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Articles 61 - 76 of 76

Full-Text Articles in Physics

Sensing Dipole Fields At Atomic Steps With Combined Scanning Tunneling And Force Microscopy, Jeong Young Park, G. M. Sacha, M. Enachescu, D. F. Ogletree, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel, J. J. Sáenz, M. Salmeron Jan 2005

Sensing Dipole Fields At Atomic Steps With Combined Scanning Tunneling And Force Microscopy, Jeong Young Park, G. M. Sacha, M. Enachescu, D. F. Ogletree, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel, J. J. Sáenz, M. Salmeron

Chemistry Publications

The electric field of dipoles localized at the atomic steps of metal surfaces due to the Smoluchowski effect were measured from the electrostatic force exerted on the biased tip of a scanning tunneling microscope. By varying the tip-sample bias the contribution of the step dipole was separated from changes in the force due to van der Waals and polarization forces. Combined with electrostatic calculations, the method was used to determine the local dipole moment in steps of different heights on Au(111) and on the twofold surface of an Al-Ni-Co decagonal quasicrystal.


Crystallographic, Electronic, And Magnetic Studies Of Ζ2-Gam (M = Cr, Mn Or Fe):  Trends In Itinerant Magnetism, Olivier Gourdon, Sergey L. Bud'ko, Darrick Williams, Gordon J. Miller Jan 2004

Crystallographic, Electronic, And Magnetic Studies Of Ζ2-Gam (M = Cr, Mn Or Fe):  Trends In Itinerant Magnetism, Olivier Gourdon, Sergey L. Bud'ko, Darrick Williams, Gordon J. Miller

Chemistry Publications

This study of the crystal structure, electronic structure, and magnetic properties of the ζ2-GaM (M = Cr, Mn or Fe) alloys is motivated by the recent reinvestigation of the crystallographic Al8Cr5 structure type of ζ2-GaMn. The isostructural compounds ζ2-GaFe and ζ2-GaCr have been refined using X-ray powder diffraction as well as neutron powder diffraction for ζ2-GaFe. Their structures have been refined using the space group Rm, with cell parameters a = 12.625(8) Å and c = 7.785(10) Å for ζ2-GaCr and a ...


Anomalous Temperature-Dependent Transport In Ybni2b2c And Its Correlation To Microstructural Features, M.A. Avila, Y.Q. Wu, C.L. Condron, Sergey L. Bud'ko, M. J. Kramer, Gordon J. Miller, Paul C. Canfield Jan 2004

Anomalous Temperature-Dependent Transport In Ybni2b2c And Its Correlation To Microstructural Features, M.A. Avila, Y.Q. Wu, C.L. Condron, Sergey L. Bud'ko, M. J. Kramer, Gordon J. Miller, Paul C. Canfield

Chemistry Publications

We address the nature of the ligandal disorder leading to local redistributions of Kondo temperatures, manifested as annealing-induced changes in the transport behavior of the heavy fermion system YbNi2B2C. The anomalous transport behavior was fully characterized by temperature dependent resistivity measurements in an extended range of 0.4


Anisotropy And Large Magnetoresistance In The Narrow-Gap Semiconductor Fesb2, Cedomir Petrovic, J.W. Kim, Sergey L. Bud'ko, A. I. Goldman, Paul C. Canfield, Wonyoung Choe, Gordon J. Miller Jan 2003

Anisotropy And Large Magnetoresistance In The Narrow-Gap Semiconductor Fesb2, Cedomir Petrovic, J.W. Kim, Sergey L. Bud'ko, A. I. Goldman, Paul C. Canfield, Wonyoung Choe, Gordon J. Miller

Chemistry Publications

A study of the anisotropy in magnetic, transport, and magnetotransport properties of FeSb2 has been made on large single crystals grown from Sb flux. Magnetic susceptibility of FeSb2 shows diamagnetic to paramagnetic crossover around 100 K. Electrical transport along two axes is semiconducting, whereas the third axis exhibits a metal-semiconductor crossover at temperature Tcr which is sensitive to current alignment and ranges between 40 and 80 K. In H=70kOe semiconducting transport is restored for T<300K, resulting in large magnetoresistance [ρ(70kOe)−ρ(0)]/ρ(0)=2200% in the crossover temperature range.


A New Look At Bonding In Trialuminides:  Reinvestigation Of Taal3, C.L. Condron, Gordon J. Miller, Joel D. Strand, Sergey L. Bud'ko, Paul C. Canfield Jan 2003

A New Look At Bonding In Trialuminides:  Reinvestigation Of Taal3, C.L. Condron, Gordon J. Miller, Joel D. Strand, Sergey L. Bud'ko, Paul C. Canfield

Chemistry Publications

Single crystals of TaAl3 were grown at high temperatures from an Al-rich, binary solution. TaAl3 adopts the D022 structure type, space group I4/mmm with a = 3.8412(5) Å, c = 8.5402(17) Å, and Z = 2. The structure type, which is the preferred structure for all group 5 trialuminides and TiAl3 as well as the high-temperature form of HfAl3, is a binary coloring of the face-centered-cubic (fcc) arrangement. The distribution of Ta atoms creates a three-dimensional network of vertex and edge-sharing square pyramids of Al atoms. Temperature-dependent electrical resistivity and magnetic susceptibility ...


The Intermetallic Compound Gd6ta4al43, Cathie L. Condron, Joel D. Strand, Paul C. Canfield, Gordon J. Miller Jan 2003

The Intermetallic Compound Gd6ta4al43, Cathie L. Condron, Joel D. Strand, Paul C. Canfield, Gordon J. Miller

Chemistry Publications

The elements Gd (99.999%; Ames Laboratory), Ta (99.999%; Ames Laboratory), and Al (99.98%; Alfa) were combined in the atomic ratio Gd6Ta4Al100 in a 2 ml alumina crucible. The crucible was placed into a fused silica tube and a second crucible, filled with SiO2 wool, was placed inverted on top of the first. The tube was sealed under 1/5 atm Ar and placed into a box furnace. The mixture was heated to 1463 K in 3 h, kept at 1463 K for 2 h, and then cooled to 1173 K over ...


Decoupling Of The Magnetic And Structural Transformations In Er5si4, Vitalij K. Pecharsky, Alexandra O. Pecharsky, Yurij Mozharivskyj, Karl A. Gschneidner Jr., Gordon J. Miller Jan 2003

Decoupling Of The Magnetic And Structural Transformations In Er5si4, Vitalij K. Pecharsky, Alexandra O. Pecharsky, Yurij Mozharivskyj, Karl A. Gschneidner Jr., Gordon J. Miller

Chemistry Publications

Er5Si4 is a member of the R5(Si4−xGex) family of alloys, where R=rare earth metal. Many of these compounds display a strong coupling between the magnetic and crystal lattices. In the naturally layered R5(Si4−xGex) materials, inter- and intralayer interactions can be controlled by chemical and physical means; thus their physical properties can be tailored within wide limits. The Er5Si4 is unique in that the temperature dependent structural sequence is opposite that of other representatives of this family. The magnetism of Er5Si4 is reflective of its exceptional place within the series.


Surface Structures Of Approximant Phases In The Al-Pd-Mn System, V. Fournée, A. R. Ross, Thomas A. Lograsso, James W. Anderegg, C. Dong, Matthew J. Kramer, I. R. Fisher, Paul C. Canfield, Patricia A. Thiel Jan 2002

Surface Structures Of Approximant Phases In The Al-Pd-Mn System, V. Fournée, A. R. Ross, Thomas A. Lograsso, James W. Anderegg, C. Dong, Matthew J. Kramer, I. R. Fisher, Paul C. Canfield, Patricia A. Thiel

Chemistry Publications

We present a study of the surface of the ξ′-Al-Pd-Mn approximant phase based upon scanning tunneling microscopy and low-energy electron diffraction. Several structures are observed on two different samples grown either by the Bridgman technique or by a self-flux method, and which contain various degrees of disorder. We also describe some other complex crystalline phases that are sometimes observed on the fivefold surface of Al-Pd-Mn quasicrystalline samples after the sputter-annealing cleaning process under ultrahigh vacuum conditions. This includes the T approximant phase resulting from surface decomposition after a high-temperature annealing.


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.


Electronic Structure Of Quasicrystalline Surfaces: Effects Of Surface Preparation And Bulk Structure, V. Fournée, P. J. Pinhero, J. W. Anderegg, Thomas A. Lograsso, A. R. Ross, Paul C. Canfield, I. R. Fisher, Patricia A. Thiel Dec 2000

Electronic Structure Of Quasicrystalline Surfaces: Effects Of Surface Preparation And Bulk Structure, V. Fournée, P. J. Pinhero, J. W. Anderegg, Thomas A. Lograsso, A. R. Ross, Paul C. Canfield, I. R. Fisher, Patricia A. Thiel

Chemistry Publications

We elucidate the nature of the surface electronic properties of quasicrystalline Al-Pd-Mn. We do this by using photoelectron and Auger electron spectroscopies, and by making a variety of comparisons—across types of bulk samples, and across methods of surface preparation. The main conclusions are these: (i) The narrow Mn 2p3/2core-level line observed in the icosahedral phase is a fingerprint of a suppression in the density of states (a pseudogap) at the Fermi level and is not unique to the quasicrystalline phase. It is also independent of the symmetry of the quasicrystalline surface. The Auger line shape is ...


Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel Oct 1998

Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel

Chemistry Publications

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below ∼700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for ...


Fivefold Surface Of Quasicrystalline Alpdmn: Structure Determination Using Low-Energy-Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, P. J. Pinhero, Cynthia J. Jenks, James W. Anderegg, C.-M. Zhang, Patricia A. Thiel Apr 1998

Fivefold Surface Of Quasicrystalline Alpdmn: Structure Determination Using Low-Energy-Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, P. J. Pinhero, Cynthia J. Jenks, James W. Anderegg, C.-M. Zhang, Patricia A. Thiel

Chemistry Publications

The atomic structure of the fivefold symmetric quasicrystal surface of icosahedral AlPdMn has been investigated by means of a dynamical low-energy-electron diffraction (LEED) analysis. Approximations were developed to make the structure of an aperiodic, quasicrystalline surface region accessible to LEED theory. A mix of several closely similar, relaxed, bulklike lattice terminations is favored, all of which have a dense Al-rich layer on top followed by a layer with a composition of about 50% Al and 50% Pd. The interlayer spacing between these two topmost layers is contracted from the bulk value by 0.1 Å, to a final value of ...


Structural Analysis Of The Fivefold Symmetric Surface Of The Al70pd21mn9 Quasicrystal By Low Energy Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, Cynthia J. Jenks, C.-M. Zhang, Patricia A. Thiel Jan 1997

Structural Analysis Of The Fivefold Symmetric Surface Of The Al70pd21mn9 Quasicrystal By Low Energy Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, Cynthia J. Jenks, C.-M. Zhang, Patricia A. Thiel

Chemistry Publications

The atomic structure of the fivefold symmetric quasicrystal surface of Al70Pd21Mn9 was investigated by means of a dynamical low energy electron-diffraction analysis. Approximations are developed to address the high structural complexity of quasicrystals, yielding average layer-by-layer structural and compositional information. A mix of several relaxed bulklike terminations is found, consistently favoring dense Al-rich outermost atomic layers. These results can be understood in terms of principles known to govern surface structures of simpler, crystalline metals.


Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch Sep 1996

Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch

Chemistry Publications

Photoelectron spectra of a fivefold quasicrystalline alloy Al70Pd21Mn9 and a related cubic alloy Al60Pd25Mn15 reveal two noteworthy features. The first is that the Pd 3dlines fall at binding energies which are 2.2 eV higher than in pure Pd. A similar shift is observed for Pd in other alloys. The second noteworthy feature is that the Mn 2p3/2 line is very sharp in the quasicrystal. Fitting the experimental peaks with a Doniach-Sunjic line shpae suggests that the position and density of Mn states near EFis very ...


Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo Mar 1990

Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo

Chemistry Publications

We present a different mechanism to explain the occurrence of long-lived oscillations in diffraction spot intensities during epitaxial growth of metal films on fcc (100) substrates at low temperature. Rather than rely on the common picture of cyclical nucleation and growth to produce the oscillations, the model invokes ‘‘downward funneling’’ deposition dynamics to fourfold-hollow adsorption sites.


The Mathematical Structure Of Arrangement Channel Quantum Mechanics, James W. Evans Aug 1981

The Mathematical Structure Of Arrangement Channel Quantum Mechanics, James W. Evans

Chemistry Publications

A non-Hermitian matrix Hamiltonian H appears in the wavefunction form of a variety of many-body scattering theories. This operator acts on an arrangement channel Banach or Hilbert space 1(;' = Ell ncr where ,r is the N-particle Hilbert space and a are certain arrangement channels. Various aspects of the spectral and semigroup theory for H are considered. The normalizable and weak (wavelike) eigenvectors ofH are naturally characterized as either physical or spurious. Typically H is scalar spectral and "equivalent" to H on an H-invariant subspace of physical solutions. If the eigenvectors form a basis, by constructing a suitable biorthogonal system, we ...