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- Molina-Aldareguia, J.M., et al.
(författare)
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Deformation structures under indentations in TiN/NbN single-crystal multilayers deposited by magnetron sputtering at different bombarding ion energies
- 2002
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Ingår i: Philosophical magazine. A. Physics of condensed matter. Defects and mechanical properties. - 0141-8610. ; 82:10 SPEC., s. 1983-1992
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Tidskriftsartikel (refereegranskat)abstract
- Work elsewhere has suggested that multilayer films with layer thicknesses of a few nanometres can be much harder than monolithic films, although there is considerable variation in the observed magnitude of this effect. To investigate this, multilayer TiN/NbN films have been deposited by reactive magnetron sputtering on to MgO single crystals. The hardnesses measured were similar to those of the TiN and NbN alone, which is consistent with the observation by transmission electron microscopy (TEM) that deformation across the interfaces was not prevented. Varying the electrical potential at which the film was grown from -10 to -200 V and the corresponding ion energy from 10 to 200 eV increased the hardness from 19 to 25 GPa, further decreases in the potential caused the hardness to decrease. Using TEM, deformation was observed to occur along the apparent columnar boundaries within the films, suggesting that the effect of the electrical potential on the measured hardness was caused by changes in the apparent strength of the columnar boundaries, possibly associated with the variations in the volume fraction of voids that were observed on these boundaries.
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- Heimdal Nilsson, Elna, et al.
(författare)
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Re-evaluation of the reaction rate coefficient of CH3Br + OH with implications for the atmospheric budget of methyl bromide
- 2013
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 80, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- The reaction rate coefficient k(CH3Br + OH) has been determined in the temperature range 298-373 K, using pulse radiolysis/UV kinetic spectroscopy, and at 298 K using a relative rate method. The Arrhenius expression obtained from a fit to the experimental results is (2.9 +/- 0.9) x 10(-12) exp(-(1230 +/- 125)/T) cm(3) molecule(-1) s(-1), which is greater than the expression currently recommended. The relative rate experiments give k(298 K) = (4.13 +/- 0.63) x 10(-14) cm(3) molecule(-1) s(-1). The results of the absolute and relative rate experiments indicate that the source budget of atmospheric CH3Br should be reinvestigated, as was recently done for CH3Cl. (C) 2013 Elsevier Ltd. All rights reserved.
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- Högberg, Hans, 1968-, et al.
(författare)
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Growth and characterization of MAX-phase thin films
- 2005
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 193, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- We report that magnetron sputtering can be applied to synthesize MAX-phase films of several systems including Ti–Si–C, Ti–Ge–C, Ti–Al–C, and Ti–Al–N. In particular, epitaxial films of the known phases Ti3SiC2, Ti3GeC2, Ti2GeC, Ti3AlC2, Ti2AlC, and Ti2AlN as well as the newly discovered thin film phases Ti4SiC3, Ti4GeC3 and intergrown structures can be deposited at 900–1000 °C on Al2O3(0001) and MgO(111) pre-seeded with TiC or Ti(Al)N. From XTEM and AFM we suggest a growth and nucleation model where MAX-phase nucleation is initiated at surface steps or facets on the seed layer and followed by lateral growth. Differences between the growth behavior of the systems with respect to phase distribution and phase stabilities are discussed. Characterization of mechanical properties for Tin+1Si–Cn films with nanoindentation show decreased hardness from about 25 to 15 GPa upon penetration of the basal planes with characteristic large plastic deformation with pile up dependent on the choice of MAX material. This is explained by cohesive delamination of the basal planes and kink band formation, in agreement with the observations made for bulk material. Measurements of the electrical resistivity for Ti–Si–C and Ti–Al–N films with four-point probe technique show values of 30 and 39 μΩ cm, respectively, comparable to bulk materials.
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- Joelsson, L. M T, et al.
(författare)
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Kinetic isotope effects of 12CH3D+OH and 13CH3D+OH from 278 to 313K
- 2016
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:7, s. 4439-4449
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Tidskriftsartikel (refereegranskat)abstract
- Methane is the second most important long-lived greenhouse gas and plays a central role in the chemistry of the Earth's atmosphere. Nonetheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including the doubly substituted species 13CH3D, offers new insight into the methane budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH in the troposphere, which accounts for around 84% of all methane removal. Here we present experimentally derived methane+OH kinetic isotope effects and their temperature dependence over the range of 278 to 313K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D Combining double low line 1.31 ± 0.01 and kCH4/k13CH3D Combining double low line 1.34 ± 0.03 at room temperature, implying that the methane+OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) Combining double low line kCH4/k13CH3D, within the experimental uncertainty, given the literature value of kCH4/k13CH4 Combining double low line 1.0039 ± 0.0002. In addition, the kinetic isotope effects were characterized using transition state theory with tunneling corrections. Good agreement between the experimental, quantum chemical, and available literature values was obtained. Based on the results we conclude that the OH reaction (the main sink of methane) at steady state can produce an atmospheric clumped isotope signal (δ(13CH3D) Combining double low line ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02. This implies that the bulk tropospheric δ(13CH3D) reflects the source signal with relatively small adjustment due to the sink signal (i.e., mainly OH oxidation).
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