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2009

University of Nebraska - Lincoln

Peter Dowben Publications

Articles 1 - 16 of 16

Full-Text Articles in Physical Sciences and Mathematics

Isomeric Effects With Di-Iodobenzene (C6H4I2) On Adsorption On Graphite, Keisuke Fukutani, Ning Wu, Peter A. Dowben Oct 2009

Isomeric Effects With Di-Iodobenzene (C6H4I2) On Adsorption On Graphite, Keisuke Fukutani, Ning Wu, Peter A. Dowben

Peter Dowben Publications

Differences are seen in the adsorption of 1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene on graphite, as a function of exposure, using core level photoemission. The isomer 1,3-di-iodobenzene exhibits significant differences from 1,2-di-iodobenzene, and 1,4-di-iodobenzene in apparent sticking coefficients and core level binding energies. 1,3-Di-iodobenzene adsorb on graphite at 110 K in a strongly Stranski–Krastanov or Volmer–Weber (island) growth mode. The implication is that, even for small molecules adsorption, the adsorbate dipole in the plane of surface and the choice of isomer may matter.

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Adsorbate/Absorbate Interactions With Organic Ferroelectric Polymers, Peter A. Dowben, Luis G. Rosa, Carolina C. Ilie, Jie Xiao Aug 2009

Adsorbate/Absorbate Interactions With Organic Ferroelectric Polymers, Peter A. Dowben, Luis G. Rosa, Carolina C. Ilie, Jie Xiao

Peter Dowben Publications

We discuss the interactions of adsorbates with the organic ferroelectric copolymer poly(vinylidene fluoride (PVDF)–trifluoroethylene (TrFE)). Range of molecular adsorbates is discussed from the smaller polar molecules like water, which is small enough to both adsorb and absorb, to the larger macrocyclic metal–organic metal phthalocyanines. The changes in local dipole orientation may affect the strength of the coupling between adsorbate or absorbate and the copolymer poly(vinylidene fluoride–trifluoroethylene). The interface dipole interactions may also affect device properties. The dipole interactions are implicated at the interface between copper phthalocyanine and poly(vinylidene fluoride with trifluoroethylene) affecting the band offsets and the diode properties.

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Fission Processes Following Core Level Excitation In Closo-1,2-Orthocarborane, E. Rühl, A. P. Hitchcock, J. D. Bozek, T. Tyliszczak, A. L. D. Kilcoyne, D. N. Mcilroy, A. Knop-Gericke, Peter A. Dowben Jun 2009

Fission Processes Following Core Level Excitation In Closo-1,2-Orthocarborane, E. Rühl, A. P. Hitchcock, J. D. Bozek, T. Tyliszczak, A. L. D. Kilcoyne, D. N. Mcilroy, A. Knop-Gericke, Peter A. Dowben

Peter Dowben Publications

Time-of-flight mass analysis with multi-stop coincidence detection was used to study the multi-cation ionic fragmentation of the closo carborane cage molecule closo-1,2-orthocarborane (C2B10H12) following inner-shell excitation in or above the B 1s regime. Electron ion coincidence spectra reveal the cationic products which are formed after core level excitation. Distinct changes in fragmentation pattern are observed as a function of excitation energy. Photoelectron–photoion– photoion coincidence (PEPIPICO) spectroscopy was used to study the dominant fission routes in the core level excitation regime. Series of ion pairs are identified, where asymmetric fission dominates, leading to ion pairs …

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Selective Nanoshaving Of Self-Assembled Monolayers Of 2-(4-Pyridylethyl)Triethoxysilane, Luis G. Rosa, Jinyue Jiang, Ocelio V. Lima, Jie Xiao, Emmanuel Utreras, Peter A. Dowben, Li Tan May 2009

Selective Nanoshaving Of Self-Assembled Monolayers Of 2-(4-Pyridylethyl)Triethoxysilane, Luis G. Rosa, Jinyue Jiang, Ocelio V. Lima, Jie Xiao, Emmanuel Utreras, Peter A. Dowben, Li Tan

Peter Dowben Publications

Single molecular layers of 2-(4-pyridylethyl)triethoxysilane have been deposited on native oxide surfaces of silicon, with the triethoxysilylethyl groups towards the silicon oxide interface and pyridine at the surface. It is possible to “shave” or mechanically break the molecular bonds at the alkoxy-silane (Si–C) bond using scanning atomic force microscope, leaving large swaths of surface area cut to a depth of 0.64 ± 0.06 nm, exposing the silicon of the alkoxy-silane ligand. Mechanical cleavage of the pyridine ligand alone is also possible, but more difficult to control selectively.

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Changes In The Adsorbate Dipole Layer With Changing D-Filling Of The Metal (Ii) (Co, Ni, Cu) Phthalocyanines On Au(111), Jie Xiao, Peter A. Dowben Feb 2009

Changes In The Adsorbate Dipole Layer With Changing D-Filling Of The Metal (Ii) (Co, Ni, Cu) Phthalocyanines On Au(111), Jie Xiao, Peter A. Dowben

Peter Dowben Publications

In combined photoemission and inverse photoemission spectroscopy studies, we observe changes in the metal phthalocyanine molecular orbital offsets with respect to the conducting gold substrate Fermi level, with the changing d-electron filling of the metal (II) (Co, Ni, Cu) phthalocyanines. The implication is that the interfacial dipole layer depends upon the choice of metal (Co, Ni, Cu) centers within the metal (II) phthalocyanines adsorbed on Au(111).

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Haloform Adsorption On Crystalline Copolymer Films Of Vinylidene Fluoride With Trifluoroethylene, Jie Xiao, Carolina C. Ilie, Ning Wu, Keisuke Fukutani, Peter A. Dowben Feb 2009

Haloform Adsorption On Crystalline Copolymer Films Of Vinylidene Fluoride With Trifluoroethylene, Jie Xiao, Carolina C. Ilie, Ning Wu, Keisuke Fukutani, Peter A. Dowben

Peter Dowben Publications

Reversible bromoform adsorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF–TrFE 70:30) was examined by photoemission and inverse photoemission spectroscopies. The adsorption of bromoform on this polymer surface is associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state, whose intensity scales with the unscreened photoemission final state.

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3d Transition Metal Doping Of Semiconducting Boron Carbides, Peter A. Dowben, Orhan Kizilkaya, Jing Liu, B. Montag, K. Nelson, Ildar F. Sabiryanov, Jennifer I. Brand Jan 2009

3d Transition Metal Doping Of Semiconducting Boron Carbides, Peter A. Dowben, Orhan Kizilkaya, Jing Liu, B. Montag, K. Nelson, Ildar F. Sabiryanov, Jennifer I. Brand

Peter Dowben Publications

The introduction metallocenes, in particular ferrocene (Fe(η5-C5H5)2), cobaltocene (Co(η5-C5H5)2), and nickelocene (Ni(η5-C5H5)2), together with the carborane source molecule closo-1,2-dicarbadodecaborane, during plasma enhanced chemical vapor deposition, will result in the transition metal doping of semiconducting boron carbides. Here we report using ferrocene to introduce Fe dop¬ants, and a semiconducting boron-carbide homojunction has been fabricated. The diode characteristics are very similar to those fabricated with Co and Ni doping.

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The Surface Core Level Shift For Lithium At The Surface Of Lithium Borate, David Wooten, Ihor Ketsman, Jie Xiao, Yaroslav B. Losovyj, J. C. Petrosky, J. Mcclory, Ya. V. Burak, V. T. Adamiv, Peter A. Dowben Jan 2009

The Surface Core Level Shift For Lithium At The Surface Of Lithium Borate, David Wooten, Ihor Ketsman, Jie Xiao, Yaroslav B. Losovyj, J. C. Petrosky, J. Mcclory, Ya. V. Burak, V. T. Adamiv, Peter A. Dowben

Peter Dowben Publications

The shallow Li 1s core level exhibits a surface-to-bulk core level shift for the stoichiometric Li2B4O7 (1 1 0) surface. Angle-resolved photoemission spectroscopy was used to identify Li1s bulk and surface core level components at binding energies –56.5 ± 0.4 and –53.7 ± 0.5 eV, respectively. We find photoemission evidence for surface states of Li2B4O7 (1 1 0) that exist in the gap of the projected bulk density of states. The existence of surface states is consistent with the large surface-to-bulk core level shift for the Li 1s core.

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Magnetism Of Cr-Doped Diamond-Like Carbon, J. A. Colón Santana, Ralph Skomski, V. R. Singh, V. Palshin, A. Petukhov, Yaroslav B. Losovyj, Andrei Sokolov, Peter A. Dowben, Ihor Ketsman Jan 2009

Magnetism Of Cr-Doped Diamond-Like Carbon, J. A. Colón Santana, Ralph Skomski, V. R. Singh, V. Palshin, A. Petukhov, Yaroslav B. Losovyj, Andrei Sokolov, Peter A. Dowben, Ihor Ketsman

Peter Dowben Publications

Chromium-doped hydrogenated diamond-like carbon (Cr-DLC) and chromium carbide hydrogenated DLC alloys were synthesized by plasma-assisted vapor deposition and investigated by x-ray absorption near edge structure spectroscopy, extended x-ray absorption fine structure, and superconducting quantum interference device (SQUID) magnetometry. Structural and magnetic properties of the doped and alloy materials were investigated as a function of the Cr concentration (0.1–20 at. %). Toward the upper end of the concentration range, Cr precipitates in the form of chromium carbide (Cr3C2) nanoclusters. For low Cr concentrations, the systems are ferromagnetic at very low temperatures, whereas the chromium carbide clusters appear …

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Comparison Of N-Type Gd2O3 And Gd-Doped Hfo2, Yaroslav B. Losovyj, David Wooten, Juan Colon Santana, Joonhee Michael An, Kirill D. Belashchenko, N. Lozova, J. C. Petrosky, Andrei Sokolov, Jinke Tang, Wendong Wang, Navamoney Arulsamy, Peter A. Dowben Jan 2009

Comparison Of N-Type Gd2O3 And Gd-Doped Hfo2, Yaroslav B. Losovyj, David Wooten, Juan Colon Santana, Joonhee Michael An, Kirill D. Belashchenko, N. Lozova, J. C. Petrosky, Andrei Sokolov, Jinke Tang, Wendong Wang, Navamoney Arulsamy, Peter A. Dowben

Peter Dowben Publications

Gd2O3 and Gd-doped HfO2 films were deposited on p-type silicon substrates in a reducing atmosphere. Gd 4f photoexcitation peaks at roughly 7 and 5 eV below the valence band maximum have been identified using the resonant photoemission of Gd2O2 and Gd-doped HfO2 films, respectively. In the case of Gd2O3, strong hybridization with the O 2p band is demonstrated, and there is evidence that the Gd 4f weighted band exhibits dispersion in the bulk band structure. The rectifying (diode-like) properties of Gd-doped HfO2–silicon and Gd2O …

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Radiation-Induced Decomposition Of The Metal-Organic Molecule Bis(4-Cyano-2,2,6,6-Tetramethyl-3,5-Heptanedionato)Copper(Ii), David Wisbey, Ning Wu, Yaroslav B. Losovyj, Ihor Ketsman, A. N. Caruso, Danqin Feng, John Belot, Elio Vescovo, Peter A. Dowben Jan 2009

Radiation-Induced Decomposition Of The Metal-Organic Molecule Bis(4-Cyano-2,2,6,6-Tetramethyl-3,5-Heptanedionato)Copper(Ii), David Wisbey, Ning Wu, Yaroslav B. Losovyj, Ihor Ketsman, A. N. Caruso, Danqin Feng, John Belot, Elio Vescovo, Peter A. Dowben

Peter Dowben Publications

The effects of vacuum ultraviolet radiation on the adsorbed copper center molecule bis(4-cyano-2,2,6,6- tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)) was studied by photoemission spectroscopy. Changes in the ultraviolet photoemission spectra (UPS) of Cu(CNdpm)2, adsorbed on Co(1 1 1), indicate that the ultraviolet radiation leads to decomposition of Cu(CNdpm)2 and this decomposition is initially dominated by loss of peripheral hydrogen.

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Induced Spin Polarization Of Copper Spin 1/2 Molecular Layers, David Wisbey, Ning Wu, Danqin Feng, A. N. Caruso, J. Belot, Yaroslav B. Losovyj, Elio Vescovo, Peter A. Dowben Jan 2009

Induced Spin Polarization Of Copper Spin 1/2 Molecular Layers, David Wisbey, Ning Wu, Danqin Feng, A. N. Caruso, J. Belot, Yaroslav B. Losovyj, Elio Vescovo, Peter A. Dowben

Peter Dowben Publications

Thin films of the metal organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)), deposited on ferromagnetic Co(111) at 40 K, exhibit a finite electron spin polarization. The spin polarization magnitude and sign for Cu(CNdpm)2 deposited on Co(111) is coverage dependent, but deviates from the mean field expectations for a simple paramagnet on a ferromagnetic substrate. The spin asymmetry is seen to favor select molecular orbitals, consistent with the predicted single molecule density of states. The overlayer polarization observed indicates a strong influence of the ferromagnetic Co(111) substrate and some extra-molecular …

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4f Hybridization And Band Dispersion In Gadolinium Thin Films And Compounds, Takashi Komesu, H.-K. Jeong, David Wooton, Yaroslav B. Losovyj, J. N. Crain, M. Bissen, F. J. Himpsel, J. C. Petrosky, Jinke Tang, Wendong Wang, I. N. Yakovkin, Peter A. Dowben Jan 2009

4f Hybridization And Band Dispersion In Gadolinium Thin Films And Compounds, Takashi Komesu, H.-K. Jeong, David Wooton, Yaroslav B. Losovyj, J. N. Crain, M. Bissen, F. J. Himpsel, J. C. Petrosky, Jinke Tang, Wendong Wang, I. N. Yakovkin, Peter A. Dowben

Peter Dowben Publications

There is interplay between intra-atomic orbital hybridization and extra-atomic hybridization in various gadolinium systems, which affects magnetic coupling and electron itinerancy (localization). The results do not always follow expectation. The experimental band structure of thin Gd(0001) films, grown on the Mo(112) surface, along the Γ − M does not agree with expectations even qualitatively. In particular, the dispersion of the gadolinium band, with strong 5d weight near 2 eV binding energy provides considerable evidence to support the case for 4f- 5d hybridization, with increasing 5d localization. On the other hand, there is also evidence of extra-atomic Gd 4f hybridization leading …

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The Effect Of Defects On The Electronic Structure Of Long Chain Ferroelectric Polymers, Jie Xiao, Xin Zhou, Q. M. Zhang, Peter A. Dowben Jan 2009

The Effect Of Defects On The Electronic Structure Of Long Chain Ferroelectric Polymers, Jie Xiao, Xin Zhou, Q. M. Zhang, Peter A. Dowben

Peter Dowben Publications

The apparent molecular density of states from combined photoemission and inverse photoemission spectroscopies is compared to the bulk conductivity and frequency dependent dielectric measurements for a variety of ferroelectric polymer poly(vinylidene fluoride) (PVDF) copolymers and terpolymers. While some extra chemical groups introduced into the PVDF long chains increase the measured conductivities at room temperature and can cause significant changes in the dielectric properties, few changes are observed in the overall experimental molecular density of states. The exception appears to be the very short polymer chains. The significance of this comparison is that profound changes can occur in the overall dielectric …

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The Minority Spin Surface Bands Of Cos2(001), Ning Wu, Renat F. Sabirianov, Wai-Ning Mei, Yaroslav B. Losovyj, N. Lozova, M. Manno, C. Leighton, Peter A. Dowben Jan 2009

The Minority Spin Surface Bands Of Cos2(001), Ning Wu, Renat F. Sabirianov, Wai-Ning Mei, Yaroslav B. Losovyj, N. Lozova, M. Manno, C. Leighton, Peter A. Dowben

Peter Dowben Publications

Angle-resolved photoemission was used to study the surface electronic band structure of high quality single crystals of ferromagnetic CoS2 (below 120 K). Strongly dispersing Co t2g bands are identified along the (100) k ǁ direction, the Γ-X line of the surface Brillouin zone, in agreement with model calculations. The calculated surface band structure includes corrections for the previously determined surface structure of CoS2(001) and is in general agreement with the experimental photoemission spectra in the region of the Fermi level. There is evidence of the existence of several minority spin surface states, falling into a gap …

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The Surface Relaxation And Band Structure Of Mo(112), Ning Wu, Yaroslav B. Losovyj, Zhaoxian Yu, Renat F. Sabirianov, Wai-Ning Mei, N. Lozova, J. A. Colón Santana, Peter A. Dowben Jan 2009

The Surface Relaxation And Band Structure Of Mo(112), Ning Wu, Yaroslav B. Losovyj, Zhaoxian Yu, Renat F. Sabirianov, Wai-Ning Mei, N. Lozova, J. A. Colón Santana, Peter A. Dowben

Peter Dowben Publications

The experimental and theoretical surface band structures of Mo(112) are compared. This surface band structure mapping is presented with corrections included for the lattice relaxation of the Mo(112) surface. Quantitative low energy electron diffraction (LEED) has been used to determine the details of the Mo(112) surface structure. The first layer contraction is 14.9% by LEED intensity versus voltage analysis and is in general agreement with the 17.6% contraction found from total surface energy optimization. The electronic band structure is mapped out along Γ-X and Γ–Y of the surface Brillouin zone (SBZ). There is strong evidence of electron–phonon coupling particularly in …

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