Papers by Ari Paavo Seitsonen
The Journal of Physical …, 2004
The RuO2 (100) surface exposes regions with (1× 1) and c (2× 2) symmetry. The (1× 1) phase is ver... more The RuO2 (100) surface exposes regions with (1× 1) and c (2× 2) symmetry. The (1× 1) phase is very active in oxidizing CO, while the c (2× 2) phase is inactive because CO does not adsorb on the c (2× 2) phase above 100 K. This experimental finding suggests the ...
Chemphyschem : a European journal of chemical physics and physical chemistry, Jan 20, 2004
The visualization of surface reactions on the atomic scale provides direct insight into the micro... more The visualization of surface reactions on the atomic scale provides direct insight into the microscopic reaction steps taking place in a catalytic reaction at a (model) catalyst's surface. Employing the technique of scanning tunneling microscopy (STM), we investigated the CO oxidation reaction over the RuO2(110) and RuO2(100) surfaces. For both surfaces the protruding bridging O atoms are imaged in STM as bright features. The reaction mechanism is identical on both orientations of RuO2. CO molecules adsorb on the undercoordinated surface Ru atoms from where they recombine with undercoordinated O atoms to form CO2 at the oxide surface. In contrast to the RuO2(110) surface, the RuO2(100) surface stabilizes also a catalytically inactive c(2 x 2) surface phase onto which CO is not able to adsorb above 100 K. We argue that this inactive RuO2(100)-c(2 x 2) phase may play an important role in the deactivation of RuO2 catalysts in the electrochemical Cl2 evolution and other heterogeneou...
Nature, 2010
Graphene nanoribbons-narrow and straight-edged stripes of graphene, or single-layer graphite-are ... more Graphene nanoribbons-narrow and straight-edged stripes of graphene, or single-layer graphite-are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices 1-3 . In particular, although the twodimensional parent material graphene 4,5 exhibits semimetallic behaviour, quantum confinement and edge effects 2,6 should render all graphene nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they have been made using chemical 7-9 , sonochemical 10 and lithographic 11,12 methods as well as through the unzipping of carbon nanotubes 13-16 , the reliable production of graphene nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene nanoribbons of different topologies and widths, which uses surface-assisted coupling 17,18 of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation 19,20 . The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots 21 , superlattice structures 22 and magnetic devices based on specific graphene nanoribbon edge states 3 . sketches the basic graphene nanoribbon (GNR) fabrication steps for the prototypical armchair ribbon 6 of width N 5 7 obtained from 10,109-dibromo-9,99-bianthryl precursor monomers. Thermal sublimation of the monomers onto a solid surface removes their halogen substituents, yielding the molecular building blocks of the targeted graphene ribbon in the form of surface-stabilized biradical species. During a first thermal activation step, the biradical species diffuse across the surface and undergo radical addition reactions 17 to form linear polymer chains as imprinted by the specific chemical functionality pattern of the monomers. In a second thermal activation step a surface-assisted cyclodehydrogenation establishes an extended fully aromatic system. shows GNRs obtained according to the scheme in , using precursor monomers 1 and a Au(111) surface. The first step to GNR fabrication-intermolecular colligation through radical addition-is thermally activated by annealing at 200 uC, at which temperature the dehalogenated intermediates have enough thermal energy to diffuse along the surface and form single covalent C-C bonds between each monomer to give polymer chains. Scanning tunnelling microscopy (STM) images of the colligated monomers show protrusions that appear alternately on both sides of the chain axis and with a periodicity of 0.86 nm , in excellent agreement with the periodicity of the bianthryl core of 0.85 nm. Steric hindrance between the hydrogen atoms of adjacent anthracene units rotates the latter around the s-bonds connecting them, resulting in opposite tilts of successive anthracene units with respect to the metal surface. This deviation from planarity explains the large apparent height of the polyanthrylenes of about 0.4 nm , with the finite size of the scanning probe tip moreover imaging the polymer with a width much larger (1.5 nm) than expected from the structural 1 Br Br Precursor monomer 'Biradical' intermediate Graphene nanoribbon Linear polymer Figure 1 | Bottom-up fabrication of atomically precise GNRs. Basic steps for
Pre-edge features in X-ray absorption spectroscopy contain key information about the lowest excit... more Pre-edge features in X-ray absorption spectroscopy contain key information about the lowest excited states and thus on the most interesting physical properties of the system. In transition metal oxides they are particularly structured but extracting physical parameters by comparison with a calculation is not easy due to several computational challenges. By combining core-hole attraction and correlation effects in first principles approach, we calculate Ni K-edge X-ray absorption spectra in NiO. We obtain a striking, parameter-free agreement with experimental data and show that dipolar pre-edge features above the correlation gap are due to non-local excitations largely unaffected by the core-hole. We show that in charge transfer insulators, this property can be used to measure the correlation gap and probe the intrinsic position of the upper-Hubbard band.
The Journal of Chemical Physics, 2015
Unlike phonons in crystals, the collective excitations in liquids cannot be treated as propagatio... more Unlike phonons in crystals, the collective excitations in liquids cannot be treated as propagation of harmonic displacements of atoms around stable local energy minima. The viscoelasticity of liquids, reflected in transition from the adiabatic to elastic high-frequency speed of sound and in absence of the long-wavelength transverse excitations, results in dispersions of longitudinal (L) and transverse (T) collective excitations essentially different from the typical phonon ones. Practically, nothing is known about the effect of high pressure on the dispersion of collective excitations in liquids, which causes strong changes in liquid structure. Here dispersions of L and T collective excitations in liquid Li in the range of pressures up to 186 GPa were studied by ab initio simulations. Two methodologies for dispersion calculations were used: direct estimation from the peak positions of the L/T current spectral functions and simulation-based calculations of wavenumber-dependent collective eigenmodes. It is found that at ambient pressure, the longitudinal and transverse dynamics are well separated, while at high pressures, the transverse current spectral functions, density of vibrational states, and dispersions of collective excitations yield evidence of two types of propagating modes that contribute strongly to transverse dynamics. Emergence of the unusually high-frequency transverse modes gives evidence of the breakdown of a regular viscoelastic theory of transverse dynamics, which is based on coupling of a single transverse propagating mode with shear relaxation. The explanation of the observed high-frequency shift above the viscoelastic value is given by the presence of another branch of collective excitations. With the pressure increasing, coupling between the two types of collective excitations is rationalized within a proposed extended viscoelastic model of transverse dynamics.
Materials Science Forum, 2009
Materials Science Forum, 1994
ABSTRACT
High Performance Computing in Science and Engineering `07, 2008
... of Emim-chloroaluminate Ionic Liquids Barbara Kirchner1 and Ari P. Seitsonen2 ... Therefore t... more ... of Emim-chloroaluminate Ionic Liquids Barbara Kirchner1 and Ari P. Seitsonen2 ... Therefore the application of GGA-density functional theory is necessary in order to make the simulation computationally tractable. ... 17. Z. Meng, A. Dölle, and WR Carper. J. Mol. ...
Surface Science, 2007
AA (Physikalisch-Chemisches Institut, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35392 G... more AA (Physikalisch-Chemisches Institut, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35392 Gießen, Germany), AB (Lehrstuhl für Technische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany), AC (IMPMC, CNRS and Université Pierre et Marie Curie, 4 ...
Surface Science, 2009
We briefly summarize our joint effort to understand catalytic reactions on the model catalyst RuO... more We briefly summarize our joint effort to understand catalytic reactions on the model catalyst RuO2 (110) on the atomic scale, applying state-of-the-art density functional theory calculations and surface chemical characterizations in parallel. This intimate theory/ ...
Surface Science, 2002
We present experimental and DFT-simulated STM images of ultrathin RuO 2 (1 1 0) films on Ru(0 0 0... more We present experimental and DFT-simulated STM images of ultrathin RuO 2 (1 1 0) films on Ru(0 0 0 1), including adsorbates such as oxygen and CO. We are able to identify the under-coordinated O atoms on the RuO 2 (1 1 0) surface with STM, i.e. the bridging O atoms and the on-top O atoms. The partial reduction of the RuO 2 (1 1 0) surface by CO exposure at room temperature leads to a surface where part of the bridging O atoms have been removed and some of the vacancies are occupied by bridging CO. When dosing 10 L of CO at room temperature, the RuO 2 (1 1 0) surface becomes fully mildly reduced in that all bridging O atoms are replaced by bridging CO molecules. Annealing the surface to 600 K produces holes on the terraces of such a mildly reduced RuO 2 (1 1 0) surface. These pits are not generated by the recombination of lattice O with CO, but rather these pits are assigned to a complex temperature-induced rearrangement of surface atoms in the topmost RuO 2 double layer of RuO 2 (1 1 0). With this process the bridging O atoms are again populated and surplus Ru atoms agglomerate in small islands at the rims of the holes.
Physical Review Letters, 1998
The structure of the (3 3 1) reconstructions of the Si (111) and Ge (111) surfaces induced by ads... more The structure of the (3 3 1) reconstructions of the Si (111) and Ge (111) surfaces induced by adsorption of alkali metals has been determined on the basis of surface x-ray diffraction and low-energy electron diffraction measurements and density functional theory. The (3 3 1) ...
physica status solidi (b), 2008
Nature Materials, 2012
Understanding the conditions which favor crystallisation or vitrification of liquids has been a l... more Understanding the conditions which favor crystallisation or vitrification of liquids has been a long-standing scientific problem . Another connected, and not yet well understood question is the relationship between the glassy and the various possible crystalline forms a system may adopt . In this context, B2O3 is a puzzling case of study since i) it is one of the best glass-forming systems despite an apparent lack of lowpressure polymorphism ii) it vitrifies in a glassy form abnormally different from the only known crystalline phase at ambient pressure [6] iii) it never crystallises from the melt unless pressure is applied, an intriguing behaviour known as the crystallisation anomaly . Here, by means of ab-initio calculations, we discover the existence of novel B2O3 crystalline polymorphs with structural properties similar to the glass and formation energies comparable to the known ambient crystal. The resulting configurational degeneracy drives the system vitrification at ambient pressure. The degeneracy is lifted under pressure, unveiling the origin of the crystallisation anomaly. This work reconciles the behaviour of B2O3 with that from other glassy systems and reaffirms the role played by polymorphism in a system's ability to vitrify . Some of the predicted crystals are cage-like materials entirely made of three-fold rings, opening new perspectives for the synthesis of boron-based nanoporous materials.
Journal of the American Chemical Society, 2001
Ruthenium dioxide (RuO 2 ) reveals unique and promising redox properties, making RuO 2 a potentia... more Ruthenium dioxide (RuO 2 ) reveals unique and promising redox properties, making RuO 2 a potential candidate for a versatile oxidation catalyst. Recently Zhang and Kisch 1 reported, for instance, that hydrated RuO 2 is a robust and efficient catalyst for room temperature oxidation of CO by humid air; recall that typical metal oxides do not tolerate humidity. In this contribution we present scanning tunneling microscopy (STM) data which directly image the catalytically important processes occurring on the RuO 2 -(110) surface after exposing the pristine surface to CO and O 2 . The STM data are substantiated by density functional theory (DFT) calculations.
Journal of Physics: Condensed Matter, 2011
We calculate the energetics of vacancies in CuInSe 2 using a hybrid functional (HSE06, HSE standi... more We calculate the energetics of vacancies in CuInSe 2 using a hybrid functional (HSE06, HSE standing for Heyd, Scuseria and Ernzerhof), which gives a better description of the band gap compared to (semi)local exchange-correlation functionals. We show that, contrary to present beliefs, copper and indium vacancies induce no defect levels within the band gap and therefore cannot account for any experimentally observed levels. The selenium vacancy is responsible for only one level, namely, a deep acceptor level (0/2−). We find strong preference for V Cu and V Se over V In under practically all chemical conditions.
The Journal of Chemical Physics, 1998
... Surface and interface chemistry. Chemisorption. Body. I. INTRODUCTION. In the past, numerous ... more ... Surface and interface chemistry. Chemisorption. Body. I. INTRODUCTION. In the past, numerous studies were devoted to the interaction of hydrogen with metal single-crystal surfaces, whereby, less frequently, adsorption geometries were also determined (for reviews, see Refs. ) ...
Chemical Physics Letters, 1997
The local adsorption geometries of the (2 × 2)-N and the ( √ 3 × √ 3)R30 • -N phases on the Ru (0... more The local adsorption geometries of the (2 × 2)-N and the ( √ 3 × √ 3)R30 • -N phases on the Ru (0001) surface are determined by analyzing low-energy electron diffraction (LEED) intensity data. For both phases, nitrogen occupies the threefold hcp site. The nitrogen sinks deeply into the top Ru layer resulting in a N-Ru interlayer distance of 1.05Å and 1.10Å in the (2 × 2) and the ( √ 3 × √ 3)R30 • unit cell, respectively. This result is attributed to a strong N binding to the Ru surface (Ru-N bond length = 1.93Å) in both phases as also evidenced by ab-initio calculations which revealed binding energies of 5.82 eV and 5.59 eV, respectively.
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Papers by Ari Paavo Seitsonen