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University of Nebraska - Lincoln

2010

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Articles 1 - 30 of 73

Full-Text Articles in Physics

Detecting Electron Motion In Atoms And Molecules, Hua-Chieh Shao, Anthony F. Starace Dec 2010

Detecting Electron Motion In Atoms And Molecules, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

The detection of spatial and temporal electronic motion by scattering of subfemtosecond pulses of 10 keV electrons from coherent superpositions of electronic states of both H and T+2 is investigated. For the H atom, we predict changes in the diffraction images that reflect the time-dependent effective radius of the electronic charge density. For an aligned T+2 molecule, the diffraction image changes reflect the time-dependent localization or delocalization of the electronic charge density.


Unl Physicists Model Potential 4-D Imaging Technique, Tom Simons, Hua-Chieh Shao, Anthony F. Starace Dec 2010

Unl Physicists Model Potential 4-D Imaging Technique, Tom Simons, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

A long-standing goal of science is to be able to understand how matter behaves at the atomic and subatomic level. How electrons rearrange when atoms or molecules come together is the essence of chemistry, and the ability to manipulate those rearrangements is the goal of the emerging sphere of nanotechnology. A fuller understanding could lead to enormous scientific and technological breakthroughs. Unfortunately, significant problems confront scientists and engineers in attacking the question. Not only are atoms and molecules very small, requiring highly specialized equipment to "see" them, everything at the atomic level happens very, very fast. For example, an electron ...


Movies Of Electrons In Atoms, Michael Schirber, Hua-Chieh Shao, Anthony F. Starace Dec 2010

Movies Of Electrons In Atoms, Michael Schirber, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

Physicists have long been able to snap atomic-scale pictures by shining a beam of electrons at a target, but filming the electronic structure of an atom as it changes in time is the next goal. A rapid "strobing" of electron pulses less than a millionth of a billionth of a second long should do the trick, according to a theoretical analysis in the 24 December Physical Review Letters. The authors demonstrate with computer simulations that ultrafast electron pulses could track the "breathing" state of an excited atom or the hopping of electrons between atoms in a molecule. Such movies open ...


Potential Barrier Effects In Two-Photon Ionization Processes, Liang-Wen Pi, Anthony F. Starace Nov 2010

Potential Barrier Effects In Two-Photon Ionization Processes, Liang-Wen Pi, Anthony F. Starace

Anthony F. Starace Publications

Potential barriers in the effective radial potential experienced by a photoexcited electron are shown to result in dramatic, resonancelike effects in two-photon ionization processes. In a two-photon ionization process, such potential barriers may affect not only the final state of the electron (as in ordinary photoionization), but also the intermediate-state electron wave packet corresponding to the absorption of one photon. We illustrate these effects for the generalized two-photon cross sections for ionization of Ar and Xe within a single-active-electron, central-potential model.


Magnetoelectric Effects In Ferromagnetic Cobalt/Ferroelectric Copolymer Multilayer Films, Abhijit Mardana, Mengjun Bai, A. Baruth, Stephen Ducharme, Shireen Adenwalla Sep 2010

Magnetoelectric Effects In Ferromagnetic Cobalt/Ferroelectric Copolymer Multilayer Films, Abhijit Mardana, Mengjun Bai, A. Baruth, Stephen Ducharme, Shireen Adenwalla

Stephen Ducharme Publications

Interactions between a ferromagnet, cobalt, and a ferroelectric copolymer, poly(vinylidene fluoride with trifluoroethylene) in thin film heterostructures result in a 5% change in the ferroelectric polarization on application of a perpendicular 6 kG magnetic field corresponding to a magnetoelectric coupling coefficient of α =5.45 V/cm Oe. The effect disappears on magnetic saturation, ruling out conventional strain coupling. A simple model posits that the ferroelectric film develops in-plane strain gradients, a consequence of the coupling to strain gradients present at the domain walls in the multidomain Co layer, resulting in the measured polarization change via the flexoelectric effect.


Potential Barrier Effects In High-Order Harmonic Generation By Transition-Metal Ions, M. V. Frolov, N. L. Manakov, Anthony F. Starace Aug 2010

Potential Barrier Effects In High-Order Harmonic Generation By Transition-Metal Ions, M. V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

The experimental finding of significant enhancement or suppression of particular harmonics generated by the ionic component of laser-produced plasmas of transition-metal atoms is explained theoretically in terms of the standard three-step scenario for strong-field harmonic generation, taking into account the potential barrier effects that lead to a strong 3p → 3d electric dipole transition that dominates the photoionization cross sections of the outer subshells of those ions.


Investigation Of State Retention In Metal–Ferroelectric–Insulator–Semiconductor Structures Based On Langmuir–Blodgett Copolymer Films, Timothy J. Reece, A. Gerber, Institut Für Festkörperforschung, Forschungszentrum Jülich, Germany, Stephen Ducharme Jul 2010

Investigation Of State Retention In Metal–Ferroelectric–Insulator–Semiconductor Structures Based On Langmuir–Blodgett Copolymer Films, Timothy J. Reece, A. Gerber, Institut Für Festkörperforschung, Forschungszentrum Jülich, Germany, Stephen Ducharme

Stephen Ducharme Publications

Among the ferroelectric thin films considered for use in nonvolatile memory devices, the ferroelectric copolymer of polyvinylidene fluoride, PVDF (C2H2F2), with trifluoroethylene, TrFE (C2HF3), has distinct advantages, including low dielectric constant, low processing temperature, relative low cost compared with epitaxial ferroelectric oxides, and compatibility with organic semiconductors. We report the operation and polarization retention properties of a metal– ferroelectric–insulator–semiconductor bistable capacitor memory element consisting of an aluminum gate, a P(VDF-TrFE) Langmuir–Blodgett film, a 30 nm cerium oxide buffer layer, and a moderately doped silicon wafer. The device exhibited ...


Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter A. Dowben Jun 2010

Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter A. Dowben

Christian Binek Publications

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with highspeed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between ...


Boron Carbide Based Solid State Neutron Detectors: The Effects Of Bias And Time Constant On Detection Efficiency, Nina Hong, John Mullins, Keith Foreman, Shireen Adenwalla Jun 2010

Boron Carbide Based Solid State Neutron Detectors: The Effects Of Bias And Time Constant On Detection Efficiency, Nina Hong, John Mullins, Keith Foreman, Shireen Adenwalla

Shireen Adenwalla Papers

Neutron detection in thick boron carbide(BC)/n-type Si heterojunction diodes shows a threefold increase in efficiency with applied bias and longer time constants. The improved efficiencies resulting from long time constants have been conclusively linked to the much longer charge collection times in the BC layer. Neutron detection signals from both the p-type BC layer and the n-type Si side of the heterojunction diode are observed, with comparable efficiencies. Collectively, these provide strong evidence that the semiconducting BC layer plays an active role in neutron detection, both in neutron capture and in charge generation and collection.


Ferroelectric Field Effect Transistors Using Very Thin Ferroelectric Polyvinylidene Fluoride Copolymer Films As Gate Dielectrics, A. Gerber, Center Of Nanoelectronic Systems For Information Technology (Cni), Research Center Jülich, Germany, R. Waser, Timothy J. Reece, E. Rije, Stephen Ducharme, Hermann Kohlstedt Jun 2010

Ferroelectric Field Effect Transistors Using Very Thin Ferroelectric Polyvinylidene Fluoride Copolymer Films As Gate Dielectrics, A. Gerber, Center Of Nanoelectronic Systems For Information Technology (Cni), Research Center Jülich, Germany, R. Waser, Timothy J. Reece, E. Rije, Stephen Ducharme, Hermann Kohlstedt

Stephen Ducharme Publications

We report electrical characterization of memory elements consisting of a p-type silicon field-effect transistor incorporating a ferroelectric polymer Langmuir–Blodgett film into the gate insulator to produce bistability through polarization hysteresis. The thin gate insulator, consisting of a 10 nm thick silicon oxide layer and a 35 nm thick ferroelectric polymer film, enabled bistable operation at 4 V. Device hysteresis as a function of gate voltage was evident both in the device capacitance, which was measured between the gate and drain, and in the source-drain conductance. The ferroelectric film polarization was not saturated, even up to operating voltages of 10 ...


Upgrade To The Pierre Auger Cosmic Ray Observatory's Lidar System, Emily B. Petermann May 2010

Upgrade To The Pierre Auger Cosmic Ray Observatory's Lidar System, Emily B. Petermann

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

The Pierre Auger Cosmic Ray Observatory currently operates four elastic lidar systems in order to characterize the atmospheric aerosol content above the observatory. The atmospheric information gained by the lidar system is then used in the calibration of the observatory’s four fluorescence detectors. Currently the four lidars in operation are unable to accurately determine the aerosol content below a distance of 1 km. A project is currently underway to upgrade the current lidar system by adding an additional detector to each of the existing lidar systems. The considered designs for this upgrade and the initial results from the upgrade ...


Substrate Dependent Buffer-Layer Assisted Growth Of Nanoclusters, Jan Honolka, Violetta Sessi, Jian Zhang, Simon Hertenberger, Axel Enders, Klaus Kern May 2010

Substrate Dependent Buffer-Layer Assisted Growth Of Nanoclusters, Jan Honolka, Violetta Sessi, Jian Zhang, Simon Hertenberger, Axel Enders, Klaus Kern

Axel Enders Publications

The role of the substrate on the morphology of nanometer size clusters fabricated by buffer layer assisted growth (BLAG) was studied using scanning tunneling microscopy. Clusters of Fe and Co were deposited on Ag(111), Cu(100), Rh(111), and Pt(111) surfaces using identical BLAG parameters, which are temperature, as well as metal and buffer layer coverage. Semi-hemispherical clusters are found on Ag(111) and Cu(100), while flat monolayer high islands are observed on Rh(111) and Pt(111) due to complete wetting. The results of this study are in agreement with the common notion that BLAG is ...


Robert Fuller Obituary (Local) Apr 2010

Robert Fuller Obituary (Local)

Robert G. Fuller Publications and Presentations

Robert G. Fuller, 76, Lincoln, died on Monday evening, April 9, 2012, as a result of complications from a severe brain aneurysm experienced on Thanksgiving morning. His enthusiasm for life and new ideas and his love of chocolate, raspberries, and conversation will be deeply missed.


Search For The Standard Model Higgs Boson In P-Pbar Interactions With The Decay Mode H -> W+ W- -> Mu+ Nu Mu- Nu At The D0 Experiment, Dale M. Johnston Apr 2010

Search For The Standard Model Higgs Boson In P-Pbar Interactions With The Decay Mode H -> W+ W- -> Mu+ Nu Mu- Nu At The D0 Experiment, Dale M. Johnston

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

A search for the standard model Higgs boson in p-pbar collisions resulting in two muons and large missing transverse energy is presented. The analysis uses 4.2 fb-1 of integrated luminosity at a center-of-mass energy of sqrt(s) = 1.96 TeV collected between April 2002 and December 2008 with the D0 detector at the Fermilab Tevatron collider. No significant excess above the background estimation is observed and limits are derived on Higgs boson production.


The Double-Mode Cepheid V371 Persei Redux, Edward G. Schmidt Apr 2010

The Double-Mode Cepheid V371 Persei Redux, Edward G. Schmidt

Edward Schmidt Publications

A metallicity of [Fe/H] = –0.05 to –0.40 was derived from four spectra of the peculiar beat Cepheid V371 Per. This conflicts with previous estimates ranging from –0.7 to –1.0 based on the period ratio. It is suggested that the discrepancy may be resolved by assuming near solar metallicity but a low mass. This is in accord with a suggestion by Sandage and Tammann that the AHB3 (or BL Her) stars are Population I analogs of short-period type II Cepheids. Further pulsational modeling is needed to clarify the status of this star and to understand the ...


More Variations On Aharonov-Bohm, Peter A. Sturock, Timothy R. Groves, Alexander Ershkovich, C. Alden Mead, Herman Batelaan And Akira Tonomura: Batelaan And Tonomura Reply, Herman Batelaan, Akira Tonomura Apr 2010

More Variations On Aharonov-Bohm, Peter A. Sturock, Timothy R. Groves, Alexander Ershkovich, C. Alden Mead, Herman Batelaan And Akira Tonomura: Batelaan And Tonomura Reply, Herman Batelaan, Akira Tonomura

Faculty Publications, Department of Physics and Astronomy

First paragraph: Werner Ehrenberg and Raymond Siday did propose the magnetic version of what is now called the Aharonov-Bohm (AB) effect, as Peter Sturrock and Timothy Groves point out. We had included this reference in the early versions of our manuscript. However, limited space directed the focus of the paper to the "effect without a force" discussion, rather than a historic perspective.


Early Stages Of Direct L10 Fept Nanocluster Formation: The Effects Of Plasma Characteristics, M. M. Patterson, A. Cochran, J. Ferina, X. Rui, T. A. Zimmerman, Zhiguang Sun, Matthew J. Kramer, David J. Sellmyer, Jeffrey E. Shield Mar 2010

Early Stages Of Direct L10 Fept Nanocluster Formation: The Effects Of Plasma Characteristics, M. M. Patterson, A. Cochran, J. Ferina, X. Rui, T. A. Zimmerman, Zhiguang Sun, Matthew J. Kramer, David J. Sellmyer, Jeffrey E. Shield

David Sellmyer Publications

The formation of FePt nanoclusters via gas condensation has attracted a great deal of attention. The clusters normally form with the magnetically soft A1 structure rather than the desired L10 structure with high magnetocrystalline anisotropy. This work has examined the effects of plasma characteristics on the early stages of order in the formation L10 FePt nanoclusters via inert gas condensation. The plasma characteristics have been modified to control ion density in the nanocluster condensation region. Increased ion density results in more cluster-ion collisions. The energy imparted to the clusters as a result of these collisions allows atomic rearrangements ...


Search For The Associated Production Of A B Quark And A Neutral Supersymmetric Higgs Boson That Decays Into Τ Pairs, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Jan 2010

Search For The Associated Production Of A B Quark And A Neutral Supersymmetric Higgs Boson That Decays Into Τ Pairs, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

We report results from a search for production of a neutral Higgs boson in association with a b quark. We search for Higgs decays to τ pairs with one τ subsequently decaying to a muon and the other to hadrons. The data correspond to 2.7 fb-1 of pp collisions recorded by the D0 detector at √s = 1.96 TeV. The data are found to be consistent with background predictions. The result allows us to exclude a significant region of parameter space of the minimal supersymmetric model.


Combination Of Tevatron Searches For The Standard Model Higgs Boson In The W+W- Decay Mode, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Jan 2010

Combination Of Tevatron Searches For The Standard Model Higgs Boson In The W+W- Decay Mode, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb-1 of pp collisions at √s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162–166 GeV at the 95% C.L.


Submillimeter-Resolution Radiography Of Shielded Structures With Laser-Accelerated Electron Beams, Viswanathan Ramanathan, Sudeep Banerjee, Nathan D. Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith, Kun Zhao, Kevin J. Brown, Donald Umstadter, Shaun Clarke, Sara Pozzi, James Beene, Randy Vane, David Schultz Jan 2010

Submillimeter-Resolution Radiography Of Shielded Structures With Laser-Accelerated Electron Beams, Viswanathan Ramanathan, Sudeep Banerjee, Nathan D. Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith, Kun Zhao, Kevin J. Brown, Donald Umstadter, Shaun Clarke, Sara Pozzi, James Beene, Randy Vane, David Schultz

Donald Umstadter Publications

We investigate the use of energetic electron beams for high-resolution radiography of flaws embedded in thick solid objects. A bright, monoenergetic electron beam (with energy >100 MeV) was generated by the process of laser-wakefield acceleration through the interaction of 50-TW, 30-fs laser pulses with a supersonic helium jet. The high energy, low divergence, and small source size of these beams make them ideal for high-resolution radiographic studies of cracks or voids embedded in dense materials that are placed at a large distance from the source. We report radiographic imaging of steel with submillimeter resolution.


Polarized Neutron Reflectometry Study Of The Magnetization Reversal Process In Yba2cu3o7 /La2/3ca1/3mno3 Superlattices Grown On Srtio3 Substrates, J. Hoppler, H. Fritzsche, V. K. Malik, J. Stahn, G. P. Cristiani, H.-U. Habermeier, M. Rössle, Jan Honolka, Axel Enders, C. Bernhard Jan 2010

Polarized Neutron Reflectometry Study Of The Magnetization Reversal Process In Yba2cu3o7 /La2/3ca1/3mno3 Superlattices Grown On Srtio3 Substrates, J. Hoppler, H. Fritzsche, V. K. Malik, J. Stahn, G. P. Cristiani, H.-U. Habermeier, M. Rössle, Jan Honolka, Axel Enders, C. Bernhard

Axel Enders Publications

Using polarized neutron reflectometry we investigated the reversal of the magnetization of a high-Tc superconductor/ferromagnet superlattice that consists of eight bilayers of YBa2Cu3O7(25.6 nm) /La2/3Ca1/3MnO3(25.6 nm) grown on a SrTiO3 substrate. The measurements were performed during a magnetization hysteresis loop at 5 K. We obtained evidence that the reversal in the vicinity of the coercive field proceeds via the switching of micrometer-sized magnetic domains that are considerably larger than the typical domains of La2/3Ca1/3MnO ...


Alignment And Orientation Of Diatomic Molecules Induced By Polarized Electron Impact, Jack W. Maseberg, Timothy J. Gay Jan 2010

Alignment And Orientation Of Diatomic Molecules Induced By Polarized Electron Impact, Jack W. Maseberg, Timothy J. Gay

Timothy J. Gay Publications

We report measurements of linear and circular fluorescence polarizations for molecular transitions in H2, D2, and N2 induced by spin-polarized electron impact. Circular polarizations resulting from some Fulcher-α transitions in H2 and D2 are found to be significant, while the null results from nitrogen’s second positive system are consistent with an earlier measurement by the Münster group. We compare this nitrogen data to that from our previous study of nitrogen’s first negative system. Emphasis is placed on understanding the mechanisms that cause the values of circular polarization from N2 to be relatively ...


Semiclassical Complex-Time Method For Tunneling Ionization: Molecular Suppression And Orientational Dependence, Gordon A. Gallup, Ilya I. Fabrikant Jan 2010

Semiclassical Complex-Time Method For Tunneling Ionization: Molecular Suppression And Orientational Dependence, Gordon A. Gallup, Ilya I. Fabrikant

Gordon Gallup Publications

We apply a previously developed semiclassical complex time method to the calculation of tunneling ionization of several diatomic molecules and CO2.We investigate the presence or absence of the molecular suppression effect by calculating ionization rates of N2 versus Ar, O2 versus Xe, F2 versus Ar, and CO versus Kr. Comparisons with other theories, including the molecular-orbital-Ammosov-Delone-Krainov (MO-ADK) model and the strong-field approximation, are given. We also analyze the dependence of the ionization rate on the angle θF between the molecular axis and the field direction. The theoretical results agree quite well with experiment for ...


Search For Higgs Boson Production In Dilepton And Missing Energy Final States With 5.4 Fb-1 Of Pp Collisions At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Jan 2010

Search For Higgs Boson Production In Dilepton And Missing Energy Final States With 5.4 Fb-1 Of Pp Collisions At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

A search for the standard model Higgs boson is presented using events with two charged leptons and large missing transverse energy selected from 5.4 fb-1 of integrated luminosity in pp collisions at √s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron collider. No significant excess of events above background predictions is found, and observed (expected) upper limits at 95% confidence level on the rate of Higgs boson production are derived that are a factor of 1.55 (1.36) above the predicted standard model cross section at mH = 165 GeV.


Interstitial-Nitrogen Effect On Phase Transition And Magnetocaloric Effect In Mn(As,Si) (Invited), W. B. Cui, X. K. Lv, F. Yang, Ralph Skomski, Y. Yu, X. G. Zhao, W. Liu, Z.D. Zhang Jan 2010

Interstitial-Nitrogen Effect On Phase Transition And Magnetocaloric Effect In Mn(As,Si) (Invited), W. B. Cui, X. K. Lv, F. Yang, Ralph Skomski, Y. Yu, X. G. Zhao, W. Liu, Z.D. Zhang

Ralph Skomski Publications

The effect of interstitial nitrogen on the phase transition and magnetocaloric behavior of MnAs1−xSixNδ (x=0.03, 0.06, and 0.09) is investigated. The interstitial nitrogen atoms cause the step-scanned x-ray diffraction peaks to shift toward lower angles and lower the Curie temperature, whereas silicon addition increases the Curie temperature to near room temperature. The thermal hysteresis is reduced to nearly 0 in MnAs1−xSixNδ, which is beneficial to practical applications. For a field change of 5 T, the largest magnetic entropy change and refrigerant capacity are 14 ...


Anisotropy Of Domain Growth In Epitaxial Ferroelectric Capacitors, D. Wu, I. Vrejoiu, M. Alexe, Alexei Gruverman Jan 2010

Anisotropy Of Domain Growth In Epitaxial Ferroelectric Capacitors, D. Wu, I. Vrejoiu, M. Alexe, Alexei Gruverman

Alexei Gruverman Publications

Piezoresponse force microscopy (PFM) has been applied to investigate the switching kinetics in microscale epitaxial Pb(Zr,Ti)O3 capacitors. It is shown that transition from low to high field range brings about a qualitative change in domain growth kinetics, namely, laterally isotropic growth in the high fields as opposed to highly anisotropic growth in the low fields. It is suggested that anisotropy of domain growth can be attributed to orientational variations in the activation energy due to film microstructure. Fitting the switching kinetics using the Kolmogorov–Avrami–Ishibashi model shows excellent agreement with the PFM experimental data and ...


Self-Assembly And Properties Of Nonmetalated Tetraphenyl-Porphyrin On Metal Substrates, Geoffrey Rojas, Xumin Chen, Cameron Bravo, Ji-Hyun Kim, Jae-Sung Kim, Jie Xiao, Peter A. Dowben, Yi Gao, Xiao Cheng Zeng, Wonyoung Choe, Axel Enders Jan 2010

Self-Assembly And Properties Of Nonmetalated Tetraphenyl-Porphyrin On Metal Substrates, Geoffrey Rojas, Xumin Chen, Cameron Bravo, Ji-Hyun Kim, Jae-Sung Kim, Jie Xiao, Peter A. Dowben, Yi Gao, Xiao Cheng Zeng, Wonyoung Choe, Axel Enders

Axel Enders Publications

The structure−electronic structure relationship of nonmetalated meso-tetraphenyl porphyrin (2H-TPP) on the (111) surfaces of Ag, Cu, and Au was studied with a combination of scanning tunneling microscopy, photoelectron spectroscopy, and density functional theory. We observe that the molecules form a 2D network on Ag(111), driven by attractive intermolecular interactions, while the surface migration barriers are comparatively small and the charge transfer to the adsorbed molecules is minimal. This is in contrast to a significant charge transfer observed in 2H-TPP/Cu(111), resulting in repulsive forces between the molecules that prevent molecular adlayer network formation. It is shown that ...


The Electron–Phonon Coupling At The Mo(112) Surface, Ning Wu, Keisuke Fukutani, Peter A. Dowben Jan 2010

The Electron–Phonon Coupling At The Mo(112) Surface, Ning Wu, Keisuke Fukutani, Peter A. Dowben

Peter Dowben Publications

We investigated the electron–phonon coupling (EPC), in the vicinity of the Fermi level, for the surface-weighted states of Mo(112) from high resolution angle-resolved photoemission data taken parallel to the surface corrugation (i.e. (111)). The surface-weighted bandwidth may be discussed in terms of electron–electron interactions, electron impurity scattering and electron–phonon coupling and exhibits a mass enhancement factor λ = 0.42, within the Debye model, determined from the experimentally derived self-energy. Gold overlayers suppress the mass enhancement of the Mo(112) surface-weighted band crossing the Fermi level at 0.54 Å-1.


Tunable Band Gap In Bi(Fe1−Xmnx)O3 Films, X. S. Xu, J. F. Ihlefeld, J. H. Lee, O. K. Ezekoye, E. Vlahos, R. Ramesh, V. Gopalan, X. Q. Pan, D. G. Schlom, J. L. Musfeldt Jan 2010

Tunable Band Gap In Bi(Fe1−Xmnx)O3 Films, X. S. Xu, J. F. Ihlefeld, J. H. Lee, O. K. Ezekoye, E. Vlahos, R. Ramesh, V. Gopalan, X. Q. Pan, D. G. Schlom, J. L. Musfeldt

Xiaoshan Xu Papers

In order to investigate band gap tunability in polar oxides, we measured the optical properties of a series of Bi(Fe1−xMnx)O3 thin films. The absorption response of the mixed metal solid solutions is approximately a linear combination of the characteristics of the two end members, a result that demonstrates straightforward band gap tunability in this system.


Optical Properties Of Quasi-Tetragonal Bifeo3 Thin Films, P. Chen, N. J. Podraza, X. S. Xu, A. Melville, E. Vlahos, V. Gopalan, R. Ramesh, D. G. Schlom, J. L. Musfeldt Jan 2010

Optical Properties Of Quasi-Tetragonal Bifeo3 Thin Films, P. Chen, N. J. Podraza, X. S. Xu, A. Melville, E. Vlahos, V. Gopalan, R. Ramesh, D. G. Schlom, J. L. Musfeldt

Xiaoshan Xu Papers

Optical transmission spectroscopy and spectroscopic ellipsometry were used to extract the optical properties of an epitaxially grown quasi-tetragonal BiFeO3 thin film in the near infrared to near ultraviolet range. The absorption spectrum is overall blue shifted compared with that of rhombohedral BiFeO3, with an absorption onset near 2.25 eV, a direct 3.1 eV band gap, and charge transfer excitations that are ~0.4 eV higher than those of the rhombohedral counterpart. We interpret these results in terms of structural strain and local symmetry breaking.