| 1. |
- Duong, T. C., et al.
(författare)
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A hierarchical computational thermodynamic and kinetic approach to discontinuous precipitation in the U-Nb system
- 2015
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Ingår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015. - : International Conference on Solid-Solid Phase Transformations in Inorganic Materials. - 9780692437360 ; , s. 887-894
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Konferensbidrag (refereegranskat)abstract
- U-Nb alloys decompose via discontinuous precipitation (DP) over a broad range of aging conditions, adversely affecting their properties. The growth kinetics, lamellar spacing, and Nb partitioning have been measured, but the thermodynamic and kinetic factors underlying these specific transformation characteristics and reaction paths, vis-a-vis the monotectoid reaction, are not fully resolved. In this work, a hierarchical computational thermodynamic and kinetic approach was carried out to investigate DP. The hierarchical approach started with density-functional theory (DFT) investigations of ground-state formation energies of bcc-based U-Nb alloys. The estimated energetic data was then utilized as an imposed first-principles-based constraint to improve the consistency of the CALPHAD thermodynamic and, subsequently, kinetic assessments of U-Nb. Phasefield simulations were then carried out to study DP's microstructure evolution using the assessed CALPHAD thermodynamic and kinetic representations. Good agreement with experiments on different physical/length scales was achieved, which validates the present theoretical contributions to a better understanding of DP in U-Nb alloys.
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| 2. |
- Jaramillo-Fernandez, Juliana, et al.
(författare)
-
Thermal conductivity of polycrystalline aluminum nitride films : Effects of the microstructure, interfacial thermal resistance and local oxidation
- 2015
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Ingår i: THERMINIC 2015 - 21st International Workshop on Thermal Investigations of ICs and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467397056
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Konferensbidrag (refereegranskat)abstract
- The thermal conductivity of polycrystalline aluminum nitride (AlN) films with inhomogeneous structures is experimentally and theoretically investigated. The influence of the grain morphology and size evolution along the cross plane direction of the films is studied by thickness-dependent 3m measurements on AlN monolayers. For AlN/AlN multilayer samples, the impact of oxygen-related defects localized at the interface between two AlN layers, is also analyzed. When the total thickness of these multilayers is downsized from 1107 nm to 270 nm, their measured effective thermal conductivity reduces by 47%, which is smaller than the corresponding reduction of 58% for monolayers. In multilayers, this decrease is due to the additive contributions of the thermal resistances arising from the AlN and AlN/AlN interfaces. The experimental data are interpreted through an analytical model developed for nanocrystalline films with inhomogeneous structures. It is shown that the size effects on the phonon mean free paths and the intrinsic thermal resistance resulting from the inhomogeneous microstructure predominate as the film thickness increases, whilst the contribution of the interface thermal resistance strengthens when the thickness is scaled down.
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| 3. |
- Jaramillo-Fernandez, Juliana, et al.
(författare)
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Tuning of heat transport across thin films of polycrystalline AlN via multiscale structural defects
- 2015
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Ingår i: ECS Transactions. - : Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; , s. 53-64
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Konferensbidrag (refereegranskat)abstract
- The effective thermal conductivity of nanocrystalline films of AlN with inhomogeneous microstructure is investigated experimentally and theoretically. This is done by measuring the thermal conductivity of the samples with the 3-omega method and characterizing their microstructure by means of electron microscopy. The relative effect of the microstructure and the interface thermal resistance on the thermal conductivity is quantified through an analytical model. Thermal measurements showed that when the thickness of an AlN film is reduced from 1460 to 270 nm, its effective thermal conductivity decreases from 8.21 to 3.12 WYm-1?K-1, which is two orders of magnitude smaller than its bulk counterpart value. It is shown that both the size effects of the phonon mean free paths and the intrinsic thermal resistance resulting from the inhomogeneous microstructure predominate for thicker films, while the contribution of the interface thermal resistance strengthens as the film thickness is scaled down. The obtained results demonstrate that the structural inhomogeneity in polycrystalline AlN films can be efficiently used to tune their cross- plane thermal conductivity. In addition, thermal conductivity measurements of epitaxially grown InP layers on silicon using Raman spectroscopy are reported.
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