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Full-Text Articles in Physics

Identification Of The Possible Defect States In Poly(3-Hexylthiophene) Thin Films, D.-Q. Feng, A. N. Caruso, Yaroslav B. Losovyj, D. L. Schulz, Peter A. Dowben Dec 2007

Identification Of The Possible Defect States In Poly(3-Hexylthiophene) Thin Films, D.-Q. Feng, A. N. Caruso, Yaroslav B. Losovyj, D. L. Schulz, Peter A. Dowben

Peter Dowben Publications

The possible origins of a low density of defect states within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap are suggested for regioregular poly(3- hexylthiophene). A number of chemical defects, impurities, and structural defects could contribute to features in photoemission for regioregular poly(3-hexylthiophene), observed within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap of regioregular poly(3-hexylthiophene).


Optimization Of The 3 M Tgm Beamline, At Camd, For Constant Initial State Spectroscopy, Yaroslav B. Losovyj, Ihor Ketsman, Eizi Morikawa, Zhenjun Wang, Jinke Tang, Peter A. Dowben Nov 2007

Optimization Of The 3 M Tgm Beamline, At Camd, For Constant Initial State Spectroscopy, Yaroslav B. Losovyj, Ihor Ketsman, Eizi Morikawa, Zhenjun Wang, Jinke Tang, Peter A. Dowben

Peter Dowben Publications

The 3 m toroidal grating monochromator (TGM) VUV beamline at CAMD/LSU was realigned to achieve better illumination of the monochromator gratings with the goal of substantially increasing the flux at the higher photon energies. This is partly accomplished through a tilting of the monochromator (by about of 13.5°), with respect to the plane defined by the synchrotron, providing a smaller grazing angle at the initial mirrors. The improved performance of the beamline permits resonant photoemission studies at Gd 4d core threshold without resorting to second order light, which we demonstrate for Gd doped HfO2.


High-Resolution Photoemission Study Of Organic Systems At The Camd 3 M Nim Beamline, Yaroslav B. Losovyj, Kevin Morris, Luis G. Rosa, John D. Scott, Peter A. Dowben Nov 2007

High-Resolution Photoemission Study Of Organic Systems At The Camd 3 M Nim Beamline, Yaroslav B. Losovyj, Kevin Morris, Luis G. Rosa, John D. Scott, Peter A. Dowben

Peter Dowben Publications

The 3 m normal incidence monochromator (NIM) VUV beamline at CAMD was designed for novel high-resolution photoemission experiments. Both solid-state samples and gas phase resolution tests demonstrate that high-resolution photoemission is possible below 10 meV, and vibronic fine structure in the photoemission final state from the crystalline copolymer poly-vinylidene fluoride with trifluoroethylene can be observed: the first direct experimental identification of symmetry dependence in electron–phonon coupling in photoemission from a solid-state system.


Half Metallic Ferromagnets, Peter A. Dowben Nov 2007

Half Metallic Ferromagnets, Peter A. Dowben

Peter Dowben Publications

Since its introduction by de Groot and colleagues in the early 1980s [1], the concept of half metallic ferromagnetism has attracted great interest. Idealized, half-metals have only one spin channel for conduction: the spin-polarized band structure exhibits metallic behavior for one spin channel, while the other spin band structure exhibits a gap at the Fermi level. Due to the gap for one spin direction, the density of states at the Fermi level has, theoretically, 100 % spin polarization. This gap in the density of states in one spin at the Fermi level, for example ↓ so N↓(EF) = 0, also causes ...


The Electronic Structure Change With Gd Doping Of Hfo2 On Silicon, Yaroslav B. Losovyj, Ihor Ketsman, Andrei Sokolov, Kirill D. Belashchenko, Peter A. Dowben, Jinke Tang, Zhenjun Wang Sep 2007

The Electronic Structure Change With Gd Doping Of Hfo2 On Silicon, Yaroslav B. Losovyj, Ihor Ketsman, Andrei Sokolov, Kirill D. Belashchenko, Peter A. Dowben, Jinke Tang, Zhenjun Wang

Peter Dowben Publications

Gd-doped HfO2 films deposited on silicon substrates undergo a crystallographic change from monoclinic to fluorite (cubic) phase with increasing Gd concentrations. The crystallographic phase change is accompanied by a small increase in the valence bandwidth and in the apparent band offset in the surface region. Electrical measurements show pronounced rectification properties for lightly doped Gd:HfO2 films on p-Si and for heavily-doped Gd:HfO2 films on n-Si, suggesting a crossover from n-type to p -type behavior with increasing doping level.


Electronic, Magnetic And Transport Properties Of Rare-Earth Monopnictides, Chun-Gang Duan, Ildar F. Sabiryanov, Wai-Ning Mei, Peter A. Dowben, Sitaram Jaswal, Evgeny Y. Tsymbal Jul 2007

Electronic, Magnetic And Transport Properties Of Rare-Earth Monopnictides, Chun-Gang Duan, Ildar F. Sabiryanov, Wai-Ning Mei, Peter A. Dowben, Sitaram Jaswal, Evgeny Y. Tsymbal

Peter Dowben Publications

The electronic structures and magnetic properties of many rare-earth monopnictides are reviewed in this article. Possible candidate materials for spintronics devices from the rare-earth monopnictide family, i.e. high polarization (nominally half-metallic) ferromagnets and antiferromagnets, are identified. We attempt to provide a unified picture of the electronic properties of these strongly correlated systems. The relative merits of several ab initio theoretical methods, useful in the study of the rare-earth monopnictides, are discussed. We present our current understanding of the possible half-metallicity, semiconductor–metal transitions, and magnetic orderings in the rare-earth monopnictides. Finally, we propose some potential strategies to improve the ...


Epitaxial Growth And Surface Properties Of Half-Metal Nimnsb Films, C. N. Borca, D. Ristoiu, H.-K. Jeong, Takashi Komesu, A. N. Caruso, J. Pierre, L. Ranno, J. P. Nozieres, Peter A. Dowben Jul 2007

Epitaxial Growth And Surface Properties Of Half-Metal Nimnsb Films, C. N. Borca, D. Ristoiu, H.-K. Jeong, Takashi Komesu, A. N. Caruso, J. Pierre, L. Ranno, J. P. Nozieres, Peter A. Dowben

Peter Dowben Publications

We present, herein, an extended study of the half-Heusler alloy NiMnSb, starting with the deposition technique, continuing with the basic structural and magnetic properties of the thin films, and finishing with the electronic and compositional properties of their surfaces. The experimental methods we apply combine magnetization and magnetoresistivity measurements, atomic force microscopy, ferromagnetic resonance, x-ray and neutron diffraction, low energy electron diffraction, angle resolved x-ray photoemission, extended x-ray absorption fine structure spectroscopy, soft x-ray magnetic circular dichroism and spin polarized inverse photoemission spectroscopy. We find that stoichiometric surfaces exhibit close to 100% spin polarization at the centre of the surface ...


Epitaxial Growth And Surface Properties Of Half-Metal Nimnsb Films, C. N. Borca, D. Ristoiu, Takashi Komesu, A. N. Caruso, J. Pierre, L. Ranno, J. P. Nozieres, Peter A. Dowben Jul 2007

Epitaxial Growth And Surface Properties Of Half-Metal Nimnsb Films, C. N. Borca, D. Ristoiu, Takashi Komesu, A. N. Caruso, J. Pierre, L. Ranno, J. P. Nozieres, Peter A. Dowben

Peter Dowben Publications

We present, herein, an extended study of the half-Heusler alloy NiMnSb, starting with the deposition technique, continuing with the basic structural and magnetic properties of the thin films, and finishing with the electronic and compositional properties of their surfaces. The experimental methods we apply combine magnetization and magnetoresistivity measurements, atomic force microscopy, ferromagnetic resonance, x-ray and neutron diffraction, low energy electron diffraction, angle resolved x-ray photoemission, extended x-ray absorption fine structure spectroscopy, soft x-ray magnetic circular dichroism and spin polarized inverse photoemission spectroscopy. We find that stoichiometric surfaces exhibit close to 100% spin polarization at the centre of the surface ...


Changing Band Offsets In Copper Phthalocyanine To Copolymer Poly(Vinylidene Fluoride With Trifluoroethylene) Heterojunctions, Jie Xiao, Andrei Sokolov, Peter A. Dowben Jun 2007

Changing Band Offsets In Copper Phthalocyanine To Copolymer Poly(Vinylidene Fluoride With Trifluoroethylene) Heterojunctions, Jie Xiao, Andrei Sokolov, Peter A. Dowben

Peter Dowben Publications

The authors have fabricated a thin film copper phthalocyanine to crystalline ferroelectric copolymer poly(vinylidene fluoride with trifluoroethylene) heterojunction diode. The formation of a diode is expected from the band offsets between the two thin film molecular systems, as ascertained from combined photoemission and inverse photoemission studies. From the temperature and field dependence of the heterojunction, dipole interactions are implicated at the interface between copper phthalocyanine and poly(vinylidene fluoride with trifluoroethylene) and affect the band offsets and resultant diode properties.


The N-Type Gd-Doped Hfo2 To Silicon Heterojunction Diode, Ihor Ketsman, Yaroslav B. Losovyj, Andrei Sokolov, J. Tang, Z. Wang, Kirill D. Belashchenko, Peter A. Dowben Jun 2007

The N-Type Gd-Doped Hfo2 To Silicon Heterojunction Diode, Ihor Ketsman, Yaroslav B. Losovyj, Andrei Sokolov, J. Tang, Z. Wang, Kirill D. Belashchenko, Peter A. Dowben

Peter Dowben Publications

Gd-doped HfO2 films were deposited on p-type silicon substrates in a reducing atmosphere. Photoemission measurements indicate the n-type character of Gd-doped HfO2 due to overcompensation with oxygen vacancies. The Gd 4 f photoexcitation peak at 5.5 eV below the valence band maximum is identified using both resonant photoemission and first-principles calculations of the f hole. The rectifying (diode- like) properties of Gd-doped HfO2 to silicon heterojunctions are demonstrated.


Corrigendum, Re: The Structure Of The Cos2 (100)-(1×1) Surface, Z. X. Yu, M. A. Van Hove, S. Y. Tong, David Wisbey, Yaroslav B. Losovyj, Ning Wu, M. Manno, L. Wang, C. Leighton, Wai-Ning Mei, Peter A. Dowben May 2007

Corrigendum, Re: The Structure Of The Cos2 (100)-(1×1) Surface, Z. X. Yu, M. A. Van Hove, S. Y. Tong, David Wisbey, Yaroslav B. Losovyj, Ning Wu, M. Manno, L. Wang, C. Leighton, Wai-Ning Mei, Peter A. Dowben

Peter Dowben Publications

Different surface terminations have been previously discussed in reference [12] of J. Phys.: Condens. Matter 19 156223 (i.e., Ying Jiu Jin and Jae Il Lee 2006 Phys. Rev. B 73 064405) and we inadvertently failed to properly cite this reference in the attribution of figure 3 of our paper.


Energetics Of The Dipole Flip-Flop Motion In A Ferroelectric Polymer Chain, Lei Cai, Xuewen Wang, Yesim Darici, Jiandi Zhang, Peter A. Dowben Mar 2007

Energetics Of The Dipole Flip-Flop Motion In A Ferroelectric Polymer Chain, Lei Cai, Xuewen Wang, Yesim Darici, Jiandi Zhang, Peter A. Dowben

Peter Dowben Publications

The authors report on a study of dipole flip-flop “local” transition in ferroelectric polyvinylidene fluoride [P(VDF)] chains, using total energy calculation based on the density functional theory. The calculated results indicate that a simple flipping of a single electric dipole moment is energetically allowed. Furthermore, such a flipping involves no change either in bond length, bond angle, or the orientation of the chain. The calculations also show that on a thin film of ordered chains, strong dipole interactions existing in P(VDF) could cause modulation of the dipole orientation thus forming superlattices on P(VDF) films. These results are ...


The Electronic Band Structure Of Cos2, Ning Wu, Yaroslav B. Losovyj, David Wisbey, Kirill D. Belashchenko, M. Manno, L. Wang, C. Leighton, Peter A. Dowben Mar 2007

The Electronic Band Structure Of Cos2, Ning Wu, Yaroslav B. Losovyj, David Wisbey, Kirill D. Belashchenko, M. Manno, L. Wang, C. Leighton, Peter A. Dowben

Peter Dowben Publications

Angle-resolved and energy-dependent photoemission was used to study the band structure of paramagnetic CoS2 from high-quality single-crystal samples. A strongly dispersing hybridized Co–S band is identified along the Γ–X line. Fermi level crossings are also analyzed along this line, and the results are interpreted using band structure calculations. The Fermi level crossings are very sensitive to the separation in the S–S dimer, and it is suggested that the half-metallic gap in CoS2 may be controlled by the bonding– antibonding splitting in this dimer, rather than by exchange splitting on the Co atoms.


The Structure Of The Cos2 (100)-(1 × 1) Surface, Z. X. Yu, M. A. Van Hove, S. Y. Tong, David Wisbey, Yaroslav B. Losovyj, Ning Wu, M. Manno, L. Wang, C. Leighton, Wai-Ning Mei, Peter A. Dowben Mar 2007

The Structure Of The Cos2 (100)-(1 × 1) Surface, Z. X. Yu, M. A. Van Hove, S. Y. Tong, David Wisbey, Yaroslav B. Losovyj, Ning Wu, M. Manno, L. Wang, C. Leighton, Wai-Ning Mei, Peter A. Dowben

Peter Dowben Publications

Quantitative low-energy electron diffraction (LEED) has been used to determine the structure of the cubic CoS2 (100)-(1 × 1) surface. The clearly favored structural model from the LEED analysis is the 1S-terminated (1 × 1) surface, in which the S–S dimer is intact and the terminal surface layer retains a complete S–Co–S sandwich structure. The surface S atoms move outwards towards the vacuum while the subsurface Co atoms move towards the bulk, by approximately 0.03 and 0.11 Å, respectively. In addition, the S atoms in the third sublayer relax outwards by about 0.12 Å ...


Polyvinylidene Fluoride–Trifluoroethylene As A Reservoir For Absorbed Water, P.A. Jacobson, Luis G. Rosa, Kristin Kraemer, Stephen Ducharme, Peter A. Dowben Feb 2007

Polyvinylidene Fluoride–Trifluoroethylene As A Reservoir For Absorbed Water, P.A. Jacobson, Luis G. Rosa, Kristin Kraemer, Stephen Ducharme, Peter A. Dowben

Peter Dowben Publications

The absorption of water in Langmuir–Blodgett films of ferroelectric copolymers of polyvinylidene fluoride with trifluoroethylene is shown to depend upon the film thickness. This water absorption can have a profound effect on the dielectric properties of the copolymer films.


Correlation Effects And Electronic Structure Of Gd@C60, Renat F. Sabirianov, Wai-Ning Mei, Jing Lu, Yi Gao, Xiao Cheng Zeng, R. D. Bolskar, P. Jeppson, Ning Wu, A. N. Caruso, Peter A. Dowben Feb 2007

Correlation Effects And Electronic Structure Of Gd@C60, Renat F. Sabirianov, Wai-Ning Mei, Jing Lu, Yi Gao, Xiao Cheng Zeng, R. D. Bolskar, P. Jeppson, Ning Wu, A. N. Caruso, Peter A. Dowben

Peter Dowben Publications

We have investigated the electronic structure of Gd@C60 using ab initio calculations, photoemission and resonant photoemission (constant initial state spectroscopy). In comparing our calculations based on the local spin density approximation and the Hubbard model description with the observed photoemission spectra, we conclude that Gd 4f states exhibit enhanced correlation energies. These correlation energies have values larger than those normally observed in metallic gadolinium and gadolinium compounds. We attributed the enhanced correlation to the diminished screening of the encapsulated Gd. Both calculation and experiment confirm a strong hybridization between the valence states of Gd and the C 2p ...


Electronic Structure Of A Metal-Organic Copper Spin-½ Molecule: Bis(4-Cyano-2,2,6,6-Tetramethyl-3,5-Heptanedionato)Copper(Ii), David Wisbey, Danqin Feng, Marshall T. Bremer, Camelia N. Borca, Anthony N. Caruso, Carter M. Silvernail, John Belot, Elio Vescovo, Laurent Ranno, Peter A. Dowben Jan 2007

Electronic Structure Of A Metal-Organic Copper Spin-½ Molecule: Bis(4-Cyano-2,2,6,6-Tetramethyl-3,5-Heptanedionato)Copper(Ii), David Wisbey, Danqin Feng, Marshall T. Bremer, Camelia N. Borca, Anthony N. Caruso, Carter M. Silvernail, John Belot, Elio Vescovo, Laurent Ranno, Peter A. Dowben

Peter Dowben Publications

The metal-organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (Cu- (CNdpm)2) (C24H36N2O4Cu, Cu(II)) is a copper spin-1/2 system with a magnetic moment of 1.05 ± 0.04 μB/molecule, slightly smaller than the 1.215±0.02 μB/molecule for the larger size copper spin-½ system C36H48N4O4Cu∙C4H8O (bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) 4,4’-bipyridylethene- THF). There is generally good agreement between photoemission from vapor-deposited thin films of the ...