Symposium Organizers
Bilge Yildiz, Massachusetts Institute of Technology
Paul Evans, University of Wisconsin-Madison
Tobias Schulli, ESRF - The European Synchrotron
Ting Zhu, Georgia Institute of Technology
MD2.1: Elastic Strain-Driven Materials Design and Discovery
Session Chairs
Paul Evans
Tobias Schulli
Bilge Yildiz
Ting Zhu
Tuesday PM, March 29, 2016
PCC West, 100 Level, Room 101 B
2:30 PM - *MD2.1.01
Tuning the Band Structure of Complex Oxides Utilizing Elastic Strain Engineering
Darrell Schlom 2
1 Department of Materials Science and Engineering Cornell University Ithaca United States,2 Kavli Institute at Cornell for Nanoscale Science Ithaca United States,
Show AbstractWe exploit elastic strain engineering to tune the band structure of the complex oxide ruthenates: CaRuO3, SrRuO3,1 and BaRuO3 with the perovskite structure as well as their two-dimensional counterparts Sr2RuO4 and Ba2RuO4.2 The ruthenate films are grown by reactive molecular-beam epitaxy (MBE) and the misfit strain is imposed by underlying substrates to strain these complex oxide thin films to percent levels3—far beyond where they would crack or plastically deform in bulk. The band structure is revealed by high-resolution angle-resolved photoemission (ARPES) on pristine as-grown surfaces of these complex oxides made possible by a direct ultra-high vacuum connection between the MBE and ARPES. Our work demonstrates the possibilities for utilizing elastic strain engineering as a disorder-free means to manipulate emergent properties and many-body interactions in correlated materials.
1. D.E. Shai, C. Adamo, D.W. Shen, C.M. Brooks, J.W. Harter, E.J. Monkman, B. Burganov, D.G. Schlom, and K.M. Shen, “Quasiparticle Mass Enhancement and Temperature Dependence of the Electronic Structure of Ferromagnetic SrRuO3 Thin Films,” Physical Review Letters 110 (2013) 087004.
2. B. Burganov, C. Adamo, A. Mulder, M. Uchida, P.D.C. King, J.W. Harter, D.E. Shai, A.S. Gibbs, A.P. Mackenzie, R. Uecker, M.R. Beasley, C.J. Fennie, D.G. Schlom, and K.M. Shen, “Epitaxial Strain Control of Fermi Surface Topology and Quasiparticle Interactions in the Spin-Triplet Ruthenate Superconductors,” (unpublished).
3. D.G. Schlom, L.Q. Chen, C.J. Fennie, V. Gopalan, D.A. Muller, X.Q. Pan, R. Ramesh, and R. Uecker, “Elastic Strain Engineering of Ferroic Oxides,” MRS Bulletin 39 (2014) 118–130.
3:00 PM - *MD2.1.02
Predicting Epitaxial-Strain-Induced Structural, Magnetic and Electronic Phase Transitions in Perovskite Oxides from First Principles
Karin Rabe 1
1 Rutgers Univ Piscataway United States,
Show AbstractFirst-principles total-energy calculations are a powerful tool for predicting phase stability and properties as a function of epitaxial strain in transition metal oxides and other chemically and structurally complex systems. This is most easily done with the "strained bulk" approach, in which the effects of epitaxial strain are studied by imposing the geometrical matching constraint on the bulk system. Here, I will describe a systematic and efficient method under development for identifying the ground state and low-energy alternative structures of ABO3 perovskites at each value of strain, including modeling of magnetic ordering and spin-lattice coupling. This method enables the development of a database of epitaxial phases for use in the design of superlattices and heterostructures with desired structure and properties; selected examples will be discussed.
3:30 PM - *MD2.1.03
Selective Control of Oxygen Sublattice Stability by Strain in Epitaxial Complex Oxides
Ho Nyung Lee 1
1 Oak Ridge National Laboratory Oak Ridge United States,
Show AbstractOxygen vacancies formed in complex oxides as point defects create extra electrons, critically modifying the electronic and ionic properties. As we witnessed over the last few decades, many important physical properties, such as superconductivity, colossal magnetoresistance, and resistive switching, are closely associated with oxygen non-stoichiometry in complex oxides, providing tremendous promise for technical breakthroughs. Exploiting such functional defects to discover new materials and properties, however, has rarely been attempted despite the fact that it can provide opportunities to discover novel functionalities. Our recent discovery of “oxygen sponges” stabilized by epitaxial synthesis of SrCoOx is one example of epitaxially stabilized oxides with intriguing physical and electrochemical properties owing to the multivalent nature of cobalt ions. In this talk, we will present the role of oxygen non-stoichiometry in oxide materials and its control by thin film epitaxy. In particular, in epitaxial films of the Ruddlesden-Popper phase La1.85Sr0.15CuO4, we found that preferential oxygen vacancy formation occurs within the equatorial position of the CuO2 plane, which could be described by a drastically reduced Gibbs free energy for oxygen vacancy formation. Interestingly, this preferential oxygen vacancy formation leads to an unexpected lattice contraction and suppression of superconductivity. The strong strain coupling of oxygen nonstoichiometry and the unusual structural response reported here can provide new perspectives and a deeper understanding of the role of strain in many other functional oxide materials.
*This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
MD2.2: Dynamically Strained Oxide Electronics
Session Chairs
Tuesday PM, March 29, 2016
PCC West, 100 Level, Room 101 B
4:30 PM - *MD2.2.01
A Strain-Based Transduction Device for Fast Low Power Digital Switching at the Nanoscale: The Piezoelectronic Transistor
Glenn Martyna 2
1 Physical Sciences IBM Research Yorktown Heights United States,2 School of Physics and Astronomy University of Edinburgh Edinburgh United Kingdom,
Show AbstractA transduction based post-CMOS device based on a piezoelectrically driven metal insulator transition is described [1]. An input voltage pulse activates a piezoelectric element (PE) which transduces input voltage into an electro-acoustic pulse that in turn drives an insulator to metal transition (IMT) in a piezoresistive element (PR); the transition effectively transduces the electro-acoustic pulse to voltage. Using the known properties of bulk materials, we predict using modeling that the devvice achieves multi-GHz clock speeds with voltages as low as 0.1 V and a large On/Off switching ratio (≈104) for digital logic [1]. The switch is compatible with CMOS-style logic. At larger scale the PET is predicted to function effectively as a large-area low voltage device for use in sensor applications and as a RF switch for applications in communications.
The performance of our device is enabled by the properties of two materials, a relaxor piezoelectric for the PE and a rare earth chalcogenide piezoresistor for the PR – provided the materials exhibit bulk properties at the nanoscale. Thus it is critical to investigate materials scaling using a combined theoretical/experimental approach. The development of thin film piezoresistive and piezoelectric materials and patterned structures, and associated characterization tools is presented, along with the theoretical models that yield insight into their behavior [2-4]. Integration of these novel materials into 3 evolutionary generations of PET devices, and device characterization, is given [5] to show that a proof of concept has been achieved.
References
1. “High Response Piezoelectric and Piezoresistive Materials for Fast, Low Voltage Switching: Simulation and Theory of Transduction Physics at the Nanometer-Scale”, G.J. Martyna, et al Adv. Mat. 24, 3672 (2012); Appl. Phys. Lett. 107, 073505 (2015);
2. “Giant Piezoresistive On/Off Ratios in Rare-Earth Chalcogenide Thin Films Enabling Nanomechanical Switching”, G.J. Martyna et al, Nano Lett. 13, 4650 (2013).
3. “Anisotropic strain in SmSe and SmTe: implications for electronic transport G.J. Martyna et al, Phys. Rev. B. 90, 245124 (2014).
4. “Lateral scaling of PMN-PT thin films for piezoelectric logic”, G.J. Martyna, et al J. Appl. Phys. 115, 234106 (2014).
5. “Pathway to the PiezoElectronic Transduction Logic Device”, Nano Lett. (2015); Nanotechnology 26 375201 (2015).
5:00 PM - MD2.2.02
Strained Oxide Heterostructures for Modulating Memristance
Sebastian Schweiger 1,William Bowman 1,Ulrich Aschauer 1,Jennifer Rupp 1
1 ETH Zurich Zurich Switzerland,2 Arizona State University Tempe United States,1 ETH Zurich Zurich Switzerland
Show AbstractRedox-based resistive memories are a promising alternative to current transistor based technologies and can be deployed e.g. as memories and logics.1 Resistive switches are usually composed of a single metal oxide building block, e.g. SrTiO3, TiO2, CeO2, sandwiched between two metal electrodes and are operated at high electric field strengths. Here, new material design concepts to modulate carrier concentration and mobility at high field strength and the related kinetics require attention2. The concept of strain engineering for metal oxide heterostructures is discussed in this work to control important resistive switching device properties like retention, Roff/Ron ratios etc. We discuss lattice strain engineering as a new powerful and versatile tool for manipulating mass and charge transport and its integration as new functional building blocks to real micro-devices.
The benefits of strain manipulation on atomistic near order and ionic transport are the biggest at low temperature and for large strain fields3; this makes it particularly interesting for low to room-temperature applications, like resistive switching memories. We show a microfabrication strategy for strained micro-dot heterostructure architectures to manipulate the in-plane nanoscopic interfaces and transport of the strained heterostructures4 for resistive switches. For this, a model system using two different set of materials is being studied. One is the system Gd0.1Ce0.9O2-x/Er2O3, with Gd0.1Ce0.9O2-x under compressive strain and the other one is Gd0.1Ce0.9O2-x with Bi/Nb Oxide, with Gd0.1Ce0.9O2-x under tensile strain. In this model, the current flows through the Gd0.1Ce0.9O2-x films while the other phase has the sole purpose to impose strain.
The magnitude of strain is changed by altering the number of interfaces while keeping the device at constant total heterolayer film thickness. We show that interfacial strain changes the ON-State of the device and can be used to vary the effective Roff/Ron ratio, frequencies and number of resistance states addressable. Building on this knowledge we investigate the near-order ionic transport interaction by Raman micro-spectroscopy which are discussed as new technique to investigate and describe the strain state and changes in the oxygen sublatttice where the carriers are transported upon resistive switching at high bias. TEM is used to study the compressively and tensely strained interfaces. Finally, we will demonstrate the very first in-operando Raman measurements capturing in real-time changes in the near order oxygen anionic-cationic lattice vs. applied field strength, frequency and strain states of the resistive switching memories. The transport and structural characterizations are supported by DFT and KMC simulations for the resistive switching materials.
[1] Messerschmitt et al., AFM, 2014, 24, 47, 7448
[2] Kubicek et al., ACS Nano, 2015, online
[3] Shi et al., Nat Mat, 2015, 14, 721
[4] Schweiger et al., ACS Nano, 2014, 8 ,5, 5032
5:15 PM - MD2.2.03
Theoretical Study of the Insulator-to-Metal Transition in LaMnO3
Jose Rivero 1,Vincent Meunier 2,William Shelton 1
1 Louisiana State University Baton Rouge United States,2 Rensselaer Polytechnic Institute Troy United States
Show AbstractWe have developed a theoretical approach for investigating systems that contain a range of correlation that varies with experimentally controlled parameters. We applied this method to the LaMnO3 system [1,2,3] to accurately describe the antiferromagnetic (AFM) insulating ground-state, the metal-to-insulator transition and the high temperature ferromagnetic (FM) state, where we observe a half-metallic behavior. Moreover, we performed uniaxial compressive strain simulations where we estimate a significant reduction in the pressure [4] needed to drive the system from the low temperature AFM state to the FM metallic state.
[1]: T. Saitoh, A. E. Bocquet, T. Mizokawa, H. Namatame, A. Fujimori, M. Abbate, Y. Takeda, and M. Takano, Phys. Rev. B, 51, 13942 (1995).
[2]: J. S. Zhou, and J. B. Goodenough, Phys. Rev. B, 60, R15002 (1999).
[3]: J. Rodriguez-Carvajal, M. Hennion, F. Moussa, A. H. Mouden, L. Pinsard, and A. Revcolevschi, Phys. Rev. B, 57, R3189 (1998).
[4]: M. Baldini, V. V. Struzhkin, A. F. Goncharov, P. Postorino, and W. L. Mao, Phys. Rev. Lett. 106, 066402 (2011).
5:30 PM - *MD2.2.04
Elastic Strain Engineering of Thermal and Charge Transport in Semiconductor Nanostructures: The Role of Heterogeneity
Kathryn Murphy 1,Arthur Tsoi 1,Brian Piccione 1,Jason Woo 1,Daniel Gianola 2
1 Univ of Pennsylvania Philadelphia United States,1 Univ of Pennsylvania Philadelphia United States,2 Materials Department University of California Santa Barbara 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 heterogeneity on thermal and charge transport will be addressed by way of two examples on Si nanostructures. First, we report experimental measurements on the effect of tensile strain on thermal conductivity of an individual suspended Si nanowire using in situ Raman piezothermography. Our results show that, whereas phononic transport in undoped Si nanowires is only marginally affected by uniform elastic tensile strain, point defects introduced via ion bombardment that disrupt the pristine lattice reduces the thermal conductivity by over 70%. The second example furthers the study of inhomogeneous strains by showing 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.
Symposium Organizers
Bilge Yildiz, Massachusetts Institute of Technology
Paul Evans, University of Wisconsin-Madison
Tobias Schulli, ESRF - The European Synchrotron
Ting Zhu, Georgia Institute of Technology
MD2.3: Strained Ferroelectric/Piezoelectric Electronic Materials
Session Chairs
Long-Qing Chen
Beatriz Noheda
Wednesday AM, March 30, 2016
PCC West, 100 Level, Room 101 B
9:30 AM - *MD2.3.01
Manipulating Domain Structures in Nanoscale Thin Films and Heterostructures via Strain Engineering
Long-Qing Chen 1
1 The Pennsylvania State University University Park United States,
Show AbstractIt has now been well established that strain can be employed as an additional thermodynamic parameter to tune and control the phase stability and properties of nanostructures such as epitaxial thin films and heterostructures. This presentation will discuss the strain contribution to the thermodynamics of crystals and strain coupling to other order parameters such as ferroelectric polarization, magnetization, and oxygen octahedral tilt. The focus will be on how one can use strain to manipulate not only the transition temperatures but also the domain structures and their ferroic responses in thin films or heterostructures via either homogeneous strains or inhomogeneous local strains or both. While the shifts in the thermodynamic instability temperatures and the nature of phase transitions can generally be predicted from purely classical thermodynamic analyses of single domain states, predicting the strain effect on the spatial distributions of domains, i.e. domain structures, requires the application of the phase-field method. It is shown that a strain can be employed to manipulate and control the phase transition temperatures, the relative phase stability of different polarization states, volume fractions of differently orientated domains, the domain-wall orientations, and domain wall motion directions. Strain may also lead the elimination of phase transitions and the emergence of new phases that otherwise do not exist in the corresponding bulk.
10:00 AM - MD2.3.02
Novel Functionalities in Strain-Gradient Engineered Labile Ferroelastic Domain Walls
Joshua Agar 1,Anoop Rama Damodaran 1,Joshua Kacher 1,Christoph Gammer 1,Rama Vasudevan 2,Shishir Pandya 1,Vengadesh Kumara Ramakrishnan Mangalam 1,Stephen Jesse 2,Nina Balke 2,Andrew Minor 1,Sergei Kalinin 2,Lane Martin 1
1 University of California Berkeley Berkeley United States,2 Oak Ridge National Lab Center For Nanophase Materials Oak Ridge United States
Show AbstractRecently, it has been shown that compositionally-graded epitaxial ferroelectric thin films can be designed to achieve large residual strains and strain gradients inconceivable in compositionally-homogenous versions. This new modality of strain engineering provides an effectual route to stabilize crystal and domain structures without regard for the equilibrium chemical phase. More recently, we have shown that these compositionally-graded heterostructures, with large strain gradients, have large built-in potentials which significantly reduce the dielectric permittivity and, in turn, enhance pyroelectric figures of merit. At first glance, it might be expected that the observed built-in potentials are primarily the result of the macroscopic strain gradient and resulting flexoelectric fields; however, in our recent work we have found that the built-in potential does not follow trends based on the strain gradient alone and, instead, is maximized in those films designed to have ferroelastic domains. Here, we explore the nanoscale structure and response of 100 nm thick, compositionally-graded PbZr1-xTixO3 heterostructures with large built-in potentials (~200 kV/cm) which exhibit ferroelastic c/a/c/a-like domain structures. We have used a combination of transmission electron microscopy-based nanobeam diffraction (NBED) strain mapping, and nano-scale band-excitation piezoresponse force microscopy switching spectroscopy to explore the nanoscale structure and response of these ferroelastic domains. We observe that the strain gradients in compositionally-graded PbZr1-xTixO3 heterostructures can drive the formation of needle-like ferroelastic domains which terminate inside the film (as compared to parallelepiped-like domains which form under homogenous strain). Local nanoscale piezoelectric probes indicate that these needle-like domains are highly-labile in the out-of-plane direction under applied electric fields and produce locally enhanced piezoresponse. Using the structural and switching spectroscopy analysis we derive a switching mechanism including consideration of the elastic and electrostatic energies which explains the contribution of strain-gradient engineered ferroelastic domains to the built-in potential. This work demonstrates the efficacy of composition and strain gradients in providing new modalities of domain engineering, in influencing the properties of materials and the response of domain walls in new ways, and in allowing for the engineering of materials with new combinations of electrical susceptibilities and potentially new modes of domain wall response which could be desirable for the booming field of domain wall nanoelectronics.
10:15 AM - MD2.3.03
Ferroelectric 180o Domain Wall Motion Controlled by Reversible Elastic Strain
Erjia Guo 2,Robert Roth 1,Andreas Herklotz 2,Dietrich Hesse 3,Kathrin Doerr 2
1 Martin-Luther-University Halle-Wittenberg Halle(Saale) Germany,2 IFW-Dresden Dresden Germany,1 Martin-Luther-University Halle-Wittenberg Halle(Saale) Germany3 Max-Plank-Institute of Microstructure Physics Halle(Saale) Germany
Show AbstractFerroelectric ordering in complex oxide films can be very sensitive to elastic strain. [1] This has been exploited in many strain-coupled ferroelectric thin-films, including BiFeO3, Pb(Zr1-xTix)O3(PZT), BaTiO3, and etc. Strong strain dependences of switching time and coercivity of ferroelectric capacitors had been found earlier by applying in-situ reversible controlled strain through a piezoelectric substrate [2, 3]. However, fundamentally understood and modeled strain determined processes in the microscopic view of domain wall motion is rather few cases, hindered the identification of underlying physical mechanism.
In this talk, we introduce a c-oriented epitaxial tetragonal PbZr0.2Ti0.8O3 film grown on 0.72Pb(Mg2/3Nb1/3)O3-0.28PbTiO3 substrates as a model system. The domain dynamics under different strain states are studied using a piezoresponse force microscopy (PFM). The velocity of non-ferroelastic 1800 domain walls in the PZT film can be reversibly changed by more than one order of magnitude through simply modulating the strain of the order of ~0.1%, as shown in the Figure 1a. [4] We attribute one part of the strain induced the velocity change to the strain-dependent built-in potentials at the electrode interfaces. The remaining part depends on the polarity of electric fields. We suggest the strain-controlled depolarizing charges on tilted domain walls to cause a polarity-dependent strain effect on the 1800 domain wall velocity [Fig. 1b]. The in-situ strain acts as a tool for “charge up” titled domain walls, based on the well-known strain dependence of polarization and the yet less understood presence of domain wall tilts. Even profound effects could be predicted in other ferroelectric oxides, like BiFeO3 or BaTiO3, due to the larger strain-dependence of polarization. Our results may help to understand the origins of resistance of wall motion and exploit them for tailoring wall mobility as well as its electronic functionalities [5, 6].
References
[1] M. Biegalski et al. Appl. Phys. Lett. 98, 142902 (2011).
[2] E. J. Guo et al. Appl. Phys. Lett. 101, 242908 (2012).
[3] A. Herklotz et al. New J. Phys. 15, 073021 (2013).
[4] E. J. Guo et al. Advanced Materials, 27, 1615 (2015).
[5] E. J. Guo et al. Appl. Phys. Lett. 105, 012903 (2014).
[6] E. J. Guo et al. Appl. Phys. Lett. 106, 072904 (2015).
10:30 AM - MD2.3.04
Flexoelectric Coupling with Ferroelectric Twin Walls in Pb(Zr0.2Ti0.8)O3 Thin Film
Ye Cao 4,Anna Morozovska 2,Long-Qing Chen 1,Sergei Kalinin 4
3 Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak Ridge United States,4 Institute for Functional Imaging of Materials Oak Ridge National Laboratory Oak Ridge United States,2 Institute of Physics National Academy of Science of Ukraine, 46, pr. Nauki Kiev Ukraine1 Department of Materials Science and Engineering The Pennsylvania State University University Park United States
Show AbstractFlexoelectricity, a long time neglected property that describes the polarization in solids caused by the inhomogeneous deformation or the strain gradient, arouses recent interest and extensive studies due to the development of nanoscale technology. On the other hand, defects such as ferroelectric domain walls are commonly found in ferroelectric oxides and play crucial roles to the fundamental properties of ferroelectric perovskites. While extensive studies have been made on the defect manipulation through electrical excitation, their couplings with flexoelectricity has been less understood. In this work we investigated the effect of flexoelectric coupling on the ferroelectric a/c twin structure, a most classic ferroelectric defect which nonetheless shows very dissimilar regions in lead ziconate titanate (Pb(Zr0.2Ti0.8)O3) thin film using phase-field simulations. We found that the strain gradient across the twin walls induces both in-plane and out-of-plane flexoelectric fields, resulting in polarization inclinations away from their normal horizontal and vertical positions in both a and c domains. This behavior is enhanced at the bottom layer of the film where the local strain gradient reaches maximum. The flexoelectric effect on twin areas, wall tilt angles and polarization rotation profiles across the twin walls at top, center and bottom layers of the film have been further analyzed. Our work could possibly answer some critical questions such as what are the critical flexocoupling strengths above which polarization rotations, twin wall tilts are experimentally observable, and further provides insight into the possible twin wall engineering via intrinsic flexoelectricity.
This research was sponsored by the Division of Materials Sciences and Engineering, Basic Energy Sciences, Department of Energy (YC, SVK). Research was conducted at the Center for Nanophase Materials Sciences, which also provided support and which is a DOE Office of Science User Facility. The phase-field simulation was performed in collaboration with Prof. Long-Qing Chen at Penn State, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-FG02-07ER46417(Chen).
11:15 AM - *MD2.3.05
Strain-Relief Engineering in Ferroelectric Oxides
Beatriz Noheda 1
1 Univ of Groningen Groningen Netherlands,
Show AbstractIt is about one decade ago when strain engineering started to become something more than an attractive concept. Today one can say that strain engineering in epitaxial thin films has reached a large degree of maturity. In the particular case of perovskite-like complex oxides, this amazing progress has definitely originated from the synergy between theory and experiment, as the extraordinary predictive power of first-principles and phenomenological (Pertsev-like) models, as well as the advances in thin film deposition techniques, have stimulated the highly focused and efficient search of novel phases and enhanced properties.
An interesting side effect of the problem is the opportunity to access and control the mechanisms that facilitate the release of the strain for a sufficiently thick film or a large enough lattice mismatch. In the case of ferroic oxides, this mechanism is typically the formation of ferroelastic domains. Here I will present our most recent work on the understanding and control of different domain structures in perovskite-like ferroelectric thin films by using epitaxial growth (by pulsed laser deposition). I will also discuss the ways in which these different domain structures can be used to enhance the materials response, that is the ferroelectric or piezoelectric behaviour.
11:45 AM - MD2.3.06
Interaction of Dislocation with Ferroelectric Domain Structure and Switching in Pb(Zr0.2Ti0.8)O3 Thin Film
Ye Cao 2,Long-Qing Chen 3,Sergei Kalinin 2,Petro Maksymovych 2
1 Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak Ridge United States,2 Institute for Functional Imaging of Materials Oak Ridge National Laboratory Oak Ridge United States,3 Department of Materials Science and Engineering The Pennsylvania State University University Park United States
Show AbstractDefects, such as space charge carriers and dislocations are commonly seen in ferroelectric thin films and could strongly affect the domain wall mobility and the ferroelectric switching behavior. Previous studies have been focused on the 90° domain wall pinning and switching by msifit dislocation through Transmission Electron Microscopy (TEM) characterization [1,2] and theoretical analysis [3,4], nevertheless detailed analysis of the dislocation couplings with ferroelectric domain wall and structures is still lacking. In this work, we studied both 90° and 180° domain switching mechanism by incorporating the dislocation model treated as additional contribution to the spontaneous strain in the context of phase-field model. By studying the local stress, field and polarization charge around the dislocation and along the domain walls, we found that pinning dislocations could create and stabilize the partial (100)a domain in the context of (001) oriented c domain in Pb(Zr0.2Ti0.8)O3 thin film, thus affecting the ferroelastic switching behavior. Dislocations are also found to strongly interact with the 180° domain walls during switching. The effects of dislocation magnitude, Burgers vector and dislocation line directions on the domain pinning behavior have also been investigated. Our work could provide further understanding to the domain structure and switching dynamics in the presence of structural defects in ferroelectric oxides.
This research was sponsored by the Division of Materials Sciences and Engineering, Basic Energy Sciences, Department of Energy (YC, SVK, PM). Research was conducted at the Center for Nanophase Materials Sciences, which also provided support and which is a DOE Office of Science User Facility. The phase-field simulation was performed in collaboration with Prof. Long-Qing Chen at Penn State, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-FG02-07ER46417(Chen).
[1] D. Su et. al., “Origin of 90° domain wall pinning in Pb(Zr0.2Ti0.8)O3 heteroepitaxial thin films”, Applied Physics Letters, 99, 102902 (2011)
[2] P. Gao et. al., “Ferroelastic domain switching dynamics under electrical and mechanical excitations”, Nature Communication, 5, 3801, (2014)
[3] A. Kontsos et. al., “Computational modeling of domain wall interactions with dislocations in ferroelectric crystals”, International Journal of Solids and Structures, 46, 6, (2009)
[4] J. Britson et. al., “First-order morphological transition of ferroelastic domains in ferroelectric thin films”, Acta Materialia, 75, 188, (2014)
12:00 PM - MD2.3.07
First-Principles High-Throughput Screening of Epitaxially Stabilized Ferroelectric Films
Thomas Angsten 1,Mark Asta 1
1 Materials Science and Engineering University of California - Berkeley Berkeley United States,
Show AbstractAdvances in thin-film deposition techniques have opened up the possibility of growing a wide variety of coherent oxide films with varying degrees of epitaxial strain. These films exist under mixed mechanical boundary conditions of fixed biaxial in-plane strain and relaxed out-of-plane stresses. Choice of the substrate allows for control of the in-plane strain and enables the exploration of epitaxially stabilized ferroelectric phases with properties differing and possibly superior to those of the bulk. Because both composition and strain are tunable parameters, this materials design challenge involves exploring a vast space of possibilities. This work demonstrates the use of high-throughput first-principles methods to screen for epitaxially stabilized phases with desirable ferroelectric properties. We build upon the King-Smith Vanderbilt model [Phys. Rev. B, 49, 5828 (1994)] by expanding energy to fourth order with respect to atomic displacements and the six homogeneous strain components. The resulting analytic energy functions can be minimized under arbitrary mechanical constraints in order to determine the stable phase under various epitaxial strain conditions. This model is first applied to perovskite structured oxides due to their diverse range of ferroelectric phase transitions, and the existence of a high-symmetry cubic phase nearby to these transitions that serves as the reference state for the energy expansions. Ferroelectric properties of perovskite films with epitaxial strains on (100), (110), and (111) surfaces are considered within the range of +/-4% biaxial misfit strain. Polarizations of the resulting stabilized phases are calculated and used as a screening parameter in the search for materials with interesting ferroelectric properties.
This work was intellectually led by the Materials Project Center, supported by the BES DOE Grant No. EDCBEE, and supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400.
12:15 PM - MD2.3.08
Modulation of Metal-Insulator Transitions by Electric-Field-Controlled Strain in NdNiO3/SrTiO3/PMN-PT (001) Heterostructures
Seungyang Heo 1,Chadol Oh 2,Man Jin Eom 3,Jun Sung Kim 3,Jungho Ryu 4,Junwoo Son 2,Hyun Myung Jang 3
1 Division of Advanced Materials Science (AMS) Pohang University of Science and Technology (POSTECH) Pohang Korea (the Republic of),2 Department of Materials Science and Engineering (MSE) Pohang University of Science and Technology (POSTECH) Pohang Korea (the Republic of)3 Department of Physics Pohang University of Science and Technology (POSTECH) Pohang Korea (the Republic of)4 Functional Ceramics Group Korea Institute of Materials Science (KIMS) Changwon Korea (the Republic of)1 Division of Advanced Materials Science (AMS) Pohang University of Science and Technology (POSTECH) Pohang Korea (the Republic of),2 Department of Materials Science and Engineering (MSE) Pohang University of Science and Technology (POSTECH) Pohang Korea (the Republic of),3 Department of Physics Pohang University of Science and Technology (POSTECH) Pohang Korea (the Republic of)
Show AbstractThe band width control through external stress has been demonstrated as a useful knob to modulate metal-insulator transition (MIT) in RNiO3 as a prototype correlated materials. In particular, lattice mismatch strain using different substrates have been widely utilized to investigate the effect of strain on transition temperature so far but the results were inconsistent in the previous literatures. Here, we demonstrate dynamic modulation of MIT based on electric field-controlled pure strain in high-quality NdNiO3 (NNO) thin films utilizing converse-piezoelectric effect of (001)-cut-(PMN-PT) single crystal substrates. Despite the difficulty in the NNO growth on rough PMN-PT substrates, the structural quality of NNO thin films has been significantly improved by inserting SrTiO3 (STO) buffer layers. Interestingly, the MIT temperature in NNO is downward shifted by ~ 3.3 K in response of 0.25 % in-plane compressive strain, which indicates less effective TMI modulation of field-induced strain than substrate-induced strain. To elucidate the effectiveness of strain transfer to the NNO thin films by the field-induced strain more clearly, we carried out in-situ reciprocal space mapping (RSM) around the (-103) Bragg reflections of NNO (25 nm)/STO (10 nm)/PMN-PT heterostructure before and after the application of in-situ electric field of + 10 kV/cm along [001] direction. This study provides not only scientific insights on band-width control of correlated materials using pure strain but also potentials for energy-efficient electronic devices.
MD2.4: Strain in Ion-Transporting Materials
Session Chairs
Nicole Benedek
Roland Kroeger
Wednesday PM, March 30, 2016
PCC West, 100 Level, Room 101 B
2:30 PM - *MD2.4.01
Ionic Transport in Complex Oxides: Understanding the Interplay between Lattice Distortions, Electronic Structure, and Epitaxial Strain
Nicole Benedek 1
1 Cornell University Ithaca United States,
Show AbstractComplex oxides are one of the largest and most technologically important materials families. The ABO3 perovskite oxides in particular display myriad fascinating physical properties. The origin of these properties (how they arise from the structure of the material) is often complicated, but in many systems previous research has identified simple guidelines or ‘rules of thumb’ that link structure and chemistry to the property of interest. For example, the tolerance factor is a simple empirical measure that relates the composition of a perovskite to its tendency to adopt a distorted structure. First-principles calculations have shown that the tendency towards ferroelectricity increases systematically as the tolerance factor of the perovskite decreases. Can we uncover a similar set of simple guidelines to yield new insights into the ionic transport properties of perovskites? I will discuss recent research from my group on the link between crystal structure and chemistry, soft lattice modes and ionic transport and chemical expansion in a family of layered perovskite oxides, the Ln2NiO4+δ Ruddlesden-Popper phases. I will show that particular structural distortion modes play a key role in the ionic transport mechanism in this family of materials and demonstrate how changes in mode softness due to crystal chemistry and epitaxial strain may be harnessed to design materials with low barriers to oxide ion migration. I will also discuss how the electronic structure of the Ni atom influences migration mechanisms and chemical expansion in this family of materials. Our work shows that although ionic transport is a complex physical process (many factors may influence activation energies and diffusion coefficients) it may be possible to correlate trends in transport properties with simple structural and crystal chemical descriptors.
3:00 PM - MD2.4.02
Influence of Dislocations on Ionic Conductivity and Surface Reactivity in Reduced and Doped Ceria
Lixin Sun 1,Bilge Yildiz 2
1 Department of Nuclear Science and Engineering Massachusetts Institute of Technology Cambridge United States,1 Department of Nuclear Science and Engineering Massachusetts Institute of Technology Cambridge United States,2 Department of Material Science and Engineering Massachusetts Institute of Technology Cambridge United States
Show AbstractStrain engineering is a new route to improve the performance of oxide materials for highly efficient catalysts and high-performance electrodes for clean energy conversion and storage devices. High density of dislocations can be found in these strained oxide nanostructures upon elastic strain relaxation, for example, in the form of misfit dislocations and threading dislocations in oxide thin films. Dislocations in red-ox active metal oxides change the local chemical and electronic properties, however, only scarcely studied. Thorough and quantitative investigation of dislocations in such oxides is needed to be able to optimize their properties for catalysis and electro-catalysis applications.
Easily reducible metal oxides have orders of magnitude higher defect concentrations compared to nominally stoichiometric oxides such as Al2O3 or MgO. The defect concentration varies around the dislocation by the local strain field and because of the charge-trapping at dislocations. Our previous atomistic simulation of an ½<110>{100} edge dislocation in 4-12% reduced and doped CeO2 (doped with Gd, Y and Sc) shows that larger dopants enrich at the tensile strain field and deplete at the compressive strain field due to elastic energy minimization; while the oxygen vacancies follow the same redistribution profile as the dopants due to the electro-static interaction. Since the bulk defect concentration has been optimized to achieve a high ionic conductivity, the defect concentration in both of the enrichment and depletion zones around the dislocation deviates from this optimal level. The associative interactions among the point defects in the enrichment zone and the lack of oxygen vacancies in the depletion zone slow down oxide ion transport. Contrary to the fast diffusion of atoms along the dislocations, well-known in Al2O3 and in metals, slow oxide ion diffusion is found along the edge dislocation in ceria, as a result of segregation of charged defects. On the other hand, this understanding motivates our new work in in modulating these defects at the dislocation by selective and local doping.
3:15 PM - *MD2.4.03
Strain Effects on Oxygen Defect Chemistry and Diffusion in Perovskites
Dane Morgan 1,Tam Mayeshiba 1
1 Univ of Wisconsin-Madison Madison United States,
Show AbstractOxygen active materials are capable of rapidly exchanging oxygen with their bulk and have a wide range of applications, including solid oxide fuel cells, gas separation membranes, oxygen sensors, chemical looping devices, and memristors. Recent work has shown that epitaxial strain can play a significant role in altering the transport of oxygen through oxygen active materials, particularly in fluorite structured compounds. However, transition metal perovskites are an important class of oxygen active materials that have received only limited attention. In this work we use ab initio methods to model the coupling of epitaxial strain and defect formation and migration energetics in a range of transition metal perovskites. We predict the formation volume and strain response of oxygen vacancy formation energy, demonstrating that non-linear coupling of strain and vacancy formation can yield responses qualitatively different than those expected from simple elasticity arguments. We also predict the migration volume and the strain response of oxygen migration energetics, again demonstrating that it can differ significantly than what is predicted by simple elastic strain models.[1] In general we find that the oxygen transport kinetics can be altered by orders of magnitude in perovskites through strain effects on both vacancy content and migration energetics. These effects could play a significant role on materials performance at interfaces and in thin-film devices.
[1] T. Mayeshiba and D. Morgan, Strain Effects on Oxygen Migration in Perovskites, Phys. Chem. Chem. Phys. 17, p. 2715-2721 (2015 ).
3:45 PM - MD2.4.04
Colossal Enhancement of Oxygen Electrocatalysis in La1-xSrxCoO3-δ Thin Films by Epitaxial Strain
Dongkyu Lee 1,Youngseok Jee 2,Sung Seok Seo 3,Jong Keum 4,Ho Nyung Lee 1
1 Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge United States,2 Department of Mechanical Engineering University of South Carolina Columbia United States3 Department of Physics and Astronomy University of Kentucky Lexington United States4 Center for Nanophase Materials Science Oak Ridge National Laboratory Oak Ridge United States
Show AbstractImproving the slow kinetics of oxygen reduction reaction (ORR) in perovskite oxides is one of the grand challenges for developing intermediate temperature solid oxide fuel cells (SOFCs). Mixed ionic and electronic conductors (MIECs) such as La1-xSrxCoO3-δ (LSC113) have been widely studied to enhance the ORR kinetics. Recent efforts have showed the influence of lattice strain on the oxygen surface exchange kinetics using lattice mismatch between the film and substrate. Controlling the film thickness is one of the simplest ways to modulate the lattice strain. However, strain manipulation by thickness control and related ORR kinetics as well as the structure-property relationship have not been much studied due to both the limited availability of phase pure, high quality epitaxial thin films and the limited measurement technique for thin film samples. Here we report the influence of the film thickness on the surface exchange kinetics of epitaxial La0.6Sr0.4CoO3-δ (LSC) thin films grown on (001)- yttria stabilized zirconia (YSZ). Interestingly, we found that the surface exchange coefficient (kq) values of ~ 10 nm LSC thin film with only ~0.5 % in-plane tensile strain could be dramatically enhanced up to two orders of magnitude compared to fully relaxed thicker films (~50, 80, and 100 nm). We also found that thinner films have distinct eg to eg* electron transitions at 550 OC relative to thicker films via in-situ optical ellipsometry. This result suggests that enormous electron transition induced by thickness-dependent strain can be attributed to the significant change in the surface exchange kinetics of LSC. Thus, our work illustrates that controlling thickness is a new strategy to design highly active oxide materials for applications of complex oxides in the solid-state electrochemistry.
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Science and Engineering Division (synthesis and physical property characterization) and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (electrochemical characterization). A part of work for XRD characterization was performed as a user project at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, BES, U.S. DOE.
4:15 PM - *MD2.4.05
The Force of Mechanochemistry
Roman Boulatov 1
1 University of Liverpool Liverpool United Kingdom,
Show AbstractThe talk will describe the group's effort to develop a conceptual framework for understanding polymer mechanochemistry at the molecular level by intergrating molecular design and synthesis, quantum-chemical computations and theory.
Mechanochemical phenomena are all around us. They affect the generation, growth and propagation of microcracks that are responsible for catastrophic failure of polymeric materials, behavior of impact-resistant materials (e.g., bulletproof vests) and tires, stabilities of surface-anchored polymers in microfluidic diagnostics and high-performance chromatography. Polymer mechanochemistry may be important in jet injection, polymer melt processing, high-performance lubrication, enhanced oil recovery and turbulent drag reduction. Exploiting mechanochemical phenomena may yield remarkable new materials and processes, including polymer photoactuation, efficient capture of waste mechanical energy, materials capable of autonomous reporting of internal stresses and self-healing, and tools to study polymer dynamics at sub-nm scales.
The recent remarkable advances in empirical polymer mechanochemistry, evidenced by the prolifiration of designer polymer that undergo specific chemistry when loaded made the need for a conceptual framework within which to rationalize and systematize such observations and to develop systematic approaches to identifying new mechanochemical phenomena without extensive trial-and-error effort. I'll describe the conceptual framework we have developed and will illustrate its capabilities by demonstrating successful (a) quantiative predictions of mechanochemical behavior of isolated polymer chains from the force-dependent reactivity of a single monomer and (b) mapping of force distribution along a single polymer chain in elongational flow using specially designed small-molecule force "gauges".
4:45 PM - *MD2.4.06
Strain-Gradient versus Grain-Boundary Driven Reactivity of Nanoparticles
Roland Kroeger 1,Leonardo Lari 1,Andrew Pratt 1,Chris Binns 2
1 University of York York United Kingdom,2 University of Leicester Leicester United Kingdom
Show AbstractThe pathways by which nanoparticles (NPs) react with the environment are of key interest for the development and understanding of a large variety of applications spanning nanomagnetics, biomedicine and environmental technologies. Our focus lies on the study of the reactivity of iron NPs produced by cluster source deposition to shed light on the mechanism of oxidation of iron NPs of different geometries. Cluster source deposition is an ideal technique to realise well-defined and clean single element and core-shell NPs that can be readily analysed by aberration-corrected scanning transmission electron microscopy (AC-STEM) with sub-Ångstrom spatial resolution. Recently, using atomic-level strain-state analysis by applying AC-STEM, we have found that strain-gradients in the oxide shell of cuboid iron NPs play a decisive role in the oxide growth rate and morphology development [1]. This analysis shows that the nanoscale geometry of the oxide shell introduces significant strain of up to 15% caused by the formation of grain boundaries between the oxide shell segments. Since on the nanoscale the formation of extended defects becomes unfavourable the lattice expansion due to the oxidation leads to the observed significant strain values. The gradual change of strain from the metal/oxide interface to the particle surface provides a pathway for a preferred oxidation perpendicular to the {001} facets of the cuboids resulting in the "cushion" shaped progression of the oxidation as a function of time. We have further studied the effect of a blocking of the oxidation pathway through the lattice by coating the NPs with a thin layer of silver. This led to the increased out-diffusion of Fe through the oxide grain boundaries resulting in the formation of voids at the core corners and "antennae" of iron oxide protruding out of the corners of the NPs. These findings emphasize the importance of strain management on the nanoscale to control the NP morphology. We also analysed NPs of different geometries (truncated octahedrons, spheres) with increasing number densities of grain boundaries and found a clear correlation between grain boundary density and oxide shell thickness. This highlights the competing character of oxide formation related strain and grain boundaries for the ionic transport affecting the resulting particle properties.
[1] A. Pratt, L. Lari, O. Hovorka, A. Shah, C. Woffinden, Steve T., C. Binns, and R. Kroeger, Nature Materials 13, 26 (2014).
5:15 PM - MD2.4.07
Tailoring the Proton-Phonon Coupling in Ceramic Electrolytes by Strain Engineering
Artur Braun 1
1 EMPA Duebendorf Switzerland,
Show AbstractCeramic fuels have the benefit of using low coast natural gas as fuels. But they operate at very high temperatures - up to 800°C. This is because the oxygen (vacancy) ion transport as charge carriers has to be thermally activated. Protons as chage carriers promise around half that temperature necessary for operation - which is true. But the proton conductivity is much lower. Hence, fuel cell enginners are waiting for more progress in materials research.
Meanwhile, by coincidence - we noticed the proton conductivity thermal activation energy scales with the lattice constant of the proton conductor. We made thus a systematic study with external compressive strain on perovskite structure ceramic electrolytes and could verify that the proton transport in the lattice is virtually phonon assisted. I will show a full range of structural studies and experiments where we have investigated the charge transfer properties of the proton conductr under strain, with very exciting outcome. We know now exactly what is going on in these proton conductors in term of chemistry, physics, and ultimate function.
In the end it turns out that epitaxial strained proton conductor films may be promising future low temperature electrolytes, at least for the miniature fuel cell projects.
5:30 PM - MD2.4.08
Strain-Induced Control of Nano-Structuring and Fast Oxide Ion Transport in Thin SrCrO3–δ Films
Peter Sushko 1,Phuong Vu Ong 1,Yingge Du 1,Hongliang Zhang 2,Mark Bowden 1,Scott Chambers 1
1 Pacific Northwest National Lab Richland United States,1 Pacific Northwest National Lab Richland United States,2 University of Cambridge Cambridge United Kingdom
Show AbstractOxygen vacancies in complex oxides can be present as isolated point defects or aggregate into ordered quasi-one-dimensional (1D) channels and quasi-two-dimensional (2D) planes, depending on the host lattice structure and chemical composition and on the vacancy concentration. Exploiting oxygen deficiency in order to generate novel structures and functional properties in a controlled way remains a challenging goal. We show that epitaxial strontium chromite films can be transformed, reversibly and at low temperature, from cubic, metallic perovskite SrCrO3–δ (SCO) to rhombohedral, semiconducting SrCrO2.8. As the oxygen vacancy concentration increases in SrCrO3–δ, the vacancies start to interact. At δ=0.2, the vacancies aggregate into ordered arrays, thus transforming {111}-oriented SrO3 planes into SrO2 planes interleaved between tetrahedrally-coordinated Cr planes and separated by ~1 nm. Accordingly, the bad-metal electronic structure of SrCrO3–δ transforms to that of a degenerate semiconductor (SrCrO2.8). Ab initio simulations provide insight into the origin of the thermodynamic stability of such quasi-2D nanostructures and, consistent with the experimental data, predict that the barrier for O2– diffusion along these nanostructures is approximately four times lower than that in the cubic SrCrO3–δ. The thermodynamic stability of these 2D oxygen vacancy arrays varies with the magnitude of the substrate-induced strain, which provides a pathway to control the conditions, e.g., temperature and external oxygen pressure, needed to switch between the rhombohedral semiconducting SrCrO2.8 and cubic metallic SrCrO3–δ phases and, accordingly, between fast and slow oxygen transport mechanisms.
5:45 PM - MD2.4.09
Growth and Properties of Strain-Tuned SrCoOx (2.5≤x
Songbai Hu 1,Sara Callori 4,Zengji Yue 2,Ji Soo Lim 3,Joel Bertinshaw 4,Atsushi Ikeda-Ohno 4,Takuo Ohkochi 5,Xiaolin Wang 2,Clemens Ulrich 4,Chan-Ho Yang 6,Frank Klose 4,Jan Seidel 1
1 UNSW Australia Sydney Australia,1 UNSW Australia Sydney Australia,4 Australian Nuclear Science and Technology Organisation Sydney Australia2 Spintronic and Electronic Materials Group, Institute for Superconducting and Electronic Materials University of Wollongong Wollongong Australia3 Department of Physics KAIST Daejeon 305-701 Korea (the Republic of)5 Japan Synchrotron Radiation Research Institute Spring-8 Sayo, Hyogo 679-5198 Japan3 Department of Physics KAIST Daejeon 305-701 Korea (the Republic of),6 Institute for the NanoCentury KAIST , Daejeon 305-701 Korea (the Republic of)4 Australian Nuclear Science and Technology Organisation Sydney Australia
Show AbstractControlling material properties by strain is one of the main concepts of thin film growth technology. [i] By altering the order parameter in ferroic materials with which the lattice is coupled, new properties can be achieved, e.g. in perovskite SrCoOx which was identified as a parent phase of strong spin-phonon coupling materials.[ii] Here, we present results on a strain-induced antiferromagnetic-ferromagnetic phase transition in high quality epitaxial SrCoOx (2.5≤x
MD2.5: Poster Session: Tuning Properties by Elastic Strain Engineering—From Modeling to Making and Measuring
Session Chairs
Thursday AM, March 31, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - MD2.5.01
Novel Method to Fabricated Ti-Al Intermetallic Compounds by the Infiltration of Al into Porous Titanium
Sumin Kim 2,Wonyoung Jeung 2,Gyeungho Kim 2,Wooyoung Lee 1
1 Department of Materials Science and Engineering Yonsei University Seoul Korea (the Republic of),2 Korea Institute of Science and Technology Seoul Korea (the Republic of),2 Korea Institute of Science and Technology Seoul Korea (the Republic of)1 Department of Materials Science and Engineering Yonsei University Seoul Korea (the Republic of)
Show AbstractTi-Al intermetallic compounds are promising candidates for high temperature structural materials for automotive, aerospace and power generation industries because of their high specific strength and stiffness, good oxidation resistance, high melting temperature and low density(3.8 ~ 4.2 g/cm3) which is about over 50% lighter than nickel based counterparts. In addition, they are expected as biomaterials for medical implant such as femur or teeth. However, low ductility of Ti-Al intermetallic compounds at room temperature makes it difficult to make intricate parts or components by machining or cutting processing.[1] So far, many attempts and significant progress has been made ranging from the development of Ti-Al alloys with multilayered structures to the processing techniques for bulk intermetallic compounds such as casting and hot forming processes.[2-6] Nevertheless, improvement of their room temperature plasticity and forming to complex shapes are still remained as formidable technological challenges. In this work, we have fabricated Ti-Al intermetallic compounds by infiltrating molten Al into porous titanium for the first time. Porous titanium was prepared by powder injection molding and subsequently binder was removed and sintered to desired shape. Infiltration of molten Al was done at 730°C for 30 s to 120s duration times. Post heat treatment was employed for the reactive formation of TiAl at range of temperatures (700~1000°C) and time schedules (30 ~ 600 min). After heat treatment, tensile test was performed for each sample. Identification of constituent phases and their distribution was characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) respectively. By adjusting the processing variables for infiltration and post heat treatment, we can produce Ti-Al intermetallic compounds having optimized mechanical properties satisfying the specific demand in different industrial applications.
References
[1] Y.W Kim. Strength and ductility in TiAl alloys. Intermetallics. 6 (1988) 623-628.
[2] SUN Yan-bo, et al. Multilayered Ti-Al intermetallic sheets fabricated by cold rolling and annealing of titanium and aluminum foils. Transactions of Nonferrous Metals Society of China. 21 (2011) 1722-1727.
[3] SUN Yan-bo, et al. Fabrication of multilayered Ti-Al intermetallics by spark plasma sintering. Journla of Alloy and Compounds. 585 (2014) 734-740.
[4] Yang Liu, et al. Novel method to fabricate Ti-Al intermetallic compound coatings on Ti-6Al-4V alloy by combined ultrasonic impact treatment and electro-spark deposition. Journal of Alloy and Compounds. 628 (2015) 208-212
[5] LIU C T, et al. Microstructural control and mechanical properties of dual-phase TiAl alloys. Intermetallics. 6 (1998) 653-661
[6] Huang Z H. Workability and microstructural evolution of Ti-47Al-2Cr-1Nb alloy during isothermal deformation. Intermetallics. 13 (2005) 245-250
9:00 PM - MD2.5.03
Strain State of TbMnO3 Epitaxial Thin Films on (010) YAlO3 Substrate Altered by Growth Condition of Pulsed Laser Deposition
Kenta Shimamoto 1,Max Dobeli 3,Thomas Lippert 2,Alexander Wokaun 1,Christof Schneider 1
1 Energy and Environment Research Department Paul Scherrer Institut Villigen PSI Switzerland,3 Laboratory of Ion Beam Physics ETH Zurich Zurich Switzerland1 Energy and Environment Research Department Paul Scherrer Institut Villigen PSI Switzerland,2 Department of Chemistry and Applied Biosciences ETH Zurich Zurich Switzerland
Show AbstractThe major approach to modify the strain state of oxide epitaxial thin films is to grow films onto substrates with different lattice parameters. A modification of strain states by selecting appropriate growth conditions is not a straightforward approach, but reported for some perovskites such as BaTiO3 [1, 2], SrTiO3 [3, 4], and SrFeO3 [5]. In Ref. 1, 3, and 4, it is revealed that the cation off-stoichiometry plays the key role, while in Ref. 2 the change of strain state is attributed to growth kinetics. Here, we demonstrate that the strain state of perovskite multiferroic TbMnO3 (TMO, Pbnm space group) thin films can be modified by the background gas pressure during film growth by pulsed laser deposition.
200 nm TMO films were grown on YAlO3 (010) substrates (lattice mismatch: 2.1 % along the a- and 0.4 % along the c-axis) with different background N2O pressure. X-ray diffraction patterns indicate that films grown at 0.7 mbar (0.7-TMO) consist of a thick coherently grown layer together with a relaxed one, while films made at 0.3 mbar (0.3-TMO) consist of a relaxed layer with a remaining thin strained layer underneath. Rutherford backscattering spectrometry revealed that 0.7-TMO has a stoichiometric cation ratio, while 0.3-TMO is Tb-rich. Deposition at different pressures varies the cation stoichiometry as observed in the case of La0.6Sr0.4MnO3 [6] and the strain state of a TMO film changes accordingly. The strain state has an influence on the in-plane electric properties probed by interdigitated electrodes patterned on their surface. They are both highly insulating so that the loss tangent remained lower than 0.006 at 1 kHz below 50 K. The ferroelectric hysteresis loops were measured by the PUND method with a maximum electric field of ±90 kV/cm. 0.7-TMO exhibits a remnant polarization (P) only along the a-axis (130 nC/cm2 at 10 K) like bulk TMO under hydrostatic pressure [7]. On the other hand, 0.3-TMO has the main polarization along the a-axis with P only up to 4 nC/cm2. The same sample shows P also along the c-axis between 23 and 28 K (max. 0.8 nC/cm2), indicating that the relaxed structure exhibits bulk-like electric properties [8] which are suppressed by either the bottom strained layer or the off-stoichiometry.
[1] D. Kan and Y. Shimakawa, Appl. Phys. Lett. 99, 081907 (2011). [2] J. Shin et al., Appl. Phys. Lett. 91, 202901 (2007). [3] C.-H. Lee et al., Appl. Phys. Lett. 102, 082905 (2013). [4] E. Breckenfeld et al., J. Mater. Chem. C 1, 8052 (2013). [5] S. Chakraverty et al., Cryst. Growth Des. 10, 1725 (2010). [6] J. Chen et al., Appl. Phys. Lett. 105, 114104 (2014) [7] T. Aoyama et al., Nat. Commun. 5, 4927 (2014). [8] T. Kimura et al., Nature 426, 55 (2003).
9:00 PM - MD2.5.04
Modifying the Ferroelectric Phase Diagram of Orthorhombic REMnO3 by Epitaxial Strain
Kenta Shimamoto 1,Thomas Lippert 2,Alexander Wokaun 1,Christof Schneider 1
1 Energy and Environment Research Department Paul Scherrer Institut Villigen PSI Switzerland,1 Energy and Environment Research Department Paul Scherrer Institut Villigen PSI Switzerland,2 Department of Chemistry and Applied Biosciences ETH Zurich Zurich Switzerland
Show AbstractApplying epitaxial strain to ferroic oxides introduces a significant change in their physical properties such as the magnitude of the order parameters and transition temperatures. It may even change the type of the ordering, in particular of materials which are close to a phase boundary. For example, quantum paraelectric SrTiO3 and EuTiO3 became ferroelectric (FE) with tensile strain [1, 2]. Orbital ordering of electron-doped perovskite manganite system is altered by epitaxial strain, changing its magnetic state accordingly [3].
Here, we focus on multiferroic orthorhombic rare-earth manganites (o-REMO, RE = Tb – Lu , Y) (Pbnm space group) whose bulk phase diagram has phase boundaries with respect to the size of the rare-earth ion. o-REMO with larger RE ions (Tb, Dy) exhibit a bc-cycloid spin structure with a c-axis polarization and those with small RE ions show an E-type ordering with an a-axis polarization. Hence, it is expected that epitaxial strain may change electric and magnetic states of o-REMO which are close to those phase boundaries, such as RE = Gd, Tb, Dy, Ho [4].
We investigated electric properties of a series of coherently grown o-REMO (Tb, Ho - Lu) films (ca. 20 nm) on (010) YAlO3 substrates. All the films are compressively strained along the a-axis, while all except for TbMnO3 are under tensile strain along the c-axis. The consequence of epitaxial strain indeed appeared in HoMnO3 and TbMnO3. The FE transition temperature of strained HoMnO3 and TbMnO3 are 37.5 and 38 K respectively, while the bulk transition temperature is ≈ 26 K for HoMnO3 [5] and ≈ 28 K for TbMnO3 [6]. Furthermore, their polarization direction is along the a- instead of the c-axis for bulk single crystal [6, 7]. The epitaxial strain from (010) YAlO3 thus modifies the FE phase diagram of o-REMO.
Since the in-plane lattice is locked for all the films investigated, the effect of chemical strain is reflected only in the b-axis lattice parameter which decreases as the size of the RE ion becomes smaller. With their in-plane lattice parameters, a and c, fixed, the FE transition temperatures of o-REMO show a positive correlation with respect to the b-axis parameter, 38 K for a TbMnO3 (b = 5.898 Å), 37.5 K for a HoMnO3 (b = 5.856 Å) and 30 K for a LuMnO3 (b = 5.765 Å).
[1] J. H. Haeni et al., Nature 430, 758 (2004). [2] J. H. Lee et al., Nature 466, 954 (2010). [3] Y. Konishi et al., J. Phys. Soc. Jpn. 68, 3790 (1999). [4] S. Ishiwata et al., Phys. Rev. B 81, 100411 (2010). [5] B. Lorenz et al., Phys. Rev. B 76, 104405 (2007). [6] T. Kimura et al., Nature 426, 55 (2003). [7] N. Lee et al., Phys. Rev. B 84, 020101 (2011).
9:00 PM - MD2.5.05
Stress Focusing and Transfer at the Graphene/Polymer Interface
Geunsoo Jang 1,Woongbin Yim 1,Van Tu Nguyen 1,Yeong Hwan Ahn 1,Soonil Lee 1,Ji-Yong Park 1
1 Ajou Univ Suwon Korea (the Republic of),
Show AbstractGraphene is considered as a candidate material for realizing flexible and stretchable electronics due to its high mechanical stiffness (Young’s modulus approaching ~1 TPa) and inherent flexibility arising from atomic thickness. In such applications as flexible and stretchable electronics, heterostructures consisting of graphene and polymer are often employed. Therefore, understanding mechanical interactions in terms of adhesion, friction, and strain at such interface is important. In this experiment, we investigated the interfacial mechanical interactions between graphene (grown by chemical vapor deposition) and polymer [PMMA(Polymethyl methacrylate)]. After graphene device is fabricated on SiO2/Si surface, it is transferred to and embedded in PMMA film. The tensile strain on the device is applied by swelling of PMMA matrix. Associated changes of the stress distribution in the device are investigated by both in situ and ex situ Raman measurements. Electrical transport measurements are also performed to assess modifications of electrical properties of the device. Strong adhesion and the large difference in modulus between two materials result in the significant stress transfer and focusing at the interface, which eventually leads to the failure of graphene and crack formation in the PMMA film. A classical model considering the role of stress transfer at the interface will be presented to explain the observed behaviors.
Symposium Organizers
Bilge Yildiz, Massachusetts Institute of Technology
Paul Evans, University of Wisconsin-Madison
Tobias Schulli, ESRF - The European Synchrotron
Ting Zhu, Georgia Institute of Technology
MD2.6: Strain Control of Low-Dimensional Materials
Session Chairs
Thursday AM, March 31, 2016
PCC West, 100 Level, Room 101 B
9:30 AM - *MD2.6.01
Elastic Strain Engineering of 1D and 2D Materials
Ju Li 1
1 MIT Cambridge United States,
Show AbstractIn accordance with Richard Feynman's 1959 statement, "there's plenty of room at the bottom," we explore the strain design space of low-dimensional materials for electronic and optoelectronic applications. Homogenous and inhomogeneous elastic strain [Nature Photonics 6 (2012) 866; Nature Communications 6 (2015) 7381], bending [ACS Nano 5 (2011) 3475], interlayer twist [Nano Letters 14 (2014) 5350] and slip [Nano Letters 15 (2015) 1302] lead to tunable, low-energy artificial atoms, artificial superlattices and pseudoheterostructures that can regulate quasiparticle motion [Adv. Mater. 26 (2014) 2572]. We also demonstrate production of kilogram-scale nanowires under large tensile elastic strain, that leads to improved superconductivity.
10:00 AM - MD2.6.02
Predictive Strain Engineering of Electron Bands and Phonon Bands in Transition Metal Dichalcogenides: Atomistic Simulation and Continuum Modeling
Bin Ouyang 1,Jun Song 1
1 McGill University Montreal Canada,
Show AbstractVI transition-metal dichalcogenides (TMDs) have attracted enormous research efforts because of their various electronic applications as well as superior elastic properties. Due to the outstanding elastic properties of TMDs, it could resist significant elastic deformation (up to 10~15% engineering strain), therefore the conventional models about elastic response of electronic and vibrational properties would fail to maintain accuracy. By employing density functional theory (DFT) calculations, the electron and phonon band shifts with existence of elastic strain has been examined. Meanwhile, we revised the traditional deformation potential theory to make it fitted for describing strain response of electron and phonon band shifts in TMDs. The prediction from our modelling has been proved to be satisfactory up to the elastic limits of TMDs with comparison to DFT calculations. In addition to that, on base of the deformation potential parameters we obtained, band shifting at arbitrary normal strain states can be well predicted. This study will provide insight into tuning the TMD electronic and vibrational properties by applying elastic deformation.
10:15 AM - MD2.6.03
Photoluminescence and Raman Modes of Transition Metal Dichalcogenides under Tensile and Compressive Strain
Sarah Bobek 1,Ariana Nguyen 1,David Barroso 1,Sahar Naghibi 1,Aimee Martinez 1,Zachary To 1,Ludwig Bartels 1
1 Univ of California-Riverside Riverside United States,
Show AbstractStrain engineering of transition metal dichalcogenide (TMD) materials is an area of rapidly increasing interest because it allows substantial modification of the material properties without the need for compositional variations. First principles calculations suggest a pronounced effect on the band gap and Raman modes for materials such as MoS2. Prior experimental work limited itself generally to measurement of the effect of tensile strain in single layer MoS2 and WS2 films. Here we report experiments in which we seamlessly vary the strain on monolayer and bilayer crystallites of chemical vapor deposition MoS2, WS2, and WSe2 in the range of ±3 %. The E12g in-plane Raman mode softens under lattice expansion, while the A1g out of plane mode remains unchanged. We observe a slight dimming of the photoluminescence (PL) upon both expansion and compression of the film. The PL peaks shift pronouncedly and the shift direction and magnitudes depend sensitively on the material composition.
10:30 AM - MD2.6.04
Highly Transparent Stretchable Ag Nanowire Circuits and Its Use for Transparent Direction-Recognizable Tactile Sensor
Insang You 1,Gyeongbae Park 1,Junghyeok Kwak 1,Unyong Jeong 1
1 POSTECH Pohang Korea (the Republic of),
Show AbstractRecent strong demand for wearable devices includes healthcare mornitoring, biotics, robotics, tactile sensors. Future electronics is expected to evolve into devices attachable to clothing or human skin and even implantable to underneath the skin or inside the body. To catch up severe mechanical deformations from body motions such as folding, pressing, twisting, and stretching, there have been a large number of studies on deformable devices showing stable performance at large strains. In addition, as skin-mounted devices, unperceivable is a critical characteristic for use in ordinary life, so transparency is pursued through material approaches in tactile sensors.
Metallic nanowires have been considered good candidates for transparent and stretchable electrodes due to its structual advantages enable to have low percolation threshold, high optical transparency and high conductivity with low surface modulus. Especially many technological advances in silver nanowires (Ag NWs) about low contact resistance, homogeneous coating and synthesis method having high aspect ratio give them to have much better performance and possibility to replace conventional transparent electrode such as indium-tin oxide (ITO). Embedding methods, as well, constructing rubber composites have been designed to obtain stretchability of Ag NWs based conductors. Embedded structure of rubber composites represents stable behavior during stretching and low surface roughness. However, there are still problems; first, entirely immersed portion of Ag NWs cannot function as electrodes and some prepolymers penetrated to Ag NWs enlarge the gaps between them during thermal curing process, disconnecting conducting paths. Furthermore, using the other methods to assure the adhesion between polymers and Ag NWs during transfer process, degraded rubber properties or limited utilizing in room temperature. Hence forming highly transparent Ag NWs rubber composite, not a three dimensional (3D) structure containing large amount of Ag NWs, has been a highly demanding work.
In this work, a novel method to fabricate highly transparent Ag NW-based stretchable conductors have developed by applying thermoplastic block-copolymer at surface of the rubber to constitute 2D percolation of Ag NWs maintaining transparency. Also we established micro patterning process for manufacturing transparent and highly conductive stretchable circuits with a negligible conductivity change at large uniaixial strains (~50 %). Finally we utilized the transparent stretchable circuits to fabricate a tactile sensor consisting of strain sensors array that can recognize a direction of shear force and a normal pressure applied on them.
11:15 AM - *MD2.6.05
Strain in Different Phases of Two Dimensional Transition Metal Dichalcogenide Nanosheets
Manish Chhowalla 1
1 Rutgers Univ Piscataway United States,
Show AbstractStrain in two-dimensional (2D) materials has profound implications on their electronic structure. Strain engineering therefore provides opportunities for exploration of interesting phenomena and tailoring the properties of 2D materials. We have studied phase transformations in three atoms thick transition metal dichalcogenide (TMD) monolayers. The co-existence of different phases in single layer TMDs gives rise to local strain. The presence of this local strain leads to enhancement in density of states at the Fermi level. We have correlated strain and the resulting increase in conductivity to improvement in catalytic activity of TMDs for the hydrogen evolution reaction. We have also studied the cumulative effect of strain in ensemble of monolayered TMD nanosheets for actuation.
11:45 AM - *MD2.6.06
The Role of Mechanical Constraints in Structural Phase Changes of Two-Dimensional Materials
Evan Reed 1,Karel-Alexander Duerloo 1,Yao Li 1
1 Stanford University Stanford United States,
Show Abstract
Single-layers of some transition metal dichalcogenide compounds have the potential to exist in more than one crystal structure. I will discuss our theoretical work combined with DFT-based calculations to identify several single layer materials and their alloys including MoxW1-xTe2 that have potential to exhibit structural phase changes under stress and strain states, temperature changes, and electrical conditions. By considering the relevant thermodynamic mechanical constraints for monolayers (e.g. the analogs of constant pressure or volume for bulk materials), we find that the detailed nature of the mechanical constraints on the monolayer can have a significant impact on the phase boundaries, shifting them hundreds of degrees in temperature and several percent in strain. Our calculations indicate that phase boundaries of MoxW1-xTe2 can be tuned from hundreds of degrees C to room temperature and below by adjusting the composition. I will discuss the conditions under which mixed phases are expected to be thermodynamically stable. Some monolayer phase changes exhibit large electronic contrast, bringing an exciting new application space to monolayer materials ranging form information and energy storage to electronic and optical electronic devices.
12:15 PM - MD2.6.07
Strain Engineered Diffusive Atomic Switching in Chalcogenide Heterostructure Superlattices
Janne Kalikka 2,Xilin Zhou 1,Ju Li 2,Simon Wall 3,Eric Dilcher 3,Robert Simpson 1
1 SUTD Singapore Singapore,2 MIT Cambridge United States,1 SUTD Singapore Singapore2 MIT Cambridge United States3 ICFO Barcelona Spain
Show Abstract
Strain engineering is an emerging route for designing materials with specific properties or functions, such as tuneable band gap, carrier mobility, chemical reactivity, and diffusivity. In this presentation we show how strain can be used to control atomic diffusion in van der Waals (vdW) heterostructures of two dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 0.5 nm thick 2D planes within an Sb2Te3–GeTe vdW superlattice. The thickness ratio of the 2D crystal layers dictates the strain in the GeTe. We use this effect to substantially lower the energy required for atomic switching. By identifying four critical rules for the superlattice configuration, we lay the foundation for a generalisable approach to the design of switchable vdW heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision that these rules may enable new methods to control spin and topological properties of materials in reversible and energy efficient ways.
12:30 PM - MD2.6.08
Strain Tuning of Phonon Dispersion Relations in Single-Walled Carbon Nanotubes
Tarek Ragab 2,Pierre Gautreau 1,Cemal Basaran 1
1 State University of New York at Buffalo Buffalo United States,2 Alexandria University Alexandria Egypt,1 State University of New York at Buffalo Buffalo United States
Show AbstractUsing supercell theory up to the fourth nearest neighbor atoms interaction in conjunction with comprehensive molecular mechanics model using the second generation reactive empirical bond order potential, the full band phonon dispersion of carbon nanotubes under uniaxial strain is calculated in armchair (10, 10) single-walled carbon nanotubes. Calculations were done at strains of 2.5%, 5%, 10%, 15%, 20%, and 25%. Results are first obtained for bulk graphene, then using the zone folding technique, results for carbon nanotubes were obtained. The lattice is first stretched from two opposite sides of the simulated graphene sheet until the appropriate strain level is reached through a series of applied prescribed displacement increments on the terminal atoms. The system is then allowed to reach equilibrium. Once at equilibrium, each atom in the supercell is moved in turn in the x-direction, y-direction and z-direction and the resulting forces are calculated on the neighboring atoms which are used to build the stiffness matrices required for the calculation of the phonon dispersion relation. Results suggest an overall phonon softening (lowering of phonon energy and flattening the dispersion curves) due to uniaxial strain. At strains higher than 15% the softening is so profound due to high nonlinearity in the force-displacement relation at those levels. The flattening of the curves results in an increase of the associated phonon density of states which results in a direct increase in the phonon-phonon scattering rates. Also the overall decrease in the phonon energy will lead to an increase in the phonon-phonon scattering rates and more importantly increase the electron-phonon scattering rates. The change in phonon quantization and the resulting increase in electron-phonon and phonon-phonon scattering rates offer further explanation to the experimental observation of electrical properties degradation for CNTs under uniaxial strain.
MD2.7: Nanomechanics and Thermal Transport in Strained Low-Dimensional Materials
Session Chairs
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 101 B
2:30 PM - *MD2.7.01
On the Griffith Criterion for Brittle Fracture in Graphene
Yujie Wei 1,Ting Zhu 2
1 Institute of Mechanics, Chinese Academy of Sciences Beijing China,2 Georgia Institute of Technology Atlanta United States
Show AbstractThere are prevailing concerns with the critical dimensions when conventional theories break down. Here we find that the Griffith criterion remains valid for cracks down to 10nm, but overestimates the strength of shorter cracks. We observe the preferred crack extension along the zigzag edge in graphene, and explain this phenomenon by local strength-based failure rather than energy-based Griffith criterion. These results provide a mechanistic basis for reliable applications of graphene in miniaturized devices and nanocomposites.
3:00 PM - MD2.7.02
Study of Flexoelectricity in Graphene Composite Structures
Mohamed Serry 2,Mahmoud Sakr 2
1 Department of Mechanical Engineering The American University in Cairo (AUC) New Cairo Egypt,2 YJ Science and Technology Research Centre The American University in Cairo (AUC) New Cairo Egypt,2 YJ Science and Technology Research Centre The American University in Cairo (AUC) New Cairo Egypt
Show AbstractWe present theoretical and experimental investigations of a new device concept for multimodal energy conversion based on integrating graphene on a metal-semiconductor junction. The key idea is that current flowing through the device is dominantly controlled by the junction’s characteristics (i.e., barrier’s height and width), which are highly sensitive to stimuli in the surrounding environment, such as heat, mechanical stress, gamma and infrared radiations. Effects of substrate type, doping level, operating temperature, and fabrication conditions are interpreted on the basis of testing the devices at elevated temperatures and theoretical models. Additionally, it was demonstrated that the barrier height of our proposed device could be effectively modulated according to tunneling or thermionic modes by separately controlling the bias voltage at the graphene surface versus that of the metal-semiconductor junction. Investigations of energy conversion by thermionic emission and flexoelectricity are presented.
Metal-semiconductor junctions have been utilized in developing highly efficient solar cells and electrochromic devices. Energy conversion efficiency of metal-semiconductor junctions can be increased significantly by employing different modes of energy conversion simultaneously, e.g., piezoelectric and thermionic. Therefore, in this work, we attempt to enhance the energy conversion efficiency of metal-semiconductor junction by integrating a CVD graphene (Gr) layer on top. The Gr layer acts as an antireflection coating allowing more radiation to be absorbed by the metal-semiconductor junction, increasing the quantum efficiency of the device. Moreover, as a result of residual stresses within the composite structure, flexoelectric behavior is observed, due to the stress gradient across the graphene layer upon heating the top surface. At the metal-semiconductor junction, a depletion region is formed as carriers migrate from semiconductor to metal. Experimental results showing the I-V behavior when the device is exposed to IR light of peak wavelength of 912 nm clearly demonstrates that the sensitivity decreases at the application of a reverse bias voltage, due to the variation of optical properties of graphene with applied voltage. Flexoelectric behavior is simulated at the atomic level, which shows the displacement of the C atoms in Gr layer due to applied stress gradient. This effect was studied experimentally by applying different magnitudes of bending stresses to the composite structure. Experimental results of the flexoelectric current generated in direct response to the applied stress at zero bias are also demonstrated. This effect is combined with the thermionic emission upon exposure to sufficient IR power. Therefore, due to the heterogeneous composite nature of the proposed structure, both thermionic and flexoelectric energy conversion behaviors can work in conjunction upon IR exposure increasing the overall efficiency of the device.
3:15 PM - *MD2.7.03
Nanomechanical Characterization and Strain Engineering of Two Dimensional Materials
Jun Lou 1
1 Rice Univ Houston United States,
Show AbstractTwo-dimensional (2D) materials, such as Graphene, hBN and MoS2, are promising candidates in a number of advanced functional and structural applications, owing to their exceptional electrical, thermal and mechanical properties. Understanding mechanical properties of 2D materials is critically important for their reliable integration into future electronic, composite and energy storage applications. However, it has been a significant challenge to quantitatively measure mechanical responses of 2D materials, due to technical difficulties in the nanomechanical testing of atomically thin membranes. Additionally, actively tuning functional properties of 2D materials by stress/strain is a very attractive approach for engineering these atomically thin components in practical applications. In this talk, we will discuss our recent effort to determine the engineering relevant fracture toughness of graphene, rather than the intrinsic strength that governs the uniform breaking of atomic bonds in perfect graphene. Our combined experiment and modeling verify the applicability of the classic Griffith theory of brittle fracture to graphene. Strategies on how to improve the fracture resistance in graphene will be discussed. In another example, we systematically characterize chemical vapour deposition-grown MoS2 by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced bandgap engineering. By evaluating the effective strain transferred from polymer substrates to MoS2 using three-dimensional finite element analysis, we demonstrate how strain concentration propagates in a triangular MoS2 monolayer crystal and propose substrates’ Young’s modulus as dominating mechanisms of strain loss.
3:45 PM - MD2.7.04
Strain Effects on Thermal Transport at the Nanoscale
Aman Haque 1,MD Alam 1,Raghu Pulavarthy 1,Baoming Wang 1
1 Pennsylvania State Univ University Park United States,
Show AbstractWhen the specimen dimension becomes comparable to the mean free path of current and heat carriers (electrons and phonons), mechanical strain can significantly impact thermal, electrical and optical properties. While the current trend is to understand the mechanics behind such breakdown in single domains, we aims to explore the ‘overlap among multiple domains’ at the nanoscale.
To study the length-scale induced coupling among thermo-electro-mechanical domains, it is imperative to perform simultaneous characterization of all these domains while varying the stimuli. However, even single domain studies are challenging at the nanoscale. Hence the literature does not have any technique to study multi-domain physics simultaneously. To address this shortcoming, we present the design and microfabrication of a chip capable of performing mechanical, electrical and thermal characterization of ultra-thin films of any material that can be deposited on a conventional substrate. In addition to quantitative studies, the technique also allows direct visualization through visually all forms of microscopy. The 3 mm x 3 mm size of the chip results in the unique capability of in-situ testing in analytical chambers such as the transmission electron microscope (TEM). The basic concept is to ‘see’ the micro-mechanisms while ‘measuring’ the deformation and transport properties of materials and interfaces.
We present strain-thermal conductivity relationship for aluminum, silicon nitride and amorphous silicon materials Under classical physics, there should be no such coupling. We therefore propose material specific hypotheses to explain the observed strong strain dependent property tuning phenomena.
4:30 PM - MD2.7.05
Thermal Conductivity in the Radial Direction of Deformed Polymer Fibers
Yanfu Lu 2,Jun Liu 1,David Cahill 2
2 Materials Science and Engineering University of Illinois at Urbana-Champaign Urbana United States,1 North Carolina State University Raleigh United States
Show AbstractThermal conductivity of polymer fibers in the axial direction has been extensively studied while thermal conductivity in the radial direction Λ remains unknown. In this work, polymer fibers with different molecular arrangements (crystalline, liquid crystalline, and amorphous) were plastically deformed. Λ was then measured at engineering strains ɛ=0.2-2.3 using time-domain thermoreflectance. Λ decreases with increasing strains for polyethylene (PE) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers and remains constant for poly(methyl methacrylate) (PMMA) fiber. The extrapolated thermal conductivity at zero strain is for crystalline PE, for liquid crystalline PBO, and for amorphous PMMA. Λ of PE drops to at ɛ=1.9 while Λ of PBO drops to at ɛ=2.1. We attribute the decreasing trend of Λ with ɛ in crystalline and liquid crystalline fibers to structural disorder induced by plastic deformation. The combination of disorder and phonon focusing effects produces a thermal conductivity in deformed PE and PBO fibers that is lower than amorphous PMMA.
MD2.8: Strain-Tuning of Semiconductor Electronic Properties I
Session Chairs
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 101 B
4:45 PM - MD2.8.01
Mapping the Full Strain Tensor and Lattice Tilts in Ge Microstructures for Photonics Applications Using Laue Microdiffraction
Samuel Tardif 1,Alban Gassenq 1,Kevin Guilloy 1,Osvaldo Dias Guilherme 2,Nicolas Pauc 1,Jose Escalante 1,Ivan Duchemin 1,Yann-Michel Niquet 1,Odile Robach 1,Francois Rieutord 1,Denis Rouchon 2,Julie Widiez 2,Jean-Michel Hartmann 2,Daivid Fowler 2,Alexei Chelnokov 2,Richard Geiger 3,Thomas Zabel 3,Hans Sigg 3,Jerome Faist 4,Vincent Reboud 2,Vincent Calvo 1
1 CEA-INAC Grenoble France,2 CEA-LETI Grenoble France3 Laboratory for Micro- and Nanotechnology Paul Scherrer Institute Villigen Switzerland4 Institute for Quantum Electronics ETH Zurich Zurich Switzerland
Show AbstractStraining a material is a convenient way to tune its physical properties. While silicon is typically strain-engineered to enhance the mobility of electrons and holes, theory predicts that under a large enough tensile strain (over 2% biaxial or over 4% uniaxial) the germanium electronic bandgap would change from indirect to direct, a pre-requisite for an efficient, CMOS-compatible light source. Models using Finite Elements Method (FEM) and indirect experimental techniques such as Raman microspectroscopy have already shown that strain values over the percent could be achieved in Ge by patterning slightly tensile-strained membranes and concentrating the strain in the small central region of a suspended micro-bridge or micro-cross1-4. Incidentally, the mechanical reliability of such highly strained micro-devices is also tightly bound to the local strain distribution, the local strain state being fully described by a 3x3 tensor. The ability to measure accurately and locally the full strain tensor is therefore of paramount importance.
Here we present experimental measurements of the full strain tensor in various Ge micro-devices using X-ray Laue micro-diffraction (µLaue) at beam-line BM32 at the European Synchrotron Radiation Facility, up to a record breaking 4.9% uniaxial strain. The µLaue technique has the major advantage of providing a local measurement of both the lattice distortions and rotations in a single shot, thus completely decoupling the evaluation of the strain amplitude from the lattice orientation. The major shortcoming of µLaue is that since a white beam is used, the measurement is limited to the deviatoric part of the strain tensor without knowing the energy of the measured Bragg reflections. We show that in fact this limitation can be circumvented either numerically or experimentally. The numerical approach assumes no normal stress on the free surfaces of the suspended devices and then solves the generalized Hooke’s equation using the tabulated values of the second order elastic coefficients of Ge. The experimental approach uses the “rainbow-filter” technique: selected energies are taken out of the incident beam and scanned across the spectrum, thus allowing a measurement of the energy of different Bragg reflections on the Laue pattern5.
Finally, we show that experimental results in stretched Ge nanowires have allowed plotting the position of their direct bandgap as a function of strain3 and that experimental strain maps in Ge membranes under either uni-axial or bi-axial tensile strain are in excellent agreement with predictions from anisotropic FEM calculations. This work shows the high potential of µLaue to probe the strain state in Ge devices for photonics applications.
1M. Suess et al., Nature Photonics 7, 466-472 (2013)
2T. Etzelstorfer et al., J. Synchr. Rad. 21, 111-119, (2014)
3G. Capellini et al., Optics Express 22, 1, (2014).
4K. Guilloy et al., Nano Lett. 15, 4, (2015)
5O. Robach et al., Acta Cryst. A69, 164-170, (2013)
5:00 PM - MD2.8.02
In Situ Strain and Lattice Orientation Distribution in SiN/Ge CMOS Compatible Light Emitting Microstructures by Quick X-Ray Nano-Diffraction Microscopy
Gilbert Chahine 4,Marvin Zoellner 1,Marie-Ingrid Richard 2,Giovanni Capellini 1,Thomas Schroeder 3,Tobias Schulli 4
4 European Synchrotron E.S.R.F. Grenoble France,1 IHP-leibniz Institute for Innovative Microelectronics Frankfurt Germany4 European Synchrotron E.S.R.F. Grenoble France,2 Aix-Marseille Université, CNRS, IM2NP UMR 7334 Marseille France1 IHP-leibniz Institute for Innovative Microelectronics Frankfurt Germany,3 Institute of physics and Chemistry, Brandenburg Technical University Cottbus Germany
Show AbstractAfter many years of development of sub-micrometer diffraction of x-rays, we have recently developed a novel type of scanning probe microscope (K-Map from quick-Mapping) [1] addressing the parameters strain and lattice orientation, in epitaxial as-grown and deeply buried structures, to a precision unobtainable by any other method. We used this non-destructive model-free technique to access in a direct way strain and lattice orientation of CMOS process fabricated Ge-based microstructures. Being a potential low cost photonic component, such devices are fabricated at the micrometer scale and have very complex geometries, as two-dimensional or three-dimensional structures, leading to non-uniform strain distribution. In this context, the characterization and quantification of locally resolved lattice distortion are relevant for understanding the engineering processes applied to control the device performances.
We will present an exhaustive synchrotron x-ray microdiffraction imaging of Ge photonic devices [2]. Different aspect ratios were probed covering a range of dimensions over which these structures may be functional for future light emitter applications.
Strain and lattice orientation distributions were imaged in great detail (FIG) that are inaccessible by any other technique, Δa/a=10-5 and 10-3 degrees respectively. They were extracted by using the strain and orientation calculation software package X-SOCS. The obtained results will be compared with the biaxial strain distribution obtained by lattice parameter-sensitive µ-Raman and µ-photoluminescence measurements. The experimental data will be interpreted with the help of finite element modelling of the strain relaxation dynamics in the investigated structures.
Moreover, the K-Map technique allowed us to conduct in-situ temperature measurements where the strain distribution behaviour between room temperature and 230 K will be discussed on improved Ge microtripe devices.
[1] Chahine et al. Journal of Applied Crystallography, 47, (2014)
[2] Chahine et al. Applied Physics Letters 106, 071902 (2015)
5:15 PM - MD2.8.03
Measuring Strain at the Nanoscale with High Precision Using Nanobeam Precession Electron Diffraction
Jean-Luc Rouviere 3,Nicolas Bernier 1,David Cooper 1,Nicolas Mante 1
2 INAC-SP2M University Grenoble Alpes Grenoble France,3 INAC-SP2M CEA Grenoble France,4 LETI, MINATEC Campus CEA Grenoble France,1 University Grenoble Alpes Grenoble France
Show AbstractIn this presentation, we present the Nanobeam Precession Electron Diffraction (N-PED) method that we have developed to measure locally at the nano-scale (spatial resolution approaching 1 nm) and with high precision the strain (precision in strain of about 0.01%), and consequently the stress present in nano-objects containing some crystals.
The experiments are performed in a Transmission Electron Microscope (TEM). At successive positions of a small electron beam, a diffraction pattern (DP) is recorded and analyzed. By comparing, the positions of the diffracted beams of a given DP to the positions of similar spots of a reference DP, local strain can be measured. In N-PED, the incident electron beam is rotated (i.e. scanned or precessed) by a small angle around the observation direction and a descan is applied after the sample in order to bring back the diffracted beams to their unprecessed positions. In fact there is a compromise between spot size i.e. spatial resolution, beam convergence, precession angle and precision. We adopted a setting where the beam convergence is about 2.2 mrad, the probe diameter is of about 1 nm, and the precession angle is below 0.5°. The advantages of this setting for strain measurement are manifold: (i) the diffraction spots have disk shapes and do not saturate, (ii) the intensity within the diffraction disks is more uniform (iii) more diffraction disks are visible (iii) a greater precision is obtained by locating the edges of the disks, (iv) the measurements are very stable versus changes in sample thickness or orientation and (v) strain maps of 4 components of the 3D strain tensor can be obtained with one zone axis orientation.
We will show how this simple and robust N-PED technique has been used successfully for the analysis of microelectronics devices and nanostructures for light-emission. In microelectronics devices, strain is used to increase the speed of electrons in the channels of transistors. By comparing N-PED experimental data to Finite Element (FE) simulations we will show how we could measure the stress present in an amorphous silicon nitride gate that introduces compressive stress in the 25-nm Si channel of a transistor. The observed nanostructures where nanowires in all-around-gate-transistors and Ge nanowires surrounded by a silicon nitride shell. The shell introduces strain/stress in the nanowire that modifies the optical emission of Ge.
5:30 PM - MD2.8.04
Phase Segregation and Elastoplastic Strain in Semiconductor Nanowires
Mehrdad Arjmand 1,Izabela Szlufarska 1
1 Univ of Wisconsin-Madison Madison United States,
Show AbstractSemiconductor nanowires, grown heteroepitaxially, have many unique properties such as the possibility of lateral relaxation, high surface to volume ratio and lower strain energy as compared to heteroepitaxial thin films. While the onset of plastic deformation and the phase stability in multi-component thin films have been studied extensively, much less is understood about these phenomena in the nanowire geometry. Here we report results of phase field model on the role of strain in controlling surface induced phase segregation in III-V semiconductor nanowires. We also present a new analytical theory of strain relaxation in incoherent core-shell nanowires. Phase segregation was studied specifically in GaAsSb nanowires. We found that initially homogeneous nanowire phase segregates to GaAs and GaSb during annealing and this segregation starts at the surface of a nanowire. This phenomenon had been previously predicted theoretically and observed experimentally in other materials. Our simulations demonstrate that phase segregation can be almost entirely suppressed by a thick enough shell grown around the core. Our analytical model is able to predict not only the onset of plastic deformation, but also evolution of stress and strain fields beyond the yield regime. This is the first analytical study of elastoplastic strain and stress fields of heteroepitaxial core-shell nanowires. The analytical model was validated against finite element simulations. We discover that the radius of plastic region linearly depends on the core radius while it has a non-monotonic dependence on the shell thickness. When shell thickness is smaller than a critical value, the radius of plastic region increases with increasing thickness. After reaching a critical value, the radius of plastic region starts to decrease with increasing shell thickness.
Symposium Organizers
Bilge Yildiz, Massachusetts Institute of Technology
Paul Evans, University of Wisconsin-Madison
Tobias Schulli, ESRF - The European Synchrotron
Ting Zhu, Georgia Institute of Technology
MD2.9: Nanomechanical and Structural Phenomena in Strained Functional Materials
Session Chairs
Friday AM, April 01, 2016
PCC West, 100 Level, Room 101 B
9:15 AM - *MD2.9.01
Coherent X-Ray Diffraction Imaging of Strain in Nanoscale Structures
Paul Fuoss 1,Wonsuk Cha 1,Martin Holt 1,Conal Murray 2,Virginie Chamard 3,Marc Allain 3,Stephan Hruszkewycz 1
1 Argonne National Lab Lemont United States,2 IBM T.J. Watson Research Center Yorktown Heights United States3 Institute Fresnel Marseille France
Show AbstractThe physical properties and performance of advanced materials depend strongly on localized structures, and strain within and near those localized structures. I will describe our studies focused on the development and use of coherent diffraction imaging techniques that can map, with exceptional sensitivity and resolution, strain fields around both isolated objects and within continuous films. Using Bragg coherent diffraction imaging, we can measure, with nanometer spatial resolution and picometer-scale sensitivity to lattice distortions, the heterogeneous strain in thin films and correlate these strains with growth behavior. I will introduce our recent development of Bragg projection ptychography that reconstructs components of three-dimensional atomic displacement fields from two-dimensional scans. In addition, I will describe the development of new coherent diffraction techniques that may enable the imaging of both the nanoscale morphological and lattice responses of materials in changing environments, and yield insight into kinetic processes ranging from defect dynamics to phase evolution and growth.
9:45 AM - MD2.9.02
In Situ Nanomechanics
Ting Zhu 1
1 Georgia Inst of Technology Atlanta United States,
Show AbstractIn situ nanomechanics is an emerging field that investigates the mechanical properties and deformation mechanisms of nanostructured materials. The study of in situ nanomechanics is typically conducted by integrating the real-time mechanical testing inside an electron microscope and the mechanics modeling with atomic resolution. It provides a powerful approach to visualize the intrinsic nanomechanical behavior of materials - seeing is believing. In this talk, I will present recent studies of in situ nanomechanics from my group, including the deformation-induced stacking fault tetrahedra in FCC nanocrystals (Nature Communications, 4, 2340, 2013); fracture toughness of graphene (Nature Communications, 5, 3782, 2014); and twinning-dominated deformation in BCC nanowires (Nature Materials, 14, 594, 2015). The in situ nanomechanics studies provide new insights that cannot be offered by traditional mechanics studies. Ultimately, the in situ nanomechanics research aims to enable the design of nanostructured materials to realize their latent mechanical strength to the full.
10:00 AM - MD2.9.03
The Nanodiffraction Beamline ID01/ESRF: Strain Microscopy by Diffraction Imaging
Gilbert Chahine 1,Marie-Ingrid Richard 2,Jan Hilhorst 1,Steven Leake 1,Peter Boesecke 1,Hamid Djazouli 1,Lucien Petit 1,Tobias Schulli 1
1 ESRF Grenoble France,2 Aix-Marseille University Marseille France
Show AbstractVery recent developments in the use of highly focused x-ray beams produced on the most advanced synchrotron sources offer a rapidly developing potential of diffraction imaging techniques for strain and strcuture in materials. At the ESRF Grenoble, ID01 is the beamline specialized on nanodiffraction imaging using scanning probe- and full-field techniques in order to supply a strain microscope essentially to the applied materials community. With the completion of the first phase of the upgrade of the European Synchrotron Radiation Facility (ESRF), the ID01 beamline has returned successfully to user operation. Offering scanning diffraction microscopy at 100Hz with sub-100nm focused x-ray beams [1], full field x-ray diffraction microscopy using compound refractive lenses [2] and coherent beams for coherent diffractive imaging applications [3] we can supply a vast spectrum of techniques for high resolution strain imaging. Even if all three methods can be described as strain microscopy in a wider sense, they differ significantly in terms of resolution, speed, experimental boundary conditions and challenges in data treatment. Depending on the sample and the questions to be answered images of strain distribution can be obtained using scanning diffraction techniques. Brought to maturity during the first phase of the ESRF upgrade these techniques allow for strain and texture imaging in thin films with a spatial resolution of 100 nm and strain sensitivity of ε=Δa/a
10:15 AM - MD2.9.04
Structure of Nanoscale Strontium Titanate Sheets Fabricated by Focused Ion Beam Milling
Jack Tilka 1,Joonkyu Park 1,Zhonghou Cai 2,Paul Evans 1
1 Materials Science and Engineering Univ of Wisconsin-Madison Madison United States,2 Advanced Photon Source Argonne National Laboratory Argonne United States
Show AbstractCrystallographic defects and elastic strain in complex oxides strongly influence materials properties. With improved crystalline quality and the ability to more easily control elastic strain in epitaxially grown thin films a wider range of attainable physical characteristics, such as electrical properties and catalytic reactivity, might be reached than is currently possible with commercially available substrates. Sub-micron-thick sheets of SrTiO3 (STO) provide a potential approach to reducing the concentration of crystallographic defects and more readily controlling elastic strain. The nanometer scale dimension can affect crystalline quality because the small dimensions reduce the distance extended defects must travel to escape to the surface to be annihilated. Tuning the thickness of the substrate can tune the elastic strain in films grown on them because the force the substrate can apply to the film will be related to its thickness. Thin sheets of STO were created by focused ion beam (FIB) milling, yielding single crystals with final dimensions of 10 μm × 10 μm × 500 nm. The effects of FIB (milling and annealing) were studied using structural characterization methods. Because the FIB processing was expected to introduce defects, unannealed milled sheets and annealed milled sheets were compared with unannealed bulk and annealed bulk STO samples. X-ray rocking curves of STO sheets were collected using nanobeam diffraction at the Advanced Photon Source (APS) in an experimental arrangement based on zone plate focusing optics. Rocking curves were simulated using the same focusing optics as in the experiment in order to compare with experimental results. The angular widths of x-ray rocking curves of the annealed sheets were similar to commercially purchased bulk STO, while the mosaic spread in the milled and unannealed sheets were a factor of two larger. Features of interest for the mosaic model, such as angular width, peak positions, and number of peaks have angular space characteristics narrower than the divergence of the focused beam. Comparing the data with the simulation allows us to resolve the mosaic width and the number of peaks. These fabrication and characterization techniques allow us to potentially create complex oxide substrates with a smaller number of crystallographic defects in a thickness regime that could allow for elastic strain sharing of epitaxially grown films.
10:30 AM - MD2.9.05
Epitaxial Growth, Strain Accommodation and Defect Creation in Epitaxial Structures
Nikolai Faleev 1,David Smith 1,Christiana Honsberg 1
1 Arizona State University Tempe United States,
Show AbstractCrystalline defects created due to accommodation of the initial elastic strain in heterostructures are a major problem for epitaxial growth, especially pseudomorphic, affecting the crystal perfection of these structures as well as other physical properties of later devices. To specify the main correlations between crystal defects and their physical effect, the process of elastic strain accommodation and defect creation must be correctly understood.
Accommodation of the initial elastic strain in heterostructures and creation of crystal defects is a natural and inevitable process because each crystalline compound tends to adopt its own lattice parameters. Accommodation can be impeded, but cannot fully prevented. Defect creation naturally correlates with growth conditions, which specify the accommodation mode, and hence, type of crystal defects, defect density and spatial distribution. If growth deterioration is greater than a critical level for edge dislocation creation, initial elastic strain will be almost fully accommodated by creation of these dislocations at the interface at the first stage of deposition. Accommodation under critical elastic strain is very fast: deposition of few monolayers leads to the creation of equidistant (~|b|/exx) net of edge dislocations at the interface. Creation of equi-spaced edge dislocations allows suggest that fast atomic rearrangement on the growth front and creation of edge dislocations on the interface is a resonance excitation of standing waves of single-atom pre-dislocation clusters followed by cluster transformation to edge dislocations. Lattice rearrangement and disturbances caused by atomic standing waves lead to creation of point defects (PDs) at the growth front. Diffused inward and accumulated at pre-dislocation clusters above the interface, PDs finally transform to ramified closed dislocation loops.
In low-deteriorated structures, the total strain energy is insufficient to activate resonance accommodation of the initial elastic strain. Energy deficiency is compensated by elastic strain locally induced by point defects accumulated at pre-dislocation clusters, extended along easy-glide directions. Elastic stress finally releases by creation of low-density “huge” primary dislocation loops (DLs), stretched from the growth surface deep into the substrate. Terminated in the substrate, these DLs do not contribute to accommodation of the initial elastic strain but they reconstruct interface and the growth surface to diminish the area of strain accommodation. After that, the initial elastic strain can be gradually released by smaller and denser secondary DLs with edge segments on the interface. The rate of strain accommodation depends on the initial elastic strain and inward diffusion of point defects, while the extent of accommodation gradually increases with the thickness of the epitaxial layer. In low-strained structures, defect creation switches from the fast resonance mode to the slower diffusion mode.
MD2.10: Strain-Tuning of Semiconductor Electronic Properties II
Session Chairs
Friday PM, April 01, 2016
PCC West, 100 Level, Room 101 B
11:15 AM - *MD2.10.01
High-Speed Control of Qubits in Elastically Strained Si Quantum Wells
Mark Eriksson 1
1 Univ of Wisconsin-Madison Madison United States,
Show AbstractQuantum dots in semiconductors are promising hosts for quantum bits: small numbers of electrons can be trapped and manipulated, and at low temperatures it is possible for this manipulation to be fully coherent. Silicon is of particular interest, because of its ubiquity in classical electronics, and because it has especially slow spin decoherence rates, making it a natural host for spin qubits. Elastically strained silicon forms a deep quantum well when grown epitaxially between relaxed SiGe barrier layers, and this system produces low-disorder electron gases in which gate-tunable quantum dots can be formed. In this talk I will present an overview of the full range of spin qubits that can be formed in such quantum dots, including qubits formed from one, two, and three electrons. The advantage of adding extra electrons is a large enhancement of qubit manipulation speed [1]. I will present data demonstrating the manipulation of a three-electron qubit in a double quantum dot – the “hybrid quantum dot qubit” – in which rotations can be performed in only 5 ns. Just like more conventional electron spin resonance, microwave fields can be used to manipulate this three-electron qubit, and the rotation axis can be controlled through the phase of the applied microwave oscillations [2]. This work was supported in part by ARO (W911NF-12-0607) and NSF (DMR-1206915). Development and maintenance of the growth facilities used for fabricating samples is supported by DOE (DE-FG02-03ER46028). Work performed in collaboration with Dohun Kim, B. Thorgrimsson, D. R. Ward, C. B. Simmons, R. H. Foote, Z. Shi, J. R. Prance, Teck Seng Koh, J. K. Gamble, D. E. Savage, M. G. Lagally, Mark Friesen, and S. N. Coppersmith.
[1] D. Kim, et al., Nature 511, 70 (2014).
[2] D. Kim et al. (http://arxiv.org/pdf/1502.03156.pdf).
11:45 AM - *MD2.10.02
Group IV Alloys for Electronic-Photonic Integrated Circuitry on Silicon
Detlev Gruetzmacher 2,Stephan Wirths 2,Daniela Stange 2,Nils von den Driesch 2,Dan Buca 2,Siegfried Mantl 2
1 Forschungszentrum Julich Julich Germany,2 Juelich Aachen Research Alliance (JARA) Juelich Germany,
Show AbstractMonolithic integration of photonic and electronic devices on Si chips is a viable route towards energy efficient information technology. Ge rich group IV alloys containing Sn have been predicted to exhibit a direct band gap. However, due to the small solid solubility of Sn in Ge (less than 1%) and the profound lattice mismatch of GeSn towards Si successful implementation is challenging. The recently developed process of reactive gas source epitaxy (RGSE) enables the deposition of GeSn alloys with Sn concentrations up to 14.5% on Ge virtual substrates with exceptional quality. In depth studies of the optical properties allow to determine the indirect-to-direct bandgap transition of GeSn alloys as function of the Sn concentration and strain: a fully relaxed GeSn film exhibits a direct band gap for Sn concentrations larger than 8.5%, whereas at 1% of residual compressive strain 13,4% Sn are required. Transmission Electron Microscopy (TEM) unravels that the GeSn film predominantly relaxes via 90° Lomer dislocations at the Ge/GeSn interface. The residual strain depends on film thickness and Sn concentration. Strikingly, completely strained GeSn films far beyond the expected critical thickness were obtained, which might be a consequence of the low deposition temperatures during RGSE. Fabry–Perot and microdisc laser structures with fully relaxed GeSn layers have been fabricated by using a substantial undercut of the mesa by removal of the Ge buffer layer underneath. The emission wavelength of optically pumped laser could be tuned from 2 to 2.6 µm while increasing the Sn content from 8.5 to 14.5%. First light emitting diodes emitting at room temperature were fabricated using GeSn p-i-n structures as well as heterostructures harboring Ge/GeSn multiple quantum wells.
The temperature dependence of the emission intensity and of emission wavelength has been measured. By fitting the experimental PL data from GeSn samples with different Sn concentrations and residual strain, measured by RBS and XRD, a set of parameters used in the 8-band k.p method was established and the band structure around the Γ point was calculated. In turn the effective mass of electrons in GeSn was calculated. The lowest masses are found for relaxed GeSn, which decreases with increasing Sn concentrations. The effective mass for Ge0.86Sn0.14 (0.024m0) is close to the effective electron mass of InAs. Moreover, the calculated mobility of electrons at room temperature in the Γ valley including band non-parabolicity effects and phonon scattering reveals very high mobilities. However, the calculation does not include alloy scattering. Still, competitive electron mobilities can be assumed. Hence GeSn may offer circuitry of p- and n-MOS as well as opto-electronic devices within the same material platform. Finally, the combination of a group IV alloy having a direct band gap and very low effective charge carrier masses might be a viable route for high performance, ultra-low power TFET devices.
12:15 PM - *MD2.10.03
Top Down Method to Introduce Ultra High Elastic Strain in Si and Ge for CMOS Based Electronics and Photonic
Thomas Zabel 1,Richard Geiger 1,Esteban Marin 1,Martin Sueess 2,Ralph Spolenak 3,Jerome Faist 2,Hans Sigg 1
1 Paul Scherrer Institut Villigen-PSI Switzerland,2 Institute for Quantum Electronics ETH Zurich Zurich Switzerland3 Laboratory for Nanometallurgy, Department of Materials Science ETH Zurich Zurich Switzerland
Show AbstractElastic strain is a widely used technique to control and modify the electrical, optical and/or magnetic properties of materials and thus offers large impact on improving device performances and the materials functionality. Commonly for semiconductors, strain is introduced by epitaxial layer growth on (virtual) substrate with larger or smaller lattice constant, or by exploiting process-induced strains and/or external loadings. However, epitaxial layers - as described by Mattews-Blackslee law – can only become a few atomic layer thick for high strains of some few %, and, the efficiency of most loading techniques, such as the SiN capping drops because of the restricted volumes available when scaling down the structure size to the nanometer scales such as for future CMOS transistors.
In contrast, we developed a method1,2 to achieve ultra high strained semiconductors - around 5% is demonstrated - using a micro-mechanical approach. The therefore shaped suspended lamellas enable the accurate control of the strain on a wafer scale by standard top-down fabrication technologies making it ultimate attractive for device applications but also for fundamental research thanks to the simplicity of the method.
We will discuss the application of our method to obtain Ge with a direct bandgap for lasing application and we give design rules for homogeneous > 2.5 GPa channel stress in sub 10 nm node CMOS transistor structures3.
1 R.A. Minamisawa et al. Nat Comms 3, 1096 (2012).
2 M.J. Süess et al. Nature Photonics 7, 466 (2013).
3 M. Schmidt et al. IEEE Electron Device Lett. 35, 300 (2014).
12:45 PM - MD2.10.04
Two-Dimensional Electron Gases in Elastically Strain Engineered Epitaxial Si/SiGe Heterostructures
Yize Li 2,Pornsatit Sookchoo 1,Xiaorui Cui 1,Robert Mohr 1,Trevor Knapp 1,Donald Savage 1,Ryan Foote 1,RB Jacobson 1,Jose Sanchez-Perez 1,Xian Wu 1,Dan Ward 1,Susan Coppersmith 1,Mark Eriksson 1,Max Lagally 1
1 University of Wisconsin-Madison Madison United States,2 California State University Bakersfield United States,1 University of Wisconsin-Madison Madison United States
Show AbstractTwo-dimensional electron gases (2DEGs) hosted at the interface of strained-Si/relaxed-SiGe hetero-structures form the foundation of Group IV based quantum electronics. Conventionally, Si/SiGe heterostructures are grown on strain-graded substrates, where intrinsic misfit dislocations and the associated strain inhomogeneities and mosaic structures are believed to have a deleterious effect for performance of quantum electronic devices. We have developed a unique strain-engineering approach to fabricate dislocation-free single-crystal SiGe nanomembranes (NMs), which serve as a seed crystal for further growth [1]. Structural characterization has demonstrated the high crystalline quality and absence of dislocation-related defects in the SiGe NMs and the subsequent overgrown Si/SiGe heterostructures [2].
We have performed magnetoresistance and Hall effect measurements to probe the electronic transport in these NM-based heterostructures. The observation of Shubnikov-de Haas quantum oscillations and the quantum Hall effect indicates the creation of high quality 2DEGs [3]. The electron mobility in NM-based 2DEGs is at least as high or higher than that in 2DEGs fabricated on conventional strain-graded substrates. Dingle analysis suggests that the overall short-range scattering is reduced in heterostructures grown on NM substrates. Our investigation on the influence of surface roughness indicates that 300-nm-scale strain variations, caused by growth-limited roughness, might limit the mobility in NM-based samples.
The measurement of a double quantum dot formed in a NM-based heterostructure is currently in progress. Initial results will be presented.
Sponsored by United States Department of Defense. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the U.S. Government. Use of growth facilities supported by DOE.
[1] D. M. Paskiewicz, B. Tanto, D. E. Savage, and M. G. Lagally, ACS Nano 5, 5814 (2011).
[2] D. M. Paskiewicz, D. E. Savage, M. V. Holt, P. G. Evans, and M. G. Lagally, Scientific Reports 4, 4218 (2014).
[3] Y. S. Li, P. Sookchoo, X. Cui, R. T. Mohr, D. E. Savage, R. Foote, RB Jacobson, J. R. Sánchez-Pérez, D. M. Paskiewicz, X. Wu, D. R. Ward, S. N. Coppersmith, M. A. Eriksson, and M. G. Lagally, ACS Nano 9, 4891 (2015).