Bulletin of the American Physical Society
2005 7th Annual Meeting of the Northwest Section
Friday–Saturday, May 13–14, 2005; Victoria, BC, Canada
Session G1: Condensed Matter II |
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Chair: Geoff Steeves, University of Victoria Room: MacLaurin D110 |
Saturday, May 14, 2005 2:00PM - 2:36PM |
G1.00001: Probing the Unique Size-Dependent Electronic and Structural Properties of Nanoclusters Invited Speaker: Materials in the nanometer size scale exhibit properties different from their bulk counterparts and these properties depend on particle size and shape. This forms the basis for nanoscience and nanotechnology. In our laboratory, we use the bottom-up approach to probe the unique electronic and structural properties of atomic clusters as a function of size from a few to few tens of atoms. Atomic clusters are produced using a laser vaporization cluster source and are studied by photoelectron spectroscopy in combination with quantum calculations. In this talk, I will focus on our recent studies on small boron and gold clusters. One of the most interesting features of elemental boron and many bimetallic boron compounds is the occurrence of highly symmetric icosahedral clusters. I will present experimental and theoretical evidence that small boron clusters in fact prefer planar structures [1-3], completely different from bulk boron. We also found that these planar boron clusters exhibit properties of aromaticity, i.e., electron delocaliztion similar to common aromatic organic molecules. Gold is very different from boron. But small negatively charged gold clusters have also been shown to assume planar structures up to 12 atoms. I will discuss joint photoelectron spectroscopic and theoretical efforts to confirm the planarity of small gold cluster [4]. The discovery of a unique 20 atom tetrahedral gold cluster [5] will be presented, and its novel properties and potentials for catalytic applications will be discussed. Recent effort to synthesize the tetrahedral Au$_{20}$ cluster in solution will also be reported [6]. \newline \newline \textbf{References} \newline [1] H. J. Zhai, A. N. Alexandrova, K. A. Birch, A. I. Boldyrev, and L. S. Wang, \textit{Angew. Chem. Int. Ed.} \textbf{42}, 6004-6008 (2003). \newline [2] H. J. Zhai, B. Kiran, J. Li, and L. S. Wang, \textit{Nature Materials} \textbf{2}, 827-833 (2003). \newline [3] S. K. Ritter, \textit{Boron Flat Out}. \textit{Chem. \& Eng. News} \textbf{82}, March 1 (2004); pp.28-32. \newline [4] H. Häkkinen, B. Yoon, U. Landman, X. Li, H. J. Zhai, and L. S. Wang, \textit{J. Phys. Chem. A} \textbf{107}, 6168-6175 (2003). \newline [5] J. Li, X. Li, H. J. Zhai, and L. S. Wang, \textit{Science} \textbf{299}, 864-867 (2003). \newline [6] H. F. Zhang, M. Stender, R. Zhang, C. M. Wang, J. Li, and L. S. Wang, \textit{J. Phys. Chem. B} \textbf{108}, 12259-12263 (2004). [Preview Abstract] |
Saturday, May 14, 2005 2:36PM - 2:48PM |
G1.00002: Size Dependence of the Magnetic Properties of Cobalt Oxide Nanoparticles Mineralized In Protein Cages Damon Resnick, Keith Gilmore, Yves Idzerda, Michael Klem, Mark Allen, Trevor Douglas, Mark Young Monodisperse and highly uniform magnetic nanoparticle sized structures have been made more possible with the help of genetically engineered biological containers as constraining vessels. In this study different size protein cages were used to synthesize spherical Co$_{3}$O$_{4}$ nanoparticles from 3 nm to 30 nm in diameter, in an attempt to understand the mechanism for the change in the magnetic anisotropy, N\'{e}el temperature and other magnetic properties. For magnetic nanoparticles, as the number of atoms that make up the surface become of the order of the number that make up the remaining volume, the uncompensated spins on the surface compete with the bulk to form unusual magnetic properties. X-ray Absorption Spectroscopy (XAS) is used to study the electronic structure and Vibrating Sample Magnetometry (VSM) and Alternating Current Magnetic Susceptibility (ACMS) are used to determine the magnetic properties of the nanoparticles. [Preview Abstract] |
Saturday, May 14, 2005 2:48PM - 3:00PM |
G1.00003: X-ray absorption spectroscopy as a direct probe of nanoparticle morphology Adam McClure, Keith Gilmore, Damon Resnick, Alex Lussier, Yves Idzerda, Michael Klem, Jessie Mosolf, Mark Allen, Trevor Douglas, Mark Young When properties of nanoparticles are found to vary from expected bulk values it is uncertain whether this is the result of a mixed-phase or amorphous product, or an observation of a true intrinsic size or surface effect. We present x-ray absorption spectroscopy (XAS) as an ideal tool for answering this technologically important and academically interesting question. The strength of XAS lies in the fact that it is a direct element specific probe of electronic structure. We present XAS data on nanoparticles (4-20 nm diameter spheres) of gamma-Fe$_{2}$O$_{3}$, Co$_{3}$O$_{4}$, and TiO$_{2}$. The data reveals that gamma-Fe$_{2}$O$_{3}$ may be grown in the pure phase down to at least 4 nm, while TiO$_{2}$ shows intrinsic size effects at around 10 nm. Our Co$_{3}$O$_{4}$ data presents an example of a mixed phase system. [Preview Abstract] |
Saturday, May 14, 2005 3:00PM - 3:12PM |
G1.00004: Characterizing Thin Film Interface Disruption by X-rays Yves Idzerda, Johnathon Holroyd, Joe Dvorak, Marco Liberati, Elke Arenholz, Shane Stadler Transition metal based alloys of La$_{x}$Sr$_{1-x}$TMO$_{3}$ films (TM=Co, Fe, Mn) have been grown by pulsed laser deposition (PLD) on substrates of varied lattice mismatches to examine the effects of strain on the film properties. Strain is introduced into these systems by depositing overlayers of varying thickness (wedges) and lattice mismatch to vary stress at the upper interface of these films. The interfacial region of these films is probed by X-ray absorption spectroscopy (XAS), X-ray Magnetic Circular Dichroism (XMCD), and X-ray Resonant Magnetic Scattering (XRMS) to characterize the interfacial disruption in this region in an element-specific, site-specific manner with magnetic contrast. These experiments show that the response of the multi-element films is to modify the chemical (and magnetic) composition of these films in the interfacial region to accommodate the stress. The XAS, XMCD, and XRS data show that in each case, the response to compressive or tensile interfacial strain is to modify the concentration of La and Sr in the interfacial by La diffusion to/away from the interface. [Preview Abstract] |
Saturday, May 14, 2005 3:12PM - 3:37PM |
G1.00005: COFFEE BREAK
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Saturday, May 14, 2005 3:37PM - 3:49PM |
G1.00006: The Transition from Purely Temporal Chaos to Spatio-Temporal Chaos in the Reaction-Diffusion Model Thomas Olsen, Yu Hou, Richard Wiener We apply the Reaction-Diffusion model\footnote{H. Riecke and H.- G. Paap, Europhys. Lett. \textbf{14}, 1235 (1991).} to Taylor- Couette flow with hourglass geometry\footnote{Richard J. Wiener \textit{et al}, Phys. Rev. E \textbf{55}, 5489 (1997).}. Previous authors have reported the model's successful prediction of a period doubling cascade to chaos in this physical system. We present the results of a series of such simulations, varying the length of the system. We report a transition from purely temporal chaotic formation of new pairs of Taylor Vortices at the waist of the hourglass, to spatio-temporal chaos of vortex pair formation across a range of locations. These results inform a program of experiments on physical systems of comparable lengths. [Preview Abstract] |
Saturday, May 14, 2005 3:49PM - 4:01PM |
G1.00007: Controlling Chaotic Dynamics in a Simple Electronic Oscillator Kristine Callan, Stephen Hall, Richard Wiener, Thomas Olsen We built an electronic circuit, described by a third order nonlinear jerk equation, which oscillates at about 1 Hz, either periodically or chaotically depending on values of the two parameters in the equation. We primarily investigated chaotic oscillations in the circuit, both numerically and experimentally. By analyzing return maps, which involve plotting each local maximum against the previous local maximum from a sequence of oscillations, we identified fixed points corresponding to unstable periodic orbits. We tried implementing three control-of-chaos algorithms: Simple Proportional Feedback (SPF), Recursive Proportional Feedback (RPF), and Doubly Recursive Proportional Feedback (DRPF). The first attempt to control oscillations using SPF failed because the system has memory, making the RPF and DRPF algorithms, which take into account previous perturbations, necessary. Both RPF and DRPF controlled the system experimentally and numerically. Once we achieved control of chaos, we investigated if control can be maintained while a parameter drifts. When we implemented a slow drift in one of the parameters in the numeric code we found that both RPF and DRPF were able to maintain control for periods of time before slipping in and out of chaos, but DRPF maintained more robust control throughout the drift. [Preview Abstract] |
Saturday, May 14, 2005 4:01PM - 4:13PM |
G1.00008: Molecular dynamics of heat pulse propagation in single and multi wall nanotube Taejin Kim, Mohamed Osman, Cecilia Richards, David Bahr, Robert Richards Molecular dynamics simulations have been used to investigate the nature of heat pulse propagation through single and multi wall nanotube. For the comparison, these simulations were carried out on armchair nanotube, (5,5) and (10,10), zigzag nanotube, (10,0) and multi wall nanotube, which is built by (5,5) and (10,10). All of the simulations were run at 0K, and the length of the pulse was 1ps. Results have shown that the heat pulse excites a variety of phonon modes. The speed of leading wave packets of single nanotube is about 20Km/sec and this is corresponding to speed of sound in longitudinal acoustic (LA) mode. The speed of following wave packets is about 16Km/s and this value is corresponding to twisted (TW) phonon modes. The strongest wave packets propagate together with the speed of 12Km/s and this speed corresponds to the second sound waves. In multi wall nanotube, the overall phonon modes show the interaction between each single nanotube phonon modes. [Preview Abstract] |
Saturday, May 14, 2005 4:13PM - 4:25PM |
G1.00009: Hydrogen donors in zinc oxide M.D. McCluskey, S.J. Jokela, W.M. Hlaing Oo Zinc oxide (ZnO) is a wide-band-gap semiconductor that has attracted resurgent interest as an electronic material for a range of applications. The efficiency of the emission is higher than more conventional materials such as GaN, making ZnO a strong candidate for energy-efficient white lighting. Another major advantage of ZnO is the fact that, in contrast to GaN, large single crystals can be grown. ZnO has been used as a transparent conductor in solar cells, and is a preferred material in transparent transistors, ``invisible'' devices which could be very useful in products such as liquid-crystal displays. In addition to optoelectronic and electronic devices, ZnO has emerged as a potentially important material for spintronic applications. Despite its numerous advantages and potential applications, ZnO suffers from a relatively high level of donor defects. These compensating impurities prevent $p$-type doping, which is essential for practical applications. In our work, we have focused on hydrogen donors in bulk ZnO, combining IR spectroscopy with electrical measurements. As dimensions approach the nano-scale, the vastly increased surface-to-volume ratio leads to interesting phenomena. At moderate annealing temperatures (350\r{ }C), hydrogen permeates nanoparticles, resulting in a dramatic increase in electrical conductivity, free-carrier absorption, and infrared reflectivity. These results could be relevant to hydrogen sensing and storage applications. [Preview Abstract] |
Saturday, May 14, 2005 4:25PM - 4:37PM |
G1.00010: Deposited Energetic Fe Particles in Co Matrix Daniel Meyer, Jiji Antony, Amit Sharma, Joe Nutting, You Qiang Currently the highest observed net magnetic moment of bulk FeCo alloys is roughly 2.45$\mu _B $. The application of deposited nano clusters to the problem of increasing net magnetization shows promise due to observations of novel magnetic properties exhibited by matter in the nano phase. It is known that the magnetic moment of isolated Fe clusters show a significant increase relative to the bulk value; however, as the particles are deposited, the surface cluster interaction reduces the net moment back to the bulk value. Theoretical studies indicate that by depositing the clusters within a matrix of atomic Co the free particle value can be retrieved. Using a gas aggregation cluster source, Fe particles of variable size will be energetically impacted upon a substrate at various impact angles and energies to affect the magnetic anisotropy. These Fe particles will then be layered between Co films. Using a SQUID to measure the magnetic properties of the resulting films it may be possible to observe increased magnetization. [Preview Abstract] |
Saturday, May 14, 2005 4:37PM - 4:49PM |
G1.00011: Electronic Properties of Carbon Nanotubes within an Ionic Shell Vladimir Dobrokhotov, Christopher Berven We report the effect on the electrical characteristics of two types of carbon nanotubes caused by the attachment of a uniformly non-conducting charged shell held at a fixed distance above the surface of the nanotube. We find that, depending on the chirality of the nanotube, the strain on the lattice causes the dispersion relationships to change resulting in a modification of the band structures which can induce either a metal-insulator transition or a change in the conductance of the nanotube. From these results, we speculate on the use of carbon nanotubes surrounded by an ionic shell as a model for a new type of sensitive detector of various ionic species. [Preview Abstract] |
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