Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U11: Focus Session: Aerosols, Clusters, Droplets: Physics and Chemistry of Nanoobjects IV: Metal Clusters I |
Hide Abstracts |
Sponsoring Units: DCP Chair: Knut Asmis, Fritz Haber Institute, Berlin Room: Baltimore Convention Center 303 |
Thursday, March 16, 2006 8:00AM - 8:36AM |
U11.00001: Infrared Spectroscopy of Metal Ion Complexes: Models for Metal Ligand Interactions and Solvation Invited Speaker: Weakly bound complexes of the form M$^{+}$-L$_{x}$ (M=Fe, Ni, Co, etc.; L=CO$_{2}$, C$_{2}$H$_{2}$, H$_{2}$O, benzene, N$_{2})$ are prepared in supersonic molecular beams by laser vaporization in a pulsed-nozzle cluster source. These species are mass analyzed and size-selected in a reflectron time-of-flight mass spectrometer. Clusters are photodissociated at infrared wavelengths with a Nd:YAG pumped infrared optical parametric oscillator/amplifier (OPO/OPA) laser or with a tunable infrared free-electron laser. M$^{+}$-(CO$_{2})_{x}$ complexes absorb near the free CO$_{2}$ asymmetric stretch near 2349 cm$^{-1}$ but with an interesting size dependent variation in the resonances. Small clusters have blue-shifted resonances, while larger complexes have additional bands due to surface CO$_{2}$ molecules not attached to the metal. M$^{+}$(C$_{2}$H$_{2})_{n}$ complexes absorb near the C-H stretches in acetylene, but resonances in metal complexes are red-shifted with repect to the isolated molecule. Ni$^{+}$ and Co$^{+}$ complexes with acetylene undergo intracluster cyclization reactions to form cyclobutadiene. Transition metal water complexes are studied in the O-H stretch region, and partial rotational structure can be measured. M$^{+}$(benzene) and M$^{+}$(benzene)$_{2}$ ions (M=V, Ti, Al) represent half-sandwich and sandwich species, whose spectra are measured near the free benzene modes. These new IR spectra and their assignments will be discussed as well as other new IR spectra for similar complexes. [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U11.00002: Adaptive Tempering Monte Carlo Optimization of Calcium Clusters. X. Dong, E. Blaisten-Barojas The global minimum energy structures of calcium clusters with 15 to 34 atoms were obtained by the Adaptive Tempering Monte Carlo (ATMC) method. The cluster binding energy was obtained within a tight binding approach with parameters reported in previous work[1]. The ATMC optimization process is fast and drives the system across configuration space very effectively reaching the global minimum within a small number of tempering events. The structure of six cluster sizes 15, 16, 18, 21, 23 and 25 corresponding to the global minimum has not been reported in the literature for any other metals. Three clusters Ca$_{15}$, Ca$_{21}$ and Ca$_{23}$ are relatively more stable than the others in this size range. Melting of these clusters are further studied with the weighted histogram analysis method and the free energy profile is predicted. The melting transition is monitored with a novel structural order parameter that reflects the mobility of surface atoms, their bonding order and bonding directionality. [1] X. Dong, G. M. Wang, E. Blaisten-Barojas, Phys. Rev. B 70, 205409 (2004). [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U11.00003: Structures and ligand binding energies of size seleceted gold and silver clusters:~ Approach to the bulk Michael T. Bowers, Manuel Manard, Paul Kemper Gold and silver clusters are formed by laser ablation, mass selected, and either reacted with ethene or subjected to ion mobility measurement.~ Structures are assigned by two methods.~ In the first sequential ligand binding energies are measured and correlated with possible structures.~ In the second experimental cross sections are correlated with cross sections from model structures.~ Both anionic and cationic clusters are measured in the size range 3 to 13.~ For the anions calculated and experimental detachment energies are also used as structural diagnostics.~ The various data are compared with bulk values and approach to the bulk assessed. [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U11.00004: A comparison of the electronic structure and optical plasmons in Cs$_{x}$ clusters, Cs$_{x}$ shells and C$_{60}$ coated with a Cs$_{x}$ shell Arne Rosen, Jens Ekengren, Johan Sjoeholm, Mats Andersson , Daniel Oestling, David Tomanek We present calculations of the electronic structure and collective excitations in Cs clusters, Cs shells and C$_{60}$ coated with a shell of Cs atoms. The ground state properties of these systems are described using the Local Density Approximation and the electronic excitations by the Random Phase Approximation. The jellium shell approximation underlying our calculations correctly predicts the magic numbers. The optical excitation spectra in Cs clusters and Cs coated C$_{60}$ are found to be in agreement with available experimental data. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U11.00005: Signatures of Random Matrix Theory in the Discrete Energy Spectra of Shaped Disordered Metallic Clusters Laura Adams, Brian Lang, Allen Goldman It has been predicted that the distribution of the discrete energy levels of disordered metallic clusters should follow random matrix theory. It has been possible to study distributions of energy levels for different shaped metallic clusters using a low temperature scanning tunneling microscope. Depending on the degree of ``shape'' disorder, the statistics either follow Wigner-Dyson statistics, a mixed state, or Poisson-like statistics for the distribution of energy levels. We will present a summary of results on Pb clusters grown by a buffer layered assisted growth technique and in addition show how it is possible to use scanning tunneling spectroscopy to image a quantity proportional to the square of the amplitude of the eigenfunctions for quantum confined systems. These images resemble images acquired in microwave cavity experiments for classically chaotic and nonchaotic systems. This work was supported by the Department of Energy under grant DE-FG02-02ER46004. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 10:00AM |
U11.00006: “Real Time Observation and Control of Cluster Chemistry” Invited Speaker: |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U11.00007: Structure in Binary Nanodroplets Hong Xia Ning, Gerald Wilemski Recent SANS measurements of core-shell structure in binary nanodroplets ($\sim $ 9 nm) have stimulated our research on the structure of droplets of this size. [Wyslouzil, et. al., Phys. Chem. Chem. Phys. \textbf{8}, xxx, (2006)] By structure, we mean the spatial distribution of chemical species within the droplet. Based on recent work by Cordeiro and Pakula [J. Phys. Chem. \textbf{109}, 4152 (2005)], we developed an efficient Lattice Monte Carlo (LMC) method to simulate binary droplets containing 5000 to 10000 particles. Simulations of nanodroplets of various compositions were made to study phenomena such as species segregation and phase separation. Depending on the relative strengths of the intermolecular interactions, various interesting structures were found. Droplets may be fairly well-mixed, strongly segregated core-shell structures, or even highly segregated nonspherical shapes resembling partially disassembled Russian dolls. We explored the temperature dependence of the droplet structures and observed that the reversible change between the core-shell and Russian doll structures could be viewed as a wetting---dewetting transition. The transition temperature was determined for a specific system. [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U11.00008: Source for a Temperature-Controlled Metal Cluster Beam Wei Jiang, Forrest Payne, Louis Bloomfield Metal clusters can be produced easily by laser vaporization of a sample into an inert cooling gas. We have used a pulsed Nd:YAG laser to evaporate cobalt from a rotating rod into a 20cm-long narrow pipe filled with helium gas, injected by a pulsed gas valve. The outgoing part of the pipe (15cm long) is attached to a helium refrigerator and an electrical heater, which allow us to control the pipe's temperature over the range from 60K to room temperature. If the gas-cluster mixture stays in the pipe long enough before supersonic expansion, it reaches thermal equilibrium with the pipe. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U11.00009: Modeling the Melting of Free and Supported Metal Clusters Kim Bolton, Feng Ding, Haiming Duan, Arne Rosen, Avetik R. Harutyunyan, Toshio Tokune, Stefano Curtarolo The growth rate and mechanism of one-dimensional structures, such as carbon nanotubes and zinc-oxide nanorods, is expected to be significantly affected by the phase of catalytic metal particle. It is therefore important to understand the structure and dynamics of these particles in their solid and liquid phases, and to know how their melting points depend on cluster size and substrate adhesion. Results from molecular dynamics studies on the structural and dynamic changes during melting of free and supported iron clusters, ranging from 150 to 10 000 atoms, will be presented. We will also present a method to determine effective diameters of supported metal clusters, so that the melting point dependence on cluster size can be predicted in a physically meaningful way by the same analytic model used for free clusters. [Preview Abstract] |
Thursday, March 16, 2006 10:36AM - 10:48AM |
U11.00010: Geometric and electronic structure of mixed metal-semiconductor clusters from global optimization.- Frank Hagelberg, Jianhua Wu In addition to pure metal and semiconductor clusters, hybrid species that contain both types of constituents occur at the metal-semiconductor interface. Thus, clusters of the form Cu(x)Si(y) were detected by mass spectrometry [1]. In this contribution, the geometric and energetic features of Me(m)Si(7-m) (Me=Cu and Li) clusters are discussed. The choice of these systems is motivated by the structural similarity of the pure Si(7), Li(7), and Cu(7) systems which all stabilize in D(5h) symmetry. On the other hand, Li and Cu, representing the alkali group (IA) and the noble metal group (IB) of the periodic system, are expected to display strongly differing behavior when integrated into a Si(n) cluster, resulting in different ground state geometries for the cases Me = Li and Me = Cu. Addressing this problem by means of geometry optimization requires, in view of the large number of possible atomic permutations for Me(m)Si(7-m) with 0 $<$ m $<$ 7, the use of a global search algorithm. Equilibrium geometries are obtained by simulated annealing within the Nose' thermostat frame. It is observed that Cu(m)Si(7-m) clusters with m $<$ 6 tend towards ground state geometries derived from the D(5h) prototype. For Li(m)Si(7-m), the Li(m) subsystem is found to adsorb on the framework of the Si(7-m) dianion. [1] J.J. Scherer, J.B. Pau, C.P. Collier, A. O'Keefe, and R.J. Saykally, J. Chem. Phys. 103, 9187 (1995). [Preview Abstract] |
Thursday, March 16, 2006 10:48AM - 11:00AM |
U11.00011: Unbiased search of minimal energy nanocluster structures Jos\'e Rogan, Griselda Garc{\'\i}a, Claudia Loyola, Walter Orellana, Ricardo Ram{\'\i}rez, Miguel Kiwi A new strategy to find global minima is applied to the structure of metallic clusters. It consists in implementing a conformational space annealing (CSA) unbiased search in combination with many body phenomenological potential techniques to create a data bank of putative minima. Next, the clusters in this data bank are examined by first principle methods to obtain the minimum energy cluster. The scheme is successfully applied to magic number 13 atom clusters of rhodium, palladium and silver. Global minimum energy cluster structures not previously reported are found through our procedure. [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