ALBERT

Description: In graphene-based electronic devices like in transistors, the field effect applied thanks to a gate electrode allows tuning the charge density in the graphene layer and passing continuously from the electron to the hole doped regime across the Dirac point. Homogeneous doping is crucial to understand electrical measurements and for the operation of future graphene-based electronic devices. However, recently theoretical and experimental studies highlighted the role of the electrostatic edge due to fringing electrostatic field lines at the graphene edges [P. Silvestrov and K. Efetov, Phys. Rev. B 77 , 155436 (2008); F. T. Vasko and I. V. Zozoulenko, Appl. Phys. Lett. 97 , 092115 (2010)]. This effect originates from the particular geometric design of the samples. A direct consequence is a charge accumulation at the graphene edges giving a value for the density, which deviates from the simple picture of a plate capacitor and also varies along the width of the graphene sample. Entering the quantum Hall regime would, in principle, allow probing this accumulation thanks to the extreme sensitivity of this quantum effect to charge density and the charge distribution. Moreover, the presence of an additional and counter-propagating edge channel has been predicted [P. Silvestrov and K. Efetov, Phys. Rev. B 77 , 155436 (2008)] giving a fundamental aspect to this technological issue. In this article, we investigate this effect by tuning a high mobility graphene wire into the quantum Hall regime in which charge carriers probe the electrostatic potential at high magnetic field close to the edges. We observe a slight deviation to the linear shift of the quantum Hall plateaus with magnetic field and we study its evolution for different filling factors, which correspond to different probed regions in real space. We discuss the possible origins of this effect including an increase of the charge density towards the edges.

Description: Over the past two decades, single-walled carbon nanotubes (SWCNTs) have received much attention because their extraordinary properties are promising for numerous applications. Many of these properties depend sensitively on SWCNT structure, which is characterized by the chiral index (n,m) that denotes the length and orientation of the circumferential vector in the hexagonal carbon lattice. Electronic properties are particularly strongly affected, with subtle structural changes switching tubes from metallic to semiconducting with various bandgaps. Monodisperse 'single-chirality' (that is, with a single (n,m) index) SWCNTs are thus needed to fully exploit their technological potential. Controlled synthesis through catalyst engineering, end-cap engineering or cloning strategies, and also tube sorting based on chromatography, density-gradient centrifugation, electrophoresis and other techniques, have delivered SWCNT samples with narrow distributions of tube diameter and a large fraction of a predetermined tube type. But an effective pathway to truly monodisperse SWCNTs remains elusive. The use of template molecules to unambiguously dictate the diameter and chirality of the resulting nanotube holds great promise in this regard, but has hitherto had only limited practical success. Here we show that this bottom-up strategy can produce targeted nanotubes: we convert molecular precursors into ultrashort singly capped (6,6) 'armchair' nanotube seeds using surface-catalysed cyclodehydrogenation on a platinum (111) surface, and then elongate these during a subsequent growth phase to produce single-chirality and essentially defect-free SWCNTs with lengths up to a few hundred nanometres. We expect that our on-surface synthesis approach will provide a route to nanotube-based materials with highly optimized properties for applications such as light detectors, photovoltaics, field-effect transistors and sensors.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sanchez-Valencia, Juan Ramon -- Dienel, Thomas -- Groning, Oliver -- Shorubalko, Ivan -- Mueller, Andreas -- Jansen, Martin -- Amsharov, Konstantin -- Ruffieux, Pascal -- Fasel, Roman -- England -- Nature. 2014 Aug 7;512(7512):61-4. doi: 10.1038/nature13607.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] nanotech@surfaces Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dubendorf, Switzerland [2] Nanotechnology on Surfaces Laboratory, Instituto de Ciencia de Materiales de Sevilla (CSIC-US), Avenida Americo Vespucio 49, E-41092 Sevilla, Spain (J.R.S.-V.); BASF SE, GVM/I-L 544, 67056 Ludwigshafen, Germany (A.M.); University Erlangen-Nuremberg, Institut fur Organische Chemie II, Henkestrasse 42, 91054 Erlangen, Germany (K.A.). ; nanotech@surfaces Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dubendorf, Switzerland. ; Laboratory for Reliability Science and Technology, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dubendorf, Switzerland. ; 1] Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany [2] Nanotechnology on Surfaces Laboratory, Instituto de Ciencia de Materiales de Sevilla (CSIC-US), Avenida Americo Vespucio 49, E-41092 Sevilla, Spain (J.R.S.-V.); BASF SE, GVM/I-L 544, 67056 Ludwigshafen, Germany (A.M.); University Erlangen-Nuremberg, Institut fur Organische Chemie II, Henkestrasse 42, 91054 Erlangen, Germany (K.A.). ; Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany. ; 1] nanotech@surfaces Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dubendorf, Switzerland [2] Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25100481" target="_blank"〉PubMed〈/a〉

Description: A two-dimensional (2D) porous layer can make an ideal membrane for separation of chemical mixtures because its infinitesimal thickness promises ultimate permeation. Graphene--with great mechanical strength, chemical stability, and inherent impermeability--offers a unique 2D system with which to realize this membrane and study the mass transport, if perforated precisely. We report highly efficient mass transfer across physically perforated double-layer graphene, having up to a few million pores with narrowly distributed diameters between less than 10 nanometers and 1 micrometer. The measured transport rates are in agreement with predictions of 2D transport theories. Attributed to its atomic thicknesses, these porous graphene membranes show permeances of gas, liquid, and water vapor far in excess of those shown by finite-thickness membranes, highlighting the ultimate permeation these 2D membranes can provide.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Celebi, Kemal -- Buchheim, Jakob -- Wyss, Roman M -- Droudian, Amirhossein -- Gasser, Patrick -- Shorubalko, Ivan -- Kye, Jeong-Il -- Lee, Changho -- Park, Hyung Gyu -- New York, N.Y. -- Science. 2014 Apr 18;344(6181):289-92. doi: 10.1126/science.1249097.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Nanoscience for Energy Technology and Sustainability, Department of Mechanical and Process Engineering, Eidgenossische Technische Hochschule (ETH) Zurich, Sonneggstrasse 3, CH-8092 Zurich, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24744372" target="_blank"〉PubMed〈/a〉