| 1. |
- Adell, Johan, 1980, et al.
(author)
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Electron spectroscopic studies of nanowires formed by (GaMn)As growth on GaAs(111)B
- 2011
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In: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 151:11, s. 850-854
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Journal article (peer-reviewed)abstract
- Valence band photoemission with photon energies around the Mn2p excitation threshold has been used to study the development of nanowires catalyzed by MnAs particles. A gradual change in the spectra with increasing nanowire length is observed, such that the resonant photoemission eventually dominates over the Auger decay channel. The change is ascribed to dilution of Mn, showing that Mn is transferred from the MnAs particles into the nanowires. (C) 2011 Elsevier Ltd. All rights reserved.
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| 2. |
- Adell, Johan, et al.
(author)
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Formation of epitaxial MnBi layers on (Ga,Mn)As
- 2009
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 2469-9950 .- 2469-9969. ; 80:7
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Journal article (peer-reviewed)abstract
- The initial growth of MnBi on MnAs-terminated (GaMn)As is studied by means of synchrotron-based photoelectron spectroscopy. From analysis of surface core-level shifts we conclude that a continued epitaxial MnBi layer is formed, in which the MnAs/MnBi interface occurs between As and Bi atomic planes. The well-defined 1×2 surface reconstruction of the MnAs surface is preserved for up to 2 ML of MnBi before clear surface degradation occurs. The MnBi layer appears to be free from intermixed As.
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| 3. |
- Adell, Johan, 1980, et al.
(author)
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Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As
- 2011
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In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 23:8
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Journal article (peer-reviewed)abstract
- Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Adell, Martin, et al.
(author)
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Postgrowth annealing of (Ga,Mn) As under As capping: An alternative way to increase T-C
- 2005
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86, s. 112501-
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Journal article (peer-reviewed)abstract
- In situ postgrowth annealing of (Ga,Mn)As layers under As capping is adequate for achieving high Curie temperatures (T-C) in a similar way as ex situ annealing in air or in N-2 atmosphere practiced earlier. Thus, the first efforts give an increase of T-C from 68 to 145 K after 2 h annealing at 180 degrees C. These data, in combination with lattice parameter determinations and photoemission results, show that the As capping acts as an efficient sink for diffusing Mn interstitials.
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| 9. |
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| 10. |
- Andreasson, Måns, 1975, et al.
(author)
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Organic molecular beam deposition system and initial studies of organic layer growth
- 2006
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In: Physica Scripta. - 1402-4896 .- 0031-8949. ; T126, s. 1-5
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Journal article (peer-reviewed)abstract
- This work describes an organic molecular beam deposition system with substrate entry/exitchamber, buffer chamber and with the possibility to transfer substrate from a III–V molecularbeam deposition system. Flux calibrations of organic molecules and the initial growth oforganic layers are described. For this purpose, the molecules 3,4,9,10 perylene tetra carboxylicdianhydride and copper phtalocyanine were used. Layers were grown on oxidized andhydrogen passivated Si(100), Indium tin oxide and glass respectively. The growth wasinvestigated with atomic force microscopy, reflection high energy electron diffraction andultraviolet photoemission spectroscopy. An investigation with x-ray photoelectron and Ramanspectroscopy on the effect of atmospheric exposure is also included, showing little effect ofsurface pollution when the samples were handled carefully. The initial formation (monolayers)of copper phtalocyanine thin films was studied by ultraviolet photoemission spectroscopy.
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| 11. |
- Andreasson, Måns, 1975, et al.
(author)
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Photoelectron spectroscopic studies of ultra-thin CuPc and PTCDA layers on Cu(100)
- 2008
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In: Synthetic Metals. - : Elsevier BV. - 0379-6779. ; 158:1-2, s. 45-49
-
Journal article (peer-reviewed)abstract
- The initial interaction and interface formation between Cu(100) and the organic semiconductors 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) and copper phtalocyanine (CuPc) has been studied by means of angle-resolved UV photoelectron spectroscopy (ARUPS). Both CuPc and PTCDA are known to adsorb strongly on the Cu(100) surface. The bonding interaction is revealed via interface-related structures in photoemission spectra. However, the spectra develop rather differently in the low coverage regime: while CuPc molecular states are observed below monolayer coverage, the first PTCDA layer is found to be reacted such that the adsorbate-induced emission is strongly modified relative that of intact PTCDA molecules. We find a number of structures that are neither PTCDA- nor Cu-derived, and that the oxygen-related component of the PTCDA spectrum is completely missing in spectra from the monolayer. Importantly for device applications, we find evidence of interfacial electronic states in the form of new peaks located in the former HOMO-LUMO gap for both molecules. In the case of PTCDA these support a chemisorptive bonding model, whereas in the case of CuPc we interpret the state as a monolayer-specific resonance.
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| 12. |
- Dehestani, M., et al.
(author)
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Enhancing the bioactivity of zirconia and zirconia composites by surface modification
- 2012
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In: Journal of Biomedical Materials Research - Part B Applied Biomaterials. - : Wiley. - 1552-4981 .- 1552-4973. ; 100B:3, s. 832-840
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Journal article (peer-reviewed)abstract
- Among bioceramics, zirconia (ZrO2) and alumina (Al2O3) possess exceptional mechanical properties suitable for load-bearing and wear-resistant applications but the poor bioactivity of these materials is the major concern when bonding and integration to the living bone are desired. This article investigates two different approaches and their underlying mechanisms to improve the bioactivity of zirconia (3Y-TZP) and a zirconia composite with alumina (10Ce-TZP/Al2O3). Chemical treatment approach applied on 3Y-TZP where the substrates were soaked in 5M H3PO4 to create chemically functional groups on the surface for inducing apatite nucleation. X-ray photoelectron spectroscopy (XPS) was used to detect chemical changes and X-ray diffraction (XRD) to monitor phase changes on the surface before and after acid treatment. Alternate soaking approach applied on 10Ce-TZP/Al2O3 consisted of soaking the composite substrates in CaCl2 and Na2HPO4 solutions alternately to make a precursor for apatite formation. The bioactivity was evaluated by apatite-forming ability of surface-treated materials in simulated body fluid (SBF). Both methods resulted in the formation of hydroxyapatite on the surface of materials; however, alternate soaking approach showed to be a simpler, faster, and more effective method than the chemical treatment approach for enhancing the bioactivity of zirconia materials.
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| 13. |
- Glover, C. J., et al.
(author)
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Stationary and dispersive features in resonant inelastic soft X-ray scattering at the Ge 3p resonances
- 2009
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 173:2-3, s. 103-107
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Journal article (peer-reviewed)abstract
- Resonant inelastic soft X-ray scattering at the 3p resonances in crystalline Ge is presented. Both stationary and dispersive features are observed in a wide energy range above as well as below the ionization limits. These observations are in agreement with theoretical predictions based on a two-step model where the initially excited electron has no influence on the emission step. Excess population of states in the conduction band is found, and discussed in terms of attosecond electron dynamics. (c) 2009 Elsevier B.V. All rights reserved.
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| 14. |
- Kanski, Janusz, 1946, et al.
(author)
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Electronic structure of (Ga,Mn)As revisited
- 2017
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In: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 19:2, s. 1-8
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Journal article (peer-reviewed)abstract
- The detailed nature of electronic states mediating ferromagnetic coupling in dilute magnetic semiconductors, specifically (Ga,Mn)As, has been an issue of long debate. Two confronting models have been discussed emphasizing host band vs. impurity band carriers. Using angle resolved photoemission we show that the electronic structure of the (Ga,Mn)As system is significantly modified from that of GaAs throughout the valence band. Close to the Fermi energy, the presence of Mn induces a strong mixing of the bulk bands of GaAs, which results in the appearance of a highly dispersive band in the gap region of GaAs.For Mn concentrations above 1% the band reaches the Fermi level, and can thus host the delocalized holes needed for ferromagnetic coupling. Overall, our data provide a firm evidence of delocalized carriers belonging to the modified host valence band.
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| 15. |
- Kanski, Janusz, 1946, et al.
(author)
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Mn-induced modifications of Ga 3d photoemission from (Ga, Mn)As: evidence for long range effects
- 2012
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In: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:43, s. 1-435802
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Journal article (peer-reviewed)abstract
- Using synchrotron based photoemission, we have investigated the Mn-induced changes in Ga 3d core level spectra from as-grown Ga(1-x)Mn(x)As. Although Mn is located in Ga substitutional sites, and therefore does not have any Ga nearest neighbors, the impact of Mn on the Ga core level spectra is pronounced even at Mn concentrations in the region of 0.5%. The analysis shows that each Mn atom affects a volume corresponding to a sphere with around 1.4 nm diameter.
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| 16. |
- Lögdberg, Sara, et al.
(author)
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Hydrocarbon production via Fischer-Tropsch synthesis from H-2-poor syngas over different Fe-Co/gamma-Al2O3 bimetallic catalysts
- 2009
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 89:1-2, s. 167-182
-
Journal article (peer-reviewed)abstract
- Fischer-Tropsch synthesis (FTS) at 20 bar. and 483 K, with H-2-poor syngas (H-2/CO ratio = 1.0) in order to simulate gasified biomass, was performed over Al2O3-supported catalysts with various ratios of Fe:Co (12 wt% bimetal) prepared by co-impregnation. Co was found to be incorporated into the Fe2O3 phase after calcination, at least for the iron-rich samples, while no evidence of Fe incorporated into Co3O4 was found. Upon reduction, most probably FeCo alloys were formed in the iron-rich bimetallic samples. The degree of reduction of the catalysts showed a non-linear behavior with respect to the Fe:Co ratio, but it is obvious that Co increases the reducibility of Fe. Alloying Co with small/moderate amounts of Fe improved the FT activity compared to the 100% Co catalyst at low conversion levels. Alloying Fe with small/moderate amounts of Co lowered the FT activity, but increased the relative water-gas-shift (WGS) activity compared to the 100% Fe catalyst. However, the overall WGS activity was very low for all catalysts, even with external water addition to the feed, resulting in low FT productivities (per gram catalyst) due to the low partial pressure of H-2. A higher Fe:Co ratio in the bimetallic catalyst generally resulted in higher relative WGS activity, but did not lower the H-2/CO usage ratio to the desired value of 1.0. For the Fe-containing catalysts, the space-time yield of hydrocarbons (HCs) decreased with increasing partial pressure of water or reduced space velocity, indicating an inhibition of water on the FT activity, most often resulting in low FT productivity under the conditions with highest relative WGS activity (usage ratios closest to the inlet H-2/CO ratio). Moreover, the co-impregnation technique resulted in a surface enrichment of Fe, at least for the Co-rich samples, covering the Co sites. For the bimetallic catalysts, both FT and WGS activities rapidly declined at high partial pressure of water due to deactivation by oxidation and sintering. However, the results indicate that WGS and FT proceeded over sites of different nature in the bimetallic catalysts. The bimetallic catalysts showed essentially no synergy effects with respect to HC selectivities and olefin/paraffin ratios, which partly can be explained by the use of a sub-stoichiometric H-2/CO ratio as feed. The higher the Fe content, the lower were the C5+ selectivity and C-3 olefin/paraffin ratio. Water addition increased the C5+ selectivity and C-3 Olefin/paraffin ratio and reduced the CH4 selectivity.
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| 17. |
- Nygren, Håkan, 1952, et al.
(author)
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Mg-corrosion, hydroxyapatite, and bone healing
- 2017
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In: Biointerphases. - : American Vacuum Society. - 1934-8630 .- 1559-4106. ; 12:2
-
Journal article (peer-reviewed)abstract
- The different capacities of magnesium in the metallic form (Mg-metal) and magnesium oxide (MgO) to stimulate bone healing are possible clues in the search for products that may promote bone healing. Since both Mg-metal and MgO can be assumed to release comparable amounts of Mg2+ ions during their reactions in the tissue where they have been implanted, it is of some importance to follow this process and analyze the resulting mineral formation in the tissue at the implantation site. Implants of MgO were inserted into rat tibia, and the bone healing was compared with sham-operated controls. Samples were taken after 1 week of healing and analyzed by histology, environmental scanning electron microscopy equipped with an energy dispersive x-ray spectroscopy analyzer, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Callus bone was seen in sham-operated controls after 1 week of healing. Implantation of MgO impaired the callus bone formation by replacing bone with apparently mineralized areas, lacking osteocytes and were denoted, amorphous bodies. Elemental analysis showed increased levels of Ca (7.1%), P (3.7%), and Mg (0.2%) in the bone marrow of MgO-treated animals versus sham-operated controls Ca (2.4%), P (2.3%), and Mg (0.1%). The Ca content of the cortical bone was also significantly increased (Ca, 29% increase) in MgO-treated animals compared to sham-operated controls. The Ca content of the cortical bone of sham-operated animals was also significantly (p < 0.05) higher than the corresponding value of untreated animals, which means that the surgical trauma induces an altered composition of the bone mineral. The Ca/P ratio was 1.26-1.68, which is compatible with that of mineralized bone with different contents of organic materials. Analysis of bone sections using ToF-SIMS showed the presence of hydroxyapatite (HA) and MgCO3 in the bone marrow and in cortical bone. Analysis using x-ray photoelectron spectroscopy of Mg, MgO, and MgCO3 after incubation with cell culture medium (DMEM), in vitro, showed binding of CaPO4 at the Mg and MgO samples. The Ca/P ratio was 0.8, indicating a higher P content than that expected for HA. Exposure of human embryonic stem cells to Mg species preincubated in DMEM resulted in HA production by the cells. Thus, two sources of CaPO4 in the bone marrow of MgO-treated bone were defined, catalytic formation on Mg-species and synthesis from activated stem-cells. The presented data suggest that bone healing near Mg implants is congruent with the fracture healing of bone, boosted by high HA levels in the bone marrow. In this context, the different capacities of Mg-metal and MgO to catalyse the formation of HA can be important clues to their different bone promoting effects. (C) 2017 Author(s).
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| 18. |
- Nygren, Håkan, 1952, et al.
(author)
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Mineralization at Titanium Surfaces is a Two-Step Process.
- 2016
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In: Journal of functional biomaterials. - : MDPI AG. - 2079-4983. ; 7:1
-
Journal article (peer-reviewed)abstract
- Mapping the initial reaction of implants with blood or cell culture medium is important for the understanding of the healing process in bone. In the present study, the formation of low crystalline carbonated hydroxyapatite (CHA) onto commercially pure titanium (Ti) implants from cell culture medium and blood, is described as an early event in bone healing at implants. The Ti-implants were incubated with cell culture medium (DMEM) or whole blood and the surface concentration of Ca, P and HA was analyzed by XPS, EDX and Tof-SIMS. After incubation with DMEM for 16 h and 72 h, EDX and XPS analysis showed stable levels of Ca and P on the Ti-surface. ESEM images showed an even distribution of Ca and P. Further analysis of the XPS results indicated that CHA was formed at the implants. Analysis with ToF-SIMS yielded high m.w. fragments of HA, such as Ca₂PO4 at m/z 174.9 and Ca₃PO₅ at m/z 230.8, as secondary ions at the Ti-surfaces. Analysis of implants incubated in blood for 16 h, with ToF-SIMS, showed initial formation of CHA yielding CaOH as secondary ion. The results indicate that early mineralization at Ti-surfaces is an important step in the healing of implants into bone.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Ulfat, Intikhab, 1966, et al.
(author)
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As3d core level studies of (GaMn)As annealed under As capping
- 2010
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In: Surface Science. - : Elsevier BV. - 0039-6028. ; 604:2, s. 125-128
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Journal article (peer-reviewed)abstract
- The surface of a Ga(0.95)Mn(0.05)As layer subjected to low temperature annealing under As capping has been studied by core level photoemission with focus on As3d spectrum. By detailed comparison with the surface of pure GaAs subjected to the same surface treatment, the As spectral component of the reacted surface layer has been identified. The relative intensity of this component is consistent with the notion of an MnAs monolayer terminating the annealed (GaMn)As surface.
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| 23. |
- Ulfat, I., et al.
(author)
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Effects of nonuniform Mn distribution in (Ga,Mn)As
- 2014
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In: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 89:4, s. art no 045312-
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Journal article (peer-reviewed)abstract
- Resonant in situ photoemission from Mn 3d states in Ga(1−x)MnxAs is reported for Mn concentrations down to the very dilute level of 0.1%. Concentration-dependent spectral features are analyzed on the basis of first-principles calculations for systems with selected impurity positions as well as for random alloys. Effects of direct Mn-Mn interaction are found for concentrations as low as 2.5%, and are ascribed to statistical (nonuniform) distribution of Mn atoms.
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| 24. |
- Ulfat, Intikhab, 1966, et al.
(author)
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Electron Spectroscopic Studies of Homogenous (GaMn)As layers
- 2012
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In: Advanced Materials Research. - 1662-8985 .- 1022-6680. - 9783037853634 ; 463-464, s. 380-384
-
Conference paper (peer-reviewed)abstract
- By incorporating magnetism into semiconductors, it may possibly be viable to enhance the functionality of materials. An exceptionally important material in this context is GaAs, which can be doped with Mn atoms. (GaMn)As has fascinated research community as a promising candidate for spintronic application. It is quite appealing due to both its compatibility with existing HI-V technology and great progress in improving its magnetic properties. Being fabricated by low temperature molecular beam epitaxy (LT-MBE), due to thermal instability at elevated temperatures, the material contains a high density of various defects compensating Mn acceptors. It is a well-established fact that the ferromagnetic state of (GaMn)As can be stabilized via post growth annealing. Nevertheless, in general, the annealed (GaMn)As layers do not remain useful for further epitaxial overgrowth that might be included in multilayer structure. We present a summary of our investigations regarding the synchrotron-based characterization of (GaMn)As layers grown via molecular beam epitaxy carried out at the Swedish National Facility of Synchrotron Radiation-the MAX-lab aiming at the reduction of the density of Mn interstitial and increase in the content of Mn.
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| 25. |
- Ulfat, Intikhab, 1966, et al.
(author)
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Post-growth annealing of (Ga,Mn)As under Sb capping
- 2012
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In: Applied Mechanics and Materials. - 1660-9336. - 9783037855102 ; 243-246, s. 243-246
-
Conference paper (peer-reviewed)abstract
- (Ga,Mn)As is a model diluted ferromagnet system in which the atomic spins of Mn ions are ferromagnetically arranged due to the exchange interaction with valence band holes. An important tecchnological concern regarding this system has been approaches that might result in reduction of the density of Mn interstitial and increase in the content of Mn in order to make the system practically feasible. To accomplish the objective we report the results of our recent synchrotron radiation based spectroscopic investigations concening annealing induced modification of as-grown (Ga,Mn)As layers covered with Sb capping.
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| 26. |
- Ulfat, Intikhab, et al.
(author)
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Reply to Comment on "As 3d core level studies of (GaMn)As annealed under As capping" by I. Ulfat, J. Adell, J. Sadowski, L. Ilver, J. Kanski, [Surface Science 604 (2010), 125] by P. Jiricek, M. Cukr, I. Bartos
- 2010
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In: Surface Science. - : Elsevier BV. - 0039-6028. ; 604:21-22, s. 2065-2065
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Journal article (other academic/artistic)
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