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Invited abstracts

Francesco Bonaccorso: Large scale production of 2D crystals and their application in energy

posted 24 Jul 2017, 05:47 by info admin

Istituto Italiano di Tecnologia, Graphene Labs, 16163 Genova, Italy

Liquid-phase exfoliation of layered materials[1] is offering a simple and cost-effective pathway to fabricate various two-dimensional (2D) crystal-based (opto)electronic[2] and energy devices[3], presenting huge integration flexibility compared to conventional methods.[2,3] However, a key requirement for the realization of such applications is the development of industrial-scale, reliable, inexpensive production processes,[1] while providing a balance between ease of fabrication and final material quality with on-demand properties. Here, I will show our scaling up approach for the solution processing of 2D crystal based on wet-jet milling of layered materials. Moreover, I will present an overview of 2D crystals for flexible and printed (opto)electronic and energy applications, from the fabrication of large area electrodes[2] to devices integration.[2,3]

[1] F. Bonaccorso, et. al., Adv. Mater. 28, 6136 (2016).
[2] F. Bonaccorso, et. al., Nature Photonics 4, 611, (2010).
[3] F. Bonaccorso, et. al., Science, 347, 1246501 (2015).

Francesco Bonaccorso gained the PhD from the University of Messina in Italy after working at the Italian National Research Council, the Engineering Department of Cambridge University (UK) and the Department of Physics and Astronomy of Vanderbilt University (USA). In June 2009 he was awarded a Royal Society Newton International Fellowship at Cambridge University, and elected to a Research Fellowship at Hughes Hall, Cambridge, where he also obtained a MA. He is currently leading the processing and prototyping group at the Istituto Italiano di Tecnologia, Graphene Labs. He was responsible in defining the ten years scientific and technological roadmap for the European Graphene Flagship. He was featured as 2016 Emerging Investigator by J. Mater. Chem. A. His research interests encompass both the fun-damental understanding and solution processing of novel nanomaterials with on-demand de-signed structures, their spectroscopic characteriza¬tion, incorporation into polymer composites and their technological application in solar and photoelectrochemical cells, lithium-ion batter-ies, light emitting devices and ultrafast lasers. He organized several conferences such as Graphene2015/2016/2017, Graphene Canada, GrapChina 2014/2015/2016, etc., and symposia in MRS, e-MRS. He has several publications in journals such as Science, Nature Nanotechnology, Nature Photonics, Chemical Society Reviews, Advanced Materials, Nano Letters, etc. These have been covered by a number of reports in the press.

Alexander Croy: Nanomechanics and strain-engineering of phosphorene

posted 5 Jun 2017, 15:25 by info admin

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden

One of the many features of atomically thin materials is the possibility to engineer their properties using deformations. Semiconducting materials, like phosphorene, are of particular interest due to their potential for optoelectronic applications. The theoretical description of the electromechanical behaviour requires a consistent
treatment of electronics and mechanics. In this spirit, a multi-scale approach is presented, which combines a recently developed valence-force model [1] - relating macroscopic strain to microscopic displacements of atoms [2] - and a tight-binding model with distancedependent hopping parameters to obtain strain-induced electronic properties. The resulting self-consistent electromechanical model is suitable for large-scale modelling of phosphorene devices. We demonstrate this for the case of an inhomogeneously deformed phosphorene drum, which may be used as an exciton funnel [3]. 

[1] D. Midtvedt and A. Croy, Phys. Chem. Chem. Phys. 18, 23312 (2016).
[2] D. Midtvedt, C. H. Lewenkopf, and A. Croy, 2D Materials 3, 011005 (2016).
[3] P. San-Jose et al, Phys. Rev. X 6, 031046 (2016).

Alexander is currently working as a senior researcher at the chair of Prof. Cuniberti (TU Dresden). His main interests are (computational) nanomechanics of 2d materials and timedependent electron and phonon transport. For his PhD on time-dependent nano electronics he joined the Max Planck Institute for the Physics of Complex Systems (MPIPKS) in Dresden. Later, working with Prof. J. Kinaret and Prof. A. Isacsson (Chalmers, Sweden), the focus of his research shifted to (carbon-based) nanoelectromechanical systems. From 2014-2016 he was Distinguished PKS Postdoctoral Fellow at the MPIPKS. 

Helge Weman: Epitaxial growth of semiconductor nanostructures on graphene

posted 2 Jun 2017, 02:14 by Peter Boggild

NTNU-Trondheim and CrayoNano AS, Norway

We have recently developed a generic atomic model, which describes the epitaxial growth of semiconductor nanostructures on graphene that is applicable to all conventional semiconductor materials[1,2]. The model was first verified by cross-sectional transmission electron microscopy studies of GaAs nanowires that grow epitaxially and dislocation-free on graphene. Recently we have also shown the vertical growth of dislocation-free GaN nanowires on graphene [3]. The epitaxial growth of semiconductor nanostructures on graphene is very appealing for device applications since graphene can function not only as a replacement of the semiconductor substrate but in addition as a transparent and flexible electrode for e.g. solar cells and LEDs.

For deep ultraviolet AlGaN based LEDs which are in huge need for various disinfection and sterilization purposes, the concept offers a real advantage over present thin film-based technology. Such thin film UV LEDs are today very expensive and inefficient due to the lack of a good transparent electrode (ITO is absorbing in deep UV), the high dislocation density in the active thin film layers, low light extraction efficiency, and the use of very expensive semiconductor substrates or buffer layers of AlN. The spin-off company CrayoNano are now developing UV LEDs based on the growth of AlGaN nanostructures on graphene, which potentially can overcome these problems, as will be further discussed in my talk.

1. A.M. Munshi, D.L. Dheeraj, V.T. Fauske, D.C. Kim, A.T.J. van Helvoort, B.O. Fimland, and H. Weman, Nano Letters 12, 4570 (2012).
2. A.M. Munshi and H. Weman, Phys. Status Solidi RRL 7, 713 (2013). (Review)
3. M. Heilmann, A.M. Munshi, G. Sarau, M. Göbelt, C. Tessarek, V.T. Fauske, A.T.J. van Helvoort, J. Yang, M. Latzel, B. Hoffmann, G. Conibeer, H. Weman, and S. Christiansen,
Nano Letters 16, 3524 (2016).

Dr. Helge Weman is a professor in nano-electronics at the Norwegian University of Science and Technology (NTNU) in Trondheim, Norway. He received his PhD in semiconductor physics in 1988 from Linköping University, Sweden. During his career, he has held various positions at UCSB, NTT, EPFL and IBM Res. Lab Zurich. Since 2005 Weman is leading a research group at NTNU on III-V semiconductor nanowires grown on Si and graphene for use in optoelectronic applications. In June 2012 he founded CrayoNano AS who are now developing deep UV LEDs using AlGaN nanostructures grown on graphene. He is the coordinator of the M-era.Net project “Semiconductor Nanowire/Graphene Hybrids for High-Efficiency LEDs” consisting of academic and industrial partners from Norway and South Korea. At CrayoNano he is also partner of the EUROSTAR project “CMOS Fab-compatible Graphene”. Since 2010 Dr. Weman is a member of the Norwegian Academy of Technical Sciences (NTVA).  

Alexey Nikitin: Nanophotonics in 2D

posted 30 May 2017, 02:44 by Peter Boggild

CIC Nanogune & Ikerbasque, SPAIN

Over the past decade, there is a growing research activity on light-matter interactions in atomically thin materials, such as graphene, topological insulators, thin polar and semiconducting layers and other van der Waals materials, including their heterostructures. Here, we will consider 2D ("flatland") materials as a promising rich platform for manipulation of infrared (IR) and terahertz (THz) waves. We will show how to launch and focus polaritons in graphene sheets and nano-cavities [1,2] and thin van der Waals multilayers (BN and graphene-BN hybrids) [3]. We will discuss both theoretical and experimental studies on 2D optics (optics in atomically-thick layers) as well as the applications of 2D plasmonics to modern IR and THz sensing and photodetecting optoelectronic nanodevices (see Fig.). Artistic representation of the concept of on-chip merging graphene photonics and electronics [3].

[1] P. Alonso-González et al, Science, 344, 1369 (2014).
[2] A. Y. Nikitin et al, Nat. Photon. 10, 239 (2016).
[3] P. Alonso-González et al. Nat. Nanotech. 12, 31 (2017).

Dr. Alexey Nikitin is an expert in theory of electromagnetic wave phenomena, particularly in nanophotonics. Recently, his main scope of interest has been light-matter interaction in low-dimensional systems (such as graphene, topological insulators, BN and other van der Waals materials). He obtained his PhD in theoretical physics in 2005 in the Institute for Radiophysics and Electronics (Kharkov, Ukraine). Starting from 2006 he had a postdoctroral stay in the University of Zaragoza (Spain) being awarded with two individual grants for talented young scientists: INTAS (sponsored by European Union) and Juan de la Cierva (sponsored by Spanish Ministry of Science). In 2013 he joined nanoGUNE research centre as an Ikerbasque Fellow. 

Roman Gorbachev: New materials for van der Waals heterostructures

posted 30 May 2017, 02:32 by Peter Boggild

National Graphene Institute, Manchester University, UK.

In the last three years, a novel field has emerged which deals with structures and devices assembled layer-by-layer from various atomically-thin crystals. These new multi-layer structures have proved to be extremely versatile, showing exceptional electronic and optical properties, new physics and new functionality. This is mostly due to the fact that each atomic layer can be chosen among many different materials including metals, semiconductors, superconductors or even topological insulators. 
In this talk I will review recent progress and discuss new additions to the 2D material family, their fabrication and transport properties. I will present our newest results on atomically thin crystals of InSe – material that hasn’t been sufficiently studied before and now shows outstanding optical and electronic properties. Other materials, such as black phosphorus, niobium diselenide and gallium selenide will be discussed with specific attention paid to fabrication and their chemical stability.

Roman Gorbachev received his B. Sc. from the Novosibirsk State University (Russia), his PhD from University of Exeter (UK). He moved on to postdoc at Manchester University and has received Royal Society University Research Fellowship in 2014. Since 2015 Roman is Senior Research Fellow at Manchester University. 

Eric Pop: Electronic, Thermal, and Unconventional Applications of 2D Materials

posted 7 Apr 2017, 08:52 by Peter Boggild

Stanford University, USA, Electrical Engineering, Materials Science & Engineering, Precourt Institute for Energy

Two-dimensional (2D) materials have applications in low-power electronics and energy-conversion systems. These are also rich domains for both fundamental discoveries as well as technological advances. This talk will present recent highlights from our research on graphene, BN, and transition metal dichalcogenides (TMDs). We have studied graphene from basic transport measurements and simulations, to the recent wafer-scale demonstration of analog dot product nanofunctions for neural networks [1]. We are also growing [2] and evaluating the electrical, thermal, and thermoelectric properties of TMDs including MoS2, MoSe2, HfSe2, and WTe2. Recent results include low-resistance contacts, 10-nm scale transistors [3], and high-field transport studies including velocity saturation. We have also examined the anisotropic thermal conductivity of these materials, for unconventional applications to thermal switches and thermal routing. If time permits, I will also discuss nanoscale thermoelectric effects in transistors and phase-change memory (PCM), which could enable energy-efficient operation. Our studies reveal fundamental limits and new applications that could be achieved through the co-design and heterogeneous integration of 2D nanomaterials.

1. N.C. Wang, S.K. Gonugondla, I. Nahlus, N.R. Shanbhag, E. Pop, "GDOT: A Graphene-Based Nanofunction for Dot-Product Computation," IEEE VLSI Tech. Symp., Jun 2016, Honolulu HI

2. K.K.H. Smithe, C.D. English, S.V. Suryavanshi, E. Pop, "Intrinsic Electrical Transport and Performance Projections of Synthetic Monolayer MoS2 Devices," 2D Materials 4, 011009 (2017)

3. C.D. English, K.K.H. Smithe, R.L. Xu, E. Pop, "Approaching Ballistic Transport in Monolayer MoS2 Transistors with Self-Aligned 10 nm Top Gates," IEEE Intl. Electron Devices Meeting (IEDM), Dec 2016, San Francisco CA

Eric Pop is an Associate Professor of Electrical Engineering (EE) and Materials Science & Engineering (by courtesy) at Stanford University. He was previously on the faculty of the University of Illinois Urbana-Champaign (2007-13) and also worked at Intel (2005-07). His research interests are at the intersection of nanoelectronics, nanomaterials, and energy. He received his PhD in EE from Stanford (2005) and three degrees from MIT (MEng and BS in EE, BS in Physics). His awards include the 2010 PECASE from the White House, the highest honor given by the US government to early-career scientists and engineers. He is also a recipient of Young Investigator Awards from the ONR, NSF CAREER, AFOSR, DARPA, and of several best paper/poster and teaching/advising awards. He is an IEEE Senior member, he served as the General Chair of the Device Research Conference (DRC), and on program committees of the VLSI, IRPS, MRS, IEDM, and APS conferences. In a past life, he was a DJ at KZSU 90.1 FM from 2001-04. Additional information about the Pop Lab is available online at http://poplab.stanford.edu.

Sarah Haigh: Understanding 2D Material Heterostructures at the Atomic Scale using Transmission Electron Microscopy

posted 7 Apr 2017, 08:50 by Peter Boggild

S.J. Haigh, A. Rooney, E. Prestat, E. Khestanova, R. Dryfe, M Velický, R.V. Gorbachev, R. Boya, Y. Cao, I. Grigorieva, R. Nair, K. Novoselov, F. Withers, A.K. Geim, National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK

2D crystals can be layered together to create new van der Waals crystals with bespoke properties. However, the performance of such materials is strongly dependent on the quality of the crystals and their interfaces at the atomic scale. Transmission electron microscopy (TEM) is the only technique able to characterize the nature of buried interfaces in these engineered van der Waals crystals and hence to provide insights into the optical, electronic and mechanical properties. I will report the use of TEM imaging technique to aid the development of 2D heterostructures. I will review our work on traditional heterostructures as well as those where individual planes of atoms have been effectively removed to produce nanochannels. The latter provide unique opportunities to help understand water flow at the nanoscale.[1] I will show the use of TEM to reveal how high pressure confinement in such channels can drive chemical transformations in aqueous salts [2]. I will further demonstrate the use of STEM characterization to understand the unusual structure of Franckeite, a natural mineral phase composed of incommensurate 2D layers, which has promising electrochemical properties when exfoliated to few-layer thickness [3].

1. Boya et al, Nature, 538, (2016) p. 222.

2. Vasu et al, Nature Communications, 7, (2016), 12168.

3. Velický et al, Nature Communications, 8, (2017), 14410.

Sarah Haigh is a Reader in Material Science and Director of the Electron Microscopy Centre at the University of Manchester, UK. Her research interests focus on improving our understanding of nanomaterials properties using transmission electron microscope (TEM) imaging and analysis techniques. She worked as consultant application specialist to JEOL UK before moving to Manchester in 2010. She completed her PhD in 2008 at the University of Oxford working on developing exit wave reconstruction in the TEM. She now leads a research group (5 PhD student, 6 MSc Students and 3 postdocs) centred on TEM imaging of nanomaterials. She has a particular interest in imaging of materials under more realistic environments and was recently awarded an ERC starter grant to develop this area of microscopy. She has more than 100 peer reviewed papers of which 78 are from the last 3 years. She is Chair of the Institute of Physics EMAG group, a member of council for the Royal Microscopy Society (UK) and a freeman of the Worshipful Company of Armourers and Brasiers. Awards include the IOM3 Silver Award (2014), RMS Medal for Innovation in Applied Microscopy (2016) and Rosenhain Medal (2017),

Alexey Chernikov: Coulomb engineering in 2D materials

posted 7 Apr 2017, 08:46 by Peter Boggild

Department of Physics, University of Regensburg, Germany

Since the discovery of graphene, a single sheet of carbon atoms, research focused on two-dimensional (2D) van der Waals materials evolved rapidly due the availability of atomically thin, thermally stable crystals with intriguing physical properties. The 2D materials naturally inherit major traits associated with systems of reduced dimensionality: strongly enhanced interactions, efficient light-matter coupling, and sensitivity to the environment. In particular, the considerable strength of the Coulomb forces introduces a rich variety of many-body phenomena including significant renormalization of the bandgap and the emergence of tightly bound exciton quasi-particles.

In this talk, I will show how atomically-thin crystals offer an alternative approach to nanoscale bandgap engineering, based on the local tuning of the Coulomb interaction and the environmental sensitivity of 2D materials. I will demonstrate how careful tailoring of the surrounding dielectric environment allows us to tune the electronic bandgap of single layers of semiconducting transition-metal dichalcogenides by many 100’s of meV and present an in-plane dielectric heterostructure as an illustration. The unique advantages of the Coulomb engineering in 2D, including nanometer sensitivity and a high flexibility of resulting dielectric heterostructures, will be further discussed. Finally, I will give a brief outlook towards new pathways for manipulating and designing electronic bandgaps in the 2D plane.

Alexey Chernikov received his Ph.D. from the University of Marburg (Germany) for the work on the optical properties of semiconducting materials and external cavity semiconducting lasers. With a Feodor-Lynen Fellowship from the Alexander von Humboldt Foundation, he joined the group of Tony F. Heinz at the Columbia University (New York, USA) in 2013 to study Coulomb phenomena in atomically-thin 2D systems. Currently, he leads a research group at the University of Regensburg (Germany) funded by the Emmy-Noether Initiative of the German Research Foundation. His research is focused on fundamental interactions of electronic and excitonic many-body states in nanostructured matter.  

Alexander Balatsky: Driven Dirac Materials

posted 7 Apr 2017, 04:51 by Peter Bøggild

Nordita and Los Alamos

Recent rapid developments in time resolved probes and in manipulation of quantum matter in time domain open opportunities to control correlations and instabilities of electronic states in time domain. I will discuss applications of these ideas to Dirac Materials[1]. Dirac Materials exhibit nodes in the spectra that result in the strong energy dependence of the Density of States (DOS). Hence the driven and nonequilibrium Dirac Materials offer a platform for investigation of collective instabilities of Dirac nodes via controlled tuning of the coupling constants with drive. I will present the results of  investigation of the many body instabilities, like excitonic instabilities, in driven Dirac Materials[2]. Recent optical pump experiments are consistent with the creation of long lived states away from equilibrium in Dirac Materials [2] and hence pave the way to tunable interactions in Dirac Materials.

1. T. O. Wehling, et.al. Dirac materials. Advances in Physics, 63(1):1–76, (2014).

2. Christopher Triola, et.al,  Excitonic Gap Formation in Pumped Dirac Materials, arXiv:1701.04206, (2017).

A.Balatsky is a Professor of Theoretical Physics at Nordita and a Director of the Institute for Materials Science at Los Alamos. He got his PhD at the Landau Institute for Theoretical Physics, 1987. After a PD at Urbana Champaign with D. Pines he moved to Los Alamos as an Oppenheimer Fellow. Awards include  fellow of  the American Physical Society (2003), Los Alamos Fellow (2005) American  Association for Advanced of Science (2013) and ITS Senior Fellow at ETHZ (2016). Main research interests include superconductivity, superfluidity and Dirac Materials. Recent focus of research at our group has been on Dirac materials and dynamic orders including odd frequency superconductivity and driven collective states in Dirac Materials.  

Maria C. Asensio: Electronic and Chemical nano-imaging of wonder materials beyond graphene

posted 7 Apr 2017, 04:44 by Peter Bøggild

Synchrotron SOLEIL & University Paris-Saclay, FRANCE

Recently, remarkable progress has been achieved in modern microscopies. However, even if they have attained exceptional results, the problem of providing powerful high-resolution spectroscopic tools for probing at nano- and  mesoscopic-scale still remains. This is particularly the case for an innovative and powerful technique named k-nanoscope or NanoARPES (Nano Angle Resolved Photoelectron Spectroscopy). This cutting-edge nanoscope is able to determine the momentum and spatial resolved electronic structure, disclosing the implications of heterogeneities and confinement on the valence band electronic states typically present close to the Fermi level, with not more than 15-20 eV of binding energy. 

In this presentation, the more relevant results of the recently built ANTARES nanoscope beamline at the synchrotron SOLEIL will be disclosed [1]. In particular, nanoARPES findings describing the electronic band structure of mono-atomic exfoliated graphene on SiO2 substrates, epitaxial and polycrystalline monolayer graphene films grown on copper and SiC [2] will be presented and Graphene/MoS2 heterostrustures. Electronic and chemical mapping with high energy, momentum and lateral resolution have provided relevant features like gap-size, doping, effective mass, Fermi velocity and electron-phonon coupling.among other properties.  Finally, special mentions will be dedicated to the recently reported results on the spin-charge separation in metallic MoSe2 grain boundary [3].

[1] C. Chen et al., Nature Communications, 6 (2015) 8585

[2] I, Razado-Colambo et al., Nature Scientific Reports 6 (2016) 27261

[3] Y. Ma, et al., Nature Communications 8 (2017) 14231.

Currently, Permanent Research Staff of the SOLEIL French synchrotron source and the Université Paris-Saclay, Professor Maria Asensio is also Permanent staff of the Institute of Material Science of Madrid, in Spain working in the area of electronic structure determination by using low energy Synchrotron radiation. Maria Asensio commenced her academic career in Argentina, where she finished her PhD degree in Surface Science. Then she held a Senior Lecturer in Physics at the Autonomous University of Madrid, followed by positions at the University of Warwick in England and at the Fritz Haber Institute of the Max-Planck in Berlin, Germany, collaborating in several large European Research Projects. Asensio’s research comprises studying the application of a wide-ranged conventional and Synchrotron Radiation Based techniques devoted to the characterization of advanced materials, in the area of Solid State Physics. Lately, she has conceived an innovative chemical and electronic imaging technique combining angle resolved photoemission and microscopy, named “k-nanoscope or NanoARPES”. She is author of more than 278 publications and had more than 100 invited talks.

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