Instituto Ciencia Of Materiales Of Madrid Csic

Santa Cruz de la Serós, Spain

Instituto Ciencia Of Materiales Of Madrid Csic

Santa Cruz de la Serós, Spain
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Otero G.,Instituto Ciencia Of Materiales Of Madrid Csic | Gonzalez C.,Instituto Ciencia Of Materiales Of Madrid Csic | Pinardi A.L.,Instituto Ciencia Of Materiales Of Madrid Csic | Merino P.,CSIC - National Institute of Aerospace Technology | And 10 more authors.
Physical Review Letters | Year: 2010

We have studied large areas of (√3×√3)R30° graphene commensurate with a Pt(111) substrate. A combination of experimental techniques with ab initio density functional theory indicates that this structure is related to a reconstruction at the Pt surface, consisting of an ordered vacancy network formed in the outermost Pt layer and a graphene layer covalently bound to the Pt substrate. The formation of this reconstruction is enhanced if low temperatures and polycyclic aromatic hydrocarbons are used as molecular precursors for epitaxial growth of the graphene layers. © 2010 The American Physical Society.


Merino P.,CSIC - National Institute of Aerospace Technology | Svec M.,ASCR Institute of Physics Prague | Martinez J.I.,Instituto Ciencia Of Materiales Of Madrid Csic | Jelinek P.,ASCR Institute of Physics Prague | And 8 more authors.
Nature Communications | Year: 2014

Polycyclic aromatic hydrocarbons as well as other organic molecules appear among the most abundant observed species in interstellar space and are key molecules to understanding the prebiotic roots of life. However, their existence and abundance in space remain a puzzle. Here we present a new top-down route to form polycyclic aromatic hydrocarbons in large quantities in space. We show that aromatic species can be efficiently formed on the graphitized surface of the abundant silicon carbide stardust on exposure to atomic hydrogen under pressure and temperature conditions analogous to those of the interstellar medium. To this aim, we mimic the circumstellar environment using ultra-high vacuum chambers and investigate the SiC surface by in situ advanced characterization techniques combined with first-principles molecular dynamics calculations. These results suggest that top-down routes are crucial to astrochemistry to explain the abundance of organic species and to uncover the origin of unidentified infrared emission features from advanced observations. © 2014 Macmillan Publishers Limited. All rights reserved.


Otero-Irurueta G.,University of Aveiro | Hernandez-Rodriguez I.,Instituto Ciencia Of Materiales Of Madrid Csic | Martinez J.I.,Instituto Ciencia Of Materiales Of Madrid Csic | Palacios-Rivera R.,CSIC - National Institute of Aerospace Technology | And 8 more authors.
Chemical Communications | Year: 2015

Direct sublimation of a Cu4Cl4 metal-organic cluster on Cu(110) under ultra-high vacuum allows the formation of ultra-large well-organized metal-organic supramolecular wires. Our results show that the large monomers assemble with each other by π-π interactions connecting dipyrimidine units and are stabilized by the surface. This journal is © The Royal Society of Chemistry 2015.


Sanchez-Sanchez C.,Instituto Ciencia Of Materiales Of Madrid Csic | Gonzalez C.,Instituto Ciencia Of Materiales Of Madrid Csic | Gonzalez C.,ASCR Institute of Physics Prague | Jelinek P.,ASCR Institute of Physics Prague | And 4 more authors.
Nanotechnology | Year: 2010

We present a combination of experimental STM images and DFT calculations to understand the atomic scale contrast of features found in high-resolution STM images. Simulating different plausible structural models for the tip, we have been able to reproduce various characteristics previously reported in experimental images on TiO2(110)-(1 × 1) under controlled UHV conditions. Our results allow us to determine the influence of different chemical and morphological tip terminations on the atomic-resolution STM images of the TiO2(110)-(1 × 1) surface. The commonest images have been properly explained using standard models for a W tip, either clean or with a single O atom located at the apex. Furthermore, a double transfer of oxygen atoms can account for different types of bizarre atomic-resolution features occasionally seen, and not conclusively interpreted before. Importantly, we discuss how typical point-defects are imaged on this surface by different tips, namely bridging O vacancies and adsorbed OH groups. © 2010 IOP Publishing Ltd.


Sanchez-Munoz L.,CSIC - Institute of Ceramics and Glass | Sanz J.,Instituto Ciencia Of Materiales Of Madrid Csic | Sobrados I.,Instituto Ciencia Of Materiales Of Madrid Csic | Gan Z.,Florida State University
American Mineralogist | Year: 2013

The structures of K-rich feldspar, (K>Na)AlSi3O8, are currently described as "ideal" crystals with periodic average structures from Bragg diffraction maxima obtained by reciprocal-space techniques. Polymorphism is explained by variable substitutional disorder of framework Si and Al cations in tetrahedral T sites, and positional disorder of cavity alkali cations in a single M site. Here, high-resolution magic angle spinning multinuclear magnetic resonance spectroscopy, leading to 29Si, 27Al, and 23Na spectra at 9.4 as well as 27Al, 39K, and 23Na spectra at 19.6 T, has been used to investigate the "real" structures along the order-disorder series of K-feldspar crystals. The "ideal" and "real" structure coincides only in the perfectly long-range ordered triclinic end-member of the low-microcline structure. Long-range disordered structures (either with monoclinic or triclinic symmetry by X-ray diffraction) show non-random disorder at the medium-range scale, triclinic-like distortions with four sets of T sites for framework atoms, two sets of M sites for alkali atoms, and Al-O-(K,Na) multi-site correlations by NMR spectroscopy. The K-feldspar structures can be described by a medium-range structure using the number of Al atoms per four-membered rings of tetrahedra, with "...-2-0-2-0-..." chains for microcline and orthoclase where the Al-occupancies t1O > t2m > t2O ≈ t1m, and with "...-1-1-1-1-..." chains for valencianite and sanidine, in which t1O > t2m ≈ t2O ≈ t1m. Framework cations respect Loewenstein's rule (Al-O-Al avoidance), as well as some additional constraints of charge dispersion involving deficiency of Si atoms in Q4 (4Si,0Al), (1Si,3Al), and (0Si,4Al) environments, constraints which are particularly strong in valencianite. These "real" structure features cannot be described by "ideal" structures owing to the lack of resolving power of the reciprocal-space techniques.


Arbi K.,Instituto Ciencia Of Materiales Of Madrid Csic | Paris M.A.,Instituto Ciencia Of Materiales Of Madrid Csic | Sanz J.,Instituto Ciencia Of Materiales Of Madrid Csic
Dalton Transactions | Year: 2011

Lithium mobility in LiM 2(PO 4) 3 compounds, M = Ge and Sn, has been investigated by 7Li Nuclear Magnetic Resonance (NMR) spectroscopy, and deduced information compared with that reported previously in Ti, Zr and Hf members of the series in the temperature range 100-500 K. From the analysis of 7Li NMR quadrupole interactions (C Q and η parameters), spin-spin T 2 -1 and spin-lattice T 1 -1 relaxation rates, structural sites occupancy and mobility of lithium have been deduced. Below 250 K, Li ions are preferentially located at M 1 sites in rhombohedral phases, but occupy intermediate M 12 sites between M 1 and M 2 sites in triclinic ones. In high-temperature rhombohedral phases, a superionic state is achieved when residence times at M 1 and M 12 sites become similar and correlation effects on Li motion decrease. This state can be obtained by large order-disorder transformations in rhombohedral phases or by sharp first order transitions in triclinic ones. The presence of two relaxation mechanisms in T 1 -1 plots of rhombohedral phases has been associated with departures of conductivity from the Arrhenius behavior. Long term mobility of lithium is discussed in terms of the cation vacancy distribution along conduction paths. © The Royal Society of Chemistry 2011.


Merino P.,CSIC - National Institute of Aerospace Technology | Svec M.,CSIC - National Institute of Aerospace Technology | Pinardi A.L.,Instituto Ciencia Of Materiales Of Madrid Csic | Otero G.,Instituto Ciencia Of Materiales Of Madrid Csic | And 2 more authors.
ACS Nano | Year: 2011

STM images of multidomain epitaxial graphene on Pt(111) have been combined with a geometrical model to investigate the origin of the coincidence Moiré superstructures. We show that there is a relation between the appearance of a particular Moiré periodicity and the minimization of the absolute value of the strain between the graphene and the substrate for the different orientations between both atomic lattices. This model predicts all the stable epitaxial graphene structures that can be grown on transition metal surfaces, and we have made use of it for reproducing previously published data from different authors. Its validity suggests that minimization of the strain within the coincident graphene unit-cell due to a strong local interaction is the driving force in the formation of Moiré superstructures. © 2011 American Chemical Society.


PubMed | Instituto Ciencia Of Materiales Of Madrid Csic
Type: Journal Article | Journal: Nanotechnology | Year: 2010

We present a combination of experimental STM images and DFT calculations to understand the atomic scale contrast of features found in high-resolution STM images. Simulating different plausible structural models for the tip, we have been able to reproduce various characteristics previously reported in experimental images on TiO(2)(110)-(1 x 1) under controlled UHV conditions. Our results allow us to determine the influence of different chemical and morphological tip terminations on the atomic-resolution STM images of the TiO(2)(110)-(1 x 1) surface. The commonest images have been properly explained using standard models for a W tip, either clean or with a single O atom located at the apex. Furthermore, a double transfer of oxygen atoms can account for different types of bizarre atomic-resolution features occasionally seen, and not conclusively interpreted before. Importantly, we discuss how typical point-defects are imaged on this surface by different tips, namely bridging O vacancies and adsorbed OH groups.


PubMed | Instituto Ciencia Of Materiales Of Madrid Csic
Type: Journal Article | Journal: Dalton transactions (Cambridge, England : 2003) | Year: 2011

Lithium mobility in LiM(2)(PO(4))(3) compounds, M = Ge and Sn, has been investigated by (7)Li Nuclear Magnetic Resonance (NMR) spectroscopy, and deduced information compared with that reported previously in Ti, Zr and Hf members of the series in the temperature range 100-500 K. From the analysis of (7)Li NMR quadrupole interactions (C(Q) and parameters), spin-spin T(2)(-1) and spin-lattice T(1)(-1) relaxation rates, structural sites occupancy and mobility of lithium have been deduced. Below 250 K, Li ions are preferentially located at M(1) sites in rhombohedral phases, but occupy intermediate M(12) sites between M(1) and M(2) sites in triclinic ones. In high-temperature rhombohedral phases, a superionic state is achieved when residence times at M(1) and M(12) sites become similar and correlation effects on Li motion decrease. This state can be obtained by large order-disorder transformations in rhombohedral phases or by sharp first order transitions in triclinic ones. The presence of two relaxation mechanisms in T(1)(-1) plots of rhombohedral phases has been associated with departures of conductivity from the Arrhenius behavior. Long term mobility of lithium is discussed in terms of the cation vacancy distribution along conduction paths.


PubMed | Instituto Ciencia Of Materiales Of Madrid Csic
Type: Journal Article | Journal: Physical review letters | Year: 2011

We have studied large areas of (33)R30 graphene commensurate with a Pt(111) substrate. A combination of experimental techniques with ab initio density functional theory indicates that this structure is related to a reconstruction at the Pt surface, consisting of an ordered vacancy network formed in the outermost Pt layer and a graphene layer covalently bound to the Pt substrate. The formation of this reconstruction is enhanced if low temperatures and polycyclic aromatic hydrocarbons are used as molecular precursors for epitaxial growth of the graphene layers.

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