Symposium Organizers
Robert F. Cook National Institute of Standards and Technology
William Ducker University of Melbourne
Izabela Szlufarska University of Wisconsin-Madison
Robert F. Antrim Rohm and Haas Company
HH1: Nano-Scale Mechanical Metrology and the Limits of Continuum Mechanics
Session Chairs
Robert Cook
Izabela Szlufarsksa
Tuesday PM, April 10, 2007
Room 3018 (Moscone West)
9:00 AM - **HH1.1
More Accurate Nanomechanical Measurements and Modeling of Adhesion in MEMS, Bacterial Exopolymers, and Tissue-growth Substrates.
Nancy Burnham 1
1 Department of Physics, Worcester Polytechnic Insitute, Worcester, Massachusetts, United States
Show Abstract9:30 AM - HH1.2
Simultaneous Measurement of Force Gradient, Topography, Tunnel Current and Barrier Height with sub-Ångström Amplitudes
Ozgur Ozer 1 , Simon O'Brien 1 , Graham Cross 1 , John Pethica 1
1 School of Physics, Trinity College Dublin, Dublin Ireland
Show AbstractThe simultaneous use of non-contact Atomic Force Microscopy and Scanning Tunnelling Microscopy is valuable for surfaces having some conductivity. In identification of adsorbates, the information on both local density of states and forces topographs enables separation of electronic from geometric effects. We have recently greatly improved the force resolution and signal/noise ratio of our small amplitude AFM[1]. This has allowed us to routinely acquire not only atom resolved force gradient and LDOS images, but also local barrier height and dissipation maps. We have imaged Si(111) extensively as model surface to demonstrate interplay of short and long range forces. Varying tip conditions and imaging parameters have revealed differing relative atomic corrugations between STM topography and force gradient. In all scans with tungsten lever/tips, corner holes appear with larger attractive force gradient than adatoms, contrary to theoretical predictions[2]. We previously attributed this to the varying contribution of long-range background forces at different sites due to the tip trajectory. This explanation requires large background contributions and hence tips with large radii of curvature. However, we always observed the same contrast with W tips of various cone angles. In order to eliminate the influence of tip path variations we also did constant height imaging experiments. The force gradient scans showed the same sign of contrast. This observation neither agrees with the theoretical calculations nor is explicable with the simple picture of distance dependent one-dimensional force interaction. We also did experiments using Si levers. The results were mostly similar. However, in some cases, after a tip change we observed an inverted contrast in force gradient. The change in the tip is unlikely to cause a considerable change in the contribution of background forces. Thus the inversion in contrast must be due to some mechanism occurring at the atomic scale. It is commonly observed in imaging of oxide surfaces like TiO2(110) and suggested by theory that a change in the charge of apex atom resulting in a change in electrostatic force causes an inversion of contrast in AFM images[3,4]. Similar change in Si tip structure might be causing an inversion in force gradient contrast even on a semiconductor surface by perturbing the local charges or potentials. We also obtained atom resolved barrier height images in both constant height and constant current scans. This may make it possible to extract the influence of topography leading to the measurement of local potentials at atomic sites. Our ultra-small amplitude AFM technique with improved sensitivity opens a good way of sensing the local charges/potentials on surfaces.[1] A. Oral et al., Rev. Sci. Instr. 74, 3656 (2003)[2] R. Perez et al., Phys. Rev. B 58, 10835 (1998)[3] J. V. Lauritsen et al., Nanotechnology 17, 3436–3441 (2006)[4] Hofer W A, Foster A S and Shluger A L, Rev. Mod. Phys. 75 1287 (2003)
9:45 AM - HH1.3
Evanescent Wave Measurement of Separation in AFM Force Studies.
William Ducker 1 , Clayton McKee 1 , Chris Honig 1 , Walz John 2
1 , University of Melbourne, Melbourne, Victoria, Australia, 2 Chemical and Biomolecular Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractThe separation between the probe and the sample is not explicitly measured in an AFM force measurement; the separation is inferred from assumptions about the force profile. We describe the use and applications of explicit probe–substrate separation measurement from the scattering of evanescent waves that are generated in the substrate. The separation between the probe and the sample is not explicitly measured in an AFM force measurement; the separation is inferred from assumptions about the force profile. We describe the use and applications of explicit probe–sample separation measurement from the scattering of evanescent waves that are generated in the substrate. The scattering–separation profile must be calibrated at the start of the experiment, but this profile can then be used to obtain the separation at later times. We validate the measurement of separation from scattering by examining the force–separation profile for (a) samples where traditional AFM analysis is unambiguous and (b) for films that we have calibrated by neutron reflectivity. By comparing our scattering measurements to conventional AFM measurements, we also show that conventional AFM measurements can give the incorrect force-distance profile under conditions where there is a compliant or time-dependent film between the probe and the sample. Applications to both polymer adsorption and this film hydrodynamics will be discussed.
10:00 AM - HH1.4
AFM Characterization of Thermoplastic Elastomer : Adhesion, Stiffness, Topography.
Natasha Starostina 1 , Paul West 1
1 R&D, PacificNanotechnology Inc., Irvine, California, United States
Show Abstract10:15 AM - HH1.5
Quantitative Studies of Nanoscale Elasticity of Polymers with AFM-Based Techniques
Lin Huang 1 , Sergey Belikov 1 , Greg Dahlen 1 , Valeriy Ginzburg 2 , Hamed Lakrout 2 , Sergei Magonov 1 , Robert McIntyre 2 , Charles Meyer 1 , Gregory Meyers 2 , 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 AbstractWe have performed quantitative measurements of elastic modulus of polymer materials at the nanometer scale. The focus of our effort has been on reducing the main sources of error and uncertainty in AFM-based nanomechanical measurements, more specifically in the following areas. The spring constant of the probe was accurately determined by a thermal tune method using a laser vibrometer. Deflection Lateral Compensation (DLC) method substantially reduces the in-plane lateral tip motion during indentation, as well as the non-axial forces that are applied to the surface because of the bending of the AFM cantilever. The shape of the indenter tip was determined by reconstruction of AFM characterizer data, acquired from a traceable VLSI standard, as well as using TEM/SEM methods. For load-displacement curves analysis, we developed a new model combining Sneddon’s elastic theory with Johnson-Kendall-Roberts (JKR) theory of adhesion. Unlike conventional JKR theory, our approach is applicable for arbitrary tip shapes. Using this new model, we estimated modulus of elasticity and work of adhesion for several polydimethylsiloxane (PDMS) samples with various molecular weights between crosslinks. We have achieved a very good agreement between our AFM results and the modulus estimates based on the theory of rubber elasticity. We will present correlation studies between commercial nanoindentation techniques and the AFM measurements. We have also used these techniques to map elasticity variations on polymer blend samples. Research supported by NIST/ATP Award #70NANB4H3055.
10:30 AM - HH1.6
Automated Analysis of Adhesive Interactions in the AFM Probing of Soft Materials
David Lin 1 , Emilios Dimitriadis 2 , Ferenc Horkay 1
1 Laboratory of Integrative and Medical Biophysics, National Institutes of Health, Bethesda, Maryland, United States, 2 National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland, United States
Show AbstractIn the linear stress-strain regime, the macroscopic indentation of a soft, elastic material with a rigid spherical probe can usually be modeled with a high degree of accuracy using the classical Hertz theory provided that the sample is thick enough to avoid substrate effects. Nanoindentation, however, even at small indentation depths, introduces the likelihood of probe-sample interactions playing a significant role in the contact mechanics. These interactive (e.g., van der Waals and electrostatic) surface forces cause the load-indentation behavior to deviate from that predicted by the Hertz theory. Probe-sample attraction is common in the AFM measurement of many biological materials and synthetic gels, and is often manifested in adhesion between the probe and the sample upon tip retraction. Theories pioneered by Johnson et al (JKR) and Derjaguin et al (DMT) incorporate adhesive interactions into the load-indentation relationship using different basic assumptions and have been shown to apply to opposite extremes of sample compliance relative to adhesive force and probe size. The Maugis-Dugdale (MD) theory unifies the JKR and DMT theories by spanning the intermediate regime, but is cumbersome to implement in practice because of the lack of a direct relationship between force and indentation.In this work, we utilize Pietrement and Troyon’s empirical approximation of the MD theory in developing an automated approach to analyzing AFM indentation datasets that exhibit significant adhesive interactions. The Pietrement-Troyon (PT) equation permits extraction of elastic moduli and interfacial energies from the force-displacement data. Using glass and polystyrene spheres glued to the tips of commercial AFM cantilevers, we performed indentations on poly(vinyl alcohol) gels of different composition and mechanical properties and on cartilage specimens. In most datasets, negligible tip-sample attraction was observed in the extension force-displacement curves, allowing points within the linear regime to be fitted with the Hertz equation. In many of the same datasets, significant adhesion was detected in the retraction curves, necessitating the use of adhesive models. We found good agreement between extension and retraction curves analyzed using the two different equations (Hertz and PT), and in the case of the poly(vinyl alcohol) gels, also between the results of AFM and macroscopic compression tests. We conclude therefore, that adhesive interactions in the nanoindentation of soft materials that otherwise exhibit linear behavior are capably modeled by the MD theory, which is cast in a more tractable form by the PT approximation.This work was supported by the Intramural Research Program of the NIH/NICHD.
11:15 AM - **HH1.7
Molecular Dynamics Simulations of Single and Multi-asperity Contacts.
Martin Muser 1
1 Applied Mathematics, University of Western Ontario, London, Ontario, Canada
Show Abstract11:45 AM - HH1.8
Nanoscale Fracture Studies using Atomic Force Microscopy.
Pradeep Namboodiri 1 , Doo-In Kim 1 , Jaroslaw Grobelny 1 2 , Robert Cook 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , University of Lodz, Lodz Poland
Show Abstract12:00 PM - HH1.9
Rigid Spheres with a Thin Elastic Coating: Contact Mechanics with Adhesion
Earl Reedy 1
1 Applied Mechanics, Sandia National Labs, Albuquerque, New Mexico, United States
Show AbstractThere is a continuing interest in the application of contact mechanics to bodies with a thin and relatively compliant elastic coating. Analyses that include adhesion are of particular interest when considering nanoscale contacts. This interest has motivated the development of a new elementary contact mechanics theory for rigid spheres with a thin, linear elastic coating that includes adhesional effects [1]. In the absence of adhesion, this theory predicts that contact area varies as the square root of the compressive load. In contrast, Hertz theory, which applies to uncoated elastic spheres, predicts that contact area varies as the two-thirds power of the compressive load. Finite element analysis confirms an approximate square root dependence of contact area on compressive load when the coating thickness-to-sphere radius ratio is less than 0.1 and when the coating Poisson’s ratio is less than 0.45. Other finite element calculations suggest that the rigid sphere idealization is reasonable when the effective coating modulus is less than five percent of the sphere’s Young’s modulus.The thin coating contact mechanics theory was formulated to include both DMT-like (work of adhesion-to-coating modulus ratio is small) and JKR-like (work of adhesion-to-coating modulus ratio is large) adhesional response. An assessment of the theory required the development of a finite element simulation capability that incorporates adhesional forces and this capability has been verified by comparison to the JKR solution for a thick, compliant substrate. The thin-coating contact theory was found to be in very good agreement with finite element results for both DMT-like and JKR-like response. Interestingly, the thin-coating contact mechanics theory predict a maximum tensile pull-off load of -2πRW (where R is the effective sphere radius and W is the work of adhesion) for both DMT-like and JKR-like response. In contrast, JKR theory, which applies to uncoated elastic spheres, predicts a tensile pull-off load of -1.5πRW. The transition between DMT-like to JKR-like response was also examined and a simple, yet accurate, procedure for interpolating between these limits has been developed.[1] Reedy, E. D., Jr. (2006). "Thin-Coating Contact Mechanics with Adhesion." Journal of Materials Research 21: 2660-2667.Acknowledgement. This work was performed at Sandia National Laboratories. 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.
12:30 PM - **HH1.11
Identifying the Limitations of Continuum Mechanics in Describing Nanoscale Contacts.
Mark Robbins 1 2 , Binquan Luan 3
1 Physics and Astronomy, Johns Hopkins Univ., Baltimore, Maryland, United States, 2 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3 Physics, University of Illinois at Urbana, Urbana, Illinois, United States
Show AbstractHH2: Tools for Nanomechanics
Session Chairs
Tuesday PM, April 10, 2007
Room 3018 (Moscone West)
2:30 PM - **HH2.1
Developing Tools for Nanomechanics Research.
John Sullivan 1
1 CINT Science Dept., Sandia National Labs, Albuquerque, New Mexico, United States
Show AbstractMicromechanical systems are ideally suited for the study of surface and interfacial forces, as evidenced by the widespread application of atomic force microscopy (AFM). The appeal of micromechanical structures, such as cantilever beams, lies in their low force constant, which translates into high sensitivity (large deflection for small forces). At the new Dept. of Energy’s Center for Integrated Nanotechnologies (CINT) we have developed a nanomechanics test platform, called the Cantilever Array Discovery Platform (CADP). This Platform contains a variety of mechanical structures to aid in the development of new force-sensitive scanning probes. Other structures on the Platform are useful for the development of sensors of mass or surface stresses and for applying compressive or tensile loading to compliant materials. The Platform consists of a small chip that is the size of a typical AFM chip and which is compatible with most AFMs. The chip is rimmed by cantilever beams and torsional beams fabricated out of polysilicon and silicon nitride, and there are a variety of microelectromechanical systems (MEMS) in the center of the chip. A unique feature of the chip is the incorporation of a shadow mask or stencil layer that overlays the chip, permitting the patterning of metal or other arbitrary materials as lines or islands on top of the micromechanical structures. This feature enables the placement of, for example, magnetic lines or islands on the ends of cantilever beams, the use of Au lines for scanning conductance measurements, or Pt coatings on cantilevers for electrochemical testing, etc. Other structures on the chip include dense arrays of cantilevers for studying the dynamics of coupled oscillators and cantilever beams suspended over a substrate for the measurement of surface adhesion energies. Electrostatic and thermal actuators in the middle of the chip exist for providing tensile and compressive loading to small scale specimens with applied forces from a few hundred nanoNewtons to over one hundered microNewtons. The actuators span through-holes in the chip, enabling in situ transmission electron microscopy during sample loading. In this work, we describe the features of the CADP and the use of this Platform for nanomechanics research. The Platform is freely available to registered visitors of CINT, and CINT facilities are available to scientists that may be interested in utilizing the CADP in their own research. This work was performed in part at the US Department of Energy, Center for Integrated Nanotechnologies. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
3:00 PM - HH2.2
Integrated AFM Cantilevers-tips Synthesized From Metal Nanocomposites.
David Mitlin 1 , Colin Ophus 1 , Zonghoon Lee 3 , Ken Westra 2 , Reza Mohammadi 1 , Erik Luber 1 , Brian Olsen 1 , Ulrich Dahmen 3 , Velimir Radmilovic 3
1 Chemical and Materials Engineering, University of Alberta and National Institute for Nanotechnology, Edmonton, Alberta, Canada, 3 NCEM, Lawrence Berkeley National Laboratory, University of California, Berkeley, California, United States, 2 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
Show AbstractWhile conventional metal films, such as Au and Pd have been used in a variety of electronic and MEMS devices, they have had limited applications in the field of cantilever-based sensing or as AFM cantilevers/tips. Despite several major advantages over insulators and semiconductors (optically reflecting, tough-ductile, electrically conducting), metals are notoriously difficult to pattern or release due to their high stress state, large surface roughness and low strength. We were able to overcome these limitations by using room temperature co-sputtering to synthesize nanocomposite alloy films with unique microstructures and properties. The aim of this report is to describe the AFM applications, the mechanical properties, and the microstructure of Au-X, Pd-X (where X is one or more alloy additions) nanocomposite thin films. We fabricated a range of compositions and microstructures of these alloys by co-sputtering from different metal targets. Nanoindentation tests indicate that the hardness of the fabricated materials is more than an order of magnitude higher than that of conventional metal films. In addition, within a certain compositional range, the nanocomposites are under nearly zero stress and possess sub-nm surface roughness. These properties are discussed in relation to the materials’ microstructure, characterized by TEM, SEM, AFM and XRD analysis. Using the microstructurally optimized versions of these alloys, we fabricated AFM-usable geometries that consist both the cantilever and the tip, made in a single process. Preliminary tests indicate the usefulness of such devices for electrically conducting AFM probing of materials.
3:15 PM - HH2.3
A Piezoresistive Cantilever Force Sensor for Direct AFM Force Calibration.
Jon Pratt 1 , John Kramar 1 , Douglas Smith 1 , John Moreland 2
1 , NIST, Gaithersburg, Maryland, United States, 2 , NIST, Boulder, Colorado, United States
Show AbstractThe calibration of an atomic force microscope (AFM) for use in force spectroscopy typically involves the measurement of the cantilever spring constant, along with an evaluation of its displacement sensitivity. However, we have shown previously that AFM force sensitivity can be calibrated directly, merely by pressing the AFM probe against a calibrated force sensor of suitable accuracy and form factor, provided one is available. In the previous work, we were constrained by the size and mechanical stiffness of the piezoresistive cantilevers that were available through commercial sources, as well as the limited capabilities of our prototype force calibration system. In this paper, we describe the design, performance testing, and calibration of a new piezoresistive cantilever force sensor fabricated in the NIST clean room facility in Boulder, CO, and tested in the NIST Small Force Metrology Laboratory in Gaithersburg, MD. The sensor is essentially a cantilever beam that rotates about a flexure hinge. The hinge is formed using two parallel beam elements nominally 10 micrometers wide, 50 micrometers long, and 3 micrometers thick, while the actual cantilever consists of a beam 50 micrometers wide, 450 micrometers long, and over 6 micrometers thick. The hinge and cantilever are fabricated as a monolithic structure from a silicon-on-insulator wafer using well-established bulk micromachining processes. The resulting silicon structure is doped with boron using a diffusion process that creates a piezoresistive strain sensor capable of detecting the moment applied to the hinge as a change in the nominal resistance of the device. The sensor can function as either a force reference or stiffness artifact, and it features a series of fiducial marks along its length indicating points of calibratable stiffness and force sensitivity. Initial measurements using the device reveal stiffness values that vary as a simple quadratic function of the distance along the beam, ranging from a high of 12.7 N/m near the cantilever base to a low of 0.4 N/m near the free end. In contrast, the force sensitivity varies linearly with this displacement, and ranges from 0.016 ohms/micronewton to 0.4 ohms/micronewton. The full paper will consider the experimental procedures for establishing the force and stiffness sensitivities of this device using the latest version of the NIST Electrostatic Force Balance (EFB). The NIST EFB is an electromechanical null balance that enables a direct comparison of a mechanical force to an electrostatic force, derived from measurements of length, capacitance, and voltage as realized in the International System of Units (SI). The balance also functions as an instrumented indentation machine, since it provides simultaneous measurement of the displacement of the balance tip and the force applied along this measurement axis. It is this feature of the balance we exploit to provide accurate stiffness and force calibration of these sensors.
3:30 PM - HH2.4
A Micromachined Stick-slip Test Apparatus.
Maarten de Boer 1 , Alex Corwin 1
1 MEMS Device Technologies, Sandia National Labs, Albuquerque, New Mexico, United States
Show Abstract3:45 PM - HH2.5
Measurement of Dissipative Forces for AFM Operation in Fluids
David Mendels 1 , Martin Lowe 1 , Alexandre Cuenat 1 , Francois Mendels 2
1 Division of Engineering and Process Control, National Physical Laboratory, Teddington, Surrey, United Kingdom, 2 , Cognoscens, Lyon France
Show AbstractAccurate determination of dissipative forces is a pre-requisite for measurement of mechanical properties of molecular features in fluids.Recently, a refined method was introduced to analyse the dynamic behaviour of AFM cantilevers in vacuum, where particular emphasis was placed on the internal damping behaviour of the cantilever and the effect of residual stresses induced by the reflective coating. Eventually, a realistic rendering of the probe was obtained by finite elements, with excellent correlation to the experimental results from a full-field Polytec scanning vibrometer.In the present work, the approach is extended in order to include the effects of a surrounding fluid medium. To do so, a two-way fluid solid interaction (FSI) scheme was used to couple the compliant cantilever with the transient fluid flow. The simulations allow the determination of the change in frequency and the quality (Q) factor of the probe in various fluids. Namely, air at various hygroscopic ratios and water were successfully simulated for a range of temperatures experimentally relevant. It is shown that the frequency as well as the tip amplitude is modified by the presence of the fluid.We also analyse the effect of constraining the probe into a small volume of fluid, where multiple reflections on surfaces tend to generate coupled vibration modes. This phenomenon is corroborated by experimental results. Finally, a number of simulations have also shown that the cantilever departs from the classical hypotheses of the dynamic AFM: when the cantilever is approached to about 30 micrometres or less from the surface, counter-rotating eddies appear in the fluid under the cantilever, which invalidate the use of one single damping coefficient.
4:30 PM - **HH2.6
Dynamics of Microcantilevers in Fluids.
John Sader 1
1 , The University of Melbourne, Victoria, Victoria, Australia
Show AbstractDue to its relevance to biological and colloidal systems and sensing applications, there is growing interest in the application of dynamic AFM methods to the quantitative determination of forces in fluid systems. While operation in fluids presents no conceptual difficulty, additional complexity arises since the dynamic properties of microcantilevers are strongly dependent on the surrounding fluid.In this talk, I shall present results of a detailed theoretical investigation of the dynamic properties of microcantilevers in fluids. This will include a discussion of the behavior of microcantilevers in proximity to a surface, as typically required in dynamic force spectroscopy studies and MEMS applications, and their behavior far from a surface as is often required in sensing applications. This work also has significant implications to the quantitative measurement of forces in liquid using dynamic methods such as Frequency Modulation AFM. Applications arising from this fundamental theoretical work shall also be presented. This will include a new general scaling law enabling the stiffness of small bodies of arbitrary shape to be determined, since the ability to calibrate microcantilevers is essential to accurate quantitative measurements.
5:00 PM - HH2.7
Precision Friction Measurements for Atomic Force Microscopy using Prototype Microfabricated Lateral Force Cantilevers.
Mark Reitsma 1 , Richard Gates 1 , Robert Cook 1
1 Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractWe introduce a new optimized cantilever design to allow for quantitative Atomic Force Microscope (AFM) friction measurements. The prototype cantilever facilitates the application of known normal and lateral forces, comparable to those acting during a typical AFM friction experiment. The in-situ calibration procedure—which can be performed before, during or after a friction experiment—produces an optical lever sensitivity for lateral forces. This sensitivity is then used to scale raw friction data to obtain quantitative friction force measurements. The microfabricated prototype is compatible with typical commercial AFM instrumentation and allows for other common AFM techniques such as imaging and contact force measurements to be performed using the same cantilever.
5:15 PM - HH2.8
AFM Spring Constant Calibration using Traceable Standard Reference Cantilevers
Richard Gates 1 , Mark Reitsma 1 , Jon Pratt 2
1 Material Science and Engineering Laboratory, NIST, Gaithersburg, Maryland, United States, 2 Manufacturing Engineering Laboratory, NIST, Gaithersburg, Maryland, United States
Show AbstractPrototype reference cantilever arrays have been microfabricated to accurately calibrate the spring constants of AFM test cantilevers. Starting with silicon-on-insulator wafers, a microfabrication process was utilized to pattern an array of uniform rectangular cantilevers onto a thin membrane of Si. The design of the array coupled with the microfabrication sequence resulted in cantilevers with excellent uniformity from die to die across the wafer. Variation in cantilever uniformity on devices from different parts of a wafer was analyzed using resonance frequency measurements. Results showed a less than 1% relative standard deviation suggesting that the spring constant variation was held to less than 3%. The stiffness of representative cantilevers was independently calibrated using an electrostatic force balance (EFB) at NIST that is traceable to the Système International d’Unité (SI) and is capable of measuring stiffness down to 0.026 N/m with a precision better than 2%. The stiffness measured by the EFB agreed to within 3% of the values predicted from the cantilever dimensions and material properties using simple Euler-Bernoulli beam theory.In parallel with the array development is method development that uses the array to calibrate the spring constant of an unknown AFM test cantilever more precisely. Calibrations were performed on each of the reference cantilevers in the array and the test cantilever stiffness was extracted from the linear regression fit of the data. Using this method, a precision of better than 2% was achieved which is considerably better than the ± 10% usually observed for single beam reference cantilever calibration methods.The prototype cantilever arrays offer the potential for calibrated, SI-traceable reference cantilevers that could be made available to the AFM community and would for the first time provide true accuracy to AFM cantilever spring constant calibration. A NIST Standard Reference Material (SRM) is currently being produced for this purpose.
5:30 PM - HH2.9
Novel Hybrid Method for the Dynamic Properties of AFM Cantilevers and the Calibration of their Spring Constants.
David Mendels 1 , Alexandre Cuenat 1 , Martin Lowe 1 , David Ellis 2 , Elena Vallejo 2 , Francois Mendels 3
1 Division of Engineering and Process Control, National Physical Laboratory, Teddington, Surrey, United Kingdom, 2 , IDAC Ltd, Croydon, Surrey, United Kingdom, 3 , Cognoscens, Lyon France
Show Abstract5:45 PM - HH2.10
High Resolution AFM-based Transducer for Instrumented Indentation and its Application.
Flavio Bonilla 1 , Roger Proksch 1
1 , Asylum Research, Santa Barbara, California, United States
Show Abstract
Symposium Organizers
Robert F. Cook National Institute of Standards and Technology
William Ducker University of Melbourne
Izabela Szlufarska University of Wisconsin-Madison
Robert F. Antrim Rohm and Haas Company
HH3: Deformation Mechanisms at Nano-scale Contacts
Session Chairs
Xiaodong (Chris) Li
Izabela Szlufarsksa
Wednesday AM, April 11, 2007
Room 3018 (Moscone West)
9:00 AM - **HH3.1
Direct-Observation Nanomechanical Testing in a Transmission Electron Microscope
Oden Warren 1 , S. Syed Asif 1 , Zhiwei Shan 1 2 , Andrew Minor 2 , Eric Stach 3
1 , Hysitron, Inc., Minneapolis, Minnesota, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractThe intense research interest in nanostructures and nanomaterials has resulted in a strong demand for direct-observation nanomechanical testing. Over the past two years, we have developed pioneering quantitative nanoindentation technology for in-situ experimentation in transmission electron microscopes, and have applied this technology to the investigation of microstructural changes that occur during nanoindentation, and to the nanocompression responses of electron-transparent structures such as nanospheres and nanopillars. This presentation will provide examples of deformation mechanisms revealed by the combination of force-displacement data and corresponding transmission electron microscopy movies. This synergistic combination of high-resolution techniques has enabled us to more fully appreciate that mechanical behavior at the true nanoscale is indeed rich and often counterintuitive.
9:30 AM - HH3.2
A Nanoindentation study of BCC Tantalum Single Crystals
Monika Biener 1 , Andrea Hodge 1 , Juergen Biener 1 , Alex Hamza 1
1 Nanoscale Synthesis and Characterization Laboratory, LLNL, Livermore, California, United States
Show AbstractAlthough nanoindentation has become a common tool to study the mechanical behavior of metals, only a few studies have been performed on BCC metals. Here we report on the deformation behavior of BCC single crystal Ta (100), (111) and (110) studied by a combination of nanoindentation and atomic force microscopy. For all three crystal orientations the onset of plasticity is marked by a discontinuity in the load displacement curve, which is most pronounced on the (100) surface. In the subcritical load range residual impressions were not observed. At higher loads, in the plastic deformation regime, a positive strain rate effect was observed, and the pile-up pattern around the indents reflects the symmetry of the crystal surface. We will discuss the origin of the "pop-in" event as well as the atomistic mechanism of the deformation process during nanoindentation.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.
9:45 AM - HH3.3
Nanoindentation of Thin Single Crystalline Gold Films
Marianne Dietiker 1 , Ralph Nylas 1 , Patric Gruber 2 , Christian Solenthaler 1 , Ralph Spolenak 1
1 ETH Zurich, Laboratory for Nanometallurgy, Zurich Switzerland, 2 Universitaet Stuttgart, Insitut fuer Metallkunde, Stuttgart Germany
Show AbstractMechanical properties of thin films are of great interest because thin films are critical components in microelectronic and microelectromechanical systems (MEMS). One of the established methods for characterizing thin film mechanical properties is nanoindentation. However, the indentation response of a thin film deposited on a substrate is a complex combination of the elastic and plastic properties of both film and substrate on which it is deposited. In the present work we illustrate the interaction between the testing setup parameters (e.g. the indentation tip radius), the sample geometry (e.g. the film thickness and/or the properties of the substrate) and the indentation response. Quasi-static and dynamic nanoindentation is used to examine thin single crystalline gold films of different thicknesses (20 nm to 1000 nm) on NaCl substrate. The incipient indentation behavior is analyzed, assuming Hertzian contact up to the first appearance of plasticity. It is shown that proximity of the Hertz point (point of maximum shear stress at the onset of plasticity) to the film/substrate interface decreases the stresses needed for plastic deformation. In addition, it is observed that the distance between Hertz point and film surface influences the onset of plasticity: proximity to the film surface increases the stresses needed for plastic deformation. The effect of the interface on the onset of plasticity as well as the effect of the substrate on film elastic properties and hardness is studied as a function of film thickness and indentation tip geometry. Results are discussed on the basis of finite element simulations.
10:00 AM - HH3.4
Nanoindentation of CuAlNi Shape Memory Alloy
Wendy Crone 1 , Adam Creuziger 2 , Henry Brock 3
1 Dept. of Engineering Physics, Univ. of Wisconsin - Madison, Madison, Wisconsin, United States, 2 Engineering Mechanics Programs, University of Wisconsin - Madison, Madison, Wisconsin, United States, 3 Materials Science Program, University of Wisconsin - Madison, Madison, Wisconsin, United States
Show AbstractInstrumented nanoindentation is an important tool for materials properties characterization at small scales. It has been widely used as a quantitative technique for a range of materials and in more recently it has been applied to shape memory alloys (SMAs). The results of such testing in SMAs is much more difficult to interpret due to the added complexity of a reversible solid-state phase transformation that can be induced mechanically or thermally. This talk will address the development of a deeper understanding of the mechanics of the deformation taking place under the indenter. Linear features experimentally observed near indentations in CuAlNi are correlated with austenite martensite interfaces predicted by the crystallographic theory of martensite. Due to the temperature dependence of the transformation stress in shape memory alloys, these stress-induced martensites are observed to diminish with heating and to reappear with cooling.
10:15 AM - **HH3.5
Deformation in Nano-scale Tungsten-Gold Contacts.
William Unertl 1 , Robert Lad 1 , Steven Smallwood 1
1 , Univ. of Maine, Orono, Maine, United States
Show AbstractExperimental studies of fully characterized nano-scale contacts are rare, but essential to validate theoretical models of elastic and inelastic contact. Deformation of well-defined nanometer sized tungsten/gold contacts was studied at room temperature in ultra-high vacuum. Tungsten probes [(110) orientation & mean-radii in the previously unstudied range of 8 -22 nm] were characterized by field ion microscopy before and after contact and also used as scanning tunneling microscope tips to image the Au(110) substrate. The tungsten tips were indented into the Au (110) surface to depths up to nm to 18 nm. Analysis of the indentations using contact mechanics models yielded effective moduli scattered about the expected bulk value. Multiple discrete yielding events occurred during the plastic deformation regime. The yield points correspond to an initial average critical yield stress of about 10 GPa. During probe withdrawal, “pop-out” events relating to material relaxation within the contact were observed. No adhesion was observed until the first yield event. STM images of indentation holes revealed various shapes that can be attributed to the {111}<110> crystallographic slip system in gold. FIM images of the probe after indentation showed no evidence of probe damage.
11:15 AM - HH3.6
Indenter Geometry Effect on Depth-sensing Indentation of Elastic-plastic Materials
Zhi-Hui Xu 1 , Xiaodong Li 1
1 Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractDepth sensing indentation has been widely used for testing material properties, such as, hardness, elastic modulus, and fracture toughness. Different shapes of indenters have been used for indentation test of materials at various scales, e.g., Vickers and Knoop indenters for micro/macro test and Berkovich and cube corner for nanoindentation. These different indenters will create different stress-strain fields in indented materials, which will influence the mechanical properties measured by indentation technique. In this study, finite element modeling was carried out to simulate the depth-sensing indentation behavior of both hard and soft materials with different shapes of indenters. The indenter geometry effects on the stress-strain fields produced by different indenters and their influences on the measured mechanical properties were also investigated. Indentations with different shapes of indenters were carried out on both soft and hard materials to validate the finite element modeling results.
11:30 AM - HH3.7
A Study of the Mechanical Properties of Nanowires using Nanoindentation.
Gang Feng 2 1 , Youngki Yoon 3 4 , William Nix 2
2 Materials Science and Engineering, Stanford University, Stanford, California, United States, 1 Engineering, Brown University, Providence, Rhode Island, United States, 3 Mechanical Engineering, Stanford University, Stanford, California, United States, 4 , Defense Acquisition Program Administration, Seoul Korea (the Republic of)
Show AbstractThe demand for higher packing density in modern devices requires the size of individual components to approach the nanometer scale. Nanomaterials generally have superior properties compared with their bulk counterparts, which have been more and more widely used in electronics, optics, and many other fields. Nanowires are important types of nanomaterials, and they may be used as gas sensors, light sensors, resonators, and high resolution tips for Atomic Force Microscopes (AFM) or Scanning Tunneling Microscopes (STM). While the mechanical properties of nanowires are of interest for both technical and theoretical reasons, the study of these properties has proven to be challenging. In this study, a Nanoindenter XP with scanning capabilities was used to perform nanoindentations on GaN and ZnO nanowires with radii in the range of 20-50nm, positioned on a silicon substrate and bonded to the substrate at their ends with focused-ion beam deposited Platinum. Since the geometry of indentation of a nanowire differs significantly from the indentation of a half space, the standard Oliver-Pharr (Oliver WC and Pharr GM, Journal of Material Research, v.7, 1992, 1564-1583) method of analysis may not be used. A two-interface contact model has been developed for the nanoindentation of a nanowire on a flat substrate, with the two interfaces, indenter/nanowire and nanowire/substrate, being in series. The contact at the indenter/nanowire interface is modeled as an elliptical contact at the sphere(indenter)/cylinder interface. The contact at the nanowire/substrate interface is modeled as a contact at the cylinder/half-space interface under some concentrated forces applied on top of the cylinder. Under these latter conditions the cylinder may be expected to recede from the half-space when the load is applied. In order to predict the contact stiffness for the two interfaces, the theories of Hertzian contacts and receding contacts have been reviewed, generalized and used. Considering the possible adhesion at the nanowire/substrate interface and the fixed ends of the nanowire, we have considered two limits for the contact at the nanowire/substrate interface: one with and one without separation at the interface; thus, we obtain two bounds for the contact stiffness and hardness. The model has been used to analyze the nanoindentation data for GaN and ZnO nanowires. We found that the hardness of the GaN nanowire is 46.7±5.6GPa, which is much higher than that of the ZnO nanowire, 3.4±0.9GPa. We also found that the Oliver-Pharr hardness may be the rough lower bound of the hardness and the Joslin-Oliver hardness (Joslin DL and Oliver WC, Journal of Materials Research, v.5, 1990, 123-126) may be the rough upper bound of the hardness.
11:45 AM - HH3.8
Multimillion-atom Nanoindentation Simulations of Silicon Carbide
Hsiu-Pin Chen 1 , Izabela Szlufarska 2 , Rajiv Kalia 1 , Aiichiro Nakano 1 , Priya Vashishta 1
1 Materials Science, University of Southern California, Los Angeles, California, United States, 2 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractNanoindentation is commonly used to examine elastic-plastic properties of thin films. We have performed million-atom molecular dynamics simulation of nanoindentation on three different crystallographic 3C-SiC planes: (110), (001), and (111). Load-displacement (P-h) curves show major and minor pop-in events during loading. Detailed analysis shows that the first minor discontinuity of P-h curve is related to the nucleation of dislocations, whereas the subsequent major load-drops are related to the dissipation of elastic energy by expansion of dislocation loops and changes of slip planes. Also, kink mechanism for the propagation of dislocation line, mutually repelling glide-set Shockley partial dislocations and extension of stacking-fault areas are observed during the expansion of dislocation loops. The simulation provides quantitative insight into stress distribution on slip planes, and stress concentration at kinks and dislocation cores. The estimated Peierls stress is ~7.5GPa. We predict similar deformation mechanisms on the three different crystallographic planes but with different hardness values; the highest hardness (27.5GPa) is for the (111) plane. Anisotropic pile-up patterns are observed after the indenter is fully unloaded. These patterns all reside on (111) and (-1-11) slip planes, which are closely related to dislocations activities on these two slip planes.
12:00 PM - HH3.9
Molecular Dynamics Simulation of Nanoindentation of Cyclotrimethylenetrintramine (RDX) Crystal
Yi-Chun Chen 1 , Priya Vashishta 1 , Rajiv Kalia 1 , Aiichiro Nakano 1
1 Physics and Astronomy, University of Southern California, Los Angeles, California, United States
Show AbstractUnderstanding of chemical decomposition of energetic materials requires the study of chemical and atomistic processes triggered by mechanical loading. Vickers micro-indentation hardness measurements have been carried out on cyclotrimethylenetrintramine (RDX) surfaces to investigate damage, chemical decomposition and heat dissipation caused by mechanical forces1. We have performed molecular dynamic (MD) simulations of nanoindentation on an RDX crystal surface (100) using reactive force field (ReaxFF) for RDX, the diamond indenter and its interaction with the RDX substrate2. The simulations reveal significant increase in temperature under the indenter, which causes localized melting and decomposition into RDX molecular fragments. Results for stress and temperature distributions in the indented RDX crystal, defect generation and pileup, and the dynamics of fragmented RDX molecules under the influence of stress gradients between the indenter and the substrate will be presented.
1 R. W. Armstrong and W. L. Elban, Mater. Sci. Eng., A, 111, 35 (1989)
2 A.C.T. van Duin, S. Dasgupta, F. Lorant and W.A. Goddard, J. Phys. Chem. A 105, 9396 (2001)
12:15 PM - HH3.10
Deformation Mechanisms of Alpha-alumina Under Hypervelocity Impact
Cheng Zhang 1 , Rajiv Kalia 1 , Aiichiro Nakano 1 , Priya Vashishta 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractDeformation mechanisms in α-alumina under hypervelocity impact are investigated using molecular dynamics (MD) simulations containing 540-million atoms. Projectile impacting normal to the (0001) surface at 18km/s generates large temperature and pressure gradients around the impact face, and consequently local amorphization of the substrate. Away from the impact face, several types of deformations emerge and disappear under the influence of local stress fields, e.g., slips along {0001} and {-1102}, twins along {0001} and {-1012}, and slip-twin-slip structure along {-1011}. During unloading, we observe extensive cracking at the intersection of deformations within an hourglass-shaped volume. The substrate eventually fails along the surface of the hourglass region due to spallation. We will also discuss shock loading on nano-crystalline alumina.
12:30 PM - **HH3.11
Links Between Friction and Structure Elucidated using Molecular Dynamics.
Judith Harrison 1
1 Chemistry, United States Naval Academy, Annapolis, Maryland, United States
Show AbstractThe development of micron-sized devices, such as microelectromechanical devices, for terrestrial and space applications has prompted the need for protection of the surfaces of these devices. Amorphous carbon films, diamondlike carbon, and self-assembled monolayers (SAMs) are all possible candidates for the passivation and lubrication of these devices. The fundamental problem associated with controlling friction is a lack ofunderstanding of the underlying atomic-scale processes that govern both friction and wear. Over the past several years, we have performed extensive molecular dynamics simulations with our AIREBO potential aimed at understanding the atomic-scale mechanisms of friction. We have examined the contact forces present at the interface influence friction and made direction connections between interfacial structure and friction. We have examined the effects of changing the interface structure in several ways.Some of these include changing the structure of the SAM and altering the roughness of the interface. We have done extensive simulations that have analyzed the tribological, mechanical, and transport properties of amorphous carbon films and diamondlike carbon films with various compositions. Some recent results will be presented in this talk. ** Work supported by The Office of Naval Research and The Air Force Office of Scientific Research as part of the Extreme Friction MURI.
HH4: Environmental and Interfacial Effects in Nanotribology
Session Chairs
William Ducker
Izabela Szlufarsksa
Wednesday PM, April 11, 2007
Room 3018 (Moscone West)
2:30 PM - **HH4.1
Nano-scale Mechanics and Tribology of Nanocarbon Materials.
Robert Carpick 1 , Rachel Cannara 2 , David Grierson 3 , Andrew Konicek 2 , Anirudha Sumant 4
1 Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 4 , Argonne National Laboratories, Argonne, Illinois, United States
Show Abstract3:00 PM - HH4.2
Atomistic Simulations of Nanomechanics and Tribology of Silicon Carbide.
Yifei Mo 1 , Izabela Szlufarska 1
1 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractWed, April 11New Title and Presenting Author - HH4.2 @ 2:00 pmAtomistic Simulations of Nanomechanics and Tribology of Silicon Carbide. Izabela Szlufarska
3:15 PM - HH4.3
Tribology In Polytetrafluoroethylene From Molecular Dynamics Simulation.
Inkook Jang 1 , Peter Barry 1 , W. Sawyer 2 , Susan Sinnott 1 , Simon Phillpot 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractMechanical devices for space applications need to be able to operate reliably in an extreme range of environments. Therefore, the physical and chemical integrity of the materials has to be assured under extremes of both high and low temperature, under ambient pressures and in near absolute vacuum, and under solar radiation. Polytetrafluoroethylene (PTFE) is known to have good thermal and chemical stability, and a low frictional coefficient. Thus polymer nanocomposites based on PTFE are considered to be promising materials for solid lubricant in aerospace applications. Like other polymer materials, many properties of PTFE depend on morphology. By changing the polymeric chain structure and combining it with other materials, it is likely that the frictional coefficient of PTFE can be made lower and its wear resistance further improved. In order to develop new material systems with superior frictional properties or to improve the existing ones, it is necessary to understand the detailed mechanisms of their frictional behavior, and the effect of molecular structure on friction. In this study, molecular dynamics (MD) simulations are performed to examine the effects of chain configuration, temperature, and the presence of wear debris, on the frictional behavior of PTFE at the molecular level, with the aim of identifying the fundamental wear mechanisms, and guiding the further refinement of the materials with low frictional coefficients for space applications. This work is supported by a MURI from the Air Force Office of Scientific Research through grant FA9550-04-1-0367.
3:30 PM - **HH4.4
Nanomechanics Approaches to Understand Tribological Processes
Richard Chromik 1 2 , Gun Lee 1 , Kathryn Wahl 1
1 Tribology Section, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 2 Mining, Metals and Materials Engineering, McGill University, Montreal, Quebec, Canada
Show AbstractFriction, wear and endurance of sliding contacts are controlled by interfacial processes including “third body” transfer films. These third body films are thin, inhomogeneous, and differ from the originating surface both chemically and mechanically. Our in situ tribological studies have shown that these films also exhibit dynamic rheological properties that depend strongly on sliding environment. In this talk, we illustrate how spatially resolved, surface sensitive nanomechanics and microtribology experiments can be used to study solid lubrication processes. We correlate nanomechanical properties of the interfacial films with macroscopic tribological response. Also, by rastering the indenter tip laterally, instrumented indentation apparatus can be used to examine microscale sliding processes and address scaling effects in solid lubrication. In both cases, knowledge of counterface geometry, penetration depth, load, and position are key, enabling evaluation of the lubrication mechanisms as well as comparison with contact mechanics models.
4:30 PM - HH4.5
Nanoscale Adhesion in Humid Air.
Dooin Kim 1 , Jaroslaw Grobelny 1 2 , Namboodiri Pradeep 1 , Robert Cook 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , University of Lodz, Lodz Poland
Show AbstractInterfacial mechanics at the nanoscale is greatly influenced by the humidity of the environment due to spontaneous condensation and the formation of a water meniscus between contacting surfaces. The force associated with the phenomenon called the “meniscus force”, modifies the contact geometry altering the adhesion mechanism between the surfaces. The origin of adhesion at nanoscale contacts in humid air is investigated by pull-off force measurements using atomic force microscopes in controlled environments from ultra-high vacuum through various humidity conditions to water. An equivalent work of adhesion (WOA) model with a simplified interface stress distribution is developed, combining the effects of screened van der Waals and meniscus forces, that describe adhesion in humid air and which self-consistently treats the contact stress and deformation. Although the pull-off force is found to vary significantly with humidity, the equivalent WOA is found to be invariant. Increasing humidity alters the nature of the surface adhesion from a compliant contact with a localized, intense meniscus force to a stiff contact with an extended, weak meniscus force.
4:45 PM - HH4.6
Surface Roughness Effect on the Humidity-Induced Ahesion in Atomic Force Microscopy
Joonkyung Jang 1
1 Nanomaterials Engineering, Pusan National University, Miryang Korea (the Republic of)
Show AbstractWe report a lattice gas Monte Carlo simulation for water menisci that form between a silicon nitride tip (with a 20nm diameter) and a mica. This water meniscus at the nanoscale gives rise to a capillary force sensitive both to surface roughness and to tip roughness. The humidity dependence of the force changes significantly with slight variation in the tip and surface morphology. The change in the capillary force due to roughness less than 0.6 nm can be larger than the change from doubling the tip radius. The roughness effect is large at low humidities and diminishes as humidity increases. Even at 80 percent humidity, the capillary force varies significantly with changes in tip-surface geometry. The capillary force tends to decrease with increasing tip roughness. The force decreases with surface roughness for small roughness (about 0.2 nm) and then it increases for larger roughness. We show that the magnitude of the capillary force is closely related to the degree of spatial confinement of the water meniscus.
5:00 PM - HH4.7
Dependence of Surface Friction on the Intramolecular Dynamics of an End-grafted Monolayer of Poly(isobutylene)
Jonathan Bender 1 , Junhong Jia 1
1 Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show Abstract5:15 PM - HH4.8
Frictional Aging of a Monolayer-coated Micromachined Actuator.
Alex Corwin 1 , Maarten deBoer 1
1 MEMS Technology Dept. 1749, Sandia National Labs, Albuquerque, New Mexico, United States
Show Abstract5:30 PM - HH4.9
Friction in Contacts of Different Adhesive Strength.
Marina Ruths 1
1 Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractThe boundary friction of self-assembled monolayers consisting of different aromatic molecules and fatty acids has been measured in a single-asperity contact with the surface forces apparatus (SFA) and with an atomic force microscope (AFM). The strength of the adhesion between the sliding surfaces is altered by working in dry N2 gas or in ethanol. Low adhesion (in ethanol) results in a linear dependence of the friction force on load already at low loads, whereas high adhesion (in N2) gives an apparent area-dependence. The reduction of the area-dependence in ethanol allows a direct, quantitative comparison of load-and velocity-dependent friction of surfaces whose radius differs by 5-6 orders of magnitude. It is also shown that when applying a contact mechanics model recently developed by Sridhar, Johnson and Fleck for adhesive, layered systems to data obtained in N2 with the AFM, it is possible to obtain critical shear stresses that agree well with data established with the SFA.
5:45 PM - HH4.10
Friction properties of Antistiction Layer for Nanoimprint Lithography (NIL) by Vapor SAM (self assembly monolayer)
Kyu Chae Kim 1 , Nam Goo Cha 1 , Min Soo Cho 1 , Jin Young Kim 1 , Jin Goo Park 1
1 , Hanyang University, Ansan Korea (the Republic of)
Show AbstractNanoimprint lithography (NIL) is a novel method of fabricating nanometer scale patterns. It has a potential to be such a method allowing low-cost, high-throughput production of nanopatterns over large areas employing a single lithographic step. It creates patterns by mechanical deformation of imprint resist and subsequent processes. The imprint resist is typically a monomer or polymer formulation that is cured by heat or UV light during the imprinting. The stiction occurred during process is a serious problem of NIL. The antistiction layer is the solution of the stiction problem. The surface energy of either mold or polymer should be low enough by either chemical modification of surfaces or applying antistiction coating on surfaces. Various anti-sticiton coating methods are available in liquid, vapor and plasma atmospheres. Among them, vapor SAM (self-assembled monolayer) method is most promising due to its capability to coat deep and narrow patterns and good adhesion properties on surfaces. In this study, the antistiction layer on Si and SiO2 by vapor SAM method with FOTS (perfluorooctyltrichlorosilane) were deposited and characterized. The frictional behavior of the film was especially investigated to estimate the reliability of films. Vapor SAM were deposited as a function of temperature to find out optimized conditions. Static and dynamic contact angles were measured. Surface energies were calculated by Lewis acid-base theory. The thickness of antistiction layer and optical properties were measured by spectroscopic ellipsometry. A measured thickness showed about 1 nm in 4 inch wafer. AFM/LFM (atomic/lateral force microscope) was conducted to compare morphology and friction force between samples. Friction coefficient was derived by the slope of lateral force and normal force graph. The quality of antistiction layer was stable when the film was coated at over 140 degree. It was possible to get successful imprinting results applying this antistiction layer on quartz stamp.
HH5: Poster Session: Surface and Interfacial Nanomechanics Posters
Session Chairs
Robert Antrim
Robert Cook
Thursday AM, April 12, 2007
Salon Level (Marriott)
9:00 PM - HH5.1
Making a Nanoscale Mechanical Spectrum Image from a Series of Single Frequency Atomic Force Acoustic Images
David Shuman 1 , Ramesh Nath 1 , Bryan Huey 1
1 Chemical Materials and Biomechanical, University of Connecticut, Storrs, Connecticut, United States
Show AbstractA novel method to characterize the nanomechanical properties of a surface is based on atomic force acoustic microscopy (AFAM) which relates to the elastic modulus. The contact acoustic resonance depends on the mechanical response of the AFM tip with the sample surface. By sweeping the frequency driving the tip vibration and then detecting cantilever deflection using either a lock-in amplifier or a data acquisition capture card numerical sampling methods. During standard AFAM imaging, the frequency is fixed at one acoustic resonant and the deflection amplitude and phase offset provide local nanoscale mechanical contrast. However, this will only provide a binary SPM image that appears white where the acoustic response is high and dark everywhere else. The dark area might have a higher or lower acoustic frequency. The other resonant peaks are found separately and then imaged. This is time consuming because there might be several weak resonant peaks for at different regions of the sample. Therefore, it is desirable to have a single AFAM image with a gray scale showing all the mechanical properties elastic modulus. One research group has created a spectrum AFAM image by scanning the frequency at each pixel (D. Hurley). Our technique uses a sequence of whole AFAM images made over the range of possible frequencies based on the sample material. Software was developed to find the maximum acoustic resonance from all of the frequency AFAM images. This method was then applied to a SiO2 – Cu IC, a co-polymer, and a refractory intermetallic compound. The results showed a gray scale AFAM image of their nanomechanical properties.
9:00 PM - HH5.10
Effect of Molecular Branching on the AFM Nanotribology of Alkanes.
Jonathan Bender 1 , Junhong Jia 1
1 Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show Abstract9:00 PM - HH5.12
Interface and Film Mechanics of Femtosecond Pulsed Laser-induced Delamination of Thermal Oxide Films from Silicon Substrates.
Joel McDonald 1 , Ben Torralva 2 , Michael Thouless 3 , Steven Yalisove 3
1 Applied Physics, University of Michigan, Ann Arbor, Michigan, United States, 2 , Lawrence Livermore National Lab, Livermore, California, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:00 PM - HH5.13
Evolution of the Nanomechanical Properties of Aging Erbium Tritide Films.
James Knapp 1 , James Browning 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe mechanical properties of tritide films can be dramatically affected by the unavoidable dispersion of He3 bubbles produced by T decay. These changes in mechanical strength, which can only be quantified in thin films using nanoindentation, in turn will affect He3 retention as well as ultimate film failure. We have been measuring a set of model ErT2 films as they age, tracking the changing hardness and elastic properties. Detailed modeling of the indentation data is used to separate the properties of the thin layer from the substrate, giving yield strength, hardness and elastic modulus of the tritide film as a function of helium concentration, with additional properties such as the shear modulus being deduced from these data. The films were formed by depositing 500 nm of Er onto 100 nm of Mo on Si substrates, followed by loading with 100% Tritium. The films have now aged nearly three years, reaching ~9 at.% He3. In the first year the hardness reached 8.5 GPa, or ~75% higher than pure ErD2 (with no He bubbles). After that the hardness leveled off and has now declined slightly. The elastic properties, on the other hand, have remained largely unchanged as the films aged, with only a slight decrease. The intent of this work is to correlate the structural and mechanical properties of the ErT2 films as they age, to further our understanding of the aging process and provide checks for theoretical modeling of the 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.
9:00 PM - HH5.14
Elastic Property Measurements of Nanometer Thick Polymer Films.
William Price 1
1 , National Insitute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractAccurate mechanical property measurements of nanoscale thin films used for electronics or protective films is a current challenge for the semiconductor industry. While the use of atomic force microscope (AFM) with instrumented indentation has encountered wide spread use in measuring properties at nanometer lateral ranges, accurate measurements with this technique still require and indentation depth of several hundred nanometers, especially when measuring polymer thin films.[1] Atomic force acoustic microscopy (AFAM)[2] has been introduced as a promising technique to overcome this limitation and accurately measure the mechanical properties thin films of 100 nm or less. Using single crystals with well-known elastic properties for calibration, both the indentation modulus and the shear modulus can be determined with nanometer precision.[3] The methodology is tested on gradient polymer films with thickness < 150 nm of polystyrene (PS) and polymethylmethacrylate (PMMA) an on nanoscale polymeric structures formed in gradient PS:PMMA block copolymer films. In addition to measuring and mapping the elasticity and shear modulus of the films, AFAM can be used to detect and locate sub-surface defects in the films and quantify their effect on the local elastic measurements.[1] - M. VanLandingham, J. Villarrubia, W. Guthrie, G. Meyers, Macromol. Symp. 167, 15 (2001).[2] - U. Rabe, S. Amelio, E. Kester, V. Scherer, S. Hirsekorn, and W. Arnold, Ultrasonics 38, 430 (2000).[3] - G. Stan and W. Price, Rev. Sci. Instrum. 77, 103707 (2006).
9:00 PM - HH5.15
The Stress Field around an Elastoplastic Contact/Indentation.
Gang Feng 2 1 , Shaoxing Qu 3 4 , Yonggang Huang 3 , William Nix 2
2 Materials Science and Engineering, Stanford University, Stanford, California, United States, 1 Engineering, Brown University, Providence, Rhode Island, United States, 3 Mechanical Science and Engineering, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States, 4 Mechanical and Energy Engineering, Zhejiang University, Hangzhou, Zhejiang, China
Show AbstractThe determination of the stress distribution around an elastoplastic contact between two bodies is a classic mechanics problem, which is potentially useful for various fields, especially nanoindentation, which has become a powerful quantitative tool for nanomechanical characterization at small scales. For example, the stress distribution around an indentation is critical for predicting fracture toughness through indentation-induced cracking and interface properties through indentation-induced film delamination. Although the stress fields around purely elastic indentations can be described in closed-form for indenters with various geometries, the indentation process is generally elastoplastic with a high degree of geometrical confinement and the presence of a plastic deformation zone, making the analysis very complex. In this study, we address the problem of determining an analytical expression for the stress distribution that develops when a rigid indenter is pressed into the surface of an elastic-plastic solid. Enlightened by both experimental and finite element (FEM) results, we present a model that we call the Embedded-Center-of-Dilatation (ECD) model, which is a potentially useful model with a simple closed-form analytical expression. According to this model, the stress distribution outside the contact-induced plastic zone can be estimated by the superposition of a Hertzian field and the field for an ECD in a half space, while the residual stress distribution can be estimated by the ECD field alone. To predict the basic parameters for the ECD field, i.e., the strength and location of the ECD, we use a refined expanding cavity model (Johnson, K.L., 1987. Contact mechanics. Cambridge University Press), which takes account of pile-up and elastic recovery effects. We demonstrate that the ECD model matches with FEM results nearly perfectly. In addition, we find the analytical expression of the ECD model is good for both the cases with and without strain hardening.
9:00 PM - HH5.17
Improving Interfacial Properties of Self-Assembled Monolayers through Detection and Correction of Defects in Silanes
Hanifa Jalali 1 , Byron Gates 1
1 Chemistry, Simon Fraser University, Burnaby , British Columbia, Canada
Show AbstractSelf-assembled monolayers (SAMs) of silane molecules are commonly used as resists to protect semiconductor surfaces from attack by corrosive chemicals, or adhesion of proteins and other biomolecules. The presence of defects in these monolayers diminishes their applicability as resists in semiconductor nano- and microfabrication. It is, therefore, important to identify and correct for these defects. This presentation will discuss the identification and correction of molecular scale (and larger) defects in SAMs on semiconductor surfaces. The position and nature of these defects are analyzed through chemical amplification as well as microscopy and spectroscopy techniques. Further results are presented on methods to chemically modify these defects, improving interfacial properties such as uniformity of etch resistance and surface chemistry of these SAMs.
9:00 PM - HH5.18
Modelling the Effect of Capillary Condensation of Water at Crack Tips in Oxide Glasses.
Matteo Ciccotti 1 , Matthieu George 1 , Antoine Grimaldi 1 , Lothar Wondraczek 2 , Christian Marliere 3
1 Laboratoire des Colloides, Verres et Nanomateriaux , University of Montpellier 2, CNRS, Montpellier France, 2 Corning European Technology Center, Corning SAS, Avon France, 3 Laboratoire de Tectonophysique, University of Montpellier 2, CNRS, Montpellier France
Show Abstract9:00 PM - HH5.19
The Poroelastic Properties of Porcine Coastal Cartilage Determined from Nanoindentation and Finite Element Modeling.
Shikha Gupta 1 , Cheng Li 3 , Jeremy Lin 3 , Lisa Pruitt 2
1 Applied Science and Technology, University of California, Berkeley, Berkeley, California, United States, 3 Bioengineering, University of California, Berkeley, Berkeley, California, United States, 2 Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractThe use of small animal models in orthopaedics research, such as rat and rabbit models, has accelerated the rate at which various clinically relevant processes, pathologies, and treatments can be explored. The orthopaedic tissues found in these small animal models are anisotropic and poroelastic, with a hierarchical structure, and they are present only in very small volumes. While these attributes permit biochemical characteriztion, they preclude the use of global mechanical testing protocols for characterizing their heterogeneous mechanical properties. Since orthopaedic tissues are load-bearing materials, characterization of biochemical properties alone is not sufficient for assessing the health of the tissues. The advent of a nanoindentation has provided a possible method for determining time-dependent mechanical properties on a size scale compatible with tissue dimensions in controlled, physiological environments. However, nanoindentation theory was developed for hard, elasto-plastic materials that are homogeneous and isotropic. Thus, it is unsuitable for the interpretation and analysis of load-displacement curves from nanoindentation of compliant, hydrated tissues. To determine the poroelastic properties, including tissue equilibrium modulus, aggregate modulus, and permeability from nanoindentation requires the results be coupled with numerical simulations. The following study assesses these properties for porcine (pig) costal rib cartilage, which is a homogeneous and isotropic hyaline cartilage.All tissue is obtained from a local butcher within 24 hours of sacrifice, dissected into circular plugs 8 mm x 5 mm thick, washed in phosphate buffered saline (PBS), snap frozen in liquid nitrogen and OCT and stored at -80 deg C. Prior to indentation testing, the tissue surface is cryosectioned. During testing, the sample is placed in a Petri dish and immersed in a room temperature PBS solution. Nanoindentation is performed with a 100 μm radius conospherical tip to an indentation depth of 2 μm with a penetration rate of 300 and 600 nm/s. The sample is allowed to relax for 60 s prior to unloading. The loading portion of the indentation curves are modeled with finite element simulations. The FE model consists of a 2-D axisymmetric mesh consisting of 4000-6000 4-node rectangular elements with linear poroelastic material properties. In order to capture contact mechanical predictions on a fine resolution, the mesh is graded with the smallest elements near the anticipated indentation surface. The indenter is modeled as a single 2-D rigid surface. All simulations are performed by applying the appropriate displacement profile to the rigid indenter surface. The solution for the material properties is obtained through an iterative FEM process that minimizes the error between the experimental and numerical data. The resulting parameters are then compared to the poroelastic properties determined from bulk unconfined compression tests.
9:00 PM - HH5.2
Structural, Mechanical and Morphological Changes in Human Tooth Enamel Due to Demineralization and Remineralization Processes.
Carmen Gaines 1 , Gerald Bourne 1 , Kenneth Anusavice 2 , Valentin Craciun 1
1 Materials Science & Engineering, University of Florida, Gainesville, Florida, United States, 2 Dental Biomaterials, University of Florida, Gainesville, Florida, United States
Show AbstractTooth decay via chemical attack results from the destruction of the highly mineralized surface enamel, a crystalline mixture of fluroapatite and carbonated hydroxyapatite. Little is known of the physical and chemical mechanisms surrounding early tooth decay. Current diagnostic techniques lack the spatial resolution required to analyze the process at the atomic level. Progress in the understanding of tooth enamel mechanical properties has been recently achieved when microindentation was replaced by nanoindentation. However, mechanical property changes are just the observable results of underlying structural, chemical or morphological changes that should be investigated and analyzed. In this study, decay-free human incisor teeth were set in an epoxy resin and polished to expose at least 5mm2 of hard, porous enamel. The teeth were subjected to various acidic demineralizing treatments. Grazing incidence x-ray diffraction (GIXD), a technique typically used in thin film analysis, provided a depth profiling of the crystallinity changes along the enamel surface with a resolution better than 100 nm. The recording and modeling of the x-ray reflectivity (XRR) spectra within the same region may provide new information about the surface morphology and mass density of enamel at an even better resolution. The demineralized enamel was then subjected to remineralizing solutions to initiate mineral regeneration, the results of which were analyzed similarly. Comparisons of changes in crystallinity, surface morphology, mechanical properties among the treated enamel will be presented.
9:00 PM - HH5.20
Tribological Reliability of Vapor Deposited 1H,1H,2H,2H-Perfluorodecyltrichlorosilane by AFM
Tae-Gon Kim 1 , Ahmed Busnaina 2 , Jin-Goo Park 1
1 Div. of Materials and Chemcial Engineering, Hanyang University, Ansan Korea (the Republic of), 2 National Science Foundation Center for Microcontamination Control, Northeastern University, Boston, Massachusetts, United States
Show AbstractHighly hydrophobic fluorocarbon (FC) films have been widely used for the prevention of stiction in nanofabricated structures and the surface modification of high energy hydrophilic surface for microfluidics and the easy removal of plastic chips from silicon mold. These films have been commonly prepared by self assembled monolayer (SAM) and chemical vapor deposition (CVD). A simple flat surface could be coated by SAM, however the nano or micro patterned structures could not be immersed in the solutions for SAM due to the destruction of the system or insufficient coatings on the bottom of nano/micro patterns. CVD has been used for the deposition of FC films on nanofabricated complex structures.The reliability of thin organic films is very important for the stable operation of micro/nano systems. Especially tribological reliability for micromolding process such as hot embossing and injection molding are very important characteristics of FC films for the long term reliability. However, it is not easy to predict quantitative tribological characteristics without applying force on films very carefully. In this study, the quantitative characterization of tribological reliability on films has been investigated by AFM.1H,1H,2H,2H-Perfluorodecyltrichlorosilane (FDTS) precursor was deposited on silicon by vapor SAM. Colloidal probe was made of 100 µm soda lime sphere glass (Duke Scientific, USA) with a silicon cantilever. Applied force was calculated by Hertz model to select proper contact pressure because typical embossing force is the order of 20~30 kN for 4 inch PMMA (polymethyl methacrylate) or PC (polycarbonate) substrate. Tip velocity and number of scan line at same line were controlled by AFM (XE-100, PSIA Co., Korea). Signal of friction loop was collected during the scan.When the force is applied to 1 nN which means that contact pressure is 3.82 MPa by Hertz model and number of times of scan was 1024, there is no change of half width of friction loop during scan. However, the half of friction loop is slightly changed at 800 times scan when force is applied to 9 nN which means that contact pressure is 7.95 MPa. It may say that if pressure applied about 8 MPa during embossing, film can be used about 800 times. Therefore reliability of film can be predicted by AFM with colloidal probe.
9:00 PM - HH5.21
Strengthening of Ni by He Nanobubbles.
David Follstaedt 2 , James Knapp 2 , Samuel Myers 2
2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNanobubbles produced by ion implanting He are found to strengthen fcc Ni to a degree consistent with their binding dislocations that contact them. Such binding occurs due to the reduction in the strain energy surrounding dislocation cores when near a bubble, which was seen in dislocation-cavity interactions in semiconductors (J. Appl. Phys. 86, 3048 (1999)) and can be generally expected to occur in metals as well. We have investigated He concentrations from 1 to 5 at.% implanted into layers ~500 nm deep in large-grained Ni implanted from room temperature up to 500°C. The strengths of the implanted layers were determined by nanoindentation to depths of ~80 nm, coupled with finite-element modeling to account for the combined response of the layer and its softer substrate. Yield strengths up to 2.3 GPa (for 5 at.% He, implanted at room temperature) were found. TEM shows that implantations at 200°C and lower result in formation of ~1 nm diameter bubbles for all concentrations. For constant-size bubbles, the number of pinning centers encountered per unit dislocation length varies as (conc.)^1/3, and indeed the yield strength varies linearly with this quantity. Implantations at 500°C produced enlarged bubbles, up to 6nm in diameter for 5 at.% He. An Orowan-type hardening model incorporating more complete treatments of particle size and interactions between dislocations, like that used for oxide nanoprecipitates in Ni (Metall. Mater. Trans. 34A, 935 (2003)), was applied to the bubble nanostructures. This treatment accounts well for the strengths of He-implanted Ni layers over the full range of concentrations and bubble sizes investigated. To understand better the binding of dislocations to the bubbles, numerical simulations were performed to examine atom energies as a function of position as dislocations move through cavities. In addition to the strain-related energy change, a further impediment to a dislocation moving out of a cavity is the energy required to create an atomic step on a cavity interior, which must necessarily occur if dislocations pass through. The computed stresses required to move dislocations through cavities are consistent with the strengths we observe for Ni with He bubbles.We will also discuss the response of He-implanted Ni at greater indentation depths, where a break in slope of the force versus depth response curves can be accounted for by the onset of dislocation nucleation in the substrate. This work is supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.
9:00 PM - HH5.22
Fabrication and Testing of NEMS Components Made From Nanocomposite Ni-Mo and Al-Mo Films.
Velimir Radmilovic 4 , Zonghoon Lee 4 , Colin Ophus 1 , Reza Mohammadi 1 , Erik Luber 1 , Nathan Nelson-Fitzpatrick 2 , Stephane Evoy 2 , Ken Westra 3 , Brian Olsen 1 , Chris Holt 1 , Ulrich Dahmen 4 , David Mitlin 1
4 NCEM, Lawrence Berkeley National Laboratory, University of California, Berkeley, California, United States, 1 Chemical and Materials Engineering, University of Alberta and National Institute for Nanotechnology, Edmonton, Alberta, Canada, 2 Electrical and Computer Engineering, University of Alberta and National Institute for Nanotechnology, Edmonton, Alberta, Canada, 3 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
Show Abstract9:00 PM - HH5.23
Excursions in Displacement and Hydrogen Effect During Loading and Creeping in Nanoindentation.
Xin Gao 1 , Lijie Qiao 1 , Jinxu Li 1 , Wuyang Chu 1
1 Dept Mater Physics, University of Science & Technology Beijing, Beijing, Beijing, China
Show Abstract9:00 PM - HH5.24
Nanomechanical Properties of Strained Silicon-on-Insulator (SOI) Films Epitaxially Grown on Si_1-x Ge_x and Layer Transferred by Wafer Bonding
Nathanael Miller 1 , Kandabara Tapily 2 , Helmut Baumgart 2 , Abdelmageed Elmustafa 1 , George Celler 3 , Francois Brunier 3
1 Mechanical Engineering, Old Dominion Unviersity, Norfolk, Virginia, United States, 2 Electrical and Computer Engineering, Old Dominion University, Norfolk , Virginia, United States, 3 , SOITEC, Bernier-Grenoble France
Show AbstractStrain engineering for mobility enhancement is an attractive option to improve CMOS device performance without further scaling the transistor gate length by introducing lattice strain into the Si channel. Si_1-x Ge_x is a leading candidate for higher mobility channel material because of its compatibility with Si based CMOS technology. The larger lattice constant of Ge produces a 4.1 % lattice mismatch with the Si crystal structure. All samples were fabricated by the wafer bonding, layer transfer and film exfoliation technique. The sSOI films were obtained with a fabrication sequence of epitaxially growing 100Å to 600Å strained Si films on a relaxed 20% Ge containing Si_1-x Ge_x layer on a donor wafer. During epitaxy the Si lattice stretches to match the larger Si_1-x Ge_x lattice. The strained Si layer enhances channel mobility and transistor switching speed. The donor wafer was subsequently bonded with an oxide intermediate layer to a Si handle wafer. Following successful bonding of both wafers, the donor wafer was split off with the SMART CUT ™ exfoliation technique and finished with a wafer etch process completely removing all traces of the Si_1-x Ge_x film. The final result is a Germanium-free strained Si film on Insulator transferred onto a handle substrate with the lattice strain frozen-in throughout the Si epitaxial film. The xsSOI films have undergone the same fabrication procedure, except they were grown on about 40% Ge content Si_1-x Ge_x layer in order to produce an enhanced level of lattice strain. The insulating buried oxide on our SOI samples was of the order of 145nm thickness. For benchmarking we also investigated strain-free Silicon-on-Insulator(SOI)thin films. Using nanoindentation, we report on the elasto-mechanical properties of multiple thin films of strained Silicon-on-Insulator (sSOI) and extreme strained Silicon-on-Insulator(xsSOI). We measured the hardness and elastic moduli of the films. Both the hardness and elastic moduli were determined for the surface layers of SOI, SiO2, and the bulk silicon using the continuous stiffness method (CSM) XP of Nano Instruments Nanoindentation tester. The measured hardness values for the xsSOI films are 5.5/6.0 GPa, whereas sSOI/SOI demonstrated higher hardness values of 9.0/9.6 GPa. The moduli are 69.0/70.0 GPa and 102.0/104.0 GPa respectively. The hardness and moduli for bulk Si are 12.5 GPa and 160.0 GPa.
9:00 PM - HH5.25
Drag Reduction by Surface Patterning Over Super-hydrophobic Surfaces.
Sivakumar Challa 1 , Richard Truesdell 2 , Peter Vorobieff 2 , Andrea Mammoli 2 , Frank van Swol 1 3
1 Chemical & Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show Abstract9:00 PM - HH5.26
Scanning Probe Recognition Microscopy Investigation of Nanoscale Mechanical and Surface Roughness Properties Along Nanofibers.
Yuan Fan 1 , Qian Chen 1 , Shiva Arun-Kumar 1 , Andrew Baczewski 1 , Lalita Udpa 1 , Virginia Ayres 1 , Alan Rice 2
1 Electrical and Computer Engineering , Michigan State University, East Lansing, Michigan, United States, 2 , Veeco Metrology Group, Santa Barbrar, California, United States
Show AbstractWednesday, April 11Transfer HH7.4 @ 2:45 pm to Poster HH5.26Scanning Probe Recognition Microscopy Investigation of Nanoscale Mechanical and Surface Roughness Properties Along Nanofibers. Yuan Fan
9:00 PM - HH5.3
Traceable Micro-force Sensor for Instrumented Indentation Calibration
Douglas Smith 1 , Gordon Shaw 2 , Richard Seugling 2 , Dan Xiang 1 , Jon Pratt 2
1 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Manufacturing Metrology Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractInstrumented indentation testing (IIT), commonly referred to as nanoindentation when small forces are used, is a popular technique for determining the mechanical properties of small volumes of material. Sample preparation is relatively easy, usually requiring only that a smooth surface of the material to be tested be accessible to a contact probe, and instruments that combine sophisticated automation with straightforward user interfaces are available commercially from several manufacturers. In addition, documentary standards are now becoming available from both the International Standards Organization (ISO 14577) and ASTM International (E28 WK382) that define test methods and standard practices for IIT, and will allow the technique to be used to produce material property data that can be used in product specifications. These standards also define the required level of accuracy of the force data produced by IIT instruments, as well as methods to verify that accuracy. For forces below 10 mN, these requirements can be difficult to meet, particularly for instrument owners who need to verify the performance of their instrument as it is installed at their site. In this paper, we describe the development, performance and application of an SI-traceable force sensor system suitable for the field calibration of commercial IIT instruments. The force sensor itself, based on an elastically deforming capacitance gauge, is small enough to mount in a commercial instrument as if it were a test specimen, and is used in conjunction with an ultra-high accuracy capacitance bridge. The sensor system is calibrated with NIST-traceable masses over the range 5.0 µN through 5.0 mN. We will present data on its accuracy and precision, as well as uncertainties introduced by varying temperature and humidity. Finally, we will describe our application of the device to the verification of force in several commercial instrumented indentation instruments.
9:00 PM - HH5.4
Aromatic Thiols as Friction Modifiers
Yutao Yang 1 , Marina Ruths 1
1 Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractAromatic molecules are known to contribute to the natural lubricity of diesel fuel. They are less flexible than alkanes and have more complex intermolecular interactions, which makes their lubrication properties interesting also from a fundamental point of view. We have used friction force microscopy (FFM) to study the boundary friction of self-assembled monolayers of simple aromatic and polyaromatic thiols on gold substrates. Experiments were done both in ethanol (low adhesion) and in dry N2 gas (higher adhesion). In both cases, systematic differences are observed between systems with different packing density.
9:00 PM - HH5.5
Influence of Temperature and Polymer/mold Surface Interactions on Nano-feature Replication at Low Pressure in Micro Injection Molding.
Varun Thakur 1 , David Angstadt 2
1 Materials Science Department, Clemson University, Clemson, South Carolina, United States, 2 Mechanical Engg. Department, Clemson University, Clemson, South Carolina, United States
Show Abstract9:00 PM - HH5.7
In-situ Study of TiO2 Thin-films Mechanical Behavior under Loading.
Rynno Lohmus 1 , Irina Hussainova 2 , Silver Leinberg 1 , Aivar Tarre 1 , Kristjan Saal 1 , Ants Lohmus 1 , Reet Nisumaa 2
1 , Institute of Physics University of Tartu, Tartu Estonia, 2 Department of Materials Engineering, Tallinn University of Technoology, Tallinn Estonia
Show Abstract9:00 PM - HH5.9
Nanoripples Formation in Single Crystals
Megan Pendergast 1 , Ramakrishna Gunda 1 , Alex Volinsky 1
1 Mechanical Engineering, University of South Florida, Tampa, Florida, United States
Show Abstract9:00 PM - HH5: Posters
HH5.16 TRANSFERRED TO HH6.11
Show Abstract
Symposium Organizers
Robert F. Cook National Institute of Standards and Technology
William Ducker University of Melbourne
Izabela Szlufarska University of Wisconsin-Madison
Robert F. Antrim Rohm and Haas Company
HH6: Mechanical Behavior of Nano-Scale Structures
Session Chairs
Robert Antrim
Robert Cook
Thursday AM, April 12, 2007
Room 3018 (Moscone West)
9:00 AM - HH6.1
Nanoscale Mechanics and Surface Charge Effects on Amorphous Polymer Interfaces.
Catherine Tweedie 1 , Georgios Constantinides 1 , Gregory Blackman 2 , Krystyn Van Vliet 1
1 , MIT, Cambridge, Massachusetts, United States, 2 , DuPont Central Research and Development, Wilmington, Delaware, United States
Show AbstractAlthough size-dependent effects of constraint and deformation volumes on elastoplastic mechanical behavior of metallic and ceramic structures are increasingly well-studied, relatively little is known about how the deformation of polymers depends on microstructural and physical length scales. In particular, it is not yet clear how the structural and mechanical properties of amorphous (glassy) polymers differ at free surfaces, at rigid interfaces, and within the bulk. Such understanding is important in that free surface and interface properties dominate the mechanical behavior relevant to (bio)polymeric thin film and nanocomposite applications. Recent experiments have demonstrated significant variation of the glass transition temperature Tg within ~100 nm of the free surface in amorphous polystyrene (PS) and poly(methyl methacrylate) (PMMA) thin films [1-3]. This indicates possible differences in the amorphous topology and/or macromolecular mobility that induce a mechanical response quite different from that indicated via bulk or μm-scale testing, even at room temperature, within 100 nm of the free surface. Several experiments have characterized aspects of the polymer surface mechanics via non-contact [4] approaches, as well as via contact deformation methods [5,6]. A study of nm-scale contact deformation of amorphous polymer surfaces has indicated a stiffening effect at the interface between a contact deformation probe and a polymer surface stemming from the formation of a mechanically and structurally unique “interphase” region. To understand the mechanism driving the formation of this interphase, we investigated the response of amorphous polymer surfaces to contact deformations between 5 nm and 200 nm with a spherical probe of controlled surface chemistry. These experiments not only provide the basis for isolating the effects of surface charge and compression on polymer surface response to contact deformation, but suggest that synthetic interfaces (such as those created in nanocomposites) may be systematically investigated as a function of geometry, material characteristics, and surface chemistry.
1.Keddie et al.Israel J Chem 35, 21-26 (1995).
2.Forrest et al. Phys Rev Lett 77, 2002-2005 (1996).
3.Priestley et al. Science 309, 456-459 (2005).
4.Stafford et al. Macromolecules (2006).
5.Amitay-Sadovsky et al. J Appl Phys 91, 375-381 (2002).
6.Chakravartula et al. Appl Phys Lett 88, - (2006).
9:15 AM - HH6.2
Direct Measurements of Length Scale-dependent Deformation Mechanisms in Confined Polymer Melts.
Harry Rowland 1 , William King 1 , Graham Cross 2 , Barry O'Connell 2 , John Pethica 2
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 SFI Nanoscience Laboratory, Trinity College, Dublin Ireland
Show Abstract9:30 AM - HH6.3
Comparison of Nanoindentation and Unconfined Compression of Agarose gel and Porcine Costal Cartilage
Cheng Li 1 , Shikha Gupta 3 , Lisa Pruitt 2
1 Bioengineering, UC Berkeley, Berkeley, California, United States, 3 Applied Science and Technology, UC Berkeley, Berkeley, California, United States, 2 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. Yet issues such as surface contact, viscoelasticity, heterogeneity, and anisotropy of these materials can complicate interpretation of the mechanical measurements. A few studies have addressed improvements in experimental techniques as well as in analytical interpretation of load-displacement data in order to increase the utility of instrumented nanoindentation of biomaterials (Carrillo et al., 2005; Ebenstein and Wahl, 2005; Ebenstein et al., 2006). To date there has not been a thorough study of nanoindentation data of soft viscoelastic materials, particularly in comparison to the conventional compression results. This study proposes to measure the equilibrium modulus of agarose gel and costal cartilage using both nanoindentation and unconfined compression. These biomaterials are characterized as homogeneous, isotropic, and exhibit poroelastic mechanical behaviour. In particular, nanoindentation will be performed on punches of 8 mm in diameter and 5 mm in thickness samples in phosphate buffered saline (PBS), and using two tips—a 100 μm spherical tip and a flat punch of the same size. The tip will approach the sample surface from out of contact. A pre-selected constant loading and unloading rate to a depth of 1000-3000 nm into the sample will be applied. The sample will be allowed to relax for >45 s at maximum indentation depth. The equilibrium modulus will then be determined from the load-displacement data using the Oliver and Pharr method (Oliver et al., 1992). Optical measurement of the Poisson’s ratios will be carried out, along with the measurement of the Young’s modulus with the samples subjected to the stress relation experiment under unconfined compression. For each sample, a range of applied strains at a pre-determined ramp strain rate will be applied to obtain a stress-strain data characteristic of the sample. The equilibrium young’s modulus from different nanoindentation tips will then be compared with that from unconfined compression. It is expected that the improved nanoindentation protocols will give relaxed modulus values of at least the same order of magnitude as unconfined compression. If this is true, nanoindentation is a step closer to serving as an alternative quantitative mechanical measurement technique for the biomechanical research community.
9:45 AM - HH6.4
Sensitivity of Point-by-Point Estimation Techniques in Dynamic Nanoindentation.
Benjamin Polly 1 , Joseph Turner 1 , Kevin Cole 2 , Mark VanLandingham 3
1 Engineering Mechanics, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 3 Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Show AbstractDynamic nanoindentation methods are relatively new experimental techniques that are used to extract the storage and loss moduli of viscoelastic materials. Often one goal is to determine the frequency dependence of the moduli. Thus, measurements of the amplitude and phase of the material response relative to the harmonic forcing input are performed at several frequencies. Conventionally, a two-parameter material model of the sample response is then combined with Hertzian or another contact theory to determine the moduli on a point-by-point basis at each frequency from the data collected. The uncertainties associated with such measurements are complicated by the dynamic response of the combined instrument-sample system that includes resonance behavior. A study of the sensitivity of this type of point-by-point analysis using simulated experimental data is discussed. Results show the point-by-point method is most sensitive to the moduli at the system resonance with decreasing sensitivity away from the resonance. Sensitivities are quantified and presented as frequency bands for the storage and loss moduli corresponding to different levels of accuracy for various degrees of measurement error and as a function of the parameters of the system. The sensitivity directly affects the ability of the instrument to extract frequency-dependent material properties. Potential experiments for determining the frequency dependence of the material properties in a more reliable fashion are discussed. Additionally, arguments are made for the development of a whole-domain estimation technique, which would fit multiple material parameters based on an assumed functional form of the moduli. [Results supported by ARL].
10:00 AM - HH6.5
Mechanical Characterization of Elastomeric Polymer through Modified JKR-Dynamic Stiffness Algorithm and Instrumented Indentation Technique
Gyujei Lee 1 , Dongil Kwon 1
1 School of Materials Science & Engineering, Seoul National University, Seoul Korea (the Republic of)
Show Abstract10:15 AM - HH6.6
Nanoindentation of Hydrated Mineralized Tissues – Effect of Fluid on Mechanical Properties.
Michelle Dickinson 1
1 , Hysitron Inc., Eden Prairie, Minnesota, United States
Show AbstractNanoindentation as a technique is expanding from traditional materials and now including biomimetic and biological materials. To ensure more realistic data, testing in fluid is becoming more commonplace to attempt to mimic in vivo conditions. The fluids used however have not been standardized and different studies have used different fluid media. In preliminary studies it has been seen that some fluids can actually degrade the mechanical properties of the material through demineralization of the specimen which can cause deviations in the results obtained. This investigation takes common fluids used to rehydrate mineralized tissues such as teeth and bones and studies the effect on the mechanical properties of the samples as a function of storage time.Human premolar tooth samples and mouse femur samples were sectioned and polished in preparation for nanoindentation testing. The quasi-static and dynamic mechanical properties were obtained initially and after storage in different fluid media for up to 7 days. Fluid media included deionized water, PBS solution, HBS solution and HAP solution. Nanoindentation testing was carried out on the same samples before hydration, and then once per day for the full 7 days to see if there was any correlation between time stored and mechanical property degradation. Storage in all fluid media had an effect on the mechanical properties of both the teeth and bone samples. In each of the fully hydrated samples there was a reduction in the hardness and modulus compared to their partially hydrated state. Although the mechanical properties degraded over time for all samples, those stored in the de-ionized water showed the greatest reduction of properties which is concerning as this is the most common fluid used currently.To date there is no controlled method for testing mineralized tissues using nanoindentation in fluid, and hence published results in this field vary greatly due to testing conditions. This study will bring awareness to the community on the effects that different fluid media have on the mechanical properties of biological samples in order aid in bringing uniformity to similar studies.
10:30 AM - HH6.7
Nanotribology as a Probe of Crystalline Structure and Disorder in Organic Thin Films for Electronics Applications.
Greg Haugstad 1 , Vivek Kalihari 2 , David Ellison 2 , Jinping Dong 1 , C. Daniel Frisbie 2
1 Institute of Technology Characterization Facility, University of Minnesota, Minneapolis, Minnesota, United States, 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show Abstract11:15 AM - HH6.8
Determining Yield Strength of Al-Al3Sc Multilayers by Micro-Compression Testing
Seung Min Han 1 , Mark Phillips 1 , William Nix 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractMultilayer thin films with bilayer thicknesses in the nanometer range have been reported to have very high strengths. A previous study has shown that the hardness of 1um Al-Al3Sc multilayer structure as measured by sharp tip nanoindentation was as high as ~3GPa for the sample with bilayer thickness of 6 nm. Although there is an existing relationship between the nanoindentation hardness and the yield strength of the material, a direct measure of the yield strengths of the Al-Al3Sc multilayers have not been studied. In this study, we directly measured the yield strengths of the Al-Al3Sc multilayers of varying bilayer thicknesses by micro-compression testing methods. Focused ion beam was used to make pillars of similar dimensions through depth of the multilayer stack, and these sub-micron sized pillars were subsequently compression tested using the flat tip of the nanoindenter. The results of the micro-compression testing show the expected trend of decreasing yield strength with increasing bilayer thickness, and compare favorably with the estimates of the yield strengths based on the sharp tip nanoindentation experiments. During deformation, the Al-Al3Sc multilayer pillars experience considerable strain softening, resulting in a “flat-top mushroom” shaped pillar after deformation. We have developed a model to account for this deformation behavior to accurately calculate stress-strain in the case for strain softening.
11:30 AM - HH6.9
Shallow Surface Nanoindentation on Nanolayered Superlattice
Scott Mao 1 , B. Ennis 1
1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractSuperlattice W(100)/NbN(100) with bilayer periods (L=5.6 and 10.4 nm) was non-isostructural superlattice material and fabricated by depositing alternating layers of single crystal tungsten (W), a body-centered cubic metal, and niobium nitride (NbN), a face-centered cubic ceramic, on a MgO single crystal substrate. The lattice constants of the ceramic and metal layers are 0.439 nm and 0.315 nm respectively. The superlattice are nanocomposites that exhibit a hardness at small bilayer repeat periods which exceeds the hardness predicted by the rule of mixtures for normal composites by deep nanoindentation, while shallow nanoindentations does not demonstrate the superhardening. The results indicate that the elastic modulus does not influence the hardness of the superlattice materials. The superhardening results at deeper indentation depths are related to the nature of the interface between the layers in the superlattice materials. Normally, superlattice gains hardness by losing deformability, however, the superlattice demonstrated excellent deformability when reaching the superhardening.
11:45 AM - HH6.10
In situ, Quantitative TEM Compression Tests on Submicron Ni Pillars.
Zhiwei Shan 1 2 , A. Minor 2 , R. Mishra 3 , S. Asif 1 , O. Warren 1
1 Research & Development, Hysitron Inc., Eden Prairie, Minnesota, United States, 2 National Center of Electron Microscope, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 General Motors R&D Center, General Motors, Warren, Michigan, United States
Show Abstract12:00 PM - HH6.11
Fabrication And Controlled Actuation Of Ultra Thin Single Crystal Nems Devices.
Oleksa Hulko 1 , Rafael Kleiman 1 2
1 Centre for Emerging Device Technologies (CEDT), McMaster University, Hamilton, Ontario, Canada, 2 Engineering Physics, McMaster University, Hamilton, Ontario, Canada
Show AbstractFabrication of devices with dimensions in the few nanometer range is important both as a venue for understanding the fundamental properties of matter on an atomic scale, and to create the ultimate sensors for many electrical, biological and chemical applications.Traditional micromachining techniques employed to build such structures rely on conventional Silicon technology and therefore suffer from inherent limitations as device dimensions scale down. The quality of SiO2 and polysilicon layers becomes difficult to control on the nanometer range, residual stress between various polycrystalline layers results in device deformation upon release, whereas mechanical actuation of such devices remains problematic and difficult to implement.In this submission we demonstrate successful utilization of a radically different approach. We make use of the extreme selectivity to wet chemical etching of the group III-V semiconductor compounds as well as the tremendous degree of flexibility and control over compositional and structural properties of epitaxially grown heterosystems that is made available by molecular beam epitaxy (MBE). For our device (actuation pad) we used a 100Å InGaAs layer that was lattice matched to a thick (1.5 μm) sacrificial layer of InP. Various arrays of such devices each with a typical surface area of less then 0.5 μm2 were defined by electron beam lithography. The actuation pads were later released by conventional wet etching. Due to the extreme scaling down of their thickness, these are the smallest and the lightest (2.7x10-17 kg) NEMS devices ever produced. In order to drive the actuation pads we modified our fabrication process by overgrowing the pads with a thin (200-300Å) layer of the SiO2 deposited by chemical vapor deposition (CVD). We relied on a known phenomenon of the densification of vitreous silica during irradiation (e.g. electron beam), to generate stress and thereby induce deformation of the SiO2/InGaAs bimorphic structures. Using a scanning electron microscope (SEM) we were able to selectively probe individual pads, inducing their bending by as much as 90 degrees, which is remarkable considering the submicron radius of curvature and single crystalline nature of our devices. It is instructive to emphasize the unique nature of our actuation process, for it offers a direct non-contact method to address individual elements of an array charting a route for controllable nano-assembly. The combined ultra light weight and large relative surface area of the NEMS devices together with straightforward instrumentation for the detection of small deflections provides the ultimate in sensing capabilities for the measurement of sub monolayer coverages of an adsorbate species. We anticipate that these devices can be further scaled to thicknesses below 50Å.
12:15 PM - HH6.12
Effect of Crystalline Substrate Plasticity on Thin Film Buckling Phenomenon.
Frederic Foucher 1 , Christophe Coupeau 1 , Jerome Colin 1 , Alain Cimetiere 1 , Jean Grilhe 1
1 Laboratoire de Métallurgie Physique, University of Poitiers, Futuroscope Chasseneuil France
Show Abstract12:30 PM - HH6.13
Conformal Bonding and Collapse of Nano-scale Features.
Kristen Mills 1 , Dongeun Huh 2 , Shuichi Takayama 2 4 , M. Thouless 1 3
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract12:45 PM - HH6.14
How do Surface Stresses Modify the Tensile Stiffness of Nano-wires with Very Small Radii?
Ravi Shankar 1
1 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractThere has been great interest recently in determining the mechanical behavior of nanostructured materials such as nano-wires. An important characteristic of nanostructured materials is the anticipated dominance of interface and surface phenomena in determining their mechanical properties. Surface and interface stresses that are generally unimportant in bulk materials gain particular importance when the surface area to volume ratio is very large, as is the case in nanostructured materials. For example, elastic deformation of a nano-wire, typically few nanometers thick not only entails the work done for varying the atomic separation but also in elastically deforming the free surface bounding the sample. Deformation of this free surface is associated with a finite surface stress that can lead to deviation of elastic mechanical response for nano-wires from that observed in bulk materials. Here, we consider the effect of surface stresses on the elastic response of a nano-wire within the framework of isotropic continuum elasticity using a formulation that explores the interplay of surface stresses, applied tensile stresses and the role of non-linearity of the constitutive behavior on the resulting tensile stiffness and mechanical response of the nano-wire. Using variational principles we show that surface stresses are only important when non-linear elastic effects become operative. In fact, when non-linear effects are completely ignored, the effect of surface stresses on the elastic response vanishes entirely irrespective of the value of the surface stresses or the dimensions of the nano-wire. By formulating this interplay of surface stresses and non-linear elasticity effects we show that a pseudo-linear elastic response can still be expected for small values of deformation strain during tension testing of the nano-wires and the effective modulus value of this pseudo-linear variation is either superior or attenuated compared to the bulk material depending on the sign of the surface stress value. Furthermore, these effects are only significant when the radius of the nano-wire is of the order of a few nanometers. Most of current experiments have focused on nano-wires typically tens of nano-meters thick and for typical values of elastic constants and surface stresses we expect negligible deviation from bulk mechanical behavior in these instances. However, future direct measurements of the elastic modulus for nano-wires in the 1-2nm radius range might offer a route for determining the effect of surface stresses on tensile response of nano-wires. The deviation from macroscopic bulk mechanical properties characterized via this analysis can also provide a route for the measurement of the magnitude and sign of surface stresses.
HH7: Nano-scale Elastic and Wear Behavior
Session Chairs
Robert Cook
Douglas Smith
Thursday PM, April 12, 2007
Room 3018 (Moscone West)
2:30 PM - **HH7.1
Quantitative Nanomechanical Measurements with Contact-Resonance AFM
D. Hurley 1
1 Materials Reliability Division, NIST, Boulder, Colorado, United States
Show AbstractThe superb spatial resolution and imaging capability of the atomic force microscope (AFM) make it an attractive tool for investigating nanoscale mechanical properties. One AFM method that shows promise for quantitative property data is contact-resonance spectroscopy. In this approach, the cantilever’s resonant frequencies are measured while the tip is in contact, and are used to determine the local contact stiffness. Nanomechanical information is obtained from the contact stiffness using an appropriate contact-mechanics model. Here we describe our work to develop quantitative contact-resonance AFM metrology and apply it to material systems. We explain the basic theoretical and experimental concepts, and show ways to implement them for accurate, reliable measurements in specific applications. For instance, measuring the flexural resonant modes yields the indentation modulus, while combined measurements of the flexural and torsional modes enable simultaneous determination of Young’s modulus and Poisson's ratio. Studies to improve the basic measurement approach, such as the contact mechanics of a nonideal tip and the accurate calibration of cantilever forces, are also described. Extension of measurement methods to achieve contact-resonance imaging is also discussed. Contact-resonance-frequency images lead to maps of the spatial distribution in properties, such as the elastic modulus of small-scale structures and the interfacial adhesion of buried interfaces.
3:00 PM - HH7.2
Elastic Property Measurements on Nano-size Structures.
Gheorghe Stan 1
1 Ceramics Division, National Institute of Standards and Technology, Ghaithersburg, Maryland, United States
Show Abstract3:15 PM - **HH7.3
Atomic Force Acoustic Microscopy and Reconstruction of the Non-linear Tip-Sample Interaction Forces
Ute Rabe 1 , Sigrun Hirsekorn 1 , Daniel Rupp 2 , Walter Arnold 1
1 Applied Research, Fraunhofer Institute for Non-destructive Testing, Saarbruecken Germany, 2 Institute of Applied Physics, University of Karlsruhe, Karlsruhe Germany
Show AbstractAtomic force acoustic microscopy (AFAM) uses the vibration modes of atomic force microscope (AFM) cantilevers. The flexural and torsional resonant frequencies of commercial cantilevers of a few 100 µm length are predominantly in the ultrasonic frequency range between 20 kHz and several MHz. In the AFAM-mode the cantilever is vibrating in one of its flexural resonant frequencies while the sensor tip is in contact with the sample surface. The radius of the tip-sample contact area ranges between several nanometers and several 100 nanometers. At low amplitudes of vibration, the sensor tip remains in elastic contact with the sample surface, and the cantilever behaves like a linear oscillator with viscous damping and a certain set of resonances. The tip-sample interaction forces can be approximated by linear springs and dashpots, and an analytical solution of the differential equation describing the cantilever-tip-surface system is available. Images can be obtained the contrast of which depends on the elasticity of the sample surface, and quantitative values of surface elastic constants can be calculated when the resonant frequencies of the cantilever are evaluated. Shear stiffness can be investigated in lateral AFAM by exploiting the torsional resonances and the lateral bending modes of AFM cantilevers.A linear approximation of the interaction forces is only valid for high static loads and small vibration amplitudes of the cantilever. With increasing amplitudes the nonlinearity of the system becomes remarkable due to the generation of higher harmonics in the spectrum of the cantilever vibrations. Quantitative measurements of the cantilever vibrations acquired with the combination of a commercially available AFM instrument and a heterodyne Mach-Zehnder-interferometer are presented. A frequency dependent conversion function can be derived from the model of the cantilever as a beam with a rectangular cross section. This function allows one to calculate the nonlinear contact and adhesion forces from the measured spectra as a function of time, and eventually as a function of distance. Numerical evaluations of the experimental results are presented and discussed.
4:30 PM - HH7.5
A Dynamic Analysis of Mode Transitions in Atomic-Scale Stick-Slip Friction
Sergey Medyanik 1
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractFriction at the nano scale has some distinct features that significantly differ it from the traditional macro-scale friction. One of such features, which is often observed in the AFM experiments, is the stick-slip behavior, when friction force has a saw-tooth wavelike form. The periodicity of this stick-slip is usually equal to the periodicity of the atomic lattice of the scanned substrate. In this case, the friction mode can be identified as a single slip. However, in many cases the period may be equal to two, three, or even more lattice spacings, thus representing various multiple slip modes. On the opposite, a regime of ultra-low friction of smooth sliding, when no stick-slip occurs, can be also observed. The conditions for transitions between these different regimes of atomic-scale friction are not completely understood yet.In a recent study [1], the conditions for atomic-scale friction mode transitions have been analytically derived for a simple idealized model of an atomic force microscope based on the static analysis of that model. The theoretical predictions were found to be in a good qualitative agreement with the experimental observations of the mode transitions. The derived conditions involved the applied normal load and lateral stiffness of a cantilever as the two most important parameters playing role in the stick-slip mode transitions. However, since the system was examined statically, the discussed transitions represent possible transitions, whereas the actual behavior in a dynamic system depends on various dynamic parameters, such as damping, the cantilever resonance frequency, and the sliding velocity.Current presentation focuses on the extension of the analysis presented in [1] to the case of dynamics. The criteria for transitions between various regimes of stick-slip friction are derived in a new form that now contains the dynamic parameters. This analysis helps to predict not just a possibility, but an actual occurrence of the stick-slip mode transitions for the given system. Such a development, in principle, may allow for predictions of the friction modes in the actual AFM experiments, based on the structural characteristics of the AFM, properties of the substrate, as well as the conditions of the experiment. References: [1] S. N. Medyanik, W. K. Liu, In-Ha Sung, R. W. Carpick. Predictions and Observations of Multiple Slip Modes in Atomic-Scale Friction. Physical Review Letters 97, 136106 (2006).
4:45 PM - HH7.6
Nanostructure Fabrication in Thin Solid Films by Small Amplitude Shear Oscillation
Graham Cross 1 , Barry O'Connell 1 , H. Ozer 1 , John Pethica 1
1 Physics, Trinity College, Dublin Ireland
Show AbstractWe introduce a new solid thin film mechanical imprint method for parallel nanostructure fabrication, Small Amplitude Oscillatory Shear Forming (SAOSF). The method works by applying a small amplitude cyclic shear displacement (up to 10 nm) to a rigid die in contact with a soft solid film leading to a plastic-ratchet forming action. As with conventional nanoimprint, nano-feature fidelity and registry are achieved, however the technique also has advantages of constant low temperature processing and hence a wide choice of materials. We discuss the underlying process of SAOSF and show that it is due to a combination of uniformly plasticizing contacted areas of the film while simultaneously activating a novel pumping action involving die-geometry-induced broken circulation of elastoplastic flow. Crucially, the process mechanism is scale independent for thin film planar imprint, since a critical shear strain is required. A minimal applied normal load largely eliminates elastic distortions thought to be responsible for residual layer non-uniformity and other replication defects common to imprint. Finite element simulations of the process with simple elastic-elastoplastic materials agree well with experimental observations. These show that the process is relatively insensitive to die-film friction, giving wide potential application in large scale nanostructure fabrication
5:00 PM - HH7.7
PEG-like Surface Treatments to Improve Lubrication in Total Hip Replacements.
Sheryl Kane 1 , Paul Ashby 3 , Lisa A. Pruitt 1 2
1 Joint Graduate Group in Bioengineering, UC San Francisco/UC Berkeley, Berkeley, California, United States, 3 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Mechanical Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractWear-mediated osteolysis, or bone loss, is the primary cause of late-stage implant failure in total hip replacements. Articulation between the metal or ceramic femoral head and the ultrahigh molecular weight polyethylene (UHMWPE) acetabular cup generates wear particles from the surfaces of the components. On the microscopic scale, these particles form when an asperity on one surface adheres to the counterbearing, pulling a small piece of material off of one surface. As these sub-micron-sized particles accumulate around the implant, they elicit an immune response that results in chronic inflammation, pain, and osteolysis, which can necessitate implant removal.The hip joint is naturally lubricated by aqueous synovial fluid, but the UHMWPE surface (the main source of wear particles) is hydrophobic and poorly lubricated. To improve lubrication, hydrophilic coatings are covalently bonded to the UHMWPE surface. The coatings have chemical structures similar to polyethylene glycol (PEG), a well-known polymer used as a lubricant for applications such as contact lenses. PEG is also known to resist protein and cell deposition, minimizing the immune response to the implanted material.Plasma polymerization of tetraglyme generates crosslinked PEG-like networks of variable thickness. This study focuses on the effects of surface chemistry and thickness on the nanotribological properties of the modified surfaces, as opposed to the macro-scale behavior determined by pin-on-disk wear testing. Atomic force microscopy (AFM) is used to evaluate the surfaces because of its sensitivity to the pico- or nanonewton adhesive forces from low-adhesion materials; it can also measure a wide range of other properties.The adhesive force is determined using force-displacement curves taken with a 10 µm borosilicate microsphere-functionalized tip. The coefficient of friction between the surfaces and the tip is calculated using lateral force microscopy. In addition, since the modulus of the PEG-like hydrogel layer is substantially lower than that of the UHMWPE, phase contrast imaging can be used to measure the thickness of the PEG-like layers. Imaging in both air and phosphate-buffered saline (PBS) allows for a determination of both not only the thickness, but also the swelling ratio of the surface treatments.AFM force curves taken in PBS show that the crosslinked PEG-like surfaces exhibit maximal adhesive forces two orders of magnitude lower than that of untreated UHMWPE. Additionally, the adhesive forces are largely independent of the relative thickness of the PEG-like layers. Preliminary lateral force data in PBS also suggest that the surface modifications decrease the friction between the surface and the tip as compared to untreated UHMWPE. Both of these results indicate that these coatings improve the lubricity of the UHMWPE surface in aqueous solution, which suggests that they show promise in decreasing wear particle formation from articulating UHMWPE.
5:15 PM - HH7.8
Size Effects during Nanoscale Wear Deformation of Single Crystal Nickel.
Megan Cordill 1 , Neville Moody 2 , S. Prasad 3 , William Gerberich 1
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 , Sandia National Laboratory, Livermore, California, United States, 3 , Sandia National Laboratory, Albuquerque, New Mexico, United States
Show AbstractStrength, friction and wear are dominant factors in the performance and reliability of nickel based nanoscale devices. The effects of frictional contacts and wear on the device performance are undefined. To examine the nanoscale wear properties nanoindentation techniques have been employed on (111) single crystal nickel in two directions. Wear boxes were created at different loads (100 to 800 uN) and number of cycles (1-10) using the scanning capabilities of a nanoindenter. The surface deformation response varies between applied load and number of cycles. Low loads generate a smooth row-like wear pattern while larger loads generate a rough woven pattern. The scanning rate and wear box size also have an effect on the morphology of the surface. Deformation theories are applied to explain the change in surface structure and subsurface structure.
5:30 PM - HH7.9
A Comparison of Tribochemical Material Removal on Al and Si at the Nanometer Size Scale.
Forrest Stevens 1 , Steve Langford 2 , Tom Dickinson 2
1 Physics, Washington State University, Pullman, Washington, United States, 2 Physics, Washington State University, Pullman, Washington, United States
Show Abstract5:45 PM - HH7.10
Nanoscale Wear Mechanisms In Polysilicon For MEMS Applications.
Daan Hein Alsem 1 2 3 , Eric Stach 4 , Michael Dugger 5 , Robert Ritchie 1 3
1 Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 School of Materials Engineering , Purdue University, West Lafayette, Indiana, United States, 5 Materials and Process Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWear is a critical factor in the reliability of polysilicon microelectromechanical systems (MEMS). Specifically, the surface generation of nanoscale wear particles is potentially catastrophic for applications where such debris may inhibit relative motion. Accordingly, it has become important to fully understand the physical mechanisms of the nanoscale processes associated with wear in polysilicon thin films. To address this issue, we have run sidewall friction and wear test MEMS devices (fabricated in the Sandia SUMMITtm process) in ambient air. Analytical scanning and transmission electron microscopy (TEM) was used to study morphology and microstructural evolution of nanoscale wear debris and worn polysilicon structural films. Local values of the static coefficients of friction for silicon on silicon were also determined as a function of number of wear cycles and also related to the surface morphology evolution. Studies indicated the presence of plowing wear tracks and amorphous debris particles, well before the friction coefficient reached its steady-state value of 0.20±0.05. The wear particles were found to vary in size from below 100 nm to agglomerates larger than 500 nm and were comprised of amorphous silicon and silica, whereas the grain size was ~500nm. Furthermore, an oxygen-rich nanocrystalline surface layer was found. With the absence of any evidence for plasticity, we propose that the nano/microstructural processes associated with the wear of polysilicon MEMS are associated with an initial short adhesive wear regime followed by a dominating abrasive wear mechanism governed by nano-scale debris particles created by local fracture through the grains.