Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z27: Surfaces |
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Sponsoring Units: DCMP Chair: Adam Hauser, Ohio State University Room: D137 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z27.00001: \textit{Ab initio} Thermodynamic Approach to Screen Good Solid Sorbents for CO$_{2}$ Capture Yuhua Duan CO$_{2}$ is the major product from coal combustion and released into the air to cause global climate warming. Current technologies for capturing CO$_{2}$including solvent-based (amines) and CaO-based materials are still too energy intensive. Solid materials have been proposed for capturing CO$_{2}$ through a reversible chemical transformation at low cost. By combining DFT with phonon lattice dynamics, the thermodynamic properties of solid materials are obtained and used for computing the thermodynamic reaction equilibrium properties of CO$_{2}$ absorption/desorption cycle based on chemical potential and heat of reaction analysis cycle. Based on our calculated thermodynamic properties of reactions for each solid capturing CO$_{2}$ varying with T and P, only those solids, which result lower energy cost in the capture and regeneration process and could work at desired conditions, will be selected as promised candidates of CO$_{2}$ sorbents and further be sent for experimental validations. Here, we first report our screening results on alkali and alkaline earth metal oxides, hydroxides and carbonates/bicarbonates and compare with available thermodynamic data, then, report the predicted good candidates of CO$_{2}$ sorbents from vast of mixing and substituted/doped solids which thermodynamic data are usually not available. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z27.00002: Kinetic Monte Carlo Simulations of a Lattice-Gas Model of Pulsed Electrodeposition with Diffusion Tjipto Juwono, Per Arne Rikvold, Ibrahim Abou Hamad We have studied the effect of diffusion during the desorption phase in pulsed electrodeposition in a square lattice-gas model using Kinetic Monte Carlo simulations. In cases without diffusion, the desorption rate increases when the size distribution of the droplets is dominated by smaller clusters at the beginning of the desorption process. For a particular initial size distribution, the presence of diffusion increases the desorption rate. As we decrease the average initial droplet size, the increase in the desorption rate becomes less pronounced. By analyzing the size distributions at different times during the desorption process we found that the dynamics of the size distribution when diffusion is present follows the same pattern as the dynamics of size distributions without diffusion, only with a difference in magnitude. Therefore, the effect of diffusion on the desorption rate also decreases when the size distribution of the droplets is dominated by smaller clusters. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z27.00003: Electronic relaxation of a photoexcitation of AgSi(111):H surface Dimitri Kilin, David A. Micha A combination of time dependent density matrix and {\it ab initio} electronic structure methods provide details of the relaxation pathways of photo-induced charge redistribution at nanostructured semiconductor surfaces, giving their changes in energy and space over time. They are applied to a Ag cluster on a Si(111) surface, initially photoexcited by a short pulse, and show that the Ag cluster adds surface-localized states that enhance electron transfer. Population density distributions in energy and in space, for valence and conduction bands, explore the energy band landscape of a Si slab, with various relaxation pathways ending up in a charge-separated state, with a hole in the Si slab and an electron in the adsorbed Ag cluster. Calculated electronic relaxation times for Si(111):H are of the same order as experimental values for similar semiconductor systems. We have also noticed that average non-adiabatic coupling and transition dipoles have similar dependence on numbers of orbitals involved in transition. Results from a reduced density matrix propagation with Hamiltonian and rates parametrized from {\it ab initio} electronic structure calculations give new insight on electronic dynamics at nanostructured surfaces. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z27.00004: Inelastic Helium Atom Scattering from the Commensurate Monolayer Solid H$_2$/NaCl(001) L.W. Bruch, F.Y. Hansen A calculation of inelastic low energy helium atomic scattering by a monolayer with one-phonon creation\footnote{F. Y. Hansen and L. W. Bruch, J. Chem. Phys. {\bf 127}, 204708 (2007)} has been adapted to treat the case where the monolayer is the dilated quantum solid H$_2$/NaCl(001). The interactions He-H$_2$ and He-NaCl are rather well known inputs, but the dilated solid presents the most corrugated surface yet treated in such calculations. Progress in performing calculations for the condition of the inelastic scattering experiments\footnote{F. Trager and J. P. Toennies, J. Phys. Chem. B {\bf 108}, 14710 (2004)} will be described. Compared to earlier work, there is remarkable sensitivity to the number of fourier components used to represent the corrugation, the number of coupled channels, and the width of the wave packet. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z27.00005: Heat transfer studies at solid/gas interfaces using time-resolved ellipsometry Chang-Ki Min, Sung Chul Bae, David Cahill, Steve Granick Heat transfer from a solid surface to gas is studied by pump laser pulses which impulsively increase the temperature of Au metal film. Transient changes of refractive index in the nearby fluid phase are monitored by off-null ellipsometry using time-delayed probe pulses with 100 fs resolution. The initial psecond rise of signals shows how acoustic waves are created and reveals energy exchange mechanisms at solid-gas and solid-liquids interfaces. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z27.00006: Mapping the spin states of surface deposited Fe(II) SCO Compounds by STM M. Stocker, M.S. Alam, A. Volkov, U. Mitra, K. Gieb, V. Dremov, P. M\"uller, M. Haryono, K. Student, A. Grohmann We describe a novel method for analyzing the spin states of surface deposited Fe(II) spin crossover (SCO) compounds. The talk focuses on the investigation of $[FeII(L)_{2}](BF_{4})_{2}$ (L=2,6-di(1H-pyrazol-1-yl)-4-(thiocyanatomethyl)pyridine)$^1$ and the comparison to a high spin compound with a similar coordination motif. Single molecules and small clusters were investigated on HOPG. We were able to show a strong current contrast for the different spin states using the CITS technique. Changes of the spin state from high- to low-spin state and vice versa were observed at room temperature. Switching was statistically distributed, indicating a widening of the spin transition compared to the bulk state.$^{2}$ \newline $^{1}$ M. Haryono, et al., Eur. J. Inorg. Chem. 2009, 2136. \newline $^{2}$ M.S. Alam, et al., Angew. Chem. (2009) (accepted). [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z27.00007: First-principles investigations for the catalytic dissociation and oxidation of methane on the Cu surfaces Ying Li, Jagan Mahadevan, Sanwu Wang The catalytic reactions of dissociation and oxidation of methane on the copper surfaces play a key role in, for example, the development of high-performance solid oxide fuel cells. We used first-principles quantum theory and large-scale parallel calculations to investigate the atomic-scale mechanism of the catalytic chemical reactions. We report the calculated results, which provide fundamental information and understanding about the atomic-scale dynamics and electronic structures pertinent to the reactions and specifically the catalytic role of the Cu(100) and Cu(111) surfaces. We also report comparison of our results with available experimental data and previous theoretical investigations. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z27.00008: Electronic properties of methyl and hydrogen terminated Si(111) surfaces Antonio Aliano, Yan Li, Giancarlo Cicero, Giulia Galli Functionalized Si(111) surfaces have many applications in photo-electrochemistry, and some of those (e.g. the use of Si rods as photo-cathodes in solar cell applications) require the development of chemical protection strategies so as to prevent uncontrolled oxidation. Recently [1] a full methylation of Si(111) has been achieved experimentally, which constiutes a promising means to protect Si(111) from oxidation. However, the apparently simple atomic structure of this surface is still under debate. In particular, low temperature STM images appear to yield a pattern in disagreement with structural, first principles optimizations. We have carried out a series of ab-initio calculations of both the structural and electronic properties of the CH3-Si(111) aimed at interpreting STM and STS measurements. A comparison between results obtained at the DFT-GGA level and by using GW calculations will be presented and compared with the corresponding ones for the H-Si(111). This work supported by grant NSF-CHE-0802907 [1]H. Yu et al., Appl. Phys. Lett. 88, 152111, (2006) [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z27.00009: Tetracosane (C$_{24}$H$_{50})$ trilayers physisorbed onto the basal plane of graphite: perpendicular patches Michael Roth, L. Firlej, B. Kuchta, Carlos Wexler Results of explicit - hydrogen Molecular Dynamics computer simulations of tetracosane (C$_{24}$H$_{50}$, or C24) trilayers deposited on a graphite substrate in the temperature range 100 K $\le \quad T \quad \le $ 550 K are presented. The third layer is perpendicular to the alkane underlayers as well as to the graphite substrate. Diffusion thakes place predominantly at the bottom of the patch through a ratcheting mechanism that is coupled to dihedral (torsional) defects. In the low - temperature solid the patch exhibits a dome - like shape and, with increasing temperature rolling of the interior molecules couple to the collapse of the patch into a droplet - like shape and, ultimately a liquid C24 patch atop the graphite layer results. Structural, thermodynamic and bond - orientational distributions and parameters are utilized in understanding the temperature evolution of the system and results are compared to those under the United Atom approximation. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z27.00010: Theoretical Investigation of TI-Doped Zirconia Surfaces Hasani Chauke, Ricardo Grau-Crespo, Phuti Ngoepe, Nora H. de Leeuw We use density functional theory calculations with Hubbard corrections (DFT+U) to investigate the electronic and redox properties of Ti-substituted zirconia (111) surfaces. It is found that titanium dopants are more likely to segregate at the surface than to migrate to the zirconia bulk. The formation energy of oxygen vacancies decreases substantially in titanium-substituted surfaces with respect to undoped surfaces. If an O vacancy is created around an isolated Ti dopant, a Ti$^{4+} \quad \to $ Ti$^{2+}$ reduction takes place, while if the vacancy is created in the vicinity of a pair of dopants, each Ti atom adopts a 3+ oxidation state, with additional decrease in the vacancy formation energy. We investigate in detail the relevant distribution of dopants and vacancies in the system, and discuss the implications of our results for some applications of zirconia-based ceramics. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z27.00011: Excess Charge Density at the Air-Electrolyte Solution Interface Jinsuk Song, Mahn Won Kim Understanding the differential adsorption of ions at the interface of the electrolyte solution is very important because it is closely related, not only to the fundamental aspects of biological systems, but also to many industrial applications. We have measured the excess interfacial negative charge density at the air-electrolyte solution interfaces by using resonant second harmonic generation of oppositely charged probe molecules. The excess charge density increased with the square root of the bulk electrolyte concentration. A new adsorption model which includes the electrostatic interaction between adsorbed molecules is proposed to explain the measured adsorption isotherm and it is in good agreement with the experimental results. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z27.00012: Polarization dependence of carbon dioxide dissociation on palladium supported on ferroelectrics Seungchul Kim, Andrew M. Rappe Using density functional theory (DFT) calculations, we investigate the effect of polarization direction on the catalytic activity of palladium supported on ferroelectrics. It is calculated how the energy barriers of the carbon dioxide (CO$_2$) dissociation process into carbon monoxide (CO) and oxygen (O) are changed for positively and negatively polarized ferroelectric lithium niobate (LiNbO$_3$) surfaces. In this study, the LiNbO$_3$ surfaces are passivated by ions, which is thormodynamically favored for a wide range of chemical potentials. Multiple possible CO$_2$ dissociation paths and their energy barriers are presented. We also perform a detailed analysis of electronic structure to explain differences in the reaction process on the two surfaces. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z27.00013: Ethanol adsorption on transition-metal surfaces: A DFT investigation Juarez L. F. Da Silva The development of low-cost and long-term stability catalyst compounds for the production of hydrogen from ethanol is one of the main problems to be solved for large scale use of direct- ethanol fuel cells. Steam reforming, which is one of the main routes to obtain hydrogen from ethanol, as well as ethanol oxidation, are critically dependent on the choice of the catalyst devices. Therefore, an atom-level understanding of the interaction of ethanol with catalysts systems is on the first problems to be addressed. In this talk, we will report first- principles calculations based on density functional theory for the adsorption of ethanol on close-packed transition-metal surfaces at the limit of low-coverage. In particular, we will report the following properties, namely, adsorption energy, work function changes, and structural parameters for a large number of substrates, which will be used to build up a simple picture to describe the interaction of ethanol with transition-metal surfaces. This work is supported by FAPESP. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z27.00014: Electron-beam irradiation of supported DPPC monolayer films -- an XPS study Radmila Panajotovic, Mark Schnietz, Andrey Turchanin, Nigel Mason, Armin Goelzhauser Chemical changes in phospholipid (DPPC -- 1,2-dipalmitoyl-sn-glycero-3-phosphocholine) monolayer films deposited on gold are studied in an X-ray photoelectron spectroscopy experiment. DPPC films have been irradiated by a monoenergetic electron beam in the energy range from 5 to 200 eV. The shifts in the binding energy of C 1s, O 1s, P 2p, and N 1s electrons, as well as the change in the intensity of corresponding photoelectron peaks, were observed before and after electron beam irradiation. We show that the electrons with energy between 20 and 100 eV have the largest effect on DPPC, mostly stripping off the protons from the tails and breaking the COO- bond in the head of the molecule, but also releasing methyl group from the choline group (N-(CH$_{3})_{3})$. The least effect of electron irradiation is shown on the P 2p band, regardless of the incident energy, which may be linked to the orientation of the DPPC molecules and additional intramolecular bonding. [Preview Abstract] |
Friday, March 19, 2010 2:03PM - 2:15PM |
Z27.00015: Nitrogen Adsorption on Graphite: Defying Physisorption Alexandre Tkatchenko, Matthias Scheffler The adsorption of a nitrogen molecule at the graphite surface can be considered a paradigm of molecular physisorption [1]. The binding of N$_2$ can be phenomenologically described in terms of a competition between quadrupole--quadrupole and van der Waals dispersion energies. Of particular interest is the relative stability of the so-called ``in-plane'', ``out-of-plane'' and ``pin-wheel'' monolayer structures, in which the nitrogen molecules alternate between parallel and perpendicular configurations on the surface. By combining state-of-the-art electronic structure methods, such as dispersion-corrected density-functional theory and M{\o}ller-Plesset second-order perturbation theory along with high-level coupled cluster [CCSD(T)] calculations, we are able to gain quantitative insight into the adsorption mechanism of N$_2$@graphite and achieve very good agreement with experimental desorption enthalpy. We challenge the commonly held view of a closed-shell adsorbed N$_2$ molecule, finding a noticeable charge-density polarization for nitrogen in a perpendicular configuration on the surface. We map out the N$_2$@graphite potential energy surface as a function of sliding and orientation and discuss the influence of quantum zero-point energy for different adsorption sites. [1] D. Marx and H. Wiechert, Adv. Chem. Phys. {\bf 95}, 213 (1996). [Preview Abstract] |
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