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Plasma Synthesis and Self-Assembly of Magnetic Nanoparticles
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanomaterials are important tools for enabling technological progress as they can provide dramatically different properties as compared to the bulk counterparts. The field of nanoparticles is one of the most investigated within nanomaterials, thanks to the existing, relatively simple, means of manufacturing. In this thesis, high-power pulsed hollow cathode sputtering is used to nucleate and grow magnetic nanoparticles in a plasma. This sputtering technique provides a high degree of ionization of the sputtered material, which has previously been shown to aid in the growth of the nanoparticles. The magnetic properties of the particles are utilized and makes it possible for the grown particles to act as building blocks for self-assembly into more sophisticated nano structures, particularly when an external magnetic field is applied. These structures created are termed “nanowires” or “nanotrusses”, depending on the level of branching and inter-linking that occurs.

Several different elements have been investigated in this thesis. In a novel approach, it is shown how nanoparticles with more advanced structures, and containing material from two hollow cathodes, can be fabricated using high-power pulses. The dual-element particles are achieved by using two distinct and individual elemental cathodes, and a pulse process that allows tuning of individual pulses separately to them. Nanoparticles grown and investigated are Fe, Ni, Pt, Fe-Ni and Ni-Pt. Alternatively, the addition of oxygen to the process allows the formation of oxide or hybrid metal oxide – metal particles. For all nanoparticles containing several elements, it is demonstrated that the stoichiometry can be easily varied, either by the amount of reactive gas let into the process or by tuning the amount of sputtered material through adjusting the electric power supplied to the different cathodes.

One aim of the presented work is to find a suitable material for the use as a catalyst in the production of H2 gas through the process of water splitting. H2 is a good candidate to replace fossil fuels as an energy carrier. However, rare elements (such as Ir or Pt) needs to be used as the catalyst, otherwise a high overpotential is required for the splitting to occur, leading to a low efficiency. This work demonstrates a possible route to avoid this, by using nanomaterials to increase the surface-to-volume ratio, as well as optimizing the elemental ratio between different materials to lower the amount of noble elements required. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 58
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2007
Keywords [en]
Plasma, Synthesis, Self-Assembly, Magnetic, Nanoparticles
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:liu:diva-161300DOI: 10.3384/diss.diva-161300ISBN: 9789176850091 (print)OAI: oai:DiVA.org:liu-161300DiVA, id: diva2:1366090
Public defence
2019-12-10, Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2019-11-08 Created: 2019-10-28 Last updated: 2019-11-08Bibliographically approved
List of papers
1. Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma
Open this publication in new window or tab >>Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma
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2018 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 5, p. 3132-3137Article in journal (Refereed) Published
Abstract [en]

Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 mu m thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H-2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm(2).

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
Keywords
Nanotrusses; nanowires; nanoparticles; iron; electrocatalysis; pulsed sputtering
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-148107 (URN)10.1021/acs.nanolett.8b00718 (DOI)000432093200055 ()29624405 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, KAW 14.0276
Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2019-11-11
2. Growth of semi-coherent Ni and NiO dual-phase nanoparticles using hollow cathode sputtering
Open this publication in new window or tab >>Growth of semi-coherent Ni and NiO dual-phase nanoparticles using hollow cathode sputtering
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2019 (English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 21, no 2, article id 37Article in journal (Refereed) Published
Abstract [en]

Anisotropic heterogenous Ni/NiO nanoparticles with controlled compositions are grown using a high-power pulsed hollow cathode process. These novel particles can be tuned to consist of single-phase Ni via two-phase Ni/NiO to fully oxidized NiO, with a size range of 5-25 nm for individual crystals. A novelty of this approach is the ability to assemble multiple particles of Ni and NiO into a single complex structure, increasing the Ni-NiO interface density. This type of particle growth is not seen before and is explained to be due to the fact that the process operates in a single-step approach, where both Ni and O can arrive at the formed nanoparticle nuclei and aid in the continuous particle growth. The finished particle will then be a consequence of the initially formed crystal, as well as the arrival rate ratio of the two species. These particles hold great potential for applications in fields, such as electro- and photocatalysis, where the ability to control the level of oxidation and/or interface density is of great importance.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Ni; NiO; Anisotropic; Nanoparticles; Hollow cathode; Nanoparticle assembly
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-154838 (URN)10.1007/s11051-019-4479-4 (DOI)000458657800001 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation [KAW 2014.0276]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Tokyo Metropolitan University; Linkoping University

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-11-11
3. Impact of nanoparticle magnetization on the 3D formation of dual-phase Ni/NiO nanoparticle-based nanotrusses
Open this publication in new window or tab >>Impact of nanoparticle magnetization on the 3D formation of dual-phase Ni/NiO nanoparticle-based nanotrusses
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2019 (English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 21, no 11, article id 21:228Article in journal (Refereed) Published
Abstract [en]

Magnetic nanoparticles with average size 30 nm were utilized to build three-dimensional framework structures—nanotrusses. In dual-phase Ni/NiO nanoparticles, there is a strong correlation between the amount of magnetic Ni and the final size and shape of the nanotruss. As it decreases, the length of the individual nanowires within the trusses also decreases, caused by a higher degree of branching of the wires. The position and orientation of the non-magnetic material within the truss structure was also investigated for the different phase compositions. For lower concentrations of NiO phase, the electrically conducting Ni-wire framework is maintained through the preferential bonding between the Ni crystals. For larger concentrations of NiO phase, the Ni-wire framework is interrupted by the NiO. The ability to use nanoparticles that are only partly oxidized in the growth of nanotruss structures is of great importance. It opens the possibility for using not only magnetic metals such as pure Ni, Fe, and Co, but also to use dual-phase nanoparticles that can strongly increase the efficiency of e.g. catalytic electrodes and fuel cells.

Place, publisher, year, edition, pages
Springer-Verlag New York, 2019
Keywords
Ni, NiO, Nanotruss, Nanoparticle, Magnetic assembly
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-161747 (URN)10.1007/s11051-019-4661-8 (DOI)000494039300001 ()
Note

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Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-19Bibliographically approved

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