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Keynote abstracts 2017

Vincent Meunier: Carbon in one-dimension: when nanoconfinement rules the show!

posted 6 Apr 2017, 09:13 by Peter Boggild

Rensselaer Polytechnic Institute

In this talk I will review the effect of quantum confinement on the electronic and vibrational properties of one-dimensional carbon nanoribbons. The talk will present research conducted at the interface between theory and experiment where a combination of disciplines is found to lead to an atomistic understanding of measurable properties of low-dimensional structures.[1-3] Inspired by the recently developed capability of assembling nanostructures from the bottom up with atomic precision, the field devoted to the detailed understanding of the physics of carbon nanostructures is poised to offer an unprecedented test-bed for predictions of quantum confinement. In particular, the emergence of magnetic states, tunable electronic properties, vibrational (and thermal) properties is now being exploited as a real possibility to develop carbon-based devices of the future, with higher density of information and processing power. I will use specific examples to illustrate that as we venture into a new regime of material science research where the position of each atom is known precisely, theoretical description is found to face new challenges that are not apparent in defective materials. 
1. N. Kharche and V. Meunier, J. Phys. Chem. Lett., 7, pp 1526–1533 (2016).
2. V. Meunier, A. G. Souza Filho, E. B. Barros, and M. S. Dresselhaus, Rev. Mod. Phys. 88, 025005 (2016)
3. L. Talirz et al, ACS Nano, 11, pp 1380–1388 (2017)
Vincent Meunier is head of the Physics, Applied Physics, and Astronomy Department at Rensselaer Polytechnic Institute where he holds the Gail and Jeffrey L. Kodosky ’70 Constellation Chair. Meunier earned his PhD from the University of Namur in Belgium in 1999 under the supervision of Professor Philippe Lambin. He was a Senior R&D staff member at Oak Ridge National Laboratory until 2010 when he joined Rensselaer. He has published approximately 210 papers in peer-reviewed journals and is a Fellow of the American Physical Society. Meunier leads the Innovative Computational Material Physics (ICMP) group at Rensselaer. His research uses computation to examine the atom-level details of materials. He is particularly interested in low-dimensional materials and domains where he can collaboratively work with engineers and experimentalists to optimize these materials, starting at the atomic level and targeting functionality.

Klaus Ensslin: Quantum structures in 2D materials

posted 6 Apr 2017, 09:09 by Peter Boggild

Laboratory for Solid State Physics, ETH Zurich

2D crystals are ideal systems for the realization of strongly confined quantum structures. Many experiments have focused on etched graphene quantum devices because of the missing band. Most devices were dominated by localized states along the graphene edges, which are difficult to control on the atomic scale. In this talk I will present two solutions to this problem. In bilayer graphene a bandgap arises for vertical electric fields. We demonstrate that a split-gate arrangement can be used to define a narrow 1D ballistic channel. An additional well positioned top gate allows to pinch off the channel. Furthermore a series of plateau-like features occurs when the channel is opened. An interesting level scheme arises in particular for high magnetic fields. Another approach is based on MoS2 encapsulated between layers of BN to obtain best electronic quality. At low magnetic fields we observe a degeneracy of 6, which is explained by the 3-fold valley degeneracy in the conduction band of MoS2 plus a factor of 2 for spin-degeneracy. In a quantum point contact again conductance pinch-off and quantization is observed. 2D materials have improved to an extent, that novel electronic quantum devices can be realized with great promise.

1. H. Overweg, H. Eggimann, M.-H. Liu, A. Varlet, M. Eich, P. Simonet, Y. Lee, K. Watanabe, T. Taniguchi, K. Richter, V. I. Fal'ko, K. Ensslin, and T. Ihn, “Oscillating magnetoresistance in graphene p-n junctions at intermediate magnetic fields”, arXiv:1612.07624

2. R. Pisoni, Y. Lee, H. Overweg, M. Eich, P. Simonet, K. Watanabe, T. Taniguchi, R. Gorbachev, T. Ihn, and K. Ensslin“Quantized conductance and broken symmetry states in MoS2 van der Waals heterostructures” , arXiv:1701.08619

Klaus Ensslin received his B. Sc. from the University of Munich, his M. Sc. from ETH Zurich, and his PhD from Max Planck Institute in Stuttgart. He moved on to postdocs at UC Santa Barbara and University of Munich and started as a professor at ETH Zurich in 1995. Since 2011 Klaus Ensslin is the Director of National Center for Competence in Research on “Quantum Science and Technology”.

Kaustav Banerjee: 2D Crystals for Smart Life

posted 6 Apr 2017, 09:05 by Peter Boggild

Director, Nanoelectronics Research Lab, Professor, Electrical and Computer Engineering, University of California, Santa Barbara

I will highlight the prospects of 2D materials for innovating energy-efficient transistors, sensors, and interconnects targeted for next-generation electronics needed to support the emerging paradigm of Internet of Things. More specifically, I will bring forward a few applications uniquely enabled by 2D materials and their heterostructures that have been demonstrated in my lab for realizing ultra-energy-efficient electronics. This will include the world’s first 2D-channel band-to-band tunneling transistor (Nature 2015) that overcomes a fundamental power consumption challenge in all electronic devices since the discovery of the first transistor in 1947, as well as a breakthrough interconnect technology based on doped-graphene-nanoribbons (Nano Letters 2016), which overcomes the fundamental limitations of conventional metals and provides an attractive pathway toward a low-power and highly reliable interconnect technology for next-generation integrated circuits. I will also bring forward a new class of ultra-sensitive and low-power sensors as well as area-efficient and high-performance passive devices, both enabled by 2D materials, for ubiquitous sensing and connectivity to improve the quality of life.

Professor Kaustav Banerjee from UC Santa Barbara is one of the world’s leading researchers of nanoelectronics. His current research focuses on the physics, technology, and applications of 2D nanomaterials and their heterostructures for designing next-generation green electronics, photonics, and bioelectronics. Initially trained as a physicist, he graduated from UC Berkeley with a Ph.D. in electrical engineering in 1999. A Fellow of IEEE, APS, and AAAS, Professor Banerjee has made seminal contributions toward extending the frontiers of energy-efficient electronics. This includes pioneering work on 3D ICs, now being widely commercialized, which has been recognized by IEEE with the 2015 Kiyo Tomiyasu Award, one of the institute's highest honors. Professor Banerjee’s radical innovations with 2D materials are setting the stage for a new generation of ultra-energy-efficient electronics needed to support the emerging paradigm of “Internet of Things”. This comprised of demonstrating the world’s first 2D-material based tunneling transistor that reduces power dissipation by over 90% (Nature 2015), as well as a novel energy-efficient interconnect technology based on graphene that also overcomes a fundamental reliability limitation of conventional interconnect materials (Nano Letters 2016).

Jonathan Coleman - Liquid exfoliated nanosheets: applications in energy, sensing and electronics

posted 6 Apr 2017, 09:01 by Peter Boggild

School of Physics, CRANN and AMBER Research Centers, Trinity College Dublin, Dublin 2, Ireland

Liquid phase exfoliation (LPE) is a simple method to exfoliate layered crystals like graphite to give 2-dimensional nanosheets such as graphene. LPE can be achieved either by sonicating or shearing layered crystals in appropriate liquids and has been used to produce nanosheets of graphene, MoS2, BN, MoO3, Ni(OH)2, phosphorene and many other materials. The nanosheets produced by this method tend to be ~100-1000 nm wide, a few monolayers thick and relatively defect free.  Using centrifugation, the dispersions can be easily size selected, solvent exchanged and concentrated to ~10 mg/ml, and are ideal for producing nanosheet networks. Here we show that, especially when combined with carbon nanotubes, such networks are of use in electrochemical devices such as supercapacitors, battery electrodes or electrocatalysts. In particular, composite films fabricated from combinations of Co(OH)2 nanosheet and carbon nanotube networks perform as state of the art oxygen evolution catalysts. When graphene nanosheet networks are combined with soft polymers, the resultant composite becomes an extremely sensitive electromechanical sensor. When mounted next to the skin, such sensors can detect pulse and even measure blood pressure. Alternatively graphene networks can be printed to act as electrodes. When combined in the correct architecture with networks of semiconducting (eg MoS2) and insulating (eg BN) nanosheets it is possible to produce all-printed, all-nanosheet field effect transistors.

Jonathan Coleman is the Professor of Chemical Physics in the School of Physics and the CRANN and AMBER Research centres, all at Trinity College Dublin. His research involves liquid exfoliation of layered compounds such as graphene, boron nitride and molybdenum disulphide. Exfoliation of these materials gives 2D nanosheets which can easily be processed into thin films or composites from applications from energy storage to sensing to electronics. He has published approximately 250 papers in international journals including Nature and Science, has a h-index of 72 and has been cited ~30000 times. He was recently listed by Thomson Reuters among the world’s top 100 materials scientists of the last decade and was named as the Science Foundation Ireland researcher of the Year in 2011. Prof Coleman has been involved in a number of industry-academic collaborative projects with companies including Hewlett-Packard, Intel, SAB Miller, Nokia-Bell Labs and Thomas Swan.

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