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Full-Text Articles in Physical Sciences and Mathematics
Strain And Strain Relief In Gd(0001) Films On Mo(112), Takashi Komesu, C. Waldfried, Peter A. Dowben
Strain And Strain Relief In Gd(0001) Films On Mo(112), Takashi Komesu, C. Waldfried, Peter A. Dowben
Peter Dowben Publications
The electronic structure of strained and unstrained Gd(0001) has been studied with spin-polarized photoemission spectroscopy and spin-polarized inverse photoemission spectroscopy. In this work, we observed that relaxation of the expansively strained in-plane crystal lattice constant, of Gd(0001) on Mo(112), significantly diminishes the differences in the electronic structure from that observed for Gd(0001) grown on W(110). The defects that are incorporated in the Gd films, with increasing film thickness, lead to an in-plane lattice relaxation. Such thickness dependent strain relief results a loss of net polarization for Gd(0001) grown on Mo(112) compared to the relatively unstrained Gd(0001) films grown on W(110).
Surface Electronic Phase Transition In Colossal Magnetoresistive Manganese Perovskites: La0.65Sr0.35Mno3, Hani Dulli, E. Ward Plummer, Peter A. Dowben, Jaewu Choi, Sy_Hwang Liou
Surface Electronic Phase Transition In Colossal Magnetoresistive Manganese Perovskites: La0.65Sr0.35Mno3, Hani Dulli, E. Ward Plummer, Peter A. Dowben, Jaewu Choi, Sy_Hwang Liou
Peter Dowben Publications
We have observed a distinct surface phase transition for an important class of giant magnetoresistance materials [La1-x Srx MnO3 (x = 0.35)]. The surface phase transition occurs at 240 K compared to 370 K for the bulk and is fundamentally different. In the bulk, a ferromagnetic metal to paramagnetic bad-metal transition occurs, while the lower-temperature surface transition is from an insulator to a semimetal. The surface of this manganese perovskite is electronically and compositionally quite different from the bulk with important implications for the behavior of artificially grown layered transition-metal oxides and for the use of surface …
Effective Surface Debye Temperature For Nimnsb.100. Epitaxial Films, C.N. Borca, Takashi Komesu, Hae-Kyung Jeong, Peter A. Dowben, D. Ristoiu, Ch. Hordequin, J. Pierre, J. P. Nozie`Res
Effective Surface Debye Temperature For Nimnsb.100. Epitaxial Films, C.N. Borca, Takashi Komesu, Hae-Kyung Jeong, Peter A. Dowben, D. Ristoiu, Ch. Hordequin, J. Pierre, J. P. Nozie`Res
Peter Dowben Publications
The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145613 K. This is far smaller than the bulk Debye temperature of 31265 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface. © 2000 American Institute of Physics. [S0003-6951(00)05127-5]
Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben
Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben
Peter Dowben Publications
We present evidence for a change in electron – phonon coupling across a bulk ph=e transition. Below the lattice stiffening transition at around 160 K, there is a change in the diffracted peak width observed by neutron and X-ray scattering techniques. Also, the electronic band structure of the copolymer is shifting in binding energy below 160 K, decreasing the density of states near the Fermi level. The value of the effective Debye temperature above the transition temperature is approximately 50 K, while below 160 K, the value of the Debye parameter is 245 K. We postulate that the coupling between …
Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben
Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben
Peter Dowben Publications
We present evidence for a change in electron - phonon coupling across a bulk phase transition. Below the lattice stiffening transition at around 160 K, there is a change in the diffracted peak width observed by neutron and X-ray scattering techniques. Also, the electronic band structure of the copolymer is shifting in binding energy below 160 K, decreasing the density of states near the Fermi level. The value of the effective Debye temperature above the transition temperature is approximately 50 K, while below 160 K, the value of the Debye parameter is 245 K. We postulate that the coupling between …
Rare-Earth Boride Thin Film System, Peter A. Dowben, Zenchen Zhong, David J. Sellmyer
Rare-Earth Boride Thin Film System, Peter A. Dowben, Zenchen Zhong, David J. Sellmyer
Peter Dowben Publications
Disclosed is a system made by a method for depositing rare-earth boride onto the surface of a substrate which is submerged in an organic solution of borane and a rare-earth halide. Application of electromagnetic radiation, preferably in the visible wavelength range, through a mask near the surface of the submerged substrate, drives the formation and deposition of rare-earth boride onto a substrate in desired patterns.
Esr Investigations On Ca Perovskite, M. Chipara, Sy-Hwang Liou, C.N. Borca, R. Shoemaker, Shireen Adenwalla, Peter A. Dowben
Esr Investigations On Ca Perovskite, M. Chipara, Sy-Hwang Liou, C.N. Borca, R. Shoemaker, Shireen Adenwalla, Peter A. Dowben
Peter Dowben Publications
Electron spin resonance studies on fine powders of La0.65Ca0.35MnO3, performed in the X band, are reported. The coexistence of paramagnetic and ferromagnetic phases, in a narrow temperature range close to the Curie temperature, is observed. The electron spin resonance measurements do not support the presence of bipolarons above the Curie temperature. Temperature dependence of the ESR linewidth is governed by the hopping of polarons and the corresponding activation energy is about 150 meV above Tc.
Magnetic Spectroscopy And Characterization Of La0.65Pb0.35Mno3, M. I. Chipara, Shireen Adenwalla, Peter A. Dowben, Qin Lan Xu, Sy_Hwang Liou, R. Shoemaker
Magnetic Spectroscopy And Characterization Of La0.65Pb0.35Mno3, M. I. Chipara, Shireen Adenwalla, Peter A. Dowben, Qin Lan Xu, Sy_Hwang Liou, R. Shoemaker
Peter Dowben Publications
Crystalline films of La0.65Pb0.35MnO3 grown on Si (100) substrates by rf sputtering have been investigated by ferromagnetic resonance and MOKE. The dependence of the ferromagnetic resonance line parameters on the sample orientation and temperature is investigated. An expression for the angular dependence of the resonance field on the orientation of the sample is proposed, based on the assumption that close to the Curie temperature the Zeeman and demagnetizing terms are dominant. MOKE data support this hypothesis. The temperature dependence of the magnetization at saturation, in relative units, estimated from ferromagnetic resonance agrees with SQUID data. …
Origin Of The Magnetic Moments In La0.65Pb0.35Mno3 Epitaxial Thin Films, C.N. Borca, R.H. Cheng, Q.L. Xu, Sy_Hwang Liou, Shane Stadler, Y.U. Idzerda, Peter A. Dowben
Origin Of The Magnetic Moments In La0.65Pb0.35Mno3 Epitaxial Thin Films, C.N. Borca, R.H. Cheng, Q.L. Xu, Sy_Hwang Liou, Shane Stadler, Y.U. Idzerda, Peter A. Dowben
Peter Dowben Publications
Crystalline films of La0.65Pb0.35MnO3 grown on (100) LaAlO 3 substrates by rf sputtering have been investigated using magnetic circular dichroism and inverse photoemission spectroscopy. We find evidence for strong hybridization between unoccupied levels associated with Mn 3d and O 2p states. The oxygen atoms "pick-up" a small magnetic moment through hybridization with Mn. ©2000 American Institute of Physics
The Surface Terminal Layer And Composition Of The Colossal Magnetoresistance Perovskite: La0.65Pb0.35Mno3, C.N. Borca, Delia Ristoiu, Q.L. Xu, Sy_Hwang Liou, Shireen Adenwalla, Peter A. Dowben
The Surface Terminal Layer And Composition Of The Colossal Magnetoresistance Perovskite: La0.65Pb0.35Mno3, C.N. Borca, Delia Ristoiu, Q.L. Xu, Sy_Hwang Liou, Shireen Adenwalla, Peter A. Dowben
Peter Dowben Publications
The composition in the surface region of the colossal magnetoresistance perovskite manganite materials, La0.65Pb0.35MnO3 has been studied using angle resolved x-ray photoemission spectroscopy. The results are consistent with a Mn–O terminal layer and Pb segregation to the near-surface region. This is similar to the behavior exhibited by La0.65Pb0.35MnO3 and La0.65Pb0.35MnO3. The O–Mn–O terminal layer appears to be close to the Mn3+ valence state. ©2000 American Institute of Physics.
The Influence Of Both Coordination Number And Lattice Constant On The Nonmetal To Metal Transition, I.N. Yakovkin, Peter A. Dowben
The Influence Of Both Coordination Number And Lattice Constant On The Nonmetal To Metal Transition, I.N. Yakovkin, Peter A. Dowben
Peter Dowben Publications
We show that both coordination and lattice constant can have an important influence on the nonmetal to metal transition and the two parameters are not easily separated. Using example theoretical calculations for barium, we provide a compelling case that atomic coordination is a critical factor in determining the critical lattice constant for the nonmetal to metal transition. A comparison between the nonmetal to metal transition three-dimensional and two-dimensional systems is not possible on the basis of the atomic coordination alone. This is discussed in the context of a comparison of the available experimental data for both elemental expanded fluids (three-dimensional) …
Selective Area Chemical Vapor Deposition Of Chromium Oxides, Ruihua Cheng, C.N. Borca, Peter A. Dowben
Selective Area Chemical Vapor Deposition Of Chromium Oxides, Ruihua Cheng, C.N. Borca, Peter A. Dowben
Peter Dowben Publications
We demonstrate that two-phase CrO2 and Cr2O3 thin films can be grown by using selective organometallic chemical vapor deposition through the oxidation of Cr(CO) 6 in an oxygen environment. While the magnetization measurements show that both chromium oxides are present, the relative weight of each phase depends on the oxygen partial pressure. Changes of the Curie temperature, Tc, and the saturation magnetization field may be possible by controlling the stoichiometry.
Manganese Surface Segregation In Nimnsb, Delia Ristoiu, J. P. Nozie`Res, C.N. Borca, B. Borca, Peter A. Dowben
Manganese Surface Segregation In Nimnsb, Delia Ristoiu, J. P. Nozie`Res, C.N. Borca, B. Borca, Peter A. Dowben
Peter Dowben Publications
A quantitative analysis of the surface composition of the Heusler alloy NiMnSb has been undertaken using angle-resolved x-ray photoemission spectroscopy and the surface composition characterized. With sufficient annealing cycles, the stoichiometric surface evolves to a surface that is manganese rich. This indicates that the surface enthalpy is different from the bulk for the Heusler alloy NiMnSb. ©2000 American Institute of Physics.
The Interplay Between The Surface Band Structure And Possible Surface Reconstructions Of Mo(112), T. Mcavoy, Jun Zhang, C. Waldfried, D.N. Mcilroy, Peter A. Dowben, O. Zeybek, T. Bertrams, S.D. Barrett
The Interplay Between The Surface Band Structure And Possible Surface Reconstructions Of Mo(112), T. Mcavoy, Jun Zhang, C. Waldfried, D.N. Mcilroy, Peter A. Dowben, O. Zeybek, T. Bertrams, S.D. Barrett
Peter Dowben Publications
The experimental band structure of Mo(112) and the effects by temperature and adsorbate are presented. A surface resonance, identified as crossing the Fermi level at about 1/3 from Γ̅ to Χ̅ of surface Brillouin zone, was observed to be very sensitive to both contamination and temperature. We find evidence of adsorbate and temperature induced reconstruction of the Mo(112) surface. Examination of low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) data provides evidence for an adsorbate induced reconstruction of the Mo(112) surface with periodicities consistent with the Fermi level crossingThe experimental band structure of Mo(112) and the effects by temperature …
Phase Transition In The Surface Structure In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), Jaewu Choi, C.N. Borca, Peter A. Dowben, A. Bune, Matt Poulsen, Shane Pebley, Shireen Adenwalla, Stephen Ducharme, Lee Robertson, V.M. Fridkin, N.N. Petukhova, S.G. Yudin
Phase Transition In The Surface Structure In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), Jaewu Choi, C.N. Borca, Peter A. Dowben, A. Bune, Matt Poulsen, Shane Pebley, Shireen Adenwalla, Stephen Ducharme, Lee Robertson, V.M. Fridkin, N.N. Petukhova, S.G. Yudin
Peter Dowben Publications
Surface structures and a surface structure phase transition are identified that are distinct from the known bulk ferroelectric-paraelectric phase transition of crystalline copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%). The temperature-dependent changes in the surface structure are accompanied by the physical rotation of the polar group (CH2-CF2). These changes in the surface structure are compared to the bulk phase transition. We show that the bulk structural transition, while distinct from the surface, is qualitatively similar in both thick and thin Langmuir-Blodgett-grown films.
Method For Depositing Rare-Earth Boride Onto A Substrate, Peter A. Dowben, Zhenchen Zhong, David J. Sellmyer
Method For Depositing Rare-Earth Boride Onto A Substrate, Peter A. Dowben, Zhenchen Zhong, David J. Sellmyer
Peter Dowben Publications
Disclosed is a method for depositing rare-earth boride onto the surface of a substrate which is submerged in an organic solution of borane and a rare-earth halide. Application of electromagnetic radiation, preferably in the visible wavelength range, near the surface of the submerged substrate drives the formation and deposition of rare-earth boride onto a substrate.
Boron-Carbide And Boron Rich Rhobohedral Based Transistors And Tunnel Diodes, Peter A. Dowben
Boron-Carbide And Boron Rich Rhobohedral Based Transistors And Tunnel Diodes, Peter A. Dowben
Peter Dowben Publications
The present invention relates to the fabrication of a boron carbideboron diode on an aluminum substrate, and a boron carbideboron junction field effect transistor. Our results suggest that with respect to the approximately 2 eV band gap pure boron material, 0.9 eV band gap boron carbide (B5C) acts as a p-type material. Both boron and boron carbide (B5C) thin films were fabricated from single source borane cage molecules using plasma enhanced chemical vapor deposition (PECVD). Epitaxial growth does not appear to be a requirement. We have doped boron carbide grown by plasma enhanced chemical vapor deposition. …
Thin Crystalline Functional Group Copolymer Poly(Vinylidene Fluoride–Trifluoroethylene) Film Patterning Using Synchrotron Radiation, Jaewu Choi, H.M. Manohara, Eizi Morikawa, P.T. Sprunger, Peter A. Dowben, S.P. Palto
Thin Crystalline Functional Group Copolymer Poly(Vinylidene Fluoride–Trifluoroethylene) Film Patterning Using Synchrotron Radiation, Jaewu Choi, H.M. Manohara, Eizi Morikawa, P.T. Sprunger, Peter A. Dowben, S.P. Palto
Peter Dowben Publications
The photodegradation mechanism due to synchrotron radiation exposure of crystalline poly[vinylidene fluoride–trifluoroetylene, P(VDF–TrFE)] copolymer thin films has been studied with ultraviolet photoemission spectroscopy (UPS) and mass spectroscopy. Upon increasing exposure to x-ray white light (h ν≤1000 eV), UPS measurements reveal that substantial chemical modifications occur in P(VDF–TrFE) 5 monolayer films, including the emergence of new valence band features near the Fermi level, indicating a semimetallic photodegradeted product. The photodetached fragments of the copolymer consist mainly of H2, HF, CHF, CH2. This x-ray exposure study demonstrates that P(VDF–TrFE) films, possessing unique technologically important properties, can be directly …
The Polarization Of Sb Overlayers On Nimnsb(100), Takashi Komesu, C.N. Borca, Hae-Kyung Jeong, Peter A. Dowben, Delia Ristoiu, J.P. Nozieres, Shane Stadler, Y.U. Idzerda
The Polarization Of Sb Overlayers On Nimnsb(100), Takashi Komesu, C.N. Borca, Hae-Kyung Jeong, Peter A. Dowben, Delia Ristoiu, J.P. Nozieres, Shane Stadler, Y.U. Idzerda
Peter Dowben Publications
We have investigated the induced polarization of paramagnetic Sb overlayers on the Heusler alloy NiMnSb. From combined X-ray absorption spectroscopy (XAS) and spin-polarized inverse photoemission spectroscopy (SPIPES), we can assign some of the unoccupied states of the Heusler alloy NiMnSb. With increasing thickness of the Sb overlayer, there is a decline in the density of states near the Fermi energy, as expected for a semimetal overlayer on a metallic substrate. While the Sb is polarized by the ferromagnetic NiMnSb substrate, consistent with the expectations of mean field theory, the polarization at the center of the surface/overlayer Brillouin zone cannot be …