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Iowa State University

2001

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Articles 1 - 19 of 19

Full-Text Articles in Physics

Absence Of Fine Structure In The Photoemission Spectrum Of The Icosahedral Al-Pd-Mn Quasicrystal, Z. M. Stadnik, D. Purdie, Y. Baer, Thomas A. Lograsso Nov 2001

Absence Of Fine Structure In The Photoemission Spectrum Of The Icosahedral Al-Pd-Mn Quasicrystal, Z. M. Stadnik, D. Purdie, Y. Baer, Thomas A. Lograsso

Ames Laboratory Publications

The results of the low-temperature ultrahigh-energy-resolution photoemission studies of a single-grain icosahedral alloy Al70Pd21.5Mn8.5 have been presented. The existence of the theoretically predicted pseudogap in the density of states at the Fermi energy has been confirmed. No evidence of the theoretically predicted spikiness of the density of states could be observed. It has been suggested that the failure to detect the predicted spikiness of the density of states in icosahedral quasicrystals is consistent with the results of Zijlstra and Janssen [Europhys. Lett. 52, 578 (2000)] who showed that the spikiness occurs only in ...


Optical Properties And Electronic Structure Of Mgausn, S. J. Lee, J. M. Park, T. A. Wiener, L. L. Miller, David W. Lynch Sep 2001

Optical Properties And Electronic Structure Of Mgausn, S. J. Lee, J. M. Park, T. A. Wiener, L. L. Miller, David W. Lynch

Physics and Astronomy Publications

The optical conductivity spectrum of single-crystal MgAuSn was measured by spectroscopic ellipsometry in the energy range 1.5–5.0 eV. The spectrum has a large peak at 2.9 eV and a small shoulder around 4.3 eV. The band structure, density of states, and interband contribution to the optical conductivity were calculated with the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation. The intraband contribution to the optical conductivity was added using the Drude response fitted to the experimental data. The total theoretical spectrum, including the intraband contribution, agrees well with experimental data.


First Results From Rhic-Phenix, Tarun Kanti Ghosh, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Aug 2001

First Results From Rhic-Phenix, Tarun Kanti Ghosh, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Conference Papers, Posters and Presentations

The PHENIX experiment consists of a large detector system located at the newly commissioned relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory. The primary goal of the PHENIX experiment is to look for signatures of the QCD prediction of a deconfined high-energy-density phase of nuclear matter quark gluon plasma. PHENIX started data taking for Au+Au collisions at √sNN = 130 GeV in June 2000. The signals from the beam-beam counter (BBC) and zero degree calorimeter (ZDC) are used to determine the centrality of the collision. A Glauber model reproduces the ZDC spectrum reasonably well to determine the participants ...


Superconducting Mgb2 Thin Films By Pulsed Laser Deposition, S. R. Shinde, S. B. Ogale, R. L. Greene, T. Venkatesan, Paul C. Canfield, Sergey L. Bud'ko, G. Lapertot, Cedomir Petrovic Jul 2001

Superconducting Mgb2 Thin Films By Pulsed Laser Deposition, S. R. Shinde, S. B. Ogale, R. L. Greene, T. Venkatesan, Paul C. Canfield, Sergey L. Bud'ko, G. Lapertot, Cedomir Petrovic

Ames Laboratory Publications

Growth of MgB2thin films by pulsed laser deposition is examined under ex situ and in situprocessing conditions. For the ex situ process, boronfilmsgrown by pulsed laser deposition were annealed at 900 °C with excess Mg. For the in situ process, different approaches involving ablation from a stoichiometric target under different growth conditions, as well as multilayer deposition involving interposed Mg layers were examined and analyzed. Magnetic measurements on ex situ processed films show Tc of ∼39 K, while the current best in situfilms show a susceptibility transition at ∼22 K.


Measurement Of The Midrapidity Transverse Energy Distribution From Root(Nn)-N-S=130 Gev Au+Au Collisions At Rhic, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Jul 2001

Measurement Of The Midrapidity Transverse Energy Distribution From Root(Nn)-N-S=130 Gev Au+Au Collisions At Rhic, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The first measurement of energy produced transverse to the beam direction at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is presented. The midrapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that ⟨ET⟩/⟨Nch⟩ remains relatively constant as a function of centrality. The energy density calculated via Bjorken’s prescription for the 2% most central Au+Au collisions at √sNN=130GeV is at least εBj=4.6 GeV/fm3, which is a factor of 1.6 larger than found at √sNN=17.2 GeV ( Pb+Pb ...


Microwave Properties Of Superconducting Mgb2, N. Hakim, P. V. Parimi, C. Kusko, S. Sridhar, Paul C. Canfield, Sergey L. Bud'ko, Douglas K. Finnemore Jun 2001

Microwave Properties Of Superconducting Mgb2, N. Hakim, P. V. Parimi, C. Kusko, S. Sridhar, Paul C. Canfield, Sergey L. Bud'ko, Douglas K. Finnemore

Ames Laboratory Publications

Measurements of 10 GHz microwavesurface resistance, Rs, of dense MgB2wire and pellet are reported. Significant improvements are observed in the wire with reduction of porosity. The data lie substantially above the theoretical estimates for a pure Bardeen–Cooper–Schrieffer s-wave superconductor. However, the Rs (20 K) of the wire is an order of magnitude lower than that of polycrystalYBa2Cu3O6.95 and matches with single-crystal YBa2Cu3O6.95. The results show promise for the use of MgB2 in microwave applications.


Phonon Softening In Ni-Mn-Ga Alloys, Lluís Mañosa, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis Jun 2001

Phonon Softening In Ni-Mn-Ga Alloys, Lluís Mañosa, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis

Ames Laboratory Publications

The TA2 phonon dispersion curves of Ni-Mn-Ga alloys with different compositions which transform to different martensitic structures have been measured over a broad temperature range covering both paramagnetic and ferromagnetic phases. The branches show an anomaly (dip) at a wave number that depends on the particular martensitic structure, and there is softening of these anomalous phonons with decreasing temperature. This softening is enhanced below the Curie point, as a consequence of spin-phonon coupling. This effect is stronger for systems with higher electronic concentration.


Phase Transitions In Mixed Adsorbed Layers: Effect Of Repulsion Between “Hard Squares” And “Point Particles”, Da-Jiang Liu, James W. Evans Jun 2001

Phase Transitions In Mixed Adsorbed Layers: Effect Of Repulsion Between “Hard Squares” And “Point Particles”, Da-Jiang Liu, James W. Evans

Mathematics Publications

It is shown that repulsive interactions between larger “hard squares” and smaller “point particles” in a mixed adlayer model modify the hard-square order–disorder transition and can produce phase separation.


Role Of Stratospheric Air In A Severe Weather Event: Analysis Of Potential Vorticity And Total Ozone, Melissa A. Goering, William A. Gallus Jr., Mark A. Olsen, John L. Stanford Jun 2001

Role Of Stratospheric Air In A Severe Weather Event: Analysis Of Potential Vorticity And Total Ozone, Melissa A. Goering, William A. Gallus Jr., Mark A. Olsen, John L. Stanford

Geological and Atmospheric Sciences Publications

The role of dry stratospheric air descending to low and middle tropospheric levels in a severe weather outbreak in the midwestern United States is examined using NCEP Eta model output, Rapid Update Cycle (RUC) analyses, and Earth probe Total Ozone Mapping Spectrometer (EP/TOMS) total ozone data. While stratospheric air was not found to play a direct role in the convection, backward trajectories show stratospheric air descended to 800 hPa just west of the convection. Damaging surface winds not associated with thunderstorms also occurred in the region of greatest stratospheric descent. Small-scale features in the high-resolution total ozone data compare ...


Structural Characterization Of Thin Film Photonic Crystals, G. Subramania, Rana Biswas, Kristen P. Constant, M. M. Sigalas, Kai-Ming Ho May 2001

Structural Characterization Of Thin Film Photonic Crystals, G. Subramania, Rana Biswas, Kristen P. Constant, M. M. Sigalas, Kai-Ming Ho

Materials Science and Engineering Publications

We quantitatively analyze the structure of thin film inverse-opal photonic crystals composed of ordered arrays of air pores in a background of titania. Ordering of the sphere template and introduction of the titania background were performed simultaneously in the thin film photonic crystals. Nondestructive optical measurements of backfilling with high refractive index liquids, angle-resolved reflectivity, and optical spectroscopy were combined with band-structure calculations. The analysis reveals a thin film photonic crystal structure with a very high filling fraction (92–94 %) of air and a substantial compression along the c axis (∼22–25%).


Optical Properties Of Rni2b2c (R=Y,Tb,Er,Dy), S. J. Lee, B. K. Cho, Paul C. Canfield, David W. Lynch May 2001

Optical Properties Of Rni2b2c (R=Y,Tb,Er,Dy), S. J. Lee, B. K. Cho, Paul C. Canfield, David W. Lynch

Physics and Astronomy Publications

The optical properties of single crystals of RNi2B2C (R=Y,Tb,Er, and Dy) were measured between 1.7 and 5.2 eV at room temperature using a spectroscopic ellipsometer. The spectra for all compounds are similar and the peak positions appear in a similar energy region. The similarity of the spectra of RNi2B2C (R=Tb,Er,Dy) to that of YNi2B2C indicates that the rare-earth 4f states are not actively involved in the optical transitions.


Physical Properties Of Heusler-Like Fe2val, Ye Feng, J. Y. Rhee, T. A. Wiener, David W. Lynch, B. E. Hubbard, A. J. Sievers, Deborah L. Schlagel, Thomas A. Lograsso, L. L. Miller Apr 2001

Physical Properties Of Heusler-Like Fe2val, Ye Feng, J. Y. Rhee, T. A. Wiener, David W. Lynch, B. E. Hubbard, A. J. Sievers, Deborah L. Schlagel, Thomas A. Lograsso, L. L. Miller

Ames Laboratory Publications

A comprehensive characterization of the compound Fe2VAl was carried out. Samples grown by arc melting or the Bridgman method have Al and Fe deficiencies of up to 5 at. %. Czochralski-grown samples were Fe rich and Al deficient. X-ray diffraction implies appreciable antisite disorder in all of our samples. Fourier-transform infrared (FTIR) spectroscopy measurements showed that the carrier density and scattering time had little sample-to-sample variation or temperature dependence for near-stoichiometric samples. FTIR and dc resistivity suggest that the transport properties of Fe2VAl are influenced by both localized and delocalized carriers, with the former primarily responsible for ...


Evolution Of Two-Dimensional Wormlike Nanoclusters On Metal Surfaces, Woei Wu Pai, John F. Wendelken, C. R. Stoldt, Patricia A. Thiel, James W. Evans, Da-Jiang Liu Apr 2001

Evolution Of Two-Dimensional Wormlike Nanoclusters On Metal Surfaces, Woei Wu Pai, John F. Wendelken, C. R. Stoldt, Patricia A. Thiel, James W. Evans, Da-Jiang Liu

Chemistry Publications

A pinch-off phenomenon is discovered in the evolution of 2D wormlike nanoclusters formed in homoepitaxial adlayers. This feature is shown to distinguish mass transport via periphery diffusion from other mechanisms. Continuum modeling of such evolution accurately describes experimental observations, particularly if one incorporates the anisotropy in step-edge line tension.


Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen Apr 2001

Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen

Ames Laboratory Publications

In this paper we present the development of a composite magnetostrictive material for automotive applications. The material is based on cobaltferrite,CoO⋅Fe2O3, and contains a small fraction of metallic matrix phase that serves both as a liquid-phasesintering aid during processing and enhances the mechanical properties over those of a simple sinteredferrite ceramic. In addition the metal matrix makes it possible to braze the material, making the assembly of a sensor relatively simple. The material exhibits good sensitivity and should have high corrosion resistance, while at the same time it is low in cost.


Centrality Dependence Of Charged Particle Multiplicity In Au-Au Collisions At Root(S)Nn=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et. Al, Phenix Collaboration Apr 2001

Centrality Dependence Of Charged Particle Multiplicity In Au-Au Collisions At Root(S)Nn=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et. Al, Phenix Collaboration

Physics and Astronomy Publications

We present results for the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at roots(NN) = 130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find dN(ch)/d eta (|eta =0) = 622 +/- 1(stat) +/- 41(syst). The results, analyzed as a function of centrality show a steady rise of the particle density per participating nucleon with centrality.


No Well-Defined Remnant Fermi Surface In Sr2cuo2cl2, S. Haffner, D. P. Brammeier, C. G. Olson, L. L. Miller, David W. Lynch Apr 2001

No Well-Defined Remnant Fermi Surface In Sr2cuo2cl2, S. Haffner, D. P. Brammeier, C. G. Olson, L. L. Miller, David W. Lynch

Physics and Astronomy Publications

In angle-resolved photoelectron spectra of the antiferromagnetic insulators Ca2CuO2Cl2 and Sr2CuO2Cl2, a sharp drop of the spectral intensity of the lowest-lying band is observed along a line in k space equivalent to the Fermi surface of the optimally doped high-temperature superconductors. This was interpreted as a signature of the existence of a remnant Fermi surface in the insulating phase of the high-temperature superconductors. In this paper it is shown that the drop of the spectral intensity is not related to the spectral function but is a consequence of the electron-photon matrix element.


Magnetic Force Microscopy Study Of Magnetization Reversal In Sputtered Fesial(N) Films, Chester C.H. Lo, J. E. Snyder, J. S. Leib, R. Chen, B. Kriegermeier-Sutton, Matthew J. Kramer, David C. Jiles, M. T. Kief Mar 2001

Magnetic Force Microscopy Study Of Magnetization Reversal In Sputtered Fesial(N) Films, Chester C.H. Lo, J. E. Snyder, J. S. Leib, R. Chen, B. Kriegermeier-Sutton, Matthew J. Kramer, David C. Jiles, M. T. Kief

Materials Science and Engineering Publications

The magnetization reversal in a series of rf-sputtered FeSiAl(N) films has been studied using magnetic force microscopy. A system has been developed which has the capability to image domain structure while an in-plane magnetic field is applied in situ. All films exhibited a stripe domain structure in zero applied field which was indicative of a perpendicular component of domain magnetization which alternates in sign. All films showed a similar sequence of magnetization processes: on reducing the applied field from saturation a fine stripe domain structure nucleated and then coarsened as the field was decreased to zero. Local switching of ...


Optical And Magneto-Optical Investigation On Electronic Structure Of Ordered Ferromagnetic Fe3pt, K. J. Kim, S. J. Lee, T. A. Wiener, David W. Lynch Jan 2001

Optical And Magneto-Optical Investigation On Electronic Structure Of Ordered Ferromagnetic Fe3pt, K. J. Kim, S. J. Lee, T. A. Wiener, David W. Lynch

Physics and Astronomy Publications

The optical and magneto-opticalproperties of ordered Fe3Pt have been investigated by spectroscopicellipsometry and magneto-opticalKerrspectroscopy. The diagonal component of the optical conductivity tensor of the compound exhibits a broad absorption peak at about 2 eV, which is shifted by about 0.5 eV to lower energies from the corresponding one in pure bcc Fe. The Kerr angle spectrum of the compound disperses quite similarly in both spectral trend and magnitude to that of pure Fe below 3.5 eV but differently above it. The lower-energy shift of the 2-eV-absorption structure of the compound is interpreted as due to the shift of ...


Fe−3s Core-Level Splitting And Local Magnetism In Fe2val, Ye Feng, M. V. Dobrotvorska, James W. Anderegg, C. G. Olson, David W. Lynch Jan 2001

Fe−3s Core-Level Splitting And Local Magnetism In Fe2val, Ye Feng, M. V. Dobrotvorska, James W. Anderegg, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

X-ray and soft x-ray photoelectron spectra were taken on Fe2VAl samples. The Fe−3s spectra show a shoulder on the higher binding energy side of the main peak, split by ≈4.7 eV. Based on current understanding of core-level multiplet splitting in transition-metal compounds, we believe this is direct evidence of a local moment in Fe2VAl.