Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M40: Surfaces, Interfaces, and Thin Film Reactions: Kinetics & Dynamics |
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Sponsoring Units: DCMP Chair: Brad Conrad, Appalachian State University Room: 349 |
Wednesday, March 20, 2013 8:00AM - 8:12AM |
M40.00001: Effects of Plasmon Excitation on Photocatalytic Activity of Ag/TiO$_{2}$ and Au/TiO$_{2}$ nanocomposites Dinko Chakarov, Raja Sellappan Model composite photocatalysts consisting of undoped TiO$_{2}$ films and optically active Ag or Au nanoparticles (NP) were prepared and examined in order to address the role of plasmon excitation in their performance. The particles were either in direct contact or isolated by thin SiO$_{2}$ layer from TiO$_{2}$. We found, as measured for the reactions of methanol and ethylene oxidation in two different photoreactors, that composites show always enhanced (up to x100) activity compared to pure TiO$_{2}$. Interfacial charge transfer between TiO$_{2}$ and NPs plays major role for the enhancement. Plasmonic near-, far-field and thermal effects are present but do not dominate. [Preview Abstract] |
Wednesday, March 20, 2013 8:12AM - 8:24AM |
M40.00002: In-situ coherent x-ray scattering from Ag (001) and Ag (111) surfaces in vacuum and gas-phase environments Robert Karl, Jr., Andi Barbour, Vladimir Komanicky, Chenhui Zhu, Daniel Hennessy, Hoydoo You, Michael S. Pierce We have been able to obtain X-ray photon correlation spectroscopy (XPCS) quality data from the Ag (001) and Ag (111) surfaces at two different locations along the specular scattering rod. We observe dynamic behavior related to temperature and gas-phase composition. We will present the methods of the XPCS analysis routines, as they have been adapted to this specific system, and the preliminary results for the dynamics, such as step edge motion, island growth, and surface phase transitions, of the Ag surface features in these different conditions. These dynamics are also q dependent and vary from slow at low q, to faster dynamics at positions near the Ag (001) anti-Bragg scattering position where the experimental sensitivity is sufficient to detect changes at a monolayer level. This indicates that the dynamics involved are occurring right at the surface and do not involve multiple layers. These results will then be compared to our recent similar measurements on the Au (001) surface [1].\\[4pt] [1] M.S. Pierce, V. Komanicky, A. Barbour, D.C. Hennessy, A. Sandy, and H. You, Physical Review B 86, 085410 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 8:24AM - 8:36AM |
M40.00003: Inhibition of Hydrogen Absorption in Pd by the Formation of a Pd-Ru Surface Alloy A.L. Cabrera, P. Ferrari, S. Rojas, Donovan E. Diaz-Droguett, E. Ramos-Moore Hydrogen absorption by palladium has been studied for decades due to the significant importance in a number of applications like production and storage of hydrogen and hydrogen sensors. Alloying Pd with just a 4{\%} of Ru drastically reduces the absorption properties of the Pd. The fcc crystal structure is preserved but the lattice constant is reduced slightly. In order to understand this phenomenon, we used three samples: a Pd foil, a Pd-Ru(4{\%}) alloy foil, and a Pd foil with a Pd-Ru surface alloy. The surface alloy was made evaporating 8 nm of Ru using an e-beam evaporation technique on top of Pd, followed with a heating the sample up to 700 $^{\circ}$C in a high vacuum system. We studied the changes in absorption properties of these samples using Thermal Program Desorption (TPD), resistance changes and grazing incidence X-ray Diffraction (GID). [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 8:48AM |
M40.00004: Pd/Ru surface alloys -- Creating a ``noble'' surface from reactive elements Xiangshi Yin, Mustafa M. \"Ozer, Hanno H. Weitering, Paul C. Snijders We have studied the growth and reactivity of ruthenium thin films on palladium (111) substrates. To obtain smooth and well-ordered film surfaces, the films were annealed to 600 $^{\circ}$C. The surface structure, morphology, and chemical composition were investigated with LEED, STM, and AES. The experiments showed that annealed Ru film surfaces contain large concentrations of Pd. The reactivity of this alloy surface towards oxygen was then studied in oxygen gas adsorption experiments at room temperature, and compared to the oxidative properties of bulk Ru and bulk Pd. The surface alloy of the film turns out to be quite inert to oxygen adsorption at room temperature. STM experiments of oxygen adsorption at 112 K reveal that oxygen does adsorb at low temperature but it readily desorbs above 200 K. This surprise finding of a ``noble'' Pd/Ru surface alloy provides an interesting contrast to the surfaces of bulk ruthenium and palladium, which oxidize easily at room temperature. Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division [Preview Abstract] |
Wednesday, March 20, 2013 8:48AM - 9:00AM |
M40.00005: Solid-State Diffusional Mixing in Cu Core/Ni Shell Nanoparticles Karl Unruh, Brian Kelly, John Klodnicki, Gerald Poirier Cu core/Ni shell nanoparticles have been prepared in a polyol process using ethylene glycol as the solvent /reducing agent solution and Cu and Ni acetates as the metal sources. The more positive reduction potential of Cu(II) relative to Ni(II) lead to the formation of Cu core/Ni shell nanoparticles. The structural evolution of these core/shell diffusion couples was studied by high temperature x-ray diffraction measurements. Between room temperature and 350 $^{\circ}$C, the evolution in the diffraction pattern was only due to lattice expansion. At higher temperatures, the elemental Cu and Ni diffraction peaks began to merge until, at a temperature of 600 $^{\circ}$C only a single set of diffraction peaks remained, indicating the formation of a single homogeneous Cu-Ni alloy. These diffraction patterns have been decomposed into a set of 11 individual subpeaks corresponding to 9 intermediate Cu-Ni compositions in addition to subpeaks corresponding to pure Cu and Ni. The angular positions of each subpeak were fixed to the values appropriate for their composition and the best fit peak areas determined. These data were then used to reconstruct the radial composition profiles of the diffusion couples as a function of the reaction temperature and time. [Preview Abstract] |
Wednesday, March 20, 2013 9:00AM - 9:12AM |
M40.00006: Investigation of Fe/CuO Interface by X-ray Photoelectron Spectroscopy A. Chourasia, R.L. Miller, H. Dong, J.L. Edmondson The Fe/CuO interfaces have been investigated by x-ray photoelectron spectroscopy. Thin films of iron were deposited on copper oxide substrates at room temperature. The spectral data show considerable reactivity at the interfaces. The spectral data have been compared with those of the oxidized iron and confirms the formation of the iron oxide at the interface. The interface is found to consist of a mixture of iron oxide and elemental copper. Presence of unreacted iron near the interface has been observed for thicknesses equal to or greater than 0.9 nm of the iron overlayer. The interface was also prepared by depositing 2.0 nm of iron on the copper oxide substrate under two different conditions. In one, the substrate temperature was kept constant during the deposition of the iron overlayer. In the other, post deposition annealing of the sample was performed. The iron overlayer was observed to be completely oxidized at the sample temperature of 450 $^{\circ}$C and the oxidation is independent of the processing conditions. The amount of elemental iron and iron oxide in the samples has been estimated by modeling the spectrum using the spectra of elemental iron and pure iron oxide. The investigation provides a new method of preparing sub-nano-oxide films of iron. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:24AM |
M40.00007: Coherent X-ray Scattering Experiments of Pt (001) Surface Dynamics near Roughening Transition Hoydoo You, Michael Pierce, Andi Barbour, Vladimir Komanicky, Daniel Hennessy We will present the results of a series of coherent x-ray scattering temperature dependent experiments from Pt (001) in high vacuum. The resulting speckled diffraction patterns are analyzed with x-ray photon correlation spectroscopy. We find that the hexagonally reconstructed Pt (001) surface exhibits orientational dynamics below 1640 K and a critical behavior as $T$ increases to $T_{\mathrm{R}} =$ 1834 K, near the roughening transition as proposed by Abernathy, et al. [Phys. Rev. Lett. \textbf{69}, 941 (1992)]. The inverse autocorrelation time constant $\tau ^{-1}$ of the surface diverges as $T$ approaches $T_{R}$. The average integrated intensity remains constant below $T_{\mathrm{R}}$ but drops suddenly over a narrow temperature range, indicating abrupt lifting of the hexagonal reconstruction with the roughening transition. This behavior is compared to that of Au (001), for which $\tau^{-1}$ approaches a finite value as the reconstruction lifts gradually over a wide temperature range. [Preview Abstract] |
Wednesday, March 20, 2013 9:24AM - 9:36AM |
M40.00008: A DFT Study of the Interaction of Monometallic Pd$_{\mathrm{n}}$/Pt$_{\mathrm{n}}$ (n$=$1, 9) Clusters with $\gamma $-Al$_{2}$O$_{3}$(100) Surfaces Nalin Fernando, Tyne Johns, Yue Qi, Chang Kim, Abhaya Datye, Boris Kiefer The reduction of carbon monoxide and hydrocarbon emissions in advanced low temperature combustion engines has become more difficult for the advanced combustion systems in transportation sector. Exploration of effect of interface formation on the electronic properties of the existing platinum group materials may provide insight for the new material development that rivals platinum. In order to address the effects of the interface on the electronic properties of small Pd$_{\mathrm{n}}$ and Pt$_{\mathrm{n}}$ clusters (n$=$1-9) with a $\gamma $-Al$_{2}$O$_{3}$(100) support we have performed density-functional-theory (DFT) computations. The preliminary results suggest that the most favorable Pd$_{9}$ binding geometry is characterized by four Pd atoms binding to both Al and O surface atoms. The average Pd-O bond length across the interface is $\sim$ 2.2 {\AA}, corroborating the formation of bonds. The preliminary analysis of the electronic density of states shows that the main electronic modifications occur at the Fermi energy, leading to an overall metallic behavior. We will discuss cluster size effects on the character of bonding across the interface, its stability, and electronic structure. [Preview Abstract] |
Wednesday, March 20, 2013 9:36AM - 9:48AM |
M40.00009: Dynamics of tungsten and cobalt carbonyls on silica surfaces Kaliappan Muthukumar, Roser Valenti, Harald O. Jeschke Metal carbonyl species adsorbed on a substrate are the starting point for the electron beam induced deposition of metallic nanostructures. We employ first principles molecular dynamics simulations to investigate the dynamics of tungsten hexa- and pentacarbonyl as well as cobalt octacarbonyl precursor molecules on fully and partially hydroxylated silica substrates. We find that physisorbed carbonyls are quite mobile on a silica surface saturated with hydroxy groups, moving around half an Angstrom per picosecond. In contrast, chemisorbed ions like [W(CO)$_5$]$^-$ or [Co(CO)$_4$]$^-$ are more stable at room temperature. We determine the vibrational spectra which can provide signatures for experimentally distinguishing the form in which precursors cover a substrate. [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:00AM |
M40.00010: Effects of biaxial strain on diffusivity of low index tungsten surfaces Zhengzheng Chen, Nasr Ghoniem Detailed knowledge of diffusion behaviors is necessary toward fully understanding of damage of tungsten serving as reactor pressure vessels. Using first-principles calculations, we observed different diffusion scenarios on W(001) and W(110) surfaces with external biaxial strains. Hopping is the major diffusion mechanism on the W(110) surface under all kinds of loadings in the present work. On the other hand, the main mechanism on the W(001) surface transfers between the adatom hopping and the formation and movement of surface crowdions depending on biaxial strains. Our results also indicate high mobile and strong anisotropy of surface crowdions on both surfaces. The microscopic explanation is presented by analyzing the charge density. We have built up the diagram of diffusion on the W(001) surface. This diagram presents that not only the diffusion mechanism, but also the diffusion direction can be modulated by patterns of biaxial strains. These results are important to the future dynamical modeling and simulations. We have further performed kinetic Monte Carlo simulations and observed (1) the modulation of diffusion of single adatom on W(001) surface by strains and (2) the aggregation of multiple adatoms on W(110) surface. [Preview Abstract] |
Wednesday, March 20, 2013 10:00AM - 10:12AM |
M40.00011: Determination of shift in electrodic reaction rates due to the presence of stress Swarnavo Sarkar, Wilkins Aquino An extension of Butler-Volmer formulation is proposed to determine the stress-induced changes in electrodic reaction rates. Gibbs-Duhem equation is used to determine the stress-dependent chemical potential and the corresponding change in the reaction rate. The scope of possible amplification or reduction in the reaction rates due to tensile and compressive stress fields is explored numerically. Though quantitative experimental validation remains to be pursued, behavioral agreement of the extended Butler-Volmer model with some observations made in the field of corrosive dissolution is established. Our numerical results also indicate that in addition to altering the speed of a reaction, a stress field can modify the shape of an anodic dissolution front. The effect of stress-generated surface patterns is also considered. It is well-established that a stress field can create surface patterns due to surface wrinkling or surface diffusion. We determine the possible significance of such patterns on the reaction rate, and identify the factors that may enhance their contribution to electrodic reaction rates. [Preview Abstract] |
Wednesday, March 20, 2013 10:12AM - 10:24AM |
M40.00012: The model that takes the Marangoni effect into account for drying process of polymer solution coated on a flat substrate Hiroyuki Kagami We have proposed and modified a model of drying process of polymer solution coated on a flat substrate for flat polymer film fabrication supposing resist coating process in photolithography process. And we have clarified dependence of distribution of polymer molecules on a flat substrate on various parameters based on analysis of many numerical simulations of the model. Then we applied the model to thickness control of a thin film after drying through thermal management. Above model consists of two elements. One is vaporization at the gas-liquid interface. The other is the diffusion inside the liquid film on a substrate. The diffusion is divided into two kinds of diffusion, that is, diffusion of solvent with solutes due to gradient of the number density of particles per space and diffusion of diffusion of concentration of solution. Because it is assumed that coated solution film on a flat substrate is very thin and therefore both Rayleigh number and Marangoni number are small enough, it is thought that B\'enard convection or Marangoni convection does not occur and therefore it is sufficient to consider only above-mentioned two kinds of diffusion inside the liquid film. However it is thought that there is some sort of Marangoni effect regardless Marangoni convection does not occur. Therefore, in this study we add the Marangoni effect to the existing model. Then we evaluate effects of the Marangoni effect in the drying process through numerical simulation of the modified model. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 10:36AM |
M40.00013: Mesoscopic Aligned and Cu-Coordinated Surface Linear Polymerization at Low Temperature Qing Li, Jonathan R. Owens, Chengbo han, Miguel Fuentes-Cabrera, Bobby G. Sumpter, Wenchang Lu, Jerry Bernholc, Petro Maksymovych, Vincent Meunier, Minghu Pan The on-surface synthesis of covalent organic aggregates and networks has received considerable attention. However, most of the polymerization reactions require high temperatures to overcome the activation barrier. We demonstrate a surface-coordinated linear polymerization, which occurred at 100 K and forms long chain that are well-organized into a ``circuit-board'' pattern on Cu(100) surface. This highly strained 1D conjugated polymer alters greatly the electronic structure compared to unperturbed polymer and it was investigated by electronic and vibrational spectroscopies, as well as \textit{ab initio} calculations. More importantly, the processes of polymerization and depolymerization can be controlled locally at the nanoscale by a using a charged metal tip. This work thus demonstrates the feasibility of accessing and controlling chain-growth polymerization at low temperature that may lead to the bottom-up construction of sophisticated architectures for molecular nano-devices. [Preview Abstract] |
Wednesday, March 20, 2013 10:36AM - 10:48AM |
M40.00014: Surface reactivity/stability and hydration of calcium silicate phases Engin Durgun, Can Ataca, Hamlin M. Jennings, Jeffrey C. Grossman Recent studies on synthetic calcium silicate structures revealed important mechanisms to tune the reactivity of various cement phases. Interaction of water with dicalcium silicate (C2S-belite) and tricalcium silicate (C3S-alite), dominant phases in Portland Cement, are the most important and anticipated reactions. In this work, using first-principles calculations, a fundamental understanding of how water pressure affects the reactivity of C3S and C2S phases is provided. In order to understand the hydration of different phases, as a first step the surface energetics of all lower index orientations are calculated and the stability/reactivity of the surfaces are determined. Taking into account the most and least energetic surfaces of the C3S phase, detailed analyses are carried out in order to understand the induction period in hydration. Surface transformation from highly reactive C3S to low reactive C2S revealed that upon increasing the water pressure, the surface with C2S character becomes energetically more favorable. Reduction of the surface energy is more intense in the case of proton exchange of surface Ca atoms. Our calculations suggest that these processes are the most probable mechanisms underlying the rapid decrease in reactivity in alite hydration. [Preview Abstract] |
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