| 1. |
- Field, M. R., et al.
(författare)
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A combinatorial comparison of DC and high power impulse magnetron sputtered Cr2AlC
- 2014
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 259, s. 746-750
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Tidskriftsartikel (refereegranskat)abstract
- Using a combinatorial approach, Cr, Al and C have been deposited onto sapphire wafer substrates by High Power Impulse Magnetron Sputtering (HiPIMS) and DC magnetron sputtering. X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and X-ray diffraction were employed to determine the composition and microstructure of the coatings and confirm the presence of the Cr2AlC MAX phase within both coatings. One location in both the DCMS and HiPIMS coatings contained only MAX phase Cr2AlC. The electrical resistivity was also found to be nearly identical at this location and close to that reported from the bulk, indicating that the additional energy in the HiPIMS plasma was not required to form high quality MAX phase Cr2AlC.
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| 2. |
- Ittermann, T., et al.
(författare)
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Standardized Map of Iodine Status in Europe
- 2020
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Ingår i: Thyroid. - : Mary Ann Liebert Inc. - 1050-7256 .- 1557-9077. ; 30:9
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Tidskriftsartikel (refereegranskat)abstract
- Background:Knowledge about the population's iodine status is important, because it allows adjustment of iodine supply and prevention of iodine deficiency. The validity and comparability of iodine-related population studies can be improved by standardization, which was one of the goals of the EUthyroid project. The aim of this study was to establish the first standardized map of iodine status in Europe by using standardized urinary iodine concentration (UIC) data. Materials and Methods:We established a gold-standard laboratory in Helsinki measuring UIC by inductively coupled plasma mass spectrometry. A total of 40 studies from 23 European countries provided 75 urine samples covering the whole range of concentrations. Conversion formulas for UIC derived from the gold-standard values were established by linear regression models and were used to postharmonize the studies by standardizing the UIC data of the individual studies. Results:In comparison with the EUthyroid gold-standard, mean UIC measurements were higher in 11 laboratories and lower in 10 laboratories. The mean differences ranged from -36.6% to 49.5%. Of the 40 postharmonized studies providing data for the standardization, 16 were conducted in schoolchildren, 13 in adults, and 11 in pregnant women. Median standardized UIC was <100 mu g/L in 1 out of 16 (6.3%) studies in schoolchildren, while in adults 7 out of 13 (53.8%) studies had a median standardized UIC <100 mu g/L. Seven out of 11 (63.6%) studies in pregnant women revealed a median UIC Conclusions:We demonstrate that iodine deficiency is still present in Europe, using standardized data from a large number of studies. Adults and pregnant women, particularly, are at risk for iodine deficiency, which calls for action. For instance, a more uniform European legislation on iodine fortification is warranted to ensure that noniodized salt is replaced by iodized salt more often. In addition, further efforts should be put on harmonizing iodine-related studies and iodine measurements to improve the validity and comparability of results.
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| 3. |
- Struzzi, C., et al.
(författare)
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Exploiting sensor geometry for enhanced gas sensing properties of fluorinated carbon nanotubes under humid environment
- 2019
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Ingår i: Sensors and Actuators B: Chemical. - : Elsevier BV. - 0925-4005. ; 281, s. 945-952
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Tidskriftsartikel (refereegranskat)abstract
- Modification of the surface electronic properties of vertically aligned and randomly distributed carbon nanotubes and the hydrophobic character after exposure to Ar:F2 and CF4 plasma are exploited to optimize the sensing characteristics of these materials. The sensing properties of fluorinated carbon nanotubes are disclosed by probing their stability and responsiveness towards the detection of two selected pollutants such as nitrogen dioxide and ammonia (NO2 and NH3). The effects of both humidity level and geometry of the sensing layer are assessed. It is demonstrated that fluorination, by increasing the surface hydrophobicity, results in increased response reproducibility and enhanced sensor response towards NH3 when using vertically aligned carbon nanotubes.
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| 4. |
- Persson, Per, et al.
(författare)
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Formation of the MAX-phase oxycarbide Ti2AlC1-xOx studied via electron energy-loss spectroscopy and first-principles calculations
- 2009
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 80:9, s. 092102-
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen incorporation in the Ti2AlC MAX phase and TiC was investigated in the electron microscope using spatially resolved fine-structure electron energy-loss spectroscopy analysis. Corresponding fine structures were calculated within the full-potential-linearized augmented plane-wave framework. In the calculations, oxygen was substituted for aluminum and carbon in Ti2AlC as well as for carbon in TiC, in concentrations of 3.1, 6.2, and 12.5 at %. Comparison of calculated and measured spectra shows that oxygen is incorporated on the carbon site in both TiC and Ti2AlC. These findings reveal the existence of MAX phase oxycarbide MA(O,C) alloys and O as a third X element in addition to C and N.
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| 5. |
- Persson, P.O.A., et al.
(författare)
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A solid phase reaction between Ti Cx thin films and Al2 O3 substrates
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:6
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Tidskriftsartikel (refereegranskat)abstract
- Ti Cx thin films were deposited on Al2 O3 substrates at 900 °C by using a multiple cathode high current pulsed cathodic arc. The Ti:C pulse ratio and, hence, the composition was varied from C rich to Ti rich. It is found that the Al2 O3 substrate is decomposed and reacts with the Ti Cx film to incorporate significant amounts of O and Al in the growing film. When the stoichiometry is suitable, epitaxially oriented Ti2 AlC MAX phase with significant O incorporated is formed. The results indicate that Al2 O3 is not an ideal substrate material for the growth of transition metal carbides and MAX phase thin films. © 2008 American Institute of Physics.
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| 6. |
- Rosen, Johanna, et al.
(författare)
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Amorphous and crystalline phases in thermal quench simulations of alumina
- 2007
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606 .- 1089-7690. ; 126:20, s. 204709-
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Tidskriftsartikel (refereegranskat)abstract
- The authors report molecular dynamics simulations of alumina (Al2O3) during crystallization from the melt. Using liquid quench methods, they investigate the effect of cooling rate on the structural evolution of the alpha, kappa, and the bixbyite phases. A critical temperature window is identified, where the time spent in this window is crucial in determining the extent to which the systems approach crystallinity. A strong dependence is observed between the final structure and the quench rate, which is most pronounced for the alpha phase and to lesser extent for the other phases. The results show that the different phases have different tendencies to crystallize that are determined by energetics, complexity of crystal structure, and the number of metastable states.
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| 7. |
- Rosen, Johanna, et al.
(författare)
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Influence of gas entry point on plasma chemistry, ion energy and deposited alumina thin films in filtered cathodic arc
- 2007
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Ingår i: Plasma chemistry and plasma processing. - : Springer Science Business Media. - 0272-4324 .- 1572-8986. ; 27:5, s. 599-608
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Tidskriftsartikel (refereegranskat)abstract
- The effect of gas entry point on the plasma chemistry, ion energy distributions and resulting alumina thin film growth have been investigated for a d.c. cathodic arc with an aluminum cathode operated in an oxygen/argon atmosphere. Ions of aluminum, oxygen and argon, as well as ions originating from the residual gas are investigated, and measurements for gas entry at both the cathode and close to the substrate are compared. The latter was shown to result in higher ion flux, lower levels of ionised residual gas, and lower ion energies, as compared to gas inlet at the cathode. These plasma conditions that apply when gas entry at the substrate is used result in a higher film deposition rate, less residual gas incorporation, and more stoichiometric alumina films. The results show that the choice of gas entry point is a crucial parameter in thin film growth using reactive PVD processes such as reactive cathodic arc deposition.
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| 8. |
- Rosen, Johanna, et al.
(författare)
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Oxygen incorporation in Ti2AlC thin films
- 2008
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 92:6, s. 064102-
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of Ti2AlC MAX phase have been deposited using a multiple cathode pulsed cathodic arc. Evidence for substantial oxygen incorporation in the MAX phase is presented, likely originating from residual gas present in the vacuum chamber during deposition. The characteristic MAX phase crystal structure is maintained, in agreement with ab initio calculations, supporting substitutional O in C lattice positions. On the basis of these results, we propose the existence of a MAX phase-like material with material properties tuned by the incorporation of oxygen. Additionally, possible unintentional O incorporation in previously reported MAX phase materials is suggested.
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| 9. |
- Rosén, Johanna, et al.
(författare)
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Oxygen incorporation in Ti2AlC: Tuning of anisotropic conductivity
- 2010
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Ingår i: APPLIED PHYSICS LETTERS. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 97:7, s. 073103-
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Tidskriftsartikel (refereegranskat)abstract
- The substitution of oxygen for carbon in Ti2AlC M((n+1))AX(n) (MAX) phase, forming Ti2AlC1-xOx, has recently been reported. In this paper we simulate the effect of oxygen incorporation on mechanical and electronic properties using ab initio calculations. While the mechanical properties are not sensitive to the change in composition, the electronic properties can be tuned by varying the oxygen concentration. As the concentration increases, the conduction changes from in plane, typical of MAX phases, to conduction also in the c-direction. The conduction along c passes from insulating to n-type and then finally to p-type. These findings reveal an anisotropic semiconducting material.
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| 10. |
- Tucker, Mark, et al.
(författare)
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A combinatorial investigation of sputtered Ta-Al-C thin films
- 2014
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 558, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- We describe a combinatorial experiment investigating the Ta-Al-C material system, conducted with the aim of determining why the tantalum-containing M-n + (1)AX(n) phases have so far proved to be not amenable to thin-film synthesis. Samples were deposited onto (0001) Al2O3 wafers at 850 degrees C and characterized by X-ray diffraction wafer maps, scanning electron microscopy, and surface optical scattering. Elemental Ta, the binary phases TaC, Ta2C, and TaAl3, and the ternary phases Ta3Al2C and Ta5Al3C were identified. The morphology, phase composition and preferred orientation of the films deposited were found to be highly sensitive to the Ta fraction of the incident flux during deposition. No MAX phase material was observed, indicating that the Ta-containing MAX phases do not form under the deposition conditions investigated. Explanations associated with inadequate coverage of stochiometries, preferential sputtering, and thermodynamic instability have been ruled out. An explanation based on reduced surface diffusion of Ta during growth is proposed. A substantially higher substrate temperature during deposition is likely to be required to synthesize Ta-containing MAX phases.
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