Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R10: Focus Session: Surfaces and Interfaces in Electronic Materials I |
Hide Abstracts |
Sponsoring Units: DCP Chair: Eric Borguet, Temple University Room: Baltimore Convention Center 302 |
Wednesday, March 15, 2006 2:30PM - 3:06PM |
R10.00001: Broad-Band Sum-Frequency Generation Spectroscopy at Platinum/Solution Interfaces Invited Speaker: Vibrational Broad-Band Sum-Frequency Generation Spectroscopy (BB-SFG) is the second-generation SFG method for studying surfaces, including wet electrochemical interfaces.~ BB-SFG measurements, which are based upon the second-order nonlinear optical process are inherently interface specific (as is SFG) but add sensitivity and control to SFG.~~ The electrochemical cell used for the reported measurements has an ideal configuration where the thickness of the supporting electrolyte (25 $\mu $m) is controlled by a spacer, allowing for rapid spectral acquisitions (5 s$^{-1})$ synchronized with the potential sweep at 5 mV s$^{-1})$.~ In the talk, simultaneous electrochemical and BB-SFG measurements will be reported for adsorption/oxidation of carbon monoxide on polycrystalline and well-ordered Pt(hkl) electrodes with both CO-free and CO-saturated electrolytes.~ The emphasis will be on the combination between thin layer electrochemistry (TLE) and vibrational electrode surface analysis, and on dynamics of Pt/solution interfaces probed by the CO molecule adsorption and oxidation. [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:18PM |
R10.00002: Charge inversion at ultra-low electrolyte concentrations Duncan J. McGillivray, Mathias L\"{o}sche, Jens Pittler, Wei Bu, Alex Travesset, David Vaknin Synchrotron x-ray reflectivity studies of the anionic phospholipid DMPA in monolayers spread on very dilute solutions of LaCl$_3$ reveal strong adsorption of the cations at nanomolar and micromolar concentrations, and a sharp transition in cation concentration at the interface as a function of ionic strength. Using anomalous X-ray reflection we determine the number of La$^{3+}$ ions per DMPA$^-$ (surface charge density, $\sigma \approx e^-/40$ \AA$^2$) over four orders of magnitude in bulk ion concentration. We find that at concentrations in the range 10--300 nM La$^{3+}$ forms a Stern layer with $\approx$ 1 La$^{3+} /$ 3 DMPA$^-$, thus neutralizing the lipid surfaces charge. At a critical bulk concentration, $C_t \approx$ 500 nM, the surface concentration of La$^{3+}$ increases steeply, up to a saturation level with $\approx$ 1 La$^{3+} /$ DMPA. The strong condensation of La$^{3+}$ above $C_t$ implies that the charge at the interface is reversed. We provide theoretical arguments that the charge reversal is facilitated by 1) strong correlations between the phosphate groups and La$^{3+}$ ions and 2) hydrogen bonding of hydroxyl groups, effectively forming the complex La$^{3+}$PO$_4^{2-} $OH$^- $. [Preview Abstract] |
Wednesday, March 15, 2006 3:18PM - 3:30PM |
R10.00003: Modeling Electrocatalysis -- Electro-oxidation of Pt(111) Timo Jacob, Matthias Scheffler Electrochemical reactions (such as in fuel cells) usually occur under conditions of finite temperature, pressure, and electrode potential, implying a very involved situation, possibly leading to novel surface materials. Especially the presence of an electrode potential, which results in the formation of an electric double-layer, affects the composition and structure of the electrode/electrolyte-interface. Towards a more realistic treatment of electrocatalysis we developed an appropriate theory in which the electrode of the interface is assumed to be in contact with a {\it bulk-electrode} reservoir (at chemical potential $\mu_{\mathrm{el}}$) while the electrolyte is in contact with a {\it bulk-electrolyte} reservoir. Although we are in the process of simulating the entire electric-double layer self-consistently, the present approach already allows us to estimate the limites of the expected effects. As a first application we studied the electro-oxidation of Pt(111) by calculating the $p/T/\phi$-phase diagram. The obtained behavior, that positive electrode potentials stabilize higher oxygen coverages, is in qualitative agreement with cyclic-voltammetry experiments. [Preview Abstract] |
Wednesday, March 15, 2006 3:30PM - 3:42PM |
R10.00004: Electrochemical oxidation in solid oxide fuel cells -- Where does it occur and how? Robert Walker, Michael Pomfret Electrochemical processes in solid-oxide fuel cells (SOFCs) are thought to occur at a ``triple phase boundary'' (TPB) -- that junction between a conducting anode, a solid oxide electrolyte and the gas phase fuel mixture. A quantitative, physical description of this boundary, however, remains elusive given difficulties associated with probing molecular species present in SOFCs under realistic operating conditions of high temperatures and reducing atmospheres. Recently, we have constructed an SOFC that has optical access to the anode assembly allowing us to probe with Raman spectroscopy the chemical intermediates present on anode and electrolyte surfaces as carbon containing fuels are electrochemically oxidized. Results show that chemistry occurs on both the anode and electrolyte surfaces as well as in the vicinity of the purported TPB. The reduced electrolyte surface is both catalytically active and, over micron distances, electrically conductive. The Ni anode shows strong evidence of adsorbed carboxylate intermediates. This talk will address mechanisms of electrochemical oxidation in SOFCs using direct and indirect experimental probes as well as the consequence of our findings for models of a well defined triple phase boundary. [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 4:18PM |
R10.00005: Epitaxial Electrodeposition of Chiral Metal Oxide Films Invited Speaker: Chirality is ubiquitous in Nature. One enantiomer of a molecule is often physiologically active, while the other enantiomer may be either inactive or toxic. Chiral surfaces offer the possibility of developing heterogeneous enantiospecific catalysts that can more readily be separated from the products and reused. Chiral surfaces might also serve as electrochemical sensors for chiral molecules- perhaps even implantable chiral sensors that could be used to monitor drug levels in the body. Our trick to produce chiral surfaces is to electrodeposit low symmetry metal oxide films with chiral orientations on achiral substrates (see, \textit{Nature} \textbf{425}, 490, 2003). The relationship between three-dimensional and two-dimensional chirality will be discussed. Chiral surfaces lack mirror or glide plane symmetry. It is possible to produce chiral surfaces of materials which do not crystallize in chiral space groups. We have deposited chiral orientations of achiral CuO onto single-crystal Au and Cu using both tartaric acid and the amino acids alanine and valine to control the handedness of the electrodeposited films. We will present results on the chiral recognition of molecules such as tartaric or malic acid and L-dopa on the chiral electrodeposited CuO. Initial work on the electrochemical biomineralization of chiral nanostructures of calcite will also be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R10.00006: Ab initio structure and energetics of ice Ih - implications for wetting Peter J. Feibelman The lattice energy of ice Ih is found to equal 0.68 eV/H$_{2}$O, in a VASP-based, GGA/PW91 optimization of a 96-molecule cell, with zero dipole moment in every hexagonal layer.\footnote{J. A. Hayward, J. R. Reimers, J. Chem. Phys. \textbf{106}, 1518(1997).} This result agrees closely with Hamann's value, obtained for a small, proton-ordered, and thus polarized unit cell.\footnote{D. R. Hamann, private communication. See, P. J. Feibelman, Science \textbf{295}, 99(2002), ref. 19.} Slight inhomogeneous broadening of the O-H stretch peak is estimated, based on the computed O-O distance distribution. Implications regarding wetting-layer formation will be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R10.00007: How Water Meets a Hydrophobic Surface -- Reluctantly and with Fluctuations Adele Poynor, Liang Hong, Steve Granick The details of how water meets a hydrophobic surface are still hotly debated. Here we use two independent methods, ellipsometry in the time-resolved phase-modulated mode, and surface plasmon resonance, to investigate the view that thermodynamics causes a nanometer-sized low-density layer to form adjacent to the hydrophobic solid. Strong evidence in favor of the hypothesis is found. This zone of depleted density shows large fluctuations even within the spatial (over a beam size of 10 $\mu $m) and temporal (with a time constant of 30 ms) averaging inherent in ellipsometry measurement. Statistical analysis of these noise spectra reveal a remarkable scaling with the area over which the measurements are averaged. [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R10.00008: Diffusion, adsorption and incorporation of antifreeze glycoprotein molecules at the ice/water interface Hiroyuki Nakaya, Salvador Zepeda, Yukihiro Uda, Shuichiro Matsumoto, Etsuro Yokoyama, Yoshinori Furukawa Antifreeze glycoproteins(AFGP) are known to inhibit ice crystal growth by adsorbing to the interface. But, there is no direct observation of the distribution of AFGP molecules around the interface of the growing ice crystal. In order to observe the growing ice/water interface, one-directional growth experiments of ice crystal growth were carried out in AFGP solution. AFGPs were labeled with fluorescent markers to see the distribution of AFGP molecules. We obtained video image of the distribution of AFGP molecules near the growing ice/water interface by using fluorescent microscopy. Incorporation and accumulation of AFGP molecules at the interface were clearly observed, and strongly depend on the growth rate of the ice crystal. We also observed the diffusion field of AFGP molecules from the ice interface and calculated diffusion and segregation coefficients. We found that AFGP molecules strongly adsorb to the growing ice crystal interface, and incorporate between grain boundaries, but found little evidence for incorporation into the crystal lattice. This is contrary to previous paradigms for AFGP function. [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R10.00009: Self-oscillatory ice crystal growth in antifreeze protein (AFP) and glycoprotein (AFGP) solutions Salvador Zepeda, Hiroyuki Nakaya, Yukihiro Uda, Etsuro Yokoyama, yoshinori Furukawa AFPs and AFGPs allow many organisms including fish, plants and insects to survive sub-freezing environments. They occur in a wide range of compositions and structure, but to some extent they all accomplish the same functions: they suppress the freezing temperature, inhibit recrystallization, and modify ice crystal growth. A complete description of the AFGP/AFP surface mechanism as well as other ice surface phenomenon has eluded scientists primarily due to a lack of direct surface studies. We study ice crystal growth in AFGP and AFP solutions with phase contrast microscopy during free solution growth under various conditions including microgravity. Free-solution growth experiments show an anisotropic self-oscillatory growth mode of the steps and interface near the freezing temperature and enhancement of the growth rates in the c-axis. These results contradict the previous ?tight-binding? mechanism thought to be responsible for antifreeze function. To study the effects of temperature driven convective flows on the interface kinetics, microgravity experiments were performed in a jet airplane during a parabolic flight path. Step propagation on the basal plane slows down considerably when entering the microgravity condition and reaches a critical condition just below 0.2g. [Preview Abstract] |
Wednesday, March 15, 2006 5:06PM - 5:18PM |
R10.00010: Simulation study of water/silicon oxide interface Christian Lorenz, Susan Rempe, Mark Stevens, Gary Grest, Mesfin Tsige The interaction of water with solid surfaces plays a crucial role in many phenomena. The water-silica interface is one of the typical systems encountered in technological and natural materials. Numerous technological applications of silica were found to rely on its specific surface properties. Large scale quantum mechanics (QM) and classical molecular dynamics (MD) simulations are used to study the molecular configurations and wetting properties of water at the interface of different silicon oxide surfaces. In order to understand how the surface coverage of silanols (-SiOH) affects the wetting behavior of the silica surfaces, both crystalline ((001) $\alpha$-quartz (coverage 9.6 nm$^{-2}$) and (100) $\beta$-cristobalite (7.8 nm$^{-2}$)) and amorphous silica (5.0 nm$^{-2}$) substrates have been studied. The binding energy of the water, the number of water molecules hydrogen-bonded to the surface and the configuration of the hydrogen-bonded water molecules are determined as a function of silanol coverage from QM simulations. The number of water molecules within a monolayer and the orientation of the water molecules within the monolayer and in the bulk are determined from MD simulations. Results from two classical force fields are compared to one another and to the relevant quantities from the QM simulations. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, March 15, 2006 5:18PM - 5:30PM |
R10.00011: Hydrogen etching and graphitization of 4H- and 6H-SiC Xuebin Li, Zhimin Song, Tianbo Li, Claire Berger, Phillip First, Walter de Heer Hydrogen etching and graphitization on the surfaces of 4H/6H-SiC with different off-axis angles were studied at temperatures ranging from 1300-1600$^{0}$C. Above 1500$^{0}$C, the scratches caused by polishing on the surfaces of SiC were effectively removed by the reaction with hydrogen. AFM images showed various topographies on the surfaces of 4H/6H SiC after hydrogen treatment, related to wafer type (4H or 6H), polar faces (Si- face or C-face), off-axis angles, and inherent substrate defects. Flat thin graphite films were grown by the thermal decomposition of SiC at high temperature on both C- and Si- faces of SiC in a vacuum furnace. Surface graphitization of 4H/6H SiC previously flattened by hydrogen etching was analyzed in UHV by LEED and AES, and in ambient air by AFM. Mobility of graphite films grown on the C-face of 4H-SiC ranges from 1000 to 10,000 cm$^{2}$/Vs. Magnetotransport of the graphite film shows 2D gas behavior, accompanying with SdH oscillations and Hall plateaus. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700