| 1. |
- Dorri, Samira, 1988-
(författare)
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Magnetron Sputter Epitaxy of CrB2/TiB2 Diboride Superlattice Thin Films
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial superlattices with their exceptional properties have been popular in a broad range of applications such as electronic, magnetic, optical, and hard coating. Another potential application for single crystal artificial superlattices is highly efficient interference neutron optics, owing to an ultimate interface width of just ±½ atomic layer. Moreover, studies of superlattices have been instrumental in understanding the hardening mechanisms in transition metal nitrides and carbides while such studies on transition metal diborides is lacking, despite extensive studies on monolithic transition metal diboride thin films.This work is an initiative to grow CrB2/TiB2 (0001) diboride superlattices epitaxially onto Al2O3 (0001) substrates by direct current magnetron sputter epitaxy implementing two different approaches; compound diboride targets, and co-sputtering of a metal target with a compound target. Effects of substrate temperature, B stoichiometry (B/TM ratio), modulation period Λ = DCrB2 + DTiB2, layer thickness ratio , and relative applied power to magnetrons on the structural and interface quality of superlattices are studied and discussed.Using compound targets, superlattices with thickness ratio Γ = 0.3 and modulation periods Λ between 1 and 10 nm, and with Λ = 6 nm and thickness ratios between 0.2 to 0.8 were synthesized at the optimum sputter gas pressure of pAr = 4 mTorr and a substrate temperature of 600 °C. It is found that superlattices with Λ = 6 nm and Γ in the range of 0.2-0.4 exhibit the highest structural quality. However, B segregation in the over-stoichiometric TiBy layers (y > 2), grown from TiB2 compound target, results in narrow epitaxial superlattice columnar growth with structurally distorted B-rich boundaries. By co-sputtering from Ti and TiB2 targets, y could be reduced from 3.3 to 0.9 in TiBy layers through controlling the relative applied target power. Co-sputtered TiBy single layers and superlattices were grown at substrate temperatures between 600 and 900 °C. 300-nm-thick TiB2.3 single layers grown at 750 °C exhibited epitaxial domains about 10x larger than non-co-sputtered films.A significant enhancement for close-tostoichiometry CrB1.7/TiB2.3 superlattices with modulation periods Λ = 6 nm was achieved at 750 °C. X-ray diffraction, time of flight elastic recoil detection analysis, scanning transmission electron microscopy, electron energy loss spectroscopy, selected area electron diffraction, and nano-indentation are used for characterization.
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| 2. |
- Magnfält, Daniel, et al.
(författare)
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Synthesis of tunable plasmonic metal-ceramic nanocomposite thin films by temporally modulated sputtered fluxes
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:17
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Tidskriftsartikel (refereegranskat)abstract
- The scientific and technological interest for metal-dielectric nanocomposite thin films emanates from the excitation of localized surface plasmon resonances (LSPRs) on the metal component. The overall optical response of the nanocomposite is governed by the refractive index of the dielectric matrix and the properties of the metallic nanoparticles in terms of their bulk optical properties, size, and shape, and the inter-particle distance of separation. In order to tune the film morphology and optical properties, complex synthesis processes which include multiple steps-i. e., film deposition followed by post-deposition treatment by thermal or laser annealing-are commonly employed. In the present study, we demonstrate that the absorption resonances of Ag/AlOxNy nanocomposite films can be effectively tuned from green (similar to 2.4 eV) to violet (similar to 2.8 eV) using a single-step synthesis process that is based on modulating the arrival pattern of film forming species with sub-monolayer resolution, while keeping the amount of Ag in the films constant. Our data indicate that the optical response of the films is the result of LSPRs on isolated Ag nanoparticles that are seemingly shifted by dipolar interactions between neighboring particles. The synthesis strategy presented may be of relevance for enabling integration of plasmonic nanocomposite films on thermally sensitive substrates. Published by AIP Publishing.
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| 3. |
- Moubah, Reda, et al.
(författare)
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Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
- 2016
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Ingår i: Physical Review Applied. - : American physical society. - 2331-7019. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.
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| 4. |
- Novoselova, Iuliia P., et al.
(författare)
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Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
- 2018
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Ingår i: Scientific Reports. - London : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, a new class of inherently nanolaminated magnetic materials, the so called magnetic MAX phases, was discovered. Following predictive material stability calculations, the hexagonal Mn2GaC compound was synthesized as hetero-epitaxial films containing Mn as the exclusive M-element. Recent theoretical and experimental studies suggested a high magnetic ordering temperature and non-collinear antiferromagnetic (AFM) spin states as a result of competitive ferromagnetic and antiferromagnetic exchange interactions. In order to assess the potential for practical applications of Mn2GaC, we have studied the temperature-dependent magnetization, and the magnetoresistive, magnetostrictive as well as magnetocaloric properties of the compound. The material exhibits two magnetic phase transitions. The Neel temperature is T-N similar to 507 K, at which the system changes from a collinear AFM state to the paramagnetic state. At T-t = 214 K the material undergoes a first order magnetic phase transition from AFM at higher temperature to a non-collinear AFM spin structure. Both states show large uniaxial c-axis magnetostriction of 450 ppm. Remarkably, the magnetostriction changes sign, being compressive (negative) above T-t and tensile (positive) below the T-t. The sign change of the magnetostriction is accompanied by a sign change in the magnetoresistance indicating a coupling among the spin, lattice and electrical transport properties.
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