Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y25: Chemical Physics and Reactivity at Surfaces |
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Sponsoring Units: DCP Chair: Marco Caricato, University of Kansas Room: 288 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y25.00001: Effective Bond Polarizability Model for Sum Frequency Generation Mark DelloStritto, Jorge Sofo Sum Frequency Generation (SFG) is a powerful, surface-specific vibrational probe ideally suited to buried interfaces, however, insight from theory is necessary to identify which surface modes give rise to the features of the vibrational spectrum. At oxide/water interfaces, strong H-bond interactions and competition between the H-bond network of water and the network of surface OH groups necessitate ab-initio MD simulations to elucidate the complex dynamics. One cannot use ab-initio methods to calculate the SFG spectrum however, due to the prohibitive cost of calculating the polarizability of large cells over long times. Thus, we develop a flexible polarizability model which takes local dipole interactions into account, rather than an additive polarizability model. We calculate bond polarizabilities and dipoles which reflect the local geometry of the H-bond network. We study the Al\(_{2}\)O\(_{3}\) (0001)-H\(_{2}\)O interface, where we reproduce the experimental spectrum and show the two OH stretching peaks come from solvent and surface modes separately, not H\(_{2}\)O molecules with different coordination numbers as previously thought. Thus, our work emphasizes the importance of treating surface and solvent at the same level of theory for accurate spectroscopy calculations. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y25.00002: Catalysis in the Diels-Alder Cycloaddition of Biomass-Derived Furan and Methyl Acrylate by Transition Metal Oxide Surfaces. TAHA SALAVATI-FARD, Glen Jenness, Stavros Caratzoulas, Douglas Doren Using computational methods, the catalytic effects of oxide surfaces on the Diels-Alder reaction between biomass-derived furan and methyl acrylate are investigated. The cycloadduct can be dehydrated later to produce methyl benzoic which is an important step toward benzoic acid production. Different systems such as clean, partially hydroxylated and fully hydroxylated ZrO2 are considered. The Langmuir and Eley-Rideal mechanisms are studied, as well. Our calculations show that the oxide surfaces catalyze the reaction significantly through the interaction of metal sites with the electron-poor reactant. The calculations are interpreted by making use of the total and projected electronic density of states and band structure of the catalyst. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y25.00003: Investigating 7-Dehydrocholesterol ring-opening dynamics as a function of liposome properties Danielle Sofferman, Roseanne Sension 7-Dehydrocholesterol (DHC, Provitamin D$_{3})$ undergoes an ultrafast photochemical transformation into previtamin D$_{3}$ upon a ring-opening reaction in the excited state. A cyclohexadiene (CHD) chromophore embedded within the DHC molecule opens to form a hexatriene previtamin D$_{3}$ species. The ring opening of isolated CHD happens on a sub-picosecond time scale, therefore it is necessary to use ultrafast techniques such as transient absorption to capture the dynamics of the DHC molecule in the excited state. Here we are studying the excited state dynamics of DHC in liposomes as a model for biologically relevant skin membranes. In isotropic solvents, the molecule is free to isomerize to previtamin D$_{3}$, however in an anisotropic solvent such as liposomes, the DHC molecule resides in a lipid bilayer and the isomerization is hindered by the lipid tails. We have observed that the excited state absorption of DHC in isotropic solvents yields a 0.5ps fast component and a 1-2ps slow component. In the anisotropic liposomes a third, longer lived, 6-10ps component is also observed. These results will be discussed in terms of the conformational relaxation of DHC. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y25.00004: Effect of iron content on the catalytic activity of Fe-MnOx electrodeposited films in water oxidation Elizabeth Selinger, Kevin Ryczko, Gregory Lopinski, Marco Armandi, Barbara Bonelli, Isaac Tamblyn We report on the experimental and computational optimization and characterization of an MnOx structure containing a small amount of Fe, used as a catalyst for the water oxidation reaction (WOR), the key limiting reaction in water splitting. MnOx materials are earth-abundant and known to be efficient for WOR, and the method of cathodically electrodepositing catalysts allows for quick synthesis and a homogeneous coverage of the substrate. We present an increase in WOR activity due to the presence of Fe in this MnOx catalyst structure. First, we explored the optimal range for Fe(NO$_{3}$)$_{3}$ concentration in an KMnO$_{4}$ solution for electrodeposition and tested for WOR activity. The catalyst structure was then analyzed using FESEM, XPS, and a Kelvin probe. We then developed a computational model of this structure, using density functional theory to obtain adsorption energies, work functions, projected density of states, and Born-Oppenheimer molecular dynamics. In this theoretical framework, we explore how these observables change with respect to concentration of Fe, and compare the theoretical model with experiment. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y25.00005: Electronic and Catalytic Properties of Iodine-Doped Graphene Robert A. Hoyt, E. Marielle Remillard, Ekin D. Cubuk, Chad D. Vecitis, Efthimios Kaxiras Polyiodide-doped graphene is an exciting recent material that exhibits significantly increased conductivity and oxygen reduction reaction (ORR) activity. Although polyiodide chains with a wide variety of lengths have been observed across a range of chemical systems, only I$_3$ and I$_5$ are observed as graphene dopants. In addition, while the mechanisms of ORR are understood for substitutionally-doped graphene, these polyiodides are reversible surface dopants so their role as active sites for ORR catalysis is unclear. To address these issues, we use density functional theory calculations to investigate the formation and desorption energies of isolated polyiodides on graphene, their electronic band structures, and degree of charge transfer. We also present results showing the stabilization of the OOH intermediate by I$_3$ on graphene, explaining the high ORR activity seen in polyiodide-doped graphene. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y25.00006: Enhanced Dressahaus spin orbit coupling in the EDTA-decorated graphene Fengqi Song, Jianlei Ge The graphene-based spin device is constructed by decorating the graphene sheet using the dysprosium complex Na[Dy(EDTA)(H2O2)3]5H2O (EDTA-Dy), which shows the typical field-induced mononuclear single-molecule magnet behavior. The spin transport parameters are extracted from the suppressed weak localization in the magnetoresistance measurements. The mononuclear single-molecule magnet can increase the spin-orbit coupling strength of graphene. The proportion relation between spin relaxation and momentum scattering time are acquired by tuned the charge carriers density, which origins from Elliot-Yafet mechanism. The relationship between the strength of spin-orbit coupling and temperature can be devided into two types, one is temperature dependent and another is temperature independent. This enhances the Dressahaus spin orbit coupling, which is attributed to the pseudomagnetic field from the ripples. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y25.00007: Magnetic properties of intercalated Dy and Eu under Graphene Nathaniel Anderson, Myron Hupalo, John Freeland, Michael Tringides, David Vaknin X-ray magnetic circular dichroism (XMCD) measurements of graphene intercalation with Dy and Eu on silicon SiC(0001) surface reveal magnetic correlations in these single layer rare-earth metals. The intercalation of Dy or Eu is achieved by depositing the metal on graphene that is grown on SiC and by annealing at high temperatures to allow diffusion through the graphene. Comparing the XMCD signal of the intercalated Dy sample with that of sample for which the Dy coverage is known, we show that the intercalated Dy forms an intact and stable monolayer under graphene. Furthermore, the field dependence of the Dy magnetic moment extracted from the XMCD by standard sum-rules (at 15 K) deviates from the paramagnetic Brillouin function indicating finite in-plane magnetic correlations in the Dy or the Eu layer. The XMCD spectra of both intercalated systems (Dy or Eu) compared to those of Dy$_2$O$_3$ and Eu$_2$O$_3$ are significantly different, respectively, demonstrating that the ex-situ intercalated metal-layer is stable in atmospheric environment over time. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y25.00008: Interface states of the topological insulator Bi$_2$Se$_3$ Niraj Aryal, Efstratios Manousakis Investigation of interface states in topological insulators is important for both potential applications and for emergent fundamental phenomena. Here, we investigate such interface states for various cases using density functional theory. We are interested in the following cases: (a) the interface of the topological insulator (TI) Bi$_2$Se$_3$ with itself when we allow an atomically thin spatial gap between the two parts, (b) the interface of the TI above with a metal (M), and (c) the interface of the TI with a typical band insulator. In the case (a) we find that as a function of the distance, the interface states undergo a drastic transformation, namely an inteface Dirac-like state forms quickly as the distance between the two TI parts increases. In the case (b) we find that the nature of the interface states depends on the type of the metallic contact. Our preliminary results for the last case (c) above indicate various different ways of reconstruction of the interface states. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y25.00009: Propane Adsorption on ZIF-8 Brice Russell, Aldo Migone We present the results of an adsorption isotherm study of Propane on the metal-organic framework ZIF-8. This material undergoes a structural transition (``gate-opening'') as a function of increasing pressure and sorbent loading for many sorbates. Gate-opening manifests itself in the isotherm data as a quasi-vertical substep, corresponding to an increase in the amount that can adsorb in the ZIF-8. We measured four Propane isotherms from 188 K to 216 K. In this range, we did not find in any of the isotherms the characteristic substep indicative of the gate-opening. It is possible that the temperature range over which this transition would manifest in the data simply has not been explored in our measurements. The adsorption isotherm data was used to determine the isosteric heat of adsorption of Propane on this sorbent as a function of sorbent loading. We have studied the adsorption kinetics for this system, i.e., how the equilibration times for adsorption change as a function of sorbent loading. Trends in the isosteric heat, and kinetics of adsorption data will be discussed. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y25.00010: Study of Carbon Monoxide and Neon Adsorption on Zeolitic Imidazolate Framework -8 (ZIF-8) Dinuka H. Gallaba, Chris Mandrell, Aldo D. Migone Zeolitic Imidazolate frameworks (ZIFs) are porous Metal Organic Framework materials that have zeolite-like structures. We will present the results of an adsorption isotherm study of carbon monoxide in ZIF-8. The adsorption isotherms display multiple sub-steps. Similar substeps have been observed before with xenon and O2 in ZIF-8; they have been interpreted as indicating a pressure-induced structural transition or ``gate-opening'' of the ZIF-8 at low temperatures. We have conducted our measurements for CO on ZIF-8 at temperatures in the range between 72K and 105K. All the isotherms measured in this range have clear sub-steps (which reflect an increase in CO loading due to gate-opening transition). We have used the isotherm data to calculate the isosteric heat of adsorption as a function of loading for this system. We found a change in isoteric heat at the loading corresponding to the structural transition; a similar feature was observed in previous experiments conducted on Xe and on O2 in the same sorbent. We have preliminary results for the sorption of neon in ZIF-8. The isotherm data for neon will be presented and compared data for other gases. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y25.00011: Molecular Insights into Dynamics of Self Pillared Two Dimensional Hierarchical Zeolites shanmuga venkatesan, Neeraj Rai Zeolites are crystalline solids that have wide applications in industrial areas for its hydrocarbon conversion, adsorption of molecules. Two-dimensional (2D) zeolites, precursor of three-dimensional (3D) zeolite, had significant advantage over 3D zeolites for systems that are rate limited by diffusion of reactants and products into interior of zeolites. Recent studies report biofuel conversion reactions like isomerization using zeolites, shows higher efficiency for 2D zeolites over 3D zeolites. In this presentation, we will share some of our recent progress in modeling diffusion process in self pillared two dimensional hierarchical zeolites. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y25.00012: Coverage and velocity dependent sticking coefficient and particle emission kinetics in the Cl$_2^{gas}$ + K$^{solid}$ reaction Lars Hellberg, Bengt Kasemo Some strongly exothermic and non-adiabatic surface adsorption events, especially those where electronegative molecules adsorb on very electropositive (low work function) surfaces, are accompanied by emission of (exo)electrons, photons, excited atoms and negative ions. The reaction of halogen molecules with halogen surfaces constitute an efficient model system for such studies. We have previously reported data for the emission of negative particles and photons in the zero coverage limit for a range of velocities of Cl$_2$ molecules impinging on cold potassium surfaces as well as the mechanism behind these emission processes. In the present work, we focus on measurements of the kinetics, i.e. the exposure/coverage dependence, of these processes for the same system. Specifically, we present data for, (i) the separated contributions from electrons and Cl$^-$ ions of the emitted negative particles, (ii) the photon emission stemming both from excited Potassium atoms and from the equivalent process causing electron emission, (iii) the change of the work function during the initial exposure and, finally, (iv) the sticking coefficient for different Cl$_2$ velocities and exposures. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y25.00013: Kinetic compensation effect in the thermal desorption of a binary gas mixture Nayeli Zuniga-Hansen, Leonardo E. Silbert, M. Mercedes Calbi The kinetic compensation effect, observed in many different areas of science, is the systematic change in the magnitudes of the Arrhenius parameters $E_a$, the energy of activation and $\nu$, the preexponential factor, as a response to external perturbing parameters. Its existence continues to be debated as it has not been explicitly demonstrated and its physical origins remain poorly understood. As part of a systematic study of different factors that alter the energy of activation during thermal desorption, we have performed numerical studies of the effects of adsorbate-adsorbate interactions on the Arrhenius parameters, as well as the effects of changes in surface morphology. Our results have consistently shown that there is a partial compensation effect between $E_a$ and $\ln{\nu}$ and a tendency towards isokinetic equilibrium when the system transitions from an interacting to a non-interacting regime. In the present work we study the effects of the presence of two different chemical species. With our systematic study we expect to provide a deeper insight into the microscopic events that originate compensation effects, not only in our system, but also in other fields where these effects have been reported. [Preview Abstract] |
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