Pulsed laser deposition have been adapted for precursor fabrication of Hg-Ba-Ca-Cu-O thin films. The preparation involves a sequential deposition of HgO and Ba2CaCu2Ox thin layers at 200 degree(s)C on MgO and SrTiO3 substrates. Processing... more
Pulsed laser deposition have been adapted for precursor fabrication of Hg-Ba-Ca-Cu-O thin films. The preparation involves a sequential deposition of HgO and Ba2CaCu2Ox thin layers at 200 degree(s)C on MgO and SrTiO3 substrates. Processing parameters were optimized by studying surface morphology of the individual layers and by strict Hg content control. Ex-situ thermal postannealing and oxygen content have not yet been optimized. The obtained films show almost single phase HgBa2CaCu2O6+(delta ) with a c-axis of 12.65 angstrom and Tc (onset) of 110 K as determined from magnetic measurements.
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ABSTRACT The surface morphology and nucleation of molecular beam epitaxy-grown ‘infinite-layer’ structure, (Sr,Ca)CuO2 films on atomically flat SrTiO3 are studied by reflection high-energy electron diffraction (RHEED) and atomic force... more
ABSTRACT The surface morphology and nucleation of molecular beam epitaxy-grown ‘infinite-layer’ structure, (Sr,Ca)CuO2 films on atomically flat SrTiO3 are studied by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The SrTiO3 (100) surfaces were prepared by an ultra-high vacuum (UHV) annealing and displayed regular arrays of 0.4 nm steps spaced by atomically flat terraces of about 400 nm. The terraces exhibited smooth edges which were parallel to the [110] substrate direction. AFM images of only a two unit cell thick (0.66 nm) (Sr,Ca)CuO2 layers were recorded. Edge roughness of the substrate terraces was found to be affected by the growth process. Atomically flat (Sr,Ca)CuO2 islands with the vertical steps of multiple heights of one unit cell were identified. The obtained AFM and RHEED data strongly suggested the island to step-growth mode of ‘infinite-layer’, (Sr,Ca)CuO2 films grown on atomically smooth (100) SrTiO3 surfaces. Different surface morphology of thicker (Sr,Ca)CuO2 films grown with other nominal compositions were also investigated by AFM.
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Superconducting HgBa2CaCu2O6+δ (Hg-1212) thin films have been prepared by laser ablation followed by post-annealing at high temperatures. Two synthesis methods were investigated, using (1) direct reaction of Hg–Ba–Ca–Cu–O precursor films... more
Superconducting HgBa2CaCu2O6+δ (Hg-1212) thin films have been prepared by laser ablation followed by post-annealing at high temperatures. Two synthesis methods were investigated, using (1) direct reaction of Hg–Ba–Ca–Cu–O precursor films in a Hg-controlled ambience, and (2) thermal diffusion of Hg into Ba–Ca–Cu–O precursor films in a controlled atmosphere containing both Hg- and Tl-bearing species. Effects of the annealing temperature, time, and bulk material composition on the Hg-1212 film and residual impurities are presented. Surface morphologies, growth defects, and transport properties of Hg-1212 on SrTiO3 substrates are discussed. Formation of Hg-1212 films on MgO and LaAlO3 substrates is briefly described.
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The adsorption of water on two silicon surfaces [reconstructed planar (100)2×1 and single domain stepped (100)2×1 cut 5° towards (011)] was studied using low-energy electron diffraction and digital imaging electron stimulated desorption... more
The adsorption of water on two silicon surfaces [reconstructed planar (100)2×1 and single domain stepped (100)2×1 cut 5° towards (011)] was studied using low-energy electron diffraction and digital imaging electron stimulated desorption ion angular distributions (ESDIAD) as a function of temperature (145–700 K) and coverage. Water has been shown previously to chemisorb dissociatively to form surface OH groups. At 300 K the H+ ESDIAD pattern for the planar surface is a nearly symmetric halo, indicating that OH is oriented with its bond vector inclined away from the surface normal, while at low temperatures (≤200 K) a four-lobed pattern that preserves substrate symmetry is observed. This reversible temperature dependence is related to librations and rotations of the OH complexes. ESDIAD from the stepped surface exhibits a two-lobed pattern, with enhanced emission towards the steps, consistent with bonding of OH to single-domain terrace sites. An interpretation is presented based on the dimer model of the Si(100) reconstruction in which the OH bond axis azimuths are oriented nearly perpendicular to the dimer azimuths.
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High resolution core-level spectroscopy was utilized to study the clean and NH3 exposed Si (100) 2× 1 surface. The clean surface exhibits two approximately equal intensity surface core-level components at− 0.48 and 0.28 eV binding energy... more
High resolution core-level spectroscopy was utilized to study the clean and NH3 exposed Si (100) 2× 1 surface. The clean surface exhibits two approximately equal intensity surface core-level components at− 0.48 and 0.28 eV binding energy referred to the bulk ...
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Research Interests: Chemistry and Adsorption
After the discovery that core level binding energies are sensitive to the charge distribution of the valence electrons, core level photoelectron spectroscopy has become one of the main analytical techniques in physics and chemistry. For... more
After the discovery that core level binding energies are sensitive to the charge distribution of the valence electrons, core level photoelectron spectroscopy has become one of the main analytical techniques in physics and chemistry. For example, an increase in oxidation number is accompanied by stepwise changes in the core level binding energy. The core level chemical shifts observed for atoms in different charge states usually range from 0.5 to 5 eV. Under the acronym ESCA (electron spectroscopy for chemical analysis), Siegbahn and co-workers developed the technique with extensive studies of chemical shifts in solid compounds,1 and later in molecules.2 This work was performed with fixed photon energy sources, MgKa and AlKa primarily. The main objective driving the field was to develop excitation sources and kinetic-energy electron analyzers with improved resolution to detect smaller chemical shifts with increased precision.
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Recently we have investigated the 4d → 4f giant resonances in electron and H+-ion yield spectra of oxidized Sm, Eu,and Yb [1]. Here we report on a continuation of this experiment, i.e., PSD from a metal overlayer system which consists of... more
Recently we have investigated the 4d → 4f giant resonances in electron and H+-ion yield spectra of oxidized Sm, Eu,and Yb [1]. Here we report on a continuation of this experiment, i.e., PSD from a metal overlayer system which consists of oxidized Yb on bulk Sm metal. Experiments were carried out at the Hamburger Synchrotronstrahlungslabor HASYLAB at the storage ring DORIS with the FLIPPER-monochromator. Photoelectron spectra were recorded with a commercial double-pass cylindrical mirror analyzer (CMA). A time-of-flight (TOF) mass analyzer utilizing the time structure of the storage ring was used for the detection of the photon-stimulated desorbed ions.
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ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise time (∼ 10−10 s) electric pulses in MBE grown Bi-Sr-Ca-Cu-O and rf magnetron sputtered Y-Ba-Cu-O submicron thickness microstrips. It was... more
ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise time (∼ 10−10 s) electric pulses in MBE grown Bi-Sr-Ca-Cu-O and rf magnetron sputtered Y-Ba-Cu-O submicron thickness microstrips. It was found that two reversible processes: fast electronic (τ∼10∼−12 s) and slow thermal (τ∼10∼−8s) one take place during switching. At high current densities (∼107 A/cm2) irreversible changes in strip material induced by thermal runaway occurred. The use of a superconducting element as fast fault-current limiter or pulse sharpening device is pointed out.
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Synchrotron radiation excited photoelectron spectra of the 4f emission region for all lanthanide metals Ce58 to Lu71 (except Pm61) have been recorded. Photon energies ranging from 30 eV to 200 eV have been used to excite the 4f electrons... more
Synchrotron radiation excited photoelectron spectra of the 4f emission region for all lanthanide metals Ce58 to Lu71 (except Pm61) have been recorded. Photon energies ranging from 30 eV to 200 eV have been used to excite the 4f electrons with maximum surface sensitivity. The 4f emission spectra of all metals studied, with the exception of Ce, show 4f emission from the surface layer atoms and the bulk atoms as clearly separated structures with different binding energies. For Ce no unambiguous separation of the 4f structure into bulk and surface emission could be made. We fitted the experimental spectra with calculated 4f emission spectra obtained by adding a bulk and a shifted surface multiplet for each metal. The intensity ratios within the multiplets were obtained from an atomic calculation utilizing the intermediate coupling scheme. The intensity ratio between bulk and surface emission (IB/IS) and the magnitude of the surface core level shift (SCS) were used as fit parameters. The deduced SCSs are all positive (towards higher binding energy), 0.40 eV-0.77 eV, and in fair agreement with calculated SCSs using the Johansson-Mårtensson-Rosengren model. For the trivalent lanthanides we found a systematic variation of the SCSs through the series, which can be attributed to differences in the actual electron distribution between s, p and d-like valence states. For the trivalent Sm we found the surface to be completely divalent and deduced a surface shift of > 0.46 eV, being the energy necessary to change the surface valency.
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ABSTRACT The influence of sulfur dioxide on the reduction of nitric oxide over copper, in the presence of isobutene and oxygen, has been examined under reducing conditions in the 720 to 820 K temperature range. The catalytic activity of... more
ABSTRACT The influence of sulfur dioxide on the reduction of nitric oxide over copper, in the presence of isobutene and oxygen, has been examined under reducing conditions in the 720 to 820 K temperature range. The catalytic activity of NO conversion was drastically decreased by the presence of a few ppm of SO2 in the gas phase, and the toxicity of sulfur was reduced when the temperature was increased. The Cu sample was characterized by X-ray photoelectron spectroscopy, at different stages of the reaction. It was demonstrated that sulfur dioxide poisoned NO conversion by hindering the partial oxidation of the hydrocarbon and by occupying the active sites, both factors contributing to a decrease in the surface concentration of the active intermediate (oxygenated product). Two kinds of adsorbed sulfided species, SO2−4 and S2−, were identified on the Cu surface. At the end of the reaction, the catalyst surface was poisoned both by carbon and sulfur species.
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ABSTRACT The mechanism of NO reduction on copper in the presence of oxygen and isobutene was studied at T = 770 K, under reducing conditions. Mass spectroscopy was used to identify gas-phase intermediates and reaction products. One... more
ABSTRACT The mechanism of NO reduction on copper in the presence of oxygen and isobutene was studied at T = 770 K, under reducing conditions. Mass spectroscopy was used to identify gas-phase intermediates and reaction products. One intermediate species resulting from the partial oxidation of isobutene was shown to be active in the NO conversion. X-ray photoelectron spectroscopy was used to analyze the copper surface at different stages of the reaction. Our conclusion is that oxygen first activates the surface, by forming coexisting phases of Cu2O and CuO. The copper surface is then reduced by the hydrocarbon, leading to Cu+ in majority, and to the formation of an active intermediate. At last, the reduction of NO proceeds rapidly on a zero-valent copper surface together with consumption of the previously formed intermediate. At the end of the reaction, the surface is poisoned by carbon.
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ABSTRACT A review of synchrotron radiation excited photoemission experiments on semiconductor surfaces is given. We stress the importance of angle resolved photoemission experiments using synchrotron radiation to study the surface and... more
ABSTRACT A review of synchrotron radiation excited photoemission experiments on semiconductor surfaces is given. We stress the importance of angle resolved photoemission experiments using synchrotron radiation to study the surface and bulk electronic structure of semiconductors. Recent progress to use excitations to energy regions, where calculated non free-electron like final bands are important, is reported. We briefly discuss photoemission core level spectroscopy results from semiconductor surfaces and their impact on deciding between different reconstruction models.
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ABSTRACTVarious compositions Bi-Sr-Ca-Cu-O thin films having 2212–1 ike structure have been synthesized on MgO substrates using Molecular Beam Epitaxy. Four Knudsen metal sources were utilized to prepare alloy films which were... more
ABSTRACTVarious compositions Bi-Sr-Ca-Cu-O thin films having 2212–1 ike structure have been synthesized on MgO substrates using Molecular Beam Epitaxy. Four Knudsen metal sources were utilized to prepare alloy films which were subsequently post annealed in air atmosphere. Quenching of the films from the annealing temperature, 800°C-820°C, increased the superconducting transition temperature Tc. The highest Tcs, 90 K - 95 K, were attained for compositions with slightly lower Ca and Sr content if compared to the nominal 2212 and 2223 ones. Plasma frequency of free carriers, ωp, determined from optical reflectivity measurements have been found to increase with the average density of CuO2 units. However, no substantial shift ofωp was displayed by the highest Tc films.
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Superconducting Bi2Sr3-xCaxCu2Oy films with x ranging from 1.05 to 2.20 have been prepared using molecular beam epitaxy (MBE) with four metal sources and post-annealing of the evaporated metal mixture films in oxygen and air atmospheres.... more
Superconducting Bi2Sr3-xCaxCu2Oy films with x ranging from 1.05 to 2.20 have been prepared using molecular beam epitaxy (MBE) with four metal sources and post-annealing of the evaporated metal mixture films in oxygen and air atmospheres. Annealing in air at 800 degrees C for 1-3 h yields a single-phase state with 2212-like structure for films with Ca content up to x=1.5. A slight decrease of the zero resistance superconducting transition temperature from 85 to 80 K and a lattice constant c from 30.8 to 30.6 AA were measured upon substituting Sr with Ca. Annealing times up to 20 h showed, for Ca-rich films, changes in the X-ray diffraction spectra as well as in superconducting transition curves. The changes are interpreted in terms of 2202- and 2223-like interlayers and intergrowth formation due to a structural instability of the 2212-like structure with Sr partially substituted by Ca.
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The performance of a scanning photoelectron microscope at the MAX I storage ring in Lund is presented. The microscope utilizes undulator radiation in the energy range 15–150 eV and is comprised of a plane-grating monochromator with a... more
The performance of a scanning photoelectron microscope at the MAX I storage ring in Lund is presented. The microscope utilizes undulator radiation in the energy range 15–150 eV and is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a gracing incidence ellipsoidal focusing mirror. The instrument with its high photon flux, 109–1010 photons/s, and narrow bandwidth, better than 0.2 eV, is excellently suited for high-resolution core-level spectroscopy and imaging of samples with lateral inhomogeneties in the micrometer range.
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The design of a photoemission microprobe beamline at the MAX laboratory is presented. The beamline will utilize the radiation from a 26 period undulator on the 550-MeV MAX storage ring. The beamline will be capable of providing about 1010... more
The design of a photoemission microprobe beamline at the MAX laboratory is presented. The beamline will utilize the radiation from a 26 period undulator on the 550-MeV MAX storage ring. The beamline will be capable of providing about 1010 photons/s of monochromatized radiation (bandwidth better than 0.25 eV) in the energy range of 20 to 150 eV focused into a submicrometer focal spot. It will be used for scanning photoemission experiments with a lateral resolution better than 1 μm. The optical system is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a specially designed ellipsoidal focusing mirror.
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Thin films of superconducting BiCaSrCuO have been grown by molecular beam epitaxy depositions of Bi, Cu, and CaF2/SrF2 on MgO and SrTiO3 followed by a high-temperature oxygen anneal. The films showed a fairly wide transition of 20 K at a... more
Thin films of superconducting BiCaSrCuO have been grown by molecular beam epitaxy depositions of Bi, Cu, and CaF2/SrF2 on MgO and SrTiO3 followed by a high-temperature oxygen anneal. The films showed a fairly wide transition of 20 K at a Tc of 80 K. Residual amounts of fluorine, detected with secondary-ion mass spectrometry, are believed to cause the broad superconducting transition. X-ray diffraction analysis of the superconducting films revealed strongly c-axis oriented films consisting of Bi2CaSr2Cu2O8 and Bi2Sr2Cu1O6 phase. Surface structure studies, with scanning electron microscopy and scanning tunneling microscopy, show oriented 1 μm sized very smooth flat grains of superconducting phase in the plane of the film with islands of CuOx scattered on top of these.
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ABSTRACT Valence‐band photoemission spectra have been studied on single‐crystal aluminum faces using polarized sychrotron radiation. New intrinsic and oxygen‐related extrinsic surface resonance features are observed within 5 eV of the... more
ABSTRACT Valence‐band photoemission spectra have been studied on single‐crystal aluminum faces using polarized sychrotron radiation. New intrinsic and oxygen‐related extrinsic surface resonance features are observed within 5 eV of the Fermi level. These surface resonances are correlated with oxygen uptake on the (100), (110), and (111) faces as observed in both valence and core‐level spectroscopy. Considerable face dependence to the oxidation is shown. Although aluminum is a free‐electron‐like metal, its surface behavior on single‐crystal faces shows effects due to localized charge.
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ABSTRACT The role of various intergrowth defects acting as charge reservoirs in infinite-layer-structure Ca1-xSrxCuO2 films is widely discussed, while internal structural properties of the CuO2 planes that are important in acquiring the... more
ABSTRACT The role of various intergrowth defects acting as charge reservoirs in infinite-layer-structure Ca1-xSrxCuO2 films is widely discussed, while internal structural properties of the CuO2 planes that are important in acquiring the charge have received significantly less attention. We present experimental evidence based on reflection high-energy electron diffraction and extended x-ray-absorption fine structure data that the epitaxial misfit strain in infinite-layer Ca1-xSrxCuO2 films grown by molecular beam epitaxy can induce oxygen displacements in the CuO2 planes resulting in a buckling of the CuO2 sheets. The displacements are explained by the relief of strain from the CuO2 planes in infinite-layer films grown under compressive stress. For films that undergo tensile stress the CuO2 sheets remain planar. The results show that observed structural properties of CuO2 planes have a large impact on charge-carrier density and can considerably promote the ability of the CuO2 planes to be optimally charged.
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ABSTRACT A review of synchrotron radiation excited photoemission experiments on semiconductor surfaces is given. We stress the importance of angle resolved photoemission experiments using synchrotron radiation to study the surface and... more
ABSTRACT A review of synchrotron radiation excited photoemission experiments on semiconductor surfaces is given. We stress the importance of angle resolved photoemission experiments using synchrotron radiation to study the surface and bulk electronic structure of semiconductors. Recent progress to use excitations to energy regions, where calculated non free-electron like final bands are important, is reported. We briefly discuss photoemission core level spectroscopy results from semiconductor surfaces and their impact on deciding between different reconstruction models.
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ABSTRACT The microstructure of Bi2Sr2Can-1CunOy multilayers grown by molecular beam epitaxy on atomically flat SrTiO3 substrates has been studied by reflection high-energy electron diffraction (RHEED), atomic force microscopy, and... more
ABSTRACT The microstructure of Bi2Sr2Can-1CunOy multilayers grown by molecular beam epitaxy on atomically flat SrTiO3 substrates has been studied by reflection high-energy electron diffraction (RHEED), atomic force microscopy, and x-ray-diffraction (XRD) techniques. The overall RHEED data, collected in situ at different Bi2Sr2CuOy/Bi2Sr2CaCu2Oy (2201/2212) multilayer growth stages, demonstrated a two-dimensional growth and rather a high quality of the interfaces. Following the evolution of RHEED patterns, some evidence of an increase in surface roughness after several multilayer periods, was detected. A one-dimensional x-ray-diffraction model was applied for a quantitative analysis of growth defects in the multilayers. The substitutional disorder in the lattice and stacking faults in the molecular layers were determined by an iterative comparison of simulated x-ray-diffraction spectra with the experimental XRD data. The observed changes in the c-axis lattice parameter of 2201 molecular layers were interpreted as being caused by ionic substitutions of Sr2+ by Ca2+ in the lattice and governed by the growth interdiffusion. The fitting procedure also revealed that two types of growth disorder were present in the layers: (1) stacking faults randomly distributed within the layers and (2) stacking faults localized at the interfaces. The two types of growth defect are expected to influence the superconducting properties differently and this has to be considered before the transport properties of superconducting multilayers are studied.
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The local structure and the electronic states of a thin oxide layer on a single-crystal Al (111) surface has been studied using surface soft-x-ray absorption and soft-x-ray photoemission spectroscopy. Unoccupied interface states are found... more
The local structure and the electronic states of a thin oxide layer on a single-crystal Al (111) surface has been studied using surface soft-x-ray absorption and soft-x-ray photoemission spectroscopy. Unoccupied interface states are found in the oxide band gap. The local structure of the thin oxide layer is compared with the structure of bulk Al2O3. The effect on the electronic
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After the discovery that core level binding energies are sensitive to the charge distribution of the valence electrons, core level photoelectron spectroscopy has become one of the main analytical techniques in physics and chemistry. For... more
After the discovery that core level binding energies are sensitive to the charge distribution of the valence electrons, core level photoelectron spectroscopy has become one of the main analytical techniques in physics and chemistry. For example, an increase in oxidation number is accompanied by stepwise changes in the core level binding energy. The core level chemical shifts observed for atoms in different charge states usually range from 0.5 to 5 eV. Under the acronym ESCA (electron spectroscopy for chemical analysis), Siegbahn and co-workers developed the technique with extensive studies of chemical shifts in solid compounds,1 and later in molecules.2 This work was performed with fixed photon energy sources, MgKa and AlKa primarily. The main objective driving the field was to develop excitation sources and kinetic-energy electron analyzers with improved resolution to detect smaller chemical shifts with increased precision.
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Key Issues: Sweden is in a process of adapting the national economic policy when taking into consideration as a response to the impact of globalisation, the expanding European Union and its monetary system. A new microeconomic focus is... more
Key Issues: Sweden is in a process of adapting the national economic policy when taking into consideration as a response to the impact of globalisation, the expanding European Union and its monetary system. A new microeconomic focus is emerging. What are the strengths and weaknesses in the Swedish national innovation system? What should be done? How would you do it and how should you do it?
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ABSTRACT Hg–Ba–Ca–Cu–O thin films prepared on SrTiO3 (100) substrates generally exhibit shorter c-axis unit cell lengths and lower zero-resistance superconducting transition temperatures as compared to bulk. Microstructural studies of... more
ABSTRACT Hg–Ba–Ca–Cu–O thin films prepared on SrTiO3 (100) substrates generally exhibit shorter c-axis unit cell lengths and lower zero-resistance superconducting transition temperatures as compared to bulk. Microstructural studies of HgBa2CaCu2O6+δ films based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) revealed shorter BaO–CuO2 interplanar distances and longer CuO2–CuO2 average distances as compared to those reported for bulk compounds. It is suggested that the observed cationic disorder causes smaller c-axis lattice parameter and is probably induced by the lattice mismatch between film and substrate. The observed atomic rearrangements are expected to influence superconducting properties of the Hg-based films.
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... dosed surface. We believe J. Vac. Sci. Teefrnof. A, Vol. 5, Ne. 4, Jul/Aug 1887 Page 3. 844 Larsson eí al.: Adsorption of H20 ors planar and stepped Si(100) S44 Fig. 3. The data treatment is the same as for Fig. 2. (a) ESDIAD ...
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Superconducting HgBa2CaCu2O6+δ (Hg-1212) thin films have been prepared by laser ablation followed by post-annealing at high temperatures. Two synthesis methods were investigated, using (1) direct reaction of Hg–Ba–Ca–Cu–O precursor films... more
Superconducting HgBa2CaCu2O6+δ (Hg-1212) thin films have been prepared by laser ablation followed by post-annealing at high temperatures. Two synthesis methods were investigated, using (1) direct reaction of Hg–Ba–Ca–Cu–O precursor films in a Hg-controlled ambience, and (2) thermal diffusion of Hg into Ba–Ca–Cu–O precursor films in a controlled atmosphere containing both Hg- and Tl-bearing species. Effects of the annealing temperature, time, and bulk material composition on the Hg-1212 film and residual impurities are presented. Surface morphologies, growth defects, and transport properties of Hg-1212 on SrTiO3 substrates are discussed. Formation of Hg-1212 films on MgO and LaAlO3 substrates is briefly described.
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Synchrotron radiation excited photoelectron spectra of the 4f emission region for all lanthanide metals Ce58 to Lu71 (except Pm61) have been recorded. Photon energies ranging from 30 eV to 200 eV have been used to excite the 4f electrons... more
Synchrotron radiation excited photoelectron spectra of the 4f emission region for all lanthanide metals Ce58 to Lu71 (except Pm61) have been recorded. Photon energies ranging from 30 eV to 200 eV have been used to excite the 4f electrons with maximum surface sensitivity. The 4f emission spectra of all metals studied, with the exception of Ce, show 4f emission from the surface layer atoms and the bulk atoms as clearly separated structures with different binding energies. For Ce no unambiguous separation of the 4f structure into bulk and surface emission could be made. We fitted the experimental spectra with calculated 4f emission spectra obtained by adding a bulk and a shifted surface multiplet for each metal. The intensity ratios within the multiplets were obtained from an atomic calculation utilizing the intermediate coupling scheme. The intensity ratio between bulk and surface emission (IB/IS) and the magnitude of the surface core level shift (SCS) were used as fit parameters. The deduced SCSs are all positive (towards higher binding energy), 0.40 eV-0.77 eV, and in fair agreement with calculated SCSs using the Johansson-Mårtensson-Rosengren model. For the trivalent lanthanides we found a systematic variation of the SCSs through the series, which can be attributed to differences in the actual electron distribution between s, p and d-like valence states. For the trivalent Sm we found the surface to be completely divalent and deduced a surface shift of > 0.46 eV, being the energy necessary to change the surface valency.
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In a series of papers, published during second half of the 1980s, the Budapest group (Braun, Glanzel, Telcs and Schubert) proposed that bibliometric distributions are to be characterized as Waring distributions. We use their methodology... more
In a series of papers, published during second half of the 1980s, the Budapest group (Braun, Glanzel, Telcs and Schubert) proposed that bibliometric distributions are to be characterized as Waring distributions. We use their methodology in order to establish a reference value for academic production within macro classes. From this we develop a combined performance model for academic research and apply the model to Australian research. This model take advantage of, first, field normalized publication rates (the productivity dimension) and, second, field normalized citation rates (the quality dimension). Based on ISI-data the performance of Australian universities is depicted in a more resource-efficient way than competing models.
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ABSTRACT Spectral distribution measurements have been made on the large, super-smooth, copper M0 collection mirrors used on the Stanford Synchrotron-Radiation Laboratory 4° beam line. The recent installation of a new mirror has presented... more
ABSTRACT Spectral distribution measurements have been made on the large, super-smooth, copper M0 collection mirrors used on the Stanford Synchrotron-Radiation Laboratory 4° beam line. The recent installation of a new mirror has presented the opportunity to characterize the effect of the high synchrotron flux on such mirrors. The original mirror was found to have an RMS roughness (186±14) Å, while the new mirror has a roughness of (38.9±1.6) Å. Visual observation of the original mirror showed no evidence for carbon buildup resulting from hydrocarbon cracking in the presence of the intense synchrotron radiation. A dramatic improvement in the spectral throughput of the beam line was observed upon installation of the smoother mirror. This amounted to an order of magnitude improvement before the dispersive loss at the carbon K edge. the monochromatized contrast at the carbon K edge is found to be betterthan 60:1. The effective cutoff range of the monochromator (where the monochromatized contrast is 1) has been extended to above 700 eV. Examples of high-energy photoemission measurements will be given.
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ABSTRACT Photoelectron spectra of Al and Si have been excited by monochromatized synchrotron radiation at different photon energies. The plasmon loss structures produced by the elastic electrons from the Si 2p and Al 2p core levels have... more
ABSTRACT Photoelectron spectra of Al and Si have been excited by monochromatized synchrotron radiation at different photon energies. The plasmon loss structures produced by the elastic electrons from the Si 2p and Al 2p core levels have been investigated for different kinetic energies at the elastic electrons. Variation of the plasmon loss intensities for electron kinetic energies of 30–330 eV explains earlier reported absence of plasmon structure in uv photoelectron spectroscopy. The results also indicate that a model of extrinsic bulk plasmon excitation developed by Mahan and modified to account for surface effects could explain the observed threshold behavior of bulk plasmon intensity at low electron kinetic energies.
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ABSTRACT Using partial yield spectroscopy, we have investigated the variation in the excitation of core electrons to the empty surface states on II–VI, III–V, and group IV semiconductors. From measurements of cleaved surfaces of ZnS,... more
ABSTRACT Using partial yield spectroscopy, we have investigated the variation in the excitation of core electrons to the empty surface states on II–VI, III–V, and group IV semiconductors. From measurements of cleaved surfaces of ZnS, ZnSe, ZnTe, CdTe, GaAs, Si, and Ge, strong transitions to empty surface states from p‐core electron initial states are observed from the anion in ZnS (110) and the cation in ZnSe (110). Neither Ga (3p) nor As (3d) core electrons were photoexcited to the GaAs (110) unfilled surface states. Further, p‐core electrons do not make optical transitions to Si (111) or Ge (111) unoccupied surface states. We propose that the empty orbitals for covalent surfaces are mainly p‐character, which for compound semiconductors are localized on the cation; if there is anion state density, it is mainly s‐like. In contrast, for ionic surfaces, s‐like anion and cation wave functions form the unoccupied surface states. The II–VI core‐to‐surface transition is ∼2.5 eV below the photoemission‐deduced conduction band edge; this final‐state effect is much larger than for either bulk transitions in the same solid or surface transitions in less ionic crystals (by an amount much greater than the ratio of the bandgaps).
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Substrate core chemical shifts upon chemisorption of oxygen on aluminum are observed using variable-excitation-energy photoelectron spectroscopy. At low exposures a unique intermediate oxidation state evolves where the Al 2p level is... more
Substrate core chemical shifts upon chemisorption of oxygen on aluminum are observed using variable-excitation-energy photoelectron spectroscopy. At low exposures a unique intermediate oxidation state evolves where the Al 2p level is shifted by only 1.3 eV toward higher binding energy as compared to the 2.6-eV shift observed for heavily oxidized aluminum (AlâOâ). Simultaneous observation of the O 2p resonance shows
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We have identified the adatom contribution in the Ge 3d core-level spectra from the clean Ge(111)c(2×8) surface, shifted 0.17 eV to higher binding energy compared to the bulk. This adatom component vanishes in the Ge(111)-Sn(7×7) surface... more
We have identified the adatom contribution in the Ge 3d core-level spectra from the clean Ge(111)c(2×8) surface, shifted 0.17 eV to higher binding energy compared to the bulk. This adatom component vanishes in the Ge(111)-Sn(7×7) surface core-level spectra where Sn occupies the adatom site. Moreover we report the observation of an earlier proposed difference between the rest atoms in the
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A structure model for the Ge(111)-Au([radical]3 [times] [radical]3 )[ital R]30[degree] surface reconstruction is proposed based on scanning tunneling microscopy (STM) and photoelectron spectroscopy on the Ge 3[ital d] and Au 4[ital f]... more
A structure model for the Ge(111)-Au([radical]3 [times] [radical]3 )[ital R]30[degree] surface reconstruction is proposed based on scanning tunneling microscopy (STM) and photoelectron spectroscopy on the Ge 3[ital d] and Au 4[ital f] core lines. The basic unit is a Au[sub 3]Ge molecule binding in one-third of the [ital T][sub 1] substrate sites with a gold trimer pointing out of the
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ABSTRACT Thin films of Bi2(Sr1-xCax)3Cu2Oy grown in situ by molecular-beam epitaxy have been studied by x-ray diffraction. The experimental results were interpreted using a general one-dimensional kinematic x-ray-diffraction model. An... more
ABSTRACT Thin films of Bi2(Sr1-xCax)3Cu2Oy grown in situ by molecular-beam epitaxy have been studied by x-ray diffraction. The experimental results were interpreted using a general one-dimensional kinematic x-ray-diffraction model. An accurate determination of the lattice structure and of the distribution of the different atoms on the lattice sites is obtained. The model uniquely reconstructs a large substitution between Ca2+ and Sr2+ at the Ca and Sr lattice sites. The model also predicts an expansion of the CuO2-CuO2 and a contraction of the SrO-CuO2 interplanar distances compared with x-ray-diffraction data reported from bulk single crystals. The large atomic substitution between different lattice sites is attributed to the growth kinetics, which for molecular-beam epitaxy plays a major role in forming the growing epitaxial structure, due to the low interaction energy between the thermal atom beams and the substrate surface inherent to the molecular-beam epitaxy process. This structural disorder is interpreted as causing the suppressed superconducting transition temperatures, Tc&#39;s and the broad superconducting transition widths, ΔTc&#39;s observed for Bi2(Sr1-xCax)3Cu2Oy films grown by molecular-beam epitaxy compared with films fabricated by magnetron sputtering or laser ablation. The relation between the structural disorder and the superconducting properties is discussed.
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ABSTRACT The application of angle-resolved photoelectron spectroscopy with synchrotron radiation as the source for excitation is demonstrated to be a powerful technique for determining valence-band dispersions as well as for yielding... more
ABSTRACT The application of angle-resolved photoelectron spectroscopy with synchrotron radiation as the source for excitation is demonstrated to be a powerful technique for determining valence-band dispersions as well as for yielding information on which final states are involved in the process. By recording electron-energy-distribution curves in normal emission from the (112¯0) surfaces of wurtzite single crystals of CdS and CdSe, transitions between valence-band states and conduction-band states along the Γ–M line have been studied. Parity rules have been observed by exciting the transitions with radiation polarized parallel or perpendicular to the mirror plane of the crystal. Eleven critical-point energies have been determined and are compared with theoretical predictions and with the results of previous experiments. By assuming direct transitions it is possible to determine the valence-band dispersions along Γ–M and, through fitting procedures, to derive the relevant final states. The results indicate that the valence-band structure is well described by the latest calculations, except for an underestimation of the width of the upper valence bands. The final states are found to deviate very little from simple parabolic bands in the normal direction, throughout the energy region studied.
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ABSTRACT Pulsed laser deposition have been adapted for precursor fabrication of Hg-Ba-Ca-Cu-O thin films. The preparation involves a sequential deposition of HgO and Ba2CaCu2Ox thin layers at 200 degree(s)C on MgO and SrTiO3 substrates.... more
ABSTRACT Pulsed laser deposition have been adapted for precursor fabrication of Hg-Ba-Ca-Cu-O thin films. The preparation involves a sequential deposition of HgO and Ba2CaCu2Ox thin layers at 200 degree(s)C on MgO and SrTiO3 substrates. Processing parameters were optimized by studying surface morphology of the individual layers and by strict Hg content control. Ex-situ thermal postannealing and oxygen content have not yet been optimized. The obtained films show almost single phase HgBa2CaCu2O6+(delta ) with a c-axis of 12.65 angstrom and Tc (onset) of 110 K as determined from magnetic measurements.
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ABSTRACT The adsorption of ${\mathrm{H}}_{2}$O on a stepped Ti(001) single crystal, oriented within 4\ifmmode^\circ\else\textdegree\fi{} of Ti(001) has been studied using synchrotron radiation from the Synchrotron Ultraviolet Radiation... more
ABSTRACT The adsorption of ${\mathrm{H}}_{2}$O on a stepped Ti(001) single crystal, oriented within 4\ifmmode^\circ\else\textdegree\fi{} of Ti(001) has been studied using synchrotron radiation from the Synchrotron Ultraviolet Radiation Facility at National Bureau of Standards. The species formed upon adsorption of ${\mathrm{H}}_{2}$O were identified through variable-wavelength ultraviolet photoemission spectroscopy. At room temperature ($\sim${}300 K), water dissociates to form O, H, and OH. At low temperature ($\sim${}90 K) and low coverage (1 L), the same species were observed. Photon-stimulated-desorption experiments were performed under these conditions yielding predominately ${\mathrm{H}}^{+}$ ions with little or no O${\mathrm{H}}^{+}$ or ${\mathrm{O}}^{+}$. At 90 K and coverages greater than 1 L, an ice overlayer was formed suppressing the ${\mathrm{H}}^{+}$-ion desorption. Separate experiments involving the adsorption of hydrogen and coadsorption of oxygen and hydrogen showed an order of magnitude less ${\mathrm{H}}^{+}$ desorption, indicating that the ${\mathrm{H}}^{+}$ desorption was associated with the presence of OH on the surface. The ${\mathrm{H}}^{+}$-ion yield as a function of photon energy showed a threshold at 25 eV perhaps due to O $2s$ excitation. A second threshold at 33 eV, a broad peak near 45 eV, and a slow decrease toward higher photon energy suggests a correlation with the Ti $3p$ core-hole excitation although other possibilities cannot be eliminated. Possible bonding configurations are proposed to explain the origins of the ${\mathrm{H}}^{+}$ emission.
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ABSTRACTStructural properties of molecular beam epitaxy-grown... more
ABSTRACTStructural properties of molecular beam epitaxy-grown Bi2Sr2Cu1Oy&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;Bi2Sr2Ca1Cu2Oy multilayers have been studied by x-ray diffraction. A one-dimensional kinematic x-ray diffraction model has been used to describe the structural quality of the multilayers. Interface roughness, stacking defects and unit cell disorder are obtained by an iterative fitting of the calculated diffraction profile to the experimental spectra. The type and amount of disorder in the films was qualitatively determined. Results demonstrate that structural imperfections are present in the multilayers and have to be considered when transport properties are studied.
... R. Dobro-zemsky et al. (Berger, Vienna, 1977) p. 869. CWB Martinson and SA Flodstr6m, Surface $ci. 80 (197911 306. JK Grepstad, PO Gartland and BJ Slagsvold, Surface Sci. ... 9 (1974) 312;J. Phys. C9 (1976) 3701. GE Laramore and CB... more
... R. Dobro-zemsky et al. (Berger, Vienna, 1977) p. 869. CWB Martinson and SA Flodstr6m, Surface $ci. 80 (197911 306. JK Grepstad, PO Gartland and BJ Slagsvold, Surface Sci. ... 9 (1974) 312;J. Phys. C9 (1976) 3701. GE Laramore and CB Duke, Phys. Rev. B5 (1972) 267. ...
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High resolution core-level spectroscopy was utilized to study the clean and NH3 exposed Si (100) 2× 1 surface. The clean surface exhibits two approximately equal intensity surface core-level components at− 0.48 and 0.28 eV binding energy... more
High resolution core-level spectroscopy was utilized to study the clean and NH3 exposed Si (100) 2× 1 surface. The clean surface exhibits two approximately equal intensity surface core-level components at− 0.48 and 0.28 eV binding energy referred to the bulk ...
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A freestanding transmission grating has been used as a dispersive element in a simple monochromator. The monochromator, to be used with the collimated light beam from a resonance lamp radiation source, has been tested in the far uv with... more
A freestanding transmission grating has been used as a dispersive element in a simple monochromator. The monochromator, to be used with the collimated light beam from a resonance lamp radiation source, has been tested in the far uv with the helium and neon emission spectra. The results show that the simple monochromator will resolve all major lines in the emission
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ABSTRACT We present experimental evidence of a unique, ordered chemisorption phase in the initial interaction of oxygen with the Al(111) surface. At high oxygen exposure or high temperature, this phase is shown to transform irreversibly... more
ABSTRACT We present experimental evidence of a unique, ordered chemisorption phase in the initial interaction of oxygen with the Al(111) surface. At high oxygen exposure or high temperature, this phase is shown to transform irreversibly to a bulklike aluminum oxide. The measured temperature dependence, as well as the low-energy electron diffraction, suggests a threefold, centered bonding site. A comparison between calculated and experimental valence-band density of states for the oxygen-covered Al(111) surface is made for the estimated oxygen-atom-substrate-surface distance.
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ABSTRACT A review is presented of a series of electron spectroscopic measurements investigating the surface properties of aluminum by its interaction with molecular oxygen. The studies performed at the Stanford Synchrotron Radiation... more
ABSTRACT A review is presented of a series of electron spectroscopic measurements investigating the surface properties of aluminum by its interaction with molecular oxygen. The studies performed at the Stanford Synchrotron Radiation Laboratory have used the unique properties of synchrotron radiation. The tunability of the excitation source in the spectral range 30-700 eV has made it possible to obtain maximum surface sensitivity and measure core-level photoabsorption.
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ABSTRACT Al(111) has been studied with angle-resolved photoelectron spectroscopy. A previously not observed surface state band located around the K point in the surface Brillouin zone is reported. The measured dispersion of the surface... more
ABSTRACT Al(111) has been studied with angle-resolved photoelectron spectroscopy. A previously not observed surface state band located around the K point in the surface Brillouin zone is reported. The measured dispersion of the surface state band falls in an absolute electron energy band gap when the three-dimensional band structure from a new LAPW (Linearized-Augmented-Plane-Wave) calculation is projected onto the surface Brillouin zone of the (111) crystal face. The existence of this surface state has been theoretically predicted by several authors. Direct transitions between bulk bands are found to give significant contributions to the photocurrent. Experimentally deduced initial-state energy dispersions of the bulk transitions are compared to the corresponding dispersions obtained from the LAPW band structure calculation.
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Synchrotron radiation (15 lesssim hnu lesssim 75 eV) has been used to study ion desorption from water and methanol adsorbed on a Ti(0001) surface, in an effort to understand ion desorption from covalently bonded systems. Both water and... more
Synchrotron radiation (15 lesssim hnu lesssim 75 eV) has been used to study ion desorption from water and methanol adsorbed on a Ti(0001) surface, in an effort to understand ion desorption from covalently bonded systems. Both water and methanol dissociate at all coverages upon adsorption on Ti at 300 K. Using variable wavelength UPS, the adsorbed fragments OH, O and H are identified for water and CH3O, C, O and H for methanol. At 90 K, dissociation occurs initially to yield the same products, while at higher exposures, condensed overlayers are formed. PSD of ions from the two adsorbates show very different behaviour. In the water experiment, ion desorption originates from the dissociated species at both 300 and 90 K. H+ emission from dissociated water is corelated with the presence of OH on the surface while ion desorption from the ice multilayer is almost an order of magnitude less. In contrast, ion emission from the dissociated methanol is immeasureably low in our instrument while a large H+ signal is observed from the condensed layer. It is obvious that different molecular states are involved in the ion desorption in these cases. The H+ emission from OH appears to be correlated with the O 2s level near 25 eV and the Ti 3p core level near 33 eV. However, ion desorption could arise strictly from different localized two hole states in OH. The H+ observed from methanol appears to be initiated by ionization of the 4a' orbital with an onset near 18 eV. Using isotopic labeling experiments, it is shown that H+ originates from the methyl group rather than the OH.
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Research Interests: Materials Engineering, Condensed Matter Physics, Electron Microscopy, Electron Diffraction, Molecular beam epitaxy, and 8 moreHigh Resolution Transmission Electron Microscopy, Thin Film, X ray diffraction, Microstructures, Structural Properties, High Tc Superconductivity, Electrical And Electronic Engineering, and Reflection High-Energy Electron Diffraction
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ABSTRACT The influence of sulfur dioxide on the reduction of nitric oxide over copper, in the presence of isobutene and oxygen, has been examined under reducing conditions in the 720 to 820 K temperature range. The catalytic activity of... more
ABSTRACT The influence of sulfur dioxide on the reduction of nitric oxide over copper, in the presence of isobutene and oxygen, has been examined under reducing conditions in the 720 to 820 K temperature range. The catalytic activity of NO conversion was drastically decreased by the presence of a few ppm of SO2 in the gas phase, and the toxicity of sulfur was reduced when the temperature was increased. The Cu sample was characterized by X-ray photoelectron spectroscopy, at different stages of the reaction. It was demonstrated that sulfur dioxide poisoned NO conversion by hindering the partial oxidation of the hydrocarbon and by occupying the active sites, both factors contributing to a decrease in the surface concentration of the active intermediate (oxygenated product). Two kinds of adsorbed sulfided species, SO2−4 and S2−, were identified on the Cu surface. At the end of the reaction, the catalyst surface was poisoned both by carbon and sulfur species.
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ABSTRACT The mechanism of NO reduction on copper in the presence of oxygen and isobutene was studied at T = 770 K, under reducing conditions. Mass spectroscopy was used to identify gas-phase intermediates and reaction products. One... more
ABSTRACT The mechanism of NO reduction on copper in the presence of oxygen and isobutene was studied at T = 770 K, under reducing conditions. Mass spectroscopy was used to identify gas-phase intermediates and reaction products. One intermediate species resulting from the partial oxidation of isobutene was shown to be active in the NO conversion. X-ray photoelectron spectroscopy was used to analyze the copper surface at different stages of the reaction. Our conclusion is that oxygen first activates the surface, by forming coexisting phases of Cu2O and CuO. The copper surface is then reduced by the hydrocarbon, leading to Cu+ in majority, and to the formation of an active intermediate. At last, the reduction of NO proceeds rapidly on a zero-valent copper surface together with consumption of the previously formed intermediate. At the end of the reaction, the surface is poisoned by carbon.
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ABSTRACT The surface morphology and nucleation of molecular beam epitaxy-grown ‘infinite-layer’ structure, (Sr,Ca)CuO2 films on atomically flat SrTiO3 are studied by reflection high-energy electron diffraction (RHEED) and atomic force... more
ABSTRACT The surface morphology and nucleation of molecular beam epitaxy-grown ‘infinite-layer’ structure, (Sr,Ca)CuO2 films on atomically flat SrTiO3 are studied by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The SrTiO3 (100) surfaces were prepared by an ultra-high vacuum (UHV) annealing and displayed regular arrays of 0.4 nm steps spaced by atomically flat terraces of about 400 nm. The terraces exhibited smooth edges which were parallel to the [110] substrate direction. AFM images of only a two unit cell thick (0.66 nm) (Sr,Ca)CuO2 layers were recorded. Edge roughness of the substrate terraces was found to be affected by the growth process. Atomically flat (Sr,Ca)CuO2 islands with the vertical steps of multiple heights of one unit cell were identified. The obtained AFM and RHEED data strongly suggested the island to step-growth mode of ‘infinite-layer’, (Sr,Ca)CuO2 films grown on atomically smooth (100) SrTiO3 surfaces. Different surface morphology of thicker (Sr,Ca)CuO2 films grown with other nominal compositions were also investigated by AFM.
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The present investigation was carried out in order to study the efficacy of oral antibiotics (A) versus oral antibiotics plus acute myringotomy (B) in the treatment of early recurrences of acute purulent otitis media. Seventy-nine... more
The present investigation was carried out in order to study the efficacy of oral antibiotics (A) versus oral antibiotics plus acute myringotomy (B) in the treatment of early recurrences of acute purulent otitis media. Seventy-nine children with early recurrences (arisen within 4 weeks of a primary episode) were randomly allocated to one of the two treatment groups (A or B). Eleven of 41 (26.8%) children in group A, and 12/38 (31.6%) in group B had healed at 4 weeks (p greater than 0.1). Seventeen children of both groups had secretory otitis media at 4 weeks and new relapses had occurred in 13 children in group A and 9 in group B. No difference between the groups was noted regarding the number of otitis episodes during the next 5 months. Thus, acute myringotomy could not be proven to affect the clinical course of an early recurrence of acute purulent otitis media as compared with that after treatment with oral antibiotics alone.