Estaneno, ¿la revolución que se viene?

Estaneno, ¿la revolución que se viene?Desde el inicio de los tiempos, los materiales fueron de suma importancia para los seres humanos: con ellos, se fabrican las herramientas. Hace poco, un grupo de físicos teóricos,anunció un nuevo material que tendría las propiedades necesarias para revolucionar la industria de los microprocesadores: el estaneno. Una lámina de estaño de un átomo de espesor, con capacidad de mantener la conductividad a temperatura ambiente. Sus creadores sueñan con que pueda reemplazar completamente al silicio en los circuitosintegrados y sea utilizado como cable. ¿Se viene un nuevo nombre para nuestra era

Band gap tuning of layered III-Te materials

Gallium telluride is a layered material with high photoresponse and is very promising for applications in optoelectronic devices such as photovoltaic cells or radiation detectors. We analyze how the properties of thin films of this material scale with its thickness and also study two other proposed materials with the same crystalline structure whose room-temperature stability we verify. We show that electronic band gaps up to 2.16 eV can be obtained by stacking up and/or applying perpendicular electric field to these III-Te monolayers. This form of band gap engineering may be promising for several technological applications.Fil: Olmos Asar, Jimena Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Rocha Leão, Cedric. Universidade Federal Do Abc; BrasilFil: Fazzio, Adalberto. Centro Brasileiro de Pesquisas Físicas; Brasi

Mechanistic Framework for the Formation of Different Sulfur Species by Electron Irradiation of n-Dodecanethiol Self-Assembled Monolayers on Au(111) and Au(100)

The electron-induced damage in self-assembled monolayers (SAMs) of n-dodecanethiolate on Au(111) and Au(100) single-crystalline surfaces is investigated in situ by X-ray photoelectron spectroscopy. The same irradiation dose produced different adsorbed groups. The damage at the headgroup–substrate interface leads to find dialkyl sulfide (RS–R′) on Au(111), while dialkyl disulfide (RS–SR) and/or thiol (RSH) were produced on Au(100). With regard to C species, significant amounts of C═C are generated on Au(111) but not on Au(100), showing that double bond formation is not triggered through the same pathways on these surfaces. Detailed analysis of a variety of mechanisms, which involved cationic (RS+), anionic (RS–), or thiyl radical (RS•) species, in combination with ab initio density functional theory (DFT) calculation, leads to the conclusion that the radical pathways successfully explain the experimental results. Molecular dynamics simulations show that the n-dodecanethiolate SAMs on both surfaces are equivalent with regard to the van der Waals interactions. The breakage of the S–Au bonds is studied by means of DFT calculations. The thiyl radical would form close to the Au(100) surface, making it likely to react with another thiyl radical or thiolate to form the RS–SR species. On the other hand, for Au(111), the thiyl radical would form farther from the surface, reacting with the alkyl chains of neighboring molecules to form RS–R′ species. The mechanistic framework proposed here is very useful to explain the behavior of related systems.This work was supported in part by CONICET (PIP 0333), ANPCyT (PICT 2017-4519), Universidad Nacional de La Plata (UNLP X786) of Argentina, and Universidad Nacional de Cuyo. J.O.-A. and M.M.M. acknowledge financial support from CONICET through Grant PIP 11220150100141CO, FONCyT PICT-2015-2191, and SeCyT UNC. This work has used computational resources from CCAD, Universidad Nacional de Córdoba (http://ccad.unc.edu.ar/) and resources provided by the CYTED co-funded Thematic Network RICAP (517RT0529)

CO on supported Cu nanoclusters: Coverage and finite size contributions to the formation of carbide via the boudouard process

The interaction of carbon monoxide with an ordered array of copper nanoclusters was investigated under ultrahigh vacuum conditions by means of in situ X-ray photoelectron spectroscopy in combination with density functional theory calculations. The Cu clusters were supported on an alumina template grown on the Ni3Al(111) termination. Adsorption and dissociation of carbon monoxide occur at the copper clusters, yielding accumulation of carbidic carbon at the metal particles through the Boudouard process. The involved mechanisms are investigated at the atomic level, unveiling the effects of cluster finite size, reconstruction, support, and of local CO coverage. It is found that the high coverage of CO at the cluster surface, which considerably exceeds that achievable on single crystal surfaces, facilitates the metal restructuring and the reaction, yielding carbon incorporation into the bulk of the particles

Ambient-pressure CVD of graphene on low-index Ni surfaces using methane: A combined experimental and first-principles study

The growth of large area single-layer graphene (1-LG) is studied using ambient pressure chemical vapor deposition on single-crystal Ni(111), Ni(110), and Ni(100). By varying both the furnace temperature in the range of 800–1100 °C and the gas flow through the growth chamber, uniform, high-quality 1-LG is obtained for Ni(111) and Ni(110) single crystals and for Ni(100) thin films. Surprisingly, only multilayer graphene growth could be obtained for single-crystal Ni(100). The experimental results are analyzed to determine the optimum combination of temperature and gas flow. Characterization with optical microscopy, Raman spectroscopy, and optical transmission support our findings. Density-functional theory calculations are performed to determine the energy barriers for diffusion, segregation, and adsorption, and model the kinetic pathways for formation of different carbon structures on the low-index surfaces of Ni.United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0001088

Nanoalloying in real time: a high resolution STEM and computer simulation study

Bimetallic nanoparticles constitute a promising type of catalysts, mainly because their physical and chemical properties may be tuned by varying their chemical composition, atomic ordering, and size. Today, the design of novel nanocatalysts is possible through a combination of virtual lab simulations on massive parallel computing and modern electron microscopy with picometre resolution on one hand, and the capability of chemical analysis at the atomic scale on the other. In this work we show how the combination of theoretical calculations and characterization can solve some of the paradoxes reported about nanocatalysts: Au-Pd bimetallic nanoparticles. In particular, we demonstrate the key role played by adsorbates, such as carbon monoxide (CO), on the structure of nanoalloys. Our results imply that surface condition of nanoparticles during synthesis is a parameter of paramount importance.Fil: Mariscal, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Mayoral, Alba. Universidad de Zaragoza. Instituto de Nanociencia de Aragón; EspañaFil: Olmos Asar, Jimena Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Magen, César. Universidad de Zaragoza. Instituto de Nanociencia de Aragón; EspañaFil: Mejia Rosales, Sergio Javier. Universidad Autónoma de Nuevo León; MéxicoFil: Pérez Tijerina, Eduardo. Universidad Autónoma de Nuevo León; MéxicoFil: José Yacamán, Miguel. University of Texas; Estados Unido

Influence of capping on the atomistic arrangement in palladium nanoparticles at room temperature

The role that protecting molecules have on the way that palladium atoms arrange themselves in nanoparticles prepared at room temperature was studied by the analysis of aberration-corrected scanning transmission electron microscopy images and atomistic Langevin dynamics simulations. It was found that the arrangement of Pd atoms is less ordered in thiolate-protected nanoparticles than in amine-protected ones. The experimental and theoretical data showed that the disorder in ∼3 nm thiolate-protected particles is promoted by the strong S–Pd bond in the sulfide layer that surrounds the nanoparticles.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Study of structures and thermodynamics of CuNi nanoalloys using a new DFT-fitted atomistic potential

Shape, stability and chemical ordering patterns of CuNi nanoalloys are studied as a function of size, composition and temperature. A new parametrization of an atomistic potential for CuNi is developed on the basis of ab initio calculations. The potential is validated against experimental bulk properties, and ab initio results for nanoalloys of sizes up to 147 atoms and for surface alloys. The potential is used to determine the chemical ordering patterns of nanoparticles with diameters of up to 3 nm and different structural motifs (decahedra, truncated octahedra and icosahedra), both in the ground state and in a wide range of temperatures. The results show that the two elements do not intermix in the ground state, but there is a disordering towards solid-solution patterns in the core starting from room temperature. This order-disorder transition presents different characteristics in the icosahedral, decahedral and fcc nanoalloys

Avoiding oxidation with coating: graphene protected magnesium surfaces

Magnesium is a promising material for automotive technology. Avoiding its spontaneous oxidation is, however, mandatory for a feasible industrial application of this metal. We perform computer simulations to demonstrate that a protective graphene layer can successfully avoid the oxidation of a magnesium material. This feature remains true even when the graphene layer has several simple defects, such as vacancies and Stone-Wales transformations. In fact, the defects actually increase the strength of the graphene/metal interaction, further enhancing the protective properties. These results are rationalized in terms of the low Mg cohesive energy, which allows the system to quickly reconstruct and adapt.Fil: Olmos Asar, Jimena Anahí. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Teórica y Computacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Mariscal, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Teórica y Computacional; Argentin