| 1. |
- Karlsson, G. P., et al.
(författare)
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Test of the short-term critical levels for acute ozone injury on plants - improvements by ozone uptake modelling and the use of an effect threshold
- 2004
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 38:15, s. 2237-2245
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Tidskriftsartikel (refereegranskat)abstract
- The current short-term critical levels for acute ozone injury on plants were evaluated based on 32 datasets from eastern Austria, Belgium and southern Sweden with subterranean clover (Trifolium subterraneum L., cv. Geraldton). Potential improvements using an exposure index related to ozone uptake (AF(st), Accumulated Stomatal Flux), a modified accumulated exposure over the threshold (mAOT) exposure index and the introduction of an effect threshold in the short-term critical level were investigated. The existing short-term critical levels did not accurately describe the effects in terms of observed visible injury. Using a mAOT based on solar radiation and vapour pressure deficit (VPD) improved the explanation of observed visible injury. However, using a simple stomatal conductance model, driven by solar radiation, air temperature, VPD and ozone uptake, the correlation between modelled and observed effects were considerably improved. The best performance was obtained when an ozone uptake rate threshold of 10 nmol m(-2) s(-1) (AF(st)10, per unit total leaf area) was used. The results suggested the use of an effect threshold of 10% leaf injury in order to minimise the risk of erroneously recorded visible injury due to observation technique or other injuries hard to distinguish from ozone injury. A new, AF(st) based exposure index was suggested, an ozone exposure of AF(st)10=75 mumol m(-2) during an exposure period of eight days was estimated to prevent more than 10% visible injury of the leaves. This study strongly suggests that a simple model for ozone uptake much better explains observed effects, compared to the currently used exposure index AOT40. However, if a lower degree of complexity, data requirements and also a lower extent of explanation of observed effects are to be considered a new short-term critical level, based on a mAOT may be suggested: a mAOT30 of 160 ppb h during an exposure period of 8 days is estimated to protect the leaves from visible injury on more than 10% of the leaves. (C) 2004 Elsevier Ltd. All rights reserved.
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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 9. |
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| 10. |
- 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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