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Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben
Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben
Peter Dowben Publications
Using spin-polarized inverse photoemission and X-ray absorption spectroscopy techniques, we show that the electronic structure of La0.65Pb0.35MnO3 thin films depends on the composition at the surface. With a gentle annealing procedure, the surface provides a maximum of 80% spin asymmetry at 0.5 eV above the Fermi level in spite of extensive Pb segregation. A heavily annealed (restructured) surface exhibits a reduced surface "ordering" temperature of 240 K (compared to the approximately 335 K bulk value) as well as a reduced spin asymmetry value of 40% at 0.5 eV above Fermi energy.
Heterojunction Diode Fabrication From Polyaniline And A Ferroelectric Polymer, B Xu, Y. Ovchenkov, Mengjun Bai, A. N. Caruso, A.V. Sorokin, Stephen Ducharme, Bermard Doudin, Peter A. Dowben
Heterojunction Diode Fabrication From Polyaniline And A Ferroelectric Polymer, B Xu, Y. Ovchenkov, Mengjun Bai, A. N. Caruso, A.V. Sorokin, Stephen Ducharme, Bermard Doudin, Peter A. Dowben
Peter Dowben Publications
We have fabricated a p – n heterojunction diode by vapor depositing a thin film of polyaniline on top of the crystalline copolymer: poly(vinylidene fluoride with trifluoroethylene). The formation of a diode is expected from the band offsets of the two polymers near the Fermi level. The interface between the two components was investigated, and an abrupt interface was found that is very different from the inorganic analog.
Oxidation Of Metals At The Chromium Oxide Interface, Ruihua Cheng, C.N. Borca, N. Pilet, Bo Xu, Lu Yuan, Bernard Doudin, Sy_Hwang Liou, Peter A. Dowben
Oxidation Of Metals At The Chromium Oxide Interface, Ruihua Cheng, C.N. Borca, N. Pilet, Bo Xu, Lu Yuan, Bernard Doudin, Sy_Hwang Liou, Peter A. Dowben
Peter Dowben Publications
Metal thin-film deposition, over the Cr2O3 surface of CrO2 thin-film substrates, exhibits a redox reaction at the interface. The transition metal forms an oxide in combination with the reduction of the near-surface chromium oxide to Cr2O3 . The insulating barrier layer Cr2O3 increases with the formation of Pb3 O4 in Pb/Cr2O3 /CrO2 and CoO in Co/Cr2O3 /CrO2 junctions, respectively.
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 carbide/boron semiconductor devices. The 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. The source gas close- 1,2-dicarbadecaborane (orthocarborane) was used to grow the …
Band Structure Of Strained Gd(0001) Films, I. N. Yakovkin, Takashi Komesu, Peter A. Dowben
Band Structure Of Strained Gd(0001) Films, I. N. Yakovkin, Takashi Komesu, Peter A. Dowben
Peter Dowben Publications
The electronic structure of strained and unstrained Gd(0001) surfaces has been studied both theoretically and experimentally with spin-polarized photoemission spectroscopy and spin-polarized inverse photoemission spectroscopy. Good agreement between calculated surface bands and surface-induced features of the spectra provides the basis for a more detailed explanation of the origin of the spin-polarized bands than was previously possible. It has been found that observed relaxation of the expansively strained in-plane crystal lattice constant, of Gd(0001) on Mo(112), significantly affects the electronic structure of the surface.
Band Filling And Depletion Through The Doping Of Polyaniline Thin Films, B. Xu, Jaewu Choi, A. N. Caruso, Peter A. Dowben
Band Filling And Depletion Through The Doping Of Polyaniline Thin Films, B. Xu, Jaewu Choi, A. N. Caruso, Peter A. Dowben
Peter Dowben Publications
The position of the molecular orbitals of polyaniline, relative to the Fermi level, shifts with the doping of polyaniline by both charge donor and charge acceptor species. Sodium as an electron donor, when added to the polyaniline system, results in an increase in electron population in the polyaniline bands but a decrease in density of states near EF . This is evident from the consistent shifts toward the greater binding energy of the occupied as well as unoccupied molecular orbitals, the valence bands and conduction band edges and characteristic core levels. In the case of iodine doping, an electron …
Spin Blockade Effects In Chromium Oxide Intergrain Magnetoresistance, Andrei Sokolov, C.S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin
Spin Blockade Effects In Chromium Oxide Intergrain Magnetoresistance, Andrei Sokolov, C.S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin
Peter Dowben Publications
CrO2 thin films with crystallites of a significant size permit investigation of the thin intergrain conduction between a limited numbers of crystals. Phoemission techniques reveal that the CrO2 films are covered by a 1–2-nm-thick Cr2O3 insulating barrier. The electronic band gap of the surface electrons is 3.4 eV at low temperatures, decreases sharply down to 2.8 eV at ambient. Electric transport though a few junctions in series shows a remarkable zero-bias anomaly, interpreted in terms of blockade effects. We show that the magnetoresistance is governed by low-bias blockade in these junctions. © 2002 American Institute …
The Finite-Temperature Densities Of States For Half-Metallic Ferromagnets, Ralph Skomski, Peter A. Dowben
The Finite-Temperature Densities Of States For Half-Metallic Ferromagnets, Ralph Skomski, Peter A. Dowben
Peter Dowben Publications
A unitary spinor transformation is used to show that the spin-down density of states (DOS) of half-metallic ferromagnets becomes nonzero at finite temperatures. In a strict sense, this thermally activated spin mixing means that half-metallic ferromagnetism is limited to zero temperature. Similar effects are created by crystal imperfections, interfaces, and surfaces. The calculations, which imply that the finite-temperature resistivity of an individual spin channel is never infinite, are used to discuss recent experimental work on half-metallic oxides and Heusler-type alloys.
A Class Of Boron-Rich Solid-State Neutron Detectors, B. W. Robertson, Shireen Adenwalla, A. Harken, P. Welsch, Jennifer I. Brand, Peter A. Dowben, J.P. Claassen
A Class Of Boron-Rich Solid-State Neutron Detectors, B. W. Robertson, Shireen Adenwalla, A. Harken, P. Welsch, Jennifer I. Brand, Peter A. Dowben, J.P. Claassen
Peter Dowben Publications
Real-time solid-state neutron detectors have been fabricated from semiconducting boron–carbon alloys, deposited by plasma-enhanced chemical vapor deposition. Single neutrons were detected and signals induced by gamma rays were determined to be insignificant. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to fabricate the boron–carbon alloys with only the natural isotopic abundance of 10B. Devices made of thicker boron–carbon alloy layers enriched in 10B could lead to increased detection efficiency and active diodes could use the inherent micron scale spatial resolution, increasing the range of possible applications. © 2002 American Institute of Physics. [DOI: 10.1063/1.1477942]
Preferential Orientation Of Short Chain Vapor Deposited Polyaniline Thin Films On Gold, B. Xu, Jaewu Choi, Peter A. Dowben
Preferential Orientation Of Short Chain Vapor Deposited Polyaniline Thin Films On Gold, B. Xu, Jaewu Choi, Peter A. Dowben
Peter Dowben Publications
Vapor deposited short chain polyaniline thin films were studied using angle-resolved photoemission spectroscopy. Films grown on two different substrates, oxidized Si surfaces and Au, show distinctly different properties. Some indication of preferential molecular orientation was observed for ultrathin films deposited on Au substrates, but not on the Si substrates with the native oxide surface. Clear indication of metallic character was observed for some of the polyaniline ultrathin films, consistent with recent theory suggesting that alignment of chains parallel with a metal substrate enhance metallicity.
Zero-Bias Anomaly In Cro2 Junctions, Andrei Sokolov, C.-S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, H.-K. Jeong, T. Komesu, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin
Zero-Bias Anomaly In Cro2 Junctions, Andrei Sokolov, C.-S. Yang, Lu Yuan, Sy_Hwang Liou, Ruihua Cheng, H.-K. Jeong, T. Komesu, B. Xu, C.N. Borca, Peter A. Dowben, Bernard Doudin
Peter Dowben Publications
CrO2thin films, with crystallites of several microns size, provide the opportunity for the investigation of the intergrain tunneling between a few crystals separated by a 1-2 nm thick Cr2O3 film. A pronounced zero-bias anomaly of the conductance is found at low temperatures. Combined photoemission and inverse photoemission temperature-dependent studies confirm the occurrence of Coulomb blockade. For the strong-tunneling case (R2), the magnetoresistance decreases strongly with bias. For the weak-tunneling case (R>>RQ), the magnetoresistance decreases by a factor two with increasing bias, as predicted by a co-tunneling model.
The Surface Composition And Spin Polarization Of Nimnsb Epitaxial Thin Films, D. Ristoiu, J.P. Nozières , C.N. Borca, T. Komesu, H.-K. Jeong, Peter A. Dowben
The Surface Composition And Spin Polarization Of Nimnsb Epitaxial Thin Films, D. Ristoiu, J.P. Nozières , C.N. Borca, T. Komesu, H.-K. Jeong, Peter A. Dowben
Peter Dowben Publications
The composition in the surface region of the Heusler alloy NiMnSb has been studied using angle-resolved X-ray photoemission spectroscopy, low-energy electron diffraction and spin-polarized inverse photoemission. The results are consistent with a generally Mn-Sb terminal layer, though the surface composition is very sensitive to preparation. The surface composition has a critical influence on the polarization near the Fermi level in spin-polarized inverse photoemission. Under some conditions, the polarization at the Fermi level for normal incidence inverse photoemission can reach values very close to 100% above background.
Neutron Powder Diffraction Studies Of The La0.65Pb0.35Mno3 Perovskite, Camelia Borca, Shireen Adenwalla, Sy-Hwang Liou, Q.L. Xu, J. L. Robertson, Peter A. Dowben
Neutron Powder Diffraction Studies Of The La0.65Pb0.35Mno3 Perovskite, Camelia Borca, Shireen Adenwalla, Sy-Hwang Liou, Q.L. Xu, J. L. Robertson, Peter A. Dowben
Peter Dowben Publications
The structure of La0.65Pb0.35MnO3 has been studied by neutron powder diffraction. From the temperature dependence of the lattice parameters, we observe that La0.65Pb0.35MnO3 remains single phase in the temperature interval from 25 to 400 K, with a rhombohedral (R3c) structure. The collinear Mn spins suffer a thermally driven reorientation transition close to the Curie temperature, as obtained from powder samples (using neutron diffraction) and from thin films [using ferromagnetic resonance (FMR)]. The reorientation transition may indicate the presence of local Jahn–Teller (JT) lattice distortions, which are prevented from …