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Contributed abstracts 2017

Marc Hvid Overgaard: Graphene Oxide: A Candidate for Screen Printing of Flexible Electrode Circuits

posted 5 Jul 2017, 07:19 by Peter Boggild

University of Copenhagen, Department of Chemistry

Graphene inks are promising for roll-to-roll printing of flexible electronics. Currently, the most widely adapted strategy for formulating graphene inks is via liquid phase assisted exfoliation of graphite, but these inks requires electrically insulating binders/stabilizers to avoid flake re-aggregation. Thermal or photonic annealing is therefore needed in order to decompose the binders after printing in order to regain conductivity. Unfortunately this restricts the use of heat-sensitive plastic substrates.

In this presentation, we demonstrate a mildly oxidized graphene oxide (GO) hydrogel ink. The ink is water-based and binder-free and can be used for screen-printing applications of electrode circuitries [1]. Chemical reduction with trifluoro acetic acid and hydroiodic acid is used to efficiently reduce the printed GO films into reduced graphene oxide (rGO) films. This strategy allow us to circumvent traditional high-temperature annealing, while simultaneously yielding conductive films with 327 Ohm/sq at 37% transmittance. We also assess the tolerance to flexing, and find that the conductivity of the films is almost completely unaffected by film flexing.  

[1] M. H. Overgaard, M. Kühnel, R. Hvidsten, S. V. Petersen, T. Vosch, K. Nørgaard, B. W. Laursen, Adv. Mater. Technol. 2017

Marc Hvid Overgaard is currently a Ph.D. under Bo Wegge Laursen and Kasper Nørgaard in the Nano-Chemistry group at the University of Copenhagen. He received his B.Sc. and M.Sc. in nanoscience at the University of Copenhagen. His research interests are the chemical synthesis of graphene and graphene nano-composites and applications of graphene.

Arkady Krasheninnikov: New morphologies in graphene on Ir and 2D transition metal dichalcogenides: insights from first-principles calculations

posted 14 Jun 2017, 00:54 by Peter Boggild

Helmholtz Zentrum Dresden-Rossendorf, Germany, and Aalto University, Finland 

Both free-standing and supported 2D materials contain defects and impurities, which may govern the electronic and optical properties of these materials. Moreover, defects can give rise to the development of new morphologies either under electron beam or atom deposition. In my talk, I will present the results [1-3] of our first-principles theoretical studies of defects and new morphologies, such as new phases or extended defects, obtained in collaboration with several experimental groups. Specifically, I will dwell upon a new type of predominantly sp2-hybridized nanostructured representing a regular array of fullerene-like, thermally highly stable carbon clusters that are covalently bonded to the underlying graphene sheet grown by depositing carbon atoms on top of graphene on Ir substrate [1]. I will further discuss the development of line defects [2] and fragments of metallic phases in free-standing TMDs [3] under electron beam irradiation. 

1.C. Herbig, T.Knispel, S. Simon, U.A. Schröder, A.J. Martínez-Galera, M.A. Arman, C. Teichert, J. Knudsen, A.V. Krasheninnikov, and T. Michely, Nano Letters 17 (2017) 3105. 
2. H.-P. Komsa and A. V. Krasheninnikov, Advanced Electronic Materials 3 (2017) 1600468. 
3. S. Kretschmer, H.-P. Komsa, P. Bøggild and A. V. Krasheninnikov, JPC Lett. (2017) in press.

Arkady Krasheninnikov is a Group Leader at the Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden- Rossendorf, Germany, and a Guest/Visiting Professor at Danish Technical University and Aalto University, Finland. He received his Ph.D. degree in 1995 from Moscow State Engineering Physics Institute, Russia. His current scientific interests include various areas of computational materials science, electronic- structure calculations, two-dimensional materials, and irradiation effects in solids. 

Adolfo De Sanctis: Extraordinary linear dynamic range in laser-defined functionalized graphene photodetectors

posted 14 Jun 2017, 00:51 by Peter Boggild

Centre for Graphene Science, College of Engineering, Mathematics and Physical Sciences, University of Exeter, EX4 4QL Exeter, UK

Graphene-based photodetectors have demonstrated mechanical flexibility, large operating bandwidth, and broadband spectral response [1]. However, their linear dynamic range (LDR) is limited by graphene’s intrinsic hot-carrier dynamics, which causes deviation from a linear photoresponse at low incident powers. At the same time, multiplication of hot carriers causes the photoactive region to be smeared over distances of a few micrometers, limiting the use of graphene in high-resolution applications [2]. We present a novel method for engineering photoactive junctions in FeCl3-intercalated graphene using laser irradiation. Photocurrent measured at these planar junctions shows an extraordinary linear response with a linear dynamic range (LDR) value of 44 dB, at least 4500 times larger than that of other graphene, while maintaining high stability against environmental contamination without the need for encapsulation. The observed photoresponse is purely photovoltaic, demonstrating complete quenching of hot-carrier effects. These results pave the way toward the design of ultrathin photodetectors with unprecedented LDR for high-definition imaging and sensing in extreme environments.

1. F. H. L. Koppens et al. Photodetectors based on graphene, other two-dimensional materials and hybrid systems. Nat. Nanotechnol. 9, 780 (2014);
2. J. C. W. Song et al. Hot carrier transport and photocurrent response in graphene. Nano Lett. 11, 4688 (2011);

Adolfo De Sanctis is currently Research Fellow in the Quantum Systems and Nanomaterials group at the University of Exeter (UK). He received his Ph.D. from the University of Exeter, with a dissertation on "Manipulating light in two-dimensional layered materials" in December 2016. He previously obtained a M.Sc. in Applied physics and Nanotechnology in University of L'Aquila, Italy, with a dissertation on "Growth and Characterization of Graphene" (Dec 2013). His research activity focuses on the interaction of light with 2D materials. In collaboration with ICFO, The Institute of Photonic Sciences in Barcelona (Spain), he studies the use of chemically functionalized graphene for opto-electronic applications, ranging from transparent and flexible electrodes to atomically-thin photodetectors. Adolfo also designed and built several experimental instruments used in his research. He is active in the field of Outreach and Scientific Communication through personal projects and collaborations.

Xinming Hu: Metal and Nitrogen Doped Porous Carbon Electrocatalysts for CO2 Reduction

posted 14 Jun 2017, 00:48 by Peter Boggild

Xin-Ming Hu, Halvor H. Hval, Steen U. Pedersen, and Kim Daasbjerg
Carbon Dioxide Activation Center (CADIAC), Interdisciplinary Nanoscience Center (iNANO), Aarhus University. Gustav Wieds Vej 14, 8000 Aarhus C, Denmark

Metalloporphyrins immobilized on carbon materials have been proved to be catalytically active for CO2 electroreduction in neutral water.[1-2] The porous carbon materials installed with metalloporphyrin-like structures are expected to be more promising due to their large surface area, high conductivity, and good chemical stability.[3] In this work, we prepared a series of transition metal and nitrogen co-doped carbon materials (M-N-C) via silica-templated pyrolysis. The resulting M-N-C features porous and metalloporphyrin-like structures. Of the materials studied, the Ni-N-C exhibits the highest Faradiac efficiency (91%) for CO2-to-CO conversion at an overpotential of 450 mV, while the Fe-N-C shows the highest current density (3.5 mA cm^-2) associated with a decent Faradiac efficiency (81%) for CO production. The acid leaching and cyanide poisoning experiments verify that the atomically dispersed metal centers embedded in the carbon platform are the origin of the catalytic activity. Importantly, the performance of the M-N-C electrocatalyst for CO2 reduction differs substantially from that of the corresponding metalloporphyrin immobilized on carbon materials. This may be attributed to the different coordination environment of the metal in M-N-C compared with that of the molecular metalloporphyrin.

1. Maurin, A.; Robert, M. J. Am. Chem. Soc. 2016, 138, 2492−2495.
2. Hu, X.-M.; Rønne, M. H.; Pedersen, S. U.; Skrydstrup, T.; Daasbjerg, K. Angew. Chem. Int. Ed. 2017, 56, 6468-6472.
3. Liang, H. W.; Bruller, S.; Dong, R. H.; Zhang, J.; Feng, X. L.; Mullen, K. Nat. Commun. 2015, 6, 7992.

Xinming Hu is currently a postdoctoral fellow at Carbon Dioxide Activation Center (CADIAC), Interdisciplinary Nanoscience Center (iNANO), Aarhus University. His research interest is to explore porous and/or surface-attached materials for electrocatalytic CO2 reduction. He received his B.S. degree (2008) in Environmental Science from Nankai University, M.S. degree (2011) in Chemistry from University of Chinese Academy of Sciences, and Ph.D. (2014) in Chemistry from University of Copenhagen where he focused on the synthesis of porous materials for gas adsorption.

Sergey Slizovskiy: Acoustic phonon cooling of Quantum Hall edge states in graphene

posted 2 Jun 2017, 03:28 by Peter Boggild

National Graphene Institute, The University of Manchester, UK

In the integer Quantum Hall effect (QHE) regime, heat in a two-dimensional (2D) electron  gas is carried by electrons in the edge states of Landau levels.
Here we study phonon-emission cooling of such heat-carrying electron at the edge of graphene  at the filling factor and determine the temperature profile extended from a hot spot where Hall current is injected into graphene from a metallic contact. Our calculations, performed for a mechanically free edge of graphene coupled by van der Waals forces to a substrate shows that losses in chiral heat transportobserved by Nahm, Hwang and Lee [PRL 110, 226801 (2013)] can be attributed to the phonon cooling mechanism.

Sergey Slizovskiy is currently a postdoctoral member of theory group of Prof. V.Fal'ko at National Graphene Institute, The University of Manchester, UK. He is interested in electronic properties of 2D materials, Quantum Hall Effect devices, topological insulators, edge states, Dirac and Weyl semimetals, topological Lifshitz transitions in interacting systems.  He received his B.S. and M.S. degrees in theoretical physics from Saint-Petersburg State University and a PhD in physics from Uppsala University where he studied instantons and non-perturbative effects in Yang-Mills theory and topological field theories. After finishing his PhD, he spent 5 years in Loughborough University studying interacting electronic systems with strong spin fluctuations   and  graphene in magnetic field. His awards include EPSRC post-doctoral fellowship, PhD stipend of Russian non-commercial foundation Dynasty  and RFBR (Russia) grants.

Mattia Scardamaglia: Spectroscopic observation of oxygen dissociation on nitrogen-doped graphene

posted 2 Jun 2017, 02:23 by Peter Boggild

1 Chemistry of Interaction Plasma Surface (ChIPS), University of Mons, Belgium
2 University of Vienna, Faculty of Physics, Boltzmanngasse 5, A-1090 Vienna, Austria
3 Elettra Sincrotrone Trieste, Strada Statale 14 km 163.5, 34149 Trieste, Italy

Carbon nanomaterials’ reactivity towards oxygen is very poor, limiting their potential applications. However, nitrogen doping is an established way to introduce active sites that facilitate interaction with gases. This boosts the materials’ reactivity for bio-/gas sensing and enhances their catalytic performance for the oxygen reduction reaction [1]. Despite this interest, the role of differently bonded nitrogen dopants in the interaction with oxygen is obscured by experimental challenges and has so far resisted clear conclusions. We study the interaction of molecular oxygen with graphene doped via nitrogen plasma by in situ high-resolution synchrotron techniques [2], supported by density functional theory core level simulations. The interaction leads to oxygen dissociation and the formation of carbon-oxygen single bonds on graphene, along with a band gap opening and a rounding of the Dirac cone. The change of the N 1s core level signal indicates that graphitic nitrogen is involved in the observed mechanism: the adsorbed oxygen molecule is dissociated and the two O atoms chemisorb with epoxy bonds to the nearest carbon neighbours of the graphitic nitrogen [3]. Our findings help resolve existing controversies and offer compelling new evidence of the oxidation reduction reaction pathway.

[1] Liu, X., Dai, L. (2016) Nat. Rev. Mater., 1, 16064.
[2] Scardamaglia, M. et al., (2016) 2D Mater., 3, 11001.
[3] Scardamaglia, M. et al., (2017) Submitted

Born in Rome, Italy, Mattia Scardamaglia received his Ph.D. in Materials Science (2012) from Sapienza University studying the growth morphology, electronic properties and interaction of organo-metallic molecules adsorbed on graphene. After moving to Belgium for a postdoc at the University of Mons, he received funding for a three-years project from the Fund for Scientific Research FNRS (2015). His main interests are mostly devoted to the heteroatom doping and characterization of carbon nanotubes and graphene by means of synchrotron-based spectromicroscopy techniques.

Emil Tveden Bjerglund: Efficient graphene production by combined bipolar electrochemical intercalation and high-shear exfoliation

posted 2 Jun 2017, 02:10 by Peter Boggild

Emil Tveden Bjerglund†, Michael Ellevang Pagh Kristensen†∥, Samantha Stambula‡, Gianluigi A. Botton‡§#, Steen Uttrup Pedersen†*, and Kim Daasbjerg†*

† Carbon Dioxide Activation Center. Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark 
‡ Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4L8, Canada
§ Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L9S 4M1
# Canadian Centre for Electron Microscopy, McMaster University, Hamilton, Ontario, Canada L8S 4M1
∥ Radisurf Aps, Arresøvej 5B, 8240 Risskov, Denmark

A multitude of bulk graphene production approaches exists, wherein electrochemical exfoliation has shown promising results for large scale production of high quality graphene suspensions. In this study, we demonstrate that bipolar electrochemistry is a viable strategy for ‘wireless’ electrochemical intercalation of graphite flakes as a true bulk process. Expansion of the graphite layers leads to a dramatic 20-fold increase in the yield of subsequent high-shear exfoliation. Large graphite flakes are readily exfoliated in a yield of 17.6 ± 0.2% when exposed to bipolar electrochemical intercalation followed by high-shear exfoliation. Successful graphene production was confirmed by Raman spectroscopy and scanning transmission electron microscopy, showing that the graphene flakes are 0.4–1.5 µm in size with the majority of flakes consisting of 4–6 graphene layers. Moreover, a low intensity of the D peak relative to the G peak as expressed by the ID/IG ratio in Raman spectroscopy along with high-resolution TEM images reveals that the graphene sheets are essentially undamaged by the electrochemical intercalation. In general, the bipolar electrochemical exfoliation method provides a pathway for intercalation on a wider range of graphite substrates and enhances the efficiency of the exfoliation. The method could be combined with electrochemical functionalization to provide graphene that is specifically designed for a given composite on a larger scale.

Emil Tveden Bjerglund is currently a Ph.d.-student in the Organic Surface Chemistry group under the supervision of Kim Daasbjerg and Steen Uttrup Pedersen. He recieved his B.Sc. degree in nanoscience in 2013 and his M.Sc. in nanoscience in 2016, both from Aarhus University. His interests are electrochemical production and functionalisation of graphene materials for polymer composites.

Bjarke Jørgensen: Graphene based broadband photodetectors for food inspections

posted 1 Jun 2017, 08:24 by Peter Boggild

Newtec Engineering A/S, Denmark

Today, farmers and food producers optimize production value by sorting products on parameter such as size, surface quality and weight. This approach unfortunately only reveals information on physical properties of the produce, while valuable biochemical information, such as information about sugar-, starch- and amino acid-content, is not taken into account. Hyperspectral imaging in the near- and short wavelength infrared (SWIR) region can reveal this type information [1]. However, existing SWIR imaging sensors are expensive, fragile and provide only relatively low spatial resolution. Graphene-quantum-dot hybrid photodetectors show great promise for such imaging applications, as large responsivities may be achieved over a broad spectral range [2]. We have recently developed a simple platform to investigate such detectors and are currently trying to optimize and scale up toward imaging applications.  At NEWTEC we have for the last six years been studying graphene, while insisting to keep a broad vision in our approach, as we see a large potential for graphene, and other two-dimensional materials, to make a significant impact on the industry. Up until now, we have established valuable insights in terms of graphene production, both from bottom up and top-down principles. Graphene synthesis on Cu by CVD as well as graphene transfer and quantum dot synthesis is routinely performed in-house.

[1] Kjær, A. et al. Prediction of Starch, Soluble Sugars and Amino Acids in Potatoes (Solanum tuberosum L.) Using Hyperspectral Imaging, Dielectric and LF-NMR Methodologies. Potato Res. 59, 357–374 (2016).
[2] Goossens, S. et al. Broadband image sensor array based on graphene–CMOS integration. Nat. Photonics 11, 366–371 (2017).

Bjarke Jørgensen is Head of Research at Newtec Engineering A/S. His research focuses on developing methods for food inspection based on impedance spectroscopy, dielectric spectroscopy and hyperspectral imaging. The research and development team at Newtec Engineering has for the last six years been focusing on the synthesis, functionalization and structuring of graphene in order to explore the potential use of this novel material for future applications.    

Luca Camilli: Self-assembly of ordered graphene nanodot arrays

posted 31 May 2017, 01:48 by Peter Boggild

Luca Camilli(1), Jakob Jørgensen(2), Jerry Tersoff(3), Adam Stoot(1), Richard Balog(2), Andrew Cassidy(2),
Jerzy T. Sadowski(4), Peter Bøggild(1) & Liv Hornekær(2)
1 Center for Nanostructured Graphene (CNG), DTU Nanotech, Technical University of
Denmark, DK-2800, Kongens Lyngby, Denmark
2 Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
3 IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, USA
4 Center for Functional Nanomaterials, Brookhaven National Lab, Upton, New York 11973,

The ability to fabricate nanoscale domains of uniform size in two-dimensional (2D) materials could potentially enable new applications in nanoelectronics and the development of innovative metamaterials. However, achieving even minimal control over the growth of 2D lateral heterostructures at such extreme dimensions has proven exceptionally challenging. Here we show the spontaneous formation of ordered arrays of graphene nano-domains (dots), epitaxially embedded in a 2D boron-carbon-nitrogen alloy [1]. These dots exhibit a strikingly uniform size of 1.6nm ± 0.2nm and strong ordering, and the array periodicity can be tuned by adjusting the growth conditions. We explain this behaviour with a model incorporating dot-boundary energy, a moiré-modulated substrate interaction, and long-range repulsion between dots. This new 2D material, which theory predicts to be an ordered composite of uniform-size semiconducting graphene quantum dots laterally integrated within a larger-bandgap matrix, holds promise for novel electronic and optoelectronic properties, with a variety of potential device applications.

[1] Camilli L. et al., Nature Communications 2017, in press

Luca Camilli is currently a Marie Curie Fellow at the Danish Technical University (Denmark). His research focuses on growth and electronic characterization of 2D materials and their heterostructures. He received his M.S. degree in Materials Science and Technology (2009) and a Ph.D. in Physics (2012) from the University of Rome "Tor Vergata" (Italy), where he was working with carbon nanotubes. After finishing his Ph.D, he spent 6 months as a postdoctoral researcher in the Laboratory of Condensed Matter Physics at the University of Rome "Tor Vergata", before joining the group of Dr. P. Sutter at Brookhaven National Laboratory (USA), where he started working with 2D materials. After one year, he joined the group of Prof. P. Bøggild at the Danish Technical University (Denmark). His awards include a DFF Mobilex postdoctoral fellowship and the Marie Curie Independent European Fellowship (MC-IEF

Patrick R. Whelan: electrical continuity mapping of graphene by terahertz spectroscopy

posted 30 May 2017, 09:16 by Peter Boggild

DTU Nanotech, Technical University of Denmark, Ørsteds Plads 345B, DK-2800 Kongens Lyngby, Denmark.

Large-area characterization of the electrical properties of graphene is of utmost importance in order for graphene to break into the market for transparent conducting electrodes. Terahertz time-domain spectroscopy (THz-TDS) is a non-contact method that can be used to spatially measure electrical properties such as sheet conductance, carrier density, and carrier mobility of graphene. In this talk, I will show that it is possible to gain insights into the spatial distribution of charge carrier scattering mechanisms from THz-TDS and discuss how this relates to the defect density of graphene. Furthermore, I will show examples of how THz-TDS can be used for quality control - for instance by assessing the electrical continuity before graphene is turned into functional devices such as OLEDs. The work has been carried out in collaboration with P. Jepsen, DTU Photonics (Denmark), W. Strupinski, ITME (Poland), C. Huyghebaert, IMEC (Belgium), B. Beyer, Fraunhofer COMEDD (Germany), and A. Ferrari, Cambridge University (UK). 

Patrick R. Whelan is currently a Postdoc in the NanoCarbon group at DTU Nanotech. He primarily works with integration and characterization of large-area graphene with focus on graphene transfers for various applications and THz spectroscopy for non-contact electrical characterization of graphene. He received his BSc in Nanotechnology (2011) and his MSc in Nanophysics (2013) from Aalborg University. He finished his PhD about transfer and characterization of large-area CVD graphene for transparent electrode applications in 2016 at the Technical University of Denmark (DTU Nanotech).

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