increasing functional groups and increasing surface roughness are affecting improvement of the adhesive strength. This method can be applied for the improvement of the adhesive strength of various polymers. And, it expand new applications of polymers.
9:00 PM - SS7.62
Photo-Induced Motions in Organic Molecular Crystal Nanorods and Microribbons.
Chris Bardeen 1 , Lingyan Zhu 1
1 Chemistry, U. California Riverside, Riverside, California, United States
Show AbstractIrradiation of a macroscopic crystal composed of photoreactive molecules usually results in fracture and crystal disintegration as the reactant and product species phase separate. But when the size of the crystal is reduced to the micron range, the high surface-to-volume ratio can alleviate this lattice strain, permitting the photochemical reaction to proceed while the overall crystal remains intact. The ability to transform the chemical composition using photochemistry can cause the molecular crystal to bend, twist, or expand. In this work, we describe the use of 9-anthracenecarboxylic acid, a molecule that undergoes a reversible [4+4] photodimerization in the crystalline state, to prepare single crystal nanostructures of different sizes and shapes. One-dimensional nanorods can undergo reversible bending. The use of highly focused near-infrared femtosecond laser pulses results in two-photon excitation of micron-scale regions and can induce transient bends at various locations along the length of a single nanorod. Bending can be observed in nanorods with diameters as small as 35 nm, and translational motion of a single nanorod could be induced by sequential bending of longer segments. 9-anthracenecarboxylic acid can also be prepared in the form of two-dimensional crystalline microribbons. When exposed to spatially uniform irradiation, these photoreactive ribbons rapidly twist. After the light is turned off, they relax back to their original shape over the course of minutes. This motion can be repeated for multiple cycles. The demonstration of reversible twisting represents a new type of photoinduced motion in molecular crystals. The twist period and cross-sectional dimensions of individual microribbons are measured using a combination of atomic force and optical microscopies. Both the nanorod bending and microribbon twisting are analyzed quantitatively in terms of a kinetic model that describes the bending and relaxation dynamics of individual rods. Analysis of this data suggests that the reversible twisting and bending involves the generation of interfacial strain between unreacted monomer and photoreacted dimer regions, with interaction energies on the order of a typical hydrogen bond. By combining control of the molecular crystal shape and size with the use of different photoexcitation conditions, we can develop different nanostructures, composed of the same molecule, where the location, rate and magnitude of the photodeformation can be controlled. This ability to remotely control the motion of these ultrasmall photomechanical structures may be useful for manipulating objects on the nanoscale.
9:00 PM - SS7.63
Effect of Cellulose Size on Its Transverse Elastic Modulus and Reinforcement Characteristics.
Anahita Pakzad 1 , John Simonsen 2 , Reza Shahbazian Yassar 1
1 Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Hoghtuon, Michigan, United States, 2 College of Forestry, Oregon State University, Corvallis, Oregon, United States
Show AbstractThe great impact of the dispersion quality and interphase on the performance of cellulose nanocrystal (CNC) reinforced composites in load bearing applications is well known. Yet, no information exists in the literature on the relationship between the size and mechanical properties of these crystals and the characteristics of the interphase. The study presented here will bridge this gap by characterization of individual CNCs and CNC-reinforced polymer composites using both experimental and numerical methods.CNCs were extracted from cotton using acid hydrolysis. Surface of these crystals were chemically treated by sulfation and carboxylation to study the effect of surface chemistry on their mechanics. Sulfated CNCs were then used to reinforce Poly(vinyl alcohol) (PVOH) at different concentrations, to investigate the dispersion quality and the interphase. Similar to cellulose, PVOH is a hydrophilic polymer and it was expected that it results in well dispersed CNC composites.In order to characterize individual CNCs, nanoindentation in atomic force microscope (AFM) was combined with finite element (FE) analysis to obtain their transverse elastic moduli. For this purpose, experimental force-displacement curves were fitted by the data acquired in a quadric symmetry FE model generated in Ansys. The peak force tapping (PFT) was used to characterize the interphase in the PVOH samples. This technique uses very shallow (2 nm) indentations on the sample surface to generate quantitative nanomechanical maps of the surface, with AFM resolution. Application of PFT mode allowed us to measure the thickness of the interphase and the variation of nanomechanical properties through this region, for the first time with resolution of less than 10 nm. As of now, not many reports exist in the literature on the properties of interphases with less than 5 μm thickness.The transverse elastic modulus obtained from combination of AFM and FE studies varied between 5 to 18 GPa. These results are comparable to theoretical predicated values. Carboxylated CNCs, which were prepared under harsher chemical treatment, had smaller diameters and higher elastic moduli compared to sulfated ones. More importantly, a direct correlation between CNC diameter and its modulus was made, and it was shown for the first time that the CNC transverse elastic modulus increases by decreasing its diameter. Similar correlation was found in quantitative maps obtained from AFM; the thickness of the interphase increased by CNC diameter. Thus, it was concluded that the elastic modulus of CNC is size dependant and in order to increase the interphase thickness in CNC reinforced composites, crystals with larger diameter or lower elastic modulus should be used.
9:00 PM - SS7.64
Nanomechanical Properties of Pulsed Laser Deposited NbN on Si Substrate Using Nanoindentation.
Cody Wright 1 , David Stegall 1 , Md. Mamun 1 3 , A. Farha 2 3 , A. Er 2 , Y. Ufuktepe 4 , D. Gu 2 3 , H. Elsayed-Ali 2 3 , A. Elmustafa 1 3
1 Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia, United States, 3 , Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia, United States, 2 Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia, United States, 4 Department of Physics, Cukurova University, Adana Turkey
Show AbstractStructural and mechanical properties of niobium nitride thin films deposited by pulsed laser deposition were investigated using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and nanoindentation. Niobium nitride was prepared on Si(100) by pulsed laser deposition of Nb in nitrogen background. A Nanoindenter XP equipped with a DCM II head was used in conjunction with the continuous stiffness method (CSM) in depth and load control modes to measure the hardness and modulus of the NbN thin films. NbN film reveals simple cubic δ-NbN structure with the corresponding reflections of (111), (200) and (220) planes. Highly textured NbN film shows a strong (111) preferred orientation with the substrate. The NbN thin films depict highly granular structure, with a wide range of grain sizes that range from 15-40 nm with an average surface roughness of 6 nm. The average composite modulus of the film is 220 GPa whereas for the substrate the average modulus is 180 GPa, which is consider higher than the average modulus for Si reported in the literature due to pile-up. The hardness of the film increases monotonically from an average of 12 GPa for deep indents measured using XP CSM or LC modes to an average of 19 GPa measured using the DCM II head in CSM or LC modules. The average hardness of the Si substrate is 12 GPa.
9:00 PM - SS7.65
Combined Electron Beam Imaging and Ab Initio Modeling of Embedded Nanoscale Precipitates in Alloys.
Christian Dwyer 1 2 3 , Laure Bourgeois 1 3 , Matthew Weyland 1 3 , Lan-Yun Chang 1 4 , Barry Muddle 2 3
1 Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria, Australia, 2 ARC Centre of Excellence for Design in Light Metals, Monash University, Clayton, Victoria, Australia, 3 Department of Materials Engineering, Monash University, Clayton, Victoria, Australia, 4 School of Chemistry, Monash University, Clayton, Victoria, Australia
Show AbstractAmong the many considerable challenges faced in developing a rational basis for designing advanced, precipitation-hardened alloys, the establishment of accurate atomistic models is one of the most fundamental. Here we will demonstrate how state-of-the-art methods in aberration-corrected transmission electron microscopy, coupled with ab-initio modeling, offer unprecedented accuracy in the characterization of embedded nanoscale precipitates and their interfaces with the matrix. We will demonstrate how quantitative annular dark-field (ADF) scanning transmission electron microscopy (STEM) can be applied to extract accurate structural information, including the chemical composition, at the atomic scale. We also show how exit-wave reconstruction by through-focal series can provide structural information that is complementary to that obtained from ADF-STEM, particularly regarding light elements, so that the combination of these experimental techniques reveals the sites of both heavy and light elements within the precipitates and surrounding matrix. The experimentally-determined structural models are further scrutinized using ab-initio calculations based on density functional theory. Such a combination of experimental and theoretical techniques provides a complete framework for the determination of nanoscale atomic arrangements, as well as an understanding their energetics. Applications to several important alloy systems will be presented, including the text-book θ' precipitate phase in Al-Cu alloys, and the T1 precipitate phase in Al-Li-Cu alloys relevant to the aerospace industry. In the former system, our approach has revealed new insights regarding the atomistics of precipitate growth, while in the latter system our methods have provided an accurate determination of a controversial atomic structure that remained unsettled for several decades. The applicability of these methods to the structural characterization of other nanomaterials systems will also be emphasized.
9:00 PM - SS7.66
Nanometer-Resolved Mechanical Characterization of Surfaces.
Alexander Jakob 1 2 , Stefan Mayr 1 2 3
1 , Leibniz-Institut für Oberflächenmodifizierung e.V., Leipzig Germany, 2 Translationszentrum für regenerative Medizin, Universität Leipzig, Leipzig Germany, 3 Fakultät für Physik und Geowissenschaften, Universität Leipzig, Leipzig Germany
Show AbstractWith proceeding miniaturization in science and technology, mechanical properties at the nanoscale have attracted increasing interest during the past years. Although commercial nanoindenters are widely available at this point, they usually probe the microscale rather than measuring nanomechanical properties. For true nanometer resolved mechanical characterization, atomic force microscopy (AFM) based techniques are highly promising – in the first place dynamical measuring modes to assess the contact resonance between AFM cantilever and sample (CR-AFM), as first proposed by Arnold et al. [1] and Yamanaka et al. [2].While our first setup employed a hardware implementation of this technique [3], we report in the present contribution about the second generation implementation of the CR-AFM mode into a commercial AFM purely on a software basis and demonstrate the capabilities and limitations for examplary surfaces. In order to obtain quantitative information of elastic surface modulus, experimental studies are supplemented by finite element modeling of the cantilever-sample interaction. Comparisons with ab-initio predictions are also presented.This project is funded by the German BMBF, PTJ-BIO, Grant Number: 0313909.[1] Rabe U., Arnold W., Appl. Phys. Lett. Vol.64, P1493-1495 (1994)[2] Yamanaka K., Ogiso H., Kolosov O., Appl. Phys. Lett., Vol.64, P178-180 (1994)[3] C. Vree, Dissertation, Göttingen 2009.
9:00 PM - SS7.67
Development of Objective Type Atomic Force Microsocopy for PSISCM-Nanoindentation Combined System.
Masayuki Fujitsuka 1
1 Technical Research Institute, Japan Society for the Promotion of Machine Industry , Higashikurume, Tokyo, Japan
Show AbstractNanoindentation test is known as instrumented indentation test (IIT) in the nano range for hardness and material parameters (ISO14577-1). It is a simple and effective method for evaluating the mechanical properties such as elasticity/stiffness, hardness and adhesion. Generally IIT is the method that doesn’t have to observe the residual impression. However, it is necessary to observe the residual impression and surface of test piece to obtain the material behavior such as pile-up/sink-in, crack. In past work, the phase shifting interferometric scanning confocal microscope (PSISCM)-nanoindenataion combined system was developed to obtain the tilt of surface and the geometrical shape of residual impression that are deeper than one micron. This system is useful to obtain the geometrical shape of the surface of test piece in macro and micro range. However, it is well known that the results of nanoindentation test become unstable in the nano range. In this work, authors focused objective type atomic force microscopy to obtain the geometrical shape in nano range. The AFM that has an excellent performance is developed by SII nanotechnology Inc. Japan, and it built into system. In many cases, it performs enough to observe the residual impression and the surface of the test piece. This system uses three methods to obtain the geometrical shape of surface in each range. Generally, AFM has the observation range at about several microns. It is difficult to search the small residual impression by only AFM. Before the observation of AFM, the observation area should be selected by using PSISCM. New measurement tool using PSISCM and AFM to obtain the surface geometry from macro range to nano range is proposed. This tool is very simple, quick and useful tool. In this forthcoming conference, we will report the detail of this system and applications.
9:00 PM - SS7.7
Structure and Mechanical Properties of Continuous Polymer and Carbon Nanofibers.
Yuris Dzenis 1 , Dimitry Papkov 1 , Yan Zou 1
1 Engineering Mechanics, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractPolyacrylonitrile (PAN) is a popular precursor for production of carbon fibers. High strength PAN-based carbon fibers require carbonization at elevated temperatures and under stretch. Significantly reducing fiber diameter to nano-scale might allow reduction in these two parameters. Electrospinning is an emerging technique that allows production of continuous polymer precursor nanofibers. PAN nanofibers were produced by electrospinning. Mechanical properties of fibers as a function of fiber diameter were examined before and after carbonization. Significant scale effects were observed with the simultaneous improvements in strength, stiffness, and toughness of the nanofibers with the reduction of the nanofiber diameters. Effects of carbonization temperature on the final structure and graphitic fraction were studied by means of Raman spectroscopy, XRD, and TEM and correlated to mechanical properties. Differences in the fiber structure as a function of fiber diameter were examined by electron diffraction.
9:00 PM - SS7.8
Individual Electrospun Poly(Vinyl Alcohol) Nanofiber Wetting Using AFM.
Shuangwu Li 1 , Asa Barber 2
1 , Queen Mary, University of London, London United Kingdom, 2 , Queen Mary, University of London, London United Kingdom
Show AbstractThe surface of polymer nanofibres plays a significant role in many applications thus measurement of their surface properties is essential but challenging due to their relatively small size. This paper details AFM wetting tests for individual electrospun polymer nanofibres in order to measure their polar and dispersive surface free energy components. The wetting behaviour of individual electrospun PVA nanofibres has been investigated in this paper using a Wilhelmy based single fibre-AFM method. The resultant calculated contact angles were used to find the dispersive and polar component for the PVA surface free energy using Owens-Wendt theory. Results show that PVA nanofibre has a dispersive surface free energy value of around 40 mJm-2 whereas the polar component is lower than a comparable PVA film of 10.4 mJm-2. Structure information of the electrospun fibre using FTIR and XPS surface techniques explore how an increase in hydrogen bonds formed within nanofibres rather than on the fibre surface enhances the dispersive contribution but lowers the polar contribution.
9:00 PM - SS7.9
Plastic Deformation of an Oriented Crystalline Polymer Modeling.
Ulmas Gafurov 1
1 , Institute of Nuclear Physics, Tashkent Uzbekistan
Show AbstractModelling of molecular processes in plastic deformation of an oriented linear crystalline polymer was carried out. The Frenkel-Kontorova’s dislocation model (crowdion) was used for condition of balance of loaded chain in polymer crystallite. The dislocation formation is accompanied local loads relaxation on interconnecting amorphous sections and by conformation regroupings of these sections in some conditions. In dependence on external load and amorphous region length different cases are realized. The load relaxation value influences on dislocation behaviour . This behaviour depends except for of macromolecular chain parameters and geometrical configuration mainly from sizes of stressed amorphous section and of initial load on it. Beside of its deformation molecular processes are complexly dependent concentration of chain ends, entanglements and cross –links.
Symposium Organizers
Peter Anderson Ohio State University
Neville Moody Sandia National Laboratories
David Bahr Washington State University
Ralph Spolenak ETH Zurich
SS8: Dislocations and Material Behavior
Session Chairs
Ruth Schwaiger
Chris Weinberger
Wednesday AM, November 30, 2011
Constitution A (Sheraton)
9:30 AM - **SS8.1
Effects of Alloying and Temperature on the Mechanical Behavior of Nanocrystalline Palladium Alloys.
Ruth Schwaiger 1 , Thomas Neithardt 1 , Oliver Kraft 1
1 Institute for Applied Materials, Karlsruhe Institute of Technology, Karlsruhe Germany
Show AbstractOver the past decade significant advances in understanding the deformation mechanisms in fine-grained metals and alloys have been made. It is now well accepted that in the grain size regime up to about 50 nm the dislocation activity is significantly reduced. Other deformation mechanisms such as nucleation and motion of partial dislocations, grain boundary sliding or grain rotation and grain boundary motion were shown to gain importance, which is corroborated by the small activation volumes and increased strain rate sensitivity typically observed in nanocrystalline metals. In our work, we investigated nanocrystalline Pd und PdAu-alloys using strain rate sensitive indentation and microcompression testing. While the hardness increases with increasing alloying content, no significant alloying effect on the strain rate sensitivity and activation volume was observed. In order to better understand the deformation mechanisms and their thermal activation, indentation and microcompression experiments were conducted at different temperatures up to 90°C for which no significant microstructural changes were observed. The observed trends will be compared to existing literature on nanocrystalline metals and alloys.
10:00 AM - SS8.2
Probing Deformation Mechanisms in Brittle Materials at Low and Intermediate Temperatures.
Sandra Korte 1 , Robert Stearn 1 , William Clegg 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractThe measurement of activation volumes and energies is one of the most useful ways of identifying particular mechanisms of plastic flow and this is most easily done by testing over a range of temperatures. In ceramics, there is a severe limitation associated with their brittleness, so that it is often impossible to probe their plastic deformation behaviour at room and intermediate temperatures.In this paper, we show how microcompression can be used as a technique to study flow in brittle materials in this temperature range. This is accomplished by the suppression of cracking in small volumes and the recently developed elevated temperature microcompression technique allowing testing at so far up to 700 °C. Examples are given of deformation studied in combination with transmission and scanning electron microscopy and in a range of materials including spinel, semiconductors and brittle intermetallics.
10:15 AM - SS8.3
Determination of Activation Volume, Energy and Peierls Stress of Single-Crystalline (001)TiN and TiAlN Coatings at 298K to 623K Using Nanoindentation Testing Technique.
Constantin Ciurea 1 2 , Vineet Bhakhri 1 2 3 , Paul Mayrhofer 4 , Finn Giuliani 1 2 3
1 Centre for Advanced Structural Ceramics, Imperial College London, London United Kingdom, 2 Department of Materials, Imperial College London, London United Kingdom, 3 Department of Mechanical Engineering, Imperial College London, London United Kingdom, 4 Department of Physical Metallurgy & Materials Testing, Montanuniversitaet Leoben, Leoben Austria
Show AbstractCutting tools are subjected to very high mechanical and thermal stresses in service conditions. TiN is a commonly used material as tribological ceramic coatings on cutting tools. Addition of aluminium renders remarkable mechanical stability at elevated temperatures to these coatings. Often out of lack of adequate measuring techniques, the characteristics of hard ceramic films are investigated at room temperature or after heat treatment. Although this approach is sometimes useful but it is sensible to test them at service temperatures, where intrinsic material properties are expected to change. In this investigation, high-temperature nanoindentation testing was employed to investigate the difference between deformation behaviour of standard (001)TiN single crystal (SC-TiN) and cubic-Ti0.44Al0.56N coating at 298K to 623K. Near-to epitaxial TiAlN film was grown on MgO single crystals (110) using a reactive magnetron sputtering system. High temperature nanoindentation experiments were carried out at three different loading rates of 0.5, 1 and 10 mN/s. This enabled us to capture the indentation hardness data at three different strain-rates at the end of loading sections of these tests. The measured average thermal drift for these experiments ranged from 0.02 nm/sec at 298K to 0.1 nm/sec at 623K. Hardness values for SC-TiN drastically dropped from 21±0.3 GPa at room-temperature to 11±0.5 GPa at 623K. On the other hand, hardness of cubic-Ti0.44Al0.56 N coating was quite stable in the measured temperature range, with 30±1.1 GPa at 298K and decreased slightly to 26±1.6 GPa at 573K. Decreasing hardness with temperature implies decrease in the resistance to dislocation flow. The activation volume, V*, of the deformation process, calculated from the stress dependence of the indentation shear strain rate for both single-crystal and coating was of the order of ~1b^3 (b is the Burgers vector) indicating that lattice-resistance controlled dislocation glide is the deformation rate controlling mechanism. The indentation shear flow stress at 0K (Peierls stress, τp) values from the temperature dependence of shear flow stress for SC-TiN and coating were calculated to be 5.9GPa and 11.24GPa respectively. Apparent activation energy (Q=τp.V*) for SC-TiN was estimated to be 0.75eV and 1.26eV for cubic-Ti0.44Al0.56N coating indicating that the resistance to plastic flow is higher for cubic-Ti0.44Al0.56N coating compared to its single-crystal counterpart and its magnitude is typical of lattice resistance controlled dislocation glide mechanism. This work outlines an analysis method to extract the fundamental deformation rate-controlling parameters from the indentation data and hence demonstrates the usefulness of nanoindentation testing technique in investigating the kinetics of plastic deformation of ceramic systems at sub-micron length scales and elevated temperatures.
10:30 AM - SS8.4
Experimental Evidences of Competing Stress Relaxation Mechanisms in Thin Al/Si and Pd Films Tested on Chip.
Michaël Coulombier 1 , Grégory Guisbiers 1 , Marie-Stéphane Colla 1 , Jean-Pierre Raskin 1 , Thomas Pardoen 1
1 , UCL, Louvain-la-Neuve Belgium
Show AbstractA novel stress relaxation technique dedicated to thin freestanding films has been developed as an extension of an on-chip tensile testing method. The technique relies on a structure made of two beams. An actuator beam is deposited with large internal stresses onto a sacrificial layer. The specimen beam is deposited next, partly overlapping with the actuator beam. By etching the sacrificial layer, the two-beam structure is released from the substrate and the test specimen is deformed until force equilibrium is reached. The specimen, being under stress, relaxes at a rate depending on the composition, microstructure, thickness, and temperature. This test is similar to a creep test on a specimen attached to a spring. The strain rate sensitivity exponent and activation volume can be derived from a record of the evolution with time of the displacement undergone by the test specimen. This technique allows measuring the relaxation response of a large amount of test structures, involving different levels of plastic strains, dimensions and loading conditions, without requiring the use of any external device such as a nanoindentor or tensometer. The technique is well suited for very long relaxation measurements. Strain rates varying between 10-6 s-1 down to 10-11 s-1 are accessible and statistically representative data can be generated.The technique has been applied to both 205 nm-thick evaporated Al 1%Si and 355 nm-thick evaporated Pd films showing interesting variations of the activation volume with strain rate and initial level of plastic deformation. Relaxation at room temperature has been studied as well as at higher temperature for the Pd films. In the AlSi films, the initial activation volume amounts to a few b3 presumably due to diffusion mechanisms. The diffusion mechanism requires stress gradients which smooth out during relaxation, leaving room, at lower strain rates, to another dominant relaxation mechanism involving a much larger activation volume. The recovery of the dislocation structure is one of the candidates for this second mechanism. These mechanisms are investigated using TEM.
10:45 AM - SS8.5
Dislocation-Interface Interaction in Crystalline-Amorphous Metallic Multilayers.
Christian Brandl 1 , Timothy Germann 1 , Amit Misra 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractTraditional ultrahigh-strength crystalline metals are obtained by reducing the governing microstructural length scale. The usual penalty to be paid is a lack of ductility, as for example in nanocrystalline metals. On the other hand, in bulk metallic glasses plastic deformation – again owning a lack of ductility - is believed to be mediated by the so-called “shear transformation zones”. However, the combination of amorphous layers with crystalline layers has exhibited extraordinarily high toughness, i.e. ultra-high strength in conjunction with high elongation-to-failure. The plastic deformation, moreover, is confined by the crystalline-amorphous interface, which additionally has to maintain deformation compatibility to mediate homogeneous plastic flow.Contrary to crystalline-crystalline interfaces, where crystalline phases exhibit long range order, the amorphous structure is characterized by a lack of long-range order. Using molecular dynamics (MD) methods, the compensation mechanism of this reduced long-range order at the interface is studied for the Cu (FCC) / CuxZr1-x (amorphous) system. The ordering decreases with increasing distance from the amorphous-crystalline interface. The implication of the interface ordering on dislocations impinging upon the interface is studied via MD. The interface response is discussed in terms of (1) rearrangement of interface order, and (2) co-deformability of the amorphous and crystalline layers, and the resulting implications on layer size effects.
11:30 AM - SS8.6
Atomistic and Continuum Simulations of Dislocation Nucleation in Gold Nanowires.
Christopher Weinberger 1 , Andrew Jennings 2 , Julia Greer 2
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, United States
Show AbstractPlasticity in confined volumes is well known now to be drastically different than that of bulk crystals and, in pristine materials, nucleation is thought to dominate plasticity. Here, we investigate the nature of dislocation surface sources using both atomistic simulations and continuum models. We use a free-end string method to compute activation volumes associated with the energy barriers required to be overcome for dislocation nucleation in gold nanowires. We then examine the associated strain rate dependence of the deformation mechanisms and compare them against direct MD simulations. We gain further physical insight through comparing our simulations with simple continuum models. These models show that nucleation is controlled by the energy of the dislocation, which is comprised of two parts: the line length and the orientation dependent line energy. These results illustrate the complex behavior of dislocation sources in small volumes and the associated plastic response.
11:45 AM - SS8.7
Lithium-Assisted Plastic Deformation of Silicon Electrodes in Lithium-Ion Batteries: A First-Principles Theoretical Study.
Kejie Zhao 1 , Weili Wang 1 , Zhigang Suo 1 , Joost Vlassak 1 , Efthimios Kaxiras 1
1 School of Engneering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractSilicon can host a large amount of lithium, making it a promising electrode for high-capacity lithium-ion batteries. Recent experiments indicate that silicon experiences large plastic deformation upon Li absorption, which can significantly decrease the stresses induced by lithiation and thus mitigate fracture failure of electrodes. These issues become especially relevant in nanostructured electrodes with confined geometries. Here, we present a study on the microscopic deformation mechanism of lithiated silicon based on first-principles calculations. We find that lithium insertion leads to breaking of Si-Si bonds and formation of weaker bonds between neighboring Si and Li atoms, which results in a decrease in Young’s modulus, a reduction in strength, and a brittle-to-ductile transition with increasing Li concentration. The microscopic mechanism of large plastic deformation is attributed to continuous lithium-assisted breaking and reforming of Si-Si bonds and the creation of nano-pores.
12:00 PM - SS8.8
Effect of Eshelby Twist on Core Structure of Screw Dislocations in Molybdenum: Atomic Structure and Electron Microscope Image Simulations.
Roman Groger 1 , Karleen Dudeck 3 2 , Peter Nellist 2 , Vaclav Vitek 4 , Peter Hirsch 2 , David Cockayne 2
1 Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno Czechia, 3 Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada, 2 Department of Materials, University of Oxford, Oxford United Kingdom, 4 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractWe address the question as to whether the core structure of screw dislocations in Mo in thebulk can be obtained from HREM images of such dislocations viewed end-on in a thin foil. Atomisticsimulations of the core structure of screw dislocations in elastically anisotropic Mo are carried outusing Bond Order Potentials. These simulations take account automatically of the effects of the surfacerelaxation displacements (anisotropic Eshelby twist). They show that the differential displacements ofthe atoms at the surface are different with components perpendicular to the Burgers vector about fivetimes larger than those in the middle of the foil, the latter being characteristic of the bulk. Nye tensorplots show that the surface relaxation stresses strongly affect the incompatible distortions. HREMsimulations of the computed structure reflect the displacements at the exit surface, modified byinterband scattering and the microscope transfer function. Nye tensor plots obtained from the HREMimages show that interband scattering also affects the incompatible distortions. It is concluded that itwould be very difficult to obtain information on the core structure of screw dislocations in the bulk Mofrom HREM images, even under ideal experimental conditions, and that quantitative comparisonsbetween experimental and simulated images from assumed model structures would be essential.
SS9: Tribology at the Nanoscale
Session Chairs
Ruth Schwaiger
Chris Weinberger
Wednesday PM, November 30, 2011
Constitution A (Sheraton)
12:15 PM - SS9.1
Analysis of Sliding-Induced Wear at the Nanoscale Using In Situ TEM Testing.
Tevis Jacobs 1 , Robert Carpick 2
1 Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Mechanical Engineering & Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractAt present, nanoscale wear at sliding interfaces is a primary limitation of small-scale devices such as micro-/nano-electronic mechanical systems (MEMS/NEMS) and atomic force microscope (AFM) probes. In many cases, even the wear of macroscopic bodies is governed by the aggregate behavior of a large number of nanoscale asperities. However, relatively little is known about the fundamental physics of nanoscale wear due to the difficulty of analyzing buried, evolving surfaces. In the present study, wear tests were conducted inside of a transmission electron microscope (TEM) using a modified in-situ nanoindentation apparatus. This permitted real-time visualization of contact between a single nanoscale asperity and a flat surface. Video and periodic high-resolution still images (with atomic lattice resolution) allowed for characterization of the contact geometry, measurement of the shape evolution of the wearing asperity, and quantification of the volume lost due to wear, all with sub-nanometer resolution. These data, which are difficult if not impossible to obtain using other techniques, enable far greater quantitative insight and deeper investigations into the contact mechanics, the role of interfacial adhesion forces, and the mechanisms of wear. This approach was used to study nanoscale silicon and silicon oxide asperities sliding against diamond. The dominant wear mechanism was consistent with a gradual tribo-chemical removal of atoms via single bond-breaking events. Larger nanoscale fracture events do occur, but with low frequency. No plastic deformation is observed. The volumes progressively lost due to wear were quantified with a precision as low as 30 nm3, a level better than anything previously reported. Wear rates for silicon and native silicon oxide against diamond are seen to be distinct. We find that Archard’s classic wear law does not apply at the nanoscale. We further evaluate wear using a model based on transition state theory1. 1 T.D.B. Jacobs et al. Tribol. Lett., 39, pg 257 (2010)
12:30 PM - SS9.2
Friction Anisotropy in 100 nm Contacts Revealed by Slidingless Micro-Slip Tests on Single Crystal Ni in Air.
James Annett 1 , Yanfei Goa 2 , Erik Herbert 2 , Barry Lucas 2 , Graham Cross 1
1 Crann, Trinity College Dublin, Dublin, Dublin, Ireland, 2 Department of Materials Science and Engineering,, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractUsing a multidimensional contact mechanics system designed for a quantitative measurement of lateral contact stiffness in the 10~106 N/m stiffness range (or 10~1000 nm contact size), we found a crystallographic-orientation-dependent lateral-stiffness reduction relative to the elastic prediction at contact sizes around 50 nm for a polished Ni single crystal surface in air. The slidingless measurement is enabled by a frequency-specific, continuous stiffness measurement technique. Based on an interface micro-slip model and an anisotropic elastic contact analysis, the resulting friction stress is found to increase monotonically when the tested lateral direction rotates away from the closely packed direction, reminiscent of a Schmid condition for easy dislocation glide. Our results differ from well known incommensurate lattice sliding effects of clean surfaces due to both the mesoscale contact size and ambient conditions for the experiments.
12:45 PM - SS9.3
Frictional Properties of the End-Grafted Polymer Layer.
Maryam Raftari 1 2 , Zhenyu Zhang 1 2 , Steve R Carter 1 , Graham J Leggett 2 , Mark Geoghegan 1
1 The Department of Physics and Astronomy, Department of Physics and Astronomy, The University of Sheffield, Sheffield United Kingdom, 2 Department of Chemistry, The University of Sheffield, Sheffield United Kingdom
Show AbstractWe have studied the frictional behaviour of end-grafted poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) films (brushes) using friction force microscopy (FFM) as a function of pH in aqueous solution. Polyelectrolyte brushes are valued for their lubrication properties, and so their frictional behaviour is of some importance when considering film properties. With this in mind the transition between different contact mechanics allows us to make conclusions as to the circumstances under which a brush can be employed most effectively. We observe that the contact mechanics is a strong function of pH, with regions whereby both single asperity contact mechanics behaviour (both Johnson-Kendall-Roberts (JKR) and Derjaguin-Müller-Toporov (DMT) models) and multiple contact mechanics (Amontons’ law) observed, depending on the pH. Amontons’ law fitted data best in the extreme pH regions (pH = 1, 2, and 12). Between these values at high and low pH, DMT behaviour was appropriate, whereas the observation of JKR behaviour depended on the surface in contact with the brush, but generally at relatively neutral pH values.In our experiments, the films were prepared on native oxide-terminated silicon substrates using the “grafting from” technique of atom transfer radical polymerization (ATRP). These brushes had constant grafting density (1.18 nm2), and of a thickness of ~66 nm, as measured by ellipsometry. Measurements were made using functionalized and unfunctionalized silicon nitride triangular probes. Functionalized probes included gold-coated probes, and ones coated with a self-assembled monolayer of dodecanethiol (DDT; a hydrophobic surface) or mercaptoundecanoic acid (MUA; a hydrophilic surface).In general, the JKR model can be used for force-load data demonstrating strong adhesion when surface forces are short-range compared to the elastic deformation. However, on stiff materials with weak adhesion forces, data are better described by the DMT model. Amontons’ law is observed for the classic situation whereby the frictional force is directly proportional to the applied load.Our results show that the contact mechanics of polyelectrolytes in water is complex and strongly dependent on the nature of the interaction, and particularly on the environmental pH. Some simple conclusions can be immediately drawn from our results, such as the friction between MUA probes and PDMAEMA being less than that for DDT probes and PDMAEMA is because the MUA (like the PDMAEMA brush) probes are hydrophilic but DDT probes are hydrophobic. Then DDT has therefore a stronger interaction with the sample and thus a concomitantly larger adhesion or friction. Other results reflect a more delicate balance in the interactions between the different components. For example, the nature of the elasticity of the interaction is different for the JKR and DDT models, and this partly is reflected in the state of the brush, the swelling of which changes as a function of pH.
SS10/FF6: Joint Session: Fundamentals of Mechanical Nanofabrication
Session Chairs
Matthew Begley
Mark Robbins
Wednesday PM, November 30, 2011
Constitution A (Sheraton)
2:30 PM - **SS10.1/FF6.1
Scaling Relationships for Synthetic Nacre and Their Implications for Materials Development.
Matthew Begley 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractSynthetic brick and mortar microstructures that mimic nacre (abalone shell) create new opportunities for high performance materials, provided the constituent properties can be controlled down to small scales. This talk will outline scaling laws that relate brick strength, mortar ductility and geometric length-scales to macroscopic modulus, strength and toughness. These scaling laws enable the generation of mechanism maps that illustrate regimes of brick failure and interface rupture, as a function of constituent properties. Inherent trade-offs between modulus, strength and toughness will be outlined and related to transitions in failure mechanisms. An important feature of the results is that the ideal brick size that optimizes strength and toughness depends strongly on the ductile properties of the mortar (and vice versa), and the interface strength that is controlled by bonding at the nanoscale. Using these models, processing targets for synthetic materials will be detailed in terms of geometry and constituent properties. The talk will conclude with a brief discussion of material synthesis via ink-jet printing of three-dimensional structures, with a focus on the key processing challenges that must be addressed to realize the material properties identified with the above models.
3:00 PM - SS10.2/FF6.2
Collective Mechanical Behavior of Multilayered Colloidal Hollow Nanoparticle Arrays.
Jie Yin 1 3 , Markus Retsch 2 3 , Edwin Thomas 2 3 , Mary Boyce 1 3
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Institute for Solider Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractHollow colloidal nanoparticle arrays have become a focal point of studies for applications in drug delivery and nanostructured materials, where the mechanical behavior of these arrays is of great importance in fulfilling the diverse application functions. Here we explore the collective mechanical behavior of two-dimensional (2D) monolayer and three-dimensional (3D) multilayer assemblies composed of close-packed arrays of hollow silica nanoparticles (NP) using a spherical nanoindentor. Such ordered multilayer arrays are self-assembled through the vertical deposition method. Several types of well-defined hollow NPs and their assembled monolayer, bilayer and trilayer arrays are studied with constituent NPs radii ranging from 100 to 300nm and shell thickness ranging from 14 to 44nm. The consecutive contacting of the indentor with an increasing number of NPs results in a nonlinear increase of the indentation force with penetration depth. Experimental results showed that the indentation load became increasingly lower as the number of layers was increased when compared at the same penetration depth, which leads to the compliant response of multilayer films. Micromechanical analytical models alongside with finite element method (FEM) simulations are employed to reveal the underlying deformation mechanisms during the indentation on 2D and 3D NP arrays. For 2D monolayer films, each contacted hollow NP successively locally bends, flattens, and then locally buckles. Based on the point-load solution of an elastic shell, the indentation load-displacement curves are predicted and the Young’s modulus of an individual particle is extracted from the measured load-displacement behavior of a monolayer array. For 3D multilayer films, a simplified parallel spring model is established to model the compliant mechanical response of multilayered NP arrays. In the trilayer NP arrays, the hexagonal close packing (HCP) and face centered cubic (FCC) packing lead to the identical indentation force-displacement curves, which implies the neglected effect of different packing methods. This study may provide useful insights and guidance for constructing high performance lightweight NP films and coatings with potential applications in tailoring stiffness and mechanical energy absorption.
3:15 PM - SS10.3/FF6.3
Tailoring and Probing Particle-Polymer Interactions in PMMA/Silica Nanocomposites.
Meng Qu 1 , Gregory Blackman 2 , Jeffery Meth 2 , Gordon Cohen 2 , Kenneth Sharp 2 , Krystyn Van Vliet 1
1 , MIT, Cambridge, Massachusetts, United States, 2 Central Research & Development, DuPont Nanocomposite Technologies, Wilmington, Delaware, United States
Show AbstractThe unique physical and mechanical properties of polymer nanocomposites have been attributed to the interfacial interactions between the organic matrix and nanoscale particles. We demonstrate the potential to tune this interaction between poly(methyl methacrylate) (PMMA) and silica nanoparticles, as a function of either nanosilica surface chemistry or polymer reactivity. Functionalized nanosilica was mechanically deposited on the surface of PMMA films, and the system then heated above the polymer glass transition temperature. Rates and extents of nanoparticle sink-in were quantified by timelapse AFM imaging, showing that the strength of particle-matrix interactions was predicted directly by polymer-particle interaction energies. Nanocomposite films created via this approach exhibited significantly enhanced elastic moduli and scratch resistance. This direct quantification of mechanical optimization via nanoparticle-polymer interfacial chemistry enables new approaches to rapidly tune nanocomposite performance.
3:30 PM - SS10.4/FF6.4
Mechanical Nanofabrication and the Origin of Life.
Helen Hansma 1
1 Department of Physics, University of California, Santa Barbara, California, United States
Show AbstractNanoscale work may have been a major energy source for the origin of life. According to the Mica Hypothesis [1], life originated between the sheets of muscovite mica, whose aperiodic up and down movements provided an endless source of mechanical energy for making and breaking covalent bonds, rearranging polymers, and blebbing off lipid micelles and protocells in the earliest form of cell division. This hypothesis for the origins of life is consistent with the behavior of biological macromolecules, which often have reproducible internal motions. The internal motions of many macromolecules are simple up-and-down motions such as the motions that occur between mica sheets in response to temperature change or water flow. The Mica Hypothesis for the origins of life evolved from research on biological Atomic Force Microscopy (AFM) [2]. 1.Hansma, H. G., Possible origin of life between mica sheets. Journal of Theoretical Biology 2010, 266, 175-188.2. The research on biological AFM was supported by NSF BIO MCB and NSF BIO DBI.
4:15 PM - **SS10.5/FF6.5
Nanomechanical Properties of Amorphous Polymers.
Ting Ge 1 , Mark Robbins 1
1 Physics and Astronomy, Johns Hopkins Univ., Baltimore, Maryland, United States
Show AbstractNanomechanical properties of amorphous polymersThis talk will describe simulation studies of the molecular mechanisms underlying the mechanical response of glassy polymers with an emphasis on regimes that may be relevant to nanopatterning and nanoassembly. First yield and strain hardening will be discussed. Strain hardening is associated with increased rates of plastic deformation as polymers become oriented by strain. Strain from previous deformation results in anisotropic mechanical properties, but the flow stress can be collapsed on a single master curve as a function of molecular orientation [1]. Anisotropy from strain hardening may impose limits on fabrication or offer opportunities for tailoring mechanical response. The next topic will be strengthening of polymer interfaces through thermally or mechanically driven interdiffusion. This is a common means of welding components or healing cracks at macroscopic scales. Simulations show a clear connection between the evolution of mechanical strength and the formation of entanglements across the interface. The final section of the talk will discuss interfacial fracture and sliding at polymer/crystal interfaces. The role of adhesive energies and surface roughness in determining the mode of failure and peak stress will be described.[1]. T. Ge and M. O. Robbins, “Anisotropic plasticity and chain orientation in polymer glasses,” J. Polymer Sci. B: Polymer Physics 48, 1473-1482 (2010).
4:45 PM - SS10.6/FF6.6
Investigation of Nanomechanical Properties Resulting from the Phase Separation Process in Ultrathin Block Copolymer Films.
Roseanne Reilly 1 , Richie Farrell 2 , Johann De Silva 1 , M. Morris 2 , Graham Cross 1
1 , Trinity College Dublin, Dublin Ireland, 2 , University City Cork, Cork Ireland
Show AbstractBlock copolymer are an important class of emerging advanced materials for nanofabrication. While reducing dimensions to the nanoscale is known to have significant implications for the mechanical properties of homopolymers [1], little is known about the nanoscale mechanics of block copolymers. Here the structural properties and deformation behavior of a diblock copolymer ultrathin film in the glassy state were investigated via a large strain indentation squeeze flow method [2]. This system is of particular interest as, further to the change in mechanical properties due to the straightforward reduction in film thickness, an additional length scale has been superimposed on the system as a direct result of the nature of microphase separation that make block copolymers (BCPs) such a useful material for fabrication. Stress vs. strain measurements of cylindrical indentation volumes in ~ 30 nm thick films were made for both the mixed and phase separated states of a 37k-37k Polystyrene-block-Polymethylacrylate (PS-b-PMMA) diblock copolymer. Measurements of both Polymethylacrylate (PMMA) and Polystyrene (PS) homopolymer thin films of similar molecular weight to the BCP system showed that the BCP system has a consistently intermediate stress-strain response to that of the homogeneous systems, whether phase separated or not. Small strain elastic and elastic-plastic yield properties of the block copolymer were found to be unaffected by phase separation, despite the significant difference between elastic modulus and yield strength of the respective PMMA and PS homopolymers. However at large strains, under conditions of large plastic flow found during nanoimprint processes, the phase separated response diverged from that of the prephase separated system and showed an increased resistance to flow. From the standpoint of models that predict strain hardening scaling with entanglement density [3], a reduction in the entanglement due to the phase separation should result in a decrease in strain hardening, opposite to the results we observe. [1]A. Raegen, M. Chowdhury, C. Calers, A. Schmatulla, U. Steiner, G. Reiter, uuml, and nter, "Aging of Thin Polymer Films Cast from a Near-Theta Solvent," Physical Review Letters, vol. 105, p. 227801, 2010.[2]G. L. W. Cross, B. S. O'connell, J. B. Pethica, H. Rowland, and W. P. King, "Variable temperature thin film indentation with a flat punch," Review of Scientific Instruments, vol. 79, pp. 013904-13, 2008.[3]Boyce MC and H. RN., The physics of glassy polymers vol. The post-yield deformation of glassy polymers. London: Chapman & Hall, 1997.
5:00 PM - SS10.7/FF6.7
Broadband Nanoindentation as a Local Probe for Mechanical Spectroscopy.
Joseph Jakes 1 , Z. Humberto Melgarejo 2 , Amirreza Sanaty-Zadeh 2 , Ken Smith 1 , Rod Lakes 3 , Don Stone 4 2
1 Performance Enhanced Biopolymers, USDA Forest Products Laboratory, Madison, Wisconsin, United States, 2 Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 4 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractMechanical spectroscopy is the assessment of a mechanical index, such as the viscoelastic Young’s modulus or the plastic flow stress, across a broad spectrum of time scale, deformation rate, or temperature. Materials scientists have long used mechanical spectroscopy to gain insight into defect motion, deformation mechanisms, and strengthening mechanisms, and to assess and predict performance across a wide range of conditions. Our goal is to develop mechanical spectroscopy methods for probing microscopic structures such as thin films, phases in alloys, and the cell wall components in wood. We have invented broadband nanoindentation creep (BNC) to measure viscoplastic properties across 4-6 decades of strain rate and broadband nanoindentation viscoelasticity (BNV) to measures viscoelastic properties across >8 decades of time scale. The measurements require an instrument with fast response that is nevertheless stable against thermal drift. Materials studied include poly methyl methacrylate, polycarbonate, polystyrene, bulk and thin-film molybdenum, Zr-Cu-Al metallic glasses, and Mg-Zn based alloys. BNC experiments generate hardness vs. strain rate. BNC data from polymers are all path-dependent (depending on initial rate of loading). BNC data from molybdenum and metallic glasses are path independent (behavior does not depend on the initial rate of loading). By a simple formula that works for the polymers and molybdenum, the hardness-strain rate data can be converted to flow stress vs. strain rate; and the converted data agree with literature compression data (uniaxial data for the metallic glasses and Mg-Zn alloys are unavailable, so we can not test this formula for these materials, but the BNC results are close based on available literature data). Likewise, BNV data follow the trend of more conventional viscoelasticity measurements made using dynamic mechanical analysis (DMA) and broadband viscoelastic spectroscopy. We perform nanoindentation measurements at temperatures between 5 and 200°C and compare the results with those obtained from conventional mechanical spectroscopy.
5:15 PM - SS10.8/FF6.8
In Situ Tensile Testing of Nanoimprinted Pt-Based Metallic Glass Rods.
Roman Ehrbar 1 3 , Golden Kumar 2 , Jan Schroers 2 , Ralph Spolenak 3 , Daniel Gianola 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Department of Materials, ETH Zurich, Zurich Switzerland, 2 Mechanical Engineering, Yale University, New Haven, Connecticut, United States
Show AbstractRecent strategies for developing amorphous metals that exhibit appreciable toughness, in addition to high strength, often involve composite geometries with secondary crystalline phases of submicron sizes. The notion that shear bands, which typically lead to catastrophic failure, can be inhibited or distributed in small confined regions suggests a shift in deformation mechanisms with decreasing size and has led to recent research interest in the mechanical behavior of monolithic amorphous metals in small volumes. Yet, many size dependant studies on the deformation mechanism in amorphous metals have been fraught with uncertainty, primarily because of the potentially deleterious effect of the focused ion beam (FIB) used in specimen preparation on mechanical effect. Since the effect of ion bombardment on the mechanical properties of amorphous specimens in the length scale regime of interest has still not been fully resolved, alternative fabrication and nanomechanical testing routes would allow for a clearer intepretation of intrinsic behavior.We demonstrate a method for in situ testing of amorphous Pt57.5Cu14.7Ni5.3P22.5 nanorods produced by a nanoimprinting approach where the amorphous alloy is heated above its glass transition, infiltrated into a nanoporous alumina template, and subsequently quenched. Individual nanorods were harvested and manipulated onto a novel nanotensile testing system to elucidate the mechanical response of nanorods as a function of size. The custom nanomechanical testing system is based on a six-axis nano positioning device combined with a load cell and a stiff linear actuator, which is integrated in a high resolution scanning electron microscope (SEM). We performed tensile tests on amorphous nanorods with diameters ranging from 100 to 200 nm. The full tensile response of these amorphous rods have been measured, and results showing both elastic and plastic behavior, as well as the propensity for shear banding in small volumes, will be presented. We discuss these results in the context of several theories predicting a transition from heterogeneous to homogenous plastic flow with decreasing specimen size.
5:30 PM - SS10.9/FF6.9
Towards a Comprehensive Approach for Modeling the Freeze Casting Process.
Frank Wendler 1 2 , Marcel Huber 2 , Britta Nestler 2 1
1 Institute of Materials and Processes, Karlsruhe University of Applied Sciences, D-76133 Karlsruhe, Baden-Württemberg, Germany, 2 IAM-IZBS, Karlsruhe Institute of Technology (KIT), Karlsruhe, Baden-Württemberg, Germany
Show AbstractIn the freeze casting process, the crystallization kinetics of an aqueous colloidal solution is exploited to produce filigree porous structures with customizable properties, applicable to a broad variety of ceramic materials with porosities between 10 and 90 vol. %. In the last ten years, great research efforts have been undertaken to optimize the process for biomedical, catalysis and metal-matrix composite applications, especially with regard to mechanical stability of the sintered end product. The patterning effect is based on the rejection of dispersed ceramic particles of an aqueous colloid by the growing ice front. It leads to the formation of domains of parallel lamellae, which can be related to the orientations of the growing crystals.In order to predict quantitatively the influence of the macroscopic and microscopic process variables (freezing conditions, solid fraction, particle size, colloidal interaction potential) on the resulting microstructure, we treat the free boundary problem by adapting a multi phase-field of Allen-Cahn type [1]. Here, a set of order parameters Φ=(Φ1, ..., ΦN) is used to describe the spatio-temporal evolution of the constitutive phases ice, colloidal particles and water, based on a thermodynamic free energy formulation. As a major subsystem, we first concentrate on the crystallization of ice in pure water, for which an expansion of the interfacial free energy and kinetic anisotropy in terms of real spherical harmonics is necessary to produce the observed growth shapes.To be able to run simulations of representative volume elements, the complex problem is separately treated at the particle – ice front scale (< 100 μm) and at a large scale (~ 1000 μm), where the particle density enters as a local solute concentration. For the former case the particles are spatially resolved, and we briefly show how the model parameters (interface tensions, higher order potential, interface width) represent the capillary properties of the colloid. Simulations results show the onset of ice front instability, which are compared to earlier theoretical analysis [2], and the interaction of particles at ice-water triple junctions. For the large scale simulations in 2D and 3D, we first verify the dynamics and morphology evolution in the pure water-ice system with available literature data. Furthermore, for a range of different solid fractions and undercooling temperatures, we compare the simulation data with recent experiments with Al2O3 particles.[1] B. Nestler, F. Wendler, M. Selzer, B. Stinner and H. Garcke, Phys. Rev. E 78 (2008) 011604-1. [2] S.S.L. Peppin, J.S. Wettlaufer and M.G. Worster, Phys. Rev. Lett. 100 (2008) 238301-1.
Symposium Organizers
Peter Anderson Ohio State University
Neville Moody Sandia National Laboratories
David Bahr Washington State University
Ralph Spolenak ETH Zurich
SS15: Poster Session: Properties and Processes at the Nanoscale II
Session Chairs
Peter Anderson
Ralph Spolenak
Thursday PM, December 01, 2011
Exhibition Hall C (Hynes)
SS11: Characterization Techniques and Methods
Session Chairs
Maarten de Boer
Timothy Renk
Thursday PM, December 01, 2011
Constitution A (Sheraton)
9:30 AM - SS11.1
Mechanical Properties Mapping: Fact and Fiction.
Warren Oliver 1 , Kermit Parks 1
1 , Nanomechanics, Inc., Oak Ridge, Tennessee, United States
Show AbstractThe application of the CSM technique to the generation of stiffness maps will be discussed. A number of applications of this technique will be shown. A few years ago a technique was proposed to allow stiffness maps to be converted to modulus maps. The stringent experimental requirements associated with this conversion technique render it inaccurate, insensitive and virtually useless. New techniques for the generation of true mechanical properties maps in reasonable periods of time will be introduced and demonstrated.
9:45 AM - SS11.2
Measuring Residual Stress on the Nanometer Scale - Novel Tools for Fundamental and Applied Research.
Ralf Wehrspohn 1 2 , Michael Krause 1 , Clemens Schriever 2 , Sebastian Brand 1
1 , Fraunhofer IWM, Halle Germany, 2 , Martin-Luther-Universität Halle-Wittenberg, Halle Germany
Show AbstractKnowledge about stress and strain at the nanometer scale is essential for tailoring the mechanical and electronic properties of materials. The effects associated with residual stresses are often very divergent, ranging from nucleation of dislocations and cracks to enhancement of carrier mobility. To date, the number of techniques used for stress measurements is very large. However, none of them is without shortcomings. Thus, there is still a strong demand for novel techniques which can provide a means of determining local strains with high spatial resolution on the one hand and high strain sensitivity on the other hand.In the present paper, we will introduce novel techniques capable for strain determination on strained, nano-sized thin films or complex microsystems. In the first stage of the paper, we will summarize the present state of development for a variety of competing strain measurement techniques, including X-Ray Diffraction, Transmission Electron Microscopy (TEM), Raman Spectroscopy, FIB Hole Drilling and Stress Photonics. Afterwards we will demonstrate the potential of second harmonic spectroscopy for strain determination in nanometer sized thin films. Here, the sources of second harmonic generation will be discussed and their relation to structural symmetry will be shown. In an illustrative application, its potential for elastic strain determination will be highlighted. As an alternative non-destructive approach to strained thin films, we will introduce Gigahertz- Scanning Acoustic Microscopy (GHz-SAM). In the third stage of the presentation, strain determination utilizing electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) will be discussed. One of the most attractive features of this technique is its unique capability to perform rapid, automated diffraction analysis of crystalline materials with excellent spatial resolution on the scale of several tens of nanometers. However, elastic strain determination is not a standard routine yet. We will show how sophisticated image processing routines can be used in order to determine small shifts of features within backscatter Kikuchi patterns (BKP) of strained sample positions with respect to an unstrained reference position and thus can be taken to calculate eight of the nine degrees of freedom in an arbitrary strain and rotation. Here, particular emphasis will be paid to appropriate sampling strategies, immanent sources of errors and artefact-free sample preparation. The issue mentioned last will be discussed with respect to strain relaxation, defect formation and efficiency by Finite Element Modelling (FEM), Molecular Dynamics Simulation (MD) and HR-TEM. Results of strain measurement in silicon devices using EBSD will be compared to reference measurements obtained by standard methods like HR-XRD and Raman spectroscopy.
10:00 AM - SS11.3
Fatigue Damage and Size Effects in Very High Cycle Fatigue of Cu Films.
Clemens Trinks 1 , Kodanda Mangipudi 1 , Anja Westphal 1 , Björn Pfeiffer 1 , Cynthia Volkert 1
1 Georg-August-University of Göttingen, Institute for Materials Physics, Göttingen Germany
Show AbstractThin metal films show completely different fatigue behavior than bulk metals. The films have longer fatigue lives and instead of extrusions and complex dislocation structures, they form interface cracks and isolated dislocations during fatigue. These observations indicate a reduction in accumulated plastic strain in the films, which is likely a manifestation of their increased strength. In order to investigate thin film fatigue under conditions comparable to those present in sensors and microelectronic devices, small strain amplitudes and large cycle numbers must be achieved. We introduce a new method based on free resonance of a film-coated cantilever in an AFM, which allows fatigue testing of high quality films with thicknesses down to 50 nm and to cycle numbers as high as 1012. A gradient in strain amplitude is imposed along the cantilever during the fatigue testing, so that a single test suffices to provide data for total strain amplitudes from zero up to a maximum of 0.2 %. The evolution of fatigue damage in Cu films with thicknesses between 50 and 200 nm will be reported. In particular, we observe a new damage mechanism characterized by nanometer size hillocks along the twin boundaries. It is most prevalent in the thinnest films but is also observed in thicker films. Whether this new damage form is favored by the higher frequencies and smaller amplitudes relative to previous tests, or has to do with possible local oxidation of the films, is not yet clear. We expect to clarify this through the use of AFM and TEM and to obtain a clearer understanding of the dominant deformation mechanisms under very high cycle fatigue conditions.
10:15 AM - SS11.4
In situ Force Measurements Made Easy: Characterizing Microstructures in the SEM.
Andrew Smith 1 , Stephan Kleindiek 1 , Klaus Schock 1 , Svien Niese 2
1 , Kleindiek Nanotechnik, Reutlingen Germany, 2 , Fraunhofer IZFP, Dresden Germany
Show AbstractUp to now, performing force measurements inside a SEM chamber requiredthe use of AFM cantilevers, laser optics, force transducers or othersophisticated electronic solutions. Combining the flexibility of theMM3A-EM micromanipulator with a simple, yet elegant solution fordetermining the force applied to a sample with a tip - virtually anytip will do - yields a quick and reliable way of performing materialcharacterization under SEM conditions.The Spring Table is a small platform with parallel beams to which thesample is mounted. The platform with the sample is set onto the samplestage in the SEM. Using an MM3A-EM micromanipulator, the sample isdeflected while recording a series of images. After the series iscomplete, the images are fed into the Force Measurement Analysissoftware. The software uses image recognition algorithms to 'follow' afeature on the substrate as well as a feature on the structure beingdeflected from one frame to the next. Since the sample is mounted on amoveable beams, applying force with the micromanipulator causes ashift of the entire sample. If the structure to which the force isbeing applied is soft, the structure will be deflected more. Thedifference in deflection from each frame to the next is plottedagainst the deflection of the substrate yielding force distancecurves.This method utilizes the SEM's high power of resolution to determinethe deflections, eliminating the need for additional expensive andcomplicated electronics.
10:30 AM - SS11.5
Imaging Stress Induced Domain Movement in Barium Titanate by In Situ Transmission Electron Microscopy.
Liam Spillane 1 , David McComb 1 , Finn Giuliani 1
1 Department of Materials, Imperial College London, London United Kingdom
Show AbstractThere has been much previous work to image ferroelectric domains by a variety of techniques and in some cases after permanent deformation such as an indent in the surface. However, in these cases only the surface domain structure has been imaged[1]. Here we have been able to image in cross-section and in situ, the effect of stress on the domain structure in Barium Titanate. In this work thin electron transparent samples of Barium Titanate were produced by focused ion beam milling, these samples were imaged along the [100] direction. Imaging was either carried out by bright field TEM or STEM at 300 kV, while loads between 15-150 micro newtons were applied in the [010] by a Hysitron picoindenter operating with a wedge indenter. During initial loading, domains were seen to nucleate within the original domain structure. These continued to spread within the elastic and plastic zones as loading progressed and were aligned along the previously reported <110> directions. However, the original domain boundary could be observed to be curved away from the applied stress. Furthermore, on the edge of the elastic zone, newly formed domains were seen to align parallel to the radial stress field, clearly moving away from the often observed <110> directions. After unloading, the vast majority of the domain structure recovered to its original state. Furthermore, due the stability of the experimental set up, low loss EELS has been used to map the electron density around the point of deformation as load is increased and will be compared with the expected hydrostatic stress field. [1] Scholz T,et al , APPL PHYS LETT, 2007, 062903 Vol:91,
10:45 AM - SS11.6
Quantifying Size Effects in Polysilicon Using an In Situ on-Chip Test Platform.
Mohamed Saleh 1 , Siddharth Hazra 1 , Frank DelRio 2 , Jack Beuth 1 , Maarten de Boer 1
1 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Nanomechanical Properties, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractAccurate measurement of polysilicon strength at small scales is of critical importance in the design of reliable MEMS and NEMS devices. However, polysilicon is brittle, with a stochastic distribution of strength, thought to be linked to processing-induced crack-like flaws at grain boundaries on sidewall surfaces. This leads to a size effect in polysilicon strength at the micron to nanometer scale, where smaller specimens exhibit significantly larger average strengths. In this research, a newly-developed on-chip test platform is used to test polysilicon tensile specimens having a 70 micron gage length, as well as smaller-scale tensile and notched specimens. Results from the 70 micron tensile tests are used to fit a three-parameter Weibull probability distribution accurately, with a threshold (lower bound) stress of 2.0 GPa. Strengths from the tests on smaller-scale specimens are then compared to predictions from the Weibull data. Preliminary data shows that mean strength increases from 2.5 GPa to 5.0 GPa as the stressed surface area decreases from by a factor of 35. In-situ Raman spectroscopy enables direct confirmation of local stress levels with ~200 nm resolution. This information allows MEMS and NEMS engineers to design safely while maximizing performance in devices with stress concentrations. Sandia ia a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
SS12: Nanoparticles, Nanocomposites, and Nanocrystalline Materials
Session Chairs
Maarten de Boer
Timothy Renk
Thursday PM, December 01, 2011
Constitution A (Sheraton)
11:30 AM - SS12.1
Nanomechanical Characterization of Nanoparticle Thin Films.
Gang Feng 1 , Majemite Dafinone 2 , Teresa Brugarolas 2 , Kwadwo Tettey 2 , Daeyeon Lee 2
1 Mechanical Engineering, Villanova University, Villanova, Pennsylvania, United States, 2 Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractNanoparticle thin films (NTFs), i.e. thin films composed of nanoparticles, exhibit synergistic properties, making them useful for numerous advanced applications. However, many NTFs have a poor resistance to mechanical loading and abrasion, presenting a major bottleneck to their widespread use and commercialization. In this study, we investigate the possibility of using atomic layer deposition (ALD) at a relatively low temperature to improve the mechanical durability of TiO2/SiO2 nanoparticle layer-by-layer (LbL) films on organic and inorganic substrates. The small-scale mechanical properties of the NTFs are characterized through nanoindentation. Due to the pores between nanoparticles, the NTFs can be considered as nanoporous materials. We demonstrate that nanoindentation would overestimate the properties of nanoporous materials due to the indentation-induced densification. By considering the densification effect in Johnson’s original expanding cavity model, a new analytical model is proposed for the indentation of nanoporous materials, which is compared with and verified by finite element analysis. The model is applied to analyze the nanoindentation results for the NTFs. Furthermore, because relatively large indentations are needed to minimize the inhomogeneity and surface-roughness effects for submicron-thick NTFs, the substrate effect is very significant in the nanoindentation data. Therefore, a recent thin-film-indentation-analysis method is used to analyze the nanoindentation measurements to correct for the substrate effect. Thus, after correcting for the substrate and densification effects, we are able to quantitatively characterize the intrinsic properties of nanoparticle thin films, and we demonstrate that the mechanical durability of TiO2/SiO2 nanoparticle thin films can be drastically improved using ALD. The strengthening mechanisms of the ALD process on NTFs are discussed. The major mechanism is believed to be the increase of interparticle interaction due to the ALD.
11:45 AM - SS12.2
Stress Transfer at Interfaces in Nanocomposites.
Robert Young 1 , Lei Gong 1 , Ian Kinloch 1 , Tamer Wafy 1 , Konstantin Novoselov 2
1 School of Materials, University of Manchester, Manchester United Kingdom, 2 School of Physics & Astronomy, University of Manchester, Manchester United Kingdom
Show AbstractEfficient interfacial stress transfer in nanocarbon-based nanocomposites, such as those reinforced by nanotubes or graphene, is essential for the nanomaterials to realize their potential as high-performance composites. The types of interface that are important in such polymer-matrix nanocomposites are: (1) the interface between the polymer matrix and the nano-reinforcement, (2) internal interfaces between individual walls in multi-walled carbon nanotubes, (3) internal interfaces between the atomic carbon layers in multi-layer graphene. Carbon nanotubes and graphene both have strong, well-defined Raman spectra and it is well established that the Raman bands shift when these nanomaterials are subjected to stress. The presentation will give a detailed account of the use of Raman spectroscopy to follow stress transfer in nanocomposites reinforced with both nanotubes and graphene. It will be demonstrated that the technique has the ability to distinguish between stress transfer between the polymer matrix and outer interface of the reinforcement and stress transfer between the constituent layers of multi-layer nanostructures. It will be shown that failure of interfacial stress transfer can be observed and the efficiency of stress transfer may be evaluated at each interface. The findings of these investigations will have important implications for the future design of nanocarbon-based nanocomposites materials.
12:00 PM - SS12.3
Micromechanisms of Plastic Deformation in Amorphous Metals Identified Using Colloidal Glasses as Experimental Model Materials.
Katharine Jensen 1 , David Weitz 1 2 , Frans Spaepen 2
1 Department of Physics, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractModels of deformation of metallic glasses postulate "shear defects" or "shear transformation zones" (STZs) that mediate plastic deformation in amorphous materials just as dislocations do in crystalline materials. These zones, however, are difficult to observe directly in the amorphous structure. Colloidal glasses provide a unique experimental model system with which to study the structure, defects, and dynamics of a generic amorphous material. We quench the sample – consisting of several billion 1.5-micron-diameter silica particles – into a glassy state by centrifugation and use a confocal microscope to image the 3D, real-time trajectories of a subset of roughly 100,000 particles during linear shear at varying strain rates.From these data, we directly observe STZs as localized high-strain regions, and correlate the development of these regions with local properties of the glass. Because this is a hard-sphere system, these properties must be a function of the density. We therefore investigate local atomic volume by the Voronoi volume as well as the free volume of both individual particles and connected clusters of particles. The first results indicate that the free volume of clusters on the order of 50 particles is a useful correlator. Furthermore, we observe an increase in cluster free volume leading up to a shear transformation event, and a subsequent drop as the particles undergo an irreversible local shear. The removal of the free volume from the cluster assures the irreversibility of the local transformation.
12:15 PM - SS12.4
The Experimental and Theoretical Analysis of Characterizing Nanoparticles through Nanoindentation.
William Albert 1 , Gang Feng 1
1 Mechanical Engineering, Villanova University, Villanova, Pennsylvania, United States
Show AbstractSpherical nanoparticles have been widely used in various applications, such as nanocomposite fillers, multifunctional coatings, and drug delivery applications. Numerous studies have demonstrated that the mechanical properties of materials can vary significantly as the size of the materials decrease into the nanoscale. Therefore, it is anticipated that the mechanical properties of nanoparticles would be size-dependent. However, the mechanical characterization of an individual nanoparticle is very challenging, and a comprehensive quantitative characterization method is still not available.The purpose of this study is to develop such a method based on single nanoparticle nanoindentation. In order to analyze the load-displacement-stiffness data for the nanoindentation of nanoparticles, we have developed a closed-form analytical solution on the basis of large-deformation contact mechanics. The classic Hertzian contact mechanics solution was modified by considering the finite size of the nanoparticle. Two contacts in series are considered: (1) the indenter/particle contact, and (2) the particle/substrate contact. The solution is general for purely elastic and elastoplastic indentations of nanospheres, which is verified by finite element analysis (FEA).The method has been applied to analyze the experimental data for ~50nm-diameter gold and ~560nm silica nanospheres. The hardnesses of the nanoparticles are determined. We found that the nanoindentation deformation of gold particle is dominated by plasticity, whereas the deformation of silica particle would change from purely elastic to elastoplastic with increasing the indentation load. The indentation results and the associated analytical analysis match the FEA results, indicating that this analytical solution is applicable to the soft gold and hard silica particles used in this study.
12:30 PM - SS12.5
Study of Mechanical Properties of Nanocrystalline Metal Thin Film Produced by High-Power Ion Beam Ablation on the RHEPP-1 Facility.
Timothy Renk 1 , S. Prasad 1 , T. Buchheit 1 , H. Padilla 1
1 Beam Applications and Initiatives, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractMetal thin films with fine-grain microstructure (~ 5-10 nm grain size) are known to have mechanical properties different from films composed of larger-grain material. We have studied the mechanical and tribological behavior of such films produced by ablation of one or more metal targets by intense pulsed ion beams on the Repetitive High Energy Pulsed Power (RHEPP-1) facility at Sandia National Laboratories. While the energetics of such ablation are similar to Pulsed Laser Deposition (PLD), the RHEPP-1 beam strength (800 keV nitrogen ions are up to 10 J/cm2) results in target ablation areas of 30 cm2, and deposition rates up to 2-20 nm/pulse over tens of cm2 depositional substrate area. We have used this deposition technique to form single-element metal films (e.g. Mo, Rh, Ni), multi-layer films composed of alternating elements (e.g. Mo/Ti, Mo/Ir), and bi-metallic films (e.g. Rh/V) formed using a composite ablation target instead of a single or alternating targets. Films have been formed with the substrate at room temperature (RT) as well as elevated temperatures of up to 380°C. The films have been characterized by nanoindentation. Friction measurements were made against a Si3N4 counterface in a ball-on-flat configuration. Films of Mo as thin as 50 nm show fine-grain structure (~ 5-10 nm grain size), exhibit hardness three times higher than sintered Mo bulk source material, and also show low friction coefficients (0.2) over thousands of linear tribology cycles. The wear durability and friction coefficient differ significantly from that of the sintered target material subjected to the same tribological testing. Grain size as examined by FIB/XTEM is observed to remain small after the tribological testing. We suspect that one factor contributing to observed wear durability is the BCC grain structure stability of the fine-grain Mo. This is in contrast to FCC films such as Rh and Ni, which evolve to much higher friction coefficients under tribological stress. We have experimented with additions of immiscible metals such as V to the Rh layer, with both RT and 290°C substrate heating. The Rh/V RT film showed further reduction in friction coefficient below the level of the pure Mo films (~0.1 for 10,000 linear cycles), whereas the heated film shows a much higher friction coefficient. Investigation of these results is underway, and latest results will be presented. In addition, multi-layer films with alternating layers such as Mo/Ir show enhanced hardness compared to the pure Mo films, although their tribological properties have not yet been studied. * Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
12:45 PM - SS12.6
Isolating the Relationship between Grain Size and Strength in Nanocrystalline Alloys.
Timothy Rupert 1 2 , Christopher Schuh 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical and Aerospace Engineering, UC Irvine, Irvine, California, United States
Show AbstractNanocrystalline alloys with controllable grain sizes and excellent thermal stability have recently become available due to improvements in processing science. While these alloys are commonly used for the study of mechanical properties, their dependence of composition on grain size and highly nonequilibrium grain boundary structures make it difficult to isolate the effects of grain size. This talk addresses the impact of alloying additions and local grain boundary structure on nanocrystalline strength, using results from recent experimental work. Armed with descriptions of these secondary strengthening mechanisms, the true relationship between crystallite size and strength in nanocrystalline materials is obtained. Finally, our results are compared to existing theoretical models to gain insight into the physics of nanocrystalline plasticity.
SS13: Modeling and Simulation of Nanomaterials
Session Chairs
Thursday PM, December 01, 2011
Constitution A (Sheraton)
2:30 PM - **SS13.1
Coupling Chemistry and Mechanics to Understand the Influence of Environments on Material Properties.
Yue Qi 1
1 Chemical Sciences and Materials Systems Lab, General Motors R&D, Warren, Michigan, United States
Show AbstractFew materials deform in vacuum. Coupling chemistry and mechanics becomes especially important for energy storage and nano structured materials. The electrode materials in Li-ion batteries are in direct contact with electrolyte, subject to lithiation and delithiation cycles, and eventually fracture due to diffusion induced stress. We used first principle thermodynamics to predict how materials’ mechanical properties vary with chemistry. We have shown that many electrode materials change their elastic properties as a function of Li concentration. In situ strain and stress measurement further confirmed Li concentration dependent material properties. It is even more complex when electrode materials fracture in Li reservoirs, as their fracture properties shall be considered as a function of Li chemical potential (or the voltage of the battery cell), in fast Li diffusion limit. For nano-structured materials, the surface to volume ratio increases dramatically, thus the surface reactions can significantly alter the deformation mechanisms. In another example, we used molecular dynamics (MD) simulations in conjunction with reactive force field (ReaxFF) to capture the deformation and chemical reactions simultaneously. The surface oxidation changed the modulus, yield stress, even fracture process of an Al nanowire.
3:00 PM - SS13.2
Defects and Transport Processes in Beryllium.
Simon Middleburgh 1 2 , Robin Grimes 1
1 Department of Materials, Imperial College London, London United Kingdom, 2 Materials and Fuel Rod Design, Westinghouse Electric Sweden, Vasteras Sweden
Show AbstractIntrinsic and substitutional defect formation and migration energies for beryllium metal have been predicted via atomic scale computer simulation and are discussed with respect to equilibrium and radiation damage processes. Schottky disorder was found to be the dominant intrinsic defect process, but its high energy implies only a small concentration of beryllium vacancies in the lattice. The Frenkel energy, being higher, means that the intrinsic interstitial concentration will be still orders of magnitude lower. The energy barriers for migration of Be vacancies and interstitials are similar at 0.72 eV and 0.64 eV respectively; both are essentially isotropic processes. Extrinsic defect properties have been calculated for hydrogen, helium, oxygen, iron, aluminium, carbon, magnesium and silicon. For example, helium has a large positive solution energy but preferentially occupies a beryllium vacancy site. Conversely, oxygen has a negative solution energy and is most stable as an interstitial species. Iron has a small solution energy while aluminium and magnesium have high solution energies. The key intermetallics FeBe5 and FeAlBe4 have also been investigated.
3:15 PM - SS13.3
Size Matters for Deformation Twinning in Single Crystals.
Qian Yu 1 , Zhi Wei Shan 2 , Ju Li 3 2 , Evan Ma 4 2
1 , UC Berkeley, Berkeley, California, United States, 2 , 1State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi'an China, 3 , Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 4 , Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractIt has been well established that sample size has a major effect on the apparent strength of single crystals, when the plastic deformation is controlled by dislocation mediated slip. In contrast, for the other major mechanism of plastic deformation, deformation twinning, which is a highly coherent inelastic shearing process that controls the mechanical behaviour of many materials, the sample size effect is much less known. Using micro-compression and in stu nano-compression experiments, we have found that the stress required for deformation twinning increases drastically with decreasing sample size of a titanium alloy single crystal, in a Hall-Petch-like relationship, until the sample size is reduced to one micrometre, below which the deformation twinning is entirely replaced by less correlated, ordinary dislocation plasticity. We developed a ‘stimulated slip’ model to explain the strong size dependence of deformation twinning. The sample size in transition is relatively large and easily accessible in experiments, making the corresponding maximum strength highly relevant for applications.
3:30 PM - SS13.4
Evolution of Residual Strains in Nanocrystalline Metals Studied by Diffraction.
Steven Van Petegem 1 , Julien Zimmermann 1 2 , Helena Van Swygenhoven 1 2
1 , Paul Scherrer Institut, Villigen Switzerland, 2 Institute of Materials, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne Switzerland
Show AbstractIn-situ x-ray diffraction is a valuable tool to investigate the evolving microstructure during deformation. Of particular interest is the evolution of residual lattice strains as a function of plastic strain. During a diffraction experiment one elastic strain component in one direction is determined for a specific grain sub-set only. Due to elastic and plastic anisotropy the different sub-sets will show different behavior during an in-situ deformation experiment, which makes the interpretation not trivial. For instance, for many elastically anisotropic f.c.c. metals undergoing intra-granular slip in uniaxial tension, when measuring either perpendicular or parallel to the loading axis, the usual trends are tensile and compressive shifts in the <200> and <220> diffraction groups, respectively. Using crystal plasticity modeling this behavior is reasonably well understood [1]; it is mainly related the distribution of Schmid factors and the material elastic constants.On the other hand, for nanocrystalline f.c.c. metals the evolution of lattice strain as a function of applied stress is highly debated. Various trends are observed, which are seemingly inconsistent. However, the results are all different from what is expected for the coarse-grained counterparts. This may lead to the conclusion that at the nanoscale intergranular slip is suppressed and grain boundary sliding mechanisms are responsible for the observed mechanical properties [2-4].In this work we present recent results obtained from in-situ mechanical testing of several nanocrystalline metals. In particular we focus on electrodeposited Ni, Ni-20%Fe and Ni-50%Fe. The results are discussed in view of insights obtained from molecular dynamics and quantized crystal plasticity simulations. It is argued that in order to understand the evolution of residual stress in nanocrystalline metals it is not sufficient to consider only the grain orientation distribution (Schmid’s law); other critical factors such as grain size distribution, nature of the grain boundaries, etc should be taken into account as well. As a consequence intra-granular slip may still be present at the nanoscale, even though its diffraction footprint differs from what is observed at larger grain sizes.[1] B. Clausen et al., Acta Mater. 46, 3087 (1998).[2] H. Q. Li et al., Physical Review Letters 101, 015502 (2008).[3] Y. M. Wang et al., Physical Review Letters 105, 215502 (2010).[4] S. Cheng et al., Physical Review Letters 103, 035502 (2009).
3:45 PM - SS13.5
Deformation in Nanocrystalline Ni: Insight Based on Quantized Crystal Plasticity Simulations.
Lin Li 1 , Steven Van Petegem 2 , Helena Van Swygenhoven 2 , Peter Anderson 1
1 Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Materials Science and Simulation, Paul Scherrer Institut, Villigen-PSI Switzerland
Show AbstractThis work provides a new insight into deformation mechanisms in nanocrystalline (NC) Ni by investigating its inter-granular stress evolution with plastic deformation. Recently various in-situ diffraction measurements reveal that NC metals display evolutions in inter-granular stress that are seemingly inconsistent, yet different from coarse-grained counterparts [1-3]. These features are investigated by our Quantized Crystal Plasticity (QCP) simulations [4] in which intra-granular slip events impart more violent inter-granular stress redistributions as grain size decreases to the NC scale. The QCP simulations successfully reproduce the major footprints of our diffraction experiment carried out on electrodeposited NC Ni and further explain the different trends observed for NC metals. Assuming that plastic flow at the grain scale is quantized and the critical stress for slip takes on a spatially nonuniform, asymmetric distribution, the QCP simulations offer an alternative view of NC deformation to hypotheses based on grain boundary sliding, and link macro stress-strain response, residual stress evolution, prior deformation history, grain size, and grain-to-grain distributions in critical strength. [1]H. Q. Li et al., Physical Review Letters 101, 015502 (2008).[2]Y. M. Wang et al., Physical Review Letters 105, 215502 (2010).[3]S. Cheng et al., Physical Review Letters 103, 035502 (2009).[4]L. Li et al., Acta Mater. 57, 812 (2009).
SS14: Stress Evolution and Phase Transformations
Session Chairs
Thursday PM, December 01, 2011
Constitution A (Sheraton)
4:30 PM - **SS14.1
Mechanically-Induced Grain Growth at 4 Kelvin?
Brad Boyce 1 , Henry Padilla 1 , Elizabeth Holm 1 , Corbett Battaile 1 , Stephen Foiles 1 , Eric Homer 1 , Garritt Tucker 1 , Blythe Clark 1 , Justin Brons 2 , Gregory Thompson 2
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractRecrystallization and grain growth are typically considered to be thermally-activated diffusive processes. However, recent observations and simulations suggest that mechanically-induced grain growth of nanocrystalline metals may occur independent of temperature, or even be encouraged at low temperatures. Zhang, Weertman, and Eastman (APL, 2005) observed indentation-induced grain growth in nanocrystalline Cu both at room temperature and at 77 K. At the lower temperature, they observed a stronger propensity for abnormal grain growth, resulting in a small number of very large grains. The possibility of low-temperature mechanically-induced grain growth is also supported by molecular statics simulations which suggest the possibility of grain growth even at 0 K (Sansoz and Dupont, APL, 2006). Our own molecular dynamics simulations of a large survey of different grain boundaries suggest that a significant fraction of these boundaries behave anti-thermally: their mobility actually increases with decreasing temperature. To further examine low-temperature mechanically-induced grain growth, we have built a liquid helium Vickers indenter. We have observed indentation-induced grain growth at 4 K, 77 K, and 293 K in both nanocrystalline and nanotwinned Cu. The nanotwinned Cu showed the highest propensity for mechanical grain growth at all temperatures, which was surprising given that coherent Sigma-3 boundaries possess zero mobility. We will discuss the role of impurity content, crystallographic texture, and boundary character on mechanically-induced boundary motion. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
5:00 PM - SS14.2
In-situ Raman Analysis of Indentation-Induced Phase Transformations in Silicon Thin Films.
Yvonne Gerbig 1 , Chris Michaels 2 , Aaron Forster 3 , Robert Cook 1
1 Ceramics Division, NIST, Gaithersburg, Maryland, United States, 2 Surface and Microanalysis Science, NIST, Gaithersburg, Maryland, United States, 3 Materials and Construction Research Division, NIST, Gaithersburg, Maryland, United States
Show AbstractSilicon (Si) can be transformed to different crystallographic phases through mechanical stress. As Si forms the basic components of most electronic devices and microelectromechanical systems and modification of the Si crystallographic structure is connected to changes in performance-crucial properties, phase transformations of Si have been intensively studied, particular by indentation techniques.However, in conventional indentation experiments, crystallographic changes can be probed only after the completion of the test and hence the exact path of Si phase transformation cannot be determined. In-situ electrical resistance measurements between a conductive probe tip and the indented Si surface can allow indirect observations of phase transformation, as the conductivity of different Si phases may vary from semiconductor to semimetal to metal-like. The unambiguous identification of phases is still very difficult with this method, as multiple phases (sometimes with similar electrical properties) can coexist in the transformation region. In order to directly analyze indentation-induced Si phase transformation, a probing technique able to identify the crystallographic structure of various phases, such as Raman spectroscopy, must be employed. This presentation reports the first direct observation of the phase transformation cycle induced by indentation in Si thin films. The study was conducted on an indentation device especially designed to be coupled with a Raman microscope, which enables the in-situ analysis of strains and phases in the mechanically deformed region under contact loading. During loading, the initial diamond cubic Si-I phase transformed gradually to β-tin Si-II, confirming previous assumptions. Simultaneously, the formation of an additional phase, which was identified as bct-5, was observed. This marks the first experimental evidence of the existence of this phase and its position in the phase transformation sequence of Si. During unloading, a sudden change from the body-centered tetragonal crystal structures of the phases generated during loading to the rhombohedral and subsequently cubic structures of Si-XII and Si-III, respectively, occurred. Furthermore, the transition pressure for the different phases could be determined and found in good agreement with theoretical calculations.
5:15 PM - SS14.3
The Influence of Film Thickness on the Development of Phase-Transformed α-Tantalum Microstructure.
Markus Chmielus 1 , Elizabeth Ellis 2 , Shefford Baker 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Theoretical and Applied Mechanics, Cornell University, Ithaca, New York, United States
Show AbstractThe phase transformation from the metastable β-phase to the stable α-phase in tantalum thin films has been shown to be very sensitive to the oxygen content. Models for the phase transformation suggest that the phase transformation should also be sensitive to the film thickness. In this study, we examine the effect of thickness on the α-β phase transformation in tantalum thin films. We report in-situ observations of how the film stress changes during the phase transformation. Phases are identified with x-ray diffraction, and microstructure and surface morphology are examined with electron backscattered diffraction and scanning electron microscopy. We show how the surface morphology and β-tantalum microstructure depend on film thickness, and how the film thickness influences the phase transformation and the final microstructure of α-tantalum. With the help of these experiments, we interpret recently presented mechanisms that describe the phase-transformed α-tantalum microstructure.
SS15: Poster Session: Properties and Processes at the Nanoscale II
Session Chairs
Peter Anderson
Ralph Spolenak
Friday AM, December 02, 2011
Exhibition Hall C (Hynes)
9:00 PM - SS15.1
Dynamic Nanoscale In Situ TEM Tribology.
Aiden Lockwood 1 , Kommunje Anantheshwara 2 , Musuvathi Bobji 2 , Beverley Inkson 1
1 Materials Science and Engineering, University of Sheffield, Sheffield, South Yorkshire, United Kingdom, 2 Mechanical Engineering, Indian Institute of Science, Bangalore, 560012, India
Show AbstractNanotribology, the study of friction, wear and lubrication at the nanoscale is an important area of research; however in practice due to the size scale, requires specifically designed tools to characterize nanoscale contacts. We have developed a TEM triboprobe incorporating an advanced nanopositioner with 3D programmable motion inside a transmission electron microscope (TEM) which allows us to selectively apply multiple reciprocating wear cycles to a nanoscale surface, and observe in real-time dynamical changes and the evolution of wear around a sliding nanocontact.Nanoscale cyclic rubbing of an automotive aluminium-silicon alloy processed by focused ion beam (FIB) reveals dynamical surface fragmentation and the generation of nanoscale debris particles. The nanoparticles undergo complex motion as they interact with the sliding nanocontact. Over hundreds of reciprocating cycles, frictional heating leads to a phase separation of the Ga ions implanted by FIB forming liquid Ga nanodroplets and liquid bridges. The addition of nanoscale debris particles and liquid droplets dramatically change the wear dynamics and transforms a 2-body sliding contact into a complex 4-body solid-liquid system exhibiting time-dependant, non-equilibrium kinetic behaviour.TEM nanotribology opens up new possibilities for the real-time quantification of cyclic friction, wear and dynamic solid–liquid nanomechanics, which will have widespread applications in many areas of nanoscience and nanotechnology.
9:00 PM - SS15.10
Atomic-Scale In Situ Observations of Lattice Dislocations Passing through Twin Boundaries and Dislocation Emitting from Twin Boundaries.
Manling Sui 1 , Yanbo Wang 2
1 , Beijing University of Technology, Beijing China, 2 , Institute of Metal Research, CAS, Shenyang China
Show AbstractThe mechanical properties of nanostructured materials depend to a large extent on the interaction of lattice dislocations with grain boundaries and twin boundaries (TBs). Recent experimental results show that the introduction of nanoscale growth twins to nanostructured materials leads to a combination of ultrahigh strength and high ductility, which are primarily attributed to the roles of TBs serving as strong barriers to dislocation movement and as dislocation emission sources. The interaction between lattice dislocations and TBs has been extensively investigated by many scientists using transmission electron microscopy, model analysis, and molecular dynamics simulations. However, the evidence for the dislocation-TB interaction was only given by the observations of diffraction contrast images and some trace analysis after deformation, and the atomic-level dislocation motion and interaction have not been observed directly. Recent molecular dynamics simulations reveal that TBs can serve both as strong barriers to dislocation movement and as dislocation emission sources. Many experimental results also supported the claim that TBs are similar to conventional grain boundaries to block dislocation motions, but seldom direct experimental evidence has been reported on TBs acting as dislocation sources. In situ transmission electron microscopy tensile experiments were carried out to investigate lattice dislocation and TB interaction as well as TBs serving as dislocation sources in thin film Cu with nanoscale growth twins. Results show that extended dislocations form inside thick twin lamellas and slip toward TBs. The extended dislocations shrink, combine, and redissociate when they pass through TBs, leaving behind detwinning partial dislocations at the TBs. The leading partial and the trailing partial exchanged their order after passing though the TB and that the dissociation width of an extended dislocation decreases when the dislocation approaches the TB. Atomic steps at TBs formed by sessile Frank partial dislocations are beneficial for TBs serving as dislocation sources.
9:00 PM - SS15.11
In Situ TEM Observation of Deforming Silicon Tips with High Bias Voltage.
Tadashi Ishida 1 , Hiroyuki Fujita 1
1 , university of Tokyo, Tokyo Japan
Show AbstractMicro electro mechanical systems (MEMS) is one of the most important technologies to make breakthroughs for the conventional device. This is because MEMS can integrate many components, such as electrical devices, sensors, actuators, into one device. In such technology, properties of silicon at high voltage condition are important because MEMS device usually needs high voltage over 10 V to drive its actuator. We found that the silicon was deformed at the nano scaled contact, when the bias voltage was over 14 V. We developed a special experimental setup combining with MEMS device with opposing tips and transmission electron microscope (TEM), called MEMS-in-TEM. With this setup, nano scale deformation between tips can be visualized with TEM. Silicon opposing tips were brought into contact thanks to MEMS actuators inside TEM specimen chamber with ultra-high vacuum, 5x10-8 Pa. The bias voltage between tips gradually increased from 0 to 14 V. The electrical current through the contact also increased from 0 to 20 μA. During this process, bending of silicon tips was observed by the contrast change in the tip. At 14 volts in bias voltage, the contrast drastically changed and finally it was deformed. The current increased from 20 to 30 μA without changing the bias voltage. In this deformation, one tip decreased in size of 10 nm order and nano-scaled tip grew out from another tip. This deformation completed in 13 seconds and the nanocontact of 30 nm in diameter was formed. After the deformation, tips were separated using MEMS actuator. The formed nano junction showed the liquid-like behavior at the beakage process, the broken corners were quickly rounded to19 nm in radius of curvature.
9:00 PM - SS15.13
Real-Time SERS Monitoring of Plasmonic Hot-Spots in Self-Assembled Gold Nanocrystals.
Abdennour Abbas 1 , Limei Tian 1 , Chang H Lee 1 , Ramesh Kattumenu 1 , Srikanth Singamaneni 1
1 Mechanical Engineering and Materials Science, Washington University, St Louis, Saint Louis, Missouri, United States
Show AbstractThe electric field enhancement through plasmonic coupling is one of the major consequences of self-organized gold nanocrystals. The hot spots generated by neighboring noble-metal nanoparticles have led to a number of applications including chemical and biosensing, sub-wavelength light confinement and waveguiding. Efficient implementation of these properties clearly lies on a better understanding of the generation and dynamic properties of the hot-spots and their relationship to the structural and chemical properties of the nanostructures. In this work, we investigate the generation of the hot spots by real-time monitoring of cysteamine-mediated self-assembly of gold colloidal nanostructures using surface enhanced Raman scattering (SERS) and absorption spectroscopy. The SERS intensity obtained using self-assembled particles is 2 to 5 times higher than that generated by single nanoparticles. This plasmonic coupling-induced enhancement and the corresponding dynamics are found to be closely related not only to the size and shape of the structures but also to the nature and localization of the involved chemical group. The results of this study will certainly help for a better understanding of self-assembly-generated hot spots but also offers new possibilities for the localization of chemical groups on the surface of colloidal metal nanostructures.
9:00 PM - SS15.14
Second Harmonic Generation for Strain Measurement at Buried Silicon Interfaces.
Clemens Schriever 1 , Christian Bohley 1 , Jens Lange 4 , Joerg Schilling 1 , Ralf B. Wehrspohn 2 3
1 Martin-Luther-University Halle-Wittenberg, Centre for Innovation Competence SiLi-nano, Halle Germany, 4 Martin-Luther-University Halle-Wittenberg, Institute of Physics, Workgroup Optics, Halle Germany, 2 Martin-Luther-University Halle-Wittenberg, µMD Group - Institute of Physics, Halle Germany, 3 , Fraunhofer-Institute for Mechanics of Materials, Halle Germany
Show AbstractThe occurrence of interface stresses leading to the creation of dislocations or even cracks can significantly degrade the performance of microelectronic devices.Hence, great efforts are put into techniques to detect such induced strains in silicon [1]. Strain can occur for example by thermal oxidation of silicon for insulation purposes, where the volumetric expansion leads to a distortion of the silicon lattice.Often the strain is not accessible by other methods, because the strained interface is buried between the silicon and the oxide layer respectively. We have investigated the technique of Second Harmonic Generation (SHG) in reflection for the measurement of this buried strain. The advantage of this method is its sensitivity to the crystal symmetry of the material investigated. As silicon is a face centered cubic crystal, it exhibits an inversion symmetry, which in principle cannot generate a second harmonic signal. However, at the interface (e.g. to the oxide) this symmetry is lifted giving rise to a Second Harmonic Signal, which reflects the rotational symmetry of the crystal surface. In the case of an oxidized surface an exponentially decaying strain field is created at the silicon surface, which stretches the crystal parallel to the interface and thus projects the surface symmetry deeper into the crystal. This leads to an additional contribution to the SH signal, which can be related to the interface stress due to the linear dependence between SH enhancement and strain [2]. By this method strain layers with a thickness of few nanometers can be investigated, even if they are enclosed by bulk material.[1] C. Schriever, C. Bohley, and R. B. Wehrspohn, "Strain induced nonlinear optics in silicon" in "Mechanical Stress on the Nanoscale", Wiley VCH, (2011)[2] C. Schriever, C. Bohley, and R. B. Wehrspohn, "Strain dependence of second-harmonic generation in silicon", Opt. Lett., 35, 273-275, (2010)
9:00 PM - SS15.15
Measurement of Stiffness of Cementite Using In Situ TEM.
Young-Jin Chang 1 , Sung-Dae Kim 1 , Dong-Su Ko 1 , Young-Woon Kim 1
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractCementite is one of the most common phases in high-carbon steel. The mechanical properties of the cementite were estimated from the theoretical calculation and the mechanical testing from the lamellar structure with alternating layers of ferrite and cementite. Cementite phase is known to be the hard phase maintaining the high strength in carbon steel. It is required to measure elastic properties with a single sheet to predict the mechanical properties with various configurations, and measurement from a single sheet of cementite has not been done yet. In this study, we measured the mechanical properties from a single sheet of cementite using a nano-probing system combined with nano-load cell at room temperature. Single sheet of cementite lamellar in pearlitic steel was extracted by selective chemical etching and mounted on the stage. Loading force and strain measurement were done from the force sensor from FemtoScience. Both microstructural change and the mechanical properties were able to be acquired from the in-situ nano-force sensing stage. Even with deformation in elastic strain range, relaxation effect was observed when the load was removed from the cantilever bending. From different crystallographic orientation of cementite sheet, stiffness for the elastic constants was evaluated and compared with the theoretical value reported. This research was supported by an appointment to Mid-career Researcher Program (2009-0080290) at the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.
9:00 PM - SS15.16
Temperature Dependent Mechanical Behavior of Si Rich Silicon Nitride and Nano-Scale Thick Metal Film.
Seungmin Hyun 1 , Yun Hwangbo 1 , Hak-Joo Lee 1 , Walter Brown 2
1 Department of Nano-mechanics, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractSilicon nitride and metal films have been extensively used in many electronic applications including semiconductors and Nanoelectromechanical Systems (NEMS). The good chemical resistance and low dielectric property enable silicon nitride films as passivation layers, etching stop layer and dielectric materials for electronic applications. Especially, the silicon nitride film is often used as a form of a membrane with metal film in a part of NEMS device. The intrinsic properties of the silicon nitride membrane and metal films are important for these NEMS applications. In this study, we have investigated the coefficient of thermal expansion, the temperature dependent residual stress and the elastic modulus of free standing silicon nitride membranes using resonance and bulge test systems with different deposition conditions. 160nm thick silicon nitride thin films were deposited on (100) silicon wafers by low-pressure chemical-vapor deposition (LPCVD) using dichlorosilane (SiH2Cl2) and ammonia (NH3) as precursor gases. The free standing silicon nitride was obtained by dry and wet etching methods. The dimension of the free standing silicon nitride is 2mm by 12 mm that is surrounded thick silicon frame. Small variations of 8% in gas ratio of dichlorosilane and ammonia increase residual stress of the free standing silicon nitride from 50MPa to about 120MPa. The modulus of the film also is changed by about 8% with changing in the gaseous ratio. Thermo-mechanical behavior of 30nm and 80 nm thick Al films on the silicon nitride membrane is also investigated. Al films are thermally cycled up to 300oC and stress relaxation behavior of the films is examined at different temperatures. The changes in stress are quite dependent on the thickness of Al films. The effect of multiple thermal cycles on the stress relaxation behavior is further demonstrated.
9:00 PM - SS15.17
Grain Boundary Strengthening in Dilute Nanocrystalline Cu Alloys.
Sezer Ozerinc 1 , Kaiping Tai 2 , Nhon Vo 2 , Robert Averback 2 , Pascal Bellon 2 , Shen Dillon 2 , William King 1 2
1 Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 2 Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States
Show AbstractMolecular dynamics simulations have suggested that the strength of nanocrystalline metals is directly related to their grain boundary energies. In the present work we have tested this prediction by experimentally measuring the strength of a series of dilute, nanocrystalline, immiscible Cu alloys using nanoindentation techniques. Thin films specimens of Cu-Nb, Cu-W, and Cu-Fe, ranging between 0.25 and and 1.0 um were prepared by magnetron sputtering. The nanomechanical properties of the films were subsequently measured as a function of annealing temperatures. All samples exhibited a decrease in hardness with increasing temperature. Characterization of these films by a combination of X-ray Diffraction (XRD) and Scanning Transmission Electron Microscopy (STEM) showed that the softening was not due to grain growth, which was negligibly small in all cases, but rather to a reduction in the concentration of solute atoms dissolved in the grain boundaries. An interesting consequence of these experiments, therefore, is that precipitation does not lead to strengthening in these nanocrystalline alloys, but to softening. The experiments also illustrate that solutes with large atomic volume compared to the Cu matrix are most effective in increasing strength; in the case of Cu-10at.%Nb the strength increased to over 5 GPa, which is more than double that of pure Cu with comparable grain size. The experimental results are compared to MD simulations.
9:00 PM - SS15.18
Nanoparticles Enhanced Solders for High Temperature Reliability.
Omid Mokhtari 1 , Ali Roshanghias 2 , Roya Ashayer 1 , Hiren Kotadia 1 , Amir H. Kokabi 2 , Michael P. Clode 1 , Samjid H. Mannan 1
1 Mechanical Engineering, King's College London, London United Kingdom, 2 Materials Science and Engineering, Sharif University of Technology, Tehran Iran (the Islamic Republic of)
Show AbstractThe reliability of lead-free solders an important issue in the electronic industry. As the creep property of the solder at high temperature is becoming more important and grain size distribution in the solder plays an important role in controlling mechanical properties of the materials, the stagnation of grain growth by a dispersed second phase is very crucial. In this research Silica (SiO2) nanoparticles have been added to the solder as a dispersed second phase to reduce solder creep. In order to prepare this nano-composite solder paste, solder particles, flux, solvent and Silica nanoparticles were mechanically blended and then placed inside an oven to carry out reflow soldering. Reflow soldering is the standard industry process for attaching electronic components to a printed circuit board. It was found that while silica nanoparticles were largely driven out of the solder along with the flux during the reflow, the use of Au coating on the silica particles to make a core-shell structure improved the wetting of the molten solder to the particles and resulted in successful incorporation of the particles. Hot compression tests were performed to investigate the mechanical properties of the nanoparticle-enhanced solder at different temperatures. Also the microstructures and grain sizes of solders have been analysed to observe the pinning effect of nanoparticles inside the solder. Results show how effective the nanoparticles are in limiting grain boundary sliding at different temperatures. Results clearly prove that nanoparticles were highly effective in this respect at room temperature but that the mechanical properties of the solder became indistinguishable from the basic solder without nanoparticles at a temperature of 150 C.
9:00 PM - SS15.19
Interfacial Effects on Local Elastic Properties of Confined Polymers Using Coupled Experiments and Modeling of Nanoindentation.
Supinda Watcharotone 1 , L. Brinson 1 2
1 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractPolymer interfaces in nanocomposites and thin films have been of vast interest because interfaces have a significant effect on nanocomposite properties. While the nanoparticles themselves contribute to the improvement, a more significant contribution comes from the polymer interphase. The interphase is the zone surrounding nanoparticles that is the less mobile, stiffer polymer region due to the physical and chemical interfacial interactions with the nanoparticle surfaces. It has been found, for the last two decades, that chemical interactions at interfaces of confined polymer films on a substrate critically impact thermomechanical properties such as glass transition temperatures. This work, however, shows physical confinement potentially influence mechanical properties such as the elastic modulus. Nanoindentation technique was used to characterize the local elastic moduli of polymer films confined and interacted with certain substrates. The nanoindentation results of the different substrate/film systems that possess different types of polymer films–substrate interactions will be presented.
9:00 PM - SS15.2
Dynamical Deformation of Cerium Oxide Nanoparticles and Clusters: An In Situ TEM Study.
Umananda Bhatta 1 , Aiden Lockwood 1 , Kevin Briston 1 , Guenter Moebus 1 , Beverley Inkson 1
1 Materials Science and Engineering, University of Sheffield, Sheffield United Kingdom
Show AbstractCerium oxide has a fluorite structure and is well known for its high mechanical strength. So in addition to widespread catalytic applications of ceria in automobiles and the energy industry, it is also widely used as a polishing agent. The mechanical strength and deformation of ceria in the form of submicron sized particles and clusters have not been widely studied. Here, individual nano to micro sized cerium oxide nanoparticles/clusters have been deformed inside an electron microscope, enabling the real-time dynamics of deformation to be characterized. Ceria powder (99.9 %, Sigma Aldrich) consisting of < 100 nm nanoparticles was subjected to in-situ nanoindentation and lateral shear using a custom made TEM triboprobe. Real-time imaging of the deformation and fracture of a range of ceria nanoclusters during compression and sliding was recorded on video. The in-situ structural changes of the ceria nanoparticles were characterized and correlated to their load-displacement curves.
9:00 PM - SS15.20
In Situ Strain Mapping of Loaded and Relaxed Polymer–Graphene Oxide Nanocomposites with Nanometer Resolutions.
Minzhen Cai 1 , Hannes Schniepp 1
1 Applied Science, The College of William & Mary, Williamsburg, Virginia, United States
Show AbstractSingle-sheet graphene oxide (GO) can be mass-produced cheaply, has excellent processing properties, and outstanding mechanical properties. It has thus great potential as a toughening and strengthening agent in polymers. Usually, the characterization of these materials is either carried out dynamically and at the macroscopic scale (via traditional stress–strain testing) or at the nanoscale, limited to static imaging of the nanocomposites (via transmission electron microscopy) and their fracture surfaces (via scanning electron microscopy). However, in order to understand, optimize and model these materials most rigorously, it would be pivotal to get access to the local, nanoscale mechanical variables of these systems — such as stress and strain — as a function of the externally applied load. This is a challenging task, since a technique with a combination of nanometer spatial resolution and strong enough contrast between single sheets and the polymer is needed. We use scanning probe techniques in order to visualize individual, nanometer-sized GO sheets that are embedded in polyvinyl alcohol (PVA). Using a built-in straining stage, we are able to track the positions and sizes of individual sheets as a function of the applied external strain. Using this information, we can visualize and quantify both the matrix strain as well as the strain of the embedded GO sheets. This data allows for a very systematic understanding of these composites. We quantified the PVA–GO load transfer and found that, surprisingly, the strain is almost perfectly transferred from the polymer to individual sheets for strains of up to 8%. For larger strains, we observe a stick–slip behavior at the sheet–polymer interface. Based on this data we can predict the macroscopic mechanical properties of these composites; furthermore, existing nano- and multi-scale models of these materials can be and tested and optimized systematically. We envision this approach to be the experimental basis of a systematic design of optimized materials with tailored mechanical properties.
9:00 PM - SS15.21
Reinforcing Copper Alloys by Nanofibrous Precipitate: Part II: Characterization.
Seong-Woong Kim 1 , Si-Young Choi 2 , Sung Hwan Lim 3 , Seung Zeon Han 1
1 Special Alloys Research Group, Korea Institute of Materials Science, Gyeongnam Korea (the Republic of), 2 Materials Characterization and Measurement Group, Korea Institute of Materials Science, Gyeongnam Korea (the Republic of), 3 Department of Advanced Materials Science and Engineering, Kangwon National Univeristy, Gangwon-do Korea (the Republic of)
Show AbstractThe deformation behavior of CNST (Cu-6wt%Ni-1.2wt%Si-0.2wt%Ti) alloy during the tensile test was investigated. The nanofibrous Ni2Si precipitates (Pbnm space group) embedded in Cu matrix were dramatically elongated during the tensile test and thus the aspect ratio of the longitudinal / sectional length of Ni2Si fiber was found to be increased from ~ 100 up to ~ 1000. This superplastic deformation of Ni2Si alloy is firstly found through the current study since the intermetallic compounds have been conventionally known as brittle materials due to the complex crystallographic alignment. This astonishing phenomenon was demystified via advanced electron microscopy technique using aberration-corrected scanning transmission electron microscope and in-situ transmission electron microscope. It was found that the matrix and the precipitate exhibit a strong coherent relationship of {111}Cu//{301}Ni2Si and the interfaces of Cu and the Ni2Si precipitates appear to be zigzagged with the alternate {301} and {001} planes. Based on these results, we proposed the new slip mechanism, even applicable to the intermetallic compound of the complicated structure and composition.
9:00 PM - SS15.22
Stress States in Si Particles of Al-Si Cast Alloy – Microstructure Based Finite Element Simulation and Raman Analysis.
Sudha Joseph 1 , S. Kumar 1
1 Materials Engineering, Indian Institute of Science, Bangalore, Karanataka, India
Show AbstractThe stress states in Si particles depend on the morphology of the particles and the particles become less brittle by Si modification. An attempt has been made in this work to study the effect of Si modification on the stress states of the particle. Such understanding will ultimately valuable for predicting the ductility of the alloy. Microstructure-based FEM is used to simulate the stress states in Si particles and experimentally verified by Raman technique. The program OOF (Object-Oriented Finite element analysis) is used to generate the finite element meshes for real microstructures with different Si morphology. The elastic-plastic response of the Al matrix is obtained from micro-hardness testing and given as an input for the simulation. It is observed that the yield strength of the modified microstructure is higher and stress transferred to the Si particles is lower for the particles having small aspect ratio. Clustering of particles generates more inhomogeneous plastic strain in the matrix. Combination of Electron Back-Scattered Diffraction (EBSD) and frequency shift, polarized micro-Raman technique is applied to determine the stress states in Si particles with {111} orientations. Stress states are measured in the as-received state and under uniaxial compression. The fracture strength of the particle is also estimated from Raman technique. Comparison of finite element calculations and Raman analysis show good agreement.
9:00 PM - SS15.23
Mechanical Properties of High ZT Thermoelectric Bi2Te3 Nanocomposite by Nanoindentation.
Guang Li 1 , Karim Gadelrab 1 , Tewfik Souier 1 , Sergio Santos 1 , Matteo Chiesa 1
1 Laboratory of Energy and Nano-Science (LENS), Masdar Institute of Science and Technology, Abu Dhabi United Arab Emirates
Show AbstractThermoelectric (TE) materials and devices have received increasing attention because of their potential applications in the fields of energy conversion and thermoelectric cooling for electronic devices. TE materials are subject to cyclic temperature gradients that may induce thermal stresses in the material. Thus a TE material should be mechanically strong enough to withstand these conditions. Recently nanostructured TE material made by ball milling and hot pressing raised much attention for their exceptional thermoelectric performance and feasibility of mass production. Understanding the mechanical properties of these materials is essential to ensure reliable performance of TE devices during service.We conduct nanoindentation experiments with a Berkovich indenter on nanostructured TE bismuth telluride (Bi2Te3) fabricated by the aforementioned method where the Oliver-Pharr (O-P) analytical solution was employed to determine the Young’s modulus of the sample. The obtained Young’s modulus is lower than Bi2Te3 bulk nominal value.TE Bi2Te3 is a very ductile material. Atomic force microscopy (AFM) scans show significant pile up in the remaining indents. Due to the uncertainty in the contact area, finite element (FE) simulation of the nanoindentation process is also carried out. AFM is used to scan the indenter and acquire the real tip geometry for the generation of the rigid indenter for FE simulation. The numerical unloading force curve from simulation is compared to the experimental ones and accordingly the Young’s modulus and yield strength of the material is estimated. The results from the numerical assisted framework and the O-P method show good agreement.
9:00 PM - SS15.24
Effect of Van der Waals Interaction Strength and Nanocluster Size on the Dynamical and Mechanical Properties of 1,4-cis-polybutadiene Melts.
Canan Atilgan 1 , Ibrahim Inanc 1 , Ali Rana Atilgan 1
1 Faculty of Engineering and Natural Science, Sabanci University, Istanbul Turkey
Show AbstractUsing molecular dynamics simulations, we have investigated the effect of embedding nanoclusters of radius 3-7 Å on the dynamical and mechanical properties of 1,4-cis-polybutadiene melts. To see the effect of polymer-nanocluster interaction strength on the bulk modulus, the van der Waals (vdw) interaction between the polymer chain and nanocluster have been varied from weak to very stong while keeping polymer-polymer and nanocluster-nanocluster interactions constant. The modulus depends on the interaction strength, but not on nanocluster size. Residence time of chains on the surface of the nanocluster (τesc) has an increasing trend that reaches to a plateau as the vdw interaction strength is increased. τesc also doubles from 100 ps to 200 ps as the nanocluster size is increased from 3 to 7 Å. Our findings give clues on how the properties of polymeric materials may be controlled by nanoparticles of different chemistry and size.
9:00 PM - SS15.26
Micromechanisms of Anelastic Deformation and Yield in a Hard-Sphere Colloidal Glass.
Nobutomo Nakamura 1 , Katharine Jensen 2 , David Weitz 1 2 , Frans Spaepen 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Physics, Harvard University, Cambridge, Massachusetts, United States
Show AbstractIn a colloidal suspension of hard-sphere particles, depending on their volume fraction, crystalline, liquid or amorphous structures form depending similar to those found in atomic systems. The particles are large enough (~1μm) to be observed by optical microscopy, and their trajectories during deformation can be fully tracked in three dimensions. Such experiments, therefore, give us unique insight into the deformation mechanisms in metallic glasses. In this paper we report results on the non-affine local deformation during straining, which allows identification of the local contributions to elastic and anelastic deformation, as well as the onset of plastic deformation (i.e., yield).The shear deformation was applied cyclically with increasing strains up to 2.5%. The local affine strain tensor as well as a non-affine parameter were calculated for all particles from changes in their nearest neighbor environments. The observed strain field was highly non-uniform. After a macroscopic strain of 2.5%, non-reversible local strains were observed upon cycling, indicative of the yield point. The average value of the non-affine parameter above yield strain was larger than that below, indicating that plastic deformation was more non-affine. Similar behavior was observed also microscopically: the residual strain appeared in regions in which the nonaffine parameter was large. The anelastic part of the reversible strain can be identified from both the affinity parameter and direct tracking of the particles.
9:00 PM - SS15.27
Mechanism for Significant Increase in Poisson's Ratio of Nanocrystalline Diamond Thin Films Studied by Ab Initio Calculations and Micromechanics Calculations.
Kenichi Tanigaki 1 , Hirotsugu Ogi 1 , Koichi Kusakabe 1 , Nobutomo Nakamura 1 , Masahiko Hirao 1
1 Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
Show AbstractNanocrystalline diamond (NCD) thin films are deposited by the chemical-vapor-deposition method by adding a small amount of nitrogen gas in methane and hydrogen gases. The increase in the nitrogen gas concentration decreases the average grain size and smoothes the film surface. They are candidate materials for high-efficiency acoustic and electronic devices. However, incorporated nitrogen gas generates non-sp3 bonded region, deteriorating attractive mechanical properties of diamond. Recently we discovered that NCD thin films show unusual elastic property using resonant ultrasound spectroscopy and picosecond laser ultrasound method; Young’s modulus and the shear modulus decrease by about 20% by incorporating nitrogen gas, but Poisson’s ratio significantly increases by more than 150% as the grain size decreases. In this study, we clarify the mechanism of the unusual elastic behavior in NCD films using ab-initio calculation and micromechanics modeling. We propose diamond structures including stacking faults as candidate atomic-scale model, where Poisson’s ratio significantly increases. The local density of states indicate that (100) and (111) stacking-fault structures exhibit non-sp3 bonded region. Their elastic constants are determined from changes in the total energy by applying strains using ab-initio calculations based on density functional theory. Reflecting weakened interlayer bonds at the stacking faults, the shear modulus decreases. We find that aggregates of these structures can explain large Poisson’s ratio as well as slightly smaller Young’s and the shear modulus. Especially, (100) and (111) stacking-fault structures show significantly larger Poisson’s ratio.For furthermore investigation on the intrinsic mechanism of enhancement of Poisson’s ratio, we investigate Poisson’s ratio of composite materials assuming various inclusions, including the stacking fault structures above, in the diamond matrix using micromechanics calculations. As a result, there is no correlation between Poisson’s ratio of inclusions and that of aggregates. Instead, we reveal that the decrease of the out-of-plane shear modulus in the local planar regions is responsible for the significant increase in Poisson’s ratio.
9:00 PM - SS15.28
Nanoscale Mechanics of Tribologically Sheared Nanocrystalline Iron Systems with Grain Level Roughness.
Pedro A. Romero 1 , Tommi Jaervi 1 , Michael Moseler 1
1 Mechanics of Materials, Fraunhofer Institute, Freiburg Germany
Show AbstractIron is one of the most important industrial materials to our technological society. Different iron based technologies require a deeper understanding of the mechanisms at the nanoscale dictating friction and wear in order to improve product performance and efficiency. However, large scale simulations of nanocrystalline iron systems have not been performed to date due to the high computational cost of accurate interatomic potentials for nanocrystalline iron materials. Here, we report results from large scale simulations of nanocrystalline iron encompassing several millions of atoms. Controlled pressure and controlled displacement simulations will expose different nanomechanisms dictating friction and wear in nanocrystalline iron composed of hundreds of nanograins. The model which includes a barostat and a thermostat in order to mimic an ambient setting captures the plasticity induced heating at the surface grains. Many aspects of the evolution of plastic deformation are captured such as the nucleation and arrest of dislocations at grain boundaries, grain elongation, grain rotation, grain clustering, grain boundary growth, and glide planes through several grains and grain boundaries simultaneously. Experiments have shown that a reduction in frictional resistance and wear occurs some time after the initiation of sliding between polycrystalline systems. Our simulations capture mechanisms which support this finding, namely surface grain softening, melting and flattening. Experiments have also shown the creation of nanograins (~50nm) when microcrystalline systems are tribologically sheared. Our simulations show that the opposite trend is also possible where systems composed of small iron nanograins (~5-10nm) result in grain agglomeration and enlargement when the systems is tribologically sheared at surfaces with nanograin size roughness. In addition, we present atomic level measures of frictional resistance and explain them based on the nanomechanisms revealed by our model for tribologically sheared nanocrystalline iron.
9:00 PM - SS15.3
Effects of Surface Compliance and Relaxation on Frictional Properties of Few-Layer Graphene.
Alex Smolyanitsky 1 , J. Killgore 1 , Vinod Tewary 1
1 Materials Reliability Division, National Institute of Standards and Technology, Boulder, Colorado, United States
Show AbstractAs device feature dimensions decrease toward the nanoscale, understanding contact mechanics and tribology at an atomic level becomes crucial. The authors of (Lee et al., Science, 2010) recently used atomic force microscopy (AFM) to study the frictional characteristics of atomically thin sheets and demonstrated the need for comprehensive atomistic models of mechanical contacts at the nanoscale.We describe the results of molecular dynamics (MD) simulations of an AFM tip on locally suspended few-layer graphene, with the number of layers ranging from one to four. Our model consists of a few-layer free-standing graphene sample and a capped 5 × 5 single wall carbon nanotube as the AFM scanning tip. A closed-loop feedback control was used to maintain a constant tip-sample contact force. The covalent bonding in the system is described by the appropriately parametrized Tersoff-Brenner bond-order potential, and the van der Waals forces are modeled by a pairwise Lennard-Jones potential, parametrized to correctly reproduce the interlayer cohesion in graphite. The simulations were performed for a variety of scanning rates and temperatures, including room temperature. The model is sufficiently general to be utilized for variety of surfaces and tip materials. We study the effects of surface compliance and temperature-dependent effective surface relaxation, as well as their interplay, on the amount of friction observed. In particular, we demonstrate that the reduction of friction with increasing number of surface layers reported in (Lee et al., Science, 2010) is mainly due to reduced local surface deflection under the scanning tip. If the scanning rate is sufficiently high, the effects of surface relaxation at a given temperature can affect the frictional characteristics of the contact.
9:00 PM - SS15.31
Creep Mechanisms and Temperature Dependent Entropic Effect in Nanocrystal.
Yunjiang Wang 1 , Akio Ishii 1 , Shigenobu Ogata 1
1 Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka Japan
Show AbstractCreep mechanism-map has been well established in conventional coarse-grained materials several decades ago[1], but the deformation mechanisms of nanostructured materials has not been totally understood yet. Here we used molecular dynamics analysis to propose a new creep-map for nanocrystalline copper at elevated temperature. With increasing stress, we found a Coble (grain boundary (GB) diffusion), GB sliding, and dislocation nucleation competing creep in nanocrsytal based on the derived (n, P) values, where n is the stress exponent, and P is the inverse grain size exponent. The calculated stress and grain size exponents of (n ≈1; P ≈3), (n ≈2; P≈ 3), and (n ≈4; P ≈1.6) for different mechanisms agree quantitatively with recent experiments. The finding of grain size dependence of dislocation creep is in contrast with coarse-grained materials, where power-law creep is grain size independent. This is because GB dislocation nucleation dominates nanocreep instead of collective inside grain dislocation activities. Small activation volume of 0.1 -10b3 coincides with experiments, validating the important role of GB diffusion in nanoplasticity. Meanwhile, we found a versatile entropic effect on nanocreep[2]. Activation entropy contributes positively to dislocation nucleation, but negatively to diffusional creep rate. Moreover, activation entropy for nanocreep is temperature dependent. The entropic effect and its temperature dependence can be both explained by the anharmonic effect of vibrational frequencies variation in high temperature. Our findings not only pointed out the importance of second derivatives of activation Gibbs free energy, namely, temperature dependence of activation entropy to creep, but also provided novel understandings of creep mechanisms in nanocrystal. References:[1] M.F Ashby, A first report on deformation-mechanism maps, Acta Metall., 20, 887, 1972.[2] S. Karato, Deformation of Earth Materials: An Introduction to the Rheology of Solid Earth, (Cambridge University Press, New York, 2008).
9:00 PM - SS15.32
Dislocation Nucleation in Copper in the Presence of Point Defects and Their Clusters.
Iman Salehinia 1 , David Bahr 1
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractStructural defects can control the deformation mechanisms and plastic deformation in metals, and can affect the transition from elastic to plastic deformation. In small volumes of single crystals, the onset of plasticity is often related to the nucleation of dislocations, either homogeneously from the defect-free material or heterogeneously from nucleation sources such as point defects and their clusters, line sources such as Frank-Read sources, surface defects like surface steps and grain boundaries and volume defects such as voids. These defects, which are almost inevitable in metals, result in stochastic experimental results making the study of the mechanical behavior of metals additionally complicated. Therefore it is essential to use modeling methods to scrutinize the behavior of metals in the presence of different types of defects. Recently nanoindentation tests have shown that point defects such as vacancies and their clusters can impact the stochastic behavior of metals at the onset of plasticity. In this current work atomistic simulations of nanoindentation tests on copper were used to find the effect of several types of point defects on the force required to initiate plasticity. The defects considered in this study are single vacancies, di-vacancies, self-interstitial atoms (SIAs) and stacking fault tetrahedra (SFTs). By positioning the defects at a variety of positions under an indenter, similar to experimental methods where it is not possible to predetermine the location of subsurface defects, the maximum weakening effect, which is indenter size independent when normalized by the maximum theoretical applied shear stress, was found to be 8%, 21%, 22% and 49% for a single vacancy, a di-vacancy, a SIA and a SFT, respectively. Since the SFT has the most significant effect on the yielding, it was chosen for more detailed investigation. SFTs are common structural defects found in irradiated, quenched or highly deformed metals, and are usually vacancy type. This defect can be formed even at temperatures close to 0 K where the agglomeration of vacancies is unlikely to occur. SFT were generated by relaxation of a triangular Frank loop platelet of vacancies in one of closely packed (slip) planes in FCC crystals. The edge length was around 2.2 nm, close to the size of experimentally observed SFTs in copper. The orientation of the SFTs, pointing either downward or upward relative to the indentation direction, was significant, with a weakening effect of 49% and 14%, respectively. This presentation will also discuss the deformation mechanisms at the onset of plasticity in the presence of SFTs at different temperatures.
9:00 PM - SS15.33
Interactions of Dislocations with Grain and Twin Boundaries in Hard-Sphere Colloidal Crystals.
Maria Persson Gulda 1 , Eric Maire 1 3 , David Weitz 2 , Frans Spaepen 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 MATEIS, INSA-Lyon, Villeurbanne France, 2 Department of Physics, Harvard University, Cambridge, Massachusetts, United States
Show AbstractInteractions between dislocations and twin and grain boundaries can produce considerable increases in strength and strain hardening. Simulations and theory show that when a perfect dislocation hits a twin boundary it can divide into two dislocations: one propagates through and the other one leads to a jog in the boundary. We have studied dislocations in a colloidal crystal containing boundaries with a confocal microscope, which allows their interactions to be mapped out in detail on the particle scale. These boundaries are prepared by sedimentation onto specially oriented templates and include the [110] Σ3 twin, the [100] Σ5 and Σ7 boundaries and [100] low-angle boundaries. The latter also allow interesting direct observations on the stability and fluctuations of the partial dislocations that make up the boundary.
9:00 PM - SS15.34
Coupled Grain Boundary Motion in a Nanocrystalline Grain Boundary Network.
Mario Velasco 1 2 , Helena Van Swygenhoven 1 2 , Christian Brandl 3 , Enrique Martinez-Saez 3 , Alfredo Caro 3
1 NUM/ASQ, Materials Science and Simulation, Paul Scherrer Institut, Villigen PSI Switzerland, 2 Institute of Materials (IMX), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne Switzerland, 3 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractCoupled grain boundary motion to shear deformation was simulated in a three dimensional nanocrystalline Al grain boundary network using molecular dynamics. It is shown that in spite of the triple junction constraints around a symmetrical Σ75(-751)[112] (θ=23.07○) tilt boundary, the GB can migrate during the microplastic regime with the same coupling factor as when simulated in a bi-crystal configuration. After reaching the full plastic regime, dislocations start coming into play changing the grain boundary structure and hindering further coupled motion. The basin-hopping algorithm is used to explore further the effect of the structural rearrangement in the triple junctions and the therein-lying implications on the coupled grain boundary motion before the onset of dislocation propagation. In summary, the geometric predictions previously confirmed by bi-crystal simulations seem to be valid also in a nanocrystalline structure. The importance of coupled grain boundary motion as a deformation mechanism in nanocrystalline metals will be discussed in relation to other mechanism such as dislocation pile-up and grain boundary sliding.
9:00 PM - SS15.35
Molecular Dynamics Analysis of Experimentally Observed Radiation Induced Reduction of Ce4+ in CeO2 Thin Films.
Amit Kumar 1 , Ram Devanathan 2 , Vaithiyalingam Shutthanandan 3 , Satya Kuchibhatla 3 , Suntharampillai Thevuthasan 3 , Sudipta Seal 1 4
1 Mechanical Materials and Aerospace Engineering, University of Central Florida, Orlando, Florida, United States, 2 Fundamental & Computational Sciences, Pacific Northwest National Laboratory, Richland, Washington, United States, 3 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States, 4 NanoScience Technology Centre, University of Central Florida, Orlando, Florida, United States
Show AbstractSingle and poly crystalline ceria (CeO2) thin films were prepared using molecular beam epitaxy on 10 mol % yttria stabilized zirconia (YSZ) and sapphire substrates, respectively. The thin films were irradiated with high energy ionizing radiation of 2 MeV He+ ions, and were characterized for oxidation state change by in-situ x-ray photoelectron spectroscopy (XPS). Classical molecular dynamics simulations of thermal spikes and displacement cascades were carried out using ceria nanoclusters to model electronic energy loss processes and nuclear stopping damage, respectively. The results from simulations suggest that the ceria lattice doesn’t show significant damage due to electronic stopping from 2 MeV He+, while nuclear stopping near the end of range creates isolated point defects, especially on the O sublattice. The oxidation state change of Ce, occurring due to radiation can be attributed to charge transfer in response to defect production. The results hold important implications for applications that exploit the redox properties of ceria.
9:00 PM - SS15.37
Influence of Surface Segregation on the Elastic Property of Metallic Alloy Nanowires.
Guofeng Wang 1 , Aditi Datta 1 , Zhiyao Duan 1
1 Department of Mechanical Engineering and Materials Science , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractNano-devices employ nanowires as their active components to generate, transmit, and convert powers and motions. The fidelity of these applications relies on the production of nanowires of controlled size, shape, composition, and crystal structure, in reasonable quantities, and further, ultimately requires that the nanowires be mechanically stable in the application environments. At the nanometer scale, where the surface/volume ratio is substantial, the properties of material surfaces (such as, surface energy and surface stress) have a profound influence on the physical properties (for instance, elastic properties) of the nanowires. Surface segregation refers to the phenomenon that chemical composition at the surface of multi-component alloy materials differs from the corresponding value in their bulk. Consequently, surface segregation process would modify the arrangement and concentration of different elements in the surface region alloy nanowires. Using atomistic simulation techniques, we found that due to surface segregation the outermost surface layer would be enriched by Pt and the second surface layer would be enriched by Ni in the annealed Pt-Ni alloy nanowires and this “sandwich” surface structure could enhance the Young’s modulus of the Pt-Ni nanowires as compared to that of the Pt-Ni nanowires with randomly distributed Pt and Ni atoms. Hence, our theoretical study suggests that surface segregation can be used as a way to tailor the surface energy and surface stress of metallic alloy nanowires and to further control the elastic property of those alloy nanowires.
9:00 PM - SS15.38
Stress Study of Lithium-Ion Intercalation into V2O5 Thin Film Deposited by Sputtering.
Dawei Liu 1 , Anton Tokranov 1 , Sumit Soni 1 , Brian Sheldon 1
1 School of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractVanadium pentoxide has been a favorable candidate as cathode materials for lithium ion battery. High intercalation capacity of more than 200 mAh/g has been reported for porous V2O5 film with good cyclic. However, for dense film or film with less porosity, the cyclic stability was compromised by the volume change experienced during lithium ion intercalation, which is also believed to be the major cause for capacity degradation in most Li-ion battery electrodes.In our experiments, we made V2O5 thin film with different thicknesses by RF sputtering and studied the stress evolution during the Li-ion intercalation/de-intercalation process in a systematic manner. As comparison, V2O5 porous film was also studied and compared to reveal the stress effect on cyclic stability of V2O5 electrodes.
9:00 PM - SS15.39
Effect of Hydrogen on Micro-Tensile Behavior of a Metastable Austenitic Stainless Steel.
Yoji Mine 1 , Koichi Hirashita 2 , Mitsuhiro Matsuda 2 , Kazuki Takashima 2
1 Department of Mechanical Engineering, Kyushu University, Fukuoka Japan, 2 Department of Materials Science and Engineering, Kumamoto University, Kumamoto Japan
Show AbstractThis study was performed by micro-tension testing and metallographic characterizations, i.e., scanning white-light interferometry (SWLI), electron back-scatter diffraction (EBSD) analysis, and transmission electron microscopy (TEM), to clarify the intrinsic effect of hydrogen on plasticity of a metastable austenitic stainless steel. In the metastable austenitic stainless steels, α’ martensite induced by straining during the tensile loading plays a crucial role on hydrogen embrittlement (HE). On the other hand, even without α’ martensite, entire hydrogenation of the stable austenitic stainless steel specimen led to a ductility loss. It is hypothesized that, in essence, ununiformity on microstructural scale caused by the interaction between hydrogen and dislocation provides macroscopic degradation of mechanical properties, although the martensitic transformation may complicate matters for the metastable austenitic stainless steels. Meanwhile, some nanoindentation experiments have successfully given useful information for mechanistically understanding HE. In the present study, plastic deformation behavior was mesoscopically examined in tension testing using micrometer-sized specimens to clarify an elementary process of the HE of austenitic stainless steel.Specimens for micro-tension testing with a gauge section size of ~30 × 25 × 50 μm3 were fabricated by focused ion beam (FIB) machining. Hydrogen charging was undertaken at a temperature of 543 K by exposure to hydrogen gas for 44 h at a pressure of 10 MPa. The saturated hydrogen content was measured was ~25 mass ppm. The micro-tension test with a micro-gluing grip was conducted at a crosshead speed of 10 nm s-1 at room temperature in laboratory air. With the micro-tension test interrupted at predetermined stress levels, the deformation behavior of the micrometer-sized specimens was examined with a SWLI. After failure, a longitudinal cross section was fabricated by FIB machining and was observed by EBSD analysis and TEM.The true stress - true strain behavior of the micrometer-sized specimens exhibited two distinct strain hardening stages despite hydrogen precharging. EBSD analysis and TEM indicated that the austenite in the gauge part of micrometer-sized specimen almost transformed to the α’ martensite. It is thought that the former and the latter strain-hardening stages were controlled by dislocation gliding and α’ martensitic transformation, respectively. Hydrogen not only shortened the term of the former stage but also decreased the strain-hardening rate in the latter stage due to the martensite formation. In-situ SWLI of the micrometer-sized specimens during the tensile test revealed that plasticity localization caused by hydrogen is predominantly responsible for the HE of the austenitic stainless steel. Coupled tensile testing using the micrometer-sized specimens with metallographic examinations enable one to elucidate the role of the α’ martensitic transformation in the HE mechanism.
9:00 PM - SS15.4
Novel Chemical Mechanical Planarization Slurry Based on Nanodiamond–Polymer Nanocomposite.
Fnu Atiquzzaman 1 2 , Manoj Ram 2 , Ashok Kumar 1 2
1 Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 2 Nanotechnology Research and Education Center (NREC), University of South Florida, Tampa, Florida, United States
Show AbstractIndustry as well as research centers around the globe are coping to address the universal demand of global planarity of various thin film layers that constitute the integrated circuits (IC) and nanometer devices. Chemical Mechanical Planarization (CMP) process being critical to the fabrication of nanometer scale device. CMP is a state-of-art technique which makes the fabrication of multi-level interconnects possible, and is achieved by action, both mechanical and chemical processes involved during polishing [1]. Besides high polish rate and high material selectivity are important parameters during CMP process so the fine slurry plays an important role for planarity of thin film. We have developed CMP slurry of composite particles containing nanodiamond dispersed within cross-linked, polymeric microspheres. The average mass fraction of nanodiamond particles is approximately 50% in the composite.The slurry was synthesized by using co-polymerization of N-isopropylacrylamide (NIPAM) with 3-(trimethoxysilyl) propyl methacrylate (MPS) containing interpenetrating (IP) chains of poly (acrylic acid) (PAAc) [2]. The various composition of slurry was formed by varying nanodiamond to polymer with hybrid microgel. The nanodiamond composite slurry was characterized using infrared, UV-visual and Raman spectroscopy, dynamic light scattering, electron microscopy and thermal gravimetric analysis, respectively. Our result has shown that interesting composite structure could be observed using different ratio of nanodiamond to siloxane copolymer. CMP performance of silicon oxide were observed using CMP bench top tester using slurry with three different concentrations viz; 0.5% , 1.0% and 1.5% nanodiamond –polymer slurry. The in-situ co-efficient of friction, removal rate and surface roughness were obtained using CMP bench-top tester, Filmetrics F20 and atomic force microscopy studies [3]. 1% wt. nanodiamond-polymer composite slurry has exhibited superior CMP performance in comparison with others. The removal rate of 120 nm/min is obtained with reduced surface roughness and lower topographical variations. CMP process involves the synthesized nanodiamond-polymer composites slurry could give surface with minimal scratches and reduced particle deposition on the surface after polishing of silicon oxide wafer. Our novel diamond composite based polymer accounts as a potential candidate for the next generation CMP slurries.References: - [1] Parshuram B. Zantye, Ashok Kumar, A.K. Sikdar, ‘Materials Science and Engineering R, Vol. 45 pp. 89-220 (2004).[2] Cecil Coutinho, Subrahmanya R. Mudhivarti, Vinay K. Gupta, Ashok Kumar, Applied Surface Science Vol. 225, pp. 3090-3096 (2008)[3] S. Mudhivarthi, N. Gitis, S. Kuiry, M. Vinogradov, Ashok Kumar, Journal of Electrochemical Society, Vol. 153, (5), G372, (2006)
9:00 PM - SS15.40
The Effect of Long-Chain Alcohols on Nanomechanical Response during Nanoindentation.
Bedabibhas Mohanty 1 2 , Adrian Mann 1 2 3 , Milca Aponte-Roman 1
1 Department of Materials Science & Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States, 2 Institute for Advanced Materials, Devices and Nanotechnology, Rutgers The State University of New Jersey, Piscataway, New Jersey, United States, 3 Department of Biomedical Engineering, Rutgers The State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractVery thin organic surface layers and viscous fluids play a vital role in many tribological processes. However, their impact on surface mechanical behavior is difficult to quantify due to their effect being confined in the near-surface region. Surface and chemomechanical effects are known to affect the elastic deformation of nanocontacts, but their role in plastic deformation is less clear. Nanoindentation has been successfully used to study the effect of environment on the mechanical response of materials at the nanoscale. In the current study, we have investigated the effect of various long-chain organic alcohols on the nanomechanical behavior of different materials. Nanoindentation tests were carried out on silicon, fused silica, gold nanofilms on a glass substrate, aluminum alloy and copper immersed in long-chain alcohols (i.e. 1-hexanol, 1-heptanol, 1-octanol and 1-nonanol). Nanoindentation tests were performed by applying a range of maximum loads in order to obtain the response from varying depths. The results consistently showed an increase in the reduced elastic modulus and hardness values for silicon and gold nanofilms immersed in the alcohols for shallow indentation depths. The results for fused silica showed that the presence of long-chain alcohols had a minimal effect on the obtained mechanical properties, while a large scatter in the data was observed in case of aluminum alloy. The observed changes in the measured nanomechanical properties are attributed to the ability of the long-chain organic molecules to sustain elastic stresses when they are in confined geometries. The effect is to distribute the normal stress of the indenter over a larger area on the sample surface. The results of this investigation have significant implications in the area of tribology and give an insight into the role of lubricants in mitigating damage due to wear. Our results are potentially relevant to other systems with adsorbed organic films on their surface, including protein layers on biomaterial surfaces.
9:00 PM - SS15.42
Microscale Tensile Testing of TiAl PST Crystals.
Hidetoshi Fujisaki 1 , Yoji Mine 2 , Mitsuhiro Matsuda 1 , Masao Takeyama 3 , Kazuki Takashima 1
1 Materials Science and Engineering, Kumamoto University, Kumamoto Japan, 2 Materials Science and Engineering, Kyushu University, Fukuoka Japan, 3 Metallurgy and Ceramics Science, Tokyo Instistute of Technology, Tokyo Japan
Show AbstractLamellar-structured TiAl alloys exhibit high fracture toughness and crack growth resistance, and these properties are influenced by the macroscopic characteristic of the lamellar structures, such as lamellar orientation, colony size, colony boundary, and lamellar plate thickness. The mechanical characterization of the lamellar structure on the microscale is therefore important for the enhancement of the fracture and fatigue properties of TiAl alloys. Micro-mechanical testing techniques have been recently applied to examine the mechanical properties of microstructural constituents of materials. The dimensions of specimens used in this tensile testing are of the order of micrometers, which is smaller than the lamellar colony size, indicating that the local deformation and fracture of lamellar structure can be examined by the microscale testing technique. In this study, microtensile specimens were prepared from TiAl PST crystals, and the tensile behavior of lamellar was investigated on the microscale. The material used was a Ti- 48at.% Al PST crystal rod. A foil with a thickness of 20 μm was prepared by mechanical polishing, and specimens for microtensile testing, with a gauge section size of 20×20×50 μm3, were fabricated by focused ion beam (FIB) machining. Two types of specimens with different lamellar orientations (P- and N-type) were prepared. The loading axis of the P-type specimen was set to be parallel to the lamellar, while that of the N-type specimen was perpendicular to the lamellar. Microtensile tests were carried out using a micro-mechanical testing machine, and the specimen surface during the test was observed in-situ by scanning white-light interferometry with a resolution of 0.1 nm in the z direction. The stress-strain curve showed an almost linear relationship, and fracture occurred by brittle failure. The tensile strength of N-type specimen was 1020 MPa. This tensile strength was higher than those obtained for bulk specimens. The fracture surface was flat and a few steps were observed. The step height was approximately 0.5 μm, which corresponded to the thickness of α2 lamellaplate, suggesting that fracture occurred between the γ/α2 interfaces. In contrast, the microtensile tests showed the P-type specimen to be ductile and the tensile strength was 550 MPa. The fracture surface of the P-type specimen had delaminations parallel to the loading axis. In-situ observation of the specimen surface during the tensile tests indicated that the delamination started to occur after the stress-strain curve began to show a nonlinear relationship, and the delaminations were consistent with the γ/α2 interphase boundaries. These results suggest that interlamellar cracking at γ/α2 dominates the macroscopic fracture of lamellar-structured TiAl.
9:00 PM - SS15.43
Probing Strain and Microstrain in Nanostructured Thin Layers.
David Simeone 2 1 , Gianguido Baldinozzi 1 2 , Jean-Francois Berar 3 , Dominique Gosset 2 1
2 DEN, DMN, SRMA, MFE, CEA, Gif-sur-Yvette France, 1 SPMS, MFE, CNRS, Chatenay-Malabry France, 3 Institut Neel, CNRS, Grenoble France
Show AbstractThe analysis of the structures and microstructures of nanostructured thin layers can be performed using laboratory grazing incidence diffraction, provided accurate corrections are performed to handle the instrumental broadening effects related to the experiment geometry for an impinging beam close to the critical angle. Implementing these corrections in a Rietveld refinement software allows the accurate extraction of quantitative relevant information about the structure (strain and atomic positions) and the microstructure (particle size and microstrain), selectively probing the material on a depth of few nanometers.
9:00 PM - SS15.44
Texture Transformation in Thin Silver Films.
Stanislav Dorokhov 1 , Shefford Baker 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractThin FCC metal films often form fiber textures with (111) and/or (100) planes parallel to the plane of the film. These orientations have very different properties, so control of texture is important to understanding and improving device reliability. However, current models of texture formation are inadequate. A common thermodynamic analysis predicts a sharp transformation from (111) to (100) fiber texture with increasing thickness but a broad and incomplete transition is often observed. To study this problem, we deposited silver films, 200-2000 nm thick, and then annealed them in high vacuum. The microstructure was studied using x-ray diffraction (XRD) and electron backscattered diffraction (EBSD), both after deposition and after heat treatment. In situ XRD patterns were also collected during annealing. As-deposited films had strong (111) texture and transformed at least partially to (100) during annealing. The rate and extent of transformation depended strongly on the film thickness with thicker films transforming less completely. The transformation rate had a maximum at intermediate film thicknesses. Effects of strain energy, surface and interfacial energy, grain evolution, and grain boundary stagnation on the texture evolution of thin silver films were considered. The results show that texture evolution is a kinetically limited process and that purely thermodynamic arguments cannot successfully predict texture.
9:00 PM - SS15.45
Extended Structure of Point Defects in Graphene.
Mark Jhon 1 , Guglielmo Vastola 1 , Paulo Branicio 1 , David Srolovitz 1
1 , Institute of High Performance Computing, Singapore Singapore
Show AbstractPoint defects in graphene such as substitutional impurities and vacancies are associated with mechanical in-plane stresses. If graphene is not constrained to be flat, these stresses can cause out-of-plane deformations, causing the shape of a defective graphene flake to be buckled. The structure of a defect in graphene is characterized not only by the local atomic arrangement of atoms, but also by this extended structure. Buckling changes the strain-state around the defect, which may affect defect-defect mechanical interactions as well as the electronic properties of the sheet. By modeling the behavior of graphene as a thin, flexible plate, we study the extended structure of point defects, finding an analytical condition for the size of the defect required to buckle the flake. We also consider the special case of chemiadsorbed hydrogen, finding a mechanical description of this defect. Our plate interpretation of graphene is compared to molecular statics calculations using empirical potentials.
9:00 PM - SS15.46
Effect of Plasma Parameters on the Properties of TiN Films by Asymmetric Pulsed DC Magnetron Sputtering.
Sung-Yong Chun 1 , Man-Geun Han 1 , Dae-Han Seo 1
1 Advanced Materials Eng., Mokpo National University, Muan, Jeonnam, Korea (the Republic of)
Show AbstractSuperior hard coatings of titanium nitride (TiN) have been prepared in reactive sputtering system using an asymmetric-bipolar pulsed DC generator. TiN coatings have also been prepared using DC generator in the same sputtering system under identical deposition conditions. The properties of these coatings are compared with the pulsed deposited coatings. FE-SEM, nanoindentation tester and AFM have been used to characterize the coatings. We present in detail coatings (e.g., growth rate, morphology, surface roughness and nanohardness). The columnar growth of the deposited films could be suppressed by using the pulsed sputtering without increasing the deposition temperature. Our studies show that TiN coatings with superior properties can be prepared using asymmetric-bipolar pulsed DC generator.ACKNOWLEDGMENTSFollowing are results of a study on the "Human Resource Development Center for Economic Region Leading Industry" Project, supported by the Ministry of Education, Science & Technology (MEST) and the National Research Foundation of Korea (NRF).
9:00 PM - SS15.47
Microstructure and Morphology during β to α Phase Transformation of Tantalum Thin Films.
Elizabeth Ellis 1 , Markus Chmielus 2 , Shefford Baker 2
1 Theoretical and Applied Mechanics, Cornell University, Ithaca, New York, United States, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractTantalum thin films can be deposited in a metastable β-phase and transformed to the stable α-phase. The microstructure of α-tantalum films formed by phase transformation shows large grains with continuous orientation gradients and a discontinuous boundary structure. The development of the microstructure during the β to α phase transformation is not well understood, but an accurate model is essential for designing α-tantalum thin film components for microelectronic devices with new tailored properties. In this study, we show how the microstructure of α-tantalum evolves during phase transformation using two test series. In the first, we evaluate tantalum thin films that have been sputtered in the β-phase and partially transformed to the α-phase using electron backscattered diffraction to obtain orientation maps and scanning electron microscopy to study the morphology of the films. In a second series of tests, in-situ x-ray diffraction is used to determine the volume fraction of the α-phase present as a function of time. The combination of these two approaches allows us to interpret how the unusual microstructures in phase-transformed α-tantalum grains are created.
9:00 PM - SS15.49
Stress Homogenization and Flaw Insensitivity in Nanocrystalline Metals Thin Films.
Xiaoyan Li 1 , Sandeep Kumar 2 , Aman Haque 2 , Huajian Gao 1
1 School of Engineering, Brown University, Providence, Rhode Island, United States, 2 Department of Mechanical & Nuclear Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractRecent in-situ experimental studies have shown the evidence of extreme stress homogenization in nanocrystalline metals thin films that results in immeasurable amount of stress concentration at a notch tip and hence flaw insensitivity. To identify possible mechanisms behind such stress homogenization, we have performed molecular dynamic simulations on scaled down experimental samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby-Verrall type of grain switching process, was observed at the notch tip to relieve stress concentration. In such process, the deformation is accomplished not through dislocation activities, but through configurational switching of an assembly of grains via grain boundary sliding and grain boundary diffusion. Based on the combination of experimental and computational investigations, we conclude that in the absence of prevalent dislocation activities, grain realignment or rotation, assisted by gain-boundary-mediated mechanisms, may have played a critical role in accommodating externally applied strain and neutralizing stress concentration at a notch tip.
9:00 PM - SS15.5
Microstructural Designing and Tribological Performance of TiC/Si3N4 Based Nanocomposites.
Ching-Huan Lee 1 , Horng-Hwa Lu 1 , Jow-Lay Huang 1 , Masahiro Yoshimura 1
1 Department of Materials Science and Engineering, National Cheng-Kung University, Tainan Taiwan
Show AbstractThe concept of microstructural designing is based on the studies based on our previous works. For nanoceramics, microcracking at grain boundary enhances the resistance to plastic deformation as a small external force is applied. The moderate heating rate (100oC/min) and conductive nano-TiC is chosen, because the nanocomposite with self-lubricating medium (TiC based phase) is supposed to be obtained. The sliding wear behavior and worn surface will be examined. From the preliminery results, although the tribological performance of Si3N4 based composites is largely influenced by large and elongated microstructure of grains, the similar mechanical response of materials between nanosized- and coarse-grained ones indicate that the nano-TiC indeed improved the wearing properties of nano-Si3N4.
9:00 PM - SS15.50
Experimental Determination of Characteristic Length Scale of Dislocation Plasticity.
Joshua Gale 1 , Ajit Achuthan 1
1 department of mechanical and aeronautical engineering, clarkson university, Potsdam, New York, United States
Show AbstractRecrystallization of the grain structure of metals into nano-sized grains by using mechanical means, has received wide attention in the last two decades. It is well known that materials with a fine-grain crystal structure have favorable properties compared to the same materials with course-grained crystal structure. Surface Mechanical Attrition Treatment (SMAT), a technique developed in the early part of this decade, has been successfully used to recrystallize the surface grains of metals into nanocrystals of the order of 10 to 100 nanometers from their original grain sizes in the order to 10 to 30 microns. Resulting enhancement in surface properties has quite interesting applications, varying from materials with improved fatigue resistance to medical devices.In this study, our focus is to experimentally determine the characteristic length scale associated with dislocation plasticity using SMAT copper samples. The load displacement behavior under nano-indentation loading is obtained on SMAT samples of different grain sizes. By correlating the characteristic features of load displacement behavior with the grain sizes it is possible to quantitatively determine the characteristic length scale of dislocation plasticity. A mathematical model will be developed to verify the experimental observations.
9:00 PM - SS15.51
The Impact of Stress on Field Crystallization of Anodic Tantalum Oxide.
Lei Yang 1 , Mark Viste 2 , Joachim Hossick Schott 2 , Brian Sheldon 1
1 Engineering, Brown University, Providence, Rhode Island, United States, 2 , Medtronic Energy and Components Center, Brooklyn Center, Minnesota, United States
Show AbstractTantalum capacitors are extensively used in demanding high-reliability applications such as military, aerospace and medical. Amorphous, anodically grown tantalum oxide (ATO) serves as a dielectric layer in these capacitors. One of the degradation mechanisms in this oxide layer is its crystallization under the influence of stress induced by an applied electric field. Since late 1950s, many studies on this field-induced crystallization have been reported However, the role of stress and strain in the crystallization process has not been explicitely studied to date. The purpose of the present study is to directly monitor the stress evolution and understand its role in the field crystallization of ATO: Tantalum was evaporated onto quartz-glass substrates by eletron beam and subsequently anodized in acidic electrolytes. A multi-beam optical technque was then used for the in situ measurement of stress in the anodic thin films during the application of electric fields with field strengths on the order of 5*10^6 V/cm in a liquid electrolyte. Field-driven crystallization in acidic elecrolytes was furthermore tracked using electron microscopy and/or X-ray diffractometry. The results indicated that field-induced crystallization of ATO is associated with large stresses. The methods used in the present study promise to provide an approach for a detailed mechanistic understanding of the stresses associated with the field crystallization process in ATOs.
9:00 PM - SS15.52
Dielectric Gradient Force Actuation and Optical Measurement SiN Nanomechanical Resonator.
Sungwan Cho 1 , Myung Rae Cho 1 , Seung Bo Shim 2 , Yun Daniel Park 1
1 Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of)
Show AbstractWe present an actuation scheme for nanomechanical resonators made from silicon nitride using dielectric gradient force. And, we also present the driving and measurement of their flexural resonance with and without effect of substrate. Doubly clamped nanomechanical resonators are made from SiN-SiOx-Si tri-layer substrate and shows quality factor up to 20,000 at room temperature and moderate vacuum condition. DC electric field induces a temporary dipole moment while a small AC electric field drives beam resonator by dielectric force. Their flexural motion shows resonance frequency tuning according to DC bias voltage and asymmetry of electrode position. And by using asymmetrical electrode, we can also excite torsional mode in doubly clamped beam resonator. With this techniques, we can drive and measure resonance motion of suspended nanoscale structures without a physically incorporated electrode, which can degrade the quality factor or the resonance motion. Their flexural motion shows resonance frequency tuning according to DC bias voltage and asymmetry of electrode position.
9:00 PM - SS15.53
Microstructure and Mechanical Properties of Cu-Zn Alloys Produced by Surfactant-Assisted Ball Milling.
Hamed Bahmanpour 1 , Khaled Youssef 1 , Mohsen Samadi Khoshkhoo 2 , Sergio Scudino 2 , Jurgen Eckert 2 3 , Ronald Scattergood 1 , Carl Koch 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Institute for Complex Materials, IFW Dresden, Dresden Germany, 3 Institute of Materials Science, TU Dresden, Dresden Germany
Show AbstractSingle phase Cu-Zn alloys were processed by high energy ball milling of elemental powder at room temperature. Sodium chloride was used to control the deformation process and prevent cold welding of the powder to the milling media. It was found that 0.125wt.% NaCl can effectively control the consolidation behavior of the powder and produce in situ consolidated samples. Vickers microshardness and tensile test were utilized to investigate the mechanical properties. It is shown that room temperature ball milling of ductile Cu-Zn alloys can be controlled to produce in situ consolidated nanostructured samples with good mechanical properties, e. g. yield strength of 741 MPa and elongation to failure of 10% for Cu-5wt.%Zn. X-ray line profile analysis and electron microscopy were used to characterize the microstructure of the ball milled samples and microstructure-properties relationships were discussed accordingly.
9:00 PM - SS15.6
Nanomechanical Characterization of Alkali-Activated Fly Ash Concrete Using Nanoindentation.
Dalmas Wambura 1 , Michael Salera 2 , Aleksandra Radlinska 2 , Gang Feng 1
1 Mechanical Engineering, Villanova University, Villanova, Pennsylvania, United States, 2 Civil and Environmental Engineering, Villanova University, Villanova, Pennsylvania, United States
Show AbstractThe production of the most commonly used construction material - concrete - generates significant carbon footprint due to the portland cement manufacturing process. Alkali activated fly ash concrete, commonly referred to as fly ash geo-polymer concrete (FAGPC), is one viable, high performance “green” alternative that does not contain ordinary portland cement, but is based solely on fly ash. Because FAGPC can be considered as a nano-structured porous composite, it is essential to characterize the material at the nanoscales in order to fully understand and optimize its mechanical performance. Although extensive research has been devoted to characterizing and improving the properties of cement-based-concrete materials, alkali-activated concrete materials have not been investigated at the nano-scale. Furthermore, the research on the relationship between the nanostructure and mechanical properties for FAGPC is still in its infancy. In order to optimize the performance of FAGPC and determine whether it is a viable replacement for the portland cement, this study aims to characterize the structure, chemical distribution, and mechanical properties of FAGPC at the nano-/micro-scales. In order to optimize the process for achieving high early-strength and high fracture toughness, FAGPC samples with systematically varied compositions, such as the Alkali to Fly Ash Ratio, were comprehensively studied through various techniques. The scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and atomic force microscope (AFM) were used to study the structural and chemical properties. Nanoindentation was used to characterize the nano-/micro-mechanical properties, including hardness, modulus, and fracture toughness. Finite element analysis was conducted to correlate the hardness and strength. The small scale properties were compared to the bulk properties.
9:00 PM - SS15.7
Numerically Assisted Nanoindentation for Evaluating the Elastic and Plastic Properties of Materials.
Karim Gadelrab 1 , Li Guang 1 , Tewfik Souier 1 , Sergio Santos 1 , Matteo Chiesa 1
1 Material Science and Engineering, Masdar Institute, Abu Dhabi United Arab Emirates
Show AbstractNanoindenter tip shape plays a significant role in accurately extracting the mechanical properties of materials from nanoindentation measurements. Since tip imperfections may govern results validity, especially at shallow depth, a new framework for estimating the elastic modulus of materials is presented. Real tip geometry obtained from atomic force microscopy AFM is directly utilized in a FE simulation. By doing so, much of the uncertainties related of the indenter tip can be removed and the focus of the experiment is shifted to the material. The elastic unloading portion of the force curve provides information on the elastic modulus of the material. Hence, the value of the elastic modulus is modified in the FEA to obtain a numerical unloading force curve that matches the experimental one. After estimating the elastic modulus, fitting can be extended to the loading section of the curve to estimate the yield strength of the material. Experiments are conducted on fused silica and Bi2Te3 nanostructured materials. The obtained results are in close agreement to the bulk values verifying the validity of the approach. We believe that this numerical framework can extract accurate results at shallow penetration depth with minimal assumptions. It can also be useful in assessing the accuracy of the current theory and the importance of correction factors.
9:00 PM - SS15.9
Micro-Tensile Tests of Long Period Stacking Ordered Structured Phase in Mg-Zn-Y Alloys.
Kazuki Takashima 1 , Hiroaki Oda 1 , Michiaki Yamasaki 1 , Yoshihito Kawamura 1
1 Materials Sciece & Engineering, Kumamoto University, Kumamoto Japan
Show AbstractMg-Zn-Y alloys that are prepared by the hot extrusion of a cast material are composed of an α-Mg matrix phase and a long period stacking ordered (LPSO) structured phase. These alloys exhibit excellent mechanical properties. Further, in these alloys, the kink bands formed by the hot extrusion in the LPSO phase are considered to contribute significantly to the strengthening mechanism of the alloys; however, the details of this contribution have not yet been reported. As the size of the LPSO phase is usually in the range of micrometers, it is rather difficult to solely measure the mechanical properties of the LPSO phase by using a conventional technique. Therefore, we have developed a micro-mechanical characterization technique to investigate the deformation of microstructure in materials. The dimensions of specimens used in this testing are in the range of micrometers, which is smaller than that of the LPSO phase, indicating that the deformation behavior can be examined by using this testing technique. In this investigation, micro-sized samples were prepared from an LPSO phase of a directionally solidified Mg-Zn-Y alloy; the tensile properties of the LPSO phase were examined by using the micro-mechanical characterization technique. A directionally solidified Mg85Zn6Y9 alloy with an LPSO phase was fabricated by using the Bridgman method. Micro-tensile specimens with a gauge section size of 20 × 20 × 50 μm3 (hereafter, DS specimens) were prepared from the directionally solidified alloy by focused ion beam (FIB) machining. The tensile direction was set to be approximately 45° from the c-axis of the LPSO phase, that is, the slip plane of the LPSO phase. Further, after applying a compressive load to the directionally solidified alloy to introduce kink bands into the LPSO phase, we prepared similar micro-tensile specimens from the kink band region (hereafter, kinked specimens). The tensile tests were performed in air at room temperature by using the mechanical testing machine for the micro-sized specimens. The yield stress of the DS specimen without the kink bands was 28 MPa; the specimen work-hardened moderately and then fractured after reaching the maximum stress of 51 MPa. After the tensile test, slip bands corresponding to the basal slip of the LPSO phase, were observed on the specimen surface. On the other hand, the yield strength of the kinked specimen was 65 MPa; this specimen work-hardened rapidly before reaching the maximum stress of 82 MPa. However, the plastic elongation was considerably small, and the specimen exhibited a brittle fracture. The surface observation of the kinked specimen indicated that the slip was suppressed by the kink band, thereby, causing inhomogeneous deformation. This suggests that the kink bands in the LPSO phase contribute to the strengthening mechanism of the Mg-Zn-Y alloy.