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- Adamovic, Dragan, 1973-, et al.
(författare)
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Kinetic pathways leading to layer-by-layer growth from hyperthermal atoms : A Multibillion time step molecular dynamics study
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 76, s. 115418-115425
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Tidskriftsartikel (refereegranskat)abstract
- We employ multibillion time step embedded-atom molecular dynamics simulations to investigate the homoepitaxial growth of Pt(111) from hyperthermal Pt atoms (EPt=0.2–50eV) using deposition fluxes approaching experimental conditions. Calculated antiphase diffraction intensity oscillations, based on adatom coverages as a function of time, reveal a transition from a three-dimensional multilayer growth mode with EPt<20eV to a layer-by-layer growth with EPt≥20eV. We isolate the effects of irradiation-induced processes and thermally activated mass transport during deposition in order to identify the mechanisms responsible for promoting layer-by-layer growth. Direct evidence is provided to show that the observed transition in growth modes is primarily due to irradiation-induced processes which occur during the 10ps following the arrival of each hyperthermal atom. The kinetic pathways leading to the transition involve both enhanced intralayer and interlayer adatom transport, direct incorporation of energetic atoms into clusters, and cluster disruption leading to increased terrace supersaturation.
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| 2. |
- Edström, Daniel, 1986-, et al.
(författare)
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Mechanical properties of VMoNO as a function of oxygen concentration : Toward development of hard and tough refractory oxynitrides
- 2019
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:6
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Tidskriftsartikel (refereegranskat)abstract
- Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl-structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem that may compromise material properties and performance. Here, the authors explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx solid solutions as a function of the oxygen concentration x. Elastic constant and intrinsic hardness calculations show that oxidation does not degrade the mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate that the presence of oxygen reduces the covalent bond character, which slightly lowers the alloy strength and intrinsic hardness. Nevertheless, the character of metallic d-d states, which are crucial for allowing plastic deformation and enhancing toughness, remains unaffected. Overall, the authors' results suggest that VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high intrinsic hardness, while still being ductile. Published by the AVS.
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| 3. |
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| 4. |
- Wallin, Erik, 1979-, et al.
(författare)
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Ab initio studies of adsorption and diffusion processes on alpha-Al2O3 (0001) surfaces
- 2007
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Ingår i: International Symposium on Reactive Sputter Deposition,2007.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- As one of the technologically most important ceramic materials, alumina (Al2O3) thin film growth has been studied extensively in the past. However, the mechanisms behind the formation of different phases and microstructures are still poorly understood, especially for physically vapor deposited films. An increased atomic scale understanding of alumina surface processes would thus be an important step towards a more complete understanding and control of the deposition process. In the present work, density functional theory based methods were used to study the adsorption of Al, O, AlO, and O2 on different terminations of alpha-alumina (0001) surfaces. The results show the existence of several metastable adsorption sites on the O-terminated surface and provide a possible explanation for the well-known difficulties in growing -Ñ-alumina at lower temperatures. Moreover, we demonstrate that Al adsorption in bulk positions is unstable, or considerably weaker, for completely hydrogenated surfaces, indicating that hydrogen stemming from residues in vacuum systems, might hinder the growth of crystalline alpha-alumina. Furthermore, nudged elastic band investigations of dynamic energy barriers for different surface diffusion processes show that Al diffusion, on the Al-terminated (0001) surface, requires only ~0.7 eV. This value is considerably lower than what is generally expected for the low temperature synthesis of alpha-alumina phase. These results add significantly to understanding the effects of several important factors on alumina growth, and their implication, on optimizing deposition processes for the synthesis of alumina films with desired properties, will be discussed.
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