| 1. |
- Beckers, M., et al.
(författare)
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Nucleation and growth of Ti2 AlN thin films deposited by reactive magnetron sputtering onto MgO(111)
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:7
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Tidskriftsartikel (refereegranskat)abstract
- The nucleation and growth of Ti2 AlN thin films on MgO(111) substrates during dual direct current reactive magnetron cosputtering from Ti and Al targets in an Ar N2 atmosphere at a substrate temperature of 690 °C have been investigated. Time and thickness dependent in situ specular x-ray reflectivity and x-ray diffraction in combination with cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy reveal the formation of competing phases for slight N superstoichiometry with respect to Ti2 AlN. The stoichiometry deviations initiate the layer-by-layer growth of a ∼380 Å thick epitaxial N-substoichiometric cubic (Ti1-x Alx) Ny layer. N-vacancy driven diffusion of Ti and Al leads to decomposition of this metastable solid solution into nanosized cubic TiN y′ and AlN y″ domains as well as to a solid-state reaction with the MgO(111) by formation of a Mg2 (Al:Ti) O4 spinel, reducing the transformed (Ti1-x Alx) Ny layer thickness down to ∼60 Å. Local AlN y″ domains serve as templates for Ti2 AlN nucleation at higher thicknesses. At the same time TiN y′ and AlN y″ serve as a sink for excess gas phase N during the subsequent polycrystalline Ti2 AlN growth with random (Ti1-x Alx) Ny renucleation as a tissue phase along Ti2 AlN grain boundaries. The individual Ti2 AlN grains with vertical sizes up to the total thickness retain local epitaxy to the substrate, with basal planes nonparallel to the substrate interface. Concurrently the (Ti1-x Alx) Ny layer is further reduced by inward Ti2 AlN grain growth along the basal planes. © 2007 American Institute of Physics.
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| 2. |
- Manfred, Beckers, et al.
(författare)
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Microstructure and nonbasal-plane growth of epitaxial Ti2AlN thin films
- 2006
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 99:3, s. 034902-1-034902-8
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of the Mn+1AXn (MAX) phase (M: early transition metal, A:A-group element, X: C and/or N, n=1-3) Ti2AlN were epitaxially grown onto single-crystal MgO(111) and MgO(100) substrates by dc reactive magnetron cosputtering from Ti and Al targets in an Ar/N2 gas mixture at a temperature of 690°C. To promote the nucleation of the MAX phase, a fcc (Ti0.63Al0.37)N seed layer was deposited before changing to Ti2AlN growth parameters. The nucleation processes have been studied by real-time in situ specular x-ray reflectivity. Independent of substrate orientation, the seed layer shows no roughening until its final thickness of approximately 100 Å, indicating pseudomorphic layer-by-layer growth. The MAX phase shows heteroepitaxial layer-by-layer growth on MgO(111), with increased surface roughening up to approximately 200 Å, whereas on MgO(100) the growth mode changes to Volmer-Weber-type already after three monolayers. X-ray scattering in Bragg-Brentano geometry of the final, approximately 1000 Å thick, Ti2AlN film reveals lattice parameters of c=13.463 Å and a=2.976 Å on the MgO(111) substrate and c=13.740 Å and a=2.224 Å on the MgO(100) substrate. From pole figure measurements the orientational relationship between film and substrate lattice was determined to be MgO{111}〈110〉//Ti2AlN{1012} 〈1210〉, regardless of the substrate orientation. This tilted, nonbasal-plane growth leads to a threefold grain orientation of Ti 2AlN along the MgO〈110〉 directions and a polycrystalline morphology confirmed by cross-sectional transmission electron microscopy. The growth can be assumed to take place in a lateral step-flow mode, i.e., emerging low surface free-energy (0001) planes, on which arriving atoms can diffuse until finding a step where they are bound to A facets. This growth process is irrespective of orientational relationship between substrate and film. However, in the present low-temperature case the partitioning of arriving Al and Ti atoms during nucleation is suppressed, which as a result of interfacial adaptation between substrate and film induces standing a-type planes during growth. © 2006 American Institute of Physics.
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| 3. |
- Manfred, Beckers, 2000-, et al.
(författare)
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Phase stability of epitaxially grown Ti2AlN thin films
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:7
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Tidskriftsartikel (refereegranskat)abstract
- The phase stability of Mn+1AXn phase (M: early transition metal, A: A-group element, and X: C and/or N) Ti2AlN thin films reactively sputtered onto MgO(111) and Al2O3(0001) substrates has been investigated by in situ x-ray diffraction and Rutherford backscattering. High substrate temperature deposition results in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. In contrast to reported high thermal stability for bulk Ti-Al-N M n+1AXn phases in air, Ti2AlN thin films in vacuum decompose already at ∼800°C. The decomposition proceeds by outward Al diffusion and evaporation, followed by detwinning of the as-formed Ti2N atomic layers into cubic TiNx and intermediate phases. © 2006 American Institute of Physics.
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| 4. |
- Schell, CO, et al.
(författare)
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Socioeconomic determinants of infant mortality: a worldwide study of 152 low-, middle-, and high-income countries
- 2007
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Ingår i: Scandinavian journal of public health. - : SAGE Publications. - 1403-4948 .- 1651-1905. ; 35:3, s. 288-297
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Tidskriftsartikel (refereegranskat)abstract
- Background: To reach the Millennium Development Goals for health, influential international bodies advocate for more resources to be directed to the health sector, in particular medical treatment. Yet, health has many determinants beyond the health sector that are less evident than proximate predictors. Aim: To assess the relative importance of major socioeconomic determinants of population health, measured as infant mortality rate (IMR), at country level. Methods: National-level data from 152 countries based on World Development Indicators 2003 were used for multivariate linear regression analyses of five socioeconomic predictors of IMR: public spending on health, GNI/capita, poverty rate, income equality (Gini index), and young female illiteracy rate. Analyses were performed on a global level and stratified for low-, middle-, and high-income countries. Results: In order of importance, GNI/capita, young female illiteracy, and income equality predicted 92% of the variation in national IMR whereas public spending on health and poverty rate were non-significant determinants when adjusted for confounding. In low-income countries, female illiteracy was more important than GNI/capita. Income equality (Gini index) was an independent predictor of IMR in middle-income countries only. In high-income countries none of these predictors was significant. Conclusions: The relative importance of major health determinants varies between income levels, thus extrapolating health policies from high- to low-income countries is problematic. Since the size, per se, of public health spending does not independently predict health outcomes, functioning health systems are necessary to make health investments efficient. Potential health gains from improved female education and economic growth should be considered in low- and middle-income countries
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