Symposium Organizers
Amit Misra Los Alamos National Laboratory
John P. Sullivan Sandia National Laboratories
Hanchen Huang Rensselaer Polytechnic Institute
Ke Lu Chinese Academy of Sciences
Syed Asif Hysitron, Inc.
Z1: Nanoscale Films
Session Chairs
Robert Cammarata
Amit Misra
Tuesday PM, April 18, 2006
Room 2003 (Moscone West)
9:00 AM - **Z1.1
Hierarchical Modeling of Grain Boundary Diffusion and Dislocation Mechanisms in Thin Films and Nanocrystalline Materials.
Huajian Gao 1 , Markus Buehler 2 , Alexander Hartmaier 1 , Shuyu Wei 3 1 , Ji Chen 3 1 , Ke Lu 3
1 -, Max Planck Institute for Metals Research, Stuttgart Germany, 2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Shenyang National Laboratory for Materials Science, Chinese Academy of Sciences, Institute of Metal Research, Shenyang, -, China
Show AbstractIn studies of diffusional creep in polycrystalline thin films deposited on substrates, a new class of defects called the grain boundary diffusion wedge has been discovered. The diffusion wedges can be formed either by mass transport between free surfaces and grain boundaries or by absorption of dislocations into grain boundaries. In thin films on substrates, the diffusion wedge induces crack-like singular stress field and as a result, dislocations moving on glide planes parallel to the substrate can be nucleated at the root of the grain boundary, which is unexpected because the biaxial stress field of a thin film does not create a resolved shear stress parallel to the substrate to cause parallel glide motion. This has been verified by recent in-situ TEM experiments conducted at the Max Planck Institute. In nanocrystalline materials, diffusion wedges can lead to brittle crack propagation as the plastic deformation mechanisms are exhausted. In order to fully understand this phenomenon, we have developed a hierarchical modeling scheme in which semi-empirical interatomic EAM potentials derived from quantum mechanical calculations are used in large-scale classical molecular dynamics simulations to clarify the atomic mechanisms of grain boundary diffusion and the associated dislocation mechanisms. The results of molecular dynamics simulations are then fed into a mesoscopic discrete dislocation model to simulate the complex interaction mechanisms between dislocations and grain boundaries at larger length and time scales. The results of these studies compare favorably with relevant experimental data, which has led, for example, to a deformation mechanism map for thin film plasticity.
9:30 AM - Z1.2
Linking the Mechanical Behavior and Deformation Microstructure of Nanoporous Gold Thin Films
Ye Sun 1 , T. John Balk 1
1 Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States
Show AbstractWhile the chemical properties of nanoporous gold (NPG) have been investigated for years, its mechanical behavior has received relatively little attention. Given its high surface-to-volume ratio and noble metal chemistry, NPG holds potential for sensor and catalysis applications, but its mechanical properties must be better understood. Recently, other researchers have studied the compressive response of NPG during indentation experiments and have found elevated strength levels that greatly exceed that of bulk gold. Nonetheless, an understanding of the deformation mechanisms at the microstructural level is still needed.This presentation will focus on stress evolution in NPG during dealloying from gold-silver precursor films and during subsequent thermal cycling. The measured mechanical behavior of these NPG films will be compared to in-situ transmission electron microscopy observations of the deformation microstructure that develops within NPG during low-temperature thermal cycling and during tensile experiments. NPG films with thicknesses of 100 nm or less were deposited on single-crystal silicon substrates for thermal cycling, or on polyimide substrates for tensile testing.The observations obtained from these experiments will help assess the fundamental deformation behavior of NPG, which has been found to be either brittle or ductile, depending on pore morphology. This study will also shed light on the role of dislocations in the plastic deformation of highly confined metal volumes.
9:45 AM - Z1.3
Mechanical Properties and Failure Mechanisms of Free-Standing Nanoporous Gold
Dongyun Lee 1 , Jeffrey Kysar 1 , Xi Chen 2
1 Mechanical Engineering, Columbia University, New York, New York, United States, 2 Civil Engineering and Engineering Mechanics, Columbia University, New York, New York, United States
Show AbstractNanoporous materials have many potential applications such as for catalysis, sensing of chemical and biological species, and as a component of actuators. In this work, free-standing nanoporous gold is synthesized from “white gold” leaf (50% Au and 50% Ag by weight) and also from the simultaneous deposition of Au and Ag by magnetron sputtering. Both types of films are initially deposited onto silicon substrate and standard lithographic techniques are employed to fabricate mechanical testing specimens of a dog-bone shape. The silicon substrate under the gauge section of the specimens is then etched away via reactive ion etching (RIE) in order to obtain free-standing specimens which are suspended by two anchors of the original silicon substrate which are not removed. The gauge length of each specimen is 7 micrometers in length and the cross-sectional dimensions of the gauge length are in the range of 100 to 150 nm by 100 to 500 nm. The specimen is then dealloyed using nitric acid, which dissolved the silver and leaves random open-pored media of gold. The sizes of the ligaments and the voids are of the order of tens of nanometers and can be tuned with processing parameters. In this study, the mechanical properties of the nanoporous Au obtained by both synthesis methods are contrasted. In addition, the dealloying parameters for each of the two synthesis methods are systematically varied in order to be able to determine the effect on the mechanical properties of changing the sizes of the voids and ligaments. The mechanical properties of the nanoporous gold are probed by deflecting the gauge section of the free-standing specimen with a nanoindenter. Results demonstrate the nanoporous gold may deform elastically up to a stress of approximately 400 MPa, after which failure occurs in what is apparently a brittle manner, although it may be accompanied by plastic deformation in some of the ligaments.
10:00 AM - **Z1.4
The Mechanisms of Small-scale Plasticity as Revealed by in-situ Nanoindentation.
Andrew Minor 1 , Zhiwei Shan 1 , Eric Stach 2 , Miao Jin 3 , J.W. Morris, Jr. 3 , Syed Asif 4 , Oden Warren 4
1 NCEM, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 3 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 4 , Hysitron, Inc., Minneapolis, Minnesota, United States
Show AbstractThe experimental technique of in situ nanoindentation in a TEM allows for real time imaging of the initial stages of plasticity in materials, including the observation of dislocation nucleation and phase transformation events. Over the past 5 years, this technique has provided significant insight into the mechanical behavior of nanocrystalline materials and nano-scale volumes. This talk will highlight the most important findings regarding the mechanical behavior of metals and ceramics that were revealed with this technique. The findings will include observations of (1) dislocation nucleation events in Al thin films, (2) grain boundary movement in sub-micron and nanocrystalline Al thin films, (3) indentation behavior of ceramic nanoparticles, and (4) dislocation plasticity and phase transformation behavior in silicon. In all cases the in situ observations and measurements will be compared to ex situ nanoindentation tests and discussed in terms of the mechanisms that determine strength in nanoscale volumes.
10:30 AM - Z1.5
Thermodynamics and Mechanics of Solid Surfaces Applied to Modeling of Nanoscale Materials and Devices
Robert Cammarata 1 2
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractA major characteristic of nanoscale materials and devices is the large surface to volume ratio, and this ratio can have a large affect on the behavior of the materials. A complete thermodynamic understanding of solid surfaces in nanoscale materials is therefore important when attempting to model and understand the mechanics of these systems. Gibbs developed a general and rigorous treatment of fluid interfaces that has become the standard treatment of surface thermodynamics. However, in the case of interfaces involving solids, Gibbs recognized that there were certain difficulties that required his analysis to be restricted to single component systems under special constraints (and was formulated without any reference to lattice sites in a crystal). However, his unrestricted approach to fluid systems has often been applied to solids without justification and has sometimes resulted in a confusing and often misleading description of solid surfaces. For example, the concept of chemical potential, which is well-defined for fluid systems, becomes problematic for solid surfaces (even under hydrostatic stress), leading to difficulties in defining quantities such as surface energy that are central to the mechanics of surfaces and nanoscale materials. It will be shown that many of these issues can be addressed by reformulating the thermodynamics of surfaces in terms of “surface availability" that is consistent with the standard thermodynamics of fluid surfaces but allows for a complete and rigorous description of interfaces involving crystals. Applications of this approach will be given to certain model nanoscale systems that show the errors introduced by using the methodology of conventional fluid thermodynamics and how the new approach gives an unambiguous and proper description of the mechanics of small solids.
11:15 AM - Z1.6
Understanding the Mechanical Properties of Nanoporous Au
Juergen Biener 1 , Luis Zepeda-Ruiz 1 , Andrea Hodge 1 , Joel Hayes 1 , Peter Bythrow 1 , Yinmin Wang 1 , Farid Abraham 1 , Alex Hamza 1
1 Nanoscale Synthesis and Characterization Laboratory, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractRecent mechanical studies on nanoporous gold (np-Au) have revealed that the yield strength of this material is approximately one order of magnitude higher than predicted by scaling equations developed for open-cell foams. The higher-than-expected yield strength seems to be linked to the nanoscale morphology of np-Au which can be described as an open sponge-like network of interconnecting ligaments on the nanometer length scale. However, even though np-Au is a prototype nanoporous metal, the mechanical properties are not well understood yet. Here, we compare experimental results with molecular dynamics simulations to elucidate the nature of the high yield strength of nanoporous gold. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract of No.W-7405-Eng-48.
11:30 AM - **Z1.7
Mechanisms of Slip Transmission in Nanolayered fcc/bcc Composites.
Richard Hoagland 1 , Srinivasan Srivilliputhur 1 , Amit Misra 1 , Michael Demkowicz 1
1 MST-08, Los Alamos National Laboratory, Santa Fe, New Mexico, United States
Show AbstractThe theoretical strength is nearly achieved in layered metallic composites when the layer thicknesses are reduced to about 5 nm or less. In cases where the constituents have the same phase and are coherent or even semicoherent, high strengths are attributable to coherency stresses. However, coherency stresses cannot be important in incoherent systems when the phases of the components are dissimilar. Nevertheless, composites that contain incoherent interfaces also achieve very high strength levels. We describe the results of atomistic simulations that reveal some of the features of fcc/bcc composite materials that are important to strength. One feature of considerable importance is the in-plane shear strength. When the interfacial shear strength is substantially lower than typical theoretical strength estimates, glide dislocations within either component may be attracted to interfaces and, on entering, dissociate via core spreading. Once this occurs, continued transmission of slip, in the absence of thermal activation, becomes very difficult. However, we find that some unusual mechanisms are available to such systems that can make slip transmission easier. These mechanisms involve cooperative interaction between small groups of dislocations. We will also reflect on the relations between the properties of the system that are important to strength.This research supported by OBES of the U. S. Dept. of Energy.
12:00 PM - **Z1.8
Fatigue of Thin Metal Films at the Submicron and Nano Scale.
Dong Wang 1 , Cynthia Volkert 1 , Sophie Eve 1 , Norbert Huber 1 , Guangping Zhang 2 , Oliver Kraft 1 3
1 Institut fuer Materialforschung II, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang China, 3 IZBS, Universitaet Karlsruhe, Karlsruhe Germany
Show AbstractOne current trend in microelectronics and MEMS/NEMS is to develop devices based on plastic substrates. For such thin film devices, cyclic mechanical or thermal loading conditions with typical strain ranges up to 1% may lead to fatigue damage formation such as cracking, surface roughening and delamination. It is well known that fatigue of metallic materials at the macro-scale is often related to the formation of long-range dislocation structures, which lead to surface roughening of a component or specimen, and subsequent crack formation starting from the roughened surface. In the light of this damage evolution, it is not obvious how materials fatigue when dimensions are reduced to the sub-micron and nano regime, as in thin films or nanostructures with grain sizes of similar magnitude. On the one hand, the ratio of surface to volume is strongly increased, which may promote crack formation, while on the other hand, the available material volume is reduced preventing long range dislocation ordering.In order to elucidate these mechanisms, we have developed a number of methods to characterize the fatigue behavior of thin metal films. These methods include uniaxial and equi-biaxial loading of Cu and Au films on polymer substrates. In both tests, the substrate material is expected to deform elastically while the film may undergo plastic deformation in both tension and compression. A study on the effect of length scale, both film thickness and grain size, on fatigue-induced damage morphology in Cu films revealed that the amount of surface roughening decreases with decreasing film thickness and that long range dislocation structures were only found in films and grains larger than 1.0 µm. Furthermore, the damage morphology changes from intra- to inter-granular cracking with decreasing dimensions. In addition other changes in surface damage are observed which suggest that diffusion is active during fatigue of the thinnest films. Currently, a more detailed investigation of the influence of film thickness in the regime of 50 to 3000 nm on the fatigue mechanisms is being performed.
12:30 PM - Z1.9
Ab initio Study of Surface Stresses of Charged Au films.
Yoshitaka Umeno 1 2 , Joerg Weissmueller 3 4 , Ferdinand Evers 3 , Martina Nothacker 3 , Christian Elsaesser 5 , Bernd Meyer 6 , Peter Gumbsch 2 5
1 Department of Mechanical Engineering and Science, Kyoto University, Kyoto Japan, 2 Institut fuer Zuverlaessigkeit von Bauteilen und Systemen, Universitaet Karlsruhe, Karlsruhe Germany, 3 Institut fuer Nanotechnologie, Forschungszentrum Karlsruhe GmbH, Karlsruhe Germany, 4 Technische Physik, Universitaet des Saarlandes, Saarbruecken Germany, 5 Physikalische Werkstoffmodellierung, Fraunhofer Institut fuer Werkstoffmechanik IWM, Freiburg Germany, 6 Lehrstuhl fuer Theoretische Chemie, Ruhr-Universitaet Bochum, Bochum Germany
Show Abstract12:45 PM - Z1.10
Atomic-Scale Analysis Of Sress-Induced Nanocrystalline Domain Formation In Ultra-Thin Metallic Films And Characterization Of The Resulting Structure And Properties.
M. Rauf Gungor 1 , Dimitrios Maroudas 1
1 Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractReducing the grain size of metallic thin films can have a dramatic influence on material properties such as ductility, hardness, electrical conductivity, and mechanical strength. Furthermore, reduction of the grain size down to a few nanometers can lead to “extreme” material properties with a potentially wide range of nanotechnological applications. Fundamental understanding based on detailed atomic-scale investigation of nanocrystalline domain formation mechanisms and characterization of the resulting material structure and properties is required to assess the application potential of such nanostructured thin-film materials. In this presentation, we report results of a systematic computational analysis of strain relaxation mechanisms due to high levels of applied biaxial tensile strain in ultra-thin Cu films with the film plane oriented normal to the [111] crystallographic direction. The major strain relaxation mechanism observed leads to transformation of an initially single-crystalline structure into a polycrystalline structure with an average grain size of 1.5 nm. The analysis is based on isothermal-isostrain molecular-dynamics simulations using an embedded-atom-method parameterization for Cu and slab supercells with millions of atoms. Under application of high biaxial strain (> 8%) to a free-standing ultra-thin Cu film, a strain relaxation mechanism is activated that leads to formation of a uniformly distributed population of dislocations and point defects. Under such conditions, nanometer-scale domains of fcc crystalline material are formed leading to the transformation of the initially single-crystalline metallic film to a nanocrystalline structure with nanometer-sized grains. We analyze the atomistic mechanisms of strain-induced nanocrystalline domain formation, mainly due to rearrangement of strain-induced defect populations to form low-angle grain boundaries. In addition, we analyze the effects of the loading rate on the mechanism of nanocrystalline phase formation by enabling ductile growth of a centrally located cylindrical void as a competing strain relaxation mechanism, which is activated at a slower loading rate and dominates at lower strain levels. Finally, by relaxing and subsequently reloading biaxially the obtained nanocrystalline structure, we characterize the nanocrystalline film in terms of its ductility, elastic properties, and fracture toughness in comparison with the single-crystalline material. We find that the elastic modulus of the nanocrystalline thin film is several times higher than that of the single-crystalline film.
Z2: Nanoscale Materials
Session Chairs
Richard Hoagland
Scott Mao
Tuesday PM, April 18, 2006
Room 2003 (Moscone West)
2:30 PM - **Z2.1
Deformation Mechanism in Nanocrystalline fcc metals: Experiments and Simulations.
Helena Van Swygenhoven 1 , Stefan Brandstetter 1 , Zeljka Budrovic 1 , Steven Van Petegem 1 , Peter Derlet 1
1 , Paul Scherrer Institution, Villigen PSI Switzerland
Show AbstractBy combining in-situ x-ray diffraction during mechanical testing, TEM analysis and large scale atomistic computer simulations synergies are created providing a different view on the outcome of the conventional mechanical testing. In-situ profile analysis allows following the XRD footprints of the microstructure during loading and TEM analysis reveals the microstructure before an after load. Atomistic simulations provides, when put in their proper context taking into account possible artefacts from the short time/high stress character of simulations and the use of empirical potentials, invaluable details on deformation mechanism and how these are influenced by external parameters such as temperature. In this talk we report on in-situ and ex-situ load-unload experiments performed as well in tension as in compression, stress relaxations, strain rate jump tests and creep tests all performed at room temperature and some also at lower temperatures. Two materials are compared, a HPT Ni sample with mean grain size of 300nm and an electrodeposited Ni sample with a mean grain size of 30nm. We also present an overview of the suggestions of atomistic simulations concerning dislocation nucleation, propagation and absorption with a particular emphasis on the aspects in terms of thermal activation. Results such as the reversibility of the peak broadening at room temperature which is lost at lower temperatures, the low activation volume at room temperature and its increase with decreasing temperature are discussed in terms of the details of dislocation nucleation and propagation as suggested by simulations.
3:00 PM - **Z2.2
Multiscale Approaches On Modeling Grain-Boundaries In Nanocrystalline Metals.
Vesselin Yamakov 1
1 , National Institute of Aerospace, Hampton, Virginia, United States
Show AbstractIt is already well understood that the mechanical properties of nanocrystalline metals are strongly related to grain-boundary (GB) mediated processes, such as GB sliding, GB diffusion, grain growth, intergranular fracture, etc. Because of this, the accurate simulation of GBs' behavior is becoming a key factor for representing the mechanical properties of nanocrystalline metals. Two mesoscale models for representing GBs in a polycrystalline metal will be discussed. Both models use molecular-dynamics simulation to parameterize and validate their behavior. The first model is based on Pan and Cock's (Pan J, Cocks ACF. 1993, Comp Mater Sci. 1, 95.) technique for evolving a GB network in a polycrystal under deformation and during grain growth. The model is applied for simulating dynamic grain growth during large-strain GB diffusion assisted plastic deformation in nanocrystalline metals at elevated temperatures. The second model is based on Tvergaard and Hutchinson (Tvergaard V, Hutchinson JW, 1992, J. Mech. Phys. Solids 40, 1377) cohesive-zone model. Cohesive zone models (CZMs) approximate traction-displacement relationships along an interface and are frequently used in conjunction with the finite element method (FEM) to study fracture in a wide variety of materials. In the present work, it is shown that CZM can equally well be used to represent GB sliding during deformation. At low temperature, and in the absence of accommodation mechanisms, this GB sliding can cause substantial inhomogeneity in the stress-strain field in the loaded specimen, which can cause material failure through the mechanism of intergranular fracture.
3:30 PM - Z2.3
Structure and Mechanical Properties of Kurdjumov-Sachs Interfaces with Low Shear Resistance.
Michael Demkowicz 1 , Richard Hoagland 1 , Srinivasan Srivilliputhur 1 , Amit Misra 1
1 Michael Demkowicz, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract3:45 PM - Z2.4
Atomistic Analysis of Small-Scale Crystal Plasticity.
R. McEntire 1 2 , Yu-Lin Shen 1
1 Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractPlastic deformation and fracture in FCC crystals are studied using three dimensional atomistic simulations. The primary objective is to gain fundamental insight into nano-scale deformation features in thin films and small structures. An initial defect is utilized in the models to trigger dislocation activities in a controlled manner. Attention is devoted to correlating atomistic mechanisms with the overall mechanical response of the material. The slip phenomena are seen to follow the Schmid’s law under uniaxial loading along various crystallographic directions. The creation of slip steps at the sample surfaces is associated with a sudden reduction in stress along the stress-strain curve. The accumulation of plasticity leads to eventual ductile fracture of the crystal. When the material is attached to a flat substrate, plastic yielding is delayed. The material behavior under equi-biaxial loading parallel to the <111> plane is also analyzed.
4:30 PM - **Z2.5
Dislocation Activities and Partial Dislocation Mediated Processes in Nanocrystalline Grains.
Evan Ma 1
1 Materials Sci & Eng, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractWe discuss the dislocation behavior in plastically deforming metals when the grain sizes are reduced to well below 100 nm. Such grain sizes are often involved in thin films and MEMS materials. We compare the activation parameters of dislocation processes in nanograins with those in conventional metals, and illustrate in particular the various manifestations of partial dislocation mediated processes. For example, we discuss when and why deformation twinning and stacking fault formation come into play during unaxial tensile deformation of nanocrystalline Ni, explain the temperature effects in addition to grain size effects, and provide details regarding the deformation twinning mechanisms in nanograins. Our results not only establish that dislocation activities and partial dislocation mediated processes are clearly activated in nanograins, but also reveal their differences from those in conventional coarse-gained metals. We also discuss the results in comparison with the predictions given by MD simulations and generalized planar fault energy curves, as well as in light of the kinetics involved in the thermally activated dislocation nucleation and propagation. This research is part of an international collaboration effort. This talk will be based on the large number of TEM observations made by Dr. X.L. Wu (Chinese Academy of Science), and the stimulating discussions with Dr. Y.T. Zhu (LANL) and Dr. M.W. Chen (Tohoku Univ.).
5:00 PM - Z2.6
In situ, Quantitative TEM Nanoindentation Tests of Materials.
Zhiwei Shan 1 , Andrew Minor 1 , Syed Asif 2 , Oden Warren 2
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , Hysitron Incorporated, Minneapolis, Minnesota, United States
Show Abstract5:15 PM - Z2.7
High-strength Sputter-deposited Cu Films with Nanoscale Growth Twins.
Xinghang Zhang 1 , Amit Misra 2 , H. Wang 3 , X. Chen 4 , L. Lu 4 , K. Lu 4 , R. Hoagland 2
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Department of Electrical Engineering, Texas A&M University, College Station, Texas, United States, 4 Chinese Academy of Sciences, Institute of Metals Research, Shenyang National Laboratory for Materials Science (SYNL), Shenyang China
Show AbstractWe have shown for the first time that nanoscale growth twins, with an average twin spacing of around 5 nm, can be synthesized in Cu using magnetron sputtering technique. Such fine growth twins have been observed in sputtered 330 stainless steel alloys before [1,2]. Sputtered Cu has an average columnar grain size of less than 100 nm. Growth twins located in columnar grains are of {111} type as confirmed by high resolution transmission electron microscopy, with {111} twin interface predominantly parallel to substrate surface. The hardness of twinned Cu reaches 3.5 GPa as determined by nanoindentation technique. Uniaxial tensile tests were performed on 20 micron thick sputtered Cu foils. Average yield strength of 1.1 GPa was observed in these Cu foils with an average true strain of 2%. 1. X. Zhang, A. Misra, et al., Journal of Applied Physics, 97 (2005) 094302.2. X. Zhang, A. Misra, et al., Applied Physics Letters, 84 (2004) 1096.
5:30 PM - Z2.8
Fatigue-Induced Dynamic Coarsening in Nanocrystalline Electrodeposited Ni-Mn MEMS Structures
Brad Boyce 1 , Joseph Michael 1 , Thomas Buchheit 1 , Steven Goods 2
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractThe methods used to produce ultra-fine grained and nanocrystalline structures, such as by electrodepostion, may produce microstructures that are susceptible to unusual mechanisms for mechanical failure. In this study, we examine the fatigue-behavior of a nanocrystalline (~80-100 nm) Ni-Mn fatigue structure produced using the LIGA process for metallic microelectromechanical systems (MEMS) fabrication. This material has useful properties for structural applications, including a yield strength >1 GPa, reasonable ductility and resistance to anneal softening. With these properties, the material could be considered for spring-like applications where cyclic fatigue-loading could lead to latent failure. Cross-sections of samples after high-cycle fatigue failure at room temperature, prepared and imaged with a Focused Ion Beam (FIB) tool, showed dramatically coarsened grains that were >10X larger than the parent microstructure. This dynamic coarsening only formed in the immediate vicinity of fatigue-cracks and subsequent crack-propagation appears to be controlled by this much coarser microstructure rather than by the nanocrystalline parent microstructure. Backscatter diffraction revealed that these grains retained the strong {110} electrodeposition texture of the parent microstructure, suggesting that the grains may have grown by an Ostwald process rather than recrystallization. Previous studies of the Ni-Mn microstructure showed similar degrees of coarsening but only after thermal-annealing at ≥600C for 1 hr. This fatigue-induced coarsening behavior of ultrafine grained Ni-Mn is in contrast to the behavior of electrodeposited Ni with coarser 3-5 μm grains where no dynamic coarsening was observed after high-cycle fatigue loading. In spite of the very different mechanisms associated with fatigue failure of these two alloys, their resulting stress-life (S-N) failure envelope was similar when normalized by the ultimate tensile strength.Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
5:45 PM - Z2.9
Analysis of Strengthening Mechanisms in a Severely-Plastically-Deformed Al-Mg-Si Alloy with Submicron Grain Size.
David Morris 1 , Ivan Gutierrez-Urrutia 1 , Maria Munoz-Morris 1
1 Physical Metallurgy, CENIM,CSIC, Madrid Spain
Show AbstractMethods of severe plastic deformation of ductile metals and alloys offer the possibility of processing engineering materials to very high strength with good ductility. After typical amounts of processing strain, a submicrocrystalline material is obtained, with boundaries of rather low misorientation angles and grains containing a high density of dislocations. In the present study, an Al-Mg-Si alloy was severely plastically deformed by equal channel angular pressing (ECAP) to produce such a material. The material was subsequently annealed for dislocation recovery and grain growth. The strength of materials in various deformed and annealed states is examined and the respective contributions of loosely-arranged dislocations, many grain boundaries, as well as dispersed particles are deduced. It is shown that dislocation strengthening is significant in as-deformed, as well as lightly annealed materials, with grain boundary strengthening providing the major contribution in further annealed materials.
Z3: Poster Session: Nano-materials and Composites
Session Chairs
Wednesday AM, April 19, 2006
Salons 8-15 (Marriott)
9:00 PM - Z3.1
Sample Size Effect on Nanoindentation Mechanical Property Measurements.
Zhi-Hui Xu 1 , Xiaodong Li 1
1 Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractNanoindentation has been widely used for measuring the mechanical properties of materials at a small volume. The current method for the analysis of nanoindentation load-penetration depth curve is based on Sneddon’s equation, an elastic solution of indentation on semi-infinite half space. For nanoindentations on tiny structures, such as nanowires, nanobelts, and nanoparticles, the sample size is often comparable to the indent size and the Sneddon’s equation may not be fully valid. In this study, a finite element simulation has been carried out to investigate the sample size effect on the mechanical properties measured by nanoindentation. It is shown that significant errors occur in both hardness and elastic modulus measurements when the sample size is comparable to the indent size. Caution should be exercised in the analysis of nanoindentation curve of tiny structures.
9:00 PM - Z3.10
Transmission Electron Microscopy Study of the Mechanical Behavior of Nanoscale Materials.
Julia Deneen 1 , William Mook 1 , Andrew Minor 2 , William Gerberich 1 , C. Barry Carter 1
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Ernest Orlando Lawrence Berkeley National Laboratory, National Center For Electron Microscopy, Berkeley, California, United States
Show AbstractThe mechanical properties of nanoparticles and nanoscale materials are of great scientific interest. The wear properties of nanoscale components of, for example, microelectromechanical systems must be addressed as these devices are scaled down. While indirect studies suggest that nanoscale materials can be harder than their bulk counterparts, the practical difficulties in characterizing their mechanical behavior have traditionally been limited to what can actually be observed. The transmission electron microscope is commonly used to investigate the deformation mechanisms of materials, as it can be used to image dislocation strain fields. In most cases, however, the sample cannot be characterized prior to deformation. This study uses nontraditional methods to investigate the mechanical behavior of nanoscale materials. Using an in-situ nanoindentation sample holder for the TEM, direct observation of nanoparticle fracture is possible by simultaneous compression and imaging. Using this method, preexisting defects and surface layers can be identified and the sample orientation can be determined using diffraction techniques. Ex-situ studies of plan-view thin-film samples are also explored. By imaging the TEM sample and subsequently indenting the sample using traditional nanoindentation methods it is possible to characterize a specific area both before and after deformation. Both in-situ and ex-situ techniques offer new insight into the mechanical behavior of nanoscale materials.
9:00 PM - Z3.11
In-situ Photoemission Electron Microscopy Study of Thermally-induced Martensitic Transformation in CuZnAl Shape Memory Alloy.
Gang Xiong 1 , M Cai 2 , A Joly 1 , Wayne Hess 1 , Kenneth Beck 1 , J Dickinson 2
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 2Department of Physics and Astronomy, Washington State University, Pullman, Washington, United States
Show AbstractPhotoemission electron microscopy, in conjunction with photoemission spectroscopy, reflectivity, and surface roughness measurements, is used to study the thermally-induced martensitic transformation in a CuZnAl shape memory alloy. Real-time phase transformation is observed as a nearly instantaneous change of photoelectron intensity, accompanied by microstructural deformation and displacement due to the shape memory effect. The difference in the photoelectron intensity before and after the phase transformation is attributed to the concomitant change of work function as measured by photoelectron spectroscopy. Photoemission electron microscopy is shown to be a valuable new technique facilitating the study of phase transformations in shape memory alloys, and provides real-time information on microstructural changes and phase-dependent electronic properties.
9:00 PM - Z3.12
In-situ Study on Effects of Annealing Temperature and Mo Interlayer on Stress Relaxation Behaviors of Pure Al Films on Glass Substrates.
Young-Bae Park 1 , Soo-Jung Hwang 2 , Yong-Duk Lee 1 , Ja-Young Jung 1 , Young-Chang Joo 2
1 School of Materials Science and Engineering, Andong National University, Andong Korea (the Republic of), 2 School of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - Z3.13
Investigation of the Influence of Grain Size, Texture and Orientation of Freestanding Polycrystalline Gold Films
Liwei Wang 1 , Bart Prorok 1
1 Materials Engineering, Auburn University, Auburn, Alabama, United States
Show AbstractThe Membrane Deflection Experiment (MDE), developed by Espinosa and co-workers [1,2] was employed to perform the wafer-level tensile testing on freestanding thin films of various FCC metals. Gold films with varying thickness of 0.25 to 1.5 µm were deposited by both E-Beam evaporation and sputtering techniques. Process parameter adjustments and annealing were performed to modulate the film microstructure. High-resolution SEM, including electron-backscattered diffraction (EBSD), was employed to provide a crystallographic analysis including grain orientation maps of the studied films. The Young’s modulus of gold deposited by E-Beam evaporation was measured consistently in the range of 53-55 GPa while 68-72 GPa for the sputtered films. Plastic yielding of the e-beam and sputtered films was contrasted due to varying microstructure of each deposition technique, which appears to assert a measure of control on the deformation mechanics. An analysis will be presented on the effects of microstructure and correlated to the obtained orientation maps. Numerical simulations were also conducted to verify the validity of the MDE test results and resulted in a correction factor to increase the accuracy of the test data.[1] Espinosa, H.D., B.C. Prorok, and M. Fischer, Journal of the Mechanics and Physics of Solids, 2003. 51(1): p. 47-67.[2] Espinosa, H.D., B.C. Prorok, and B. Peng, Journal of the Mechanics and Physics of Solids, 2004. 52(3): p. 667-689.
9:00 PM - Z3.16
Effect of Microstructures and Textures on Mechanical Properties in Electrodeposited Ni foils
Yong Bum Park 1 , Nak Hyeon Lim 1
1 Materials Sicence and Metallurgical Engineering, Nanomaterials Research Center, Sunchon National University, Sunchon Korea (the Republic of)
Show AbstractPure Ni electrodeposits with different microstructures and textures were fabricated under different electrodeposition conditions. The evolution of microtextures taking place during annealing was quantitatively investigated by means of the orientation imaging microscopy analysis. In the sample consisting of equiaxed crystallites ranging between 10 and 15 nanometers, the as-deposited texture characterized by a mixture of strong <100>//ND and weak <111>//ND fiber components was transformed into the growth texture with the strong development of the <111>//ND components during annealing above 230oC. In the sample where columnar grains ranging from a few hundreds of nanometers to a few micrometers were formed in the as-deposited state, the <112>//ND grains, a minor component in the initial texture, grew readily to dominate the final texture. The mechanical properties such as hardness and elastic modulus were measured using a nanoindentation test and discussed in terms of the possible effects of the grain morphology and orientation distribution developing in the specimens.
9:00 PM - Z3.17
Cracking and Adhesion at Small Scales: Atomistic and Continuum Studies of Flaw Tolerant Nanostructures.
Markus Buehler 1 , Haimin Yao 2 , Huajian Gao 2
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Max Planck Institute for Metals Research, Stuttgart Germany
Show AbstractOnce the characteristic size of materials reaches nanoscale, the mechanical properties may change drastically and classical mechanisms of materials failure cease to hold. In this paper, we focus on joint atomistic-continuum studies of failure and deformation of nanoscale materials. In the first part of the paper, we discuss the size dependence of brittle fracture. We illustrate that if the characteristic dimension of a material is below a critical length scale on the order of several nanometers, the classical Griffith theory of fracture no longer holds. An important consequence of this finding is that materials with nano-substructures become flaw-tolerant, as the stress concentration at crack tips disappears and failure always occurs at the theoretical strength of materials, regardless of defects. Our atomistic simulations complement recent continuum analysis (Gao et al., PNAS, 2003) and reveal a smooth transition between Griffith modes of failure via crack propagation to uniform bond rupture at theoretical strength below a nanometer critical length. This indicates that materials with characteristic features below a critical length scale always achieve their optimal, theoretical strength, independent of the presence of flaws. Our results have important consequences for understanding failure of many small-scale materials. In the second part of this paper, we focus on the size dependence of cylindrical adhesion systems. We demonstrate that optimal adhesion can be achieved by either length scale reduction, or by optimization of the shape of the surface of the adhesion element. We find that whereas change in shape can lead to optimal adhesion strength, only reducing the dimension results in robust adhesion devices. An important consequence of this finding is that even under presence of surface roughness, optimal adhesion is possible provided the size of contact elements is sufficiently small. Our atomistic results corroborate earlier theoretical modeling at the continuum scale (Gao and Yao, PNAS, 2004). We discuss the relevance of our studies with respect to nature’s design of bone nanostructures and nanoscale adhesion elements in Geckos.
9:00 PM - Z3.19
Atomistic Modeling of Deformation Twinning in Nanocrystalline Cobalt.
Guangping Zheng 1
1 Mechanical Engineering, The University of Hong Kong, Hong Kong Hong Kong
Show AbstractDeformation mechanism of nanocrystalline metals with typical grain size of tens of nanometers is an interesting issue since dislocation slip is unlikely dominant in these materials. Recently it has been observed by experiments that deformation twinning plays an important role in cobalt nanocrystals. In this study, molecular dynamics simulation is employed to investigate the atomistic details of deformation twinning in nanocrystalline hcp cobalt. The plastic deformation is observed to induce an hcp-to-fcc allotropic transformation and consequently trigger twinning structures in an fcc matrix. First-principles calculation is further employed to explain the twinnability and lamellar fcc phase in hcp cobalt during deformation.
9:00 PM - Z3.2
Size Related Plasticity Effects in AFM Silicon Cantilever Tips.
Malgorzata Kopycinska-Mueller 1 , Roy Geiss 1 , Donna Hurley 1
1 Materials Reliability Division, NIST, Boulder, Colorado, United States
Show Abstract9:00 PM - Z3.21
Modelling of the Glass Transition of Oertho-terphenyl in Bulk and Thin Films.
Jayeeta Ghosh 1 , Roland Faller 1
1 Chem Eng & Mat Sci, UC Davis, Davis, California, United States
Show Abstract9:00 PM - Z3.22
Size-Dependent Elastic Moduli of Nanofilms
Shih-Hsiang Chang 1 , I-Ling Chang 2
1 Mechanical Engineering, Far East College, Tainan Taiwan, 2 Mechanical Engineering, National Chung Cheng University, Chia-Yi Taiwan
Show AbstractA semi-continuum model is presented to study the size dependence of the elastic properties for nanofilms. Unlike the classic continuum theory, the current model directly takes the discrete nature in the thickness direction into consideration. In-plane and out-plane Poisson's ratios as well as in-plane Young's modulus are investigated using this model. It is shown that the values of Young's modulus and Poisson's ratios depend on the total number of atomic layer in the thickness direction and approach the bulk values asymptotically.
9:00 PM - Z3.23
Shear-rate and Temperature Dependent Strength of SWNT Bundles: Creep of the Cross-links.
Boris Yakobson 1 , Yu Lin 1
1 MEMS, Rice University, Houston, Texas, United States
Show AbstractCross links have been discussed as reinforcement for the single-walled carbon nanotube (SWNT) bundles. Now we propose a phenomenological model of strength and yield of SWNT bundles via the movement of the inter-tube cross links, at finite temperature and shear rate, V. Further, the dynamics of specific chemical link is treated as a shear-modulated chemical reaction: the energy surface and transition states are computed with quantum-mechanical methods as function of tube-tube displacement. Due to possibility of the thermally-activated link relocation (creep), the strength S of the bundle (or fiber) depends on the shear rate and temperature. Analytical formulae for the resultant strength are obtained for two limits: (i) high shear rate or low temperature, S ~ const + ln (V/Vo), similar to known tribology relationship; (ii) slow shear limit, S ~ V/T. Molecular dynamics simulation of two carbon nanotubes with a >C=C< cross link reveals the details of such "creep". Based on computed energy and barrier parameters, we further conducted series of Monte Carlo simulations of multiple (up to a thousand) cross links connecting two narrow SWNT. The results at various rate V and temperature T agree with the derived formulae, and show that typical realistic conditions correspond to the high shear rate (i.e. low T) regime. This work is supported by the Office of Naval Research (DURINT) and by NASA (URETI TIIMS).
9:00 PM - Z3.24
Thermo Mechanics of Pre-stressed Polydimethylsiloxane Carbon Nanotube Composite.
Suresh Valiyaveettil 1 2 3 , Jinu Paul 1 , Sindhu Swaminathan 3 , Nurmawati Bte Muhammad Hanafiah 1 , Ajikumar Parayil Kumaran 2
1 Department of Chemistry, National University of Singapore, Singapore Singapore, 2 Singapore - MIT Alliance, National University of Singapore, Singapore Singapore, 3 NUSNNI, National University of Singapore, Singapore Singapore
Show Abstract9:00 PM - Z3.25
Raman Spectroscopy Investigation of Carbon Nanowalls.
Zhenhua Ni 1 , Haiming Fan 1 , Yuanping Feng 1 , Zexiang Shen 2 , Haoming Wang 3 , Yihong Wu 3
1 physics, National University of Singapore, singpoare Singapore, 2 Physics and applied Physics, Nanyang Technological University, Singapore Singapore, 3 Electrical and Computer Engineering, National University of Singpore, Singapore Singapore
Show AbstractThe two-dimensional carbon nanostructures carbon nanowalls (CNWs) have been grown vertically on the catalyzed substrates using microwave plasma-enhanced chemical vapor deposition (PECVD) [1-2]. The large surface area of aligned carbon nanowalls are useful as templates for the fabrication of other types of nanostructure materials, and would provide much potential applications in energy storage and electrodes for fuel cell [3-4].The growth of carbon nanowalls has been described in detail in refs1-2. Scanning Electron Microscopy (SEM) was used to observe the morphology of the film sample. Micro-Raman measurements were recorded in different sample orientations and polarizations. And also, Raman spectra were taken by different excitation lasers: 325 and 633nm (Renishaw Raman system), 488, 514.5 and 532nm (Jobin-Yvon T64000 Raman system). All the Raman spectra were measured in the backscattering geometry and at room temperature. The output power of excitation laser is below 1 mW, to ensure that the lasers do not heat the samples, which will make the peak shift. The resolution of the Micro-Raman is below 1cm-1, and the laser focus point is about 1 micron in diameter (with 100 magnification lens). All the observed peaks were assigned and compared with graphite. The G band of CNWs shifts slightly to higher frequency while its full width at half maximum (FWHM) is broader than that of graphite, indicating the finite size effect. The extremely strong D band of CNWs was thought due to the high edge density. While in different sample orientations and laser polarization, the ID/IG of the five conditions is 2.43(a), 2.31(b), 1.48(c), 1.46(d) and 1.35(e) respectively. This difference may be due to the Z polarization effect of G band. Different laser line was used to excite the sample, the laser energy dependence of the frequency of D band shift with the slope of 46.19 cm-1/eV has been observed, and the results agree well with the theoretical value by double resonance effect [5]. The 2D and G’ band shifts with the rate of 107.5 and 48.98 cm-1/eV respectively. And also, the decreasing intensity ratios ID/IG and ID’/IG with the increasing laser energy are observed and discussed.References[1] Y. H. Wu, P.W. Qiao, T.C. Chong, and Z.X. Shen, Adv. Mater. 2002, 14: 64[2] Y. H. Wu and B.J. Yang, Nano Letters 2002, 2: 355[3] M. Hiramatsu, K. Shiji, H. Amano, and M. Hori, Applied Physics Letters 2004, 84: 4708[4] B.J.Yang, Y.H.Wu, B.Y. Zong and Z.X. Shen, Nano Letters 2002, 2: 751[5] C. Thomsen and S. Reich, Physical Review Letters 2000, 85: 5214.
9:00 PM - Z3.26
Controlled Growth of Separated and Aligned Carbon Nano Tubes using Hydrogen Plasma and Nickel Film Interaction.
Santanu Patra 1 , Mohan Rao 1
1 Department of Instrumentation, Indian Institute of Science, Bangalore, Karnataka, India
Show Abstract9:00 PM - Z3.27
Carbon Nanotube Oscillator Operation by Encapsulated Gas Expansion.
Jeong Won Kang 1 , Ki Oh Song 1 , Jun Ha Lee 2 , Hoong Joo Lee 2 , Oh Keun Kwon 3 , Young-Jin Song 4 , Ho Jung Hwang 1
1 School of Electrical and Electronic Engineering, Chung-Ang University, Seoul Korea (the Republic of), 2 , Sangmyung University, Chonan Korea (the Republic of), 3 , Semyung University, Jecheon Korea (the Republic of), 4 Electronic Information Engineering, Konyang University, Nonsan Korea (the Republic of)
Show Abstract9:00 PM - Z3.29
Forming of Ceramic Nanocomposites using Spark Plasma Sintering Technology
Dustin Hulbert 1 , Dong Tao Jiang 1 , Amiya Mukherjee 1
1 Chemical Engineering & Materials Science, University of California, Davis, California, United States
Show Abstract9:00 PM - Z3.3
Depth-Dependent Nanomechanical Response of Soft Biomaterials.
Cheng Li 2 , Lisa Pruitt 1
2 Bioengineering, UC Berkeley, Berkeley, California, United States, 1 Mechanical Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractRecently there has been an increase in the application of nanoindentation to non-traditional materials such as polymers and biological tissues. Amongst efforts to increase the utility of instrumented nanoindentation are investigations into alternative parameters for characterizing these materials at the micron/nano length scales (Ebenstein, 2002). Effects which complicate interpretation of mechanical measurements include surface roughness, time dependence, heterogeneity, and anisotropy. Recently the role of adhesion has been examined (Carrillo et al., 2005; Ebenstein and Wahl 2005). However depth-dependent properties of highly compliant and structured materials have not yet been fully characterized. The observed depth-dependence of hardness and modulus values particularly at shallow indentation depths, known as indentation size effect (ISE), is well acknowledged in the nanoindentation community (Lee et al., 2005; Xu and Zhang, 2004). In this work we examine the depth-dependent nanomechanical response of polycarbonate, agarose gel, and articular cartilage tissue. For comparative purposes, the same protocol is applied to the standard fused silica.
9:00 PM - Z3.30
Carbon Nanotube Based “Nose” For Detecting Of Aliphitic Hydrocarbons.
Sudhaprasanna Padigi 1 , Shalini Prasad 1
1 Electrical and Computer Engineering, Portland State University, Portland, Oregon, United States
Show AbstractDetection of hydrocarbons has a broad impact in terms of environmental monitoring of pollutants. We report the use of chemically functionalized carbon nanotubes as an “electronic nose” to detect the presence of aliphatic hydrocarbons like ethanol, methanol, proponal and butanol. We have adopted the approach of integrating the microfabrication techniques with nanomaterials like carbon nanotubes. We demonstrate to selectively pattern and trap the carbon nanotubes on a micro-electrode array using electrophoresis and di-electrophoresis by creating non-uniform electric field effects on the chip and also by creating nano trenches on the order of a few hundreds of nanometers on the chip. These patterned clusters of nanotubes are selectively exposed to the above mentioned hydrocarbons resulting in the detection of multiple hydrocarbons simultaneously on a single chip. We also compare the performance of a randomly aligned homogeneous distribution of nanotube array with that of a selectively positioned and aligned nanotube array for sensing applications. We also intend to compare the single-walled nanotubes versus multi-walled nanotubes from the sensing perspective. This is believed to be an important step towards the realization of reliable and practical nano-scale sensors and it also allows us to explore the possibilities of creating nano-scale electronic and photonic devices.
9:00 PM - Z3.31
Surface Morphology of GaInP Grown on GaAs Vicinal Substrates with Ga Content Increasing.
Hao Wang 1
1 , South China Normal University, Guang Zhou China
Show Abstract9:00 PM - Z3.32
White MicroBeam Analysis of the Near Surface Nanostructure State in Ti After Friction Stir Processing
Rozaliya Barabash 1 , G. Ice 1 , O. Barabash 1 , Z. Feng 1 , S. David 1
1 Metals and Ceramics Div., Oak Ridge National Laboratory, Oak Ridge TN, Tennessee, United States
Show AbstractSpatially resolved white beam Laue X-ray nano- and micro- diffraction at the synchrotron together with scanning electron and orientation imaging microscopy were used to characterize the structural changes in the Ti near surface region after Friction Stir Processing (FSP). It was established that after FSP a special surface layer with nanocrystalline structure is formed within the depth of 300 microns. Grain size within this zone is within the depth of 30-60nm. Probing of this zone with a white microbeam (diameter ~0.5 microns) did not get any detectable signal. However probing of this zone with the white nanosize beam (diameter ~100nm) gave a distinct diffraction patter. Typically several grains were observed within each probing location. Most of the diffraction pattern consisted of long streaked Laue spots. Such streaking is indicating strong plastic deformation in this zone with the formation of strain gradients, geometrically necessary dislocations and boundaries, and resulting in the local lattice curvature in each grain. Two specific zones are formed underneath the above nanocrystalline layer: thermal mechanical affected zone (TMAZ) and heat affected zone (HAZ). The size and structure of all zones is determined. The grain size increased sharply (by two orders of magnitude) from FSZ to TMAZ zones and reached micron size (5 - 30 microns) in the TMAZ. Then grain size decreased again and reached the size typical for base material. Intensive streaking of the Laue spots are observed with a microbeam in the TMAZ and HAZ zones. Large densities of geometrically necessary dislocations and strain gradients are found in the TMAZ based on Laue microdiffraction. Dislocation density gradually decreases with depth and reaches the value typical for base material. The geometrically necessary dislocations were inhomogeneously distributed within the TMAZ and HAZ. Inhomogeneity of geometrically necessary dislocations distribution was found at both scales: within the individual grains and between separate grains.
9:00 PM - Z3.33
Biomechanical Characterization of the Murine Fracture Callus
Shikha Gupta 1 , Fernando Carrillo 5 , Ralph Marcucio 4 , Christian Puttlitz 3 , Lisa Pruitt 2 4
1 Applied Science and Technology, University of California, Berkeley, Berkeley, California, United States, 5 Chemical Engineering, Polytechnique University of Catalonia, Barcelona, Terrassa, Spain, 4 Orthopaedic Surgery, University of California, San Francisco, San Francisco, California, United States, 3 Mechanical Engineering, Colorado State University, Fort Collins, Colorado, United States, 2 Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractApproximately 6 million people in the United States sustain skeletal fractures each year. Although advances in orthopaedic technology have improved greatly during the past 25 years, more than 10% of fractures still heal incompletely. The want for better treatment strategies that ensure the normal fracture repair require a more complete understanding of the structure-function relationships of the fracture healing tissues. The healing tissue, known as a fracture callus, is spatially and temporally heterogeneous. It undergoes a complex transformation from an amorphous matrix to a highly-organized mineralized tissue. The mechanisms that govern this tissue transformation sequence and the resulting tissue composition are partially influenced by global loads and interfragmentary motions. However, the relationships between the global mechanical environment and extracellular matrix composition and local tissue stiffness (mechanobiology) remain primarily qualitative. Current mechanobiolgical principles were primarily developed by correlating globally measured forces and displacements with morphological features and local stress distributions determined from analytical techniques such as the finite element method. For the results to be robust a precise description of the material properties of the callus is paramount. However, the spatial heterogeneity of the fracture callus precludes the use of bulk mechanical testing and chemical analysis techniques to quantify the local tissue properties. This lack of fundamental knowledge makes present mechanobiological predictions difficult judge on a quantitative basis. With and accurate measurement of various material parameters on a size scale that offers intra-callus resolution, contemporary mechanobiologic theories may be advanced and used in the discovering treatments that enhance skeletal repair. The better characterize the fracture healing tissue, our study is analyzing the local chemical and mechanical tissue properties of a murine tibial fracture callus at 7 and 14 days post fracture with Raman microspectroscopy and nanoindentation. During unstabilized fracuture healing, the callus is composed of a soft, collagenous matrix and newly mineralized cartilage and bone. Our study focuses on the mineralizing regions. Raman spectra are collected on native tissue specimens in the region encompassing the prominent mineral (phosphate and carbonate) and the organic matrix (collagen) frequency shifts with 2 micron resolution. The spectra are analyzed to determine the tissue composition and structure from peak intensities, tissue maturity, and the ratio of the organic and inorganic phases of the tissue. Following spectroscopy, quasi-static nanoindentation experiments are conducted with hydrated specimens in the same regions to determine local tissue stiffness from load-displacement data. These results are important in the development of better treatment strategies for enhanced fracture repair.
9:00 PM - Z3.34
Mechanics of Boron Nitride Nanotubes from Density Functional Theory Calculations
Traian Dumitrica 1 , Paolo Valentini 1 , Boris Yakobson 2
1 Mechanical Engineering, Univ of Minnesota, Minneapolis, Minnesota, United States, 2 Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States
Show Abstract9:00 PM - Z3.4
Wear Resistance Tests on a Grasshopper Mandible – Abrasion of a Biomaterial.
Thomas Schoeberl 1 , Ulrike Wegst 2
1 , Erich Schmid Institute of Materials Science, Leoben Austria, 2 , Max-Planck-Institut fuer Metallforschung, Stuttgart Germany
Show Abstract9:00 PM - Z3.5
The Deformation Micromechanisms of Nanocrystalline Ge-Si Film During Indentation.
Ziwen Xu 1 , A.H.W. Ngan 1
1 , The University of Hong Kong, Hong Kong Hong Kong
Show AbstractThe deformation micromechanisms of bulk Ge and Si have been drawing increasing attention. However, less reports studied the deformation behaviors of nanocrystalline Group-IV semiconductors. In this study, the thin films of Ge-Si duplex nanocrystals were fabricated on a soft substrate by magnetron co-sputtering. Indentations were made on the Ge-Si film using a nanoindenter. Transmission electron microscopy (TEM) and Raman spectroscopy was used to analyze the deformed microstructures in the residual indentations. The experimental results have revealed that different loading methods lead to different deformation behaviors. Amorphisation, diamond cubic (dc)/non-dc phase transformation were observed and considered the major micromechanisms in the deformation of Ge-Si duplex nanocrystals.
9:00 PM - Z3.6
Nanomechanical and Nanotribological Properties of Contact Lenses – Effect of Hydration and Temperature.
Michelle Dickinson 1
1 , Hysitron Inc., Minneapolis, Minnesota, United States
Show AbstractThe mechanical and tribological properties of contact lenses are known to affect both the comfort level and durability of the lens. These properties are therefore of major importance when designing new lenses as there is a correlation between the level of comfort felt and the coefficient of friction of an individual lens. Contact lenses and many other biomaterials are known to have varying mechanical properties depending on environmental testing conditions such as temperature and hydration. Although this is well known, there have been many tests measuring the mechanical properties of biomaterials at room temperature and humidity. Mostly, this is due to the ease to ease of testing in ambient conditions and the additional considerations needed to test in fluids and at elevated temperatures. A realistic testing environment varies depending on the function of the biomaterial, with contact lenses being a small group of non-implanted biomaterials which do not need complete immersion in fluid to simulate in vivo conditions.Contact lenses are specifically designed to have a high water content to aid oxygen permeability and thus testing of these samples should be carried out with the lens hydrated to the level that it would be on the eye. Even a small amount of dehydration within the sample can cause a change in mechanical properties of the lens material. Temperature is well known to have an effect on the properties of soft polymers including contact lenses and care must be taken to ensure test conditions are accurately controlled to mimic those in vivo.Sample mounting is also an important consideration, as cutting or stretching the lens to fit a flat sample holder can create residual stresses resulting in an unrealistic material response upon testing. By using a spherical substrate, mimicking the size and shape of a human eyeball, the lens can be tested without creating any additional stresses within the polymer.The testing of thin, soft polymer based materials in fluid and elevated temperature is not trivial, and considerations such as tip shape and size, drift correction time, time dependence effects, adhesion and pull off force need to be determined to create an accurate test procedure. This investigation uses nanoindentation to test the nanomechanical and nanotribological properties of commercial contact lenses at different temperatures and hydration levels to emphasize the importance of accurate and realistic environmental control before data collection. By understanding how relatively small fluctuations in these conditions can create large changes in the measured mechanical properties, and defining tip selection and load functions, more accurate test protocols can be determined for the testing of biomaterials.
9:00 PM - Z3.7
An Investigation of Nanoindentations of Hydrogen Silsesquioxane.
SunZen Chen 1 , Henry Chen 2 , FonShan Huang 3
1 Center for Nano-Science and Technology, National Tsing Hua University, Hsinchu Taiwan, 2 Department of Electrical Engineering, National Chi Nan University, Nantou Taiwan, 3 Institute of Electronics Engineering, National Tsing Hua University, Hsinchu Taiwan
Show Abstract9:00 PM - Z3.8
Imaging Mechanical and Chemical Properties on the Nanometer Scale
Ute Schmidt 1 , Matthias Kress 1 , Olaf Hollricher 1 , Klaus Weishaupt 1
1 , WITec GmbH, Ulm Germany
Show AbstractPolymer films are widely used as protective coatings, adhesives, and lubricants, but a thorough knowledge of physical and chemical properties on the nanometer scale of these films is essential for the development of advanced polymeric materials required in semiconductor and data storage industry, for drug delivery and biomedical applications, etc. Some details about the phase-separation process in polymers are difficult to study with conventional characterization techniques due to the inability of these methods to chemically differentiate materials with good spatial resolution and without damage, staining or preferential solvent washing. One technique that has been successfully used is Atomic Force Microscopy (AFM). AFM can provide topographic information of a polymer film with resolution on the order of 1 nm. By investigating the tip-sample interaction, one can obtain not only the high resolution topographic structure of the surface but also information about the local mechanical properties of the sample components. In this case the AFM is operated in Pulsed Force Mode, where a sinusoidal modulation is imposed on the cantilever typically with a frequency of 1 kHz, which is far below the resonance frequency of the cantilever. Thus, the applied force can be controlled using the beam deflection technique while the cantilever is approached to and retracted from the sample. The Pulsed Force curve shows the variation of the force signal as a function of time. Therefore it contains all information about the tip-sample interaction. The resulting Pulsed Force curve obtained during the whole cycle is recorded at every image point. With this mode material properties like stiffness, adhesion, viscosity, can be imaged together with the topography of the films. Nevertheless, this methods are limited to the sample surface. An very thin surface layer can completely hide the bulk components of the film. By combining AFM with Confocal Raman Microscopy, the high resolution topography images can be supplemented with chemical information.Polymer films with a thickness below 100 nm were characterized with the Confocal Raman AFM. The high resolution phase images allow the identification of two styrene butadiene copolymers (SBS and SBR) with different chain nanostructure. The Raman spectra collected from the thin films of the copolymers show differences in the peak intensities, indicating that a very small sample volume is enough to identify the chemical and structural composition of the films. Well separated domains are formed, when these copolymers are blended with PMMA and spin coated as thin films on glass substrates. The stiffness images obtained in Pulsed Force mode show that SBS is 3.5 times stiffer than SBR, in good agreement with the observed chain nanostructure.
Symposium Organizers
Amit Misra Los Alamos National Laboratory
John P. Sullivan Sandia National Laboratories
Hanchen Huang Rensselaer Polytechnic Institute
Ke Lu Chinese Academy of Sciences
Syed Asif Hysitron, Inc.
Z4: 1-D Nanomaterials
Session Chairs
Wednesday AM, April 19, 2006
Room 2003 (Moscone West)
9:00 AM - Z4.1
Atomistic Simulation of Inelasticity and Failure in Gold Nanowires.
Jonathan Zimmerman 1 , Harold Park 2
1 Science-Based Materials Modeling Department, Sandia National Laboratories, Livermore, California, United States, 2 Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractWe present molecular dynamics simulations of [100] and [110] oriented gold nanowires subjected to tensile deformation. The nanowires were modeled using various forms of the embedded-atom method, and our simulations focused on investigating the yield and fracture properties of the wires. It clearly demonstrated that the accurate modeling of stacking fault and surface energies is critical in capturing the fundamental deformation behavior of gold nanowires. By doing so, phenomena such as the formation of atom-thick chains (ATCs) prior to fracture, zigzag, helical rotational motion of atoms within the ATCs, structural reorientation of the ATCs to a hexagonal crystal structure, and {111} faceting of the nanowires in the yielded neck region by the ATCs, are accurately captured. We find that [110] gold nanowires tend to form long, stable nanobridges upon necking, as well as a multishell lattice structure believed to account for the stability of the nanobridges observedexperimentally.Sandia is 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.
9:15 AM - Z4.2
Exploring the Mechanical Properties of Ag Nanowires and Au Thin Films.
David Miller 1 2 , Brad Boyce 2 , Ken Gall 3
1 Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 2 Microsystem Materials Group, Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractIn recent years, theoretical and experimental efforts have pointed to a wealth of nano-scale mechanical phenomena that provide insight into fundamental material behavior. In our study, we explore new methods for the evaluation of mechanical properties of Au thin films as well as Ag nanowires. Au and Ag are chosen for their similar nobility (chemical inertness) and well-understood FCC structure. The nanowires, fabricated at University of South Carolina, are ~100 nm in diameter and several micrometers in length. In our studies, for example, instrumented indentation of films was seen to result in non-uniform hardness (through-thickness direction) and discrete deformation events for annealed films but not for otherwise identical as-deposited films. While nanoindentation provides a readily available method for exploring mechanical properties of nano-scale volumes, it results in a complex multiaxial stress state and is geometrically challenging to implement for nanowire characterization. An alternative test method concerns the development of a microelectromechanical systems (MEMS) based test bed for evaluating nanowires and other nano-scale materials. We have fabricated such a test bed using the Silicon-On-Insulator (SOI) Multi-User MEMS Process (MUMPS). Similar to structures produced by other researchers using surface micromachined silicon technology, this device consists of a thermal actuator capable of actuating at forces up to and beyond 20 mN and differential capacitive displacement sensing capable of resolving displacements in the sub-nanometer range. A SOI-MEMS based sieve is used to isolate nanowires and a focused-ion beam (FIB) machine equipped with a manipulation tool is used to attach the nanowires to the testbed. Characterization of nanowire defect structure is performed in a transmission electron microscope (TEM). We will discuss the viability and limitations of this newly developed test bed for mechanically evaluating nanowires. This method will be compared to alternative methods for mechanical characterization, including nanoindentation, and nano-indenter based bending. These new methods for mechanical testing are expected to lead to fundamental insight into mechanisms of mechanical behavior as well as to provide methods to manipulate nano-scale materials for use in enabling technologies.
9:30 AM - **Z4.3
Micro-Compression Testing of Metals
Cynthia Volkert 1
1 , Forschungszentrum Karlsruhe, Karlsruhe Germany
Show AbstractRecent developments in micro-mechanical testing methods involving the use of focused ion beam machining and nanoindentation offer unique opportunities to systematically study deformation of small samples. We have performed tests on micron and sub-micron columns made from a variety of materials, including single crystalline (Au, Cu, Al, Ta), nanocrystalline (nc-Ni), nanoporous (np-Au), and amorphous metal columns (a-PdSi), as well as multilayer columns (a-PdSi/Cu) and columns containing individual grain and twin boundaries (Al, Cu). These tests provide a unique opportunity to investigate mechanical behavior under uniform stress in samples as small as 200 nm. The single crystalline columns confirm that “smaller is stronger”, with sub-micron specimen strengths close to theoretical values. The large yield strengths and strain hardening rates can be understood in terms of dislocation source depletion in small volumes. The nanocrystalline, nanoporous, and multilayer columns do not show a column size effect once FIB machining artifacts are accounted for. However, the micro-compression tests allow plastic instabilities in these materials such as shear band formation, buckling, and fracture to be investigated as a function of the sample volume. The amorphous metal columns exhibit serrated flow and shear band formation as well as a column size effect. These trends will be discussed in terms of a critical size for shear band nucleation. Finally, an outlook for the use of focused ion beams for nano-fabrication as well as what can be achieved by tailoring length scales in various materials will be presented.
10:00 AM - Z4.4
Deformation Behavior of Nanocrystalline Metals Investigatedby Microcompression Tests.
Ruth Schwaiger 1 , Benedikt Moser 2
1 IMF2, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 , EMPA, Thun Switzerland
Show AbstractThe deformation of nanocrystalline materials results from the competition between various mechanisms, the activation of which is size dependent. Hence, at different grain sizes, different mechanisms dominate deformation. Dislocation activity is reduced when the grain size is in the range of 30 nm and below. For this grain size range, grain rotation, grain boundary sliding, and diffusion mechanisms have been proposed. By varying microstructural and geometrical length scales, we study the effect of external size and internal structure on the deformation mechanisms in nanostructured metals.Recently, a method for performing compression tests on micron-sized specimens has been introduced [1]. The test procedure consists of machining cylindrical compression samples into the surface of bulk materials using a Focused Ion Beam and then compressing these columns with a flat probe in a nanoindenter. Such experiments involve small deformation volumes and negligible strain gradients. We study the deformation behavior of nanocrystalline (nc) and ultra-fine crystalline (ufc) electrodeposited Ni with average grain size of 30 and 300 nm, respectively. Columns with diameters ranging from 0.3 to 7 micrometers were deformed, some of them in situ in a Scanning Electron Microscope. The initial test results on ufc Ni show no influence of specimen size on the yield stress over the range of diameters investigated. The in situ experiments showed that the columns are not deformed uniformly. This effect is more pronounced for smaller diameter columns. In addition to the results obtained on nanostructured materials, data from single crystal columns will be presented. [1] Uchic, M. D., D. M. Dimiduk, et al. (2004). Science 305(5686): 986-989.
10:15 AM - Z4.5
Plasticity in Aluminum Nanocolumns.
Richard Wagner 1 , Francesca Tavazza 2 , Lyle Levine 2
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 AbstractWe have investigated the onset of plasticity in aluminum nanocolumns by atomistic simulation with an embedded atom method. By varying size, shape, temperature, and indentation rate we find that the mechanics of deformation in these columns differ notably from continuum theory. We also observe the conditions leading to nucleation of dislocations, the carriers of plasticity.
10:30 AM - Z4.6
Dislocation Dynamics in Micro and Nano-scale Cylinders
Christopher Weinberger 1 , Keonwook Kang 1 , Wei Cai 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractA dislocation-starvation model was proposed to explain the dramatic increase of flow stress as the diameters of gold micro-pillars go to nanoscale (Greer and Nix, Applied Physics 2005). On the other hand, recent indentation experiment on gold nanowires indicates dislocation hardening even at the nanoscale (Wu et al. Nature Materials, 2005). To investigate this controversy, we develop Dislocation Dynamics (DD) simulation models in a cylinder with its diameter ranging from micro to nanoscale. Such simulations are enabled by an efficient algorithm to account for the image stress of the traction-free cylindrical surface, based on the analytic expressions of the elastic displacement potentials. The DD simulations also account for the orientation dependence of dislocation core energy and mobility computed from atomistic models. Stress-strain curves calculated by these simulations will be compared with experimental measurements.
11:15 AM - Z4.7
Mechanical Property Measurements of 1D Nanomaterials Using AFM Three-point Bending Techniques.
Hai Ni 1 , Xiaodong Li 1
1 Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractMaterial properties are size-dependent. The mechanical properties of 1D nanomaterials cannot be extrapolated from the results of bulk materials and structures. Although many 1D nanomaterials have been synthesized/fabricated by various techniques, their mechanical properties have not been well explored. This has limited their applications in constructing reliable nanodevices. In this study, amorphous SiO2 nanowires and ZnO nanobelts were synthesized using CVD via vapor-liquid-solid method, after characterizing their microstructure and composition using various electron microscopy techniques, we successfully measured the mechanical properties of the amorphous SiO2 nanowires and ZnO nanobelts through performing three-point bending tests using an AFM tip to directly bend individual SiO2 nanowires and ZnO nanobelts. We also report a reliable clamping technique for the manipulation and mechanical testing of 1D nanomaterials.
11:30 AM - **Z4.8
Chemomechanics of Amorphous Silica: Lessons from Nanowires
Emilio Silva 1 , Sidney Yip 1 2 , Krystyn Van Vliet 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractAmorphous silica is a naturally occurring and industrially important material for which mechanical properties depend strongly on local chemical environment (presence of water). Silica nanowires afford an important model system to study the coupled effects of chemistry and mechanics on covalently bonded amorphous networks. Here, we present direct measurement and computational simulation of the elastic and plastic properties of silica wires with diameters ranging from the micro- to the nanoscale. While similar mechanical characterization of carbon nanotubes, silicon carbide, gold and silver nanowires has been reported, the elastic and plastic properties of silica nanowires were heretofore available only through indirect measurements. We present several complementary approaches to direct interrogation of nanowire mechanical properties, and find that the elastoplastic behavior for nanowires of diameter > 250 nm is consistent with that of bulk silica, whereas molecular dynamics simulations predict elastic stiffening for nanowires of < 50 nm diameter. The continuum-level and atomistic effects of aqueous chemical environments on the degradation of nanowire mechanical properties will be discussed.
12:00 PM - Z4.9
Direct Nanomechanical Measurement of Elastic and Plastic Deformation of Single Si Nanowires Grown by CVD.
Michael Gordon 1 , Thierry Baron 1 , Florian Dhalluin 1 , Pascal Gentile 2 , Pierre Ferret 3
1 Laboratoire des Technologies de la Microelectronique, LTM-CNRS, Grenoble France, 2 DRFMC, CEA, Grenoble France, 3 LETI, CEA, Grenoble France
Show Abstract Electromechanical devices (oscillators, sensors, actuators) and composite materials of the future will probably include some type of one-dimensional nanofilament-like materials such as metallic/semiconductor nanowires (NWs) or carbon nanotubes (CNTs). As such, it is extremely important to measure and understand the mechanical behavior of these materials at the single nanostructure level. Specifically, very little is known about the mechanical properties of directly-grown nanowire structures in comparison to those created using the top-down fabrication techniques of MEMS (albeit somewhat larger in size). In this talk, we present AFM-based measurements on the elastic response and fracture of single Si nanowires (D<300 nm, L=0.1-5 μm) grown directly on patterned substrates by metal-catalyzed CVD (vapor-liquid-solid technique). Straight and kinked wires in different orientations (vertical, inclined, or horizontal to the substrate) were studied to show that both vertical and lateral load testing of nanostructures is feasible using AFM. Individual Si NWs (one end fixed, one end free) were directly forced at several positions along their lengths with an AFM tip using static and cyclical loading. A simple double beam model (rectangular AFM cantilever + circular NW) was used to extract NW defection vs bending force from the cantilever load-unload curves, allowing the spring constant and elastic modulus (E) of the wire to be determined. For example, [111] oriented Si NWs (D=180-200 nm, L=4 μm) grown on (100) Si exhibit elastic moduli (86-125 GPa) lower than bulk (111) Si (188 GPa), while smaller wires (D=120 nm, L=3.2 μm) typically have larger values in the 235-250 GPa range. Evolution of elastic properties and failure were investigated with respect to wire diameter, length, and material (Si vs SiGe modulated wires). Some wires show sudden jumps in the loading curve which may indicate partial fracturing or localized brittle relaxation caused by defect creation long before ultimate failure occurs. In addition, the ultimate strength of NWs was seen to depend on the wire diameter.
12:15 PM - Z4.10
Wrinkling of Ultrathin Polymer Films.
Christopher Stafford 2 , Bryan Vogt 2 , Rui Huang 1
2 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 1 Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, Texas, United States
Show AbstractRecently, a wrinkle-based metrology was developed to measure elastic properties of thin polymer films. For ultrathin polymer films (thickness less than 30 nm), the measured wrinkle wavelengths deviate from the conventional theory, and the deduced elastic modulus decreases with decreasing film thickness. In addition, the measured wrinkle amplitudes also differ significantly from the conventional analysis. These experimental results raise a fundamental question as to what are the physical origins for the deviations, in particular, the thickness-dependence of the elastic modulus for the ultrathin films. This paper proposes a bilayer model to account for the surface effect on wrinkling that leads to such a change in the deduced modulus. It is found that, while surface stress has no effect on wrinkle wavelength, the thickness and modulus of the surface layer lead to a size effect in the wavelength-to-thickness ratio, with longer wavelength (thus lower modulus effectively) as the film thickness decreases in the ultrathin regime. The bilayer model provides a consistent understanding of the experimental results (both wrinkle wavelengths and amplitudes), from which a set of material properties for the surface and the bulk of the polymer films are deduced.
12:30 PM - Z4.11
Mechanics of Crystalline Boron Nanowires
Weiqiang Ding 1 , Lorenzo Calabri 2 , Xinqi Chen 1 , Kevin Kohlhaas 1 , Rodney Ruoff 1
1 Mechanical Engineering Dept, Northwestern University, Evanston, Illinois, United States, 2 Dipartimento di meccanica e tecnologie industriali, Universita di Firenze, Florence Italy
Show AbstractOne-dimensional nanostructures such as nanowires attract attention in part due to their promise in sensing, materials reinforcement, and nanoelectronics. Crystalline boron nanowires have been synthesized by the chemical vapor deposition method with preformed metal catalyst particles.[1] They have p-type semiconductor behavior, and show rectification. We report the Young’s modulus and fracture strength values of these boron nanowires, studied with the mechanical resonance method and by tensile testing.The mechanical resonance of cantilevered B nanowires was excited with an electrically, or mechanically, induced periodic load, and their frequencies were used to obtain the Young’s modulus of the nanowires according to simple beam theory. The effect of boundary conditions was studied and imperfect clamping yielded a lower resonance frequency then for more rigidly clamped nanowires. Tensile loading measurements on these B nanowires were performed to obtain the Young’s modulus (E) and fracture strength sf. The fracture strength of the nine boron nanowires tested ranged from 2 to 8 GPa. The modulus values from tensile tests are consistent with the set of values obtained from the mechanical resonance tests. A comparison is made for E and sf for these B nanowires and larger diameter (conventional, thermal CVD grown) boron fibers.Reference:1.Otten, C.J., et al., Crystalline boron nanowires. Journal of the American Chemical Society, 2002. 124(17): p. 4564-4565.*Corresponding author. R.S. Ruoff: Tel: +1 847 467 6596; Fax: +1 847 491 3915; Email address: r-ruoff@northwestern.edu Acknowledgement:This work was funded by NSF EEC-0210120, and in part by ONR #N000140210870 (partial support, W. Ding) and by the NASA BIMat URETI # NCC-1-02037 (support for X Chen). The SEM and TEM work was performed in the EPIC facility of NUANCE Center at Northwestern University. The NUANCE Center is supported by NSF-NSEC, NSF-MRSEC, Keck Foundation, the State of Illinois, and Northwestern University. We appreciate receiving the boron nanowires from Dr. C. Otten (Buhro group, Washington University-St. Louis.)
12:45 PM - Z4.12
Development of Electrostatic Actuated Nano Tensile Testing Device for Mechanical and Electrical Characteristics of FIB Deposited Carbon Nanowire.
Yoshitada Isono 1 , Mario Kiuchi 2 , Shinji Matsui 3 4
1 Department of Micro System Technology, Ritsumeikan University, Kusatsu, Shiga, Japan, 2 Graduate School of Science and Engineering , Ritsumeikan University, Kusatsu, Shiga, Japan, 3 Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Himeji, Hyogo, Japan, 4 CREST JAT, Japan Science and Technology Agency, kawaguchi, Saitama, Japan
Show AbstractNovelty: This research develops electrostatic actuated nano tensile testing devices (EANAT) for revealing mechanical and electrical properties of carbon nanowires deposited by FIB-CVD. The carbon nanostructures deposited by FIB-CVD is one of promising nanomaterials used for NEMS. In this research, mechanical properties of 85 nm-diametric carbon nanowires were evaluated using three types of EANAT including electrostatic comb-drive actuators. Consequently, we have, for the first time, succeeded in obtaining accurate stress-strain curves of carbon nanowires. Young’s modulus of carbon nanowires averaged 80 GPa, which was close to reported values of ultra-thin diamond like carbon films. The tensile strength of nanowires was also 6 GPa in average. We will present I-V characteristic of carbon nanowires under uniaxial tensile loading for measuring piezoresistance coefficient.Background: FIB-CVD using a phenanthrene gas has demonstrated its ability to fabricate three-dimensional carbon nanostructures, which is used as parts of NEMS such as piezoresistive nanomechanical sensors, nano actuators and nano manipulation tools. However, insufficient understanding of physical properties of the carbon nanostructures hinders safe and reliable design of NEMS. This is due to problems associated with measuring ultra-small physical phenomena in material tests. As the first trial, this paper focuses on performing nano mechanical characterization of carbon nanowires using EANAT.Results: The EANAT is composed of three parts; (1) the specimen part including a carbon nanowire with a diameter of 85 nm and a length of 5 μm, (2) electrostatic actuator array part that are supported by suspended beams for applying uniaxial load to the nanowire, and (3) the measurement part including a cantilever used as lever motion amplification for calibrating load and displacement. The EANAT was fabricated by a conventional micro machining process. After fabricating the actuators and the cantilever on the SOI, the nanowire was deposited on the EANAT by the FIB-CVD. Electrostatic actuated nano tensile tests were carried out under a stereomicroscope with CCD camera. The tensile displacement was analyzed from images of moving the cantilever obtained by the CCD. The tensile load is also calibrated from the position of cantilever and the spring constant of the suspended beams. We succeeded in obtaining the variation of displacement at the free end of cantilever with the applied voltage. Here, the difference in the displacement of cantilever before and after failure of the nanowire represented the tensile force spent on deformation of the nanowire. From the variation of cantilever displacement, the stress-strain curve was calculated. The stress-strain curve showed a linear relationship, and Young’s modulus of the nanowire of 78 GPa was obtained, The tensile strength was also 6.5 GPa, so that it can be sufficient for a usage as nanostructures in NEMS.
Z5: 1-D Nanomaterials II
Session Chairs
Hanchen Huang
Jonathan Zimmerman
Wednesday PM, April 19, 2006
Room 2003 (Moscone West)
2:30 PM - **Z5.1
Nanomechanics: a Continuum Theory Based on the Interatomic Potential.
Yonggang Huang 1
1 , university of illinois at urbana-champaign, urbana, Illinois, United States
Show Abstract3:00 PM - Z5.2
Atomistic and Mesoscale Modeling of Self-folding and Unfolding of Carbon Nanotubes.
Markus Buehler 1 , Yong Kong 2 , Huajian Gao 2
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Max Planck Institute for Metals Research, Stuttgart Germany
Show Abstract3:15 PM - Z5.3
Adhesion and Collapse of Carbon Nanotubes.
Vikram Gadagkar 2 , Prabal Maiti 2 , Yves Lansac 3 , Ajay Sood 2 , Anand Jagota 1 , Tian Tang 1 , Chung-Yuen Hui 4
2 , Indian Institute of Science, Bangalore India, 3 , Universite Francois Rabelais, Tours France, 1 , Lehigh University, Bethlehem, Pennsylvania, United States, 4 , Cornell University, Ithaca, New York, United States
Show Abstract3:30 PM - Z5.4
Deformation Micromechanics of Carbon-Nanotube/Epoxy Composites
Robert Young 1 , Chih-chuan Kao 1
1 Materials Science Centre, University of Manchester, Manchester United Kingdom
Show AbstractRaman spectroscopy has been extensively used to characterize the deformation behavior of single-walled carbon nanotube (SWNT) reinforced composites over the last decade. In this study, the micromechanical behavior of randomly-oriented epoxy/SWNT composites has been investigated by using polarized Raman spectroscopy. In particular, the shift of the nanotube Raman G’ band with composite strain has been monitored as a function of the angle between the direction of polarisation and the direction of the tensile axis of the deformation. This has been undertaken for both parallel-parallel and parallel-perpendicular configurations of the laser polarisation and analyzer.The behavior has been modeled in terms of the deformation of a composite with randomly-oriented fibres taking into account the dependence of the intensity of the Raman scattering from the SWNTs upon the 4th power of the cosθ, where θ is the angle between the tensile direction and the axis of the nanotube. Using the known dependence of the rate of shift of the G' band as a function of stress for high modulus carbon fibres, it has been possible to show that the behavior is consistent with the SWNTs having a Young's modulus in excess of 1 TPa. Moreover, it has been demontrated that there is a strong interface and good stress transfer between the epoxy matrix and SWNTs up to about 0.5% strain but at matrix higher strains the interface appears to break down.
3:45 PM - Z5.5
Shape Memory and Pseudoelasticity in Metal Nanowires.
Harold Park 1 , Ken Gall 2 , Jonathan Zimmerman 3
1 Civil and Environmental Engineering, Vanderbilt University, Nashville, Tennessee, United States, 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 , Sandia National Laboratories, Livermore, California, United States
Show AbstractStructural reorientations in metallic FCC nanowires are controlled by a combination of size, thermal energy and the type of defects formed during inelastic deformation. By utilizing atomistic simulations, we show that FCC nanowires can exhibit both shape memory and pseudoelastic behavior that was previously believed to be limited to exotic alloys such as NiTi. Using gold, copper and nickel nanowires, we also show that the formation of defect free twins, a process related to the material stacking fault energy, is the mechanism that controls the ability of FCC nanowires of different materials to show reversibility in loading and thus shape memory and pseudoelasticity.
4:30 PM - Z5.6
Non-linear Effects in Size Dependent Elasticity of Nanowires.
Moneesh Upmanyu 1 , Haiyi Liang 1 , Hanchen Huang 2
1 Engineering Division, Materials Science Program, Colorado School of Mines, Golden, Colorado, United States, 2 Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWe employ a molecular statics approach based on embedded-atom-method (EAM) inter-atomic potentials to study the elasticity of copper nanowires along [001], [110] and [111] crystallographic directions. Self-consistent comparison with the bulk response clearly shows that the overall nanowire elasticity is primarily due to non-linear response of the nanowire core. While the surface stress induced surface elasticity modifies the behavior for ultra-thin nanowires, their contribution is always considerably smaller than that due to non-linear elasticity of the nanowire core. More importantly, for all three orientations, the surface is softer than an equivalently strained bulk, and the overall nanowire softening or stiffening is determined by orientation dependent core elasticity. Finally, we also investigate the effect of lateral facets on the overall elasticity.
4:45 PM - Z5.7
Brittle and Ductile Failure Mechanisms of Semiconductor Nanowires.
Keonwook Kang 1 , Christopher Weinberger 1 , Wei Cai 1
1 , Stanford University, Stanford, California, United States
Show AbstractWe study the mechanical behavior of silicon and germanium nanowires under tensile and other loading conditions using Molecular Dynamics simulations. Several failure mechanisms have been observed depending on temperature, strain rate and interatomic potential models (such as Stillinger-Weber, Tersoff, and MEAM). The two dominant mechanisms are dislocation and crack nucleation initiated from the surface. The critical nuclei are identified and their activation energy barriers are calculated using transition path sampling techniques, with both the atomistic model and a micromechanical model (of the Peierls-Nabarro type). A quantitative comparison between the two models brings new understanding to dislocation/crack nucleation at the nanoscale. Results will be compared with recent deformation tests on nanowires.
5:00 PM - **Z5.8
Multi-timescale Mechanics of Nanotubes and SWNT-materials.
Boris Yakobson 1 , Yu Lin 1 , Ming Hua 1 , Traian Dumitrica 1 2
1 Dept. of ME&MS, and Dept. of Chemistry, Rice University, Houston, Texas, United States, 2 Dept. of ME, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractA bulk of work in theoretical modeling has been dedicated to the abrupt--essentially, threshold-instantaneous--failure of nanostructures. In this case system is brought "cold" to a large deformation where it abandons its stability domain and fails. Even in the finite temperature molecular dynamics simulations, the observation time is very limited depending on the tradeoff of the force-field accuracy versus the time of simulation (up to pico-or nanoseconds). In contrast, all experimental tests and especially service conditions correspond to rather long time scales. In our recent work we successfully applied a combined approach, where accurate potential surface calculations and the established activation barriers (for the yield-determining events) are passed to the probabilistic kinetic-rate models. This has permitted predictions of nanotube strength limits for extensive "engineering" timescales. Similarly, such time-multiscale approach is applied to inter-tubular cohesion in a material-array or a composite. It starts from detailed quantum-mechanical analysis of the key atomistic rearrangements, which is then passed to the more efficient and less expensive methods like Monte-Carlo simulation or rate theory. This work is supported by the Office of Naval Research (DURINT), by NASA (URETI TIIMS), and AFRL.
Symposium Organizers
Amit Misra Los Alamos National Laboratory
John P. Sullivan Sandia National Laboratories
Hanchen Huang Rensselaer Polytechnic Institute
Ke Lu Chinese Academy of Sciences
Syed Asif Hysitron, Inc.
Z6: Mechanics of Small-scale Devices
Session Chairs
Thursday AM, April 20, 2006
Room 2003 (Moscone West)
9:00 AM - **Z6.1
Towards Quantum Nanomechanics
Raj Mohanty 1
1 Physics, Boston University, Boston, Massachusetts, United States
Show AbstractRecent technological advances have made it possible to createnanomechanical structures that can move over a billion times in a second. If cooled to millikelvin temperatures, these nanomechanical structures enter the quantum regime of mechanical motion; this has finally enabled the long-awaited realization of the text-book example of quantum "mechanical" harmonic oscillator. Such experiments in the quantum regime are now beginning to prospect the ground for a new direction for studies of quantum measurement and quantum computation, involving macroscopic quantum oscillators.I will describe recent experiments in my group, which demonstrate the first observation of mechanical motion in the quantum regime with some of the fastest-moving manmade structures. I will also discuss the prospect of classical nanomechanical computation with memory elements created by nanomechanical silicon beams. Reminiscent of Babbage's original idea of analytical computing, this technology has the potential to supercede current memory technologies in both speed and density.
9:30 AM - Z6.2
The Energy Dissipation from Joule Heating in GaAs Nanomechanical Resonator.
Seung Bo Shim 1 2 , June Sang Chun 1 , Pritiraj Mohanty 2 , Yun Park 1
1 School of Physics and CSCMR, Seoul National University, NS50, Seoul Korea (the Republic of), 2 Physics Department, Boston University, Boston, Massachusetts, United States
Show Abstract9:45 AM - Z6.3
Fabrication and Testing of Polycrystalline Diamond Nanoresonators.
Nelson Sepulveda 1 , Dean Aslam 2 , John Sullivan 3
1 Electrical and Computer Engineering, University of Puerto Rico at Mayaguez, Mayaguez, Puerto Rico, United States, 2 Electrical and Computer Engineering Department, Michigan State University, East Lansing, Michigan, United States, 3 Nanostructures and Semiconductor Physics, Sandia National Laboratories, Albuqueruqe, New Mexico, United States
Show Abstract10:00 AM - Z6.4
Carbon Nanotubes for High Performance Switching Applications.
Anupama Kaul 1 , Eric Wong 1 , Larry Epp 1 , Michael Bronikowski 1 , Brian Hunt 1
1 , Jet Propulsion Laboratory, Pasadena, California, United States
Show AbstractWe describe the fabrication and characterization of a nanoelectromechanical (NEM) device based on carbon nanotubes (CNTs) which is under development for switching applications. Carbon nanotubes are attractive for switching applications since electrostatically-actuated CNT switches have low actuation voltages and power requirements, while allowing GHz switching speeds that stem from the inherently high elastic modulus and low mass of the CNT. Our NEM structure consists of suspended single-walled nanotubes (SWNTs) that lie above a sputtered Nb base electrode, where contact to the CNTs is made using evaporated Au/Ti. The nanotube growth is done on-chip on Fe-catalyst islands using a methane chemical vapor deposition (CVD) process. The evaporated Fe-catalyst layer is deposited on a thin layer of plasma-enhanced CVD SiO2, where the thickness of the latter serves to define the height of the air-gap for the switch. Electrical measurements of these devices show well-defined ON and OFF states as a dc bias is applied between the CNT and the Nb-base electrode. Actuation voltages for electromechanical switching were measured to be as low as 1.4 V and comparisons are made to first-order calculations. Compared to MEMS-based electrostatically-driven switches, the CNT switches were measured to have speeds that are 3-orders of magnitude higher, with switching times down to a few nanoseconds. We also describe FEMLAB modeling of these co-planar waveguide-based devices to calculate the quasi-static capacitance, and present an equivalent circuit of our switch, from which the swept frequency S-parameter response is simulated using Ensemble Design up to 100 GHz. Finally, we will also describe our work on vertical multi-walled nanotubes (MWNTs) that are being fabricated into novel vertical single-pole-double-throw switch configurations.
10:15 AM - Z6.5
In-Situ TEM Electromechanical Resonance Studies of Gallium Nitride Nanowires
Papot Jaroenapibal 1 , Chang-Yong Nam 1 , Doug Tham 1 , John Fischer 1 , David Luzzi 1 , Stephane Evoy 2
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
Show AbstractOne-dimensional gallium nitride (GaN) nanowires have drawn extensive research interest recently for their unique optical properties and nanoscale device applications. Their intrinsic enhanced physical properties, high aspect ratio, and naturally smooth surfaces have also opened up possibilities for the development of new nanoelectromechanical system (NEMS) devices. We have studied the electromechanical properties of GaN nanowires through observations of their mechanical resonances in a transmission electron microscope. Our custom designed specimen holder allows us to directly observe the mechanical resonance of nanowires under external AC actuation. Diameter-dependent Young’s modulus E and quality factor Q of GaN nanowires were measured using this technique. For a large diameter nanowire (d = 84 nm), E is close to the theoretical bulk value ~ 300 GPa but is significantly smaller for smaller diameters. At room temperature, Q is as high as 2800 for d = 84 nm and also appears to decrease with decreasing diameter. For all diameters, Q is significantly greater than is obtained from conventionally micromachined Si resonators of comparable surface-to-volume ratio, implying significant advantages of GaN nanowire resonators for NEMS applications. We will also discuss the observed two closely-spaced resonances that are attributed to the low symmetry triangular cross-section of the nanowires.
10:30 AM - Z6.6
In-situ Observation of Nanoscroll Formation Dynamics.
Terence Yeoh 1 , Mehmet Tasci 2 , James Coleman 2
1 Laboratory Operations, The Aerospace Corporation, El Segundo, California, United States, 2 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractSelf assembled nanoscrolls from strained thin films have generated much interest in recent years due to potential applications in future nanoelectromechanical systems (NEMS). Work by V. Ya. Prinz, M. Grundmann, and O. Schumacher have shown that such structures provide unique physical and electronic properties not available to microelectromechanical systems (MEMS). However, there has not been work observing the formation of nanoscrolls. A dual beam focused ion beam Strata 400 has been used to initiate and observe the formation of nanoscrolls from preprocessed InGaAs/GaAs strained bridges 7-10 microns in length, 1.5 microns in width, and 14 nm thick. A video capture of the scrolling action revealed that the time required for the relaxation of the strained films exceeded 20 minutes in duration. Analysis of the scrolling with time showed unexpected scrolling dynamics such as an initial vertical relaxation of the bridge before the initiation of lateral twisting action. This twisting created a curled nanohelix of diameter half of the expected diameter of a nanoscroll. Simulation of the scrolling action and 3-D modeling and visualization was developed in order to understand the scrolling dynamics of the film. This visualization technique ruled out the possibility of both incremental strain relief along the bridge as expected from wet etched films and simultaneous strain relief as expected from a released bridge structure. Instead, the simulations suggest that the strain relief occurs with a combination of both incremental and simultaneous strain relief that is a result of the topological restrictions of the strained bridge on the curling action of the film.
11:15 AM - Z6.7
Quantitative Nanomechnical Studies with Novel AFM-Based Techniques.
Lin Huang 1 , Sergey Belikov 1 , Hamed Lakrout 2 , Sergei Magonov 1 , Charles Meyer 1 , Gregory Meyers 2 , Nghi Phan 1 , Alan Rice 1 , Chanmin Su 1 , Natalia Yerina 1 , Craig Prater 1
1 , Veeco Instruments Inc., Santa Barbara, California, United States, 2 , The Dow Chemical Company, Midland, Michigan, United States
Show Abstract11:30 AM - **Z6.8
Optical Interactions with Nanomechanical Resonators.
Dustin Carr 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe use coherent light for the study of nanomechanical structures can enable many new explorations into the fundamental properties of these systems. This rich field draws upon complex phenomena from many different areas of interest to materials researchers, including optical absorption, dynamic heat transfer and thermal delay, and coupled thermomechanical phenomena. By using novel optical designs, it may be possible to harness this complexity into useful sensor systems. We will describe new types of nanomechanical structures that are designed to optimize these effects, utilizing rigorous optical modeling techniques and fabricated with electron beam lithography.
12:00 PM - Z6.9
Nanotribology of Chemical Vapor Deposited Microcrystalline Diamond: The Effect of Surface Termination and Orientation on Nanoscale Friction and Adhesion.
Rachel Cannara 1 , Anirudha Sumant 2 , Robert Carpick 2 , Graham Wright 2 , Katherine Cimatu 3 , Steven Baldelli 3
1 Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Chemistry, University of Houston, Houston, Texas, United States
Show AbstractThe increased surface-to-volume ratio at small scales means that surface forces can be devastating for nanoscale devices. Friction, adhesion and wear cause device failures, inhibiting the implementation of nano-electromechanical systems (NEMS) that incorporate sliding, contacting interfaces. A much harder, stiffer, and more inert material than the conventionally-used silicon, chemical vapor deposited (CVD) diamond coatings have been proposed for these applications. To evaluate diamond’s potential for NEMS, it is crucial to investigate its nanoscale surface properties, including friction and adhesion. We compare the nanotribological properties of diamond (100) and (111) surfaces, as well as the effect of hydrogen (H)- versus deuterium (D)-termination, by applying variable-temperature, ultra-high vacuum atomic force microscopy (UHV-AFM) to a series of diamond samples. AFM tips used in these experiments are characterized before and after measurements using transmission electron microscopy, and friction and load forces are fully calibrated. For hydrogen-terminated, <111>-oriented, single crystal diamond at temperatures ranging from 130 to 300 K we find that cantilever tilt-compensation [Cannara, et al., Rev. Sci. Instrum. 76, 053706 (2005)] is required due to surface roughness and inhomogeneities. These non-idealities are endemic to diamond single crystals whose surfaces are extremely difficult to polish to atomic-scale smoothness. Using AFM topographs, regions with roughness < 0.3 nm RMS are selected. We find that the work of adhesion between titanium nitride tips and these regions falls consistently within the range of 0.025-0.095 J/m^2, based on the application of the Derjaguin-Müller-Toporov adhesive contact model. These low values suggest that adhesion arises primarily from van der Waals interactions. The load-dependence of friction shows significant measurement-to-measurement variation, but we estimate the interfacial shear strength to fall between 3.0 – 6.5 GPa, again by using continuum contact mechanics to estimate the contact area. Attempts to determine the temperature dependence of adhesion and friction were prevented by surface inhomogeneity and roughness despite the tilt-compensation procedure used. Thus, we chose to grow microcrystalline diamond (MCD) films using a custom hot-filament (HF) CVD system. MCD was grown with a distribution of flat or terraced <100>- and <111>-oriented grains. The nanotribological properties are measured as a function of load, temperature, surface termination, and local crystal orientation. We H- or D-terminate the surfaces using HFCVD, and verify the termination by sum frequency generation and elastic recoil detection. We compare the results with effects predicted by the known changes in phonon structure due to both the crystallographic orientation and the isotopic substitution of H with D. This represents the first fully-calibrated, quantitative study of the nanotribology of diamond.
12:15 PM - Z6.10
Combined Molecular and Continuum Analysis of IFM Experiments on a Self-Assembled Monolayer
Kenneth Liechti 1 , Mingji Wang 1 , Peter Rossky 2 , John White 2
1 ASE/EM, UT Austin, Austin, Texas, United States, 2 Chemistry & Biochemistry, UT Austin, Austin, Texas, United States
Show AbstractMolecular self-assembled monolayers (SAMs) are used to minimize stiction in MEMs devices and control adhesion in composites. Nanomechanical models of friction, adhesion and fracture require the properties of these SAMs. This talk examines the use of molecular dynamics and continuum analyses and a novel scanning probe microscope for this purpose. An interfacial force microscope (IFM) was used to probe self-assembled monolayers of octadecyltrichlorosilane (OTS) on silicon. Its unique self-balancing force sensor allows the full attractive and repulsive portions of the force-displacement response of the tip/surface interactions to be obtained. The measured force profiles were used judge the validity of linear and nonlinear elastic models of the OTS behaviour in continuum analyses that included surface interactions. The nonlinear behaviour was motivated by molecular dynamics analyses of simple stress states. A hypo-elastic model of the OTS mechanical behaviour, coupled with a traction-separation law representing adhesive interactions, provided excellent agreement with measured force profiles. These results set the stage for a surprisingly simple link between atomistic and continuum analyses of this class of materials.
12:30 PM - Z6.11
Laser Release of Tetrahedral Amorphous–Carbon MEMS Structures.‡
Thomas Friedmann 1 , J. Sullivan 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractAdhesive surface forces resulting in adhered MEMS structures are a well-known problem in devices that cause manufacturing yield reductions. As MEMS device dimensions shrink to the nanoscale (NEMS) these stiction problems can be exacerbated due to reduced restoring forces exerted by less stiff structures and supporting ligaments. There are several common methods for reducing or eliminating stiction such as self-assembled monolayers (SAMS), CO2 supercritical drying, and dry release. One method that has not received much attention is release by laser radiation.We have used a pulsed excimer laser (248 nm) to irradiate tetrahedral amorphous-carbon (ta-C) MEMS structures adhered to the underlying silicon substrate. We find that it is possible to fully release large structures with only a few laser pulses at relatively low fluences near 50 – 100 mJ/cm2. At these low fluences there is no detectable modification of the ta-C material. The 5 eV photons are strongly surface absorbed resulting in a high temperature heat pulse that travels through the material to the ta-C/Si interface. The release mechanism is unknown at this time, but could be due to mechanical vibrations caused by rapid thermal expansion and contraction and/or explosive heating of any trapped volatile components at the interface. We will present the results of laser releasing adhered cantilever beams of different lengths and thicknesses to characterize the adhesive forces on the beams and the efficacy of the release process.‡Sandia is 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.
12:45 PM - Z6.12
Fabrication and Characterization of Ultra Thin Resonant Nanocantilevers in Aluminium-Molybdenum Composites.
Nathaniel Nelson-Fitzpatrick 1 , Colin Ophus 2 , Yongliang Wang 2 , David Mitlin 2 , ZongHoon Lee 3 , Velimir Radmilovic 3 , Ulrich Dahmen 3 , Stephane Evoy 1
1 , National Institute of Nanotechnology, Edmonton, Alberta, Canada, 2 Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractNanoelectromechanical (NEMS) resonators are of great interest for the assaying of molecular masses and external forces with ultra-high sensitivity. In addition, these devices are amenable to their implementation into large arrays, enabling the realization of multiplexed binding assays that could identify and quantify complex protein mixtures with high throughput. To this date, NEMS research and development have focused on the machining of materials such as silicon [1], silicon carbide [2], and silicon nitride [3]. Metallic materials have mostly been overlooked given their limited stiffness and hardness, as well as the challenge associated with the nanomachining of an inherently polycrystalline system. However, the development of NEMS-based devices in such materials would enable new areas of applications for the direct sensing of various chemical compounds without need of intermediate surface derivatization. The development of bimetallic alloys featuring nanometer scale grain structure and enhanced hardness has now opened new opportunities for such development. We here report the fabrication and characterization of nanocantilevers from a novel aluminium-molybdenum nanocomposite. Using a co-sputtering approach, we have realized thin films of Al-Mo alloys of varying composition with amorphous aluminium domains having dimensions on the order of 10nm, as measured by atomic force microscopy (AFM). Mechanical properties of the thin films were also assessed using nanoindentation. The alloys possessed a Young’s modulus as high as 155 GPa, compared to 190 GPa for Si and 70 GPa for pure Al. The alloys also possessed hardness as high as 6 GPa, 2.5 times the value that would be expected from a simple rule of mixtures. Resonant nanocantilevers of width ranging from 200nm to 800nm, thicknesses as small as 20nm, and lengths ranging from 1 to 8um were fabricated in this alloy using a combination of electron beam lithography and lift-off. Resonance frequencies in the 100kHz-1MHz range were measured using a laser interferometric technique. We will present a description on the nucleation and growth of this alloy, report a full analysis of its nanomechanical properties as function of composition and thickness, present preliminary data of the machining and operation of sub-100nm wide resonant devices in this material.[1] D. W. Carr, S. Evoy, L. Sekaric, J. M. Parpia, and H. G. Craighead, Appl. Phys. Lett. 75, 920 (1999).[2] Y. T. Yang, K. L. Ekinci, X. M. H. Huang, L. M. Schiavone, C. A. Zorman and M. Mehregany, and M. L. Roukes, Appl. Phys. Lett. 78, 162 (2001).[3] L. Sekaric, D.W. Carr, S. Evoy, J.M. Parpia, HG Craighead Sens & Act. A 101, 215 (2002).
Z7: Strain Effects in Electronic, Polymer and Bio-Materials
Session Chairs
Markus Buehler
Moneesh Upamanyu
Thursday PM, April 20, 2006
Room 2003 (Moscone West)
2:30 PM - **Z7.1
Growth of Quantum Dots and Wires -- Role of Mechanical Forces in Nanoscale Evolution.
Jerry Tersoff 1
1 , IBM Watson Center, Yorktown Heights, New York, United States
Show Abstract3:00 PM - Z7.2
Strain Mapping From Hrtem Images Of Quantum Dots Structures And Comparison With Fem Simulations.
D. L. Sales 1 , J Pizarro 2 , P Galindo 2 , G Trevisi 3 , P Frigeri 3 , L Nasi 3 , S Franchi 3 , S. I. Molina 1
1 Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz, Spain, 2 Departamento de Lenguajes y Sistemas Informaticos, Universidad de Cadiz, Puerto Real, Cadiz, Spain, 3 , CNR - IMEM Institute, Fontanini, Parma, Italy
Show AbstractStrain can be mapped at nanometric resolution by applying image processing techniques to High Resolution Transmission Electron Microscopy (HRTEM) images obtained in conditions for which a constant spatial relationship between the intensity maxima of the image and the relative positions of the atomic columns in the specimen exists. The most common algorithms used for strain mapping are based on peak finding (real space) and geometric phase (Fourier space). Peak finding methods work in real space, building a two-dimensional reference lattice associated to a non-distorted region of the material, and identifying the local displacements of a grid that is built up from the set of intensity maxima in the HRTEM image. The strain distribution is easily derived from lattice displacements. A new peak finding method, known as the Peak Pairs method, has recently been introduced to map the strain on materials from HRTEM images. This method is based on the detection of pairs of intensity maxima in the affine transformed space. In this paper we apply the Peak Pairs method to map the strain to the nanoscale in self-assembled InAs quantum dots (QDs) laser structures grown on GaAs substrates by atomic layer molecular beam epitaxy. These structures have attracted a great deal of interest for optoelectronic devices applications. The Peak Pairs method allows us to determine the strain distribution around the QDs. The strain distribution determined by using the Peak Pairs approach agrees with the strain maps determined using Finite Element Method (FEM) simulations. Stacking faults are commonly found emerging from some QDs in the studied nanostructures. Strain maps calculated and measured applying the above mentioned methods contribute to improve the understanding of the nucleation mechanism of the stacking faults from the QDs.
3:15 PM - Z7.3
Fabrication and Mechanics of Cu Nanowires/Nanorods.
Jian Wang 1 , Hanchen Huang 1 , S. V. Kesapragada 2 , Daniel Gall 2
1 Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract3:30 PM - Z7.4
Stress Driven Rearrangement Instability of Crystalline Films with Electromechanical Interaction
Peter Chung 1 , Clayton John 1 , Michael Grinfeld 1 , Pavel Grinfeld 2 , William Nothwang 1
1 Weapons and materials Research Directorate, US Army Research Laboratory, AberdeenProving Ground, Maryland, United States, 2 Mathematics Department, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractIt was demonstrated, on general thermodynamic grounds, that, in non-hydrostatically stressed elastic systems, phase and grain interfaces undergo morphological destabilization due to different mechanisms of "mass rearrangement". Destabilization of free surfaces due to the combined action of mass rearrangement in the presence of electrostatic or magnetostatic field are well known from the end of 19th century. Currently, morphological instabilities of thin solid films with electro- or magnetomechanical interactions found various applications in physics and engineering. In the paper, we investigate the combined effects of the stress driven rearrangement instabilities and the destabilization due to the electro- or magnetomechanical interactions. The paper presents relevant results of experimental and theoretical studies for ferroelectric thin films. Theoretical analysis involves highly nonlinear equations allowing analytical methods only for the initial stage of unstable growth. At present, we are unable to explore analytically the most important deeply nonlinear regimes of growth. To avoid this difficulty we develop numerical tools facilitating the process of solving and interpreting the results by means of visualization of developing morphologies.
3:45 PM - Z7.5
Control of Electrical Conductance of Stretchable Gold Films on Nano-patterned Elastomeric Substrates.
Prashant Mandlik 1 , Stephanie Lacour 1 , Jason Li 1 , Stephen Chou 1 , Sigurd Wagner 1
1 Department of Electrical Engineering and PRISM, Princeton University, Princeton, New Jersey, United States
Show AbstractElastically stretchable gold films on elastomeric substrates are a recent discovery that may enable stretchable microelectrode arrays and mechanical-impedance matched contacts to biological tissue. Typically, the resistance of such films rises with applied mechanical strain. We now have observed for the first time that nano-patterned gold films may be stretched by up to 30% with nearly zero change in their resistance. By a novel technique that we developed we control, at the nanometer scale, the initial morphology of the gold film on the elastomeric silicone substrate. This controlled morphology has the effect of keeping the electrical resistance variation with applied strain small. 0.5mm thick polydimethylsiloxane (PDMS) substrates are prepared by casting a precursor mixture on a nano-patterned silicon mold. Chromium/gold (5nm/25nm thick) conductor films are electron-beam evaporated on the nano-patterned PDMS surface through a polyimide shadow mask. Individual conductors are then evaluated by uni-axial stretching while their electrical resistance is measured in situ as a function of the applied strain. The morphology prior to and after stretching is studied using both optical and scanning electron microscopy. After presenting a brief review of elastically stretchable thin-film conductors we will describe the nanopatterning experiments and their effect on the mechano-electrical performance of nanopatterned conductors.
4:30 PM - **Z7.6
An Overview of Capabilities in Multiscale Modeling and Issues in Computational Nanoscience
Eliot Fang 1
1 Computational Materials Science & Engineering, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNanoscale materials provide both scientific opportunities and challenges for theory and simulation. A key opportunity arises from the fact that nanostructured materials have responses governed, in part, by structure on length scales that are readily accessible to computer modeling methods. Thus simulation approaches can be used to explore the structure of molecular assemblies on nanometer length scales, of nanostructured interfaces, of self-assembled nanostructured composite materials, and electronic structure methods can access the optical and electronical behavior of electronically active nanoscale components, just to give a few examples. Although promising progresses have been made in computing technologies and modeling approaches which enables detailed studies of collective and cooperative materials phenomena at nanoscale, significant challenges in theory and numerical algorithm developments still remain to be overcome. It is well recognized that fundamental understanding of the behaviors of nanostructured materials will not be addressed by simple extensions of current theoretical methods that are focused on either atomic or macro scales, but will require bridging the gap between these scales with new concepts, new modeling frameworks and new simulation schemes.In this presentation, recent efforts of computational modeling of nanoscale materials will be reviewed, highlighting their successes and challenges. General issues existing in the computational modeling community will be discussed. Lessons learned from bridging physics at the same and different length scales and coupling different simulation codes will also be shared.
5:00 PM - Z7.7
The Synthesis and Mechanical Characterization of High-Porosity Silica Films.
Darren Dunphy 1 , Thomas Buchheit 1 , Carol Ashley 1 , Scott Reed 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States
Show AbstractSilica films possessing high porosity (ca. 90%) are potentially useful as low-k materials, thermal barriers, or optical coatings. However, these materials generally possess poor mechanical properties, a barrier to their integration into practical devices. Here we describe our efforts to synthesize a material with superior mechanical characteristics relative to current materials used to produce low density silica films (specifically aerogel films formed using an ambient-pressure “spring-back” process), and to measure the mechanical properties (modulus and hardness) of these films using a nanoindentation technique. Our materials synthesis utilizes sol-gel chemistry to form silica films; material porosity is obtained through the use of organic templates. Unlike previous templating schemes which produce materials with a narrow pore size distribution (e.g. surfactant-mesophase templating), or multiple well-defined pore sizes (such as hierarchical templating with surfactants and latex particles), we employ multiple templates (small molecule porogens, surfactants, and latex particles) simultaneously to yield a wide pore size distribution, thus allowing a high maximum porosity, while limiting the largest pore size to ca. 20 nm, preventing the unwanted degradation of physical properties (i.e. optical clarity) that accompanies materials with significant macroporosity. Although nanoindentation is a convenient technique for measuring the mechanical properties of thin films, both surface and substrate effects can impair the analysis of soft materials, such as our templated silica or aerogel films. We have therefore undertaken a series of studies to identify the proper experimental protocol needed to yield significant nanoindentation results on these materials. In addition to measuring hardness and elasticity as a function of film thickness (thus examining the contribution of the substrate to the experimental data), we have explored the effect of tip geometry and data workup algorithm on our results. For example, we have found that large errors (100% or more) in the measured modulus can appear if the surface depth of the film is not properly determined during data analysis.Sandia is 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.
5:15 PM - Z7.8
Nanocracking and Surface Buckling of Oxidized Poly(dimethylsiloxane).
Kristen Mills 1 , Xiaoyue Zhu 2 , Shuichi Takayama 2 4 , Michael Thouless 1 3
1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Department of Biomedical Engineering, University of Michigan, Ann Arbor , Michigan, United States, 4 Macromolecular Science and Engineering Program, University of Michigan, Ann Arbor , Michigan, United States, 3 Department of Materials Science and Engineering, University of Michigan, Ann Arbor , Michigan, United States
Show Abstract5:30 PM - Z7.9
Fracture of Nanoporous Polymer Thin-Films
Andrew Kearney 1 , Heitor Chang 1 , Reinhold Dauskardt 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractNanoporous layers are being considered for a range of applications, from low permittivity materials for interlayer dielectric (ILD) and anti-reflective coatings to biosensors and size-selective membranes for biotechnologies. Continued scaling of these applications requires film thickness of a few hundred nanometers and thus individual pores of only a few nanometers in size to ensure uniformity and feature sizes. While successfully achieving many desired film properties, removing material to form such nano-scale porosity generally degrades mechanical properties. In the present study, we present surprising evidence that nanoporous polymer films exhibit increasing fracture energy with increasing porosity. Such behavior is in stark contrast to a wide range of reported behavior for porous solids, which indicates that the fracture resistance typically decreases markedly with increasing porosity. A ductile nano-void growth and coalescence fracture mechanics-based model is presented to rationalize the increase in fracture resistance of the porous polymer film. The model is shown to explain the behavior in terms of a specific scaling of the size of the pores with pore volume fraction. It is demonstrated that the pore size must increase with close to a linear dependence on the volume fraction in order to increase rather than decrease the fracture energy. Independent characterization of the pore size as a function of volume fraction is shown to confirm predictions made by the analytical model. Multi-scale finite element modeling (FEM) was also used to investigate the effect of plastic strain and pore growth upon debonding. The simulations also demonstrate a similar increase in fracture resistance with increased porosity with appropriate pore size and distributions. This multi-scale FEM work confirms how the addition of nanopores fundamentally changes the local deformation and fracture behavior of these materials. Scaling and distribution of pores with porosity are considered in both analytical and multi-scale FEM analysis.
5:45 PM - Z7.10
Biological Nano-adhesive that Strengthens with Tensile Force
Wendy Thomas 1 , Olga Yakovenko 1 , Manu Forero 4 3 , Evgeni Sokurenko 2 , Viola Vogel 3
1 Bioengineering, University of Washington, Seattle, Washington, United States, 4 Physics, University of Washington, Seattle, Washington, United States, 3 Materials, ETH , Zurich Switzerland, 2 Microbiology, University of Washington, Seattle, Washington, United States
Show AbstractAdhesives hold together biological as well as man-made structures. Natural adhesives often have sophisticated functional properties that, if properly understood, can inspire novel man-made adhesives. For example, the biotin-streptavidin system has high specificity and is easily integrated into other nanoscale components, an adhesive from mollusks can anneal irreversibly in the presence of water, and the tiny hairs on gecko feet bind very strongly but reversibly to a wide range of surfaces. Just as biological adhesion displays complex regulation by outside stimuli, there are also efforts to make “smart” adhesives whose properties change reversibly in response to particular inputs. In this talk, I will introduce a biological nano-adhesive that strengthens with tensile forces, and explore its applications. The bacterial adhesive protein FimH binds to the carbohydrate mannose more strongly under mechanical force. Our data suggest that it forms “catch-bonds” that are activated by mechanical force to convert to an alternate long-lived state. These catch-bonds allow the bacteria to bind firmly to host cells or surfaces at high shear but to roll or detach at low shear, in a reversible manner. Thus, the FimH bond functions as a nanoscale seatbelt, locking under dangerously disruptive force, but allowing movement otherwise. In order to engineer adhesive materials from this nanoscale protein, it is necessary to characterize and eventually engineer the mechanical properties of the bond itself and of its integration into microscale materials. In addition to proposing future applications of this smart nanoadhesive, I will demonstrate its use in building a shear-stress sensor that is orders of magnitude smaller that previous sensors that can be introduced into a microfluidic system without complicated integration.
Z8: Poster Session: Nano-devices, Polymers and Composites: Experiments and Modeling
Session Chairs
Friday AM, April 21, 2006
Salons 8-15 (Marriott)
9:00 PM - Z8.1
Using Reactive Force Fields ReaxFF to Model the Mechanics of Small-scale Materials with High Chemical Complexity: Unifying Chemistry and Mechanics.
Markus Buehler 1 , Adri Duin 2 , William Goddard 2
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry, California Institute of Technology, Pasadena, California, United States
Show Abstract9:00 PM - Z8.10
Nano-scale Oscillators and Coupled Oscillators in Tetrahedral Amorphous Carbon.
J. Sullivan 1 , D. Czaplewski 1 , T. Friedmann 1 , D. Carr 1 , B. Keeler 1 , J. Wendt 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States
Show AbstractReducing mechanical oscillator dimensions down to the nano-scale (10’s of nm) and coupling the motion of mechanical oscillators together permits new device functionality. Small mechanical oscillators exhibit higher resonance frequencies (up to the radio frequency range) and do not diffract visible light, which is advantageous for one class of optomechanical devices. Coupled oscillators may exhibit a collective response to a stimulus that far exceeds the response of individual elements of the coupled system, including localization of vibratory modes at regions of heterogeneity or stochastic resonance. One advantage of mechanical systems is that the degree of coupling and the nature of the coupling (e.g. linear or non-linear) may be controlled by the mechanical design. In this work, we have fabricated and measured the characteristics of nano-scale mechanical oscillators and coupled oscillator arrays that were synthesized from tetrahedral amorphous carbon -- a low stress, diamond-like carbon thin film material that is advantageous for MEMS due to its high hardness and resistance to stiction. The nano-scale oscillators were defined using e-beam lithography of an Al etch mask, followed by dry etching in an oxygen plasma and wet etching of the underlying SiO2 layer to create free-standing structures. The structures consisted of cantilever oscillators with defined dimensions as small as 50 nm and a fundamental oscillatory mode in the plane of the film. Interdigitated cantilevers were fabricated to permit a new type of optical detection of motion with sensitivity better than 100 fm/Hz1/2. The coupled oscillator arrays were fabricated as a two-dimensional square lattice with 10,000 nodes. Each node supports a 1 micron square tungsten proof mass, and the nodes are connected by tetrahedral amorphous carbon beams of