| 1. |
- Karlsson, H S, et al.
(författare)
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Electron accumulation at the InAs(110) cleavage surface
- 1998
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 402:1-3, s. 590-594
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Tidskriftsartikel (refereegranskat)abstract
- The InAs(110) cleavage surface is studied by photoelectron spectroscopy based on an amplified short-pulse titanium:sapphire laser system in both probe-only and pump-and-probe modes. The probe-only spectra show that electrons accumulate in the conduction band at the surface as a function of time after cleavage, while the pump-and-probe spectra show a different response from the excited accumulation layer peak when using s- and p-polarized probe pulses. Moreover, no surface photovoltage is detected when the accumulation layer is optically pumped. (C) 1998 Elsevier Science B.V. All rights reserved.
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| 2. |
- Karlsson, H S, et al.
(författare)
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Electron dynamics and accumulation on the InAs(110) surface
- 1998
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 407:1-3, s. L687-L692
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Tidskriftsartikel (refereegranskat)abstract
- Time- and angle-resolved pump-and-probe photoelectron spectroscopy has been used to study the electron dynamics on the InAs(110) surface. Two states, separated by similar to 0.2 eV, can be identified in the conduction band. The time evolution and energy location of these states suggest that they originate from transiently excited levels related to the InAs bulk conduction band. (C) 1998 Elsevier Science B.V. All rights reserved.
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| 3. |
- Karlsson, H S, et al.
(författare)
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System for time- and angle-resolved photoelectron spectroscopy based on an amplified femtosecond titanium:sapphire laser system
- 1996
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 67:10, s. 3610-3615
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Tidskriftsartikel (refereegranskat)abstract
- A system for time- and angle-resolved photoelectron spectroscopy based on an amplified femtosecond titanium:sapphire laser system is described. Using this type of system, angle-resolved photoemission is extended to include the possibility of following the time development of excited electrons at and near a solid surface. Time resolution is accomplished by using pump-and-probe technique and the photoemitted electrons are energy analyzed in a time-of-fight detector. In order to perform photoemission, the near-infrared light from the titanium:sapphire laser is frequency up-converted to the vacuum ultraviolet range. This is accomplished by using the high peak power pulses from the laser system to produce short-wavelength radiation by means of harmonic generation. The system described uses cascaded frequency doubling and tripling, reaching a photon energy close to 10 eV. (C) 1996 American Institute of Physics.
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| 4. |
- Andersson, C B M, et al.
(författare)
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Bulk and surface electronic structure of InAs(110)
- 1998
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 398:3, s. 395-
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Tidskriftsartikel (refereegranskat)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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| 5. |
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| 6. |
- Andersson, C B M, et al.
(författare)
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Surface atomic structure of InAs((111)over-bar)2x2 and InSb((111)over-bar)2x2 studied by core level spectroscopy
- 1996
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 347:1-2, s. 199-206
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Tidskriftsartikel (refereegranskat)abstract
- Surface sensitive high resolution core level spectroscopy has been applied to the molecular beam epitaxy grown InAs((111) over bar)2 x 2 and InSb((111) over bar)2 x 2 surfaces. For both systems the In 4d core level consists of one dominating component while the Group V core levels are deconvoluted into four components. This analysis is consistent with a surface model where the topmost layer consists entirely of arsenic or antimony. In this model, Group V atoms form trimers bound to Group V atoms in the first double layer, leaving a single Group V rest atom per unit cell.
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| 7. |
- Bjorkqvist, M, et al.
(författare)
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NH3 on Si(111)7x7 : Dissociation and surface reactions
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:4, s. 2327-2333
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Tidskriftsartikel (refereegranskat)abstract
- Core-level and valence-band photoelectron spectroscopy on the dissociative adsorption of ammonia on Si(111) 7 X 7 is presented. Adsorption at room temperature produces three nitrogen 1s components, of which two are assigned to NH2 and one to NH, with an initial tendency for double dissociation. These doubly dissociated species can be connected to the development of silicon atoms coordinated with two nitrogen atoms, necessitating silicon-silicon bonds to be broken. The dominating picture evolving is thus adatoms saturated by NH2 with a NH group inserted into one backbond, and hydrogen preferentially capping restatoms. The dissociation proces is hence much more complex than generally proposed before. This is further accentuated by the fact that not all adatoms appear reacted. When annealed above 600 K the dissociation process progresses and atomic nitrogen appears at 700 K, to be the only remaining specie at 850 K. At 1200 K, further changes in the N 1s core level indicates true silicon nitride formation.
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| 8. |
- Bjorkqvist, M, et al.
(författare)
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Nitride formation and dangling-bond passivation on Si(111)-(7x7) with NH3
- 1997
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 394:1-3, s. L155-L161
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Tidskriftsartikel (refereegranskat)abstract
- Thermal nitridation of the Si(111)-(7 x 7) reconstructed surface with ammonia has been investigated using scanning tunneling microscopy (STM). True nitride formation in the form of ring-like structures as in stoichiometric silicon nitride (Si3N4) was observed at imperfections on the surface, which otherwise preserved the characteristics of the (7 x 7) reconstruction. However, the ratio of reacted adatoms in the reconstruction never exceeded similar to 50%, indicative of a frustrated saturation behavior for the adatom dangling bonds in the Si(111)-(7 x 7)-NH3 reaction system. (C) 1997 Elsevier Science B.V.
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| 9. |
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| 10. |
- Dimberg, Ulf, et al.
(författare)
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Facial reactions to different emotionally relevant stimuli
- 1997
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Ingår i: SCANDINAVIAN JOURNAL OF PSYCHOLOGY. - : SCANDINAVIAN UNIVERSITY PRESS. - 0036-5564. ; 38:4, s. 297-303
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Tidskriftsartikel (refereegranskat)abstract
- Facial EMG activity was measured from the Corrugator supercilii and the Zygomatic major muscle regions while 48 subjects were exposed to pictures of angry and happy facial expressions, snakes and flowers as well as low and high preference nature scenes.
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| 11. |
- Fergedal, May, et al.
(författare)
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Differences in CD14 and alpha-naphthyl acetate esterase positivity and relation to prognosis in AML
- 1998
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Ingår i: Leukemia Research. - Oxford, United Kingdom : Elsevier. - 0145-2126 .- 1873-5835. ; 22:1, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- Alpha-naphthyl acetate esterase (ANAE) and CD14 expression, used for determination of monocytic cells, were compared and related to prognosis in 65 AML patients. Bone marrow aspiration material from AML patients has been used for the cytochemistry as well as flow cytometry. All non-erythroid cells have been included in the evaluation in both methods. 17/65 cases showed at least 15% difference between the proportion CD14 and ANAE positive cells. Cases with 20% or more CD14 positivity had poorer prognosis. For FAB classes M0-M3, presence of 10% or more CD14 was negative for overall survival (P = 0.01). ANAE did not show significant prognostic influence.
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| 12. |
- Gebre, Negussie, et al.
(författare)
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Improved microscopical diagnosis of pulmonary tuberculosis in developing countries
- 1995
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Ingår i: Transactions of the Royal Society of Tropical Medicine and Hygiene. - : Oxford University Press (OUP). - 1878-3503 .- 0035-9203. ; 89:2, s. 191-193
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Tidskriftsartikel (refereegranskat)abstract
- The diagnosis of pulmonary tuberculosis (TB) relies on the bacteriological examination of sputum. However, microscopy of smears made directly from sputum has a low sensitivity and there is an urgent need for improved methods. We have compared microscopy of smears made directly from sputum with microscopy after liquefaction of sputum with household bleach (NaOCl) and concentration of bacteria by centrifugation. In 3 studies performed in Ethiopia and India, the use of the NaOCl method increased the number of samples positive for acid-fast bacilli by more than 100%. The technique is appropriate for developing countries and its application would increase the efficiency of TB control programmes. As a potent disinfectant, NaOCl also has the advantage of lowering the risk of laboratory infection.
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| 13. |
- Girard, R T, et al.
(författare)
-
Electronic structure of ZnO(0001) studied by angle-resolved photoelectron spectroscopy
- 1997
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 373:2-3, s. 409-417
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the ZnO(0001) surface was studied by angle-resolved photoelectron spectroscopy. The recorded normal emission spectra give information about the Valence band states as well as the Zn 3d states. The dispersions of the four valence bands observed in the (0001) direction were compared with theory and are in good agreement with recent calculations which consider the Zn 3d electrons as part of the valence band. The Zn 3d states are seen to separate into two groups of four and six bands, which show dispersion with k(perpendicular to). This is in agreement with theoretical results but the location of these states were not accurately predicted. The present photoemission results show that they lie around 10.5 eV below E(F). Two surface states were observed on the (0001) surface. One, at 7.5 eV binding energy, was predicted by theory and is interpreted as arising from the ''back-bondings'' of the Zn 4s-O 2p mixed bulk states. The other one at 4.5 eV below E(F), most likely Zn 4p-0 2p derived, was not predicted by theoretical calculations and this is discussed further in the text. (C) 1997 Elsevier Science B.V.
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| 14. |
- GOTHELID, M, et al.
(författare)
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ADSORPTION OF TIN ON THE GE(111)-C(2X8) SURFACE STUDIED WITH SCANNING-TUNNELING-MICROSCOPY AND PHOTOELECTRON-SPECTROSCOPY
- 1995
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 328:1-2, s. 80-94
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Tidskriftsartikel (refereegranskat)abstract
- The growth and epitaxy of Sn on Ge(111) have been investigated using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and core level photoelectron spectroscopy for coverages ranging from 0.4 monolayers (ML) to above the critical coverage at 1.6 ML. At the lowest coverage a (root 3 X root 3)R30 degrees reconstruction is formed at an annealing temperature of 250-300 degrees C while an annealing above 500 degrees C creates a dimer-adatom-stacking fault (DAS) (7 X 7) structure. In the (7 X 7) structure we argue that Sn occupies both adatom and dimer sites. A previously suggested difference in the (root 3 X root 3)R30 degrees reconstruction at different coverages could not be revealed in our STM images and it seems likely that the structure is the same both at 0.4 and 0.7 ML Sn coverage. We also report the observation of a new superstructure, a (4 X root 7) reconstruction in the submonolayer regime, which appears as a minority structure in disordered regions adjacent to a (5 X 5) DAS structure, Finally in the post-monolayer region a (3 X 2 root 3) structure, surrounded by vast areas of an amorphous tin overlayer, has been imaged by STM. As the coverage was increased, the amorphous layer completely covered the ordered (3 X 2 root 3) phase, which still could be observed in LEED. Additional room temperature deposition of Sn deteriorated the fractional order LEED spots presumably due to indiffusion of Sn from the interface as the critical coverage was surpassed.
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| 15. |
- Gothelid, M, et al.
(författare)
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Etching and a disordered overlayer on the Ge(100)-S surface
- 1997
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 115:1, s. 87-95
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Tidskriftsartikel (refereegranskat)abstract
- High resolution core level photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) have been used to study the adsorption and desorption of S on and off the Ge(100) surface. The previously proposed bridge adsorption site of S is consistent with our results at low coverage. At saturation the substrate contains several GeSx species, with x = 0.5 to 4. Both photoemission and STM reveals a non-ideal surface, with a saturation coverage above one monolayer. Furthermore, S is found to etch the substrate. The reaction products forms a disordered overlayer on top of the interface. This overlayer is transparent in the filled state STM images.
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| 16. |
- Gothelid, M, et al.
(författare)
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Ge/(111)3x1:K/Sn; On the influence of tin substitution in a metal induced 3x1 reconstruction
- 1996
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 104, s. 113-117
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Tidskriftsartikel (refereegranskat)abstract
- Go-adsorption of tin and potassium is found to induce a 3x1 reconstruction on the Ge(lll) surface. A very small amount of tin influences the Ge 3d core level spectra substantially compared to the Ge(111)3x1:K reconstruction. This is interpreted as resulting from a relaxation of the strain in the rows Ge atoms running along the surface, as proposed for this structure.
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| 17. |
- Gothelid, M, et al.
(författare)
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Iodine reaction and passivation of the Ge(111) surface
- 1997
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 371:2-3, s. 264-276
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Tidskriftsartikel (refereegranskat)abstract
- The Ge(111)-I surface has been studied at different I coverages ranging from 0.05 hit up to saturation, and different annealing temperatures, using photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). At saturation the surface is covered with I in the top site and Gel, species in the bridge site, coexisting with small islands/clusters comprising GeI2, giving a total coverage of I in GeIx species of 1.15 ML. The chemically induced shifts in the Ge 3d core level are 0.39 eV per attached I atom. The coverage determined from the I 4d core level is higher than 1.15 ML, which we explain by the presence of I not bound to Ge. Annealing at 200 degrees C decreases the iodine coverage, whereas the I 4d and Ge 3d line profiles are practically unchanged. Further heating desorbs the iodide species and restores the virgin c(2 x 8) structure.
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| 18. |
- GOTHELID, M, et al.
(författare)
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METAL-SEMICONDUCTOR FLUCTUATION IN THE SN ADATOMS IN THE SI(111)-SN AND GE(111)-SN (ROOT-3X-ROOT-3)R30-DEGREES RECONSTRUCTIONS
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:20, s. 14352-14355
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Tidskriftsartikel (refereegranskat)abstract
- The two components of the Sn 4d core level in the Si(111)-Sn and Ge(111)-Sn. (root 3 X root 3)R30 degrees structures are proposed to arise from semiconductor-metal fluctuations in the Sn adatom layer. Adsorption of potassium on the Si(111)-Sn (root 3 X root 3)R30 degrees surface suppresses the metallic component and shifts the tin into a purely semiconducting phase with a filled dangling bond state.
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| 19. |
- GOTHELID, M, et al.
(författare)
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STRUCTURAL AND ELECTRONIC EVOLUTION ON THE GE(111)-AG SURFACE
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:19, s. 14104-14110
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution core-level photoelectron spectroscopy has been used to study three different silver induced surface reconstructions on the Ge(111) surface. At the lowest coverage a (4 X 4) structure is formed, which displays a similar Ge 3d core-level line shape as the clean c(2 X 8) surface. Details in the spectra are discussed with respect to possible models. The Ge(111)-Ag (root 3 X root 3)R30 degrees structure Ge 3d spectrum is dominated by a very strong contribution assigned to the two topmost Ge layers in a missing top layer structure, similar to the Si(111)-Ag (root 3 X root 3)R30 degrees surface. A weak bulk peak is present on the high-binding-energy side of the spectrum, while a third contribution assigned to Ge in phase boundaries is included in the fit on the lower-binding-energy side. A comparison with results obtained from the Ge(111)-Au root 3 structure points to substantial differences between the two noble-metal-induced root 3 reconstructions on the Ge(111) surface. Finally, after further deposition of silver at room temperature, the root 3 geometry is locally broken creating a (6 X 6) structure and a new surface-related peak emerges on the low-binding-energy side of the Ge 3d spectrum, which was interpreted as being due to Ge atoms floating on top of the outermost surface layer. The valence band also revealed the existence of small metallic silver islands.
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| 20. |
- GREHK, TM, et al.
(författare)
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CLEAN AND CS-EXPOSED SI(111)ROOT-3X-ROOT-3-B SURFACE STUDIED WITH HIGH-RESOLUTION PHOTOEMISSION
- 1995
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 52:15, s. 11165-11171
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Tidskriftsartikel (refereegranskat)abstract
- Both the clean and Cs-exposed Si(111)root 3X root 3R30 degrees:B surfaces have been investigated by high-resolution photoemission. In the spectra from the Si 2p level, contributions were identified from the bulk, the adatoms plus the first layer, the second and 2/3 ML of the third-layer atoms not binding to the B atoms, and, finally, the 1/3 ML of third-layer atoms binding to the boron atoms. The interaction between the Cs atoms and the surface is found to be dependent on the coverage. At low coverages the geometric and electronic structure of the Si(111)root 3X root 3R30 degrees:B interface is only to a minor degree affected by the presence of Cs on the surface. At high coverage the Cs atoms react with the surface and alter the binding configuration of the Si adatoms.
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| 21. |
- Hakansson, M C, et al.
(författare)
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The electronic structure of In- and As-terminated InAs(001) surfaces
- 1997
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 374:1-3, s. 73-79
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Tidskriftsartikel (refereegranskat)abstract
- The InAs(001) 2 x 4 and 4 x 2 surfaces have been investigated by angle-resolved photoemission. The X(3) and X(5) points were found to be located 6.0 and 2.7 eV below the valence band maximum, respectively, and the dispersion of bulk bands along the Gamma-X direction in the bulk Brillouin zone were well described by a theoretical calculation. From angle-resolved valence band spectra measured along the high symmetry directions [110] and [1(1) over bar0$], three surface induced stares were identified on both the InAs(001)4 x 2 and the InAs(001)2 x 4 surface. (C) 1997 Elsevier Science B.V.
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| 22. |
- HAKANSSON, MC, et al.
(författare)
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PHOTOEMISSION-STUDY OF THE BAND-GAP ON CESIATED GE(111)1X1-AS
- 1995
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 52:16, s. 11646-11649
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Tidskriftsartikel (refereegranskat)abstract
- Deposition of small amounts of cesium on the As-terminated Ge(111) surface results in population of the lowest unoccupied surface state centered around the Gamma point in the surface Brillouin zone. By using angle-resolved photoemission we have directly determined the gap between this state and the lone-pair surface state to be 0.85 eV. This result provides support for recent quasiparticle band-structure calculations.
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| 23. |
- Hammarström, Ulf, et al.
(författare)
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EMV - a PC program for calculating exhaust emissions from road traffic : program description and user guide
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A PC program named EMV has been developed for describing total exhaust emissions from road traffic on a national or regional level. The model is used by the Swedish Environmental Protection Agency and the Swedish National Road Administration for reporting and monitoring total exhaust emissions from road traffic. The program is specially designed to evaluate changes relating to traffic, the vehicle fleet and use of different fuel types and fuel qualities.
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| 24. |
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| 25. |
- He, Z Q, et al.
(författare)
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As overlayer on GaAs(110) studied with photoemission
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:23, s. 16602-16607
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Tidskriftsartikel (refereegranskat)abstract
- As-terminated GaAs(110) surfaces were prepared on ex situ cleaved substrates by molecular-beam epitaxy. The surface stoichiometry was controlled by postgrowth As deposition. Photoemission from a surface covered with a monolayer As was investigated in detail using synchrotron radiation. Two different surface components were found in core-level spectra, which are interpreted as due to adatoms bonding to the surface anions and cations. In the valence-band spectra several surface states were identified, in analogy with previous reports on the isoelectronic Sb/GaAs(110) system. The polarization dependence is not the same, however, which leads us to the conclusion that the adlayer bonding mechanisms are different in the two cases.
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| 26. |
- He, Z Q, et al.
(författare)
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Band structure evolution in InAs overlayers on GaAs(110)
- 1996
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 104, s. 608-614
-
Tidskriftsartikel (refereegranskat)abstract
- An angle-resolved photoemission study of MBE grown InAs/GaAs(110) hetero-structures was carried out to investigate the establishment of valence bands as a function of overlayer thickness. The valence band spectra were found to change gradually up to thicknesses well above 10 nm. The data are interpreted in terms of excitations within the overlayer from a combination of substrate and overlayer initial states, the former tailing into the overlayer.
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| 27. |
- Hirschauer, B, et al.
(författare)
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CeO2 on Si(111) 7 X 7 and Si(111)-H 1 X 1, an interface study by high-resolution photoelectron spectroscopy
- 1999
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 148:3-4, s. 164-170
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Tidskriftsartikel (refereegranskat)abstract
- The formation of the CeO2-Si(111) interface was studied by high-resolution photoelectron spectroscopy. It is shown that CeO2 and Si(111) forms a highly reactive: interface with a strong interdiffusion of Si into the CeO2. A passive silicon surface formed by saturating the Si dangling bonds with hydrogen is considerably less reactive. Defects on the surface, however, act as nucleations centres for reactions of a Si:Ce:O matrix. Oxygen leaves the surface at about 800 degrees C and at 1000 degrees C a surface reconstruction of Si(111)-Ce 2 X 2/root 3 X root 3 is formed. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 28. |
- Hirschauer, B, et al.
(författare)
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Highly oriented alpha-alumina films grown by pulsed laser deposition
- 1997
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 305:1-2, s. 243-247
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Tidskriftsartikel (refereegranskat)abstract
- Highly oriented thin films of alpha-alumina have been grown by pulsed laser deposition on Si(lll). The influence of the substrate temperature on the film growth was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (MID). Ablation at temperatures between room temperature and 850 degrees C gave rise to incorporated crystalline aluminium (Al), while the stoichiometric and highly oriented alpha-Al2O3 films were obtained only at 850 degrees C. The XRD rocking curve measurements of the ablated films showed the full-width-at-half-maximum (FWHM) Of 0.2 degrees. Further annealing at 1000 degrees C in air for 26 h slightly improved out-of-plane orientation. (C) 1997 Elsevier Science S.A.
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| 29. |
- Ilver, L, et al.
(författare)
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Quantum size effects in epitaxial ErAs on GaAs(001)
- 1996
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 77:24, s. 4946-4949
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of very thin epitaxial ErAs layers on GaAs(100) is studied with angle resolved photoelectron spectroscopy. Clear evidence is found for confinement induced quantization of states around the Fermi level. From the dispersive properties of the quantum well states effective masses are obtained, representing electron motion parallel to the surface layers and orthogonal to the layers. We find, for the first time, that effective masses along equivalent bulk directions (XW) are significantly different in the thin layers. Furthermore, the bottom of the highest occupied band shifts towards the Fermi level when going from very thin to thick ErAs layers.
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| 30. |
- Janin, E, et al.
(författare)
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Hydrogen adsorption on the Pt(111)(root 3x root 5)R30 degrees-Sn surface alloy studied by high resolution core level photoelectron spectroscopy
- 1996
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 99:4, s. 371-378
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Tidskriftsartikel (refereegranskat)abstract
- Investigation of the clean and atomic hydrogen covered Pt(111)(root 3 x root 3)R30 degrees-Sn surface alloy has been carried out using high resolution core level photoelectron spectroscopy, The Pt 4(7/2) spectrum recorded from the clean surface alloy shows a single surface peak shifted - 0.25 eV relative to the bulk. Its interpretation by means of a thermodynamical model using Born-Haber cycles confirms the surface alloy model. Adsorption of H does not change the line shape of the Sn 4d core level while a new surface component shifted by 0.59 eV compared to the bulk peak appears in the Pt 4(7/2) spectrum. These results are discussed in the light of the thermodynamical calculations, H atoms are believed to bind only to Pt atoms, and their adsorption site seems to be influenced by the tin present in the surface layer.
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| 31. |
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| 32. |
- Jemt, Torsten, 1950, et al.
(författare)
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Laser-welded titanium frameworks supported by implants in the edentulous maxilla: a 2-year prospective multicenter study.
- 1998
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Ingår i: The International journal of prosthodontics. - 0893-2174. ; 11:6, s. 551-7
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study was to evaluate the clinical and radiographic performance of patients who received implants and fixed prostheses with laser-welded titanium frameworks. MATERIALS AND METHODS: Fifty-eight consecutive patients were treated with 349 osseointegrated implants ad modum Brånemark in the edentulous maxilla at 6 implant centers. The patients were randomly arranged into 2 groups at the time of final impression. Twenty-eight patients received laser-welded titanium frameworks and 30 patients received conventional cast frameworks. Clinical and radiographic data were collected for 2 years in function. RESULTS: The 2 groups of patients showed similar results. The 2-year overall cumulative implant survival rate from the time of implant placement and prosthesis insertion was 93.7% and 96.2%, respectively. The corresponding cumulative survival rate for prostheses was 96.6%. Two patients, 1 from each group, failed completely and resumed using conventional complete dentures. The only obvious factor that could possibly be related to the 2 complete failures was a smoking habit. However, it was not possible to significantly correlate implant failures to smoking habits in this study. No fractures were observed in the frameworks or implant components, and both groups experienced the same frequency of resin veneering material fractures. The overall average marginal bone loss was 0.4 mm (SD 0.8 mm). CONCLUSION: Patients treated with implant-supported prostheses fabricated with laser-welded titanium frameworks in the edentulous maxilla presented comparable results to patients with conventional cast frameworks after 2 years in function.
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| 33. |
- Jonsson, B J, et al.
(författare)
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Method to extract the critical current density and the flux-creep exponent in high-T-c thin films using ac susceptibility measurements
- 1998
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 58:9, s. 5862-5867
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Tidskriftsartikel (refereegranskat)abstract
- High-precision ac susceptibility measurements have been made on high-quality Hg-1212 thin films. A method to analyze chi(1)'(T,H-0,f) and chi(1)" (T,H-0,f) and extract the temperature dependence of the critical current density J(c)(T), as well as the temperature and field-dependent flux-creep exponent n(T,H-0), is presented. With specific measurements at external ac fields Ho in the range 7-100 Oe(rms) we determine the temperature dependence of the critical current density from a single temperature scan. The obtained temperature dependence, J(c)(T), is found to be in good agreement with data obtained from measurements using the traditional "loss-maximum" approach. In addition we present a method to extract the temperature and ac field-dependent flux-creep exponent n(T,H-0) from a set of temperature scans taken at different cc fields and driving frequencies. The observed power law describing the frequency dependence of chi' is consistent with a current-dependent effective activation energy of the form U(J)= U(0)ln(J(c)/J). Furthermore, the flux creep is found to increase with ac field and with temperature except at about 20-30 K below T-c, where our data suggest a slowing down of the flux creep.
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| 34. |
- Jukna, A, et al.
(författare)
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Electric properties of planar Ag/HgBa2CaCu2O6+delta interface
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 316:1-2, s. 83-88
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Tidskriftsartikel (refereegranskat)abstract
- Silver coatings were magnetron sputtered onto the surface of highly c-axis-oriented HgBa2CaCu2O6+delta superconducting thin films exhibiting zero resistance T-c at about 120 K and the critical current density similar to 10(5) A/cm(2) at 100 K. Electrical resistance of the Ag/HgBa2CaCu2O6+delta planar interface and current-voltage dependencies were investigated in a course of post-deposition annealing of the Ag/HgBa2CaCu2O6+delta at 50-350 degrees C in both purl oxygen and oxygen-free ambient. Results of the electrical measurements are explained in terms of the insulating layer formation at the Ag/HgBa2CaCu2O6+delta interface. It is assumed this insulator is a product created by oxygen non-stoichiometry and decomposition of the superconductor at the interface between both materials. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 35. |
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| 36. |
- Lu, H, et al.
(författare)
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Catalytic reduction of nitric oxide over copper Part III : Influence of water vapour
- 1999
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Ingår i: Journal of Molecular Catalysis A. - 1381-1169 .- 1873-314X. ; 138:2-3, s. 227-236
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the effect of water vapour on the reduction of NO over copper in the presence of oxygen and isobutene. Reactions were studied at 700 K and at 770 K. Mass spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS) were used to monitor the gas phase composition during reaction and to analyse the catalyst surface, respectively. XPS spectra show that the presence of water vapour influences the Cu oxidation state. At 700 K adsorption of aldehyde is partly blocked by copper oxide resulting in a decrease in the activity of the reaction, although the main mechanism is not changed. At 770 K, water vapour generates an even more oxidised surface, which promotes a complete oxidation of hydrocarbon, the main mechanism of NO reduction is changed, and the activity of the reaction is slightly increased. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 37. |
- Miniotas, A, et al.
(författare)
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Large magnetoresistance effect in as-grown epitaxial LaxCa1-xMnO3 films prepared by a molecular beam epitaxy coevaporation technique
- 1998
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 16:3, s. 1268-1271
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of LaxCa1-xMnO3 (0.64 less than or equal to x less than or equal to 0.68) have been grown by NO2-assisted molecular beam epitaxy on single crystal SrTiO3(100) and LaAlO3(100) substrates. As-grown films are found to be grown epitaxially, b-axis oriented on both SrTiO3 and LaAlO3 substrates, and exhibit a large magnetoresistance effect {[R(O)-R(H)]/R(H)X100} of about 1500% at 214 K. The magnetoresistance effect values obtained are similar to those reported for as-grown LaxCa1-xMnO3 (0.60 less than or equal to x less than or equal to 0.7) films synthesized either by so-called "block-by-block" or "layer-by-layer" molecular beam epitaxy techniques, but the effect appears at significantly higher temperatures. For epitaxial La0.68Ca0.32MnO3 films grown on SrTiO3 a relatively large resistance suppression of 200% at 1.0 T is observed. (C) 1998 American Vacuum Society.
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| 38. |
- OLSSON, LO, et al.
(författare)
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ANOMALOUS QUENCHING OF PHOTOEMISSION FROM BULK STATES BY DEPOSITION OF CS ON INAS(100)
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:3, s. 1470-1473
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Tidskriftsartikel (refereegranskat)abstract
- The effect of angle-resolved valence-hand photoelectron spectra from adsorption of small amounts of Cs on InAs(100)4 X 2 has been studied. It is shown that a bulk interband transition is totally quenched at a coverage of Cs that leaves the 4 X 2 reconstruction practically intact. The surface order was monitored by low-energy electron diffraction and photoemission from surface states. A shift of the surface Fermi level to well above the conduction-band minimum is also observed. It is proposed that the resulting development of a two-dimensional electron gas at the surface affects the bulk states probed in photoemission.
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| 39. |
- Olsson, L O, et al.
(författare)
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Charge accumulation at InAs surfaces
- 1996
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 76:19, s. 3626-3629
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoelectron spectroscopy has been used to directly prove the existence of a charge accumulation layer at clean InAs surfaces. The formation of an accumulation layer is shown to be a common property of polar InAs surfaces, with the precise surface Fermi level position above the conduction band minimum determined by the surface geometry. The emission from states in the accumulation layer is studied with respect to its photon energy and angular dependence.
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| 40. |
- Olsson, L O, et al.
(författare)
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Core level and valence-band studies of the (111)2x2 surfaces of InSb and InAs
- 1996
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:8, s. 4734-4740
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Tidskriftsartikel (refereegranskat)abstract
- The valence and core electronic surface states on the (111)2X2 surfaces of InSb and InAs have been studied by angle-resolved photoelectron spectroscopy. Similarities in data show that the vacancy-buckling model, which is known to describe the InSb(111)2x2 surface, also applies to InAs(111)2X2. Three surface valence bands are identified and their dispersions are mapped along symmetry directions in the surface Brillouin zone. The In 4d core levels show one surface shifted component while no surface shifted components of the Sb 4d or As 3d core levels could be resolved.
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| 41. |
- OLSSON, LO, et al.
(författare)
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SURFACE ELECTRONIC-STRUCTURE OF INSB(100)4X1 STUDIED BY ANGLE-RESOLVED PHOTOELECTRON-SPECTROSCOPY
- 1995
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 331, s. 1176-1180
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Tidskriftsartikel (refereegranskat)abstract
- The surface electronic structure of the In-rich InSb(100)4 X 1 surface has been studied by angle-resolved photoelectron spectroscopy. To determine the origin of different contributions in spectra, direct bulk interband transitions were first identified using a semi-empirical band structure calculation and assuming direct transitions into free electron-like final bands. Three surface-induced features were identified and their dispersions have been mapped along symmetry directions of the surface Brillouin zone.
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| 42. |
- Qvarford, M, et al.
(författare)
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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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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:22, s. 14753-14756
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Tidskriftsartikel (refereegranskat)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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| 43. |
- Qvarford, M, et al.
(författare)
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Photoemission and x-ray absorption study of superconducting and semiconducting Ba1-xKxBiO3 single crystals
- 1996
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:9, s. 6700-6707
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Tidskriftsartikel (refereegranskat)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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| 44. |
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| 45. |
- Simpson, W C, et al.
(författare)
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Role of surface stoichiometry in the Cl-2/GaAs(001) reaction
- 1996
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 14:3, s. 1815-1821
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Tidskriftsartikel (refereegranskat)abstract
- The room-temperature reaction of Cl-2 with GaAs(001)-4x6, -c(2x8), and -c(4x4) surfaces is studied with synchrotron soft x-ray photoelectron spectroscopy. The chemical composition of the reacted surfaces is found to depend on the stoichiometry of the starting surface. In all cases, the reaction occurs stepwise, with Ga and As monochlorides formed prior to the dichlorides. The Ga-rich surface is initially more reactive than either of the As-rich surfaces and it forms more GaCl than the As-rich surfaces, which instead form more AsCl. The sticking coefficient for chlorine on GaAs(001) decays exponentially with coverage. A contribution from Cl atoms comprising the surface dichlorides is identified in the Cl 2p core-level spectra. (C) 1996 American Vacuum Society.
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| 46. |
- Soderholm, S, et al.
(författare)
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A photoelectron spectroscopy and x-ray absorption study of Bi2Sr2CaCu2O8 single crystal with adsorbed Cs : On the origin of the states affected by electron doping and evidence for spatially resolved electron doping
- 1996
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 8:9, s. 1307-1320
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Tidskriftsartikel (refereegranskat)abstract
- The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of Bi2Sr2CaCu2O8 has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O Is, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O Is, Cu 2p and Ca 2p edges. The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu-O layer. It is evident from bulk- and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of Bi2Sr2CaCu2O8 locally through spatially resolved electron doping. When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi-O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.
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| 47. |
- TJERNBERG, O, et al.
(författare)
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ANGLE-RESOLVED PHOTOEMISSION ON NIO - ON THE NATURE OF THE VALENCE-BAND
- 1995
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 46:8-10, s. 1215-1218
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Tidskriftsartikel (refereegranskat)abstract
- Angle resolved photoelectron spectroscopy has been performed on the valence band of NiO at the National Swedish Laboratory for Synchrotron Radiation. Normal emission spectra have been recorded for photon energies between 17 and 140 eV in order to study the electronic structure of the valence band. The experimentally determined band structure has been compared with a local density augmented plane wave band structure calculation. Signs of the influence of antiferromagnetic ordering are found and the general agreement between experimental and theoretical oxygen derived bands indicates strong hybridization between Ni 3d and O 2p orbitals.
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| 48. |
- Tjernberg, O, et al.
(författare)
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Influence of magnetic ordering on the NiO valence band
- 1996
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:15, s. 10245-10248
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Tidskriftsartikel (refereegranskat)abstract
- The influence of magnetic ordering on the NiO valence band has been studied by angle resolved photoelectron spectroscopy. Measurements have been performed at temperatures above and below the Neel temperature (T-N), as well as at room. temperature. The results show temperature dependence but no significant changes in the valence band structure are detected in connection to the passing of T-N. The reported data suggest that the magnetic phase transition does not influence the valence band structure significantly.
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| 49. |
- Tjernberg, O, et al.
(författare)
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Resonant photoelectron spectroscopy on NiO
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 53:15, s. 10372-10376
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Tidskriftsartikel (refereegranskat)abstract
- Resonant photoelectron spectroscopy studies have been performed on the NiO valence band at photon energies corresponding to the Ni 2p, 3p, and O 1s absorption thresholds. Strong resonances are seen in the vicinity of the Ni 2P threshold, which confirm earlier conclusions from the weaker resonances seen at the Ni 3p threshold. No valence-band resonance is observed at the O 1s threshold. The analysis of this data confirms the picture of NiO as a strongly correlated charge-transfer insulator by identifying the highest-lying states as being of mainly 3d(8)L final-state character. The existence of localized excited Ni states, as well as the delocalized nature of the O states, are confirmed. Comparisons with the configuration-interaction model and quasiparticle calculations are also made.
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| 50. |
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