| 1. |
- Almyras, Georgios, 1983-, et al.
(författare)
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Semi-Empirical Force-Field Model For The Ti1-XAlXN (0 ≤ x ≤ 1) System
- 2019
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a modified embedded atom method (MEAM) semi-empirical force-field model for the Ti1-xAlxN (0 x 1) alloy system. The MEAM parameters, determined via an adaptive simulated-annealing (ASA) minimization scheme, optimize the models predictions with respect to 0 K equilibrium volumes, elastic constants, cohesive energies, enthalpies of mixing, and point-defect formation energies, for a set of approximate to 40 elemental, binary, and ternary Ti-Al-N structures and configurations. Subsequently, the reliability of the model is thoroughly verified against known finite-temperature thermodynamic and kinetic properties of key binary Ti-N and Al-N phases, as well as properties of Ti1-xAlxN (0 amp;lt; x amp;lt; 1) alloys. The successful outcome of the validation underscores the transferability of our model, opening the way for large-scale molecular dynamics simulations of, e.g., phase evolution, interfacial processes, and mechanical response in Ti-Al-N-based alloys, superlattices, and nanostructures.
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| 2. |
- Chen, Zhuo, et al.
(författare)
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Large mechanical properties enhancement in ceramics through vacancy-mediated unit cell disturbance
- 2023
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Tailoring vacancies is a feasible way to improve the mechanical properties of ceramics. However, high concentrations of vacancies usually compromise the strength (or hardness). We show that a high elasticity and flexural strength could be achieved simultaneously using a nitride superlattice architecture with disordered anion vacancies up to 50%. Enhanced mechanical properties primarily result from a distinctive deformation mechanism in superlattice ceramics, i.e., unit-cell disturbances. Such a disturbance substantially relieves local high-stress concentration, thus enhancing deformability. No dislocation activity involved also rationalizes its high strength. The work renders a unique understanding of the deformation and strengthening/toughening mechanism in nitride ceramics.
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| 3. |
- 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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| 4. |
- Gervilla Palomar, Víctor, 1992-
(författare)
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Metal film growth on weakly-interacting substrates : Multiscale modeling
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films are nanoscale layers of material used to functionalize surfaces or to serve as building blocks in more complex devices. In recent years, thin metal films have become vital for modern devices within, e.g., biosensing, catalysis, and nanoelectronics, whereby synthesis of metal layers with specific morphological features on two-dimensional (2D) crystals and oxides is required. However, this entails a great scientific challenge: in most of the afore-mentioned film/substrate combinations substrate and metal atoms interact weakly, causing the latter to self-assemble without control into three-dimensional (3D) clusters.Nowadays, a significant fraction of thin films is synthesized via condensation from the vapor phase, a far-from-equilibrium process in which film morphology is governed by the kinetic rates of atomic-scale structure-forming processes. It is, therefore, evident that knowledge-based synthesis of metal layers in high-performance devices necessitates a comprehensive understanding of the dynamic competition among these processes at the nano- and mesoscale. Such understanding is today incomplete, since experimental materials science tools are often not capable of providing nanometer and sub-nanometer insights at time scales that are relevant for thin-film synthesis. Computational approaches offer the possibility to fill the afore-mentioned gap in knowledge by allowing to explore atomistic behaviors with picosecond resolution. Hence, in the present thesis, a combination of modern computer simulation techniques is used to investigate thin metal film growth on weakly-interacting substrates from a purely atomistic point of view and to elucidate the ways by which atomic diffusion mechanisms give rise to the final film morphologies.In the first part of the thesis, an in-house kinetic Monte Carlo (KMC) simulation code and analytical modelling are used to investigate the early growth stages of Ag films supported on a generic weakly-interacting substrate. The results show that the weak interaction strength between film atoms and substrates leads to the formation of strongly-faceted 3D Ag islands, whose vertical growth is mediated by the temperature-dependent upward adatom diffusion across the facets. Eventually, the 3D islands impinge on each other and coalesce via surface migration of facet layers. Migration can be promoted by an increase of the deposition flux, but it can also be hindered by material agglomeration if the flux exceeds a critical threshold. These findings provide the foundation for explaining several effects observed during thin film growth on weakly-interacting substrates, including the increase of film roughness with temperature, the transition from 3D to 2D film morphology upon suppression of coalescence, and the origin of changes in thin film roughness and grain boundary number densities when varying the magnitude of vapor flux arrival rate.In the second part, ab initio and classical Molecular Dynamics simulations are used to investigate the diffusion dynamics of several transition metal adatoms (Ag, Au, Cu, Pd, Pt and Ru) and multi-atomic clusters (Ag, Au, Cu and Pd) on single layer graphene at room temperature (300K). The simulated diffusion trajectories reveal that diffusing adspecies experiencing a deep (hundreds of meV) potential energy landscape (PEL) on the substrate surface follow random walks; whilst those with a weak interaction with the substrate (PEL depth of a few meV) follow a superdiffusive motion pattern known as Lévy walk. This type of anomalous movement— also observed in other phenomena in physical, biological, and social systems—manifests itself as a continuous atomic motion with occasional flights over distances covering multiple adsorption sites. The fact that adspecies follow a distinctly different type of motion than what is observed in classical homoepitaxial growth theory implies that energy barriers readily available from static (0K) calculations may not be able to provide a physical accurate description of surface diffusion of metal adspecies on 2D crystals. As such, anomalous diffusion is a potentially important aspect to be considered when modelling growth of metal films and nanostructures on 2D materials.The results and insights generated in the present thesis provide key knowledge for controlled synthesis of films and nanostructures with tailored properties. This, in turn, is relevant for developing high-performance energy-saving windows, improving the turnover frequency of catalytic reactions, and integrating 2D materials into novel nanoelectronic devices. Moreover, the techniques developed and employed herein contribute toward bringing modern computational tools closer to the field of thin film growth.
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| 5. |
- Gervilla, Víctor, 1992-, et al.
(författare)
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Anomalous versus Normal Room-Temperature Diffusion of Metal Adatoms on Graphene
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - Washington, DC, United States : American Chemical Society. - 1948-7185. ; 11:21, s. 8930-8936
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Tidskriftsartikel (refereegranskat)abstract
- Fabrication of high-performance heterostructure devices requires fundamental understanding of the diffusion dynamics of metal species on 2D materials. Here, we investigate the room-temperature diffusion of Ag, Au, Cu, Pd, Pt, and Ru adatoms on graphene using ab initio and classical molecular dynamics simulations. We find that Ag, Au, Cu, and Pd follow Lévy walks, in which adatoms move continuously within ∼1–4 nm2 domains during ∼0.04 ns timeframes, and they occasionally perform ∼2–4 nm flights across multiple surface adsorption sites. This anomalous diffusion pattern is associated with a flat (<50 meV) potential energy landscape (PEL), which renders surface vibrations important for adatom migration. The latter is not the case for Pt and Ru, which encounter a significantly rougher PEL (>100 meV) and, hence, migrate via conventional random walks. Thus, adatom anomalous diffusion is a potentially important aspect for modeling growth of metal films and nanostructures on 2D materials.
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| 6. |
- Jamnig, Andreas, 1991-, et al.
(författare)
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Atomic-scale diffusion rates during growth of thin metal films on weakly-interacting substrates
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We use a combined experimental and theoretical approach to study the rates of surface diffusion processes that govern early stages of thin Ag and Cu film morphological evolution on weakly-interacting amorphous carbon substrates. Films are deposited by magnetron sputtering, at temperatures T-S between 298 and 413 K, and vapor arrival rates F in the range 0.08 to 5.38 monolayers/s. By employing in situ and real-time sheet-resistance and wafer-curvature measurements, we determine the nominal film thickness Theta at percolation (Theta(perc)) and continuous film formation (Theta(cont)) transition. Subsequently, we use the scaling behavior of Theta(perc) and Theta(cont) as a function of F and T-s, to estimate, experimentally, the temperature-dependent diffusivity on the substrate surface, from which we calculate Ag and Cu surface migration energy barriers E-D(exp) and attempt frequencies nu(exp)(0). By critically comparing E-D(exp) and nu(exp)(0) with literature data, as well as with results from our ab initio molecular dynamics simulations for single Ag and Cu adatom diffusion on graphite surfaces, we suggest that: (i) E-D(exp) and nu(exp)(0) correspond to diffusion of multiatomic clusters, rather than to diffusion of monomers; and (ii) the mean size of mobile clusters during Ag growth is larger compared to that of Cu. The overall results of this work pave the way for studying growth dynamics in a wide range of technologically-relevant weakly-interacting film/substrate systems-including metals on 2D materials and oxides-which are building blocks in next-generation nanoelectronic, optoelectronic, and catalytic devices.
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| 7. |
- Kashiwaya, Shun, et al.
(författare)
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Synthesis of goldene comprising single-atom layer gold
- 2024
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Ingår i: Nature Synthesis. - : Nature Publishing Group. - 2731-0582.
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of monolayer gold has so far been limited to free-standingseveral-atoms-thick layers, or monolayers confned on or inside templates.Here we report the exfoliation of single-atom-thick gold achieved throughwet-chemically etching away Ti3C2 from nanolaminated Ti3AuC2, initiallyformed by substituting Si in Ti3SiC2 with Au. Ti3SiC2 is a renown MAX phase,where M is a transition metal, A is a group A element, and X is C or N. Ourdeveloped synthetic route is by a facile, scalable and hydrofuoric acid-freemethod. The two-dimensional layers are termed goldene. Goldene layerswith roughly 9% lattice contraction compared to bulk gold are observedby electron microscopy. While ab initio molecular dynamics simulationsshow that two-dimensional goldene is inherently stable, experiments showsome curling and agglomeration, which can be mitigated by surfactants.X-ray photoelectron spectroscopy reveals an Au 4f binding energy increaseof 0.88 eV. Prospects for preparing goldene from other non-van der WaalsAu-intercalated phases, including developing etching schemes,are presented.
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| 8. |
- Pshyk, Oleksandr V., 1990-, et al.
(författare)
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Discovery of Guinier-Preston zone hardening in refractory nitride ceramics
- 2023
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 255
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Tidskriftsartikel (refereegranskat)abstract
- Traditional age hardening mechanisms in refractory ceramics consist of precipitation of fine particles. These processes are vital for widespread wear-resistant coating applications. Here, we report novel Guinier-Preston zone hardening, previously only known to operate in soft light-metal alloys, taking place in refractory ceramics like multicomponent nitrides. The added superhardening, discovered in thin films of Ti-Al-W-N upon high temperature annealing, comes from the formation of atomic-plane-thick W disks populating {111} planes of the cubic matrix, as observed by atomically resolved high resolution scanning transmission electron microscopy and corroborated by ab initio calculations and molecular dynamics simulations. Guinier-Preston zone hardening concurrent with spinodal decomposition is projected to exist in a range of other ceramic solid solutions and thus provides a new approach for the development of advanced materials with outstanding mechanical properties and higher operational temperature range for the future demanding applications.
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| 9. |
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| 10. |
- Salamania, Janella, 1992-, et al.
(författare)
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Elucidating dislocation core structures in titanium nitride through high-resolution imaging and atomistic simulations
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 224
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Tidskriftsartikel (refereegranskat)abstract
- Although titanium nitride (TiN) is among the most extensively studied and thoroughly characterizedthin-film ceramic materials, detailed knowledge of relevant dislocation core structures is lacking. Byhigh-resolution scanning transmission electron microscopy (STEM) of epitaxial single crystal (001)-oriented TiN films, we identify different dislocation types and their core structures. These include, besidesthe expected primary a/2{110}h110i dislocation, Shockley partial dislocations a/6{111}h112i and sessileLomer edge dislocations a/2{100}h011i. Density-functional theory and classical interatomic potentialsimulations complement STEM observations by recovering the atomic structure of the different disloca-tion types, estimating Peierls stresses, and providing insights on the chemical bonding nature at the core.The generated models of the dislocation cores suggest locally enhanced metal–metal bonding, weakenedTi-N bonds, and N vacancy-pinning that effectively reduces the mobilities of {110}h110i and {111}h112idislocations. Our findings underscore that the presence of different dislocation types and their effects onchemical bonding should be considered in the design and interpretations of nanoscale and macroscopicproperties of TiN.
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