Peter Blake: Graphene and Boron Nitride hybrid structures

posted 8 Aug 2011, 06:48 by Peter Bøggild

Graphene and hexagonal boron nitride (hBN) are certainly interesting materials in their own rights, but combinations of the two can be more appealing. For example, when hBN is used as a substrate for graphene instead of silicon oxide, carrier mobilities increase 10-fold, giving mean free paths of over 1μm at room temperature. In double layer graphene devices, hBN can serve as an ultra-thin insulator between the two graphene layers - isolating them electrically, but allowing the layers to remain coupled via Coulomb interactions. Such hBN/graphene heterostructures may allow a variety of phenomena including exciton condensation.

This talk will describe the optical and Raman signatures [1] used for identifying mono- & few-layer hBN flakes and the subsequent steps for fabricating graphene/hBN devices. We will look at transport results from these devices that show a range of effects including tunnelling, micrometer-scale ballistic transport [2] and Coulomb drag.

[1] Gorbachev et al., Hunting for Monolayer Boron Nitride: Optical and Raman Signatures, Small (2011), http://dx.doi.org/10.1002/smll.201001628
[2] Mayorov et al., Micrometer-Scale Ballistic Transport in Encapsulated Graphene at Room Temperature, Nano Letters (2011), http://dx.doi.org/10.1021/nl200758b

Peter Blake is the Managing Director of Graphene Industries and a postdoctoral researcher in the Condensed Matter Physics Group at the University of Manchester. Since 2004, he has been studying the optical & electronic properties of graphene and developing related micro-fabrication procedures. He is currently exploring potential uses of graphene for transparent conductive coating and membrane applications.

Hugh Churchill: Dispersive readout of as-grown carbon nanotube double quantum dots

posted 5 Aug 2011, 06:22 by Peter Bøggild

Department of Physics, Harvard University, 11 Oxford St. Cambridge MA, US

This talk will describe the fabrication and measurement of carbon nanotube quantum dot devices designed to satisfy the requirements of spin qubit applications. These requirements include low disorder for reliable access to the few-electron regime, detection of charge states, and rapid manipulation with multiple gates. Low disorder is achieved by completing all lithography steps prior to nanotube growth; however, this fabrication method is incompatible with charge detection using proximal charge sensors. We eliminate the need for dedicated charge sensors by demonstrating multiplexed dispersive readout of charge states. In this approach, superconducting resonators are attached to a gate and both leads of the quantum dot to enable reflectometry measurements.

Hugh Churchill is a PhD candidate in the group of Charles Marcus at Harvard University. His research has focused on quantum transport measurements of carbon nanotube and Ge/Si nanowire quantum dot devices, with a particular emphasis on charge detection schemes in these systems.

Vladimir Fal'ko: Graphene optics and magnetooptics

posted 20 Jul 2011, 08:24 by Peter Boggild

Department of Physics, Lancaster University, Lancaster LA1 4YB, UK

Optical properties of graphene will be reviewed, including the manifestation of chiral properties of electrons in ARPES, absorption of light by monolayers and bilayers, and magnetooptics. Signature of electronic excitations in Raman and theory of magnetophonon resonance will be discussed, with reference to recent experimental observations.

Vladimir Falko is Distinguished Professor and Head of Theory Division at Physics Department, Lancaster University. He works on theory of low-dimensional electronic materials, quantum transport in mesoscale systems, and fundamentals of nanoelectronics. Since 2005, his main interest lies in modelling physical properties of graphene and graphene-based devices.

Francesco Bonaccorso: Solution processing of carbon nanomaterials for photonics and optoelectronics

posted 20 Jul 2011, 03:19 by Peter Bøggild

Department of Engineering, University of Cambridge, Cambridge CB3 0FA, UK

The introduction of new, low cost nanomaterials, including graphene, Single Wall Nanotubes (SWNTs) and nanodiamonds, is set to have a disruptive impact on current products based on conventional materials, not only because of cost/performance advantages, but also because they can be manufactured in more flexible ways, suitable for a growing range of applications. In particular, the ability to manipulate the structure and composition of these carbon nanomaterials opens huge opportunities to create new products and devices with superior performance. Here I will review the main approaches to solution process carbon nanomaterials. I will first discuss how to achieve chirality-controlled SWNT dispersions [1,2] via Density Gradient Ultracentrifugation (DGU)[2]. I will then show how this technique can be extended to graphite processing [3] to produce graphene flakes of controlled number of layers[4] and dimensions[5]. A fracture mechanics model is presented to explain the exfoliation process via sonication, in order to optimise it and produces flakes with controlled dimensions[5,6]. I will show how DGU can also be used for sorting nanodiamonds in terms of shape and dimensions. These approaches for nanocarbons processing are general, and can be applied to all layered materials, such as Boron Nitride, Tungsten Disulfide, Molybdenum Disulfide[7].  The nanocarbon dispersions produced using the above mentioned approaches, are used to fabricate composites and thin films for application in photonics and optoelectronics [8]. In particular, I will discuss the application of nanotube and graphene composites and films in fully flexible transparent conductors[8], liquid crystal based smart windows[8], dye sensitized solar cells [8], and ultrafast lasers[9,10,11]. 

1. F. Bonaccorso, et al. J. Phys. Chem. C, 114, 17267, (2010). 
2. M.C. Arnold et al. Nature Nanotech.1, 60, (2006)
3. Y. Hernandez, et al. Nature Nanotech. 3, 563 (2008).
4. A. A. Green, M. C. Hersam, Nano Lett. 9, 4031, (2009).
5. O. M. Maragò, et al. ACS Nano 4, 7515, (2010)
6. T. Hasan, et al. Physica Status Solidi B, 247, 2953, (2010).
7. J.N. Coleman et al. Science 331, 568, (2011).
8. F. Bonaccorso, et al. Nature Photon. 4, 611, (2010). 
9. T. Hasan, et al. Advanced Materials 21, 3874, (2009).
10. Z. Sun, et al. ACS Nano, 4, 803 (2010). 11. F. Wang, et al. Nature Nanotech.3, 738, (2008).

Francesco Bonaccorso gained a PhD from the Department of Physics, 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 the Engineering Department of Cambridge University, and elected to a Research Fellowship at Hughes Hall, Cambridge. He is currently Honorary Research Convenor at Hughes Hall and research associate at the nanomaterials spectroscopy group (NMS) in the Department of Engineering, Cambridge University. His research interests encompass solution processing of carbon nanomaterials (such as graphene, nanotubes and nanodiamonds), their spectroscopic characterization, incorporation into polymer composites and application in solar cells, light emitting devices, smart windows and touch-screens.

Saad A Hasan: Controlling Noncovalent Interactions in Chemically Modified Graphene

posted 20 Jul 2011, 00:42 by Kasper Nørgaard

University of Uppsala, Sweden

Chemically modified graphene can be a platform to investigate noncovalent interactions (electrostatic forces, van der Waals forces, pi-pi stacking, etc.) with potential technological applications. In this presentation, I will briefly review chemical methods to isolate and form graphene with a focus on the highly versatile graphene oxide, which is derived from graphite. For graphene oxide sheets suspended in water, the balance between repulsive electrostatic and attractive van der Waals forces can be mediated by pH. In the presence of an electric field, these interactions can be directed to produce multilayered films with vastly different surface wetting characteristics. 

Graphene oxide can be simultaneously reduced to graphene and functionalized with groups such as amines via solvothermal reactions. We have found that a simple hydrothermal reaction with ammonia can be used to accomplish both. The evolution of the structure and surface charge can be observed in accordance with the reaction time. The newly introduced basic groups in this nitrogen-doped graphene (NDG) shift its isoelectric point to higher pH values. Thus, interesting assemblies could be formed in a range of moderate pH values. The widely tunable surface charge and graphitic character of these graphene materials suggest they may be useful in some unconventional settings. I will discuss applications in catalysis and encapsulation on the basis of controlling electrostatic and pi-pi stacking interactions in these graphene materials.

Saad A. Hasan is a researcher at Uppsala University in Sweden. His research focuses on the chemical modification of graphene coupled with their assembly and use as templates. Saad is also developing a joint project with partners in the United States to study the biomolecule interactions of oxygen- and nitrogen-functionalized graphenes. He completed his PhD in 2010 at Vanderbilt University (Nashville, USA).

Thomas Sand Jespersen: Spin-orbit coupling in multielectron carbon nanotube quantum dots

posted 19 Jul 2011, 03:39 by Peter Bøggild

Niels Bohr Institute, Nanophysics. Universitetsparken 5, Copenhagen Ø, Denmark. 

The coupling of the spin of electrons with their orbital motion is a central theme in quantum dot research. For carbon nanotubes the coupling was overlooked in the first decade of experiments. Recently, spin-orbit interactions were observed in a disorder-free few-electron quantum dot [1]. Here we demonstrate the spin-orbit coupling in the general multielectron regime (0-200) and in the presence of finite disorder [2].

The spin-orbit coupling is found to depend on the electron occupation of the dot in a systematic manner that follows from the curvature induced spin-orbit splitting of the Dirac cones for graphene. The modified spectrum is fully accounted for by a single-particle model. 

[1] F. Kuemmeth et al, Nature 452, 448 (2008). 
[2] T.S. Jespersen, K. Grove-Rasmussen et al, Nature Physics 7, 348 (2011)

Thomas Sand Jespersen obtained his masters degree in 2003 in physics from the Niels Bohr Institute and University of California, Berkeley, and obtained his PhD degree in 2007 from NBI and Harvard university, entitled  "Electron Transport in Semiconductor Nanowires and Electrostatic Force Microscopy on Carbon Nanotubes". He is currently assistant professor at Niels Bohr Institute, University of Copenhagen, working with low-temperature quantum transport in carbon nanotubes and semiconductor nanowires. His current interests include topological insulators and Majorana modes, spin-orbit effects (the relativistic coupling of the electron spin to its orbital motion) in carbon nanotubes and InAs nanowires, single-spin control in InAs nanowires and carbon nanotubes using electric fields, physics of superconductor/quantum dot/superconductor devices, where the quantum dot is usually formed in nanowires or nanotubes, (Universal) conductance fluctuations and Kondo physics in nanowires and scanning probe investigations and Raman spectroscopy of nano structures (nanowires, nanotubes, graphene).

Pagona Papakonstantinou: Metal free graphene as electrocatalysts for fuel cells

posted 18 Jul 2011, 01:04 by Peter Bøggild

Nanotechnology and Advanced Materials Research Institute, University of Ulster, Newtownabbey BT37 0QB, UK, p.papakonstantinou@ulster.ac.uk

Today, proton exchange membrane fuel cells (PEMFCs), which use hydrogen fuel and oxygen from the air to produce electricity and just pure water as the only reaction by-product, are considered a key enabling technology for replacing internal combustion engines for automotive industry. However, the prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of current PEMFC technology. Recently, several breakthroughs have occurred, by the introduction of surface heteroatoms (e.g., nitrogen) into carbon nanomaterials such as carbon nanotubes and graphene, with their performance approaching, that of platinum-based systems. The talk will highlight our recent findings on new synthesis methods of nitrogen doped electrocatalysts for ORR and will critically review recent activity and understanding that have led to these breakthroughs

Pagona Papakonstantinou is a Professor of Advanced Materials at the School of Engineering of the University of Ulster. Currently her group specializes on the fabrication and functionalization of low dimensional carbon based nanomaterials (carbon nanotubes. graphene, diamond nanorods) the characterization of their unique physical and physicochemical properties and the demonstration of these materials in biological sensing and energy areas. Research efforts are directed on engineering the structure of these carbon based nanomaterials and probing the local atomic environment by synchrotron light in view of understading their properties. In a series of papers the details of the interaction of foreign molecules such as nitrogen, oxygen and chlorine with the graphene lattice have been investigated by synchrotron based spectroscopies (NEXAFS, PEEM, XPS, VB). Pagona serves/(d) on various committees including Diamond Synchrotron Light Source, EPSRC College Panel(s), Royal Society International grants and National Access Programme (SFI) at Tyndall Institute in Cork. She is author or coauthor of more than 75 scientific papers and is recipient of a Leverhulme Trust Senior Research Fellowship (2011) from the Royal Academy of Engineering.

Arkady Krasheninnikov: Tailoring the atomic and electronic structure of 2D carbon and boron-nitride materials by electron and ion beams

posted 12 Jul 2011, 14:46 by info admin

Recent experiments (see Refs. [1,2] for an overview) on ion and electron bombardment of nanostructures demonstrate that irradiation can have beneficial effects on such targets and that electron or ion beams can serve as tools to change the morphology and tailor mechanical, electronic and even magnetic properties of various nanostructured materials.

We systematically study irradiation effects in nanomaterilas, including two-dimensional (2D) systems like graphene and hexagonal boron-nitride (h-BN) sheets. By employing various atomistic models ranging from empirical potentials to time-dependent density functional theory we simulate collisions of energetic particles with 2D nanostructures and calculate the properties of the systems with the irradiation-induced defect.

In this talk, our latest theoretical results on the response of graphene [3,4] and h-BN [5] to irradiation will be presented, combined with the experimental results obtained in collaboration with several groups. The electronic structure of defected graphene sheets with adsorbed transition metal atoms will be discussed, and possible avenues for tailoring the electronic and magnetic structure of graphene by irradiation-induced defects and impurities will be introduced. The effects of electron irradiation on boron-nitride sheets and nanotubes will also be touched upon. Finally, we will discuss [6] how electron irradiation and electron beam-assisted deposition can be used for engineering hybrid BN-C nanosystems by substituting B and N atoms with carbon with a high spatial resolution.

[1] A. V. Krasheninnikov and F. Banhart, Nature Materials, 6 (2007) 723.
[2] A.V. Krasheninnikov and K. Nordlund, Appl. Phys. Rev., 107 (2010) 071301.
[3] J. Kotakoski, A. V. Krasheninnikov, U, Kaiser, and J. Meyer, Phys. Rev. Lett. 106 (2011) 105505.
[4] J. Kotakoski, J. C. Meyer, S. Kurasch, D. Santos-Cottin, U. Kaiser and A. V. Krasheninnikov, Phys. Rev. B 83 (2011) 245420.  
[5] J. Kotakoski, C. H. Jin, O. Lehtinen, K. Suenaga, and A. V. Krasheninnikov, Phys. Rev. B 82 (2010) 113404.
[6] N. Berseneva, A. V. Krasheninnikov, and R.M. Nieminen, Phys. Rev. Lett. (2011) in press.

Arkady Krasheninnikov, Department of Physics, University of Helsinki, Finland, Department of Applied Physics, Aalto University, Finland. arkady.krasheninnikov@helsinki.fi. 
Docent degree from University of Helsinki, 2005. Senior scientist, Accelerator Laboratory, University of Helsinki and Researcher, Laboratory of Physics, Helsinki University of Technology. Ph.D. Degree in Physics (Solid State Physics), Moscow State Engineering Physics Institute, 1995.  Thesis "The effect of defects and nonmagnetic impurities on the superconducting correlations with s- and d- symmetry in high-temperature superconductors". 15 years of experience in Computer simulations in irradiation effects in solids; Electronic structure calculations at the DFT and tight-binding levels of theory; Empirical-potential atomistic simulations;  Effects of ion irradiation on carbon nanostructures; Simulation of scanning tunneling microscopy (STM) images; theory of STM; Theoretical investigation of semiconductor nanosystems, including resonant-tunneling structures, quantumcascade lasers and nano-scale quantum devices for nanocomputing; Quantum computing in solid-state systems;  Theoretical study and computer modeling of the influence of radiation defects and impurities on both normal and superconducting properties of superconductors; Strongly correlated systems; exact diagonalization of finite clusters

Johan Liu: Thermal Management of Electronics Using Carbon Nanotubes

posted 12 Jul 2011, 06:44 by info admin

Electronic systems today generate a large amount of heat due to increased demand in miniaturization and more functionality. According to Eric Pop, out of the total electricity used for running data servers in USA in 2006, Over 50% were used to cool the systems. Similar to the rest of the electronics industry, mobile communication electronics hardware for instance, radio-base stations are also producing a huge amount of heat that has to be dissipated. Next generation radio base stations consist of more than 5-6 DSPs in many cases (each of them produces more than 5-6 W on a size of less than 0,25 cm2) dissipating roughly 30 W per radio base station unit. Locally, the heat intensity can be up to 25-30 W/cm2 in this case. With this constant heat generated, it is obvious that mobile communication electronics industry has also to look for new cooling technologies to manage the heat dissipation.

The above-mentioned is just a few examples of the heat dissipation problems that are facing electronics industry. In fact, heat dissipation provides great challenges in many applications including also automotive electronics, power electronics and LED business sectors. In automotive electronics systems, single device can pump out up to 80 W continuously and in transient stage up to 300 W (within 10 nanoseconds). LED devices can have heat intensity between 1000 and 2000 W/cm2 due to its extremely small size. Therefore, we anticipate that thermal management of heat dissipation will be of strategic importance for the development of many future products.

To cope with this issue, we have developed a number of carbon nanotube thermal management technologies such as dry densification of carbon nanotube bundles, rapid and low temperature transfer of carbon nanotubes using Indium as well as vertical interconnect using Carbon Nanotube based TSV concept for thermal and electrical path. Major publications are Fu et al, Adv. Mat, DOI: 10.1002/adma.201002415, Wang et al, DOI: 10.1002/smll.201100615, Wang et al, DOI: 10.1016/j.carbon.2010.06.042. 

To fully achieve the large potential of carbon nanotubes in thermal control of electronics, progresses in a number of aspects must be made in the future. For the first, we need to investigate the long term reliability of 3 D carbon nanotube thermal dissipation systems and demonstrate this against copper based technology 

Dr Johan Liu graduated with a master and Ph D degree in materials science from the Royal Institute of Technology, Sweden. Before joining Chalmers University of Technology, he served in various positions at the Swedish Institute for Production Research (IVF) as project manager, group leader and division manager. He is currently full professor in electronics production, Department of Microtechnology and Nanoscience in Chalmers University of Technology, Sweden. He is also director of SMIT Center both at Chalmers University of Technology and Shanghai University, China (A joint center between Sweden and China). As a member of the Royal Swedish Academy of Engineering Sciences and a Fellow of IEEE, he has published 2 books, 370 papers in journals, proceedings and 14 book chapters with a Hirsch index of 19 and with an citation of over 1096 times, He has 21 patents accepted or filed and has given about 35 key note/invited talks during the last 20 years. He has also received many awards including IEEE Exceptional Technical Achievement Award, IEEE CPMT Transaction Best paper Award in “Advanced Packaging”. His research field covers mainly nanopackaging materials and process for electronics and MEMS including 3D CNT TSV technology, CNT Cooling technology, CNT Bumping, high temperature stable conductive adhesives, nano soldering, nano thermal interface materials, nanomaterials for thermo-electrical applicatoins and nanoscaffolds for biomedical applications.Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden
SMIT Center and School of Mechatronics and Mechanical Engineering, Shanghai University, China, Email:jliu@chalmers.se

Eleanor Campbell: In situ studies of carbon nanotube growth and the mechanical properties of graphene membranes

posted 12 Jul 2011, 06:03 by Peter Bøggild

In situ spectroscopy has been used to obtain insight into the growth mechanisms of carbon nanotubes and the processes behind the extremely rapid growth that is observed for nanotubes grown on a local micro-scale heater. Studies of local heater growth will be presented and the dependence of the growth kinetics and morphology of the nanotubes on the growth conditions will be shown.  In the second part of the talk, studies of the mechanical properties of graphene membranes, carried out in collaboration with colleagues at Chalmers University, will be shown where the behaviour of membranes under electrostatic actuation will be presented and scanning probe microscopy and Raman spectroscopy has been used to gain insight into the graphene behavior. The studies allow the first determination of the bending rigidity of mono- and few-layer graphene.

Eleanor Campbell obtained her PhD from the University of Edinburgh (1985) and then spent over 20 years working in Germany (Freiburg University and Max Born Institute) and Sweden (Chair of Atomic and Molecular Physics at Gothenburg University) before returning to Edinburgh to take up the Chair of Physical Chemistry in 2007. She is currently also a guest professor in the Division of Quantum Phases and Devices at Konkuk University, Korea. Her research interests range from fundamental studies of the excited state properties of large molecules and clusters in the gas phase to studies of the growth, manipulation and characterization of carbon nanomaterials. She has published over 250 papers and serves/has served on the Editorial Boards of Applied Physics A, Chemical Physics Letters, EPJD and Nano.

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