Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session P12: Metal Islands and Clusters |
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Sponsoring Units: DCMP DMP Chair: Jim Hannon, IBM T.J. Watson Research Center Room: Baltimore Convention Center 304 |
Wednesday, March 15, 2006 11:15AM - 11:27AM |
P12.00001: The crossover from collective motion to periphery diffusion for small adatom-islands on Cu(111) and Ag(111) Altaf Karim, Abdelkader Kara, Ahlam Al-Rawi, Oleg Trushin, Talat Rahman The diffusion of two dimensional adatom islands (containing 2-100 atoms) on Cu(111) and Ag(111) has been studied, using the newly developed self-learning Kinetic Monte Carlo (SLKMC) method [Phys. Rev. B 72, 115401, 2005]. A variety of multiple and single atom processes are revealed in the simulations and the size dependence of the diffusion coefficients and effective diffusion barriers are calculated. From the tabulated frequencies of events found in the simulation, we show a crossover from diffusion due to the collective motion of the island to a regime in which the island diffuses through the periphery dominated mass transport. This crossover occurs for island sizes of 8 to 11 atoms. For islands containing 19 to 100 atoms the scaling exponent is 1.5, which is in good agreement with previous work. The diffusion of islands containing 2 to 10 atoms can be explained primarily on the basis of a linear increase of the barrier for the collective motion with the size of the island. [Preview Abstract] |
Wednesday, March 15, 2006 11:27AM - 11:39AM |
P12.00002: Excitation of frustrated translation and nonadiabatic adatom hopping induced by inelastic tunneling Kai Liu, Shiwu Gao The dynamics of lateral manipulation for cobalt/Cu(111) has been investigated combining the model of vibrational heating and first-principles density functional calculations~[1]. The frustrated translational mode responsible for lateral excitation is identified as a vibrational resonance involving a concerted motion between the adatom and surface phonons. The calculated frequency shows good agreement with the onset energy for adatom hopping induced by inelastic tunneling. Simulation of the power law, compared with experiment, suggests that the atom hopping overcomes a nonadiabatic barrier due to the nonequilibrium local heating of the translational mode. \\ \\ \noindent [1] Kai Liu and Shiwu Gao, Phys. Rev. Lett. 95, 226102 (2005) [Preview Abstract] |
Wednesday, March 15, 2006 11:39AM - 11:51AM |
P12.00003: Metal Island Coalescence Stress for Varying Surface Traction Steven Seel, Edmund Webb III, Jonathan Zimmerman During Volmer-Weber thin film growth, discrete metal islands grow on a substrate. When the separation between their adjacent free surfaces becomes small enough, islands coalesce and trade surface energy for elastic strain energy. While it is understood that traction between island and substrate directly influences coalescence stress, questions remain. For instance, wafer curvature measurements during growth of low traction systems indicate zero stress in the growing film. This results from a lack of mechanical coupling between film and substrate so island stress cannot be accurately determined from experimental data. We examine, via atomistic simulations, coalescence between two metal islands as a function of island size and island-substrate traction. We reveal the stress state in the coalesced structure for low traction where entire islands are able to slide along the substrate. This is compared to higher traction where islands can only slide near the point of coalescence resulting in local tensile strain. We conclude by examining the dependence upon island size of the traction above which only local sliding is observed. 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 11:51AM - 12:03PM |
P12.00004: Effects of Strain on Island Morphology and Size Distribution in Submonolayer Island Growth G. Nandipati, J.G. Amar We have carried out kinetic Monte Carlo simulations of submonolayer heteroepitaxial growth using a model in which the strain energy is approximated by a long-range $1/r^3$ interaction. For the case of irreversible growth with rapid island relaxation due to edge-diffusion we find that the island-shape changes from square to rectangular in the presence of sufficient strain. However, in this case fluctuations play an important role and the scaled island-size distribution is only weakly affected by strain. General scaling forms for the island-width and island-length distributions are also derived. Simulation results for a reversible model of Cu/Ni(001) growth, for which an interesting shape transition has been experimentally observed, are also presented and compared with experiments. [Preview Abstract] |
Wednesday, March 15, 2006 12:03PM - 12:15PM |
P12.00005: Incidence-angle dependence of optical reflectivity difference from an ultrathin film on a solid surface J. P. Landry, J. Gray, M. K. O'Toole, X. D. Zhu The oblique-incidence reflectivity difference (OI-RD) technique is a special form of polarization-modulated nulling ellipsometry that has been judiciously used in studies of ultrathin films and other surface-bound changes on a solid or even liquid substrate. We have recently studied the incidence angle dependence of the optical reflectivity difference signals in response to ultrathin films on transparent and opaque substrates. We find that the classical three-layer model reproduces the experimentally obtained angular dependence for a monolayer of xenon on Nb(110) and for a monolayer of protein molecules on functionalized glass. We report the findings of this recent experimental investigation and explore the enhancement of the optical response near the Brewster angle (or its equivalent for opaque substrates) in thin film detection. [Preview Abstract] |
Wednesday, March 15, 2006 12:15PM - 12:27PM |
P12.00006: Time Resolved Study of Ordering Between Quantum Well Islands by Wide-Area k-Space Mapping Hawoong Hong, L. Basile, P. Czoschke, A. Gray, T.-C. Chiang The growth of Pb quantum well islands on Si(111) was investigated in time resolved manners. The wide-area momentum space mapped in our x-ray diffraction techniques allows simultaneous observation of the lateral ordering and height distributions of Stranski-Krastanov (S-K) islands during deposition, annealing, and cycling between deposition and annealing. These islands are formed not by strain relaxation but through quantum phase separation. The ordering of these islands exhibits unusual behaviors not well described by existing strained island theories. The population of islands always decreases monotonically during all three processes. However, the island ordering was stable without coarsening with time, at least within the experimental condition. This study suggests that quantum well effect may provide a new mechanism for uniform self-assembled nanostructures. [Preview Abstract] |
Wednesday, March 15, 2006 12:27PM - 12:39PM |
P12.00007: Sublimation of Atomic Layers from a Chromium Surface Wacek Swiech, Shu-Jung Tang, Suneel Kodambaka, Ivan Petrov, Peter Flynn, Tai-Chang Chiang We employ low-energy electron microscopy to study the kinetics of thermal etching, or sublimation, of Cr(001) at $\sim $1100 K. Atomic layers are removed from the surface by spontaneous nucleation and growth of two-dimensional vacancy islands, by rotation of spiral steps, and by island decay. The growth rates of vacancy islands and the rotation frequencies of double spirals are measured as a function of temperature, and the results are correlated with activation barriers of surface processes. Mass transport between the surface and bulk is shown to be unimportant. [Preview Abstract] |
Wednesday, March 15, 2006 12:39PM - 12:51PM |
P12.00008: Iso-coverage diffusion zones observed with LEEM during annealing of Ag on Si(001) Kelly Roos, Kimberly Roos, Frank Meyer zu Heringdorf, Michael Horn-von Hoegen, Joachim Krug During high temperature annealing of 3D Ag islands grown on Si(001) PEEM images reveal the emergence of a bright zone surrounding the decaying islands. Microdiffraction patterns from these bright areas display a (2x3) Ag reconstruction. The decaying Ag islands act as sources of Ag adatoms which then diffuse on the surface. The (2x3) reconstruction spreads away from the island to a distance determined by the interplay of diffusion and desorption, and by the local coverage of Ag: the outer boundary of the imaged diffusion zones constitutes an ``iso-coverage boundary.'' We describe the time and temperature behavior of these iso-coverage zones, and present a simple continuum model that describes the iso-zone size as a function of the diffusion and desorption rates. [Preview Abstract] |
Wednesday, March 15, 2006 12:51PM - 1:03PM |
P12.00009: Imprinting Chirality into inorganic CuO Thin Films Roland Widmer, Roman Fasel, Oliver Groening, Franz-Josef Haug, Pierangelo Groening Switzer et al. [1] have shown, that thick ($>$300nm) films of CuO grown electrochemically in the presence of chiral tartaric acid (TA) acquires a chiral orientation with respect to the growth surface. We have investigated this growth on Au(100) in the presence of chiral TA for low film thicknesses by X-ray Photoelectrons Spectroscopy and X-ray Photoelectron Diffraction (XPD). The resulting XPD patterns were analyzed by single scattering cluster calculations. XPD revealed that using chiral L(+)- or D(-)-TA in the deposition process results in a chiral CuO surface which exhibits mirror-symmetric, non-superimposable patterns with the corresponding chirality imprinted already for film thicknesses below 3nm. Whereas the XPD patterns of the CuO films deposited with the racemic DL-TA and the ``achiral'' meso-TA are completely symmetric. The selectivity of enantiomeric CuO films was demonstrated by subsequent deposition of CuO from a solution containing DL-TA onto a CuO film grown with only one of the enantiomeric forms. Additionally, films with alternating chirality were produced. [1] J. A. Switzer, H. M. Kothari, P. Poizot, S. Nakanishi, E. W. Bohannan, Nature, 2003, 425, 490 [Preview Abstract] |
Wednesday, March 15, 2006 1:03PM - 1:15PM |
P12.00010: Geometry and Electronic Structure of Alumina Supported Ag Clusters Elizabeth A. Sokol, Sara E. Mason, Valentino R. Cooper, Andrew M. Rappe We use DFT/GGA to model silver clusters supported on Al-terminated alpha-alumina. A variety of cluster sizes and geometry are considered. We find that the adsorption of the Ag clusters causes dramatic surface relaxations and polarization of the Ag clusters as some Ag atoms of the clusters bond with O, while others bond with Al. For comparison, we also model adsorption of a single Ag atom, which bonds at a hollow site (relative to surface oxygen). We use the electronic structure of the adsorbed clusters to interpret the bonding interaction between the Ag atoms and surface O and Al atoms. The differences in Ag-surface bonds within the cluster give rise to different electronic environments at each Ag atoms. This effect has implications of this result to reactivity. [Preview Abstract] |
Wednesday, March 15, 2006 1:15PM - 1:27PM |
P12.00011: Adsorptive and chemical properties of supported silver clusters Sara E. Mason, Elizabeth A. Sokol, Valentino R. Cooper, Andrew M. Rappe Unlike bulk metal slabs, clusters of transition metals on nonmetallic supports have a finite electron reservoir. Additionally, the interaction of clusters with the support can lead to polarization in the cluster. These effects give rise to adsorption properties quite different from those of bulk metal. We characterize the adsorption of different atomic and molecular species on silver clusters supported by Al-terminated alpha-alumina using DFT/GGA calculations. A range of cluster sizes and cluster geometries is onsidered and the adsorption energetics and geometries are compared with those of bulk silver metal. [Preview Abstract] |
Wednesday, March 15, 2006 1:27PM - 1:39PM |
P12.00012: Alkali ion scattering from sputter-induced Au nanoclusters P. Karmakar, G.F. Liu, Z. Sroubek, J.A. Yarmoff The neutralization of scattered 3 keV $^{23}$Na$^{+}$ ions is used to probe the confined states of sputter induced Au nanoclusters on a TiO$_{2 }$(110) substrate. The neutral fraction of Na scattered from Au nanoclusters deposited on TiO$_{2}$(110) is high compared to bulk Au, as described earlier (G.F. Liu, Z. Sroubek, J.A. Yarmoff, Phys. Rev. Lett. \textbf{92}, 216801 (2004)). Here, normal incidence 0.5 keV Ar$^{+}$ ion bombardment of a thin Au film is employed as an alternative method for the self-organized formation of Au nanoclusters. The interplay between curvature dependent sputtering and surface diffusion during Ar$^{+}$ bombardment works to develop the Au nanoclusters. The neutral fraction of the scattered Na gradually increases from 5{\%} to 50{\%} as the cluster dimensions decrease due to the Ar$^{+}$ sputtering. XPS is used to quantify the reduction of Au coverage with sputtering time. STM revels a decrease of both the rms roughness and the correlation length of Au nanoclusters with Ar$^{+}$ fluence. [Preview Abstract] |
Wednesday, March 15, 2006 1:39PM - 1:51PM |
P12.00013: CO oxidation reaction on Au clusters supported on the TiO$_{2}$(110) surface Davide Ricci, Angelo Bongiorno, Uzi Landman, Anke Woerz, Matthias Arenz, Ueli Heiz We have studied by means of density functional theory (DFT) plane waves calculations, the CO oxidation reaction on Au$_{8}$ clusters adsorbed on both the stoichiometric and reduced rutile TiO$_{2}$(110) surfaces. O$_{2}$ molecules bind at the interface between the TiO$_{2}$(110) surface and the gold particle, where they become partially charged through the population of the anti-bonding molecular orbital, resulting in the extension of the O-O bond length to values of peroxo-like states. When CO is co-adsorbed on the gold-particles, the Langmuir-Hinshelwood and the Elay-Rideal mechanisms are possible for the oxidation reaction. Both the catalytic cycles have been considered and the theoretical results have been compared with experimental findings obtained on size-selected Au$_{8}$ clusters deposited on thin, oxidized and reduced TiO$_{2}$ films. [Preview Abstract] |
Wednesday, March 15, 2006 1:51PM - 2:03PM |
P12.00014: High photocatalytic activity of immobilized non-crystalline nanometric titanium oxide: key role of interface Andrei Kanaev, Mohamed Benmami, Khay Chhor Thinnest coatings prepared by \textit{chemical} deposition of\textit{ non-crystalline} nanomertic titanium oxide particles (2R=5.0 nm) show important photocatalytic activity, which can be higher than that of the reference sample, crystalline \textit{Degussa} P-25 TiO$_{2}$. We describe an original method of the sol particles preparation and immobilization on complex supports in the sol-gel reactor. The effect of the coating thickness on its photocatalytic activity is studied. We show that the very first layer of the deposited nanoparticles possesses both high mechanically stability and the highest efficiency. We describe main features on the nanocoatings behavior in photocatalysis (gas-phase trichloroethylene degradation) and show that their internal efficiency increases with the decrease of the deposited mass. These results suggest a new approach to the active component design, while earlier non-crystalline TiO$_{2}$ has been considered inactive. [Preview Abstract] |
Wednesday, March 15, 2006 2:03PM - 2:15PM |
P12.00015: Ab-Initio Studies of Properties of 2D Rare-Earth Silicide Surfaces Christopher Eames, Steve Tear, Matthew Probert Rare Earth overlayers on the Si(111) surface have attracted interest due to their novel properties [1,2] and the unusual reconstruction that is formed with a flat rare earth layer buried inside the Silicon [3,4,5,6]. Here we present the results of ab-initio calculations done using the CASTEP [7] code to determine the structural and electronic properties of these reconstructions. We compare these to those derived experimentally. \\ \ \\ {[}1{]} {F. P. Netzer, {\it J. Phys.: Cond. Matt.}, {\bf 7} (1995) 991-1022}\\ {[}2{]} {K. N. Tu {\it et al}, {\it App. Phys. Lett.}, {\bf 38} (1981) 626-628}\\ {[}3{]} {M. Lohmeier {\it et al}, {\it Phys. Rev. B.}, {\bf 54} (1996) 2004-2009}\\ {[}4{]} {D. J. Spence {\it et al}, {\it Phys. Rev. B.}, {\bf 61} (2000) 5707-5713}\\ {[}5{]} {D. J. Spence {\it et al}, {\it Surf. Sci.}, {\bf 512} (2002) 61-66}\\ {[}6{]} {C. Rogero {\it et al}, {\it Phys. Rev. B.}, {\bf 66} (2002) 235421-235427}\\ {[}7{]} {M. D. Segall {\it et al}, {\it J. Phys.: Cond. Matt.}, {\bf 14} (2002) 2717-2743} \\ [Preview Abstract] |
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