Symposium Organizers
Steven Boles, The Hong Kong Polytechnic University
In-Suk Choi, Korea Institute of Science and Technology
Christoph Eberl, Fraunhofer Institute for Mechanics of Materials
Hang Yu, Virginia Polytechnic Institute and State University
Symposium Support
The Hong Kong Polytechnic University
CM5.1: Strain-Coupling in Ferroelectric Materials
Session Chairs
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 126 B
11:30 AM - *CM5.1.01
Self-Assembled Nanocomposite Oxide Films—Strain Coupling, Magnetoelectricity and Phonon Transport
C. A. Ross 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractNanocomposite films are self-assembled nanostructures that consist of two different phases, such as pillars of spinel grown inside a perovskite matrix, with well-defined vertical interfaces. The film therefore exhibits properties of both phases, and strain-transfer at the interfaces can lead to emergent properties. We describe the growth and microstructure of nanocomposites consisting of 10-50 nm diameter pillars of ferrimagnetic spinel, (Co,Ni)Fe2O4 (CNFO) within a ferroelectric perovskite BiFeO3 (BFO) on a perovskite substrate, including strategies for controlling the locations of the magnetic pillars by pre-patterning the substrate and for selecting between rhombohedral and tetragonal BFO. These nanocomposites can be integrated onto Si using an 8 nm SrTiO3 buffer layer, and composites with modulated pillar widths or compositions can be grown. We demonstrate magnetoelectric behavior as a result of interfacial mechanical coupling, in which an electric field leads to a change in the magnetic anisotropy of the pillars. The magnetostatic coupling between CNFO pillars and the magnetic anisotropy were tuned via the Co:Ni composition ratio, enabling the pillars to form an ac-demagnetized state consisting of alternating up and down magnetized pillars. Phonon transport through the nanocomposites was characterized using time domain thermoreflectance as a function of the interface density, showing an increase in thermal conductivity with pillar volume fraction. These materials provide a playground for the investigation of nanoscale magnetic, ferroelectric, phononic and multiferroic phenomena.
12:00 PM - CM5.1.02
Multiferroic and Magnetoelectric Architectured Oxide Film
Yanxi Li 1 , Jiefang Li 1 , Dwight Viehland 1
1 Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractMultiferroic materials attract much scientific and technological interests due to their ability to exhibit a magnetoelectric (ME) effect which enables the control of the polarization/ magnetization with an applied magnetic/ electric field, respectively. In recent years, compared with bulk multiferroics, research interest has focused more and more on thin films with the development of advanced thin film growth techniques, which enable deposition under epitaxial engineering and non-equilibrium conditions. Among the most widely studied two-phase multiferroic composite thin films, the self-assembled epitaxial BiFeO3-CoFe2O4 (BFO-CFO) nanostructured composite thin films, which contain nanopillars of one phase embedded inside second phase matrix, have been found to be able to present different multiferroic properties and structures by depositing on various oriented SrTiO3 (STO) substrates by pulsed laser deposition (PLD) method.
In this work, we have utilized self-assembled BFO nanopillars in a BFO-CFO two phase layer on STO as a seed layer on which to deposit a secondary top BiFeO3 layer by PLD. The growth mechanism of this secondary BFO layer has been explored, and its multiferroic properties studied. From cross-section images of electron microscopy studies, it has been found that the top BFO layer would preferentially grow from the bottom BFO seeds and its grain size could be properly controlled by these seeds. The multiferroic properties of this new heterostructures have also been studied.
Furthermore, based on that above mentioned heterostructures with controlled growth, we optimized the experimental procedures and designed to grow another BFO layer on the top of that heterostructures. Thus, a novel structure with second phase magnetic CFO nanoparticles embedded in a primary ferroelectric BFO matrix has been fabricated. Enhanced multiferroic properties of this heterostructures have been confirmed by several kinds of characterization methods. Moreover, we demonstrated, by focusing on switching characteristics of the piezoresponse, that the newly designed oxide film showed magnetic field dependence of piezoelectricity due to the improved coupling enabled by good connectivity amongst the piezoelectric and magnetostrictive phases. The improved connectivity amongst the constituent phases of the composite heterostructure has been examined by the state-of-the-art electron microscopy. We have also provided statistical study for the characteristics and confirmed that the yielding notable ME effects result from a better coupling between the ferromagnetic and ferroelectric phases of this special architecture. Such new epitaxial multiferroic oxide heterostructures may provide new opportunities to the multi-functional application areas.
12:15 PM - CM5.1.03
Stress-Tuning of Functional Properties of Polycrystalline Piezoelectric and Ferroelectric Thin Films
Angus Kingon 1 , Sebastjan Glinsek 2 , Seunghyun Kim 1
1 , Brown University, Providence, Rhode Island, United States, 2 , Luxembourg Institute of Science and Technology, Esch-sur-Alzette Luxembourg
Show AbstractAn exciting field of strain-tuning of epitaxial functional oxide thin films received a great attention in the scientific community in last decade. We demonstrate that polycrystalline films can also be stress-tuned by imposing large biaxial thermal expansion mismatch stresses. We have prepared polycrystalline Pb(Zr0.52Ti0.48)O3 and 0.95(K0.5Na0.5)NbO3-0.05LiNbO3 thin films by chemical solution deposition on flexible metal foils and on standard platinized silicon substrates. We show that the choice of the substrate has an important influence on domain state, their dynamics under sub-switching conditions, and ferroelectric properties. In both non-lead and lead-based materials, the impact on 2Pr values of the films on the metal substrates is dramatic – they are approximately doubled as compared to the values of the films on platinized silicon. The main source of this enhancement is the compressive residual biaxial stress in the films on foils, which appears on cooling from the crystallization temperature due to lower thermal expansion coefficient of the films compared to the substrate. Values of biaxial stress in the range >0.5 GPa and approaching 1 GPa can reliably be achieved, while maintaining excellent integrity of the films. We show that stress tuning allows properties to be optimized for different applications. For example, the stress-tuned PZT thin films are particularly suitable for pyroelectric and for certain piezoelectric applications. Examples are discussed.
12:30 PM - CM5.1.04
Science and Technology of Interface-Engineered BiFeO3 /SrTiO3/ BiFeO3 Nanolaminates with High Piezoelectricity and Low Leakage for Multifunctional and Biomedical MEMS/NEMS Devices
Orlando Auciello 1 , Geunhee Lee 2 , Erika Fuentes-Fernandez 2 , Guoda Lian 2 , Ram Katiyar 3
1 Materials Science and Engineering, and Bioengineering, University of Texas at Dallas, Richardson, Texas, United States, 2 Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States, 3 Department of Physics and Astronomy, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractLead-free ferroelectric/piezoelectric BiFeO
3 (BFO) thin films can provide superior piezoelectric properties in both epitaxial and polycrystalline thin films for potential applications to multifunctional MEMS/NEMS devices (actuators and sensors), particularly for medical applications, for which BFO may provide biocompatibility as opposed to Pb(Zr
xTi
1-x)O
3, which contains non-biocompatible lead. The remnant polarization
Pr and out-of-plane converse piezoelectric coefficient
d33 of BFO films are comparable to those of tetragonal Ti-rich PZT films. However, BFO films exhibit large coercive fields and large leakage current, which might limit the applicability of BFO in devices. Prior work focused on reducing the leakage current of BFO films via insertion of dopants in the material, but still the reduction in leakage is limited. This talk will focus on reviewing the R&D performed during the last three years on a novel approach to reduce the leakage current and increase the piezoelectric response of BFO film-based MEMS/NEMS devices by producing structured nanolaminates involving BFO films via insertion of an insulating layer like SrTiO
3 between two BFO layers, all with nanometer-scale thickness. The BFO/STO/BFO nanolaminates provide the means to achieve a strain-engineered structure at the BFO/STO interfaces, which result in very high piezoelectric deflection with low leakage current (~ 10
-7 - 10
-8 A/cm
2 at 1 V). This review will include a discussion of the mechanism responsible for the observed high piezoelectricity and low leakage current behaviors of the BFO/STO/BFO nanolaminates, as revealed by systematic high-resolution TEM and PFM based studies. The BFO/STO/BFO NLs properties provide the bases for excellent potential application of the BSB-NLs into lead-free piezoelectrically actuated MEMS/NEMS devices, especially for biomedical applications (e.g., biosensors and drug delivery systems) based on the potential demonstrable biocompatibility of BFO components.
To whom correspondence should be addressed. E-mail:
[email protected]12:45 PM - CM5.1.05
Nanodomain Engineering in Ferroelectric Capacitors with Graphene Electrodes
Haidong Lu 1 , Bo Wang 2 , Tao Li 1 , Alexey Lipatov 1 , Hyungwoo Lee 3 , Anil Rajapitamahuni 1 , Ruijuan Xu 4 , Xia Hong 1 , Saeedeh Farokhipoor 5 , Lane Martin 4 , Chang-Beom Eom 3 , Long-Qing Chen 2 , Alexander Sinitskii 1 , Alexei Gruverman 1
1 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States, 2 , The Pennsylvania State University, University Park, Pennsylvania, United States, 3 , University of Wisconsin–Madison, Madison, Wisconsin, United States, 4 , University of California, Berkeley, Berkeley, California, United States, 5 , University of Groningen, Groningen Netherlands
Show AbstractPolarization switching in ferroelectric capacitors is typically realized by application of an electrical bias to the capacitor electrodes and occurs via a complex process of domain structure reorganization. As the domain evolution in real devices is governed by the distribution of the nucleation centers, obtaining a domain structure of a desired configuration by electrical pulsing is challenging, if not impossible. Recent discovery of polarization reversal via the flexoelectric effect has opened a possibility for deterministic control of polarization in ferroelectric capacitors. Here we demonstrate mechanical writing of arbitrary-shaped nanoscale domains in thin-film ferroelectric capacitors with graphene electrodes facilitated by a strain gradient induced by a tip of an atomic force microscope (AFM). A strong effect of graphene thickness on the threshold load required to initiate mechanical switching has been observed experimentally. Deliberate voltage-free domain writing represents a viable approach for development of functional devices based on domain topology and electronic properties of the domains and domain walls.
CM5.2: Piezoactive Materials and Applications
Session Chairs
Chang-Beom Eom
Susan Trolier-McKinstry
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 126 B
2:30 PM - *CM5.2.01
Giant Piezo-Driven Multiferroic Heterstructures by Design
Chang-Beom Eom 1
1 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractStrain coupling between piezoelectric and ferromagnetic layers in multiferroic thin films and heterostructures is a fascinating opportunity for both fundamental scientific research and potential multifunctional device applications. Specifically, hyper-active heterostructures with giant piezoelectricity have sufficiently large responses to revolutionize low power piezo-driven magnetoelectric devices. Recently, we have demonstrated giant piezoelectricity in Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) epitaxial thin film heterostructures on silicon1. The giant piezo-response and novel structural and piezoelectric characteristics make this an excellent material platform to realize low power multifunctional devices. We now have the capability to engineer the material and design its interfaces with other active materials to produce magnetoelectrically coupled device structures. We have demonstrated rotation of the in-plane magnetic anisotropy of the ferromagnetic nickel overlayer on PMN-PT thin films through application of electric field as well as large magneto-electric coupling at room temperature. We will discuss the fundamental mechanisms of magnetoelectric coupling and multiscale characteristics that control the properties and device performances.
1. S.H. Baek et al., Science, 334, 958 (2011)
This work has been done in collaboration with W. J. Maeng, J. Irwin, K.-Y. Kim, S. Lindemann, A.A. Brewer, J. C. Frederick, S. D. Kim, T. H. Kim, L. Hong, L. Q. Chen, S.-Y. Choi, M. S. Rzchowski. This work was supported by the Army Research Office through grant N00014-07-1-0215 and W911NF-13-1-0486.
3:00 PM - *CM5.2.02
Piezoelectric Microelectromechanical Systems with Integrated Electronics
Susan Trolier-McKinstry 1 , Thomas Jackson 1 , Paul Reid 3 , Margeaux Wallace 2 , Tianning Liu 1 , Julian Walker 1
1 , Pennsylvania State University, University Park, Pennsylvania, United States, 3 , Smithsonian Astrophysical Observatory, Boston, Massachusetts, United States, 2 , General Electric, Niskayuna, New York, United States
Show AbstractThe integration of electronics with piezoMEMS enables a wide variety of applications, including adjustable & reconfigurable surfaces, conformal actuators, self-powered electronics, and replacement of conventional semiconductor chips with a far more energy efficient computation methodology. This, in turn, should boost the functionality of a wide variety of systems, by providing large, readily controlled displacements, increasing the charge collection efficiency for energy scavenging for unattended sensors, and facilitating efficient computation/storage at local nodes in low-power networks. The paper will discuss implementation of ZnO thin film transistors on lead zirconate titanate actuator arrays on glass for the mirror segments for X-ray telescopes. The role of electromechanical coupling in governing device reliability will also be discussed.
3:30 PM - CM5.2.03
Exploiting Piezoelectrochemical Phenomena in Lithium-Ion Batteries for Low Frequency Mechanical Energy Harvesting and Storage
Craig Arnold 1 , Zachary Schiffer 1 , John Cannarella 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractLow frequency (<10 Hz) mechanical loading presents challenges for traditional energy harvesting materials, which can require resonant and higher frequencies to meet minimal operational needs. In this work we explore a new class of material systems for mechanical energy harvesting based on “off-the-shelf” Li-ion batteries. Li-ion batteries are known to exhibit changes in their electrochemical state due to applied mechanical loading and by taking advantage of this “piezoelectrochemical” phenomena, it is possible to construct a thermodynamic process that can harvest mechanical stress at low frequencies. In this presentation, we show that materials exhibiting this behavior are expected to exhibit orders of magnitude higher energy density per mechanical loading cycle than conventional alternatives such as piezoelectrics. This higher energy density is a result of the high charge density associated with electrochemical processes compared with electrostatic processes. We discuss how the piezoelectrochemical effect can be exploited to harvest mechanical energy and experimentally demonstrate the working principle using a commercial pouch cell configured to harvest mechanical energy.
CM5.3: Strain-Enhancements of Thermal Transport Properties
Session Chairs
Christoph Eberl
Juejun Hu
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 126 B
4:30 PM - *CM5.3.01
Real-Time Probing of Strain Enhancement of Thermal Conductivity in Polyethylene Films
Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractThermally conductive polymers are highly desired for flexible electronics packaging and other thermal management applications. Although the strain enhancement of thermal conductivity in polyethylene has been known for decades, the upper bounds of this enhancement and how they might be achieved in actual samples remain unclear. Here, we use transient grating spectroscopy, a non-contact optical method, to probe the real-time strain enhancement in thermal conductivity and in-plane thermal anisotropy of stretched polyethylene films. Our work provides insights into how to realize exceptionally thermally conductive yet flexible polymers.
5:00 PM - *CM5.3.02
Elastic Strain Engineering of Semiconductor Nanostructures—The Role of Strain Gradients
Eric Yao 1 , Gyuseok Kim 2 , Daniel Gianola 1
1 , University of California Santa Barbara, Philadelphia, Pennsylvania, United States, 2 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractA variety of emergent phenomena in mechanical behavior, heat conduction, and electronic charge transport arise in materials when length scales associated with the physical dimensions or intrinsic structure approach the nanoscale. For instance, defect ensemble interactions and poor mechanical strength give way to discrete plasticity and ultra high strength in elemental nanostructures; facile thermal transport gives way to abundant phonon scattering in nanomaterials; and electronic band structure becomes altered in quantum-confined systems. Despite novel structural and transport physics discovered in many inorganic nanostructures, the interconnections between these various fields to exploit further property enhancements have received only recent attention.
In this talk, we describe the combination of a large dynamic range of elastic strain available in nanostructures with unique transport physics to enable tunable functional response via elastic strain engineering. In particular, the effect of strain gradients on thermal and charge transport will be addressed in Si nanostructures. We report tunable thermal and electrical conductivity as well as Seebeck coefficients in strained silicon nanomeshes with architected porosity. Using batch fabrication of freestanding nanomesh films from silicon-on-insulator wafers, we present a platform for exploring the effects of the changes in nanomesh geometry and the corresponding strain state on thermal transport. We complement these experimental results with a numerical study of electron mobility in strained silicon nanomeshes where strain gradients are present. Our results show that the nonuniform and multiaxial strain fields defined by the nanomesh geometry give rise to spatially varying band shifts and warping, which in aggregate accelerate electron transport along directions of high stress. Combined with our measured reductions in lattice thermal conductivity, this allows for global electrical conductivity and Seebeck enhancements beyond those of homogenous samples under equivalent far-field stresses, ultimately increasing thermoelectric power factor over unstrained samples. The role of strain gradients in breaking crystalline symmetry and introducing length scales that can be tailored is highlighted.
5:30 PM - CM5.3.03
Measurement of Nano-Scale Out-of-Plane Warpage and In-Plane Strain at Material Interfaces Using Laser Diffraction
Todd Houghton 1 , Hongbin Yu 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThe microelectronics industry relies on sophisticated electronic package design in order to protect delicate silicon chips from damage, dissipate heat, and provide electrical connections. In a microelectronics package, materials with different coefficients of thermal expansion are in contact with each other. During operation, the package temperature increases, inducing strain/stress on the material interfaces. If not accounted for, excessive stresses and strains can cause mechanical cracks and warping, which leads to device failure.
In-plane strain fields (responsible for cracks) and out-of-plane warping can be experimentally mapped using digital image correlation (DIC) and or micro-Moiré interferometry. DIC provides high resolution, but is limited to narrow field of view and requires complex image processing algorithms. Moiré interferometry provides a wider viewing field at lower resolution, with only a limited ability to detect strain across material interfaces. Additionally, because both tools rely on 2D imaging, it is difficult to decouple out-of-plane warping from in-plane displacement.
In order to address the limitations of DIC and Moiré interferometry, an alternative strain sensing technique was developed. This technique utilized a gold diffraction grating bonded to cross-sectional surface of a microelectronics package. By observing the angles of the n=1 and n=-1 optical diffraction orders, in-plane strain and the out-of-plane warping was measured simultaneously, with nano-scale resolution. The strain and warping field were then mapped across the entirety of the grating ROI using two motorized linear stages.
The experimental setup, sample preparation, and measurement procedure will be described in detail. Additionally, both the in-plane and out-of-plane strain/warpage resolution will be discussed.
5:45 PM - CM5.3.04
In Situ Mechanically Controlled Thermal Transport in 2D van der Waals’ Materials
Joon Sang Kang 1 , Ming Ke 1 , Yongjie Hu 1
1 Department of Mechanical and Aerospace Engineering, University of California, Los Angeles (UCLA), Los Angeles, California, United States
Show AbstractControlling the properties of low-dimensional materials by coupling the mechanics may lead to new fundamental discoveries and novel operation frameworks . A clear and straightforward in-situ diagnostic method that can simultaneously monitor the coupled properties during the device normal operation process is highly desirable [1] and can elaborate the fundamental materials dynamics for superior performance. In this talk, we will present our recent progress in exploring the dynamic lattice and ionic mechanics of 2D van der waals’ materials using ultrafast optical spectroscopy, electrochemical control, and multi-scale modeling [2]. We developed a novel platform to in situ investigate two different mechanic regimes: the coherent lattice behaviors (i.e. phonons) in solid-state energy materials (e.g., thermoelectrics), and the ionic behaviors in electrochemical materials (e.g., battery electrodes). We will present these spectral mapping and in-situ mechanics results to show that such development enables a new fundamental understanding from the nanoscale.
Reference:
[1] S. Chu and A. Majumdar, “Opportunities and Challenges for a sustainable energy future,” Nature 488, 294-303 (2012).
[2] Y. Hu, L. Zeng, A. Minnich, M. S. Dresselhaus, and G. Chen, “Spectral mapping of thermal conductivity through nanoscale ballistic transport,” Nature Nanotechnology 10, 701-706 (2015).
CM5.4: Poster Session
Session Chairs
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - CM5.4.01
Structural Characterization of Fiber Textured Au/Ti/Si Thin Films
Qiyin Lin 1
1 The Laboratory for Electron and X-Ray Instrumentation, University of California, Irvine, Irvine, California, United States
Show AbstractGold thin films have been widely used in many technical applications, such as micro-electro-mechanical systems, semiconductor devices, medical devices and conductive coatings. A series of gold thin films ranging in thickness from 25 to 60 nm were deposited on Ti-coated silicon substrates in a high vacuum electron beam evaporation chamber interfaced with a thin film deposition controller. These oxide-free Au films were verified with X-ray Photoelectron Spectroscopy (XPS). Their structural properties were studied in details by various X-ray diffraction (XRD) techniques combined with high resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurement, including out-of-pane and in-plane scattering, 3D pole figure, depth profile glazing incident scattering and rocking curve measurement. All films exhibited a strong {111}-fiber texture component along surface normal direction and a strong {220} texture distributed in-plane direction. The degree of fiber texture in these films were given by the FWHM of center {111} pole: ~2.5°. The in-plane crystallite grain sizes were 15-17 nm little dependent of film thickness while the through-thickness grain sizes increased with film thickness. The stain/stress, mosaicity, surface morphology and roughness of the films were investigated.
9:00 PM - CM5.4.02
Micromechanical Analysis of Piezoelectric—Piezomagnetic Fibrous Composites under Imperfect Contact Using Asymptotic Homogenization Method
Yoanh Espinosa Almeyda 1 , Hector Camacho 1 , Jose A. Otero Hernandez 2 , Reinaldo Rodríguez Ramos 3 , Juan López Realpozo 3 , Raul Guinovart Diaz 3 , Federico J. Sabina 4
1 , Instituto de Ingeniería y Tecnología. Universidad Autónoma de Ciudad Juárez, Ciudad Juárez, Chihuahua, Mexico, 2 , Escuela de Diseño Ingeniería y Arquitectura. Instituto Tecnológico y de Estudios Superiores de Monterrey, Atizapán de Zaragoza, Estado de México, Mexico, 3 , Facultad de Matemática y Computación. Universidad de La Habana, La Habana, La Habana, Cuba, 4 , Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico
Show AbstractThe behaviors of the effective properties of magneto-electro-elastic composites are studied by mean of the Asymptotic Homogenization Method (AHM). The composites are two-phase fiber-reinforced periodic structures whose representative volume elements are parallelograms. The fibers are cylindrical, unidirectional and they are periodically distributed in the matrix. Also, the piezoelectric and piezomagnetic phases have transversely isotropic properties and either perfect or imperfect boundary conditions are considered at the interfaces. The resultant analytical expressions of the homogenized effective coefficients are explicitly dependent on the physical and geometrical properties of the material phases and the constants that characterize the existence of the imperfections. The magneto-electro-elastic behavior is the result of the mechanical interactions between the constituents phase. In addition, the effects of the fiber spatial distribution, the selection of constituents and the kind imperfections on the effective properties are analyzed. Numerical results for the antiplane local problems and associated effective coefficients are reported. Some comparison with the eigenfunction expansion-variational method (EEVM) and other theoretical models are shown.
9:00 PM - CM5.4.03
Stress in Wurtzite Zinc Oxide and the Potential for Electron Device Applications
Poppy Siddiqua 1 , Michael Shur 2 , Stephen O'Leary 1
1 , University of British Columbia, Kelowna, British Columbia, Canada, 2 ECSE, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWurtzite zinc oxide (ZnO) is a II-VI compound semiconductor that has become a focus of attention in recent years. ZnO offers a constellation of material properties that make it an attractive material for a number of important high-frequency and high-power electron device applications. In addition to its wide and direct energy gap, elevated inter-valley energy separation, and large polar optical phonon energy, its availability in bulk wurtzite crystalline form greatly adds to its appeal; the fact that it is almost exactly lattice matched with gallium nitride (GaN) further adds to its appeal, making it possible to use ZnO as a substrate in GaN epitaxy. ZnO is also amenable to wet chemical etching, possesses a large exciton binding energy, and is able to robustly function in extreme radiation conditions. In this paper, we explore how stress applied to ZnO changes the band structure associated with this material. We cast this initial phase of the analysis within the framework of the Kane model for the band structure associated with this material. With the dependence of the band structure on the application of stress, we then examine the nature of the corresponding electron transport. Monte Carlo simulations of the electron transport within bulk wurtzite ZnO will be employed for the purposes of this second phase of the analysis. Finally, the potential for device applications will be explored.
9:00 PM - CM5.4.04
Measurement of Shrinkage of 6061 Al Alloy in Casting Process
Seok Yong Seo 1 , Jeon Taik Lim 1 , Jae Im Jeong 1 , Sung Hyuk Lee 1 , Suk Jun Kim 1 , Gyutae Jeon 1
1 , Koreatech University, Cheonan Korea (the Republic of)
Show AbstractAl6061 alloy has been known it is difficult to produce a product with the casting process different from the common aluminum alloy for casting. In order to overcome this problem, previous studies was presented a tailored step casting technology, research was conducted on a representative to apply for A356.2 aluminum alloy casting alloy. Accordingly it is necessary to measure the amount of shrinkage of the alloy in the same experiment as the previous studies to apply this technology to Al6061 alloy. The tailored step casting method is injecting melt into a mold step by step so that a liquid-air interface is sustained during casting but a solid-air interface is prohibited. For this method, thus, the study of shrinkage of Al-6061 alloy is essential. Shrinkage of Al6061 was measured using a Tatur mold in this study. The effects of four factors – mold temperature, melt temperature, pouring nozzle diameter, and minor alloying elements – on shrinkage was studied. When mold temperature, pouring temperature, pouring nozzle diameter were 350 °C, 760°C, and 10mm, respectively, the shrinkage was shown 5.36 %. The shrinkage reduced to 4.62 % when mold temperature was room temperature. In addition, pouring temperature had little effect on shrinkage in comparison to other factors. The addition of 100 ppm and 200 ppm of Zr altered the trend of shrinkage of Al-6061 alloy.
Correspondence to : Prof. Suk Jun Kim (
[email protected])
9:00 PM - CM5.4.05
Mechanical Stress-Induced Switching Kinetics of Ferroelectric Thin Films at the Nanoscale
Abdullah Alsubaie 1 , Jan Seidel 1
1 School of Materials Science and Engineering, University of New South Wales, Sydney, New South Wales, Australia
Show AbstractWe investigate ferroelectric domain structure and piezoelectric response under variable mechanical compressive stress in Pb(Zr0.2TiO0.8)O3 (PZT) thin films using high-resolution piezo response force microscopy (PFM) and an in-situ sample bending stage. Measurements reveal a drastic change in the ferroelectric domain structure along with elucidating details of the mediating switching process which involve domain wall motion, nucleation, and domain wall roughening under an applied external mechanical stimulus. Furthermore, local PFM hysteresis loops reveal significant changes in the observed coercive biases under applied stress. The PFM hysteresis loops become strongly imprinted under increasing applied compressive stress.
9:00 PM - CM5.4.06
Abnormal Characteristics in the Pore Formation in Graphene due to Si-Nanoparticle Bombardment
Ramki Murugesan 1 , Jaekwang Lee 2 , Narayana Aluru 3 , Jae Hyun Park 1
1 , Gyeongsang National University, Jinju Korea (the Republic of), 2 , Pusan National University, Busan Korea (the Republic of), 3 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractNanopores in graphene are expected to be utilized in various notable applications such as water desalination, chemical species separation, DNA sequencing, etc. Also, because of their atomically thin nature extremely high efficiency can be realized which cannot be achievable in classical approaches. Even though there have been many significant efforts taken in the past, the formation of stable nanopore (long life-time) is still challenging due to the self-healing nature of graphene. The C adatoms are easily combined with the neighboring C atoms in graphene and fills the hole. Recently, the researchers found that the passivation of pore perimeter with Si-atoms can stabilize the nanopore due to the repulsion of Si-atoms. However, the efficient introduction of Si-atoms to the nanopore has not been explored yet. In the present study, by using the extensive molecular dynamics simulations with rigorous many-body potentials, we implement the formation of nanopore in graphene with Si-nanoparticle bombardment and characterize the abnormal features of the pore formation. When the particle hits the graphene with high velocity, it penetrates the membrane by forming a hole with the disruption of the ball. The strong Si-C interaction makes the Si atoms detached from the particle to be bonded with the dangling C atoms in the perimeter of the hole. Interestingly, the normalized pore size (i.e, pore size/particle size) initially increases in proportional to the particle size and then decreases with further increase in the particle size. Besides, the number of Si-atoms left on the perimeter does not increases linearly with the particle size. These observations are closely related with to the shape of the particle during collision. In the collision process, the incident particle is deformed first by a stretched belly in the graphene, and then penetrate the membrane with while forming a hole. When the particle size is small and the kinetic energy is not enough to cause full penetration, the particle is deformed into a “pancake” and then disrupted. The bigger particle experiences less deformation during collision (“oblate” for mid-size; “spherical” for large-size). For the “pancake” shape, the Si-C interaction becomes stronger and confine the movement of Si-atoms while for the “spherical” shape, the strong Si-Si interaction immobilize the Si-atoms. However, for “oblate” shape, the Si-Si and S-C interactions are balanced and thereby the total interaction on Si-atoms becomes minimized which gives much more freedom in the motion of Si-atoms. The strong Si-Si interaction for large particle prevent the detachment of Si-atoms and the number of Si-atoms left in graphene does not increase in proportional to the particle size. The comprehensive quantifications about these observations will be presented in the conference. All the findings in this study will be greatly helpful in designing a controlled pore formation process for stable nanopores in graphene.
9:00 PM - CM5.4.07
Atomic Force Microscopy (AFM) Analysis of Adhesion and Mechanical Properties in Polydimethyl Siloxane (PDMS)-Based Systems for Nanoelectronics
Alin Cristian Chipara 1 2 , Sina Najmaei 1 , Matthew Chin 1 , Robert Burke 1 , Barbara Nichols 1 , Alex Mazzoni 1 , Pulickel Ajayan 2 , Madan Dubey 1
1 , Adelphi Laboratory Center, Adelphi, Maryland, United States, 2 Materials Science and Nanoengineering, Rice University, Houston, Texas, United States
Show AbstractThe properties of 2D materials, such as MoS2, are heavily dependent on the strain transfer from the substrate to the 2D layer. Everything from transfer processes to environmental effects alters the properties of 2D materials, however, strain is one of the key parameters which can be finely controlled. Although macroscale strain is a well-understood topic, it is necessary to precisely understand the effects of varying strain levels in 2D materials. In order to fully comprehend strain transfer to 2D materials, it is essential to use a single material system whose adhesive and mechanical properties (Young’s modulus) can be easily tuned (in the range of 0.5-3.5 MPa). To this end, Sylgard 184 polydimethyl siloxane (PDMS) was utilized and tuned by changing the crosslinker-to-base ratio (from 1:2.5 to 1:30). The change in adhesion and Young’s modulus is a result of the incomplete cross-linking reaction, which leads to variation of the surface chemistry from Si-H dangling bonds to Si-C=C bonds, depending on the crosslinker-to-base ratio. By employing atomic force microscopy (AFM), it was possible to quantify the differences in both adhesion and mechanical properties, which are key parameters in strain transfer. Atomic force microscopy data shows an inverse relationship between the degree of crosslinking in PDMS and its adhesive properties. Specifically, less crosslinking leads to mechanically weaker PDMS (<1 MPa) but, imparts very high adhesion to the polymer. As a result, the PDMS crosslinking and surface chemistry can be altered to vary the strain transfer to a MoS2 flake. By using PDMS with various crosslinking ratios, it is possible to measure and compare strain transfer effects between MoS2 and polymer layers, which will provide a controlled way to tune the strain to a desired value for specific applications. This study also elucidates the role of adhesion and Young’s modulus on strain transfer.
9:00 PM - CM5.4.08
Nano-Mechanical Properties of Novel Oxide Nanocomposites
Treva Brown 1 , Sara Akbarian-Tefaghi 1 , Taha Rostamzadeh 1 , Alex Blanco 1 , Zachary Highland 2 , Jayne Garno 2 , John Wiley 1
1 , University of New Orleans, New Orleans, Louisiana, United States, 2 Chemistry, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractExtensive force modulation studies were performed by atomic force microscopy (AFM) to investigate stress-induced nanomechanical properties of various novel oxide nanostructures with different elemental compositions and thicknesses. Facile wet-chemical synthetic protocols, recently demonstrated by our group, were used for the fabrication of a series of hexaniobate composites including functionalized nanosheets, scrolled nanosheets, and nanopeapod structures. These composites were analyzed by topological contact studies such as tapping or contact. By implementing particular scanning techniques, it is possible to determine information such as topology, magnetic behavior, and frictional forces of nanoscale materials. In addition to using conventional modes of AFM for surface studies, we have also measured the mechanical properties of these nanocomposites via dynamic lateral force modulation (DLFM). By utilizing the capabilities of the DLFM imaging mode, elastic properties such as Young’s Modulus can be measured from force-distance curves. This information can be helpful in determining the relative structural behavior of these nanocomposites and gauge their use in various applications such as structural engineering of nanoarchitectures.
9:00 PM - CM5.4.10
Fluorites and Perovskites with a Large Concentration of Point Defects Exhibit Large Non-Classical Electrostriction
Nimrod Yavo 1 , Ellen Wachtel 1 , Igor Lubomirsky 1 , Ori Yeheskel 2
1 , Weizmann Inst of Science, Rehovot Israel, 2 , Nuclear Research Center—Negev, Beer Sheva Israel
Show Abstract
In our 2012 report (Advanced Materials) on large, non-classical (non-Newnham) electrostriction in Gd-doped ceria (CGO), one of the most studied oxygen conductors, we posed the question of whether such unusual electromechanical activity is limited to this material or that CGO represents but one example of a more general phenomenon. In order to answer this question, we expanded our investigation to include four ionic conductors with a large concentration of point defects, oxygen vacancies or proton interstitials: Gd and Eu doped ceria; (Y,Nb)-stabilized cubic Bi2O3; partially hydrated, Y-doped barium zirconate ; (Sr,Mg) doped LaGaO3.
We found that, depending on dopant type and concentration, all these ceramics exhibit electrostrictive strain considerably in excess of that expected on the basis of the classical theory scaling law. The electrostrictive strain coefficient (M33) of 10 mol% Gd-doped ceria (10CGO) reaches 3x10-16 m2/V2 at frequencies below a few Hz, but drops 100-fold above. Replacing Gd with Lu reduces M33 by an order of magnitude. The electrostrictive strain coefficient of 30CGO was found to be < 10-18 m2/V2, close to that expected from classical electrostriction. (Y,Nb)-stabilized cubic Bi2O3, partially hydrated Y-doped barium zirconate and (Sr,Mg)-doped LaGaO3 exhibit values of M33 within the range 10-18-10-17 m2/V2 at 10-100 Hz without marked frequency-dependence. Interestingly, the electrostriction in cubic Bi2O3 scales with oxygen vacancy concentration. These data taken together indicate a correlation between ionic conductivity at elevated temperature and non-classical electrostriction at room temperature.
EXAFS and high-energy resolution fluorescence detection (HERFD) measurements on 10CGO provide evidence for local lattice distortions in the vicinity of oxygen vacancies, reaching a few% of the normal Ce-O bond length. These distortions weaken under electric field. Comparison of the local strain (4.7% for 10CGO), the concentration of distorted units (»3.5%) and the macroscopic strain ( - ), suggested that the macroscopic electrostrictive strain results from a spatial average of the sparsely distributed local strains. This is very different from classical electrostriction. Electrostriction in doped ceria persists until at least 200 °C, the temperature at which no permanent local lattice distortions can be detected.
Comparison of all four materials implies the existence of a wide class of materials displaying non-classical electrostriction. The common feature for these materials is a large concentration of point defects that become mobile at moderately elevated temperatures.
9:00 PM - CM5.4.11
Elastocaloric Effect in Polycrystalline Ni-Ti-V Shape Memory Alloy
Yanghoo Kim 1 , Min-Gu Jo 1 , Ju-Won Park 1 , Heung Nam Han 1
1 Material Science & Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractLately, many attentions has been focused on elastocaloric effect which is a promising candidate for substitutive refrigeration system in small scale due to its excellent features such as environment-friendliness, fast response and relatively simple installation. In this study, elastocaloric effect in polycrystalline Ni-Ti-V shape memory alloy was investigated using compression test near room temperature. Temperature changes by different removal stresses up to 350MPa were observed by direct monitoring temperature during the reversible martensitic phase transformation. The efficiency of elastocaloric cooling was analyzed using various parameter such as the cooling strength and coefficient of performance. Subsequently, functional fatigue test was performed. After 104 loading-unloading cycles, no significant degradation was detected in elastocaloirc cooling ability and superelastic stress-strain curve showing a good endurance limit. Also, the transformation behavior of the present shape memory alloy was characterized by differential scanning calorimetry and microstructure and phase information were confirmed by means of electron back scattered diffraction and X-ray diffraction.
Symposium Organizers
Steven Boles, The Hong Kong Polytechnic University
In-Suk Choi, Korea Institute of Science and Technology
Christoph Eberl, Fraunhofer Institute for Mechanics of Materials
Hang Yu, Virginia Polytechnic Institute and State University
Symposium Support
The Hong Kong Polytechnic University
CM5.5: Shape Memory Materials
Session Chairs
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 126 B
9:00 AM - *CM5.5.01
Shape Memory Alloys at Small Scales
Ying Chen 1 , Rebecca Dar 1
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractShape memory alloys have the remarkable capability to switch between two “programmed” geometries upon the application and removal of stimuli such as stress, heat, or magnetic field. Their shape memory properties originate from a diffusionless and crystallographically reversible martensitic phase transformation that occurs primarily by shear. At small scales, the transformation transitions from bulk response to surface- or interface-dominated response. The transformation also exhibits hysteretic behavior, and the mechanical or thermal hysteresis varies with sample or crystal sizes. I will review recent progress made in the area of small-scale shape memory alloys, and will also discuss our recent work on transformation-surface interactions in shape memory wires and transformation-interface interactions in shape memory polycrystals. Mechanical modeling of martensitic transformation in confined volumes will also be discussed.
9:30 AM - *CM5.5.02
Highly Cyclic Superelasticity in CeO2-ZrO2 Shape Memory Ceramics Particles at Microscales
Zehui Du 2 , Xiao Mei Zeng 2 1 , Chee Lip Gan 1 2
2 Temasek Lab, Nanyang Technological University, Singapore Singapore, 1 Materials Science & Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractNano- and microscale CeO2-ZrO2 (CZ) shape memory ceramics (SMC) are promising materials for smart micro electro-mechanical systems (MEMs), actuation and energy damping applications thanks to their excellent superelasticity with large strain and high transformation stress. However, the superelasticity reported up to date can only be cycled for ~50 times (in Lai et.al, Science, 2013, 341, 1505), which is much lower than that required for practical engineering applications (at least hundreds or even thousands of cycles). In this work, by using micro-particles as a model, we have systematically studied the particle size and grain boundary effects and uncovered the crucial structural conditions that lead to highly reproducible superelasticity. Superelasticity over hundred strain cycles, with dissipated energy up to ~40 MJ/m3 per cycle and compression strain up to ~4.7% is achieved in the 16 mol% ceria doped CZ particles. Furthermore, the effects of cycling and the fatigue mechanisms in terms of structural evolution and fracture during cyclic loading are also explored.
10:00 AM - CM5.5.03
A New Type of Superelastic and Shape Memory Materials—ThCr2Si2-Structured Novel Intermetallic Compounds at Small Length Scales
Seok-Woo Lee 2 , John Sypek 2 , Hang Yu 1 , Keith Dusoe 2 , Hetal Patel 2 , Amanda Giroux 2 , Alan Goldman 3 , Andreas Kreyssig 3 , Paul Canfield 3 , Sergey Bud'ko 3 , Christopher Weinberger 4
2 Materials Science and Engineering, University of Connecticut, Storrs, Connecticut, United States, 1 Mechanical Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 3 , Ames Laboratory, Ames, Iowa, United States, 4 Mechanical Engineering, Colorado State University, Fort Collins , Colorado, United States
Show AbstractCrystalline, superelastic materials typically exhibit large recoverable strains due to the ability of the material to undergo a reversible phase transition between martensite and austenite phases. Applicable to various alloys, ceramics and intermetallic compounds, this reversible transition serves as a general mechanism for superelasticity and shape memory effect. Recently, we noticed that ThCr2Si2-structured intermetallic compounds exhibit a reversible phase transition between a tetragonal (or orthorhombic) phase to a collapsed tetragonal phase under compression along c-axis of the unit cell by making and breaking Si-Si type bonds. This process has nothing to do with martensitic transformation. This unique reversible phase transformation process motivated us to investigate their potential as a superelastic and shape memory material.
In this study, we studied CaFe2As2, which is one of ThCr2Si2-structured intermetallic compounds and has been extensively studied in the field of solid-state physics due to its remarkable pressure sensitive electronic, magnetic and superconducting properties. Millimeter-sized single crystals were grown by Sn-flux solution growth technique, and micropillar compression was performed along c-axis to characterize their mechanical behavior. We confirmed CaFe2As2 exhibits over 3 GPa strength and over 13% recoverable strain, both of which lead to the ultrahigh elastic energy storage and release 10~1000 times higher than that of conventional high strength materials. Furthermore, we found the exceptional repeatability of cyclic deformation and superior fatigue resistance, compared to shape memory ceramics, which is known as the current state-of-the-art shape memory material. Furthermore, our in-situ cryogenic neutron scattering experiment under pressure showed that CaFe2As2 exhibits linear shape memory effect below 100 K by restoring the original orthorhombic phase from the collapsed-tetragonal phase. This ultra-low temperature shape memory effect could be used to develop a cryogenic linear actuation and sensor technology for deep space exploration. Note that our observation is only one manifestation of a wider class of such transitions found in significant number of ThCr2Si2-structured intermetallic compounds Thus, we believe that our results will represent a paradigm shift in the area of superelastic and shape memory materials with a new phase transformation mechanism, enable an innovative design of cryogenic linear actuators, sensors, and switching devices in extremely cold environments, and more broadly, suggest a mechanistic path to a whole new class of shape memory materials.
10:15 AM - CM5.5.04
Modeling the Coupled Mechanical-Magnetic and Shapememory Properties of ThCr2Si2-Type Crystals
Christopher Weinberger 1 , Ian Bakst 1 , John Sypek 2 , Keith Dusoe 2 , Hang Yu 3 , Paul Canfield 4 , Seok-Woo Lee 2
1 , Colorado State University, Fort Collins, Colorado, United States, 2 , University of Connecticut, Storrs, Connecticut, United States, 3 , Drexel University, Philadelphia, Pennsylvania, United States, 4 , Iowa State University, Ames, Iowa, United States
Show AbstractCrystals of the ThCr2Si2-type structure comprise the largest class of known superconductors, which has generated significant interest in these materials. Some of these compounds also exhibit magnetic-related phase transformations as a function of temperature and pressure. Recently, nano-indentation experiments have shown that at room temperature, small-scale crystals of CaFe2As2 exhibit superelastic behavior with recoverable strains of over 10%. These experiments also demonstrate the potential for shape memory effects at cryogenic temperatures. In this talk, we investigate these phase transitions in these materials using density functional theory in conjunction with analytical models. The models are able to demonstrate that both uniaxial and hydrostatic loading can give rise to these phase change behaviors and the two loading methods are compared and contrasted. The behavior of CaFe2As2 is then compared to LaRu2P2, which does not exhibit a magnetic phase change and hence has little potential for shape memory behavior. These results open up the potential for chemical tuning of the properties of these materials.
10:30 AM - CM5.5.05
A Phase Field Study of the Role of Grain Size Distribution in Nanocrystalline Shape Memory Alloys
Jakub Mikula 1 2 , Jerry Quek Siu Sin 1 , Shailendra Joshi 2 , David Wu 1 , Rajeev Ahluwalia 1
1 , A*Star, Singapore Singapore, 2 , NUS, Singapore Singapore
Show AbstractConventional shape memory alloys are made as polycrystals. Recently, nanocrystalline shape memory alloys have also been studied. Properties such as the shape memory effect are highly dependent on the grain size. The martensitic transformation, which is the underlying mechanism for the shape memory effect, may even become completely suppressed if the grain size falls below a critical value. On the other hand, mechanical properties can often be improved by reducing the grains size. Controlling both the mechanical and shape memory properties by a single parameter – mean grain size – leads to many restrictions on the microstructural design of shape memory alloys at nanoscale.
It has been shown that a bimodal grain size distribution can yield a superior combination of mutually exclusive properties as strength and ductility, enhancing both properties at the same time. While the study of the role of grain size on shape memory properties has been investigated in earlier studies, how such properties are influenced by the distribution of grain size is still not understood. We use phase field simulations to investigate how the shape memory properties can be controlled by altering the distribution of grain sizes. We propose novel microstructures in which one class of the grains is refined down to very small sizes to suppress the martensitic transformation and the other class contains large enough grains to allow for forming of the martensite. By this, we design shape-memory nanocomposites, where the composite is made of the austenite and the martensite, both phases stabilized even at low temperatures. We show that unlike the unimodal case where the recoverable strain is small, this strain can be enhanced by considering a bimodal distribution of grain size. At the same time, a good mechanical response is expected.
Our study is focused on detwinning processes and phase transformations of stress-loaded nano-grain systems. Numerical simulations are based on a thermodynamically consistent phase field model of martensitic transformations in nanocrystals. Statistically analysed stress-strain curves obtained from the simulations offer a great insight into the dependence of the recoverable strain on different grain size distributions. The simulation results are applicable to any shape memory alloy undergoing cubic-to-tetragonal transformation and the results provide insights which can be useful for the design of nanoscale shape memory devices.
10:45 AM - CM5.5.06
Shape Memory Behavior of Pressure-Sensitive Photonic Crystal Polymers Determined by Material Composition and Structural Geometry
Curtis Taylor 1 , Yongliang Ni 1 , Yin Fang 2 , Peng Jiang 2
1 Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States, 2 Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractIn this study, we seek to gain a fundamental understanding of the effects of chemical composition and pore size on the mechanical behavior and composition-structure-property relationship of pressure-sensitive photonic crystal shape memory polymers (PCSMPs). Reconfigurable photonic crystals are key components that could ultimately enable all-optical integrated circuits and quantum information processing. Unfortunately, traditional reconfigurable/tunable photonic crystals cannot memorize the temporarily configured optical microstructures during the tuning process. PCSMPs enable unusual "cold" programming and instantaneous shape recovery at ambient conditions triggered by multiple unconventional stimuli, such as contact pressure, a large variety of vapors and liquids (e.g., acetone and ethanol), ultrasonic waves, and lateral shear stress. The 2015 Fang et al., Nature Communications paper, “Reconfigurable photonic crystals enabled by pressure-responsive shape-memory polymers”, details the recent discovery of this new series of multi-stimuli-responsive shape memory polymers.
These PCSMPs are made from a ratio of ethoxylated (20) trimethylolpropane triacrylate (ETPTA) and polyethylene glycol (600) diacrylate (PEGDA). A free-standing macroporous photonic crystal membrane with 3-D ordered macropores is fabricated using self-assembled silica colloidal crystals as templates. In order to understand the role of chemical composition and pore size on the mechanics of the PCSMP, we vary the oligomer volumetric ratio of PEGDA to ETPTA and pore size (200-400 nm). The surface topography and pore structure is characterized by scanning electron and atomic force microscopies. Normal-incidence optical reflection spectroscopy is performed to characterize chromo-mechanical coupling of the PCSMPs. Microindentation with in-situ optical microscopy is used to measure material deformation as a function of applied force. The results demonstrate that we are able to isolate and measure deformation of the porous layer via real-time video capture of the contact area and indentation process. The effective elastic modulus is determined as a function of pore size and composition using contact mechanics models including consideration of adhesive effects via the Johnson-Kendall-Roberts (JKR) theory. The outcomes of this study allow for a method to tune the mechanical response to stimuli and pressure sensitivity by varying chemical composition and/or pore size enabling a wider range of applications and material versatility. The in-situ measurements provide for real-time observation of soft multi-layer thin film responses and accurate determination of mechanical properties, which is important for emerging soft matter mechanics and applications.
CM5.6: Strain-Coupling in Devices
Session Chairs
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 126 B
11:30 AM - *CM5.6.01
Thin Film Mechanics and Electrical Properties of Amorphous Materials for Electronic Devices
Young-chang Joo 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe investigated the phase stability and electrical property of amorphous materials, and helped to build a framework to describe the properties of amorphous materials in the application of electronic and energy devices through the thin film mechanical stress analysis. Amorphous materials have been actively applied in multi-functional devices, thanks to their unique properties originated from disordered atomic structure distinct from crystalline materials; phase-change random access memory (PcRAM) and thin-film transistor (TFT). However, electronic devices based on the amorphous materials have suffered from the reliability issues originated from their phase instability. The amorphous materials are in in-equilibrium, therefore, various structural changes occur (e.g. structural relaxation, glass transition, crystallization), which lead to the changes in material properties. Therefore, it is crucial to characterize and tune the phase stability for the development of the device characteristics. In this study, mechanical stress analysis using the substrate curvature measurement method was utilized to detect the structural changes and phase stability in amorphous thin films.
The crystallization kinetics of the amorphous phase change materials were explored; crystallization temperature (Tx), glass transition temperature (Tg), super-cooled liquid region (Tx - Tg) of amorphous Ge2Sb2Te5 (GST) films doped with various elements. Besides, the viscosity and the fragility were also determined. Doping effects on the thermal stability and atomic mobility show successful matching with PcRAM characteristics; data retention and SET speed, respectively. Microscopic origin of the resistance drift has also been investigated by revealing the relationship between the structural relaxation and the time-dependent resistance changes. The novel in-situ measurement of mechanical stress and resistance were conducted to correlate two phenomena.
Amorphous In-Ga-Zn-O (a-IGZO) is an active material for TFT, however, experiences phase instability originated from surface. Surface-to-volume ratios of the a-IGZO film were varied by thickness variation. The thickness dependence of Tg and fragility indicates the phase stability of a-IGZO was significantly reduced due to the unstable surface layer.
12:00 PM - CM5.6.02
Mechanical Reliability of Flexible Perovskite Solar Cell
Seung-min Ahn 1 , Eui Dae Jung 1 , Myoung Hoon Song 1 , Ju-Young Kim 1
1 School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919 Korea (the Republic of)
Show AbstractThe Sun is a sustainable, reliable and nearly infinite energy source, and photovoltaic energy is currently drawing attention as an alternative energy source. Organic-inorganic halide perovskite solar cells hold promise for next-generation photovoltaic devices due to their remarkable optical properties, high light-absorption coefficient and good cost-effectiveness, and the photovoltaic efficiencies of perovskite-based solar cells have rapidly soared from 3.8% to above 20%. In addition, perovskite devices have recently attracted substantial interest for flexible/stretchable electronic devices. In these various applications, especially flexible solar cells, one of the most important issues in device reliability and durability is mechanical properties. Most flexible perovskite solar cells are occurred degradation of photovoltaic properties after severe bending environment due to crack propagation on weakest layer in solar cell. However, it is unclear which mechanism is correct in fracture system. For this reason, estimation of mechanical properties in flexible perovskite solar cell is important. Researchers have used nanoindentation testing to study the elastic properties of perovskite-based solar cells. Unfortunately, the results of nanoindentation tests are strongly affected by the presence and makeup of the substrates, or under layers. For this reason, here we fabricated various free-standing component thin films of flexible perovskite solar cells using a simple solution process and transferred hole-substrates and evaluated their elastic deformation limits using nanoindentation on the hole-substrates. Hole size is proportional to the thickness of each thin film. We confirmed that the perovskite layer is by far the most fragile of all the components. Therefore, we evaluated and analyzed the intrinsic tensile properties of perovskite layers by an in-situ tensile testing system using push-to-pull devices. We believe that this study sheds light on the durability and fundamental mechanism of flexible perovskite solar cells.
12:15 PM - CM5.6.03
Coherent EUV Acoustic Nanometrology for Sub-50nm Thin Film Complete Mechanical Characterization
Nico Hernandez Charpak 1 , Travis Frazer 1 , Joshua Knobloch 1 , Begona Abbad Mayor 1 , Kathleen Hoogeboom-Pot 1 , Damiano Nardi 1 , Weilun Chao 2 , Margaret Murnane 1 , Henry Kapteyn 1
1 JILA, University of Colorado Boulder, Boulder, Colorado, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractPrecise characterization of the mechanical properties of ultrathin films is at key to both a fundamental understanding of low-scale materials and for the continuing improvement of nanotechnology. Emerging silicon technology and device design require reliable characterization tools to discover, optimize and monitor new nano-manufacturing techniques. Moore’s Law scaling has pushed the frontiers of nanofabrication so far that the thinnest films and smallest nanostructures being made today cannot be easily characterized using established metrology techniques. Precise characterization of materials in nanostructured systems is necessary for understanding the unique physics which become apparent in such small-scale systems, such as thickness dependent or fabrication dependent elastic properties.
To address these challenges, we have implemented a non-destructive, photoacoustic metrology technique that uses coherent extreme ultraviolet (EUV) light from tabletop high-order harmonic generation (HHG) in place of more conventional visible-wavelength laser probes [1]. The shorter wavelength of EUV beams is sensitive to picometer-scale dynamics of the surface, while the femtosecond duration of HHG pulses is fast enough to capture sub-picosecond thermal and acoustic dynamics in few-nm scale structures.
Our samples consist of low-k dielectric thin films on silicon substrates coated with periodic gratings of metallic nanolines. A femtosecond 800nm laser pump pulse is focused onto the samples to impulsively heat the nanowires and launch both surface acoustic waves (SAWs) and longitudinal acoustic waves (LAWs). SAWs can propagate within the thin film or penetrate into the substrate, depending on their wavelength as set by the grating period. LAWs are launched within the nanowires and the thin film beneath them, reflecting from any buried interfaces. All these dynamics can be monitored simultaneously by tracking the diffraction efficiency of our 30nm-wavelength EUV probe beam from the nano-grating on the surface of the thin film as a function of pump-probe delay time [2].
We have used our technique to study the thickness dependence of the c11 component of the elastic tensor in sub-10nm metallic films [3]. Here we use the simultaneous tracking of LAWs return times and sub-100nm wavelength SAWs to measure the mechanical properties of a series of sub-100nm low-k dielectric thin films, down to 11nm in thickness. We fully characterize the elastic tensor of these isotropic thin films in a single measurement and report on the fabrication and thickness dependence of their elastic properties. These results not only represent the capability of fully characterizing the thinnest film to date, but also presents a path forward to systematic and in-situ characterization of sub-10nm films using coherent EUV acoustic nanometrology.
1. Popmintchev et al., Science 336, 1287 (2012)
2. Hernandez et al., Proc. SPIE 9778, 97780I (2016)
3. Hoogeboom et al. Nano Lett., 16 (8), pp 4773–4778 (2016)
12:30 PM - CM5.6.04
Ultra-High Fracture Strength of ALD Alumina Nanostructure for GaN LED Application
Sung-gyu Kang 1 2 , Daeyoung Moon 1 , Euijoon Yoon 1 , In-Suk Choi 2 , Heung Nam Han 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractIt has been reported that ceramic materials exhibit superior fracture strength when the sample dimension gets into the nanometer regime. However, practical application of nanostructured ceramic materials has been very limited. In this study, we fabricated different types of alumina nanoshell structures with ultra-high tensile strength for the application of GaN LED. We systematically evaluated the mechanical properties of cylindrical nano-shell structure by combining the in-situ nanoindentation and the finite element analysis. The cono-spherical indentation on the top surface of cylindrical nanoshells initiated cracks from the underneath of indenter at exceptionally high fracture strength, around 13 GPa, in all ALD alumina nanoshell structures. However, there was no noticeable “smaller is stronger” trend among the nanoshells when we varied the shell thickness of 63 nm, 73 nm, and 115 nm. Thickness-independent fracture strength was attributed to presence of spherical nano-caivities in nanoshells which can be a representative intrinsic length scale. We could evaluate the tensile stress concentrated around spherical cavities inside each nanoshells reaches near-theoretical fracture strength, around 32 GPa. This mechanically robust ALD alumina nanoshells can be successfully implemented in light emitting diodes. The nanoshell structures placed between GaN thin film and sapphire substrate decrease residual thermal stress while increasing light-emitting efficiency compared to conventional LEDs without nanostructured alumina.
12:45 PM - CM5.6.05
Stress-Directed Compositional Patterning of Compound Semiconductors to Create 2D Quantum Dot Arrays—Path to Mechanically Triggered Circuits
Brian Rummel 1 , Sang Han 1
1 , University of New Mexico, Albuquerque, New Mexico, United States
Show AbstractWe have previously demonstrated that a patterned elastic stress field can be used to change the near-surface atomic composition in an epitaxial compound semiconductor film.1 This compositional patterning laterally manipulates quantum barriers within the film in a press-and-print manner, completely eliminating the need for Stranski-Krastanov growth. In this example, an array of silicon pillars is pressed against a relaxed Si0.8Ge0.2 substrate in a mechanical press, and the entire assembly is heated to high temperatures. This serves to promote germanium diffusion away from the compressed regions, leaving 100% silicon-enriched areas. The careful assembly and design of the silicon nanopillar array allows for controllable SiGe or pure Si/Ge regions which can ultimately be used in the production of a mechanically triggered quantum dot circuit. As a first step towards addressing these individual dots, we make use of micro-Raman spectroscopic imaging to visualize the tensile stress field produced by stress-directed compositional patterning. This method allows us to locate the dot positions. To further demonstrate the broad applicability of mechanically triggered quantum dot array formation, we have also translated the press-and-print approach to the InGaAs/GaAs system to create 3D confined quantum structures. We will further discuss micro-photoluminescence characterization of InGaAs/GaAs quantum structures in this presentation.
1 S. Ghosh, D. Kaiser, J. Bonilla, T. Sinno, and S. M. Han, "Stress-Directed Compositional Patterning of SiGe Substrates for Lateral Quantum Barrier Manipulation," Applied Physic Letters 107, 072106-1:5 (2015).
CM5.7: Strain-Optical Coupling
Session Chairs
Steven Boles
Austin Minnich
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 126 B
2:30 PM - *CM5.7.01
Strain-Optical Coupling in Mechanically Flexible Microphotonic Systems
Lan Li 1 , Hongtao Lin 1 , Jerome Michon 1 , YiZhong Huang 1 , Junying Li 1 , Shutao Qiao 2 , Nanshu Lu 2 , Anupama Yadav 3 , Kathleen Richardson 3 , Juejun Hu 1 , Tian Gu 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , University of Texas at Austin, Austin, Texas, United States, 3 , University of Central Florida, Orlando, Florida, United States
Show AbstractStrain-optical coupling is a known property since the pioneering work by Sir David Brewster on photoelasticity dating back to the early 19th century. The emergence of micro- and nano-photonics in the past decade, however, shed new light on this centuries-old phenomenon. Besides strain-induced modifications to material optical properties due to photoelastic coupling, strain also leads to deformation of microphotonic device structures and a plethora of intriguing optomechanical effects on device behavior. In this talk, we will discuss the tensorial strain-optical coupling theory in the context of microphotonic devices, and apply the fundamental insight to engineering novel flexible integrated photonic systems with extraordinary mechanical compliance and durability.
3:00 PM - CM5.7.02
Interfacial Mechanical Properties of Graphene on Self Assembled Monolayers—Experiments and Simulations
Qing Tu 1 2 , Hoshin Kim 3 2 , Thomas Oweida 3 , Zehra Parlak 1 , Yaroslava Yingling 3 2 , Stefan Zauscher 1 2
1 Mechanical Engineering & Materials Science, Duke University, Durham, North Carolina, United States, 2 NSF Research Triangle MRSEC, Duke University, Durham, North Carolina, United States, 3 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractSelf-assembled monolayers (SAMs) have been widely used to engineer the electronic properties of substrate-supported graphene devices. However, little is known about how the surface chemistry of SAMs affects the interfacial mechanical properties of graphene on SAMs. Variations in these properties affect the stress transfer between substrate and the supported graphene and thus the performance of the graphene-based devices. The changes in interfacial mechanical properties can be characterized through out-of-plane elastic properties measurements. Here we show that the identity of the head group chemistry of a SAM has a significant effect on the interfacial mechanical properties of SAM-supported few layer graphene. CR-AFM experiments reveal that the heterostructure of FLG supported on hydrophilic NH2-terminated SAMs is softer than that of FLG supported on hydrophobic CH3-terminated SAMs. Raman spectroscopy suggests that these differences might be due to a different amount of water molecules associated with the different SAM head groups, present at the FLG-SAM interface. The experimentally observed stiffness differences are successfully captured via steered and all-atom Molecular Dynamics (MD) simulations. The simulation results clearly show that water molecules located at the FLG-SAM interfaces mediate the interaction between graphene and the SAM and are the key factor for the observed stiffness difference between graphene on hydrophobic and hydrophilic SAMs. The protonation of the amine head groups renders NH2-SAMs even more hydrophilic, and consequently weakens the graphene-SAM interactions. Vacuum annealing of the sample removes water molecules from the interfaces and causes an overall decrease in the out-of-plane stiffness. These observations suggest that hydrophobic surfaces are preferable over hydrophilic surfaces to achieve better mechanical and electronic stability. Our results thus provide an important and often overlooked aspect for the fabrication of substrate-supported graphene electronics, including but not limited to SAM-engineered substrate surfaces.
3:15 PM - CM5.7.03
Ultra-Fast Coherent X-Ray Diffraction of Deformation Modes in ZnO Nanoscrystals
Mathew Cherukara 1 , Kiran Sasikumar 1 , Wonsuk Cha 1 , Badri Narayanan 1 , Ian McNulty 1 , Eric Dufresne 1 , Haidan Wen 1 , Subramanian Sankaranarayanan 1 , Ross Harder 1
1 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractObserving the dynamic behavior of materials following ultra-fast excitation can reveal insights into the response of materials under non-equilibrium conditions of pressure, temperature and deformation. Such observations are extremely challenging to characterize especially at the nano to mesoscopic spatiotemporal scales. We demonstrate three-dimensional imaging of the structure and strain of the transient deformation of a ZnO crystal on sub-ns timescales following excitation by a laser ‘pump’ using stroboscopic ‘probes’ of X-rays. The excitation induced in the ZnO crystal from the laser pump is observed to excite characteristic resonant modes in the crystal at different time scales, corresponding to the propagation of acoustic phonons and the characteristic frequency of the crystal. By directly importing the experimentally reconstructed nanocrystal structure into a continuum deformation model, we elucidate the deformation mechanisms following laser excitation and the development of potential gradients across the nanocrystal with implications for nanoscale power generation.
CM5.8: Strain-Induced Transformations in Vanadium Dioxide
Session Chairs
Dan Gianola
Heung Nam Han
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 126 B
4:30 PM - *CM5.8.01
Investigations of Coupled Mechanical and Electrical/Electrochemical Phenomena in VO2 and Si Nanowires
Reiner Moenig 1 2
1 , Karlsruhe Institute of Technology, Karlsruhe Germany, 2 , Helmholtz Institute Ulm, Ulm Germany
Show AbstractSmall scale objects and in particular nanowires are important components for many future technologies due to their unique physical properties which are often a consequence of their high surface areas. In order to mechanically characterize nanowires, an experimental platform to perform tensile tests inside a dual beam SEM/FIB was developed. With this setup, nanowires of different materials with diameters down to 30nm can be tested and reliable stress-strain curves can be recorded while the samples are imaged. In the same experiment, a voltage can be applied to the sample and the resulting current can be measured. This technique was used on VO2 nanowires in order to monitor their strain induced phase transformation and to further investigate their electrical properties under strain. By adding ionic liquids as vacuum compatible electrolytes also electrochemical experiments can be performed with this setup. Silicon is a promising material for the negative electrode of lithium-ion batteries. It can accommodate up to 3.75 lithium atoms per silicon atom. This leads to large volume changes of about 300% and phase transformations during battery operation. The combined mechanical-electrochemical experiments on silicon nanowires reveal that silicon electrodes strongly change their mechanical behavior during battery operation. The unlithiated wires are brittle and only become ductile once significantly lithiated. It was found that when fully lithiated, the nanowires show a viscoplastic behavior. This observation may explain the ability of silicon nanowires to tolerate the large volume changes required for storing large amounts of lithium.
5:00 PM - *CM5.8.02
“Smart” Applications with Metal-Insulator Phase Transition
Kaichen Dong 1 , Sukjoon Hong 1 , Yang Deng 1 , Kai Liu 1 , Costas Grigoropoulos 1 , Jie Yao 1 , Junqiao Wu 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractThe metal-insulator phase transition in VO2 is accompanied with a structural transition from monoclinic phase at low temperatures (<67oC) to tetragonal phase at high temperatures (>67oC). These two phases differ distinctly not only in electronic properties (conductivity, and dielectric and optical constants), but also in mechanical features (shape, size, volume, etc.) of the sample. As a result, a wide range of “smart” applications can be developed to exploit these properties. In this talk, I will discuss two new applications recently developed in our labs. The first one is a microscale actuator and solid engine that could convert thermal gradient into mechanical motion at high energy efficiencies and high power densities. The second one is a meta-canvas that allows rapid writing and erasing of nearly arbitrary metaphotonic patterns on a thin film.
5:30 PM - CM5.8.04
Rule of Composition Design for Crystal Growth in Modified Potassium Sodium Niobate Ceramics
Cheol-Woo Ahn 1 , Attaur Rahman 1 , Jungho Ryu 1 , Jong-Jin Choi 1 , Jong-Woo Kim 1 , Woon-Ha Yoon 1 , Joon-Hwan Choi 1 , Dong-Soo Park 1 , Byung-Dong Hahn 1
1 , KIMS, Changwon Korea (the Republic of)
Show AbstractIn Pb-free ceramics, (K,Na)NbO3 (KNN)-based ceramics have gained considerable attention, owing to their high piezoelectric properties. They consist of polycrystalline ceramics and single crystals. Although single crystals show excellent properties, their high price is an obstacle for device application. In this presentation, therefore, it is reported how the single crystals can be obtained by a low-cost process, which is a conventional ceramic process, in KNN-based ceramics. The large crystal can be grown by the composition design of KNN-based materials. In KNN-based ceramics, the abnormal grain growth (AGG) can be expedited by considering three factors, such as the stoichiometry of compositions, the large amount of liquid phase, and the donor-doping to enhance the growth rate of a large grain. Through the composition design, the growth rate of large grains was enhanced approximately 1000 times and the single crystal (approximately 3 cm) was successfully obtained. In addition, this single crystal showed an excellent sensor property and Curie temperature which were higher than them of Pb(Zr,Ti)O3 (PZT)-based single crystals.
Symposium Organizers
Steven Boles, The Hong Kong Polytechnic University
In-Suk Choi, Korea Institute of Science and Technology
Christoph Eberl, Fraunhofer Institute for Mechanics of Materials
Hang Yu, Virginia Polytechnic Institute and State University
Symposium Support
The Hong Kong Polytechnic University
CM5.9: Strain-Coupling in Carbon Based Materials and Devices
Session Chairs
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 126 B
9:00 AM - *CM5.9.01
Strengthening in Metal-Graphene Nanolayered Composites Synthesized via Roll-Based Graphene Transfer Methods
Seung Min Han 1 , Sangmin Kim 1
1 , Korea Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractThe two-dimensional geometry, high intrinsic strength and modulus of graphene can effectively constrain the dislocation motion, resulting in the significant strengthening of metals. Nanolayered composite consisting of alternating layers of metal and monolayer graphene was previously demonstrated to be ultra high strength that could be used in applications requiring extreme mechanical properties such as stretchable interconnects. The drawback of the previous wet-transfer method of fabrication for metal-graphene nanolayers is that each graphene transfer is time consuming and is therefore has limitations for large-scale synthesis. In this work, dry, roll-based graphene transfer method with electroplated metal was used to fabricate Cu-graphene nanolyared composite with layer spacing ranging from 100 nm to 400 nm. Nanopillar compression results indicate strength ranging from 850 MPa to 1.1 GPa, which is in agreement with the previously reported strengthening in wet-transferred metal-graphene nanolayers. Thus, the roll-based transfer of graphene can more efficiently be used to create large-scale metal-graphene nanolayered composite with ultra high strength for potential applications such as the stretchable interconnect.
9:30 AM - CM5.9.02
Self-Ion Irradiation Effects on Mechanical and Thermal Properties of Nanocrystalline Zirconium Films
Baoming Wang 1 , Raghu Pulavarthy 3 , Khalid Hattar 2 , Aman Haque 1
1 , The Pennsylvania State University, University Park, Pennsylvania, United States, 3 , Intel Corporation, Hillsboro, Oregon, United States, 2 , Sandia National Laboratory, Albuquerque, New Mexico, United States
Show AbstractZirconium thin films, with nominal thickness and grain size of 100 and 10 nm respectively, were irradiated at room temperature with an 800 keV Zr+ beam using a 6 MV HVE Tandem accelerator. Freestanding tensile specimens with doses of 3*10^n ions*cm-2 (n = 10 – 14, corresponding to displacement per atom of 2.1x10^-4 to 2.28) were co-fabricated with micro-mechanical testing devices. Uniaxial tensile tests were performed in-situ inside a transmission electron microscope to reveal the effect of irradiation on microstructure and mechanical properties. Significant grain growth (>300%) and rotation were observed in addition to the evolution of defects due to the irradiation. Mechanical properties were therefore compared by the grain size as a measure of the irradiation dosage. Young’s modulus decreased by up to 25% for grain sizes below 20 nm, after which no change was observed. The stress-strain profiles were mostly linear elastic below 20 nm grain size, after which it started to show yielding and strain hardening. Such behavior is explained with a diffusion-dislocation competing mechanism, where the role of irradiation is to inject defects that lead to grain growth. The growth mechanism is accelerated above the critical grain size of around 20 nm, with the introduction of dislocations. Contrary to plastic instability typical to bulk materials, we observe sustained train hardening indicating improved radiation tolerance at this length-scale. An energy balance approach was used to estimate the thermal conductivity of the specimens as function of irradiation dosage. Up to 32% reduction of thermal conductivity was measured for dose of 2.1 dpa or 3x1014 ions/cm2.
9:45 AM - CM5.9.03
In Situ Mechanical Properties of 3D Materials Synthesized from Graphene and Carbon Nanotubes
Sanjit Bhowmick 1 , Chandra Tiwary 2 , Syed Asif 1 , Pulickel Ajayan 2
1 , Hysitron Inc, Eden Prairie, Minnesota, United States, 2 , Rice University, Houston, Texas, United States
Show AbstractNanoengineered 3D materials manufactured from 2D graphene and 1D carbon nanotubes gained visibility in the recent past due to numerous novel applications, primarily in the two most challenges before mankind today, namely, environment and energy. This study focuses on understanding the variation in mechanical properties and deformation mechanism of such 3D materials as a function of temperature. An in-situ nanomechanical instrument, PI 87xR SEM PicoIndenter was used to conduct uniaxial compression of pillar samples that were FIB milled from 3D materials. Materials synthesized from graphene sheets showed completely elastic behavior and brittle fracture at RT. A considerable amount of plasticity was observed at higher temperature. In contrast, carbon nanotube-based bulk materials showed strain softening in loading and significant recovery during unloading both at RT and elevated temperatures.
10:00 AM - CM5.9.04
Mechanical Testing and Characterization of CNTs-Based Thin-Film Conductive Tracks on Flexible Polymeric Substrates
Yuran Kang 1 , Joachim Binder 1 , Patric Gruber 1 , Oliver Kraft 1
1 , Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen Germany
Show AbstractFlexible electronics are not any more emerging fields of research, there are already sound applications in the wearable electronics market. The booming of this new market demands advanced electronic materials, which exhibit excellent mechanical robustness and electronic functionality at higher strains. The requirements in the aspect of mechanical stretchability, reliability, and durability are high but still intangible. Depending on different applications, there is currently no defined standard of how much strain a device would sustain during service, and how much lifetime the material should guarantee. The most important material layer in a flexible circuitry are the conductive tracks, rather they serve as highways of electrical signals, they should bear a large extent of external strains. Even minor damages induced by strains in the conductive tracks could lead to the failure of the whole device.
Conventional materials, such as metallic interconnects, or conductive oxides thin-film-conductors would typically fail at a few percent of strains. One of the most significant hurdles to achieving stretchable conductive tracks using those materials arises from their intrinsic limitations like poor mechanical stretchability. As an alternative, carbon nanotubes (CNTs) offer outstanding electrical and mechanical properties. When CNTs are deposited as thin films on polymer substrates, they provide superior mechanical stretchability. In addition, CNTs can be formulated as inks and adapted for different solution processes, which are suitable for the fabrication of flexible electronics.
In our study, we have fabricated conductive tracks, composed of monolithically patterned CNT films on polymer substrates, and we have investigated the relationship between film thickness, film morphology, and their electro-mechanical properties. Experimental results showed that those films offer excellent mechanical and electrical properties. Micro-tensile testings showed excellent mechanical stretchability up to 50% of tensile strain for one layer of CNT thin-film, without significantly degrading their electrical performance. Bending fatigue testings showed outstanding mechanical durability up to 1 million cycles at a strain amplitude of 2%. The electrical resistance of those conductive tracks showed an increase of less than 100% at 50% of tensile strain, which is much less than that of the metallic counterparts. Microscopic observations and in-situ tensile testing in SEM revealed no fatal cracks form on the CNT-based thin-film conductive tracks till 50% of tensile strain, especially when the deposited layer of CNT is increased to 3 layers. Not only the electrical performance of more layered CNT conductive tracks are significantly improved, but also the more layered conductive tracks showed improved resistance to crack formation. Those promising properties of CNT-based conductive tracks will benefit the production of high-performance stretchable electronic devices.
10:15 AM - CM5.9.05
Nanoscale Correlated Mechanical and Chemical Measurements on Patterned Porous Organo-Silicate Fins
Gheorghe Stan 1 , Richard Gates 1 , Kelvin Kjoller 2 , Craig Prater 2 , Alan Myers 3 , Kanwal Jit-Singh 3 , Ebony Mays 3 , Hui Yoo 3 , Sean King 3
1 Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Anasys Instruments, Santa Barbara, California, United States, 3 , Intel Corporation, Hillsboro, Oregon, United States
Show AbstractStructure-property characterization is of increasing relevance in the semiconductor industry, where the achievement of desired functionalities is provided by the precise shaping and ordering of materials into component structures. As this control aims to advance toward the atomic limit, better optimization of the fabrication process is sought to be realized not only by dimensional metrology but also by various material property characterizations with necessary spatial resolution. In this regard, nanoscale mechanical and chemical measurements are two primary characterizations that can be used to observe the modifications sustained during processing. In this work, we have combined atomic force microscopy infrared (AFM-IR) chemical structure and contact resonance AFM (CR-AFM) mechanical property measurements in the investigation of 20 - 500 nm wide fin structures fabricated in a nano-porous organo-silicate material; such high-aspect ratio patterns feature geometries anticipated in the next generations of microprocessor interconnects. In our study, both mechanical and chemical properties were found to correlate with one another, the feature size, and fabrication process. Thus, by comparing side-by-side CR-AFM and AFM-IR measurements on the same structures, we observed that the mechanical stiffness of the fins showed an inverse correlation with the concentration of terminal organic groups: The selective removal of the organic component during etching determined an increase in stiffness and its reinsertion by chemical silylation produced a decrease in stiffness. From measurements as a function of the fin width we further established that the loss of terminal organics and increase of stiffness occur primarily in the outer exposed surfaces of the fins over a length scale of 10 - 20 nm. Furthermore, by using depth-dependent intermittent CR-AFM measurements we were able to probe the sub-surface inhomogeneous stiffness profile of the fins. This was done in the form of tomographic elastic modulus sections across the measured structures. Applications of such combined nanoscale near-surface mechanical and chemical interrogations can be envisioned for other organic or inorganic materials of interest.
CM5.10: Small-Scale Nanomechanical Testing
Session Chairs
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 126 B
11:15 AM - CM5.10.01
Ultra-Light, Scalable and High-Temperature Resilient Ceramic Nanofiber Sponges
Xuan Zhang 1 , Xiaoyan Li 1 , Huajian Gao 2
1 Centre for Advanced Mechanics and Materials, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing China, 2 School of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractUltra-light and resilient porous nanostructures have been fabricated in various material forms including carbon, polymers, and metals. However, the development of ultra-light and high-temperature resilient structures still remains extremely challenging. Ceramics exhibit good mechanical and chemical stability at high temperatures, but their brittleness and sensitivity to flaws significantly complicate the fabrication of resilient porous ceramic nanostructures. Here, we report the manufacturing of large-scale, lightweight, high-temperature resilient, three-dimensional (3D) sponges based on a variety of oxide ceramic (e.g., TiO2, ZrO2, yttria-stabilized ZrO2 (YSZ) and BaTiO3) nanofibers through an efficient solution blow-spinning process. The ceramic sponges consist of numerous tangled ceramic nanofibers, with density varying from 8 to 40 mg/cm3. In-situ uniaxial compression inside a scanning electron microscope showed that the TiO2 nanofiber sponge exhibits high energy absorption (e.g., dissipation up to 29.6 mJ/cm3 in energy density at 50% strain), and recovers rapidly after compression in excess of 20% strain at both room temperature and 400 °C. Remarkably, the sponge exhibits excellent resilience with residual strains of only ~1% at 800 °C after 10 cycles of 10% compression strain, and maintains good recoverability after compression at ~1300 °C. We show that the ceramic nanofiber sponges can serve multiple functions, such as elasticity-dependent electrical resistance, photocatalytic activity and thermal insulation.
11:30 AM - CM5.10.02
Experimentally Studying the Mechanical Properties of GaN Nanowires Based on Couple Stress Theory
Mohammad Reza Zamani Kouhpanji 1 , Mahmoud Behzadirad 1 , Tito Busani 1
1 , University of New Mexico, Albuquerque, New Mexico, United States
Show AbstractThe mechanical properties of GaN nanowires (NWs) have been marginally studied, despite a large number of conducted researches on the GaN optoelectronic and photonic properties. Study and prediction of these properties is crucial due to the potential application of GaN in piezoelectric, tip metrology, and lithography areas. GaN is mainly grown on sapphire substrates whose lattice constant and thermal expansion coefficient are significantly different from GaN. These discrepancies cause mechanical defects and high residual stresses and strains in GaN, which reduce its quantum efficiency, by decreasing the charge carrier mobility and increasing an inhomogeneous distribution of charge density over the active region.
Specifically, for nanoscale applications, the mechanical properties of materials differ significantly compared to the bulk properties due to size-effects. In order to take into account the size-effects on mechanical properties of GaN NWs, we used the couple stress theory to evaluate our experimental data collected using Atomic Force Microscopy, we applied an infinitesimal deflection on the top of clamped-free NWs while we were monitoring the lateral and normal forces. Experimentally the NWs were prepared by using top-down approach to etch (combination of dry and wet etch) c-plane GaN layer grown in Metal Organic Chemical Vapor Deposition (MOCVD) chamber, to achieve high aspect ratio NWs.
Using the couple stress theory, we managed to determine, the Young’s modulus, the shear modulus and the length scale parameter, defined in the couple stress theory, of GaN NWs experimentally. The average values of these elastic constants were measured to be 330 GPa, 133 GPa and 10 nm, respectively. In contrast to the classical continuum theory, which does not capture the size-effects on mechanical properties of nanostructures, using these three constants enables a more accurate prediction of the nanoscale mechanical behaviors of different aspect ratios GaN NWs. We also evaluated our experiment data using the classical continuum theory to explain the discrepancy between the available results from different experiments of GaN NWs regarding to the behaviors of GaN NWs for wide ranges of aspect ratios, especially for radiuses very close to the length scale parameter.
11:45 AM - CM5.10.03
Piezotronic Effect Modulated Heterojunction Electron Gas in AlGaN/AlN/GaN Heterostructure Microwire
Xingfu Wang 1 , Ruomeng Yu 1 , Zhong Lin Wang 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractElectric transport properties of heterostructured semiconductors are dominated by an electron gas formed at local junctions due to intrinsic spontaneous polarizations and lattice mismatch. Here, the existence of heterojunction electron gas in AlGaN/AlN/GaN nanowires is experimentally and theoretically proven. The piezotronic effect is then introduced to modulate the physical properties of electron gas near heterojunctions at various temperatures ranging from 77 K to 300 K. The conductance of AlGaN/AlN/GaN nanowires is increased by 165% under -1.78% compressive strains and reduced by 48% under 1.78% tensile strains at room temperature, due to the modulations of heterojunction electron gas by the strain-induced piezotronic effect. This modulating effect is further improved at 77 K by 890% and 940% under compressive and tensile strains, respectively, indicating the enhanced piezotronic effect at low temperature. Theoretical simulations are presented to systematically illustrate and confirm the proposed working mechanism. This study provides an in-depth understanding about the piezotronic-effect modulation of low-dimensional electron gas in heterostructured nanomaterials, with potential applications in high electrons mobility transistors and MEMS/NEMS.
12:00 PM - CM5.10.04
Exploring the Brittle-to-Ductile Transition of Silicon at the Microscale In Situ under Bending
Mohamed Elhebeary 1 , Tristan Harzer 2 , Stefan Hieke 2 , Gerhard Dehm 2 , Taher Saif 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 , Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf Germany
Show AbstractMost MEMS structures are subjected to bending during operation. This motivated our interest in the design of a novel micro-chip that can test materials at the micro/nanoscale under bending. Here we propose a new method to test micro-beams at high temperature under bending. The new stage minimizes uniaxial state of stress in the specimen, but maximizes bending stress over a small volume such that high stresses can be reached within a small volume on the specimen without a premature failure by fracture. A test setup was designed to fit inside an SEM and be able to heat the sample up to 500°C while applying sufficient bending stress by stretching the micro-chip. Most of the reported bending tests were carried out using AFM or nanoindentation. In our method the sample is co-fabricated with the micro-chip to eliminate any misalignment error and avoid any handling difficulties. The dimensions of the structure have lithographic accuracy. The chip-based stage, actuated by a piezo-actuator, applies bending moments on micro/nanoscale beam specimens. Analytical and finite element (FE) models were developed to predict the behavior of the novel stage and calculate the stresses at the anchors.
The method is applied to test the strength of single crystal silicon (SCS) micro-beams under bending. At room temperature, bending tests revealed strengthening of SCS compared to that under uniform tension. This strengthening is contributed by stress localization near the surface of the beams close to the anchors, and the stress gradient from the surface to the neutral axis. The study further reveals significant reduction in the Brittle to Ductile Transition (BDT) temperature of SCS micro-beams compared to their bulk counterparts. The load-deflection relation during loading and unloading shows large permanent deformation at 400°C and significant slip traces appear on the sidewalls of the beam.
12:15 PM - CM5.10.05
AM-FM—A Quantitative Nanomechanical Characterization Technique for Small-Scale and Low-Dimensional Materials
Marta Kocun 1 , Aleksander Labuda 1 , Waiman Meinhold 1 , Jason Li 1 , Roger Proksch 1
1 , Asylum Research, Santa Barbara, California, United States
Show AbstractCharacterization techniques for small-scale and low-dimensional materials are crucial to the advancement of this field of research as they enable the investigation of properties of newly developed materials. Atomic force microscopy (AFM) is a powerful characterization technique as it is a nondestructive, high spatial resolution technique that can be used in ambient conditions with minimal sample preparation. Tapping mode AFM imaging, also known as amplitude-modulated (AM) AFM is fast, gentle and can provide images of features ranging from fractions of a nanometer to tens of microns in size. Although tapping mode imaging provides quantitative topography information, until recently, only qualitative mechanical properties of the surfaces could be obtained. AM-FM imaging mode is a bimodal (dual-frequency) technique that provides quantitative contact stiffness data, from which elastic modulus can be calculated with appropriate models for the tip sample contact mechanics. During AM-FM imaging the first resonant mode is operated in AM, whereas a higher resonant mode is frequency modulated (FM). One of the remaining challenges is the calibration of the cantilever’s higher mode spring constant and sensitivity. Here, we will discuss calibration procedure that delivers higher mode cantilever oscillation amplitude in nanometers, which allows for the exact same experimental settings from one experiment to another. We will report results on various samples such as metals, alloys and polymers will be presented to demonstrate the applicability of AM-FM mode for materials with a wide range of modulus (MPa-GPa). Furthermore, recent advances in AM-FM imaging will be discussed, such as the use of photothermal excitation to achieve molecular-level resolution on semi-crystalline polymers. With the growing demand for mechanical characterization of materials at the micro and nanoscale, AM-FM technique provides quantitative nanomechanical information while simultaneously offering all the familiar advantages of tapping mode.
12:30 PM - CM5.10.06
Investigating the Mechanical and Piezoelectric Properties of Combinatorially Deposited (Al,Sc)N Thin Films Using Nano-Indentation Techniques
Dong Wu 1 , Kevin Talley 1 , Andriy Zakutayev 2 , Paul Constantine 1 , Geoff Brennecka 1 , Corinne Packard 1 2
1 , Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractAluminum nitride (AlN) thin films are widely used in piezoelectric MEMS devices due to acceptable piezoelectric properties and excellent compatibility with microelectronics. Recently, efforts have increased to develop new nitride alloys with better piezoelectric behavior, and combinatorial growth methods combined with high-throughput measurements allow rapid screening of candidate compositions. In this study, (Al,Sc)N thin films with an intentional composition gradient were deposited by reactive co-sputtering, and film characteristics were determined by a number of complementary techniques. The hardness and reduced elastic modulus of the films were investigated using dynamic mechanical indentation. After eliminating substrate effects via iterative numerical methods, the true reduced elastic moduli of the thin films were determined. The piezoelectric strain response of (Al,Sc)N thin films was also evaluated using a nanoindenter to detect nanoscale displacement. Screening via coupled measurements of composition, elastic properties, and piezoelectric behavior enabled by instrumented indentation is helping to accelerate piezoelectric nitride alloy evaluation and development.
12:45 PM - CM5.10.07
Elasto-Plastic Deformation of Gold Thin Film Investigated by Hole-Nanoindentation
Na-Hyang Kim 1 , Ju-Young Kim 1
1 Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractGold is used as an electrode in nano-devices such as MEMS and NEMS because of its superior properties of high electrical conductivity, biocompatibility and chemical stability, among others. It is generally used as a nanometers-thick film, and the mechanical properties of each layer in a device must be measured to confirm reliability. Mechanical properties can be measured by tensile test, compression test, indentation, etc. Above all, the uni-axial tensile test is known as to obtain the most quantitative mechanical properties such as yield strength, ultimate tensile strength, failure elongation and strain-hardening exponent. However, for nanometer-thick films, specimen fabrication and testing technique are complex. In contrast, indentation is nondestructive, has relatively simple sample preparation and testing method, and can measure elastic modulus. Although nanoindentation makes possible the precise measurement of the properties of micro-scale materials, it is not suitable for sub-micron films due to substrate effects. Recently hole-nanoindentation is well used to measure the mechanical properties of 2-D materials. It also has simple sample fabrication method and test method, but it can only measure several mechanical properties such as elastic modulus and fracture strength. In the present study, we introduce method to evaluate yield strength of Au thin film by hole-nanoindentation. Since yield strength is the stress when elasto-plastic behavior begins, measuring yield strength for designing device is significant. For sample preparation, 100 nm-thick gold film is deposited by sputtering on 1 μm-thick wet oxide silicon substrate and by etching silicon dioxide and drying-off the film, freestanding gold thin film is obtained. We perform tensile test and hole-nanoindentation, obtain yield strength from hole-nanoindentation, and compare its results with those from tensile testing.
CM5.11: In Situ TEM of Mechanical Deformation
Session Chairs
In-Suk Choi
Seung Min Han
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 126 B
2:30 PM - *CM5.11.01
Tracking Shear-Migration Coupling of Grain Boundaries Using In Situ TEM
Marc Legros 1 , Armin Rajabzadeh 3 , Nicolas Combe 1 2 , Frederic Mompiou 1 2
1 , CEMES CNRS, Toulouse France, 3 , Mc Gill University, Montreal, Quebec, Canada, 2 , Université Paul Sabatier, Toulouse France
Show AbstractNanocrystalline metals (d≤100 nm) possess a much greater resistance to plastic deformation because they contain very few mobile dislocations. On the other side, their large proportion of grain boundaries (GBs) may compensate this if GB-based plastic deformation becomes significant. Few observations indicative of these alternative mechanisms have been obtained. Shear-coupled GB migration may be especially efficient to carry out plasticity through GB motion. It has been mainly studied theoretically or experimentally in bicrystals. Quantitative measurement of GB-based plasticity and shear are even more challenging. We have conducted both in-situ TEM experiments on small-grain polycrystals and molecular dynamic simulations using the NEB technique (Nudge Elastic Band). We could show that shear-migration coupling involves the displacement of linear defects called disconnections that are specific to grain boundaries. As dislocations in the crystal, the properties of these disconnections seem to guide the coupling mechanism of migrating grain boundaries. Because of the much higher degree of freedom of a grain boundary compared to the crystal lattice, the shear-coupling factor that characterizes the amount of coupling a given moving GB can produce is not unique, as indicated by our experiments.
3:00 PM - CM5.11.02
In Situ TEM Study on the Dislocation Behavior in Micronanoscaled Single Crystal Metals
Zhiwei Shan 1
1 , Xi'an Jiaotong University, Xi'an China
Show AbstractIn this talk, I will review our recent progress in exploring the extraordianry mechanical behavior of micronanosclaed metals [1] which has attracted interests of researchers throughout the world in the past decade. We found that single crystal pillars fabricated through focused ion beam always contain high density of defects[1-4]. However, if the sample size is small enough, both face-centered-cubic and body-centered-cubic metal pillars can experience ‘‘mechanical annealing,’’ i.e., a phenomena referring to the reduction of dislocation density in the deforming volume, when dislocation generation is outweighed by dislocation annihilation through the free surface [1-3]. Most recently, we demonstrate that when aluminum single crystals of sub-micrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of pre-existing dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density. Real-time, in-situ transmission electron microscope (TEM) observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence and number of strain cycles. Those dislocations moving closer to the free surface of the thin specimens are then further attracted to the surface by image forces that facilitate the egress of such unpinned mobile dislocations from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in sub-micrometer sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that causes change in shape and/or dimensions of the specimen [4].
References
[1] Shan Z. W., JOM, 64, 1229-1234 (2012).
[2] Shan, Z. W.; Mishra, R. K.; Asif, S. A. S.; Warren, O. L.; Minor, A. M. NATURE MATERIALS 7, 115-119 (2008).
[3] Huang, L.; Li, Q. J.; Shan, Z. W.; Li, J.; Sun, J.; Ma, E. Nature Communications 2, 547, (2011)
[4] Z. J. Wang, Q. J. Li, Y. N. Cui, Z. L. Liuc, E. Ma, J. Li, J. Sun, Z. Zhuang, M. Dao, Z. W. Shan, and Subra Suresh, Proceedings of the National Academy of Sciences of the United States of America, 112, 13502–13507 (2015, Sep.).
3:15 PM - CM5.11.03
Investigating the Deformation Behavior of Ultrafine-Grained Aluminum Films Using In Situ TEM Straining with Automated Crystal Orientation Mapping
Ehsan Izadi 1 , Amith Darbal 2 , Jagannathan Rajagopalan 1
1 , Arizona State University, Tempe, Arizona, United States, 2 , AppFive LLC., Tempe, Arizona, United States
Show AbstractIn situ TEM deformation is a key technique to probe the deformation mechanisms of ultrafine-grained and nanocrystalline metals. However, obtaining statistically meaningful information about microstructural changes using conventional bright-field/dark-field imaging or diffraction techniques is time consuming. Here, we use automated crystal orientation mapping in TEM (ACOM-TEM) to track orientation changes in hundreds of grains during in situ deformation of ultrafine-grained (UFG) aluminum films. Our experiments on non-textured UFG Al films show extensive grain orientation changes during loading, with both the fraction of grains that undergo rotations and their magnitude increasing with strain. The rotations are reversible in a significant fraction of grains during unloading, leading to notable inelastic strain recovery. More surprisingly, a small fraction of grains continue to rotate in the same direction during unloading, even when the applied stress has been reduced significantly. The experiments also provide evidence of reversible and irreversible grain/twin boundary migration in these films. In contrast, UFG Al films with a bicrystalline texture show substantially smaller grain rotations and fewer microstructural changes during loading and unloading. This stark difference in the underlying deformation mechanisms explains the vast disparity in the strain rate sensitivity and inelastic strain recovery of textured and non-textured UFG Al films.
3:30 PM - CM5.11.04
Crack Propagation in Monolayer MoS2—An In Situ TEM Study
Baoming Wang 1 , MD Zahabul Islam 1 , Kehao Zhang 1 , Joshua Robinson 1 , Aman Haque 1
1 , The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractWe report the preparation and crack propagation mechanism of monolayer MoS2 thin film. Monolayer MoS2 was grown on sapphire using chemical vapor deposition (CVD) approach and transferred to TEM grid using a newly developed fast transfer method. The crack propagation of atomic layer MoS2 was directly observed in transmission electron microscope (TEM). Our results show that the crack can be initiated by electron beam and it was found to propagate mostly in the Zig-Zag (ZZ) direction, mixed with very few Arm-Chair (AC) direction. Strain field near the crack tip is measured to very complex and an atomic-scale crack was found to nucleate in front of crack tip to lead the propagation from certain crack depth, which is measured to be around 630nm. We proposed that the formation of the atomic-scale crack is related to the crack depth and crack-opening stress concentration.
3:45 PM - CM5.11.05
Quantitative Measurements of Electromechanical Response with Interferometric Atomic Force Microscopy
Aleksander Labuda 1 , Marta Kocun 1 , Roger Proksch 1
1 , Asylum Research, Santa Barbara, California, United States
Show AbstractOne of the ongoing challenges in the field of piezoresponse force microscopy (PFM) is the accurate quantification of the piezoelectric coefficients. Conventional PFM systems almost exclusively use an optical beam deflection (OBD) system where a laser is focused on the back of the cantilever and the angle of the reflected light is used to deduce the cantilever normal and lateral tip motion. However, non-desirable buckling and torsion of the cantilever may be misinterpreted as cantilever tip motion. This is a shortcoming of the OBD method which measures the angle of the cantilever, rather than the displacement of the tip.
Here, we describe results on highly sensitive PFM imaging and spectroscopic studies of ferroelectrics (LiNbO3 crystals and Pb(Zr,Ti)O3 and BaTiO3 thin films) performed with an interferometric AFM. This AFM is based on a commercial Cypher S AFM and combines the existing OBD system with a separate quantitative interferometric Laser Doppler Vibrometer (LDV) system to enable accurate measurements of the displacement and velocity of the cantilever tip. This combined instrument allows a host of quantitative measurements to be performed including measuring a variety of in-situ PFM cantilever oscillation modes, as well as accurately measuring the cantilever spring constant prior to making contact with the surface. Importantly, the piezoelectric coefficients extracted from several LDV measurements showed an order of magnitude less variability compared to the error-prone OBD measurements acquired simultaneously. By performing simultaneous LDV and OBD measurements, we were able to conclude that most of the measurement error and variability in PFM measurements thus far can be attributed to the shortcoming of the OBD method.
We present a systematic methodology for accurate PFM measurement of d33 and d15 coefficients. In this context, the notable differences between the OBD and LDV results are demonstrated and discussed. Even though the interferometer provides an intrinsically quantitative measurement of the cantilever motion, there are additional requirements for quantification of the tip-sample electromechanical response that prevent cantilever dynamics and stray electrostatic interactions from overwhelming the PFM signal. Further considerations about the effects of finite loading forces that may reduce the apparent piezoelectric sensitivity are also discussed. In addition, quantitative lateral PFM results, determined from sequential LDV measurements at various LDV spot positions, are also presented.
CM5.12: Plasticity
Session Chairs
Marc Legros
Reiner Moenig
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 126 B
4:15 PM - *CM5.12.01
Electric Current-Induced Deformation Behavior in Metallic Materials
Heung Nam Han 1 , Moon-Jo Kim 2 , Miyoung Kim 1 , In-Suk Choi 3 , Sung-Tae Hong 4 , Seung Hyun Cho 5
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Korea Institute of Industrial Technology, Inchen Korea (the Republic of), 3 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 4 , University of Ulsan, Ulsan Korea (the Republic of), 5 , Korea Research Institute of Standards and Science, Seung Hyun Cho Korea (the Republic of)
Show AbstractThe deformation behavior of various alloys under electric current is investigated. In the uniaxial tensile deformation mode, generally, the elongation increased drastically with softening of flow stress under the electric current. Microstructural observations confirmed that the electric current itself could play a distinct role to induce the recovery of dislocation apart from the conventional Joule heating. It could be said that ‘electric current-induced annealing’ takes place when an electric current is applied during plastic deformation without surpassing the critical annealing temperature.
As for some precipitation hardening alloys, both elongation and flow stress of solution treated specimen under electric current was increased in comparison to the results without applying an electric current. The ageing effect could be described by the formation of early stage of precipitation or atomic clustering due to the applying electric current. It was also confirmed that the electric current itself could play a distinct role to induce the ageing apart from the conventional Joule heating. Therefore, this phenomenon could be called ‘electric current-induced ageing’.
These electroplasticity phenomena, in this presentation, which are known that applying electric current through metallic materials can enhance the plastic deformation, will be introduced. In addition, the origin of electroplasticity will be discussed based on microstructural change, measurement of elastic constant, atomic simulation and finite element modelling under electric current.
4:45 PM - CM5.12.02
Selective Oxidation-Induced Strengthening of Zr/Nb Nanoscale Multilayers
Miguel Monclus 2 , Ling Wei Yang 2 , M. Callisti 3 , Tomas Polcar 3 , Jon Molina-Aldareguia 2 , Javier Llorca 1
2 , IMDEA Materials Institute, Getafe, Madrid, Spain, 3 , University of Southampton, Southampton United Kingdom, 1 , IMDEA Materials Institute & Technical University of Madrid, Getafe, Madrid Spain
Show AbstractThe paper presents a new approach, based on controlled oxidation of nanoscale metallic multilayers, to produce strong and hard oxide/metal nanocomposite coatings with high strength and good thermal stability. The approach is demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale metallic multilayers and investigating the evolution of their microstructure and mechanical properties by combining analytical transmission electron microscopy, nano-mechanical tests (nanoindentation and micropillar compression) and finite element models. As-deposited multilayers were annealed at 350C in air for times ranging between 1 – 336 hours. The elastic modulus increased by ~ 20% and the hardness by ~ 42% after 15 hours of annealing. Longer annealing times did not lead to changes in hardness, although the elastic modulus increased up to 35% after 336 hrs. The hcp Zr layers were rapidly transformed into monoclinic ZrO2 (in the first 15 hours), while the Nb layers were progressively oxidised, from top surface down towards the substrate, to form an amorphous oxide phase at a much lower rate. The sequential oxidation of Zr and Nb layers was key for the oxidation to take place without rupture of the multi-layered structure and without coating spallation, as the plastic deformation of the metallic Nb layers allowed for the partial relieve of the residual stresses developed as a result of the volumetric expansion of the Zr layers upon oxidation. Moreover, the development of residual stresses induced further changes in mechanical properties in relation to the annealing time, as revealed by finite element simulations. Finally, the strengthening induced by oxidation increased as the layer thickness decreased from 30 nm to 5 nm.
5:00 PM - CM5.12.03
Using Nanoindentation as a Mechanical Spectroscopy Tool—Investigating Incipient Plasticity Using In Situ 4-pt Bend Stage
Hakan Yavas 1 , Hengxu Song 1 , Bryan Crawford 3 , Kevin Hemker 1 , Stefanos Papanikolaou 1 2
1 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, United States
Show AbstractDuring initial stages of nanoindentation, the displacement of the indenter tip first corresponds to elastic deformation, i.e. Hertzian response, and then continues by plastic yielding where the displacement significantly deviates from the Hertzian law. A very good indication of yielding is associated with the first pop-in event (~around 20 nm for polycrystalline Cu). Pop-in events can be used to reveal the fundamental mechanisms of the elastic-plastic transition and provides a fingerprint of a dislocation-starved microstructure. This presentation will discuss a novel nanoindentation technique to probe dislocation dynamics by statistically tracking pop-in events during application of in-plane stresses via a custom 4-pt bending stage. Additionally, we will also present the dynamic response maps of nanoindentation and correlate them to dislocation activity: This approach may be considered as a way of using nanoindentation as a mechanical spectroscopy tool.
5:15 PM - CM5.12.04
Mechanical Behavior of Nanotwinned Nanoporous Gold
Eun-Ji Gwak 1 , Ju-Young Kim 1
1 School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractNanoporous gold (np-Au) has been extensively studied for catalyst, sensor, actuator and other applications due to its open-cell porous structure with high surface-to-volume ratio. Np-Au shows brittle behavior even though individual ligaments are composed of ductile metal, making it difficult to use to MEMS devices and other applications, and hence the mechanical properties of np-Au need further investigation. In previous work, we found that high grain-boundary density in precursor alloys lower the flexural strength of np-Au, while nanoindentation hardness is independent of the within-ligament microstructure. Recent studies have shown that a nanotwin (nt) structure in Cu and Ag can significantly enhance both strength and ductility over an ultra-fine or coarse grain structure due to the large density of twin boundaries. The nt structure can be created in electrodeposited and sputtered films by exploiting stacking fault energy, deposition rate and temperature. Here we fabricate nanotwined nanoporous gold (nt np-Au) thin film and measure its mechanical properties using nanoindentation and tensile testing.
We fabricate nt Ag-Au thin film by co-sputtering of Ag and Au targets in a magnetron sputtering machine. Varying the annealing time after deposition lets us control grain size and twin density in the nt precursor thin film. After free corrosion dealloying in nitric acid, microstructures of precursor and np-Au are observed by TEM (transmission electron microscope), SEM (scanning electron microscope) and EBSD (electron back-scattered diffraction) and mechanical properties are investigated by nanoindentation and tensile testing to correlate the np-Au morphology and plasticity.
5:30 PM - *CM5.12.05
Helium Ion Microscope Fabrication Causing Changes in the Structure and Mechanical Behavior of Silicon Micropillars
Yuecun Wang 1 , Evan Ma 2 , Zhiwei Shan 1
1 , Xi’an Jiaotong University, Xi'an China, 2 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractHelium ion microscope (HIM) has several advantages over the more familiar gallium ion microscope (often referred to as focused ion beam, FIB), for fabrication of micro- or nano- scale samples. One hitherto unexplored problem, however, is the potential alteration of the structure and properties of the small-volume material being micro-machined or examined. Here we use silicon as a prominent case study, to demonstrate the dramatic effects of helium ion irradiation. Structurally, a sub-micron Si pillar can turn completely amorphous at helium ion doses typically used for micromachining, forming nanobubbles at higher doses. In terms of mechanical properties, the flow stress decreases markedly with the increasing dosage, and the softened amorphous Si exhibits spread-out plastic flow with a “drum-like” sample morphology. On the positive side, such beam effects may be taken advantage of, for tailoring materials properties and for shaping via plastic deformation. For example, the irradiated a-Si, being more compliant and ductile, could be a useful structural material for certain MEMS/NEMS applications, and be amenable to re-shaping via deformation under externally imposed stresses.