Nicolás Agraït
Autonomous University of Madrid
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Featured researches published by Nicolás Agraït.
Nature | 1998
A. I. Yanson; G. Rubio Bollinger; H. E. van den Brom; Nicolás Agraït; J. M. van Ruitenbeek
The continuing miniaturization of microelectronics raises the prospect of nanometre-scale devices with mechanical and electrical properties that are qualitatively different from those at larger dimensions. The investigation of these properties, and particularly the increasing influence of quantum effects on electron transport, has therefore attracted much interest. Quantum properties of the conductance can be observed when ‘breaking’ a metallic contact: as two metal electrodes in contact with each other are slowly retracted, the contact area undergoes structural rearrangements until it consists in its final stages of only a few bridging atoms. Just before the abrupt transition to tunnelling occurs, the electrical conductance through a monovalent metal contact is always close to a value of 2e2/h (≈12.9 Ω−1), where e is the charge on an electron and h is Plancks constant. This value corresponds to one quantum unit of conductance, thus indicating that the ‘neck’ of the contact consists of a single atom. In contrast to previous observations of only single-atom necks, here we describe the breaking of atomic-scale gold contacts, which leads to the formation of gold chains one atom thick and at least four atoms long. Once we start to pull out a chain, the conductance never exceeds 2e2/h, confirming that it acts as a one-dimensional quantized nanowire. Given their high stability and the ability to support ballistic electron transport, these structures seem well suited for the investigation of atomic-scale electronics.
Advanced Materials | 2012
Andres Castellanos-Gomez; Menno Poot; Gary A. Steele; Herre S. J. van der Zant; Nicolás Agraït; Gabino Rubio-Bollinger
We study the elastic deformation of few layers (5 to 25) thick freely suspended MoS2 nanosheets by means of a nanoscopic version of a bending test experiment, carried out with the tip of an atomic force microscope. The Youngs modulus of these nanosheets is extremely high (E = 0.33 TPa), comparable to that of graphene oxide, and the deflections are reversible up to tens of nanometers.
Nature | 1998
Elke Scheer; Nicolás Agraït; J. Cuevas; Alfredo Levy Yeyati; Bas Ludoph; A. Martin-Rodero; Gabino Rubio Bollinger; Jan M. van Ruitenbeek; C. Urbina
Fabrication of structures at the atomic scale is now possible using state-of-the-art techniques for manipulating individual atoms, and it may become possible to design electrical circuits atom by atom. A prerequisite for successful design is a knowledge of the relationship between the macroscopic electrical characteristics of such circuits and the quantum properties of the individual atoms used as building blocks. As a first step, we show here that the chemical valence determines the conduction properties of the simplest imaginable circuit—a one-atom contact between two metallic banks. The extended quantum states that carry the current from one bank to the other necessarily proceed through the valence orbitals of the constriction atom. It thus seems reasonable to conjecture that the number of current-carrying modes (or ‘channels’) of a one-atom contact is determined by the number of available valence orbitals, and so should strongly differ for metallic elements in different series of the periodic table. We have tested this conjecture using scanning tunnelling microscopy and mechanically controllable break-junction techniques, to obtain atomic-size constrictions for four different metallic elements (Pb, Al, Nb and Au), covering a broad range of valences and orbital structures. Our results demonstrate unambiguously a direct link between valence orbitals and the number of conduction channels in one-atom contacts.
Physical Review Letters | 2001
Gabino Rubio-Bollinger; Sune Rastad Bahn; Nicolás Agraït; Karsten Wedel Jacobsen; Sebastian Vieira
A scanning tunneling microscope supplemented with a force sensor is used to study the mechanical properties of a novel metallic nanostructure: a freely suspended chain of single gold atoms. We find that the bond strength of the nanowire is about twice that of a bulk metallic bond. We perform ab initio calculations of the force at chain fracture and compare quantitatively with experimental measurements. The observed mechanical failure and nanoelastic processes involved during atomic wire fabrication are investigated using molecular dynamics simulations, and we find that the total effective stiffness of the nanostructure is strongly affected by the detailed local atomic arrangement at the chain bases.
Applied Physics Letters | 2010
Andres Castellanos-Gomez; Nicolás Agraït; Gabino Rubio-Bollinger
We present a systematic study of the optical contrast of niobium diselenide and molybdenum disulfide flakes deposited onto silicon wafers with a thermally grown silicon oxide layer. We measure the optical contrast of flakes whose thickness, which is obtained by atomic force microscopy, ranges from 200 layers down to a monolayer using different illumination wavelengths in the visible spectrum. The refractive index of these thin crystals has been obtained from the optical contrast using Fresnel law. In this way the optical microscopy data can be quantitatively analyzed to determine the thickness of the flakes in a fast and nondestructive way.
Physical Review Letters | 2002
Nicolás Agraït; Carlos Untiedt; Gabino Rubio-Bollinger; Sebastian Vieira
Electronic transport at finite voltages in free-standing gold atomic chains of up to seven atoms in length is studied at low temperatures using a scanning tunneling microscope. The conductance vs voltage curves show that transport in these single-mode ballistic atomic wires is nondissipative up to a finite voltage threshold of the order of several mV. The onset of dissipation and resistance within the wire corresponds to the excitation of the atomic vibrations by the electrons traversing the wire and is very sensitive to strain.
Advanced Materials | 2013
Andres Castellanos-Gomez; E. Cappelluti; Rafael Roldán; Nicolás Agraït; F. Guinea; Gabino Rubio-Bollinger
This work was supported by MICINN/MINECO (Spain) through the programs MAT2011-25046 and CONSOLIDER-INGENIO-2010 “Nanociencia Molecular” CSD-2007-00010, Comunidad de Madrid through program Nanobiomagnet S2009/MAT-1726 and the European Union (FP7) through the programs RODIN and ELFOS. E.C. acknowledges a Marie Curie Grant, PIEF-GA-2009-251904.
Nano Letters | 2013
Charalambos Evangeli; Katalin Gillemot; Edmund Leary; M. Teresa González; Gabino Rubio-Bollinger; Colin J. Lambert; Nicolás Agraït
We report the measurement of conductance and thermopower of C60 molecular junctions using a scanning tunneling microscope (STM). In contrast to previous measurements, we use the imaging capability of the STM to determine precisely the number of molecules in the junction and measure thermopower and conductance continuously and simultaneously during formation and breaking of the molecular junction, achieving a complete characterization at the single-molecule level. We find that the thermopower of C60 dimers formed by trapping a C60 on the tip and contacting an isolated C60 almost doubles with respect to that of a single C60 and is among the highest values measured to date for organic materials. Density functional theory calculations show that the thermopower and the figure of merit continue increasing with the number of C60 molecules, demonstrating the enhancement of thermoelectric preformance by manipulation of intermolecular interactions.
Nanoscale Research Letters | 2012
Andres Castellanos-Gomez; Menno Poot; Gary A. Steele; Herre S. J. van der Zant; Nicolás Agraït; Gabino Rubio-Bollinger
We fabricate freely suspended nanosheets of molybdenum disulphide (MoS2) which are characterized by quantitative optical microscopy and high-resolution friction force microscopy. We study the elastic deformation of freely suspended nanosheets of MoS2 using an atomic force microscope. The Youngs modulus and the initial pre-tension of the nanosheets are determined by performing a nanoscopic version of a bending test experiment. MoS2 sheets show high elasticity and an extremely high Youngs modulus (0.30 TPa, 50% larger than steel). These results make them a potential alternative to graphene in applications requiring flexible semiconductor materials.PACS, 73.61.Le, other inorganic semiconductors, 68.65.Ac, multilayers, 62.20.de, elastic moduli, 81.40.Jj, elasticity and anelasticity, stress-strain relations.
Nano Letters | 2008
Joshua Hihath; Carlos R. Arroyo; Gabino Rubio-Bollinger; Nongjian Tao; Nicolás Agraït
Presented here is a study of electron-phonon interactions in a single molecule junction where the molecule is covalently connected to two electrodes. In this system, vibration modes in a single molecule junction are measured by sweeping the bias voltage between the two electrodes and recording the differential conductance while the strain in the junction is changed by separating the two electrodes. This unique approach allows changes in conductance to be compared to changes in the configuration of a single molecule junction. This system opens a new door for characterizing single molecule junctions and a better understanding of the relationship between molecular conductance, electron-phonon interactions, and configuration.