Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session Y31: Quasicrystals, Adsorption on Quasicrystals, Porous and Random Materials |
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Sponsoring Units: DCMP Chair: Stefano Curtarolo, Duke University Room: Baltimore Convention Center 329 |
Friday, March 17, 2006 8:00AM - 8:12AM |
Y31.00001: Magnetism in Fe$_{4}$Al$_{13}$ and related FeAl intermetallics Ji Chi, Yang Li, Weiping Gou, V. Goruganti, K. D. D. Rathnayaka, Joseph H. Ross, Jr. We report the results of an experimental study of FeAl alloys, including Fe$_{4}$Al$_{13}$, FeAl$_{2}$ and Fe$_{2}$Al$_{5}$. By using NMR, dc magnetic susceptibility, and specific heat, we found that Fe$_{4}$Al$_{13}$ and Fe$_{2}$Al$_{5}$ are non-magnetic with some dilute magnetic moments, while FeAl$_{2}$ can be characterized as a concentrated local moment system. Fe$_{4}$Al$_{13}$ is a decagonal quasicrystal approximant with 102 atoms in its unit cell. The $^{27}$Al NMR spin-lattice relaxation indicates a very narrow pseudogap in the electronic density of states [$g(E)$] in the vicinity of the Fermi energy. The observations could be fit assuming a parabolic variation of $g(E)$, consistent with observations in other quasicrystals and approximants. NMR lineshape measurements also agree with this analysis, and show that the system is dilute-magnetic, in strong contrast to the FeAl$_{2}$ ordered intermetallic. We use specific heat to analyze the dilute moment density. This work was supported by the Robert A. Welch Foundation, Grant No. A-1526, by the National Science Foundation (DMR-0103455), and by Texas A\&M University through the Telecommunications and Informatics Task Force. [Preview Abstract] |
Friday, March 17, 2006 8:12AM - 8:24AM |
Y31.00002: 3D octagonal quasicrystals fabricated by phase mask lithography Taeyi Choi, Ion Bita, Edwin Thomas Quasicrystals were discovered in 1984 and have shown unusual physical and mechanical properties. Artificially patterned quasicrystalline structures have attracted a lot of attention due to their promise as photonic and phononic crystals. A challenge is to create 3D quasicrystalline patterns on the 100nm scale. Using phase mask lithography, we successfully fabricated in photopolymer films 3D quasicrystals having eight-fold rotation axes on a submicron length scale. Conformable phase masks of eight-fold rotation symmetry were first made with multiple interference lithography on a silicone substrate. Light at normal incidence to the phase mask generates a 3D distribution of intensity with quasicrystalline eight-fold symmetry. This intensity distribution is then transferred into a photosensitive material, SU8, generating 3D quasiperiodic structures that we further characterize both structurally and optically. [Preview Abstract] |
Friday, March 17, 2006 8:24AM - 8:36AM |
Y31.00003: Band Structure, Density Waves, and the Third Invariant David Rabson, John Huesman There are three types of invariants in crystals. The first two, corresponding to electronic degeneracies, are well known, but the third is novel, realized in incommensurate crystals of non-minimal rank. Since the first two invariants have consequences in band structure, it is natural to look there for the third type as well. Rather than developing an atomic or tiling model with the third type of symmetry, we introduce a tight-binding approach based on a density-wave pattern, which is easy to generate from the Rokhsar-Wright-Mermin phase functions. [Preview Abstract] |
Friday, March 17, 2006 8:36AM - 8:48AM |
Y31.00004: Epitaxial orientations and temperature dependence of the 5- to 6-fold ordering transition Stefano Curtarolo, Wahyu Setyawan, Nicola Ferralis, Milton W. Cole, Renee Diehl The ordering of Xe films on an Al$_{73}$Ni$_{10}$Co$_{17}$
quasicrystalline surface is studied using grand canonical Monte
Carlo simulations with an empirical adsorption potential based on
Lennard-Jones interatomic potentials. At all temperatures
studied (20-140K), there is a continuous 5- to 6-fold ordering
transition in the monolayer [1]. The ordering transition shows
interesting temperature-dependent phenomena [2]. At intermediate
$T$ (40K$ |
Friday, March 17, 2006 8:48AM - 9:00AM |
Y31.00005: Evolution of noble gas films on a decagonal Al-Ni-Co quasicrystal surface. Wahyu Setyawan, Nicola Ferralis, Renee D. Diehl, Milton W. Cole, Stefano Curtarolo The evolution of Ne, Ar, Kr, and Xe films on an Al$_{73}$Ni$_{10}$Co$_{17}$ quasicrystalline surface is studied using grand canonical Monte Carlo simulations with an empirical adsorption potential based on Lennard-Jones interatomic potentials. Layer by layer growth is observed for all the studied noble gases. The monolayer of Ar, Kr, and Xe grows abruptly, where as the monolayer of Ne grows gradually. The next layers of all gases grow step wise. At a comparable range of temperatures, the evolution of the monolayer density profiles shows a continuous commensurate 5-fold to incommensurate 6-fold ordering transition for all gases. However, the degree of completeness of the transition varies and shows an increase from Ne, Ar, Kr, to Xe. Research sponsored by NSF. [Preview Abstract] |
Friday, March 17, 2006 9:00AM - 9:12AM |
Y31.00006: Argon adsorption on a microporous metal organic framework, Cu$_{3}$(BTC)$_{2}$(H$_{2}$O)$_{3 }$(Benzene-1,3,5-tricarboxylate) K. Lask, V. Krungleviciute, L. Heroux, A. D. Migone, J.-Y. Lee, J. Li We will present results for argon adsorbed on Cu$_{3}$(BTC)$_{2}$(H$_{2}$O)$_{3 }$(Benzene-1,3,5-tricarboxylate) metal-organic frameworks. Full adsorption isotherms (up to saturation) were measured at four temperatures between 66 and 92 K. We observe three distinct sub-steps in the data, indicating that there are at least three different types of binding sites available for argon. We have calculated isosteric heats of adsorption as a function of coverage for this system. We have also measured four isotherms at low coverage for temperatures between 112 and 143 K in order to determine the binding energy for argon on the strongest binding sites available on this microporous metal organic framework. Our results will be compared to previous experimental and computer simulations for this system. [Preview Abstract] |
Friday, March 17, 2006 9:12AM - 9:24AM |
Y31.00007: Microstructure of a phase-separating liquid mixture confined in mesoporous Controlled Pore Glass -- A study combining SANS, NSE and adsorption measurements Gernot Rother, Sebastian Schemmel, Dirk Woywod, Martin Schoen, Gerhard H. Findenegg The physical properties of liquid mixtures with miscibility gap in pores of mesoscopic size are drastically altered from their bulk states, due to adsorption on the pore walls and confinement effects, and it is highly desirable to gain knowledge in the adsorption and separation processes, due to the widescale use of such media in chromatography and other applications [1]. In this work, three complementary techniques were used to address this issue, including both elastic (SANS) and inelastic (neutron- spin-echo) techniques, backed up by physical adsorption measurements of binary liquid mixtures with a miscibility gap [i.e. iso-butyric acid and heavy water] [2,3]. We found a shift in the phase separation temperature by $\sim $ 10 K towards the two-phase region and a drastical slowing down of the dynamics in the two-phase region. [1] K. Binder and E. Luijten, Phys. Reports 344, 179 (2001) [2] S. Schemmel et al., \textit{J. Chem. Phys.} \textbf{122}, 244718 (2005) [3] T. Hellweg et al., \textit{Eur. Phys. J. E} \textbf{12}, s01 (2003) 001 [Preview Abstract] |
Friday, March 17, 2006 9:24AM - 9:36AM |
Y31.00008: Time dependent diffusion in a disordered medium with partially absorbing walls Jiang Qiang, Pabitra N. Sen We present an analytical and numerical study of time dependent diffusion coefficient in systems with partially absorbing boundary condition. We obtain a perturbative expansion for time dependent propagator in terms of volume fraction $f$ of spheres in a dilute suspension of spheres. Exact single sphere $t$-operator for partially absorbing boundary condition is used to obtain a time-dependent diffusion coefficient $D(t)$ for a random distribution of spheres, accurate to the lowest order of volume fraction $f$. Short and long time limits of $D(t)$ are obtained and compared to the known exact results. We then present a significantly improved numerical method for dealing with random walk with partially absorbing boundary on curved surfaces. The method is applied to the dilute suspension of spheres to obtain $D(t)$ and compared with the analytical solution. Numerical simulation on a random closed packed (Finney pack) is used to study correlation between time-dependent relaxation and diffusion. [Preview Abstract] |
Friday, March 17, 2006 9:36AM - 9:48AM |
Y31.00009: Percolation and diffusion in two dimensional random media Bong June Sung, Arun Yethiraj The diffusion of hard disc fluids in two dimensional porous media (composed of immobile hard discs) is studied using discontinuous molecular dynamics (DMD) simulations and analyzed using a Voronoi tessellation procedure. A pore is defined as a circle tangential to three neighbor matrix discs with a pore center at a Voronoi vertex. If an edge of Voronoi diagram connecting two pores is too narrow for a fluid particle to move along, the edge is considered disconnected. This procedure maps the system onto a lattice model with diffusion possible in the bond percolation limit. The percolation threshold, $p_c$ of edges connecting pores is found to be 0.526, where p is the fraction of connected edges. $p_c$ is significantly different from $p_r$ = 2/3 of random bond percolation theory where the edge connectivity of the same Voronoi diagram is determined randomly. This suggests that the edge connectivity is strongly correlated even for randomly distributed medium particles. DMD simulations show normal diffusion for $p > p_r$, confined dynamics for $p < p_c$, and anomalous diffusion for $p_c < p < p_r$. [Preview Abstract] |
Friday, March 17, 2006 9:48AM - 10:00AM |
Y31.00010: Well defined arrays of silica nanotubes for the study of processes at nanoscale: example of one-dimensional diffusion Yaroslav Kievsky, Brent Carey, Daniel ben-Avraham, Igor Sokolov Using organic templating synthesis of inorganic precursor, silica, we synthesized well defined fibers of $\sim $2 microns in diameter and 5 microns in length. Structurally these fibers are parallel arrays of closely packed silica nanotubes (ASNT). BET, SAXS, SEM, TEM, and light scattering techniques were used to characterize these ASNT. Each nanotube is $\sim $3nm in diameter, and extends to the full length of the fiber, 5 microns. Thus, each array has about a quarter of a million of nanotubes in parallel. We expect these ASNT to be a popular system for the study of processes at nanoscale confined space. Signals from the processes that happen inside each silica nanotube will be amplified by the number of nanotubes, i.e., a few hundred thousand times for each fiber. High monodespersity of the fibers ($\sim $10{\%} standard deviation in the length distribution) allows for amplifying the signals even more. To demonstrate the proposed method, we study diffusion of a dye from a single silica nanotube. Due to the size of the dye molecule, one can treat this process as truly one-dimensional diffusion. Experimental data are compared with a diffusion model. Apart from just pure demonstration, these data show the potential of ASNT in the controlled drug release. [Preview Abstract] |
Friday, March 17, 2006 10:00AM - 10:12AM |
Y31.00011: A Two-dimensional Porphyrin-based Porous Network Featuring Communicating Cavities A. Kiebele, H. Spillmann, M. Stoehr, N. Wintjes, T. Jung, D. Bonifazi, F. Cheng, F. Diederich Metallo-porphyrins and their derivatives have been shown to be exceedingly useful building blocks for the construction of 3D supramolecular functional networks due to their excellent thermal and chemical stability and synthetic versatility. Nonetheless, no 2D analogon has been reported so far, although these could be interesting for various potential applications such as molecular sieves or chemical sensors. Herein we report on an unprecedented 2D porphyrin network featuring pores capable of hosting fullerenes following a bottom-up approach at a single crystal silver surface. Surface- and porphyrin-driven long-range interactions between the C$_{60}$ guest molecules and porphyrin layer resulted in the formation of exceptionally large supramolecular hybrid chains and islands as evidenced by Scanning Tunneling Microscopy. [Preview Abstract] |
Friday, March 17, 2006 10:12AM - 10:24AM |
Y31.00012: Analysis of the Complex Dielectric Permittivity Behavior of Porous Al$_{2}$O$_{3}$-SiC Composites in the 1 MHz -- 18GHz Frequency Range Jacob Battat, Jeffrey Calame The complex dielectric permittivity of electrically lossy, porous Al$_{2}$O$_{3}$-SiC composites was measured as a function of frequency over the range of 0.001-18 GHz (broadband). These composites were fabricated by an infusion method of incorporating SiC polymer precursor into porous alumina discs. Repeat polymer infusions and pyrolysis steps to 1000$^{o}$C were carried out, with some samples undergoing an additional air-fire prior to each subsequent step. Generally, it was found that for non-air-fired samples, moderate, controllable losses were attainable over a broad frequency range with $\log \varepsilon ''$ being inversely proportional to $\log f$. By contrast, the dielectric loss attainable for air-fired samples was generally very low. For all samples, various aspects of the variation of permittivity components $\varepsilon '$ and $\varepsilon ''$ with frequency were analyzed, with a view to determine the various factors contributing to dielectric response. In addition, the ramifications of this behavior on the properties of the material as a lossy composite were addressed. [Preview Abstract] |
Friday, March 17, 2006 10:24AM - 10:36AM |
Y31.00013: Low field NMR study of the pre-asymptotic Stokes flow in porous rocks. Philip Singer, Gabriela Leu, Edmund Fordham, Pabitra Sen Dispersion in porous media is a powerful tool for probing the micro-geometry of porous media and the topology of flow fields. Pulsed field gradient nuclear magnetic resonance (PFG-NMR) methods are emerging as very powerful techniques for measuring fluid propagation and dispersion. However, high magnetic field techniques have proven limited since the susceptibility contrast between fluid components and solid interfaces can give rise to strong internal field gradients which corrupt the measurement, and which cannot be easily corrected for. Here for the first time we present PFG-NMR data on a variety of rocks (Bentheimer and Berea sandstones, Portland carbonate) using an unusually low applied magnetic field (2 MHz for protons) to limit these internal field artifacts. We find remarkable differences with the high field data, and we quantify these differences as a function of the mean flow velocity and the interrogation time. [Preview Abstract] |
Friday, March 17, 2006 10:36AM - 10:48AM |
Y31.00014: Influence of Local Field Effects on the Radiative Properties of Nd:YAG Nanoparticles in a Liquid Suspension Ksenia Dolgaleva, Robert Boyd Local field effects can significantly modify the optical properties of laser materials. Neodymium-doped yttrium-aluminum garnet (Nd:YAG) nanopowder with particle sizes on the order of 50 nm was suspended in different organic and inorganic liquids to produce Maxwell-Garnett-type composite materials. The fluorescence decay time of Nd:YAG nanocomposites was experimentally investigated as functions of the refractive index of the liquid, Nd:YAG filling fraction, and the pump-radiation wavelength. The results of these measurements were compared to the predictions of various theoretical models that include in influence of local field effects in nanocomposite materials. [Preview Abstract] |
Friday, March 17, 2006 10:48AM - 11:00AM |
Y31.00015: Thermodynamic studies of one and two dimensional Neon adsorbed on single walled carbon nanotube bundles Subramanian Ramachandran, Gregory Dash, Oscar Vilches In this study we report heat capacity measurements between 2 and 20 K for films of Neon adsorbed on single-walled closed end carbon nanotube bundles. The heat capacity of the adsorbed layer is measured from 1/60$^{th}$ (2 scc) of a monolayer to $\sim $ 1.2 monolayer (155 scc). The heat capacity is used to identify if the phases are solid, liquid or gaseous. The heat capacity at a fixed coverage (less than 12 scc) as a function of temperature reveals some agreement with the values predicted from a 1D solid model by Kostov et.al \textbf{(}Phys. Rev. B \textbf{68, }245403 (2003)\textbf{)} between 2 and 4 K. For coverage higher than 24 scc, the heat capacity at low temperature shows a clear T$^{2}$ dependence. The calculated 2D Debye Temperatures are in the range of 50-60K and are in good agreement with what has been measured by G.B. Huff and J. G. Dash \textbf{(}JLTP\textbf{ 24, }1 / 2, 1976\textbf{) }for Neon adsorbed on Grafoil. The specific heat values are greater than 2 for temperatures greater than $\sim $ 14 K. There is no evidence of first order phase transition due to melting. [Preview Abstract] |
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