| 1. |
- Ternero, Pau, et al.
(author)
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Effect of the carrier gas on the structure and composition of Co–Ni bimetallic nanoparticles generated by spark ablation
- 2023
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In: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 170
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Journal article (peer-reviewed)abstract
- Spark ablation is a versatile technique for producing pure size-selected nanoparticles. The carrier gas used in spark ablation affects the nanoparticles’ generation, crystalline structure, and chemical composition. The comprehension of this phenomenon can contribute to the design of nanoparticles with tailored properties. In this paper, we evaluate the effects of reducing (95%N2 + 5%H2), inert (N2), and oxidative (air) carrier gases in a spark ablation setup with Co–Ni alloyed electrodes. The agglomerates’ particle size distribution, morphology, structure, and composition were highly dependent on the carrier gas, especially its relative oxygen content. The agglomerates were then sintered into compacted particles. Three different crystalline structures and chemical compositions were observed with X-ray diffraction and confirmed with transmission electron microscopy for the compacted particles. For 95%N2 + 5%H2 and air, single-phase (Co,Ni) and (Co,Ni)O particles were identified, respectively, whereas for N2, two-phase (Co,Ni) and (Co,Ni)O particles were obtained. This work opens up new possibilities of tuning the structure and composition, i.e., distribution of metallic and oxide phases, of the produced particles and thus tailor their properties for specific applications by simply changing the carrier gas.
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| 2. |
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| 3. |
- Blomberg, Sara, et al.
(author)
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A high pressure X-ray photoelectron spectroscopy study of oxidation and reduction of Rh(100) and Rh nanoparticles
- 2014
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In: Surface Science. - : Elsevier BV. - 0039-6028. ; 628, s. 153-158
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Journal article (peer-reviewed)abstract
- We have studied the oxidation and reduction of Rh(100) and SiO2 supported Rh particles using high pressure X-ray photoelectron spectroscopy. We show that the formation and reduction of Rh bulk oxide can be followed in situ in O-2 and CO pressures in the range of 0.1 Torr. In general, the oxidation/reduction processes are similar on Rh(100) and the nanoparticles, but there are significant differences in temperature dependence. Already at a sample temperature of 140 degrees C, the particles show clear signs of a thin bulk oxide, while an ultra-thin so-called surface oxide covers the single crystal at the same temperature. Both of these oxide films, however, hinder further oxidation, and a thick oxide is only found at a temperature of at least 300 degrees C, for both samples. The reduction, in contrast, starts at a higher temperature on the particles as compared to the single crystal, but once started the particles are completely reduced at lower temperatures. (C) 2014 Elsevier B.V. All rights reserved.
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| 4. |
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| 5. |
- Bulbucan, Claudiu, et al.
(author)
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Cr-substituted Fe3O4 nanoparticles : The role of particle size in the formation of FexO sub-domains and the emergence of exchange bias
- 2023
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 570
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Journal article (peer-reviewed)abstract
- Here we study the influence of particle size on the formation of antiferromagnetic FexO subdomains and the emergence of exchange bias in novel ferrimagnetic Cr-substituted Fe3O4 nanoparticles generated using an aerosol technique based on spark ablation. Cooling in an applied magnetic field across the Néel temperature of the FexO subdomains results in significant shifts in the hysteresis loops, which decrease in magnitude with the particle diameter for the two large systems (D≈20nm&D≈40nm), whereas only minor exchange fields are observed for the smallest system (D≈10nm). The reduced exchange bias is attributed to the metastable FexO's lower volume fraction and size due to a facile transformation into the thermodynamically stable (Fe,Cr)3O4 phase with decreasing particle diameter.
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| 6. |
- Bulbucan, Claudiu, et al.
(author)
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Large exchange bias in Cr substituted Fe3O4nanoparticles with FeO subdomains
- 2021
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:37, s. 15844-15852
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Journal article (peer-reviewed)abstract
- Tuning the anisotropy through exchange bias in bimagnetic nanoparticles is an active research strategy for enhancing and tailoring the magnetic properties for a wide range of applications. Here we present a structural and magnetic characterization of unique FeCr-oxide nanoparticles generated from seed material with a Fe : Cr ratio of 4.71 : 1 using a physical aerosol method based on spark ablation. The nanoparticles have a novel bimagnetic structure composed of a 40 nm ferrimagnetic Cr-substituted Fe3O4 structure with 4 nm antiferromagnetic FexO subdomains. Cooling in an applied magnetic field across the Néel temperature of the FexO subdomains results in a significant shift in the hysteresis, demonstrating the presence of a large exchange bias. The observed shift of μ0HE = 460 mT is among the largest values reported for FexO-Fe3O4-based nanoparticles and is attributed to the large antiferromagnetic-ferrimagnetic interface area provided by the subdomains.
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| 7. |
- Deppert, Knut, et al.
(author)
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Magnetic-field directed self-assembly and chain formation of functional aerosol nanoparticles
- 2020
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Conference paper (peer-reviewed)abstract
- Self-assembly of nanoparticles into vertical structures or larger ensembles can be a powerful method to achieve a strong collective behavior while still obtaining many of the same properties of the individual nanoparticles. In this study, we achieve directed self-assembly of magnetic nanoparticles into nanochains when depositing in a combined magnetic and electric field (M-ESP). We show that the Co nanoparticles are spontaneously magnetized in the aerosol phase, and that the role of the external magnetic field is mainly to guide the deposition in a certain direction.Lastly, we will present chain formation of mixed materials. Here, we combine a strong magnetic material, with other elements to achieve the same chain structure, but with a desired surface functionalization. Nanoparticle chains can therefore be formed with different functionalities, depending on the mixing material. This opens up for further combination to tune the functionalization of the nanoparticle chain structure.
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| 8. |
- Messing, Maria, et al.
(author)
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Generation of Pd Model Catalyst Nanoparticles by Spark Discharge
- 2010
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:20, s. 9257-9263
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Journal article (peer-reviewed)abstract
- We present a method to deposit Pd nanoparticles with a very small size distribution by an aerosol process onto oxide substrates for the creation of model systems in catalytic research. The Pd nanoparticles are characterized by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. We confirm the small size dispersion from the desired particle size, and we show that the particle surface coverage can he highly controlled. Further, our measurements indicate that an amorphous shell surrounding a crystalline core of the Pd particles may form during the particle synthesis and that the shell contains carbon.
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| 9. |
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| 10. |
- Messing, Maria, et al.
(author)
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Iron-based magnetic nanoparticles by spark ablation
- 2019
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Conference paper (peer-reviewed)abstract
- Magnetic nanoparticles have shown great potential for use in drug delivery and bioimaging applications and are prospective building blocks in future high-performing permanent magnets. Today, magnetic nanoparticles are most often produced in batches by chemical methods resulting in the risk of chemical impurities and production of vast amounts of chemical waste. Aerosol generation methods on the other hand, particularly spark ablation, are promising for future generation of magnetic nanoparticles since they are simple, fast, continuous, scalable, provide good control of size and composition, and offer the possibility to form alloys of material combinations not miscible on the macroscopic scale. High controllability is of utmost importance when generating magnetic nanoparticles since small deviations in size can significantly alter the magnetic coercivity. Also, the composition of the particles is of high significance since the magnetic properties can be completely transformed by changes in elemental composition or the oxidation state of the particle.In this work, we present the successful generation of monodisperse bimetallic FeCr and FeMn nanoparticles by spark ablation, and the results from the thorough characterization of individual particles with aerosol instruments, transmission electron microscopy, and synchrotron-based X-ray photoelectron spectroscopy. We demonstrate how the carrier gas can be used to dictate the oxidation and how to alternate between self-passivated and completely oxidized nanoparticles. We also show how the produced particles can be deposited to yield a low surface concentration which is critical for minimizing interparticle interactions during magnetic measurements. Finally, as a proof of concept, measurements using a magnetometer equipped with a SQUID on samples with different particle coverages are presented.
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