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Anomalous Lattice Dynamics And Thermal Properties Of Supported Size- And Shape-Selected Pt Nanoparticles, B. Roldan Cuenya, A. I. Frenkel, S. Mostafa, F. Behafarid, J. R. Croy, L. K. Ono, Q. Wang
Anomalous Lattice Dynamics And Thermal Properties Of Supported Size- And Shape-Selected Pt Nanoparticles, B. Roldan Cuenya, A. I. Frenkel, S. Mostafa, F. Behafarid, J. R. Croy, L. K. Ono, Q. Wang
Faculty Bibliography 2010s
Anomalous lattice dynamics and thermal behavior have been observed for ligand-free, size-, and shape-selected Pt nanoparticles (NPs) supported on nanocrystalline gamma-Al(2)O(3) via extended x-ray absorption fine-structure spectroscopy. Several major differences were observed for the NPs with respect to bulk Pt: (i) a contraction in the interatomic distances, (ii) a reduction in the dynamic (temperature-dependent) bond-length disorder and associated increase in the Debye temperature (theta(D)), and (iii) an overall decrease in the bond-length expansion coefficient coupled with NP stiffening. The increase in the Debye temperature is explained in terms of the NP size, shape, support interactions, and adsorbate effects. For a …
Vibrational Dynamics Of A C(2x2) Phase Induced By Nitrogen Adsorption On Cu(001), E. Z. Ciftlikli, L. V. Goncharova, B. J. Hinch, Marisol Alcántara Ortigoza, Sampyo Hong, Talat S. Rahman
Vibrational Dynamics Of A C(2x2) Phase Induced By Nitrogen Adsorption On Cu(001), E. Z. Ciftlikli, L. V. Goncharova, B. J. Hinch, Marisol Alcántara Ortigoza, Sampyo Hong, Talat S. Rahman
Faculty Bibliography 2010s
Helium-atom scattering and density-functional perturbation theory (DFPT) calculations invoking the linear-response approximation and the pseudopotential approach have been used to study the vibrational dynamics of c(2x2)-like phases produced by nitrogen-ion implantation and subsequent annealing of Cu(001) surfaces. We find that, while the c(2x2) phonon dispersion relations are different from those of clean Cu(001), neither the acoustic nor the optical surface phonon mode energies measured along both [100] and [110] directions are dependent on N coverage once the c(2x2) pattern is formed. We show that the dispersion of the surface phonon modes is well reproduced with an analysis of the DFPT …
Tunneling And Inversion Symmetry In Single-Molecule Magnets: The Case Of The Mn-12 Wheel Molecule, E. Del Barco, S. Hill, C. C. Beedle, D. N. Hendrickson, I. S. Tupitsyn, P. C. E. Stamp
Tunneling And Inversion Symmetry In Single-Molecule Magnets: The Case Of The Mn-12 Wheel Molecule, E. Del Barco, S. Hill, C. C. Beedle, D. N. Hendrickson, I. S. Tupitsyn, P. C. E. Stamp
Faculty Bibliography 2010s
We present a detailed study of the influence of various interactions on the spin quantum tunneling in a Mn-12 wheel molecule. The effects of single-ion and exchange (spin-orbit) anisotropy are first considered, followed by an analysis of the roles played by secondary influences, e.g., disorder, dipolar and hyperfine fields, and magnetoelastic interactions. Special attention is paid to the role of the antisymmetric Dzyaloshinski-Moriya (DM) interaction. This is done within the framework of a 12-spin microscopic model, and also using simplified dimer and tetramer approximations in which the electronic spins are grouped in two or four blocks, respectively. If the molecule …
Entanglement Of Photons Due To Nonlinear Optical Response Of Quantum Wells, Mikhail Erementchouk, Michael N. Leuenberger
Entanglement Of Photons Due To Nonlinear Optical Response Of Quantum Wells, Mikhail Erementchouk, Michael N. Leuenberger
Faculty Bibliography 2010s
We study photons entangling in the short-time response of a quantum well excited by a short intense pulse. At the time scales, where the biexciton effect is not yet pronounced, the Pauli principle is responsible for many-body correlations among excitons, giving rise to the production of entangled photons with a yield similar to 10(-2). The quantum-field theoretical two-particle density matrix in second quantization is used to calculate the entanglement for arbitrary emission angles of the entangled pairs of photons. At the time scales, where the heavy-light hole splitting is resolved, the resonances corresponding to different two-exciton states develop, which allow …
Diffusion Of The Cu Monomer And Dimer On Ag(111): Molecular Dynamics Simulations And Density Functional Theory Calculations, Sardar Sikandar Hayat, Marisol Alcántara Ortigoza, Muhammad A. Choudhry, Talat S. Rahman
Diffusion Of The Cu Monomer And Dimer On Ag(111): Molecular Dynamics Simulations And Density Functional Theory Calculations, Sardar Sikandar Hayat, Marisol Alcántara Ortigoza, Muhammad A. Choudhry, Talat S. Rahman
Faculty Bibliography 2010s
We present results of molecular dynamics (MD) simulations and density functional theory (DFT) calculations of the diffusion of Cu adatom and dimer on Ag(111). We have used potentials generated by the embedded-atom method for the MD simulations and pseudopotentials derived from the projected-augmented-wave method for the DFT calculations. The MD simulations (at three different temperatures: 300, 500, and 700 K) show that the diffusivity has an Arrhenius behavior. The effective energy barriers obtained from the Arrhenius plots are in excellent agreement with those extracted from scanning tunneling microscopy experiments. While the diffusion barrier for Cu monomers on Ag(111) is higher …
Uncovering The Dominant Scatterer In Graphene Sheets On Sio2, Jyoti Katoch, J. -H. Chen, Ryuichi Tsuchikawa, C. W. Smith, E. R. Mucciolo, Masa Ishigami
Uncovering The Dominant Scatterer In Graphene Sheets On Sio2, Jyoti Katoch, J. -H. Chen, Ryuichi Tsuchikawa, C. W. Smith, E. R. Mucciolo, Masa Ishigami
Faculty Bibliography 2010s
We have measured the impact of atomic hydrogen adsorption on the electronic transport properties of graphene sheets as a function of hydrogen coverage and initial, pre-hydrogenation field-effect mobility. Our results are compatible with hydrogen adsorbates inducing intervalley mixing by exerting a short-range scattering potential. The saturation coverages for different devices are found to be proportional to their initial mobility, indicating that the number of native scatterers is proportional to the saturation coverage of hydrogen. By extrapolating this proportionality, we show that the field-effect mobility can reach 1.5 x 10(4) cm(2)/V s in the absence of the hydrogen-adsorbing sites. This affinity …
Double-Stage Glass Transition In A Metallic Glass, Dmitri V. Louzguine-Luzgin, Ichiro Seki, Tokujiro Yamamoto, Hitoshi Kawaji, C. Suryanarayana, Akihisa Inoue
Double-Stage Glass Transition In A Metallic Glass, Dmitri V. Louzguine-Luzgin, Ichiro Seki, Tokujiro Yamamoto, Hitoshi Kawaji, C. Suryanarayana, Akihisa Inoue
Faculty Bibliography 2010s
Glass-transition region is still a somewhat "dark area" in the field of materials science. In order to shed more light on this phenomenon, the glass-transition behavior was studied in a Zr(55)Cu(30)Al(10)Ni(5) glassy alloy by monitoring its specific-heat capacity measured using a differential scanning calorimeter during heating in a step-scan mode. This reduces the influence of kinetic effects which shield the transition. It is suggested that two types of relaxation (likely related to the diffusivities of different alloying elements Cu and Ni on the one hand as well as Zr and Al on the other hand) take place and compete in …
Spectral And Temperature Dependence Of Two-Photon And Free-Carrier Absorption In Insb, Peter D. Olszak, Claudiu M. Cirloganu, Scott Webster, Lazaro A. Padilha, Shekhar Guha, Leonel P. Gonzalez, Srini Krishnamurthy, David J. Hagan, Eric W. Van Stryland
Spectral And Temperature Dependence Of Two-Photon And Free-Carrier Absorption In Insb, Peter D. Olszak, Claudiu M. Cirloganu, Scott Webster, Lazaro A. Padilha, Shekhar Guha, Leonel P. Gonzalez, Srini Krishnamurthy, David J. Hagan, Eric W. Van Stryland
Faculty Bibliography 2010s
The nonlinear absorption spectrum of InSb was measured using a combination of tunable similar to 160 fs, similar to 10 ps, and similar to 150 ns IR sources along with a cryostat for controlling the sample temperature to vary the band gap energy from 0.17 to 0.23 eV. The measured nonlinear optical properties in InSb are consistent with those predicted by the models which include two-and three-photon absorption (2PA and 3PA), multiphoton generated free-carrier absorption (FCA) and various recombination mechanisms. Temperature-dependent Z-scan and nonlinear transmission measurements yield information on the temperature and spectral dependence of 2PA, FCA, and carrier recombination …
First-Principles Study Of Formation Of Se Submonolayer Structures On Ru Surfaces, Sergey Stolbov
First-Principles Study Of Formation Of Se Submonolayer Structures On Ru Surfaces, Sergey Stolbov
Faculty Bibliography 2010s
The Ru nanoparticles with Se submonolayer coverage (Se/Ru) demonstrate high electrocatalytic activity toward oxygen reduction reaction (ORR) on cathodes of proton exchange membrane fuel cells. To understand the mechanisms of formation of Se structures on Ru surfaces, the geometric and electronic structures and energetics have been calculated in the present work for various distributions of Se atoms on the Ru (0001) surface and in the vicinity of the edge between the (0001) and (1101) facets. The calculations were performed within the density-functional theory with plane-wave expansion for wave functions and the projector augmented wave potentials. It has been found that …
Effective Elastic Properties Of A Van Der Waals Molecular Monolayer At A Metal Surface, Dezheng Sun, Dae-Ho Kim, Duy Le, Øyvind Borck, Kristian Berland, Kwangmoo Kim, Wenhao Lu, Yeming Zhu, Miaomiao Luo, Jonathan Wyrick, Zhihai Cheng, T. L. Einstein, Talat S. Rahman, Per Hyldgaard, Ludwig Bartels
Effective Elastic Properties Of A Van Der Waals Molecular Monolayer At A Metal Surface, Dezheng Sun, Dae-Ho Kim, Duy Le, Øyvind Borck, Kristian Berland, Kwangmoo Kim, Wenhao Lu, Yeming Zhu, Miaomiao Luo, Jonathan Wyrick, Zhihai Cheng, T. L. Einstein, Talat S. Rahman, Per Hyldgaard, Ludwig Bartels
Faculty Bibliography 2010s
Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young's modulus of 1.5 GPa and a Poisson ratio approximate to 0.1. These values suggest interpretation of the molecular monolayer …
Surface And Grain-Boundary Scattering In Nanometric Cu Films, Tik Sun, Bo Yao, Andrew P. Warren, Katayun Barmak, Michael F. Toney, Robert E. Peale, Kevin R. Coffey
Surface And Grain-Boundary Scattering In Nanometric Cu Films, Tik Sun, Bo Yao, Andrew P. Warren, Katayun Barmak, Michael F. Toney, Robert E. Peale, Kevin R. Coffey
Faculty Bibliography 2010s
We report a quantitative analysis of both surface and grain-boundary scattering in Cu thin films with independent variation in film thickness (27 to 158 nm) and grain size (35 to 425 nm) in samples prepared by subambient temperature film deposition followed by annealing. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with physical models that include the effects of surface and grain-boundary scattering. Grain-boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is observed for surface scattering. We find …
Time-Dependent Density-Matrix Functional Theory For Biexcitonic Phenomena, Volodymyr Turkowski, Carsten A. Ullrich, Talat S. Rahman, Michael N. Leuenberger
Time-Dependent Density-Matrix Functional Theory For Biexcitonic Phenomena, Volodymyr Turkowski, Carsten A. Ullrich, Talat S. Rahman, Michael N. Leuenberger
Faculty Bibliography 2010s
We formulate a time-dependent density-matrix functional theory (TDDMFT) approach for higher-order correlation effects like biexcitons in optical processes in solids based on a reduced two-particle density-matrix formalism within the normal orbital representation. A TDDMFT version of the Schrodinger equation for biexcitons in terms of one- and two-body reduced density matrices is derived, which leads to finite biexcitonic binding energies already with an adiabatic approximation. Biexcitonic binding energies for several bulk semiconductors are calculated using a contact biexciton model.
Decoherence By Electromagnetic Fluctuations In Double-Quantum-Dot Charge Qubits, Diego C. B. Valente, Eduardo R. Mucciolo, F. K. Wilhelm
Decoherence By Electromagnetic Fluctuations In Double-Quantum-Dot Charge Qubits, Diego C. B. Valente, Eduardo R. Mucciolo, F. K. Wilhelm
Faculty Bibliography 2010s
We discuss decoherence due to electromagnetic fluctuations in charge qubits formed by two lateral quantum dots. We use effective circuit model to evaluate correlations of voltage fluctuations in the qubit setup. These correlations allows us to estimate energy (T(1)) and phase (T(2)) relaxation times of the qubit system. Our theoretical estimate of the quality factor due to dephasing by electromagnetic fluctuations yields values much higher than those found in recent experiments, indicating that other sources of decoherence play a dominant role.