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Ravensburg, A. L., Brucas, R., Music, D., Spode, L., Pálsson, G. K., Svedlindh, P. & Kapaklis, V. (2024). Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion. Applied Physics A: Materials Science & Processing, 130(2), Article ID 74.
Open this publication in new window or tab >>Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion
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2024 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 130, no 2, article id 74Article in journal (Refereed) Published
Abstract [en]

The conditions whereby epitaxy is achieved are commonly believed to be mostly governed by misfit strain. We report on a systematic investigation of growth and interface structure of single crystalline tungsten thin films on two different metal oxide substrates, Al2O3 (11‾20) and MgO (001). We demonstrate that despite a significant mismatch, enhanced crystal quality is observed for tungsten grown on the sapphire substrates. This is promoted by stronger adhesion and chemical bonding with sapphire compared to magnesium oxide, along with the restructuring of the tungsten layers close to the interface. The latter is supported by ab initio calculations using density functional theory. Finally, we demonstrate the growth of magnetic heterostructures consisting of high-quality tungsten layers in combination with ferromagnetic CoFe layers, which are relevant for spintronic applications.

Place, publisher, year, edition, pages
Springer, 2024
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520683 (URN)10.1007/s00339-023-07212-w (DOI)001137900100005 ()
Funder
Swedish Research Council, 2019-03581Swedish Research Council, 2021-0465Swedish Energy Agency, 2020-005212Olle Engkvists stiftelse, 217-0023National Academic Infrastructure for Supercomputing in Sweden (NAISS)Swedish Research Council, 2022-06725
Available from: 2024-01-14 Created: 2024-01-14 Last updated: 2024-01-31Bibliographically approved
Ravensburg, A. L. (2024). Order and interfaces in epitaxial heterostructures: Structure and magnetism. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Order and interfaces in epitaxial heterostructures: Structure and magnetism
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work in this dissertation is devoted to investigating order and interfaces in epitaxial heterostructures. To achieve that the software tool box GenL was developed for simulating and fitting x-ray diffraction patterns from epitaxial thin films, which is used to access structural information on the length scales of interfaces and atomic bonds. Employing GenL, it is shown that a small lattice mismatch between substrate and epitaxial layer is not the sole origin of high crystal quality, as demonstrated for nearly strain-free epitaxial growth of tungsten on sapphire with a lattice mismatch of up to 19.4 %. Furthermore, it is discussed that electronic states at the substrate/film interface can have substantial significance for the crystal structure of an epitaxial layer. For instance, despite a nearly mismatch-free interface of body-centered cubic iron on spinel, the presence of a boundary-induced interface layer with tetragonally distorted crystal structure is discovered, which has a profound impact on the magnetic properties. Finally, when creating multilayered structures, not only the interface states but the total structure is found to influence the physical properties, which is demonstrated for the interlayer exchange coupling in [Fe/MgO]Nsuperlattices.

Note: This PhD thesis is partly based on the licentiate dissertation "Growth of high quality Fe thin films" by Anna L. Ravensburg, Uppsala University, 2022. Particularly parts of: Chapter 1, Sections 2.0, 2.1, 2.2, 3.0, 3.1, 3.2, 3.3, 5.1, and Fig. 2.6 are adapted from the licentiate thesis with minor edits and updates.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 106
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2356
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520686 (URN)978-91-513-2010-6 (ISBN)
Public defence
2024-03-01, Heinz-Otto Kreiss Föreläsningssal, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2024-02-07 Created: 2024-01-15 Last updated: 2024-03-12
Ravensburg, A. L., Pálsson, G. K., Pohlit, M., Hjörvarsson, B. & Kapaklis, V. (2022). Influence of misfit strain on the physical properties of Fe thin films. Thin Solid Films, 761, Article ID 139494.
Open this publication in new window or tab >>Influence of misfit strain on the physical properties of Fe thin films
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2022 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 761, article id 139494Article in journal (Refereed) Published
Abstract [en]

We investigate the growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The crystal quality of Fe layers deposited on MgAl2O4 is found to be substantially higher as compared to Fe grown on MgO substrates. The effects of the crystal quality on the magnetic and electric transport properties are discussed. 

Place, publisher, year, edition, pages
Elsevier, 2022
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-473435 (URN)10.1016/j.tsf.2022.139494 (DOI)000867640600006 ()
Funder
Swedish Research Council, 2019-03581Swedish Research Council, 2019-05379Swedish Energy Agency, 2020-005212
Available from: 2022-04-26 Created: 2022-04-26 Last updated: 2024-04-22Bibliographically approved
Keuter, P., Ravensburg, A. L., Hans, M., Aghda, S. K., Holzapfel, D. M., Primetzhofer, D. & Schneider, J. M. (2020). A Proposal for a Composite with Temperature-Independent Thermophysical Properties: HfV2-HfV2O7. Materials, 13(21), Article ID 5021.
Open this publication in new window or tab >>A Proposal for a Composite with Temperature-Independent Thermophysical Properties: HfV2-HfV2O7
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2020 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 21, article id 5021Article in journal (Refereed) Published
Abstract [en]

The HfV2-HfV2O7 composite is proposed as a material with potentially temperature-independent thermophysical properties due to the combination of anomalously increasing thermoelastic constants of HfV2 with the negative thermal expansion of HfV2O7. Based on literature data, the coexistence of both a near-zero temperature coefficient of elasticity and a coefficient of thermal expansion is suggested for a composite with a phase fraction of approximately 30 vol.% HfV2 and 70 vol.% HfV2O7. To produce HfV2-HfV2O7 composites, two synthesis pathways were investigated: (1) annealing of sputtered HfV2 films in air to form HfV2O7 oxide on the surface and (2) sputtering of HfV2O7/HfV2 bilayers. The high oxygen mobility in HfV2 is suggested to inhibit the formation of crystalline HfV2-HfV2O7 composites by annealing HfV2 in air due to oxygen-incorporation-induced amorphization of HfV2. Reducing the formation temperature of crystalline HfV2O7 from 550 degrees C, as obtained upon annealing, to 300 degrees C using reactive sputtering enables the synthesis of crystalline bilayered HfV2-HfV2O7.

Keywords
thermoelasticity, negative thermal expansion, composites, magnetron sputtering
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-427122 (URN)10.3390/ma13215021 (DOI)000589693900001 ()33171727 (PubMedID)
Funder
Swedish Research Council, 2017-00646-9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2020-12-09 Created: 2020-12-09 Last updated: 2020-12-09Bibliographically approved
Ravensburg, A. L., Keuter, P., Music, D., Miljanovic, D. J. & Schneider, J. M. (2020). Experimental and Theoretical Investigation of the Elastic Properties of HfV2O7. Crystals, 10(3), Article ID 172.
Open this publication in new window or tab >>Experimental and Theoretical Investigation of the Elastic Properties of HfV2O7
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2020 (English)In: Crystals, ISSN 2073-4352, Vol. 10, no 3, article id 172Article in journal (Refereed) Published
Abstract [en]

We investigated the elastic properties of the HfV2O7 high-temperature phase, exhibiting negative thermal expansion, in a synergetic strategy of first-principle calculations and nanoindentation experiments performed on sputtered films. Self-consistent results were obtained for the measured elastic modulus (73 +/- 14 GPa) and dispersion-corrected density functional theory calculations. The elastic properties of HfV2O7 are affected by long-range dispersion interaction, which may be induced by severe modification in the second-nearest neighbor O-O bond distance as obtained upon compression. HfV2O7 is composed of HfO6, VO4, and V2O7 building blocks, whereby the latter is characterized by an increasing V-O(-V) bond length upon compression.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
negative thermal expansion, flexible network structure, elasticity, sputtering, density functional theory
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-409931 (URN)10.3390/cryst10030172 (DOI)000523512100092 ()
Available from: 2020-05-07 Created: 2020-05-07 Last updated: 2020-05-07Bibliographically approved
Hunold, O., Keuter, P., Bliem, P., Music, D., Wittmers, F., Ravensburg, A. L., . . . Schneider, J. M. (2017). Elastic properties of amorphous T0.75Y0.75B14 (T = Sc, Ti, V, Y, Zr, Nb) and the effect of O incorporation on bonding, density and elasticity (T ' = Ti, Zr). Journal of Physics: Condensed Matter, 29(8), Article ID 085404.
Open this publication in new window or tab >>Elastic properties of amorphous T0.75Y0.75B14 (T = Sc, Ti, V, Y, Zr, Nb) and the effect of O incorporation on bonding, density and elasticity (T ' = Ti, Zr)
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 8, article id 085404Article in journal (Refereed) Published
Abstract [en]

We have systematically studied the effect of transition metal valence electron concentration (VEC) of amorphous T0.75Y0.75B14 (a-T0.75Y0.75B14, T = Sc, Ti, V, Y, Zr, Nb) on the elastic properties, bonding, density and electronic structure using ab initio molecular dynamics. As the transition metal VEC is increased in both periods, the bulk modulus increases linearly with molar- and mass density. This trend can be understood by a concomitant decrease in cohesive energy. T' = Ti and Zr were selected to validate the predicted data experimentally. A-Ti0.74Y0.80B14 and a-Zr0.75Y0.75B14 thin films were synthesized by high power pulsed magnetron sputtering. Chemical composition analysis revealed the presence of up to 5 at.% impurities, with O being the largest fraction. The measured Young's modulus values for a-Ti0.74Y0.80B14 (301 +/- 8 GPa) and a-Zr0.75Y0.75B14 (306 +/- 9 GPa) are more than 20% smaller than the predicted ones. The influence of O incorporation on the elastic properties for these selected systems was theoretically studied, exemplarily in a-Ti0.75Y0.75B12.75O1.25. Based on ab initio data, we suggest that a-Ti0.75Y0.75B14 exhibits a very dense B network, which is partly severed in a-Ti0.75Y0.75B12.75O1.25. Upon O incorporation, the average coordination number of B and the molar density decrease by 9% and 8%, respectively. Based on these data the more than 20% reduced Young's modulus obtained experimentally for films containing impurities compared to the calculated Young's modulus for a-Ti0.75Y0.75B14 (without incorporated oxygen) can be rationalized. The presence of oxygen impurities disrupts the strong B network causing a concomitant decrease in molar density and Young's modulus. Very good agreement between the measured and calculated Young's modulus values is obtained if the presence of impurities is considered in the calculations. The implications of these findings are that prediction efforts regarding the elastic properties of amorphous borides containing oxygen impurities on the at.% level are flawed without taking the presence of impurities into account.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keywords
amorphous boron rich solids, elastic properties, ab initio, influence of oxygen, thin films, BAM materials
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-322228 (URN)10.1088/1361-648X/aa5375 (DOI)000400158300001 ()28081008 (PubMedID)
Funder
German Research Foundation (DFG), SFB-TR 87/2Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2017-05-17 Created: 2017-05-17 Last updated: 2022-05-02Bibliographically approved
Ciuciulkaite, A., Scheuer, L., Ravensburg, A. L., Pohlit, M., Warnatz, T., Torosyan, G., . . . Kapaklis, V.Impact of the magnetic layer crystal growth optimization on the THzemission from spintronic Fe/Pt emitters.
Open this publication in new window or tab >>Impact of the magnetic layer crystal growth optimization on the THzemission from spintronic Fe/Pt emitters
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We investigate the THz emission characteristics of ferromagnetic/non-magnetic metallic heterostructures, focusing on thin Fe/Pt bilayers. In particular, we report on the impact of optimized crystal growth of the epitaxial Fe layers on the THz emission amplitude and spectral bandwidth. We demonstrate a 5 % enhancement of the emitted intensity, related to reduced spin scattering and higher interface transmission. Our work provides a pathway for devicing optimal spintronic THz emitters based on epitaxial Fe. It also highlights how THz emission measurements can be utilized to characterize the changes in out-of-equilibrium spin current dynamics in metallic heterostructures, driven by subtle structural refinement.

National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-473634 (URN)10.48550/arXiv.2010.12457 (DOI)
Funder
Stiftelsen Anna Maria Lundins stipendiefondKnut and Alice Wallenberg Foundation, 2015.0060Swedish Research Council, 2019-03581The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), KO2016-688
Available from: 2022-04-29 Created: 2022-04-29 Last updated: 2022-05-02
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9502-8599

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