posted 2 May 2019, 03:30 by Peter Boggild
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updated 2 May 2019, 03:34
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Department of Electrical and Computer Engineering at National University of Singapore
There are hundreds of companies worldwide claiming to produce “graphene,” showing a large variation in its properties. A systematic and reliable protocol is developed to test graphene quality using electron microscopy, atomic force microscopy, Raman spectroscopy, elemental analysis, X-ray photoelectron spectrometry, and scanning and transmission electron microscopy, which is used to study graphene from 60 producers. The statistical nature of the liquid-phase exfoliation of graphite is established. It is shown that the current classification of graphene flakes used in the market is erroneous. A new classification is proposed in terms of distribution functions for number of layers and flake size. It is shown unequivocally that the quality of the graphene produced in the world today is rather poor, not optimal for most applications, and most companies are producing graphite microplatelets. This is possibly the main reason for the slow development of graphene applications, which usually require a customized solution in terms of graphene properties. It is argued that the creation of stringent standards for graphene characterization and production, taking into account both the physical properties, as well as the requirements from the particular application, is the only way forward to create a healthy and reliable worldwide graphene market.
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posted 1 May 2019, 07:27 by Peter Boggild
 Studying the intrinsic behavior 2D
materials requires attention to both external and internal sources of disorder.
This talk will first review the techniques used to create clean
heterostructures with hBN to reduce environmental disorder. In graphene, ten years
of progress has led to device performance now rivaling he highest-quality
GaAs-based heterostructures.
Semiconducting transition metal dichalcogenides (TMDs) also benefit from
hBN encapsulation but are limited by atomic defects. The types and density of atomic defects in
TMDs will be reviewed, as well as progress in synthesis of TMDs with
dramatically lower defect density.
Combining higher crystal quality and clean encapsulation allows
observation of greatly enhanced optical properties, including near-unity
photoluminescence quantum yield, and long excited-state lifetime in TMD
heterostructures. In addition, electronic transport measurements show improved
carrier mobility and reveal many new details of the Landau spectra, including
observation of fractional quantum Hall states in monolayer TMDs.
 James Hone is currently Wang Fong-Jen
Professor of Mechanical Engineering at Columbia University, and director of PAS3,
Columbia’s Materials Science Research and Engineering Center (MRSEC). He received his BS in physics from Yale in
1990, and PhD in experimental condensed matter physics from UC Berkeley in
1998, and did postdoctoral work at the University of Pennsylvania and Caltech,
where he was a Millikan Fellow. He
joined the Columbia faculty in 2003.
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posted 30 Apr 2019, 06:32 by Peter Boggild
ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain 2ICREA – Institució Catalana de Recerça i Estudis Avancats, Barcelona, Spain. Frank.koppens@icfo.eu
Several two-dimensional materials are model systems with tunable topological electronic bands that exist only in a few exotic materials. Here, we will discuss the progress and prospects of topological nanophotonics with two-dimensional materials. We exploit THz and infrared near-field imaging and spectroscopy techniques to directly spatially visualize the strongly compress optical modes at topological interfaces, polariton propagation and effects of disorder.
We also discuss the nanophotonic properties of twisted bilayer graphene, which has demonstrated unconventional superconductivity when twisted with specific “magic” angles.
Topological nanophotonics may enable novel future applications in miniaturized photonic isolators, diodes and logic circuits and could lead to completely new concepts for communication systems, optical transistors and optical information processing.
Prof. Frank Koppens obtained his PhD in experimental physics at Delft University, at the Kavli Institute of Nanoscience, The Netherlands. After a postdoctoral fellowship at Harvard University, Since August 2010, Koppens is group leader at the Institute of Photonic Sciences (ICFO). The quantum nano-optoelectronics group of Prof. Koppens focuses on both science and technology of novel two-dimensional materials and quantum materials. Prof. Koppens is vice-chairman of the executive board of the graphene flagship program, a 1000 MillionEuro project for 10 years. He is also the leader of the optoelectronics workpackage within the flagship. Prof. Koppens holds a GSMA Chair with activities related to the Mobile World Congress. Koppens has received five ERC awards: the ERC starting grant, the ERC consolidator grant, and three ERC proof-of-concept grants. Other awards include the Christiaan Hugyensprijs 2012, the national award for research in Spain, and the IUPAP young scientist prize in optics. In total, Koppens has published more than 70 refereed papers (H-index above 47), with more than 35 in Science and Nature family journals. Total citations >17.500 (google scholar).
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posted 30 Apr 2019, 03:17 by Peter Boggild
Physics Department, University of
California at Berkeley, and Lawrence Berkeley National Lab, Berkeley,
California 94720 U.S.A.
 Symmetry, interaction and topological
effects, as well as environmental screening, dominate many quantum properties
of reduced-dimensional systems, leading often to manifestation of counter-intuitive
concepts and phenomena that may not be so prominent or have not been seen in
bulk materials. In this talk, I present some fascinating discoveries in
recent studies of atomically thin one-dimensional (1D) and two-dimensional (2D)
materials. A number of interesting and unexpected behaviors have been found –
e.g., strongly bound excitons (electron-hole pairs) with unusual energy level
structures and new topology-dictated optical selection rules, tunable magnetism
and plasmonic properties, novel topological phases, correlated multi-particle
excitations, excitonic shift currents, etc. – adding to the promise of these 1D
and 2D materials for exploration of new science and valuable applications.
 Professor Steven G. Louie received his
Ph.D. in physics from the University of California at Berkeley (UC Berkeley) in
1976. After having worked at the IBM Watson Research Center, Bell Labs, and U of
Penn, he joined the UC Berkeley faculty in 1980, where he is professor of
physics and concurrently a faculty senior scientist at the Lawrence Berkeley
National Lab. He is an elected member of the National Academy of Sciences, the American
Academy of Arts & Sciences, and the Academia Sinica (Taiwan), as well as a
fellow of the American Physical Society (APS), the American Association for the
Advancement of Science, and the Materials Research Society. Among his other honors, he is recipient of
the APS Aneesur Rahman Prize for Computational Physics, the APS Davisson-Germer
Prize in Surface Physics, the Materials Theory Award of the Materials Research
Society, the Foresight Institute Richard P. Feynman Prize in Nanotechnology,
the U.S. Department of Energy Award for Sustained Outstanding Research in Solid
State Physics, as well as Jubilee Professor of the Chalmers University of
Technology in Sweden and H. C. Ørsted Lecturer of the Technical University of
Denmark. Professor Louie’s research
spans a broad spectrum of topics in theoretical condensed matter physics and
nanoscience. He is known for his groundbreaking work on the ab initio GW method
and for his seminal work on surfaces and interfaces, nanostructures, and
reduced-dimensional systems. |
posted 25 Apr 2019, 07:34 by info admin
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updated 25 Apr 2019, 07:38
]
University of Texas –
Austin
This talk will present our latest research adventures on 2D nanomaterials towards greater scientific understanding and advanced engineering applications. In particular the talk will highlight our work on flexible electronics, zero-power devices, monolayer memory (atomristors), non-volatile RF switches, and wearable tattoo sensors. Non-volatile memory devices based on 2D materials are an application of defects and is a rapidly advancing field with rich physics that can be attributed to sulfur vacancies or metal diffusion. Atomistic modeling and atomic resolution imaging are contemporary tools under use to elucidate the memory phenomena. Likewise, from a practical point, electronic tattoos based on graphene have ushered a new material platform that has highly desirable practical attributes including optical transparency, mechanical imperceptibility, and is the thinnest conductive electrode sensor that can be integrated on skin for physiological measurements. Much of these research achievements have been published in nature, IEEE and ACS journals, and widely covered by the news media including Time magazine, BBC, Nature news, IEEE spectrum, and several dozen media outlets.
[1] X. Wu, R. Ge, P.-A. Chen, H. Chou, Z. Zhang, Y. Zhang, S. Banerjee, M.-H. Chiang, J. C. Lee, and D. Akinwande, "Thinnest Nonvolatile Memory Based on Monolayer h-BN," Advanced Materials, vol. 0, p. 1806790, 2019.
[2] M. Kim, R. Ge, X. Wu, X. Lan, J. Tice, J. C. Lee, and D. Akinwande, "Zero-static power radio-frequency switches based on MoS2 atomristors," Nature Communications, vol. 9, p. 2524, 2018/06/28 2018.
[3] S. Kabiri Ameri, R. Ho, H. Jang, L. Tao, Y. Wang, L. Wang, D. M. Schnyer, D. Akinwande, and N. Lu, "Graphene Electronic Tattoo Sensors," ACS Nano, vol. 11, 2017.
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