| 1. |
- Lu, J., et al.
(författare)
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Chemical vapour deposition of molybdenum carbides : aspects of phase stability
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 370:02-jan, s. 203-212
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of different molybdenum carbides (delta-MoC1-x, gamma'-MoC1-x and Mo2C) have been deposited from a gas mixture of MoCl5/H-2/C2H4 at 800 degrees C by CVD. The H-2 content in the vapour has a strong influence on the phase composition and microstructure. Typically, high H-2 contents lead to the formation of nanocrystalline delta-MoC1-x films while coarse-grained gamma'-MoC1-x, is formed with an H-2-free gas mixture. This phase has previously only been synthesized by carburization of Mo in a CO atmosphere and it has therefore been considered as an oxycarbide phase stabilized by the presence of oxygen in the lattice. Our results, however, show that gamma'-MoC1-x films containing only trace amounts of oxygen can be deposited by CVD. Stability calculations using a FP-LMTO method confirmed that the gamma'-MoC1-x phase is stabilized by oxygen but that the difference in energy between e.g. delta-MoC0.75 and oxygen-free gamma'-MoC0.75 is Small enough to allow the synthesis of the latter phase in the absence of kinetic constraints. Annealing experiments of metastable delta-MoC1-x and gamma'-MoC1-x films showed two different reaction products suggesting that kinetic effects play an important role in the decomposition of these phases.
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| 2. |
- Lu, J, et al.
(författare)
-
Chemical vapour deposition of molybdenum carbides: aspects of phase stability
- 2000
-
Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 370:1-2, s. 203-212
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of different molybdenum carbides (δ-MoC1−x, γ′-MoC1−x and Mo2C) have been deposited from a gas mixture of MoCl5/H2/C2H4 at 800°C by CVD. The H2 content in the vapour has a strong influence on the phase composition and microstructure. Typically, high H2 contents lead to the formation of nanocrystalline δ-MoC1−x films while coarse-grained γ′-MoC1−x is formed with an H2-free gas mixture. This phase has previously only been synthesized by carburization of Mo in a CO atmosphere and it has therefore been considered as an oxycarbide phase stabilized by the presence of oxygen in the lattice. Our results, however, show that γ′-MoC1−x films containing only trace amounts of oxygen can be deposited by CVD. Stability calculations using a FP-LMTO method confirmed that the γ′-MoC1−x phase is stabilized by oxygen but that the difference in energy between e.g. δ-MoC0.75 and oxygen-free γ′-MoC0.75 is small enough to allow the synthesis of the latter phase in the absence of kinetic constraints. Annealing experiments of metastable δ-MoC1−x and γ′-MoC1−x films showed two different reaction products suggesting that kinetic effects play an important role in the decomposition of these phases.
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| 3. |
- Palmquist, J.-P., et al.
(författare)
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Deposition of epitaxial ternary transition metal carbide films
- 2002
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 405, s. 122-128
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Tidskriftsartikel (refereegranskat)abstract
- Thin epitaxial carbide films have been deposited in UHV by co-evaporation of Mo, Nb, Ti and V, with C60 as carbon source. Two separate systems were studied, Ti1-xVxCy on MgO(001) and Nb1-xMoxCy on MgO(111). We demonstrate the possibility to tune the cell parameter of an epitaxial ternary carbide film by control of the composition. Analysis with reciprocal space mapping show that deposition of Ti0.34V0.66C0.81 at 500 °C yields a strain-free film with perfect match towards the MgO(001) substrate. Also, a good manual control of the individual fluxes allows the design of tailor-made compositional gradient structures. An epitaxial linear carbide gradient film going from TiC to VC was deposited at 500 °C. Furthermore, the low deposition temperature allows the deposition of metastable carbide structures. This was shown with epitaxial growth of a Nb1-xMoxCy film at 500 and 600 °C. © 2002 Elsevier Science B.V. All rights reserved.
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| 4. |
- Palmquist, J.-P., et al.
(författare)
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Magnetron sputtered W-C films with C60 as carbon source
- 2003
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 444:1-2, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- Thin films in the W–C system were prepared by magnetron sputtering of W with coevaporated C60 as carbon source. Epitaxial deposition of different W–C phases is demonstrated. In addition, nanocrystalline tungsten carbide film growth is also observed. At low C60/W ratios, epitaxial growth of α-W with a solid solution of carbon was obtained on MgO(001) and Al2O3(001) at 400 °C. The carbon content in these films (10–20 at.%) was at least an order of magnitude higher than the maximum equilibrium solubility and gives rise to an extreme hardening effect. Nanoindentation measurements showed that the hardness of these films increased with the carbon content and values as high as 35 GPa were observed. At high C60/W ratios, films of the cubic β-WC1−x (x=0–0.6) phase were deposited with a nanocrystalline microstructure. Films with a grain size <30 Å were obtained and the hardness of these films varied from 14 to 24 GPa. At intermediate C60/W ratios, epitaxial films of hexagonal W2C were deposited on MgO(111) at 400 °C. Polycrystalline phase mixtures were obtained on other substrates and hexagonal WC could be deposited as minority phase at 800 °C.
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