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| 13. |
- Karlsson, P. G., et al.
(författare)
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Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(1 0 0) and Si(1 1 1) studied by electron spectroscopy
- 2007
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 601:4, s. 1008-1018
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Tidskriftsartikel (refereegranskat)abstract
- The growth of ultrathin ZrO2 films on Si(100)-(2x1) and Si(111)-(7x7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50Å thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7x7) the local structure of t-ZrO2 is not observed until a film thickness of 51Å is reached. On Si(100)-(2x1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11Å. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr–O valence electron matching to the number of dangling bonds per surface Si atom. The Zr–O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C–O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.
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| 14. |
- Karlsson, P.G., et al.
(författare)
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Ultrathin ZrO2 films on Si-rich SiC(0 0 0 1)-(3 × 3) : Growth and thermal stability
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:11, s. 2390-2400
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Tidskriftsartikel (refereegranskat)abstract
- The growth and thermal stability of ultrathin ZrO2 films on the Si-rich SiC(0 0 0 1)-(3 × 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that growth at 400 °C yields tetragonal ZrO2. An interface is formed between the ZrO2 film and the SiC substrate. The interface contains Si in several chemically different states. This gives evidence for an interface that is much more complex than that formed upon oxidation with O2. Si in a 4+ oxidation state is detected in the near surface region. This shows that intermixing of SiO2 and ZrO2 occurs, possibly under the formation of silicate. The alignment of the ZrO2 and SiC band edges is discussed based on core level and valence PES spectra. Subsequent annealing of a deposited film was performed in order to study the thermal stability of the system. Annealing to 800 °C does not lead to decomposition of the tetragonal ZrO2 (t-ZrO2) but changes are observed within the interface region. After annealing to 1000 °C a laterally heterogeneous layer has formed. The decomposition of the film leads to regions with t-ZrO2 remnants, metallic Zr silicide and Si aggregates. © 2007 Elsevier B.V. All rights reserved.
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| 15. |
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| 16. |
- Lindgren, Johan, et al.
(författare)
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Interpreting melanin-based coloration through deep time : A critical Review
- 2015
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : Royal Society of London. - 0962-8452 .- 1471-2954. ; 282:1813
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Forskningsöversikt (refereegranskat)abstract
- Colour, derived primarily from melanin and/or carotenoid pigments, is integral to many aspects of behaviour in living vertebrates, including social signalling, sexual display and crypsis. Thus, identifying biochromes in extinct animals can shed light on the acquisition and evolution of these biological traits. Both eumelanin and melanin-containing cellular organelles (melanosomes) are preserved in fossils, but recognizing traces of ancient melanin-based coloration is fraught with interpretative ambiguity, especially when observations are based on morphological evidence alone. Assigning microbodies (or, more often reported, their ‘mouldic impressions’) as melanosome traces without adequately excluding a bacterial origin is also problematic because microbes are pervasive and intimately involved in organismal degradation. Additionally, some forms synthesize melanin. In this review, we survey both vertebrate and microbial melanization, and explore the conflicts influencing assessment of microbodies preserved in association with ancient animal soft tissues.We discuss the types of data used to interpret fossil melanosomes and evaluate whether these are sufficient for definitive diagnosis. Finally, we outline an integrated morphological and geochemical approach for detecting endogenous pigment remains and associated microstructures in multimillion-year-old fossils.
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| 17. |
- Richter, J H, et al.
(författare)
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Electronic structure of lithium-doped anatase TiO2 prepared in ultrahigh vacuum
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 71:23, s. 1-235418
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Tidskriftsartikel (refereegranskat)abstract
- Insertion of lithium in anatase TiO2, giving LixTiO2, is performed under ultrahigh vacuum (UHV) conditions and studied using synchrotron radiation based electron spectroscopy. Core level photoemission spectra are directly compared to results obtained after electrochemical insertion, illustrating the usefulness of the UHV approach. The growth of a state of mainly Ti 3d character in the band gap is monitored and the amount of charge transferred from Li to the band gap state is quantified. The result that the Ti 3d level is occupied by 0.85 +/- 0.10 electronic charge is in good agreement with theoretical predictions. Binding energy shifts of the core levels suggest that the population of the Ti 3d states does not follow a simple rigid band behavior. It is concluded that the formation of the Li-poor phase (x < 2%) is associated with pinning of the Fermi level to the bottom of the conduction band. The Li-poor phase can therefore be envisaged as related to defects. Changes in the valence photoemission spectrum and O 1s x-ray absorption spectrum are interpreted in terms of a decreased O 2p-Ti 3d interaction upon Li insertion. Shifts in the sample work function are finally found to agree reasonably well with the measured cell voltage for electrochemical Li insertion into a nanoporous anatase film.
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| 18. |
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| 19. |
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| 20. |
- Sandell, A, et al.
(författare)
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Metalorganic Chemical Vapor Deposition of Anatase Titanium Dioxide on Si: Modifying the Interface by Pre-Oxidation.
- 2003
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 530:1-2, s. 63-70
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Tidskriftsartikel (refereegranskat)abstract
- The formation of TiO2 films on clean and pre-oxidized Si(1 1 1) through chemical vapor deposition of titanium(IV) isopropoxide (TTIP) in ultra-high vacuum has been examined by synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy. In both cases, TTIP deposition at 500 °C eventually results in an anatase TiO2 film with a carbon-free surface and the surface morphology of the anatase films is very similar. By using a novel way of combining photoemission and XAS data, it is demonstrated that the two situations have substantially different interfacial properties. Pre-oxidation of the surface at 500 °C passivates the surface so that the thickness of the amorphous TiSixOy interface layer decreases from 30–35 to 15–25 Å and eliminates the formation of interfacial carbon completely.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Andersen, J., et al.
(författare)
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Far-Infrared Investigation of the Benzene-Water Complex : The Identification of Large-Amplitude Motion and Tunneling Pathways
- 2020
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 124:3, s. 513-519
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Tidskriftsartikel (refereegranskat)abstract
- The far-infrared spectrum of the weakly OH···πhydrogen-bonded benzene-water complex has been studied in neon and argon matrices, below 30 K. The in-plane water libration has been observed in both neon and argon for H2O and D2O complexed with C6H6 and C6D6 but not for the corresponding complexes involving HDO. Both H2O and D2O can tunnel between the two possible hydrogen bonds. This is not possible for HDO. The reported far-infrared observations have implications for the interpretation of the previously obtained molecular beam microwave spectrum of the benzene-water complex.
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| 25. |
- Andersson, M P, et al.
(författare)
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First-Principle Calculations of the Experimental Vibrational Spectrum of a Surface Adsorbate: Anharmonic Resonance Coupling between Fundamental and Binary Modes.
- 2003
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Ingår i: Physical Review Letters. - 1079-7114. ; 90:7, s. 076103-076103
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Tidskriftsartikel (refereegranskat)abstract
- By including relevant physical properties in our modeling of a surface adsorbate system we can, from first principles, correctly calculate all experimentally observed features in the vibrational spectrum of CH3CH2O– and CD3CH2O– adsorbed on Cu(100). That is, we reproduce the number of observed modes, the vibrational frequencies, and intensities of the modes including the presence/absence of binary overtone and combination modes. No scaling was performed. Our calculations show that the anharmonic terms of the potential energy surface of free ethanol are transferrable to the corresponding surface adsorbate, ethoxy, while the harmonic terms are not. ©2003 The American Physical Society
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| 26. |
- Andersson, M P, et al.
(författare)
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New scale factors for harmonic vibrational frequencies using the B3LYP density functional method with the triple-xi basis set 6-311+G(d,p)
- 2005
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Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 109:12, s. 2937-2941
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated optimal frequency scaling factors for the B3LYP/ 6-311+G(d,p) method for fundamental vibrational frequencies on the basis of a set of 125 molecules. Using the new scaling factor, the vibrational frequencies calculated with the triple-zeta basis set 6-311+G(d,p) give significantly better accuracy than those calculated with the double-zeta 6-31G(d) basis set. Scale factors were also determined for low-frequency vibrations using the molecular set of 125 molecules and for zero-point energies using a smaller set of 40 molecules. We have studied the effect on the calculated vibrational frequencies for various combinations of diffuse and polarization functions added to the triple-zeta 6-311G basis set. The 6-311+G(d,p) basis set is found to give almost converged frequencies for most molecules, and we conclude that our optimum scaling factors are valid for the basis sets 6-311 G(d,p) to 6-311++G(3df,3pd). The new scale factors are 0.9679 for vibrational frequencies, 1.0100 for low-frequency vibrations, and 0.9877 for zero-point vibrational energies.
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| 27. |
- Andersson, M P, et al.
(författare)
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Surface-induced C–O bond anharmonicity of methoxy adsorbed on Cu(100): Experiments and density-functional theory calculations
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:22, s. 1-224714
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Tidskriftsartikel (refereegranskat)abstract
- The anharmonic properties of a surface intermediate, methoxy, adsorbed on Cu(100) are investigated by surface infrared overtone spectroscopy and density-functional-theory electronic structure calculations. The anharmonicity is measured in the zero-coverage limit, and it is observed that the anharmonicity is increased upon adsorption as compared with the free methanol. By combining experiments with calculations we demonstrate that modifications of the anharmonicity of the methoxy species is indeed induced by adsorption onto the copper surface and not by the formation of the methoxy species.
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| 28. |
- Andersson, M P, et al.
(författare)
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The adsorption site of methoxy and ethoxy on Cu(100) as determined by vibrational spectroscopy and first principle calculations
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 549:1, s. 87-96
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we determine the adsorption site of two polyatomic molecules, methoxy and ethoxy, on Cu(100). This is accomplished by comparing experimental intramolecular vibrational modes to the corresponding modes calculated by first principle methods. We explore the three different high symmetry adsorption sites on top, bridge and hollow using several different metal clusters to represent the Cu(100) surface. The experimental results for both methoxy and ethoxy are best reproduced by the most realistic representation of the hollow position, a Cu-5 cluster. (C) 2003 Elsevier B.V. All rights reserved.
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| 29. |
- Blomquist, Jakob, et al.
(författare)
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Inducing H/D Exchange in Ultrathin Ice Films by Proton Deficiency
- 2011
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Ingår i: Physical Review Letters. - 1079-7114. ; 107:21
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Tidskriftsartikel (refereegranskat)abstract
- We show that H/D exchange between H2O and D2O in ultrathin ice films adsorbed on Cu(100) does not occur through autoionization at temperatures below 140 K. The exchange is, however, facile if a proton deficiency is induced in the ice films by having small amounts of OH preadsorbed on the copper surface. The system was studied using surface infrared vibrational spectroscopy with the aid of density functional theory calculations.
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| 30. |
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| 31. |
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| 32. |
- Karlsson, P G, et al.
(författare)
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Interfacial properties of the nanostructured dye-sensitized solid heterojunction TiO2/RuL2(NCS)(2)/CuI
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:23, s. 11224-11232
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Tidskriftsartikel (refereegranskat)abstract
- The interfaces of the nanostructured dye-sensitized solid heterojunction TiO2/Ru-dye/CuI have been studied using photoelectron spectroscopy of core and valence levels, x-ray absorption spectroscopy and atomic force microscopy. A nanostructured anatase TiO2 film sensitized with RuL2(NCS)(2) [cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothio-cyanato)-ruthenium(II)] was prepared in a controlled way using a novel combined in-situ and ex-situ (Ar atmosphere) method. Onto this film CuI was deposited in-situ. The formation of the dye-CuI interface and the changes brought upon the dye-TiO2 interface could be monitored in a stepwise fashion. A direct interaction between the dye NCS groups and the CuI is evident in the core level photoelectron spectra. Concerning the energy matching of the valence electronic levels, the photoelectron spectra indicate that the dye HOMO overlaps in energy with the Cu 3d-I 5p hydrid states. The CuI grow in the form of particles, which at the initial stages displace the dye molecules causing dye-TiO2 bond breaking. Consequently, the very efficient charge injection channel provided by the dye-TiO2 carboxylic bonding is directly affected for a substantial part of the dye molecules. This may be of importance for the functional properties of such a heterojunction. (C) 2004 American Institute of Physics.
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| 33. |
- Karlsson, P. G., et al.
(författare)
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Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(100) and Si(111) studied by electron spectroscopy
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:4, s. 1008-1018
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Tidskriftsartikel (refereegranskat)abstract
- The growth of ultrathin ZrO2 films on Si(100)-(2 x 1) and Si(111)-(7 x 7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50 angstrom thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7 x 7) the local structure of t-ZrO2 is not observed until a film thickness of 51 angstrom is reached. On Si(100)-(2 x 1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11 angstrom. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr-O valence electron matching to the number of dangling bonds per surface Si atom, The Zr-O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C-O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range. (c) 2006 Elsevier B.V. All rights reserved.
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| 34. |
- Karlsson, P. G., et al.
(författare)
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TiO2 chemical vapor deposition on Si(111) in ultrahigh vacuum: Transition from interfacial phase to crystalline phase in the reaction limited regime
- 2011
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 605:13-14, s. 1147-1156
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between the metal organic precursor molecule titanium(IV) isopropoxide (TTIP) and three different surfaces has been studied: Si(111)-(7 x 7), SiOx/Si(111) and TiO2. These surfaces represent the different surface compositions encountered during TTIP mediated TiO2 chemical vapor deposition on Si(111). The surface chemistry of the titanium(IV) isopropoxide precursor and the film growth have been explored by core level photoelectron spectroscopy and x-ray absorption spectroscopy using synchrotron radiation. The resulting film morphology has been imaged with scanning tunneling microscopy. The growth rate depends on both surface temperature and surface composition. The behavior can be rationalized in terms of the surface stability of isopropoxy and isopropyl groups, confirming that growth at 573 K is a reaction limited process. (C) 2011 Elsevier B.V. All rights reserved.
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| 35. |
- Karlsson, P G, et al.
(författare)
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UHV-MOCVD growth of TiO2 on SiOx/Si(111): Interfacial properties reflected in the Si 2p photoemission spectra
- 2005
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 580:1-3, s. 207-217
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Tidskriftsartikel (refereegranskat)abstract
- Metal-organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 degrees C and flux-limited growth at 500 degrees C. The interfacial properties have been characterized by monitoring synchrotron radiation excited Si 2p photoemission spectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiOx/Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiOx/Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO2)(x)(SiO2)(y) where x and y changes linearly and continuously over the interface. The model quantifies how (TiO2)(x)(SiO2)(y) mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon. (c) 2005 Elsevier B.V. All rights reserved.
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| 36. |
- Karlsson, P. G., et al.
(författare)
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Ultrathin ZrO2 films on Si-rich SiC(0001)-(3x3): Growth and thermal stability
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 601:11, s. 2390-2400
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Tidskriftsartikel (refereegranskat)abstract
- The growth and thermal stability of ultrathin ZrO2 films on the Si-rich Si(0001)-(3 x 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that growth at 400 degrees C yields tetragonal ZrO2. An interface is formed between the ZrO2 film and the SiC substrate. The interface contains Si in several chemically different states. This gives evidence for an interface that is much more complex than that formed upon oxidation with O-2. Si in a 4+ oxidation state is detected in the near surface region. This shows that intermixing of SiO2 and ZrO2 occurs, possibly under the formation of silicate. The alignment of the ZrO2 and SiC band edges is discussed based on core level and valence PES spectra. Subsequent annealing of a deposited film was performed in order to study the thermal stability of the system. Annealing to 800 degrees C does not lead to decomposition of the tetragonal ZrO2 (t-ZrO2) but changes are observed within the interface region. After annealing to 1000 degrees C a laterally heterogeneous layer has formed. The decomposition of the film leads to regions with t-ZrO2 remnants, metallic Zr silicide and Si aggregates. (c) 2007 Elsevier B.V. All rights reserved.
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| 37. |
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| 38. |
- Klementieva, O., et al.
(författare)
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Nano-scale Infrared Imaging of β-sheet Structures in Synaptic Junctions of Primary Neurons Isolated from Transgenic Mice
- 2018
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Ingår i: 2018 43rd International Conference on Infrared Millimeter and Terahertz Waves, IRMMW-THz 2018. - 9781538638095 ; 2018-September
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Konferensbidrag (refereegranskat)abstract
- Aβ is a class of aggregation-prone proteins, which may misfold into stable, β-sheet rich fibrils. Aβ is linked to the development of synaptic pathology in Alzheimer's disease (AD). However, a main question in the AD field is how Aβ contributes to AD neuropathology? Up to now there is little evidence for protein structural changes in diseased neuron. Our aim is to study the distribution of β-sheet structures in AD transgenic neurons in order to uncover sub-cellular mechanism(s) by which amyloid β-sheet structures are involved in AD pathology.
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| 39. |
- Klementieva, O., et al.
(författare)
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Pre-plaque conformational changes in Alzheimer's disease-linked Aβ and APP
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Reducing levels of the aggregation-prone Aβ peptide that accumulates in the brain with Alzheimer's disease (AD) has been a major target of experimental therapies. An alternative approach may be to stabilize the physiological conformation of Aβ. To date, the physiological state of Aβ in brain remains unclear, since the available methods used to process brain tissue for determination of Aβ aggregate conformation can in themselves alter the structure and/or composition of the aggregates. Here, using synchrotron-based Fourier transform infrared micro-spectroscopy, non-denaturing gel electrophoresis and conformational specific antibodies we show that the physiological conformations of Aβ and amyloid precursor protein (APP) in brain of transgenic mouse models of AD are altered before formation of amyloid plaques. Furthermore, focal Aβ aggregates in brain that precede amyloid plaque formation localize to synaptic terminals. These changes in the states of Aβ and APP that occur prior to plaque formation may provide novel targets for AD therapy.
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| 40. |
- Larsson, Emanuel, et al.
(författare)
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Morphological characterization of the human calvarium in relation to the diploic and cranial thickness utilizing X-ray computed microtomography
- 2014
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Ingår i: 13th Mediterranean Conference on Medical and Biological Engineering and Computing 2013, MEDICON 2013; Seville; Spain; 25 September 2013 through 28 September 2013. - Cham : Springer. - 9783319008455 ; , s. 194-197
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Konferensbidrag (refereegranskat)abstract
- When attempting to establish accurate models for the human diploe, micro-scale morphological differences in the four main areas of the calvaria could also be considered. In this study, X-ray computed microtomography (μ-CT) images were analyzed in order to quantitatively characterize the micro-architecture of the human calvarium diploe. A bone specimen from each area of the skull (temporal, frontal, parietal and occipital) was extracted from a set of 5 human donors and each specimen was characterized in terms of density, specific surface area, trabecular thickness, trabecular spacing. The obtained results revealed that subject-individual structural differences could be related with the diploic as well as the total cranial thickness of the human skull bones. Some tendencies of dependency could also be made with respect to the age of the subject. A consideration of these individual variations can improve traditional models that assume equal conditions throughout the skull.
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| 41. |
- Larsson, E., et al.
(författare)
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Quantification of Structural Differences in the Human Calvarium Diploe by Means of X-ray Computed Microtomography Image Analysis : A Case Study
- 2012
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Ingår i: 5th European Conference of the International Federation for Medical and Biological Engineering. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642235078 ; , s. 599-602
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Konferensbidrag (refereegranskat)abstract
- Accurate models for the human diploe have to take into account any structural differences in the four main areas of the calvaria bones. In this study the technique of X-ray computed microtomography (mu-CT) along with image analysis was used in order to visualize and quantitatively analyze differences in the micro-architecture of the human calvarium diploe. A bone specimen from each area of the skull (temporal, frontal, parietal and occipital) was extracted from a human donor and each specimen was characterized in terms of density, specific surface area, trabecular thickness and anisotropy. The obtained results reveal that in the considered case there are structural differences which therefore can be useful for refining traditional models that assume equal conditions throughout the skull.
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| 42. |
- Lazzaroni, R., et al.
(författare)
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Electronic Structure of Metal/Polymer Interfaces : aluminum on Conjugated Polymers
- 1991
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Ingår i: Metallized Plastics 2. - Boston, MA : Springer. - 9781489907370 - 9781489907356 ; , s. 199-212
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Aluminum has been deposited on two types of conjugated polymers, polyalkylthiophene and polyaniline. The polymers were in the undoped, neutral form which possesses semiconducting properties. The chemical structure of the metal/polymer interface has been investigated by X-ray and UV photoelectron spectroscopy. Core level spectra indicate that aluminum reacts with the sulfur atom of the polythiophene chain, strongly perturbing the π-electron system. In the case of polyaniline, the interaction with the metal depends on the oxidation state of the polymer. UPS data, combined with the results of band structure calculations, are interpreted in terms of the Al-induced modifications of the π-electron system.
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| 43. |
- Lindgren, Johan, et al.
(författare)
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Molecular composition and ultrastructure of Jurassic paravian feathers
- 2015
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Feathers are amongst the most complex epidermal structures known, and they have a well-documented evolutionary trajectory across non-avian dinosaurs and basal birds. Moreover, melanosome-like microbodies preserved in association with fossil plumage have been used to reconstruct original colour, behaviour and physiology. However, these putative ancient melanosomes might alternatively represent microorganismal residues, a conflicting interpretation compounded by a lack of unambiguous chemical data. We therefore used sensitive molecular imaging, supported by multiple independent analytical tests, to demonstrate that the filamentous epidermal appendages in a new specimen of the Jurassic paravian Anchiornis comprise remnant eumelanosomes and fibril-like microstructures, preserved as endogenous eumelanin and authigenic calcium phosphate. These results provide novel insights into the early evolution of feathers at the sub-cellular level, and unequivocally determine that melanosomes can be preserved in fossil feathers.
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| 44. |
- Lindgren, Johan, et al.
(författare)
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Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 564:7736
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Tidskriftsartikel (refereegranskat)abstract
- Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.
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| 45. |
- Ragazzon, Davide, et al.
(författare)
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Chemical vapor deposition of ordered TiOx nanostructures on Au(111)
- 2013
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 617, s. 211-217
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Tidskriftsartikel (refereegranskat)abstract
- The deposition of TiOx (x <= 2) structures on Au(111) by chemical vapor deposition (CVD) in ultrahigh vacuum (UHV) has been investigated with high-resolution core level photoelectron spectroscopy (PES), low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Using titanium tetra-isopropoxide as single source precursor it is possible to form different TiOx phases on the surface after deposition: at low coverages, we observe large two-dimensional (2D) honeycomb-lattice Ti2O3 islands with a (2 x 2) registry with the substrate. Higher coverages are dominated by the formation of three-dimensional (3D) TiO2 structures. The TiO2 structures are atomically well ordered provided that the deposition temperature is high enough (500 degrees C). The ordered structure exhibits a LEED pattern characteristic for a rectangular surface unit cell. By performing the deposition at different temperatures it is possible to tune the balance between the 2D and 3D phases: Growth at 500 degrees C significantly favors the formation of 3D TiO2 islands as compared to growth at 200 degrees C and 300 degrees C. (C) 2013 Elsevier B.V. All rights reserved.
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| 46. |
- Richter, Jan Hinnerk, et al.
(författare)
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Phase separation and charge localization in UHV-lithiated anatase TiO2 nanoparticles
- 2005
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Ingår i: Physical Review B. - 1098-0121. ; 71:23, s. 235419-
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Tidskriftsartikel (refereegranskat)abstract
- The insertion of lithium in anatase TiO2 nanoparticles under ultrahigh vacuum (UHV) conditions is studied using x-ray absorption spectroscopy (XAS) and resonant photoelectron spectroscopy (RPES) at the Ti L2,3 edge. It is demonstrated that XAS can be used to monitor the separation into an anatase phase and a lithium titanate phase of formal stoichiometry Li0.5TiO2. The initial state properties of the Ti 3d states of the lithium titanate phase are investigated using ab initio electronic structure calculations. The calculations show a correlation driven separation of Ti 3d states from the conduction band in agreement with previous studies. It is shown that Ti in different oxidation states (Ti3+ and Ti4+) is formed as a direct consequence of the electron-electron interaction. RPES and XAS spectra confirm the presence of electronically inequivalent Ti sites. The site-sensitivity of the RPES spectra at selected electron binding energies is found to be consistent with the calculations.
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| 47. |
- Sandell, A., et al.
(författare)
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Probing and modifying the empty-state threshold of anatase TiO2 : Experiments and ab initio theory
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:7, s. 075113-
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Tidskriftsartikel (refereegranskat)abstract
- O 1s x-ray absorption spectroscopy (XAS) in conjunction with photoelectron spectroscopy has been used to explore the conduction-band edge of single crystalline and nanostructured anatase TiO2. The experiments are supported by ab initio density-functional calculations in which both the initial and core hole final states are considered. The calculations show that the states at the conduction-band edge of anatase are of pure d(xy) character. This is also the case in the presence of an O 1s core hole. In the O 1s XAS process pure Ti d states cannot be probed and, by appropriate energy referencing, the separation between the Ti d derived conduction-band edge and the threshold of the unoccupied Ti d-O p states can therefore be revealed. The electronic charge needed per Ti to eliminate this offset is discussed in quantitative terms. The theoretical and experimental values are in good agreement, showing that 4 +/- 2% of an electronic charge per Ti ion is sufficient to change the character of the empty states at threshold from pure Ti d to Ti d-O p.
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| 48. |
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| 49. |
- Schaefer, Andreas, 1981, et al.
(författare)
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Defect-Induced Water Bilayer Growth on Anatase TiO2(101)
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 34:37, s. 10856-10864
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Tidskriftsartikel (refereegranskat)abstract
- Preparing an anatase TiO2(101) surface with a high density of oxygen vacancies and associated reduced Ti species in the near-surface region results in drastic changes in the water adsorption chemistry compared to adsorption on a highly stoichiometric surface. Using synchrotron radiation excited photoelectron spectroscopy, we observe a change in the water growth mode, from layer-by-layer growth on the highly stoichiometric surface to bilayer growth on the reduced surface. Furthermore, we have been able to observe Ti3+ enrichment at the surface upon water adsorption. The Ti3+ enrichment occurs concomitant with effective water dissociation into hydroxyls with a very high thermal stability. The water bilayer on the reduced surface is thermally more stable than that on the stoichiometric surface, and it is more efficient in promoting further water dissociation upon heating. The results thus show how the presence of subsurface defects can alter the wetting mechanism of an oxide surface.
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| 50. |
- Schaefer, Andreas, 1981, et al.
(författare)
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First layer water phases on anatase TiO2(101)
- 2018
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 674, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- The anatase TiO2(101) surface and its interaction with water is an important topic in oxide surface chemistry. Firstly, it benchmarks the properties of the majority facet of TiO2 nanoparticles and, secondly, there is a controversy as to whether the water molecule adsorbs intact or deprotonates. We have addressed the adsorption of water on anatase TiO2(101) by synchrotron radiation photoelectron spectroscopy. Three two-dimensional water structures are found during growth at different temperatures: at 100 K, a metastable structure forms with no hydrogen bonding between the water molecules. In accord with prior literature, we assign this phase to chains of disordered molecules. Growth 160 K results in a metastable structure with expressed hydrogen bonding between the water molecules. At 190 K, the water molecules become disordered as the thermal energy is too high and hence the hydrogen bonds break. The result is a structure with isolated monomers. Partial dissociation is observed for all three growths, with the molecular state only slightly favored in energy (20–40 meV) over the dissociated state. Heating of a thick film leads to more dissociation compared to a bilayer, when formed at 100 K. Thus, extending the water network facilitates proton transport and hence dissociation. The results reconcile apparent conflicting experimental results previously obtained by scanning tunneling microscopy (STM) and core level photoelectron spectroscopy.
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