| 561. |
- Kostov Gueorguiev, Gueorgui, et al.
(author)
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Dangling bond energetics in carbon nitride and phosphorus carbide thin films with fullerene-like and amorphous structure
- 2009
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In: CHEMICAL PHYSICS LETTERS. - : Elsevier BV. - 0009-2614. ; 482:1-3, s. 110-113
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Journal article (peer-reviewed)abstract
- The energy cost for dangling bond formation in Fullerene-like Carbon Nitride (FL-CNx) and Phosphorus carbide (FL-CPx) as well as their amorphous counterparts: a-CNx, a-CPx, and a-C has been calculated within the framework of Density Functional Theory and compared with surface water adsorption measurements. The highest energy cost is found in the FL-CNx ( about 1.37 eV) followed by FL-CPx compounds (0.62-1.04 eV). (C) 2009 Elsevier B. V. All rights reserved.
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| 562. |
- Kota, Sankalp, et al.
(author)
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Magnetic properties of Cr2AlB2, Cr3AlB4, and CrB powders
- 2018
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In: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 767, s. 474-482
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Journal article (peer-reviewed)abstract
- The MAB phases are ternary, atomically laminated compounds that crystallize with orthorhombic structures and consist of transition metal (M) boride sublattices interleaved with single or double layers of Al. To date, the magnetic properties of ferromagnetic Fe(2)AIB(2) have been well-studied experimentally, but those of most end member MAB phases with other transition metals remain poorly understood. Herein, predominantly single-phase Cr(3)AIB(4) and Cr(2)AIB(2) powders, with minor amounts of CrB impurities, were synthesized by heating mixtures of chromium monoboride (CrB), aluminum (Al), and boron or CrB and Al under flowing Ar. These reactants were found to substantially suppress the formation of undesired phases in the Cr-Al-B system. The magnetic properties of Cr(3)AIB(4), Cr(2)AIB(2) and CrB powders were characterized. All compounds exhibit paramagnetic behavior down to 4 K, with susceptibilities that are quite weakly temperature dependent at higher temperatures and a Curie-Weiss-like component prominent at low temperatures. Magnetization isotherms of the three compounds, showed approximately linear behavior above 5 kOe and no saturation of the magnetic moment up to 40 kOe, which is consistent with paramagnetism. The magnitude of the magnetic moments showed little variation with composition, on a per Cr atom basis. While the exact nature of the Curie-Weiss component is not entirely clear, we tentatively attribute it to dilute extrinsic impurities. (C) 2018 Elsevier B.V. All rights reserved.
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| 563. |
- Kota, Sankalp, et al.
(author)
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Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB
- 2016
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In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 6:26475
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Journal article (peer-reviewed)abstract
- The MAlB phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36-0.49 mu Omega m) and - like a metal - drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm(-1)K(-1) at 26 degrees C). In the 25-1300 degrees C temperature range, its thermal expansion coefficient is 9.5 x 10(-6) K-1. Preliminary results suggest the compound is stable to at least 1400 degrees C in inert atmospheres. Moderately low Vickers hardness values of 10.6 +/- 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 +/- 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures.
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| 564. |
- Koutna, Nikola, et al.
(author)
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Atomistic mechanisms underlying plasticity and crack growth in ceramics : a case study of AlN/TiN superlattices
- 2022
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In: Acta Materialia. - : Pergamon-Elsevier Science Ltd. - 1359-6454 .- 1873-2453. ; 229
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Journal article (peer-reviewed)abstract
- Interfaces between components of a material govern its mechanical strength and fracture resistance. While a great number of interfaces is present in nanolayered materials, such as superlattices, their fundamental role during mechanical loading lacks understanding. Here we combine ab initio and classical molecular dynamics simulations, nanoindentation, and transmission electron microscopy to reveal atomistic mechanisms underlying plasticity and crack growth in B1 AlN(001)/TiN(001) superlattices under loading. The system is a model for modern refractory ceramics used as protective coatings. The simulations demonstrate an anisotropic response to uniaxial tensile deformation in principal crystallographic directions due to different strain-activated plastic deformation mechanisms. Superlattices strained orthogonal to (001) interfaces show modest plasticity and cleave parallel to AlN/TiN layers. Contrarily, B1-to-B3 or B1-to-B4(B-k) phase transformations in AlN facilitate a remarkable toughness enhancement upon in plane [110] and [100] tensile elongation, respectively. We verify the predictions experimentally and conclude that strain-induced crack growth-via loss of interface coherency, dislocation-pinning at interfaces, or layer interpenetration followed by formation of slip bands-can be hindered by controlling the thicknesses of the superlattice nanolayered components.
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| 565. |
- Koutna, Nikola, et al.
(author)
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Phase stability and mechanical property trends for MAB phases by high-throughput ab initio calculations
- 2024
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In: Materials & design. - : ELSEVIER SCI LTD. - 0264-1275 .- 1873-4197. ; 241
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Journal article (peer-reviewed)abstract
- MAB phases (MABs) are atomically-thin laminates of ceramic/metallic-like layers, having made a breakthrough in the development of 2D materials. Though offering a vast chemical and phase space, relatively few MABs have been synthesised. To guide experiments, we perform high-throughput ab initio screening of MABs that combine group 4-7 transition metals (M); Al, Si, Ga, Ge, or In (A); and boron (B) focusing on their phase stability trends and mechanical properties. Considering the 1:1:1, 2:1:1, 2:1:2, 3:1:2, 3:1:3, and 3:1:4 M:A:B ratios and 10 phase prototypes, synthesisability of a single-phase compound for each elemental combination is estimated through formation energy spectra of competing dynamically stable MABs. Based on the volumetric proximity of energetically-close phases, we identify systems in which volume-changing deformations may facilitate transformation toughening. Subsequently, chemistry- and phase-structure-related trends in the elastic stiffness and ductility are predicted using elastic-constants-based descriptors. The analysis of directional Cauchy pressures and Young's moduli allows comparing mechanical response parallel and normal to M-B/A layers. The suggested promising MABs include Nb 3 AlB 4 , Cr 2 SiB 2 , Mn 2 SiB 2 or the already synthesised MoAlB.
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| 566. |
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| 567. |
- Kukli, Kaupo, et al.
(author)
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Atomic Layer Deposition of Ruthenium Films on Strontium Titanate
- 2011
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In: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 11:9, s. 8378-8382
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Journal article (peer-reviewed)abstract
- Atomic layer deposition of ruthenium on SrTiO(3) layers was investigated using (C(2)H(5)C(5)H(4)) center dot (NC(4)H(4))Ru and air as precursors. For comparison, the growth was studied also on ZrO(2) films and SiO(2)/Si surfaces. Deposition temperature was 325 degrees C. Using rather short but intense air pulses, smooth and uniform Ru films were deposited on SrTiO(3). The films were crystallized at early stages of the growth. The nucleation density and rate on SrTiO(3) were notably lower compared to that on ZrO(2) and SiO(2), but the physical qualities including the film conductivity were considerably enhanced after reaching Ru film thickness around 10 nm.
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| 568. |
- Kukli, Kaupo, et al.
(author)
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Holmium and titanium oxide nanolaminates by atomic layer deposition
- 2014
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In: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 565, s. 165-171
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Journal article (peer-reviewed)abstract
- Nanolaminate (nanomultilayer) thin films of TiO2 and Ho2O3 were grown on Si(001) substrates by atomic layer deposition at 300 degrees C from alkoxide and beta-diketonate based metal precursors and ozone. Individual layer thicknesses were 2 nm for TiO2 and 4.5 nm for Ho2O3. As-deposited films were smooth and X-ray amorphous. After annealing at 800 degrees C and higher temperatures the nanolaminate structure was destroyed by solid-state reaction to form Ho2Ti2O7. The films demonstrated diamagnetic or paramagnetic behaviour in the as-deposited state. After annealing, the films possessed net magnetic moment, allowing one to record saturation magnetization and weak coercivity.
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| 569. |
- Kuo, Yu-Hung, et al.
(author)
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Influence of InAiN Nanospiral Structures on the Behavior of Reflected Light Polarization
- 2018
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In: Nanomaterials. - : MDPI. - 2079-4991. ; 8:3
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Journal article (peer-reviewed)abstract
- The influence of structural configurations of indium aluminum nitride (InA1N) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and pitch. The handedness of reflected circularly polarized light in the ultraviolet-visible region corresponding to the chirality of nanospirals is demonstrated. A high degree of circular polarization (P-c) value of 0.75 is obtained from a sample consisting of 1.2 mu m InA1N nanospirals grown at 650 degrees C. A film-like structure is formed at temperatures lower than 450 degrees C. At growth temperatures higher than 750 degrees C, less than 0.1 In-content is incorporated into the InA1N nanospirals. Both cases reveal very low P-c-A red shift of wavelength at P-c peak is found with increasing nanospiral pitch in the range of 200-300 nm. The P-c decreases to 0.37 for two-turn nanospirals with total length of 0.7 mu m, attributed to insufficient constructive interference. A branch-like structure appears on the surface when the nanospirals are grown longer than 1.2 mu m, which yields a low P-c around 0.5, caused by the excessive scattering of incident light.
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| 570. |
- Kurapov, D., et al.
(author)
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Influence of the normalized ion flux on the constitution of alumina films deposited by plasma-assisted chemical vapor deposition
- 2007
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 25:4, s. 831-836
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Journal article (peer-reviewed)abstract
- Alumina thin films were deposited onto tempered hot working steel substrates from an Al Cl3 - O2 -Ar- H2 gas mixture by plasma-assisted chemical vapor deposition. The normalized ion flux was varied during deposition through changes in precursor content while keeping the cathode voltage and the total pressure constant. As the precursor content in the total gas mixture was increased from 0.8% to 5.8%, the deposition rate increased 12-fold, while the normalized ion flux decreased by approximately 90%. The constitution, morphology, impurity incorporation, and the elastic properties of the alumina thin films were found to depend on the normalized ion flux. These changes in structure, composition, and properties induced by normalized ion flux may be understood by considering mechanisms related to surface and bulk diffusion. © 2007 American Vacuum Society.
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