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| 11. |
- Sandell, A., et al.
(author)
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Observation of a low-energy adsorbate core-level satellite for CO bonded to palladium : Coordination-dependent effects
- 1998
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In: Physical Review B (Condensed Matter). - 0163-1829. ; 57:20, s. 13199-13208
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Journal article (peer-reviewed)abstract
- A strong low-energy shake-up satellite for CO adsorbed on Pd is observed. The occurrence of the satellite is established for the CO/1 ML Pd/Mo(110) system at a coverage where CO adsorbs exclusively on-top. Comparisons with CO adsorbed on Pd single-crystal surfaces and small supported Pd particles indicate that the strongly increased satellite intensity is due to the decreased CO-Pd interaction strength for on-top adsorbed CO. This can be used to get further insight into the structure and bonding properties of the adsorbate system. Since a low-energy shake-up feature may be misinterpreted as a chemically shifted component, the conclusion is that great care has to be taken in the evaluation of adsorbate core-level spectra for systems with large variations in adsorption strength depending on the adsorbate sites. Large variations in the CO site distribution may furthermore occur depending on the nature of the Pd substrate: Adsorption of CO on 1 ML Pd/Mo(110) leads to an overlayer dominated by an on-top species and, likewise, the CO overlayer formed on small Pd particles after large doses has a large fraction of on-top bonded species. This is in strong contrast to Pd single-crystal surfaces, where CO adsorbed in more highly coordinated sites is abundant.
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| 12. |
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| 13. |
- Beutler, A., et al.
(author)
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Adsorption properties of a mixed surface studied by high resolution core level photoemission : CO/0.5 ML Pd/Rh(111)
- 1998
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In: Surface Science. - 0039-6028. ; 411:1-2, s. 111-122
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Journal article (peer-reviewed)abstract
- The coverage-dependent adsorption properties of a laterally heterogeneous bimetallic surface have been investigated by high resolution core level photoemission and low energy electron diffraction. The specific system under study was CO adsorbed on a Rh(111) surface onto which 2D Pd islands (coverage 0.5 ML) were formed by vapor deposition. The CO adsorption properties of the heterogeneous surface were compared with CO adsorption on a Rh(111) surface covered with a full Pd monolayer and with previous results for the CO/Rh(111) system. For low exposures CO is only found on the Rh(111) patches which can be explained by diffusion of CO from the Pd islands onto Rh parts in the adsorption process. At higher exposures CO diffusion from Rh to Pd is indicated. The origin of the diffusion processes can be found in the different coverage-dependent CO adsorption energies on the two surface parts.
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| 14. |
- Beutler, A., et al.
(author)
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Coverage- and temperature-dependent site occupancy of carbon monoxide on Rh(111) studied by high-resolution core-level photoemission
- 1998
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In: Surface Science. - 0039-6028. ; 396:1-3, s. 117-136
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Journal article (peer-reviewed)abstract
- High-resolution core-level photoemission is used to study structural aspects for the molecular adsorption of CO on the Rh(111) single-crystal surface, and in particular to derive the adsorption sites. The site sensitivity of the core-level binding energy and the fact that the core level photoemission signal is proportional to the adsorbate coverage make it possible to study quantitatively how the occupation of different sites changes with temperature and/or CO coverage. For the CO/Rh(111) adsorption system we find two sites (on-top and three-fold hollow) to be occupied by the CO molecules. At coverages up to 0.33 ML only on-top sites are occupied, whereas at higher coverages a mixture of three-fold hollow and on-top sites are found. The distribution between these two sites is found to depend strongly on temperature. Quantitative studies of these reversible, temperature-dependent site changes have been carried out for a number of CO coverages. For coverages between 0.33 and ∼0.54 ML, increasing the temperature results in part of the molecules moving from on-top to three-fold hollow sites. This change is strongest for a (4 × 4) structure formed at 0.5 ML where an order-disorder transition is observed at a temperature of 120 K. For coverages above ∼0.54 ML, increasing the temperature leads instead to a decrease of the relative occupation of the three-fold hollow sites. For coverages below 0.33 ML, the molecules occupy on-top sites at all temperatures.
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| 15. |
- Beutler, A., et al.
(author)
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The influence of preadsorbed oxygen on the adsorption of CO on two-dimensional Pd islands on a Rh (111) surface
- 1998
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In: Surface Science. - 0039-6028. ; 418:2, s. 457-465
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Journal article (peer-reviewed)abstract
- The influence of preadsorbed oxygen on the CO adsorption properties of a laterally heterogeneous bimetallic surface consisting of Pd islands on Rh(111) at a Pd coverage of 0.5 monolayers has been studied by high resolution core level photoemission. A surface consisting of clean Pd islands surrounded by oxygen-covered Rh(111) patches was prepared by predosing oxygen at room temperature. By applying core level photoemission to the Pd 3d5/2 and the C 1s levels, the adsorption of CO on this surface was studied with particular attention being paid to possible CO diffusion between the two surface parts. The CO molecules are found to diffuse from the oxygen-covered Rh(111) patches onto the Pd islands for low to medium CO exposures. This diffusion direction is opposite of that found previously for the 0.5 ML Pd on Rh(111) system with no oxygen predosing. This reversal of the diffusion direction is argued to be due to a large reduction of the CO adsorption energy on the Rh patches of the surface caused by the preadsorbed oxygen.
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| 16. |
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| 17. |
- Caidahl, Kenneth, 1949, et al.
(author)
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New concept in echocardiography: harmonic imaging of tissue without use of contrast agent.
- 1998
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In: Lancet (London, England). - : Elsevier BV. - 0140-6736. ; 352:9136, s. 1264-70
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Journal article (peer-reviewed)abstract
- Endocardial border detection is important for echocardiographic assessment of left-ventricular function. Second harmonic imaging of contrast agents enhances this border detection. We discovered that harmonic imaging improves tissue visualisation even before contrast injection. We therefore sought objectively to demonstrate the degree of enhancement of endocardial and myocardial visualisation.An ATL HDI-3000 scanner with software for contrast harmonic imaging was used to record short-axis images of the left ventricle in 27 patients with possible myocardial disease and 22 controls, in the fundamental mode and with harmonic imaging. A computer program measured the relative grey-scale values within six segments of the endocardium and myocardium. An Acuson Sequoia scanner equipped with software for tissue harmonic imaging was used to investigate the reproducibility of ejection-fraction calculations in 22 patients with ischaemic heart disease.Harmonic imaging produced brighter endocardium within each segment. Relative to the mean grey value of the total imaging sector, the values for harmonic and fundamental imaging were 171.5 vs 85.6% (p<0.0001) in end diastole and 194.1 vs 106.7% (p<0.0001) in end systole. Results for the myocardial segments were also significantly better for harmonic imaging. Structure enhancement of similar magnitude was seen among patients and healthy controls. Use of harmonic imaging reduced the proportion of unacceptable images by 14-46% in different views and improved the reproducibility of biplane ejection-fraction measurements.In comparison with fundamental imaging, the relative endocardial and myocardial brightness is enhanced by harmonic imaging.
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| 18. |
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| 19. |
- Jaworowski, A. J., et al.
(author)
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Adsorption sites in O and CO coadsorption phases on Rh(111) investigated by high-resolution core-level photoemission
- 1999
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In: Surface Science. - 0039-6028. ; 431:1, s. 33-41
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Journal article (peer-reviewed)abstract
- High-resolution core-level spectroscopy is used in combination with low-energy electron diffraction (LEED) and photoelectron diffraction to identify the adsorption sites for three different coadsorbed phases consisting of ordered overlayers of oxygen coadsorbed with CO on the Rh(111) single-crystal surface. The three ordered overlayer structures, which may be denoted as 2O + CO/Rh(111), O + CO/Rh(111) and O+2CO/Rh(111), all show (2 × 2) LEED patterns. In the 2O + CO and O + CO phases the CO molecules are found to occupy only on-top sites while the O + 2CO phase shows CO molecules in both on-top and three-fold hollow sites. In all cases the oxygen atoms are found in three-fold hollow sites. For the O + CO and O + 2CO phases our results confirm previous determinations by LEED, while the 2O + CO phase has not been observed before on Rh(111). The core-level binding energies of the C 1s and O 1s core levels for both adsorbates are characteristics of the adsorption site and are very close to the binding energies found for the pure cases of only oxygen or CO adsorbed on Rh(111). In the coadsorption phases we find that the interaction between the adsorbates has only a minor influence on the core-level binding energies. For the O + 2CO/Rh(111) coadsorption phase we find that a full CO coverage is not obtained; less than 80% of the unit cells contain two CO molecules, in line with previous findings.
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| 20. |
- Lundgren, E., et al.
(author)
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On the temperature induced transformation between the two Al(111)-(√3 × √3)R30°-Rb structures
- 1995
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In: Surface Science. - : Elsevier BV. - 0039-6028. ; 343:1-2, s. 37-43
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Journal article (peer-reviewed)abstract
- The dynamics of the temperature induced transformation between low and high temperature adsorption phases of Rb on Al(111) has been followed by high resolution core level spectroscopy. Particular emphasis has been paid to the order-preserving transformation between the low and high temperature Al(111)-Rb-(√3 × √3)R30° structures in which Rb atoms occupy on-top and substitutional sites, respectively. For a Rb coverage of 0.33 monolayer the rate of conversion from on-top ti substitutional sites is found to increase strongly at 250 K. For Rb coverages below 0.33 but above approximately 0.14 monolayers the conversion occurs at lower temperatures. Increasing the coverage above 0.33 monolayers increases the conversion temperature. The possibility to detect the Al atoms which are expelled from the first Al layer during the conversion is demonstrated.
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| 21. |
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| 22. |
- Strisland, F., et al.
(author)
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Adsorption sites in coadsorption systems determined by photoemission spectroscopy : K and CO coadsorbed on Rh(111)
- 1998
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In: Surface Science. - 0039-6028. ; 410:2-3, s. 330-343
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Journal article (peer-reviewed)abstract
- The adsorption sites of coadsorbed K and CO on the Rh(111) surface have been determined using high-resolution core-level spectroscopy, low-energy electron diffraction and site-resolved photoelectron diffraction. For both a (2 × 2)-2CO-1K and a (2√3 × 2√3)-6CO-1K structure, we find that the CO molecules occupy threefold hollow sites and the K atoms on-top sites, contrary to the adsorption sites of K (threefold hollow site) and CO (on-top site below 0.5 monolayers) if adsorbed alone on Rh(111). Deposition of K onto a CO precovered surface is found to induce large shifts towards lower binding energy of the C and O 1s core levels (∼0.7 eV for C 1s and ∼1.5 eV for O 1s). The major part of these shifts is shown to arise from the K-induced site change of the CO molecules. This finding may be of importance in the interpretation of XPS data of related co-adsorption systems. Finally, it is suggested that the C and O 1s binding energies provide useful fingerprints of the CO adsorption site also for co-adsorption systems.
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| 23. |
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| 25. |
- Andersen, J. N., et al.
(author)
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Vibrational fine structure in the C 1s core level photoemission of chemisorbed molecules : Ethylene and ethylidyne on Rh(111)
- 1997
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In: Chemical Physics Letters. - 0009-2614. ; 269:3-4, s. 371-377
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Journal article (peer-reviewed)abstract
- The origin of fine structure in the core-level photoemission spectra of the C2H4, C2D4, C2H3 and C2D3 molecules chemisorbed on Rh(111) is probed in a careful high-resolution study showing that this structure arises from internal molecular vibrations rather than from other chemically-shifted carbon atoms. It is shown by comparison of the adsorbate and gas-phase spectra that the underlying features are the same despite differences arising from adsorption. This new approach to the investigation of adsorbed molecules may prove to be useful in further studies of other systems and the possibility that such effects may exist could lead to the reinterpretation of other adsorbate systems.
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| 26. |
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| 27. |
- Andersson, C B M, et al.
(author)
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Bulk and surface electronic structure of InAs(110)
- 1998
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In: Surface Science. - 0039-6028 .- 1879-2758. ; 398:3, s. 395-
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Journal article (peer-reviewed)abstract
- The InAs(110) cleavage surface has been investigated by angle-resolved photoelectron spectroscopy. A separation between the In 4d(5/2) bulk component and the valence band maximum of 16.8 eV is found to be consistent with normal emission spectra. Experimental energy band dispersions, E-i(k), for the four bulk valence bands are established along the Sigma-line of the bulk Brillouin zone. A bulk band structure calculation utilizing the augmented plane-wave method is made. The experimental and calculated E-i(k) dispersions are found to be in good agreement with each other. E-i(k(parallel to)) dispersions for two surface-related structures are established along the lines <(Gamma)over bar>-(M) over bar and (Y) over bar-(M) over bar of the surface Brillouin zone. (C) 1998 Elsevier Science B.V.
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| 28. |
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| 29. |
- Beutler, A., et al.
(author)
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On the adsorption sites for CO on the Rh(111) single crystal surface
- 1997
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In: Surface Science. - 0039-6028. ; 371:2-3, s. 381-389
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Journal article (peer-reviewed)abstract
- High resolution photoemission applied to the C 1s and Rh 3d core levels has been used to investigate the adsorption sites at low temperature of CO on the Rh(111) single crystal surface as a function of CO coverage. Two different sites are found to be occupied by the CO molecules. At coverages up to 0.5 monolayers the majority of the molecules are found to adsorb in on-top sites whereas at higher coverages three-fold hollow sites become increasingly populated. The different C 1s binding energy of the CO molecules in these two sites makes it possible to measure diffraction induced intensity variations versus photon energy in a site specific manner. The saturation (2 x 2)-3CO structure formed at a coverage of 0.75 monolayers is argued to contain one on-top and two three-fold hollow molecules per unit cell.
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| 30. |
- Bille-Brahe, U, et al.
(author)
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The WHO-EURO Multicentre Study : risk of parasuicide and the comparability of the areas under study.
- 1996
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In: Crisis. - 0227-5910 .- 2151-2396. ; 17:1, s. 32-42
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Journal article (peer-reviewed)abstract
- The 15 areas under study in the WHO/Euro Multicentre Study on Parasuicide vary considerably with regard to socio-economic factors, culture, life-styles, etc. In this paper, the authors discuss whether the traditional high risk factors for suicidal behavior (such as unemployment, abuse, divorce, etc.) take on different weights depending on local societal and cultural settings. Results from analyzing covariations between various background factors characteristic of the different areas under study and the frequency of attempted suicide showed weak or insignificant correlations, indicating that high-risk factors can only be identified from international pooled data with great care.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
- Heskett, D., et al.
(author)
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Core-level satellite excitations of K/Al(100) and K/Al(111)
- 1995
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In: Physical Review B (Condensed Matter). - 0163-1829. ; 52:16, s. 12366-12371
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Journal article (peer-reviewed)abstract
- Alkali-metal-induced satellite peaks associated with the K 3p and Al 2p core levels have been measured with photoemission for K/Al(111) and K/Al(100) under both low- and room-temperature preparation conditions. For low-temperature deposition we observedddd loss peaks in good agreement with electron-energy-loss spectroscopy studies of analogous systems which we assign to the excitation of collective plasmonlike modes in the alkali-metal overlayer. For room-temperature preparation conditions, we observed significant changes in the satellite loss structure which we attribute to a decrease or loss of metallic behavior in the alkali-metal layer. We account for some of our results as a change in bonding configuration of the K atoms from on-top-of surface to substitutional adsorption for low versus room-temperature preparations.
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| 37. |
- Hillerdal, Gunnar, et al.
(author)
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Pleural disease during treatment with bromocriptine in patients previously exposed to asbestos
- 1997
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In: European Respiratory Journal. - : European Respiratory Society (ERS). - 0903-1936 .- 1399-3003. ; 10:12, s. 2711-2715
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Journal article (peer-reviewed)abstract
- Bromocriptine, which is used in the treatment of Parkinson's disease, can cause adverse pleuropulmonary reactions. Exposure to asbestos can result in similar lesions. Fifteen patients with former exposure to asbestos, who developed pleural fibrosis after treatment with bromocriptine, were observed independently in Sweden (11 patients) and Australia (four patients). The patients complained of malaise, often associated with weight loss, dyspnoea, and a disturbing cough. Laboratory values included increased erythrocyte sedimentation rate and a low haemoglobin level. Lung function tests showed a restrictive lung function defect. Chest radiographs showed bilateral pleural fibrosis, with small amounts of fluid in some cases. Soon after bromocriptine was withdrawn, the patients improved clinically, and the laboratory values returned to normal. However, in most cases, pleural fibrosis and a restrictive lung function defect persisted to some extent. In conclusion, in patients who develop pleuropulmonary fibrosis whilst being treated with bromocriptine, former exposure to asbestos should be investigated. Conversely, when pleural changes develop in a patient on bromocriptine and with prior exposure to asbestos, the possible causative role of the drug should be discussed. Special follow-up may be indicated when bromocriptine is planned in a patient with previous asbestos exposure, and if symptoms or signs of pleural fibrosis develop, bromocriptine withdrawal should be considered.
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| 38. |
- Kall, M., et al.
(author)
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Resonance Raman scattering as a probe of oxygen dynamics in YBa2Cu3Ox
- 1998
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In: Journal of Physics and Chemistry of Solids. - 0022-3697 .- 1879-2553. ; 59, s. 1988-1990
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Journal article (peer-reviewed)abstract
- We report on the metastable photo-bleaching of the 2.15 eV yellow Raman resonance in oxygen deficient YBa2Cu3Ox (x = 6.35-6.87), extending investigations by Wake ct al. (Phys. Rev. Lett., 1991,67, 3728) for x approximate to 7. Polarization, x dependence and phonon spectra indicate that the resonance is localized at oxygen vacancies in long CuO-chains. The resonance is thermally reactivated from the metastable bleached state with a relaxation time tau similar to exp[Delta/k(B)T] with Delta approximate to 1 eV. The resulting temperature dependent equilibrium resonance intensity essentially miners the oxygen superstructure disordering around T* approximate to 100 degrees C observed in the same crystals by hard X-ray diffraction, thus offering a new effective probe of chain-oxygen dynamics in YBa2Cu3Ox. (C) 1998 Elsevier Science Ltd. All rights reserved.
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| 39. |
- Krogh Andersen, A.M., et al.
(author)
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Preparation and Characterization of a New 3-Dimensional Zirconium Hydrogen Phosphate, τ-Zr(HPO4)2; Determination of the Complete Crystal Structure Combining Synchrotron X-ray Single Crystal Diffraction and Neutron Powder Diffraction.
- 1998
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In: Inorganic chemistry. - : American Chemical Society. - 1520-510X .- 0020-1669. ; 37:5, s. 876-881
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Journal article (peer-reviewed)abstract
- A new 3-dimensional zirconium hydrogen phosphate, τ-Zr(HPO4)2, was prepared by hydrothermal syntheses. The preparation, characterization, and determination of the crystal structure of this new material are reported. The structure was solved from single-crystal synchrotron diffraction on a 25 × 25 × 50 μm crystal. The position of the hydrogen atom was found using high-resolution neutron powder diffraction data. The unit cell is tetragonal, space group I41cd (No. 110), with lattice parameters a = 11.259(1) Å, c = 10.764(1) Å, and Z = 8. The structure can be described as a 3-dimensional framework built from ZrO6 octahedra bound together by hydrogen phosphate groups (PO3(OH)). The OH groups form a hydrogen-bonded spiral along the 41 axes, with each hydrogen phosphate both donating and accepting hydrogen bonds. The thermal transformations of τ-Zr(HPO4)2 were studied using in-situ temperature-resolved powder diffraction experiments. Hereby the existence of two new phases was discovered. The new phases have been indexed and the unit cell parameters are as follows. Intermediate I: a = 8.172(1), b = 7.691(1), and c = 10.794(2) Å. Intermediate II: a = 8.283(2), b = 6.620(2), and c = 10.643(2) Å.
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| 40. |
- Lundgren, E., et al.
(author)
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Na and K on Al(100) studied by low-energy electron diffraction and high-resolution core-level spectroscopy
- 1997
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In: Surface Science. - 0039-6028. ; 370:2-3, s. 311-323
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Journal article (peer-reviewed)abstract
- Experimental results for Na and K deposited at 100 K on the A1(100) surface using low-energy electron diffraction and high-resolution core-level spectroscopy are presented. Our results show that from a coverage of 0.20 monolayers (ML), Na condenses into dense islands with a local Na coverage of 0.50 ML. In the case of K, the overlayer condenses into islands at a coverage of 0.18 ML, with a local coverage of 0.30 ML. A compilation of various geometric parameters of the present systems and of alkalis on Al(111) suggests that the condensation of K on Al(100) differs from that of other alkalis on Al systems which undergo condensation into two-dimensional islands. Furthermore, all the island-forming structures display an alkali-alkali distance which is expanded relative to the nearest-neighbour distance in the respective alkali metal. The reasons for and implications of this are discussed.
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| 41. |
- Lundgren, E., et al.
(author)
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Unified behavior of alkali core-level binding-energy shifts induced by sp metals
- 1997
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In: Physical Review B (Condensed Matter). - 0163-1829. ; 56:19, s. 12560-12565
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Journal article (peer-reviewed)abstract
- Thin overlayers of Na, K. Rb, and Cs on different sp-metal substrates have been investigated using photo-electron spectroscopy. The alkali core levels show clearly resolved binding-energy shifts between the surface layer, the intermediate layer(s), and the interface layer. The magnitude of these shifts depends on sp metal and on alkali metal. The layer-resolved core-level binding-energy shifts are well reproduced by models based on a thermodynamical description. For three-layer alkali films the core-level binding energy of the intermediate layer is found to exhibit a small but significant shift between different sp-metal substrates. A simple relationship between the core-level binding-energy shift for the interface layer and the difference in rs value between the sp substrate and the adsorbate is shown to exist.
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| 42. |
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| 43. |
- Nylén, H., et al.
(author)
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O KVV Auger emission versus resonant photoemission at the O K edge of high-Tc superconductors
- 1998
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In: Physica C: Superconductivity and its Applications. - 0921-4534. ; 300:3-4, s. 161-170
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Journal article (peer-reviewed)abstract
- Photoelectron spectroscopy results on single crystals of the superconductors Bi2Sr2CaCu2O8,Bi2Sr 2CuO6, Ba0.6K0.4BiO3 and the semiconductor Ba0.9K0.1BiO3 are reported for the photon energy region around the O K absorption threshold. The development of the O-KVV Auger structure has been carefully monitored as a function of photon energy. A non-monotonic behavior displaying a feature at a constant binding energy of about 14 eV was found for Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 in a narrow photon energy region of 1 eV at the main edge of the O K absorption spectrum around 530 eV. The corresponding enhancement, connected with the autoionization of O 2 p states, is absent in Ba1-xKxBiO3 in contrast to Bi2Sr2CaCu2O8 and Bi2Sr2CuO6. The resonant enhancement is more pronounced for Bi2Sr2CuO6 as compared to Bi2Sr2CaCu2O8, which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2 p states. The model parameters Cu d-d and O p-p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments.
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| 44. |
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| 45. |
- Qvarford, M, et al.
(author)
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Doping dependence of the O 1s is core-level photoemission in bi-Sr-Ca-Cu-O superconductors
- 1996
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:22, s. 14753-14756
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Journal article (peer-reviewed)abstract
- The O 1s core level of three different Bi-Sr-Ca-Cu-O superconductors has been studied by means of high-resolution x-ray-photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). The O 1a XPS spectra could be decomposed into three components that were unambiguously assigned to the emission from the three different oxide layers in the crystal structure. These are, in order of increasing binding energy, Cu-O-2, Sr-O, and Bi-O. Furthermore, the component assigned to the Cu-O-2 layers exhibits a shift which depends on the hole doping as monitored by the XAS spectra.
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| 46. |
- Qvarford, M, et al.
(author)
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Photoemission and x-ray absorption study of superconducting and semiconducting Ba1-xKxBiO3 single crystals
- 1996
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:9, s. 6700-6707
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Journal article (peer-reviewed)abstract
- Semiconducting Ba0.9K0.1BiO3 and superconducting Ba0.6K0.4BiO3 single crystals cleaved in situ have been studied by core level and valence band photoelectron spectroscopy and O K edge x-ray absorption spectroscopy. It was found that the general shape of the valence band spectrum agrees with the shape predicted by band structure calculations, but the intensity near the Fermi level, was lower in the experimental spectrum as compared to the calculated. The O K edge spectra showed that the metallic phase is not related to the presence of doping inducted O 2p holes. This property of Ba1-xKxBiO3 shows that the semiconductor-metal transition of this system is of a different nature than that of the hole doped cuprate high-T-c superconductors. The core level photoemission spectra of the cations showed a small asymmetry for Ba0.9K0.1BiO3. Corresponding spectra for Ba0.6K0.4BiO3 showed a larger asymmetry resulting in a resolved high binding energy shoulder in the Bi 4f spectrum. The origin of this feature is discussed.
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| 47. |
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| 48. |
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| 49. |
- Sandell, A., et al.
(author)
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Adsorption of acetylene and hydrogen on Pd(111) : Formation of a well-ordered ethylidyne overlayer
- 1998
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In: Surface Science. - 0039-6028. ; 415:3, s. 411-422
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Journal article (peer-reviewed)abstract
- The C2H2(+H)/Pd(111) system has been studied using high resolution core level spectroscopy and low energy electron diffraction (LEED). Two ordered phases were found when adsorbing C2H2 at 125 K, giving rise to a (2 × 2) and a (√3 × √3)R30° LEED pattern, respectively. When preadsorbing H at 110-150 K, the sticking probability of the C2H2 molecules is strongly reduced and only the (√3 × √3)R30° overlayer is formed. In all three of the ordered structures the C2H2 molecules are suggested to occupy the hollow sites. Heating of the (√3 × √3)R30° C2H2 + H layer to 350 K yields a well ordered (√3 × √3)R30° overlayer consisting exclusively of ethylidyne (CCH3) positioned in the hollow sites. The formation of ethylidyne is furthermore found to be preceded by the formation of an intermediate species ("β") which probably is vinylidene.
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| 50. |
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