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Virginia Commonwealth University

Series

2009

Articles 1 - 19 of 19

Full-Text Articles in Physical Sciences and Mathematics

Poly(Styrene-Co-Vinylbenzylchloride-Co-Divinylbenzene) Coated Iron Oxide: Synthesis And Effects On Size And Morphology, M. D. Shultz, J. R. Marin, S. H. Naik, J. Wilkins, J. M. Laza, J. L. Vilas, M. Rodriguez, N. Perez, E. E. Carpenter Jan 2009

Poly(Styrene-Co-Vinylbenzylchloride-Co-Divinylbenzene) Coated Iron Oxide: Synthesis And Effects On Size And Morphology, M. D. Shultz, J. R. Marin, S. H. Naik, J. Wilkins, J. M. Laza, J. L. Vilas, M. Rodriguez, N. Perez, E. E. Carpenter

Chemistry Publications

Iron oxide nanoparticles were coated with a polymer synthesized from the monomers of styrene, divinylbenzene, and vinylbenzylchloride. The resultant polymer microspheres from synthesis without nanoparticle loading are primarily monodispersed with a diameter of 3.45 μm as measured by scanning electron microscopy. The addition of 1% nanoparticles by mass appears to decrease the size of the microspheres down to 2.04 μm as well as increase the polydispersity. This trend is also seen to continue as you add more nanoparticles to the system going from 3.45 μm with 0% nanoparticles down to below 1 μm for 5% nanoparticles. This indicates that the …

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Microscopic Dynamics Of The Orientation Of A Hydrated Nanoparticle In An Electric Field, C. D. Daub, D. Bratko, A. Towshif, A. Luzar Jan 2009

Microscopic Dynamics Of The Orientation Of A Hydrated Nanoparticle In An Electric Field, C. D. Daub, D. Bratko, A. Towshif, A. Luzar

Chemistry Publications

We use atomistic simulations to study the orientational dynamics of a nonpolar nanoparticle suspended in water and subject to an electric field. Due to molecular-level effects we describe, the torque exerted on the nanoparticle exceeds continuum-electrostatics based estimates by about a factor of two. The reorientation time of a 16.2×16.2×3.35 ̊A3 nanoparticle in a field E > 0.015V/ ̊A is an order of magnitude less than the field-free orientational time (∼ 1 ns). Surprisingly, the alignment speed is nearly independent of the nanoparticle size in this regime. These findings are relevant for design of novel nanostructures and sensors and development of …

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Origin Of The Anatase To Rutile Conversion Of Metal-Doped Tio2, Sa Li, Puru Jena Jan 2009

Origin Of The Anatase To Rutile Conversion Of Metal-Doped Tio2, Sa Li, Puru Jena

Physics Publications

Extensive calculations using density functional theory enable us to explain the origin of the surprising room-temperature conversion of anatase to rutile phase of TiO2 when doped with Co and Ni, but not with Cu. Contrary to earlier suggestion, neither high spin nor strain of the transition metals is found to be responsible for this phase conversion. The driving mechanism, instead, is attributed to the increased interaction between Co and Ni atoms forming a linear chain in the rutile phase. We predict that Cr and Mn which have even larger spins than Co and Ni cannot induce this phase conversion.

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Magnetic Properties Of Transition-Metal-Doped Zn1−Xtxo (T=Cr, Mn, Fe, Co, And Ni) Thin Films With And Without Intrinsic Defects: A Density Functional Study, Qian Wang, Qiang Sun, Puru Jena, Y. Kawazoe Jan 2009

Magnetic Properties Of Transition-Metal-Doped Zn1−Xtxo (T=Cr, Mn, Fe, Co, And Ni) Thin Films With And Without Intrinsic Defects: A Density Functional Study, Qian Wang, Qiang Sun, Puru Jena, Y. Kawazoe

Physics Publications

Theoretical calculations based on density-functional theory and generalized gradient approximation have been carried out in studying the electronic structure and magnetic properties of transition-metal-doped Zn1−xTxO (T=Cr, Mn, Fe, Co, and Ni) (112¯0) thin films systematically with and without intrinsic point defects (e.g., vacancies and interstitials), and as function of concentration and distribution of dopants and vacancies. Using large supercells and geometry optimization without symmetry constraint, we are able to determine the sites that metal atoms prefer to occupy, their tendency to cluster, the preferred magnetic coupling between magnetic moments at transition-metal sites, and the effect of intrinsic point defects on …

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Electronic Behavior Of The Zn- And O-Polar Zno Surfaces Studied Using Conductive Atomic Force Microscopy, J. C. Moore, S. M. Kenny, C. S. Baird, H. Morkoç, A. A. Baski Jan 2009

Electronic Behavior Of The Zn- And O-Polar Zno Surfaces Studied Using Conductive Atomic Force Microscopy, J. C. Moore, S. M. Kenny, C. S. Baird, H. Morkoç, A. A. Baski

Physics Publications

We have used conducting atomic force microscopy (CAFM) to study the morphology and electronic behavior of as-received and air-annealed (0001) Zn- and (0001¯) O-polar surfaces of bulk ZnO. Both polar surfaces exhibit relatively flat morphologies prior to annealing, which rearrange to form well-defined steps upon annealing in air at 1050 °C for 1 h. Long-term exposure to air results in surface layer pitting and the destruction of steps for both the as-received and air-annealed (0001¯)surfaces, indicating its enhanced reactivity relative to the (0001) surface. CAFM I-V spectra for polar surfaces are similar and indicate Ohmic to rectifying behavior that depends …

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Magnetic Response Of Core-Shell Cobalt Ferrite Nanoparticles At Low Temperature, K. Maaz, M. Usman, S. Karim, A. Mumtaz, S. K. Hasanain, M. F. Bertino Jan 2009

Magnetic Response Of Core-Shell Cobalt Ferrite Nanoparticles At Low Temperature, K. Maaz, M. Usman, S. Karim, A. Mumtaz, S. K. Hasanain, M. F. Bertino

Physics Publications

Cobaltferritenanoparticles (size: 26±4nm) have been synthesized by coprecipitation route. The coercivity of nanoparticles follows a simple model of thermal activation of particle moments over the anisotropy barrier in the temperature range of 30–300K in accordance with Kneller’s law; however, at low temperatures (

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Photoelectron Imaging And Theoretical Investigation Of Bimetallic Bi1–2ga−0–2 And Pb−1–4 Cluster Anions, M. A. Sobhy, J. Ulises Reveles, Ujjwal Gupta, Shiv N. Khanna, A. W. Castleman Jr. Jan 2009

Photoelectron Imaging And Theoretical Investigation Of Bimetallic Bi1–2ga−0–2 And Pb−1–4 Cluster Anions, M. A. Sobhy, J. Ulises Reveles, Ujjwal Gupta, Shiv N. Khanna, A. W. Castleman Jr.

Physics Publications

We present the results of photoelectron velocity-map imaging experiments for the photodetachment of small negatively charged BimGan (m=1–2, n=0–2), and Pbn (n=1–4) clusters at 527 nm. The photoelectron images reveal new features along with their angular distributions in the photoelectron spectra of these clusters. We report the vertical detachment energies of the observed multiple electronic bands and their respective anisotropy parameters for the BimGan and Pbn clusters derived from the photoelectron images. Experiments on the BiGan clusters reveal that the electron affinity increases with the number of Ga atoms from n=0 to 2. The BiGa−2 cluster is found to be …

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Doping Induced Anisotropic Growth In C60, Miao Miao Wu, Qiang Sun, Puru Jena, Yoshiyuki Kawazoe Jan 2009

Doping Induced Anisotropic Growth In C60, Miao Miao Wu, Qiang Sun, Puru Jena, Yoshiyuki Kawazoe

Physics Publications

Using density functional theory with generalized gradient approximation for exchange and correlation energy, we show that substitution of a Si atom at one of the C sites in C60 not only allows C59Si to have a hydrophobic head with a hydrophilic tail but also the Si atom acts as a seed for anisotropic growth of the heterofullerene. This is demonstrated by interacting C59Si with N7Sc and B8Si. The resulting complex structures exhibit enhanced electric dipole moments and anisotropy. Thus, doping induced anisotropic growth of nanostructures provides a novel route for the synthesis of bifunctional particles with atomic-level control on selectivity …

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Stabilizing A 22 Karat Nanogolden Cage, Q. Wang, Q. Sun, P. Jena Jan 2009

Stabilizing A 22 Karat Nanogolden Cage, Q. Wang, Q. Sun, P. Jena

Physics Publications

Since the discovery of C60 fullerene, considerable efforts have been devoted to find other elements with similar hollow cage structures. However, search for hollow metallic cages with a diameter similar to that of C60 fullerene has been elusive. We describe a procedure for the rational design of metallic cages by suitably choosing their size, composition, and charge state. A 22 karat nanogolden cage with a diameter of about 8.5 Å and consisting of 12 Al and 20 Au atoms is found to be metastable, which can be stabilized by embedding a Mn4 cluster. In contrast to bulk Mn, which is …

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Photoadsorption And Photodesorption For Gan, M. Foussekis, A. A. Baski, Michael A. Reshchikov Jan 2009

Photoadsorption And Photodesorption For Gan, M. Foussekis, A. A. Baski, Michael A. Reshchikov

Physics Publications

The effect of an ambient environment on the surface photovoltage and photoluminescence observed for GaN is studied. In air ambient the upward band bending gradually increases under UVillumination and is explained by the photoinduced chemisorption of surface adsorbates. Specifically, the increase in negative surface charge is consistent with the transfer of electrons from surface states or bulk to oxygen species physisorbed at the GaNsurface. In contrast, the upward band bending gradually decreases in vacuum under UVillumination and can be explained by the photoinduced desorption of these species. The photoadsorption and photodesorption of negatively charged species cause the surface depletion region …

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Functionalized Heterofullerenes For Hydrogen Storage, Qiang Sun, Qian Wang, Puru Jena Jan 2009

Functionalized Heterofullerenes For Hydrogen Storage, Qiang Sun, Qian Wang, Puru Jena

Physics Publications

Using density functional theory, we show that Li decorated B doped heterofullerene (Li12C48B12) has the following desired properties of a hydrogen storagematerial. (1) The Li atoms remain isolated. (2) Through charge transfer to electron deficient C48B12 heterofullerene, the Li atoms become positively charged. (3) Each Li atom is able to bind up to three H2molecules, which remain in molecular form, and the binding energies of successive H2molecules are in the range of 0.135–0.172 eV/H2, suitable for ambient temperature storage. (4) The gravimetric density reaches the 9 wt % limit necessary for applications in the mobile industry.

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Mg-Doped Gan Nanostructures: Energetics, Magnetism, And H2 Adsorption, Qian Wang, Qiang Sun, Puru Jena, Yoshiyuki Kawazoe Jan 2009

Mg-Doped Gan Nanostructures: Energetics, Magnetism, And H2 Adsorption, Qian Wang, Qiang Sun, Puru Jena, Yoshiyuki Kawazoe

Physics Publications

Using density functional theory and generalized gradient approximation for exchange and correlation potential we show that Mg-doped GaN nanocages and nanotubes can be magnetic with Mg-contributed spins distributed over the neighboring N sites. Mg atoms show no tendency for clustering due to the positive charge residing on them; they can trap hydrogen in molecular form via the charge polarization mechanism. The binding energies of hydrogen lie in the range of 0.1–0.2 eV/H2, which are ideal for storage applications under ambient thermodynamic conditions.

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Highly Efficient (Cs8v) Superatom-Based Spin-Polarizer, Haiying He, Ravindra Pandey, J. Ulises Reveles, Shiv N. Khanna, Shashi P. Karna Jan 2009

Highly Efficient (Cs8v) Superatom-Based Spin-Polarizer, Haiying He, Ravindra Pandey, J. Ulises Reveles, Shiv N. Khanna, Shashi P. Karna

Physics Publications

Quantum transport through molecules and the possibility to manipulate spin has generated tremendous excitement. Here, we demonstrate unusual spin transport through a molecule of twoCs8V magnetic superatoms. Calculations based on density functional theory and nonequilibrium Green’s function methods find a much higher current for the spin-down charge carriers relative to the spin-up carriers in the model Au–(Cs8V)–(Cs8V)–Au device system with almost 100% spin polarization, indicating a highly efficient spin polarizer. The new behavior is rooted in strong coupling of the localized magnetic core on V and the itinerant electrons of the Cs shell atoms leading to nearly full spin polarization.

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Magnetism In Assembled And Supported Silicon Endohedral Cages: First-Principles Electronic Structure Calculations, R. Robles, Shiv N. Khanna Jan 2009

Magnetism In Assembled And Supported Silicon Endohedral Cages: First-Principles Electronic Structure Calculations, R. Robles, Shiv N. Khanna

Physics Publications

First principles electronic structure calculations on a free CrSi12cluster, a (CrSi12)2 dimer, and CrSi12 clusters supported on Si(111) surfaces have been carried out within a gradient corrected density functional formalism using a supercell approach. The ground state of CrSi12 is a Cr centered hexagonal biprism of Si atoms in which the Cr spin moment is completely quenched. As two CrSi12 motifs are brought together, they form different composite units depending on initial direction of approach and, in most cases, the composite cluster is found to have a net spin moment. Cluster assemblies obtained by depositing CrSi12 motifs on a Si(111) …

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Al13h−: Hydrogen Atom Site Selectivity And The Shell Model, A. Grubisic, X. Li, S. T. Stokes, K. Vetter, G. F. Ganteför, K. H. Bowen, P. Jena, B. Kiran, R. Burgert, H. Schnöckel Jan 2009

Al13h−: Hydrogen Atom Site Selectivity And The Shell Model, A. Grubisic, X. Li, S. T. Stokes, K. Vetter, G. F. Ganteför, K. H. Bowen, P. Jena, B. Kiran, R. Burgert, H. Schnöckel

Physics Publications

Using a combination of anion photoelectron spectroscopy and density functional theory calculations, we explored the influence of the shell model on H atom site selectivity in Al13H−. Photoelectron spectra revealed that Al13H− has two anionic isomers and for both of them provided vertical detachment energies (VDEs). Theoretical calculations found that the structures of these anionic isomers differ by the position of the hydrogen atom. In one, the hydrogen atom is radially bonded, while in the other, hydrogen caps a triangular face. VDEs for both anionic isomers as well as other energetic relationships were also calculated. Comparison of the measured versus …

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Stable T2sin (T=Fe,Co,Ni,1≤N≤8) Cluster Motifs, R. Robles, S. N. Khanna Jan 2009

Stable T2sin (T=Fe,Co,Ni,1≤N≤8) Cluster Motifs, R. Robles, S. N. Khanna

Physics Publications

First principles studies on the geometry, electronic structure, and magnetic properties of neutral and anionic Fe2Sin, Co2Sin, and Ni2Sin (1≤n≤8) clusters have been carried out within a gradient corrected density functional framework. It is shown that these clusters display a variety of magnetic species with varying magnetic moment and different magnetic coupling between the two transition metal atoms. While Fe2Sin clusters are mostly ferromagnetic with large moments, Ni2Sin clusters are mostly nonmagnetic. Our studies of the variation of the binding energy upon addition of successive Si atoms and the gap between the highest occupied molecular orbital and the lowest unoccupied …

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One Parameter Control Of The Size Of Iron Oxide Nanoparticles Synthesized In Reverse Micelles, M. D. Shultz, W. Braxton, C. Taylor, E. E. Carpenter Jan 2009

One Parameter Control Of The Size Of Iron Oxide Nanoparticles Synthesized In Reverse Micelles, M. D. Shultz, W. Braxton, C. Taylor, E. E. Carpenter

Chemistry Publications

Iron oxide nanoparticles were synthesized via reverse micelle methods. The initial iron concentration was varied, while maintaining all other parameters constant, in order to investigate the effect of the iron concentration on the resultant iron oxide nanoparticle size. Increasing the iron concentration from 0.125M to 0.5M yielded an increase in average nanoparticle diameter from 4.71 to 7.95 nm, as measured by transmission electron microscopy. Three other concentrations between 0.125M and 0.5M showed corresponding size variations, all with statistical significance. Magnetic characterization by vibrating sample magnetometry and powder x-ray diffraction was performed to verify proper phase and material. Further insight into …

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Location, Location, Location: A Transaction Comparison Of Catalog Searches Originating From The Library Homepage And Aleph, Jimmy Ghaphery, Thomas Mcnulty, Susan Teague Rector Jan 2009

Location, Location, Location: A Transaction Comparison Of Catalog Searches Originating From The Library Homepage And Aleph, Jimmy Ghaphery, Thomas Mcnulty, Susan Teague Rector

VCU Libraries Faculty and Staff Presentations

Jimmy Ghaphery, Head, Library Information Systems, Virginia Commonwealth University (VCU); Thomas McNulty, Integrated Library Systems Librarian, VCU; Susan Teague-Rector, Web Applications Manager, VCU. We will analyze several weeks of search terms from February 2009 in order to determine how different points of entry impact user searches. Specifically we will compare user searches originating from a search tool on the library homepage and searches originating directly from Aleph. This session should be of interest to those who are involved with usability and OPAC design as well as system administrators tasked with measuring OPAC activity.

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Superhalogen Properties Of Cufn Clusters, Q. Wang, Q. Sun, P. Jena Jan 2009

Superhalogen Properties Of Cufn Clusters, Q. Wang, Q. Sun, P. Jena

Physics Publications

A first-principles calculation based on gradient corrected density functional theory reveals unusual properties of a Cu atom interacting with F. Up to six F atoms are bound to a single Cu atom with electron affinities steadily rising as successive F atoms are attached, reaching a peak value of 7.2 eV in CuF5. The large energy gaps between the highest occupied and lowest unoccupied molecular orbitals, both in neutral and anionic form, provide further evidence of their stability. These unusual properties brought about by involvement of inner shell 3d-electrons not only allow CuFn to belong to the class of superhalogens but …

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