News & Events

Speaker: Jong-Hyun Ahn
Affiliation: Yonsei University, Republic of Korea
Abstract Details: With the emergence of unusual format electronics such as flexible and wearable devices, an effort has been made to integrate devices with various functions in smart clothing for providing enhanced flexibility and convenience for the users. Thus, many experts believe that an important future in electronics is with systems that avoid the rigid, brittle and planar nature of existing classes of electronics, to enable new applications. However, it is very difficult to accomplish such electronics with conventional electronic materials. Graphene, the thinnest elastic material, has superb electronic properties that make it a promising host for device applications. In particular, graphene has an extremely good mechanical property, offering a great opportunity to flexible and stretchable electronics that should maintain a stable operation under a high strain. The recent advances in large-scale synthesis of graphene films by chemical vapour deposition are expected to enable various macroscopic applications such as semiconducting and transparent conducting films useful for flexible and stretchable electronics. In addition, to overcome the limitation of conventional materials, we developed the fabrication method of ultra-thin Si nanomembrane with thickness of nanometer scale from a single crystal wafer using the top town process. The resulting materials display outstanding electrical, optical and mechanical properties for high performance flexible and transparent electronics. 1. J.-H. Ahn et al., 'Graphene for displays that bend', Nature Nanotechnology, 9, 737 (2014) 2. J.-H. Ahn et al., 'Graphene Based Conformal Devices', ACS Nano, 8(8), 7655 (2014) 3. J.-H. Ahn et al., 'Quantum Confinement Effects in Transferrable Silicon Nanomembranes and Their Applications on Unusual Substrates', Nano Lett., 13, 5600, (2013)."
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Speaker: Inti Sodemann
Affiliation: MIT, USA
Abstract Details: In quantum Hall bilayers at total filling fraction one the electrons can develop a many-body state in which they occupy a common coherent combination of both layers. This state behaves as a superfluid for the layer density imbalance and displays several unusual transport properties including an analogue to the Josephson effect in which dissipationless tunneling between the layers can occur. In the first part of this talk, I will describe how a simple macrospin picture is able to capture the tunneling current-voltage characteristics of this state, and in particular those in which current is simultaneously injected through both rims of a Corbino annular device. In the second, I will describe an analogue of this system realized in XY magnets, and in particular how this principle can be exploited in the development of novel spintronic devices with non-local transport characteristics."
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Speaker: Keola Wierschem
Affiliation: National Taiwan University
Abstract Details: The Haldane phase in antiferromagnetic spin-1 Heisenberg chains is an early example of a nontrivial symmetry protected topological (SPT) state. The topological nature of this phase is manifest by a hidden symmetry breaking characterized by nonlocal string order. The Haldane phase has been experimentally observed in low dimensional spin-1 quantum magnets, such as NENP and NDMAP. These systems possess weak interchain couplings that prevent any meaningful characterization by string order, so it is unclear whether or not they remain SPT states. Recently, a so-called strange correlator has been proposed to detect SPT states. Defined as a correlation function at the temporal boundary between an SPT state and a trivial product state, the strange correlator has been shown to be long-range or quasi-long-range in one or two dimensions. In this talk, I will describe how to measure the strange correlator using quantum Monte Carlo and present some results for the strange correlator in quasi-one-dimensional Haldane gap systems."
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Speaker: Stephan Roche
Affiliation: ICN2 - Catalan Institute of Nanoscience Nanotechnology
Abstract Details: In this talk, I will discuss charge and spin transport in complex forms of graphene (chemically reduced, polycrystalline graphene, chemically functionalized) of relevance for current and future applications in flexible electronics, energy harvesting and spintronics. The crucial contribution of multiscale simulation will be illustrated, demonstrating an achieved high level of predictive capability for very large system sizes (with up to 1 billion atoms), reaching the experimental and technology scales. One illustration will be the quantitative analysis on the transport properties of structural imperfections produced during the wafer-scale production of graphene through chemical growth (CVD), or the mechanical/chemical exfoliation and chemical transfer to versatile substrates, followed by the device fabrication. Fundamental properties of charge mobilities in polycrystalline graphene, accounting the variability in average grain sizes and chemical reactivity of grain boundaries as observed in real samples grown by CVD will be presented, together with their relevance for device optimization and diversification of applied functionalities such as chemical sensing. In a second part, I will focus on spin transport in graphene functionalized by adatom deposits (gold, thallium). Unique spin dynamics phenomena in graphene, such as the formation of the Quantum Spin Hall state and a crossover to the Spin Hall effect under adatom segregation will be shown, as well as the role of spin-pseudospin entanglement in driving the spin relaxation mechanism in the ultraclean graphene limit. These results could open unprecedented perspectives for achieving proofs of concepts of spin manipulation, contributing to the progress towards non-charge based revolutionary information processing and computing. [1] L. E. F. Foa Torres, S. Roche, and J. C. Charlier, Introduction to Graphene- Based Nanomaterials: From Electronic Structure to Quantum Transport (Cambridge University Press, Cambridge, 2014). [2] D. Van Tuan, J. Kotakoski, T. Louvet, F. Ortmann, J. C. Meyer, S. Roche, Nano Lett. 13, 1730−1735 (2013); A.W. Cummings, D. Duong, V. Luan Nguyen, D. Van Tuan, J. Kotakoski , J.E. Barrios Vargas, Y. Hee Lee, S. Roche; Advanced Materials 26, Issue 30, 5079-5094 (2014). [3] Dinh Van Tuan, F. Ortmann, D. Soriano, S. O. Valenzuela, S. Roche, Nature Physics, 10, 857–863 (2014) [4] A. Cresti, D. Van Tuan, D. Soriano, A. W. Cummings, S. Roche, Phys. Rev. Lett (in press), arXiv:1411.5837"
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Speaker: Boris Yakobson
Affiliation: Rice University, USA
Abstract Details: Connecting the underlying chemical processes with the growth and emergent form remains an unsurmountable problem in life sciences [0]. In materials research, the current outlook is more optimistic. Establishing such connection, from the basic interatomic forces to growing nanostructure shape and properties becomes a real possibility. We will discuss several important examples of current interest including theory of carbon nanotubes chirality [1], growth and morphology of graphene [2] and other important 2D-materials [3], including the shape of equilibrium or growing islands, polycrystallinty and grain boundaries, and the unexpected functionality they bring about in electronics, magnetism, energy storage, and catalysis. [0] On Growth and Form, by D’Arcy W. Thompson (Cambridge U, 1917). [1] F. Ding et al. PNAS 106, 2506 (2009); R. Rao et al. Nature Mater. 11, 213 (2012); Q. Yuan et al. PRL 108, 245505 (2012); V. Artyukhov, et al. Nature Comm. 5:4892 (2014). [2] Y. Liu et al. PRL 105, 235502 (2010); V. Artyukhov et al. PNAS 109, 15136 (2012); Y. Hao et al. Science, 342, 720 (2013). [3] X. Zou et al. Nano Lett. 13, 253 (2013); Z. Zhang et al., ACS Nano, 7, 10475 (2013); S. Najmaei et al., Nature Mater. 12, 754 (2013).
About the Speaker: Boris I. Yakobson is an expert in theory and computational modeling of materials nanostructures, of their synthesis, mechanics, defects and relaxation, transport and electronics. Presently, Karl F. Hasselmann Endowed Chair in Engineering, professor of Materials Science and Nano- Engineering, and professor of Chemistry, Rice University, Houston, Texas. PhD 1982 in Physics and Applied Mathematics, from Russian Academy of Sciences. 1982- 1989, Head of Theoretical Chemistry lab at the Institute of Solid Materials of the Russian Academy. 1990-1999, on the faculty of the Department of Physics, North Carolina State University. His research, sponsored over the years by the National Science Foundation, Department of Energy, NASA, Department of Defense, Army Research Office, Air Force Research Laboratory and AFOSR, Office of Naval Research, as well as private industry and foundations, resulted in over 250 publications and seven patents. Received Department of Energy Hydrogen Program Award, Nano 50 Innovator Award from Nanotech Briefs (Boston), Royal Society (London) Professorship Award, Department of Energy R & D Award, NASA Faculty Award. Yakobson has mentored a number of PhD students and postdoctoral associates, serves on the editorial boards of several journals and on steering committees."
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Speaker: Prof Brian Schmidt, Prof Chorng-Haur Sow and Prof Tanya Monro
Abstract Details: In occasion of the 28th General Assembly of the International Union of Pure and Applied Physics, the Institute of Advanced Studies of the Nanyang Technological University will be hosting Special Public Lectures with: Prof Brian Schmidt, Novel Laureat in Physics 2011, Australian National University's Mount Stromlo Observatory; Prof Chrong-Haur Sow, NUS; Prof Tanya Monro, University of Adelaide.
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Speaker: Johan Nilsson
Affiliation: University of Gothenburg, Sweden
Abstract Details: A scheme is presented that enables a description of a paramagnetic Mott insulator in terms of free fermions. The main idea is to view the physical fermions as a part of a multi-band system and to allow for a correlation between the physical fermions and the auxiliary ones. Technically this is implemented through a non-linear canonical transformation, which is conveniently formulated in terms of Majorana fermions. The transformed Hamiltonian is in the next stage approximated with a free fermion theory. The approximation step is variational and provides an upper bound on the ground state energy at zero or the Free energy at finite temperature. In this way we are able to extend the domain of applicability of mean field theory and free fermions."
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Speaker: Petr Král
Affiliation: University of Illinois at Chicago, USA
Abstract Details: In this talk, we review many nanofluidic phenomena predicted and observed at the interfaces of carbonaceous nanostructures [1]. First, we discuss material drag effects around nanotubes and graphene induced by electronic currents, coupling of moving molecules, and mechanical vibrations. Then, we describe electronic sensing of a fluid motion around such nanostructures. Ultrasensitive molecular sensing was also reported at graphene grain boundaries. In a similar way, molecules passing through graphene nanopores can be sensed electronically. These nanopores could be used in water purification, molecular filtration, and DNA sequencing. Finally, we describe the self-assembly of carbon nanostructures by water droplets and nanotubes, mention experiments with water confined between graphene layers, and discuss the formation of filled micelles on the surfaces of carbon nanotubes. [1] P. Král and B. Wang, Material Drag Phenomena in Nanotubes, Chem. Rev. 113, 3372 (2013)."
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Speaker: Kurt Stokbro
Affiliation: Quantum Wise and Copenhagen University
Abstract Details: As device features near atomic dimensions, simulations of electrical currents need to be based on a quantum?mechanical description rather than a classical one. New phenomena appear which can be exploited for novel device characteristics, but also fundamental challenges arise when the influence of single defects can have devastating effects. The very definition of electrical current should be based on the quantum conductance, but in order to compare measurements and calculations accurately, a realistic atomistic description of the device configuration is required in order to properly describe impurities and defects. Although atomic?scale calculations of ballistic tunneling currents are becoming mainstream over the last decade, many challenges remain. Tight?binding models may work for some systems, but fail to capture the electronic structure of metallic systems, or interfaces combining metals and semiconducting materials, in which cases first?principles [1] or semi?empirical [2] approaches becomes necessary. For transistor applications it is necessary to include gates and dielectric screening regions, and in other cases we may need to consider sequential tunneling in the weak coupling limit [3], rather than the coherent tunneling picture. Moreover, all of the above needs to be carried out for large?scale systems that might involve thousands of atoms. We will provide an overview of the state?of?the?art atomic?scale modeling techniques, and show examples of how our software Atomistix ToolKit is used used to study a wide variety of nanoelectronic device structures, such as graphene field?effect transistors, conductance of nanowires, molecular junction diodes, contact resistance of metal?semiconductor interfaces, leakage currents in ultrathin oxide layers, and magnetic tunnel junctions. The latter involves noncollinear calculations with spin?orbit coupling and the calculation of spin?transfer torque. Recent developments on the electron?phonon interaction will also be discussed. [1] M. Brandbyge, J.?L. Mozos, P. Ordejón, J. Taylor, and K. Stokbro, Phys. Rev. B, 65, 165401 (2002) [2] Kurt Stokbro et al., Phys. Rev. B, 82, 075420 (2010) [3] Kurt Stokbro, arXiv:1006.0082v1
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