| 1. |
- Deppert, Knut, et al.
(author)
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Complex Aerosol Nanostructures: Revealing the Phases from Multivariate Analysis on Elemental Maps Obtained by TEM-EDX
- 2020
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Conference paper (peer-reviewed)abstract
- Transmission electron microscopy (TEM) is a popular off-line technique to study aerosol nanoparticles. Coupled with an X-ray detector, high-resolution elemental maps of the sample can be obtained by scanning the focused electron beam and collecting the emitted X-ray spectra, called energy dispersive X-ray spectroscopy (EDX). Interpretation of the acquired data can be difficult in the case of complex particles having regions of different and overlapping phases because the elemental distributions do not reveal phase information. However, the resulting large datacubes collected are well-suited for multivariate statistics techniques to reveal information clouded by the noise of raw spectra. In this work, we show the comparison between two multivariate techniques, hierarchical clustering and non-negative matrix factorization, to separate elemental maps into phase maps of Cu@Ag core@shell aerosol nanoparticles and aerotaxy nanowires. We compare the results of the Cu@Ag sample to X-ray photoelectric spectroscopy measurements as an independent measure of surface composition.
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| 2. |
- Deppert, Knut, et al.
(author)
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One-step Gas-phase Synthesis of Core-shell Nanoparticles via Surface Segregation.
- 2019
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Conference paper (peer-reviewed)abstract
- A great amount of research effort has been devoted to theproduction of core-shell nanoparticles for applications in variousfields including biomedical imaging, catalysis, and plasmonics.Such attention to core-shell nanoparticles arise from the fact thatthey can exhibit enhanced physical and/or chemical properties.Furthermore, core-shell particles with distinctly new propertiescompared to those of the constituent materials can be designedby tuning, for example, their size, shell thickness, and structure [1,2].Although chemical synthesis techniques are currently the mostpopular methods for fabricating core-shell nanoparticles,interface and surface contaminations are often an unavoidableissue in the solution-based approaches. Aerosol based methodsare cleaner alternatives and have been used to produce core-shellnanoparticles [3-6]. Here we present aerosol core-shellnanoparticles generated via spark discharge generation (SDG) [7].Cu-Ag core shell nanoparticles were fabricated via surfacesegregation using SDG accompanied by sintering directly in thegas phase. The surface segregation employed in this methodrefers to the phenomenon of the enrichment of one componentof a mixture in the surface region and is attributed to theinterplay between the atomic radii, cohesive energy, and surfaceenergy of the core and shell materials [8].Depending on the sintering temperature, the SDG-generatednanoparticles form Janus-like or core-shell structures. Themorphology, crystallinity, and composition of the SDG-generatedbimetallic nanoparticles were investigated by scanning electronmicroscopy, high-resolution transmission electron microscopy,and energy-dispersive X-ray spectroscopy. Molecular dynamicssimulations were carried out to investigate the structuralevolution of Cu-Ag nanoparticles during heating and coolingprocesses corresponding to the sintering. This appealingly simpleone-step gas-phase synthesis method presented here can beemployed for other bimetallic systems.
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| 3. |
- Eom, Namsoon, et al.
(author)
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A Continuous One-Step Aerosol Method for Producing Core@Shell Cu@Ag Nanoparticles
- 2019
-
Conference paper (peer-reviewed)abstract
- The synthesis of core@shell nanoparticles has predominantly been carried out by chemical methods or physical deposition of a shell material post-growth onto core particles. By combining immiscible materials that differ in surface energy, we demonstrate the spontaneous atomic rearrangement to monodisperse Cu@Ag core@shell particles directly in the aerosol phase, starting from pure Cu and Ag electrodes with the spark discharge generation (SDG) method. The morphology and crystallinity were investigated by SEM and HRTEM, and the composition was confirmed by STEM EDX, which indicated that the Ag shell acts as an oxidation barrier for the Cu core. The current material system may find applications in antibacterial coatings. The method presented can be extended to other bimetallic systems with applications in catalysis, plasmonics and as seed-particles for nanowire growth. Owing to the simple, zero-waste and continuous production method, SDG is an ideal platform for such nanoparticle generation and investigation.
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| 4. |
- Eom, Namsoon, et al.
(author)
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Core-shell Cu-Ag Nanoparticles Produced by Spark Discharge Generation
- 2019
-
Conference paper (peer-reviewed)abstract
- The synthesis of core@shell nanoparticles has predominantly been carried out by chemical methods or physical deposition of a shell material post-growth onto core particles. By combining immiscible materials that differ in surface energy, we demonstrate the spontaneous atomic rearrangement to monodisperse Cu@Ag core@shell particles directly in the aerosol phase, starting from pure Cu and Ag electrodes with the spark discharge generation (SDG) method. The morphology and crystallinity were investigated by SEM and HRTEM, and the composition was confirmed by STEM EDX, which indicated that the Ag shell acts as an oxidation barrier for the Cu core. The current material system may find applications in antibacterial coatings. The method presented can be extended to other bimetallic systems with applications in catalysis, plasmonics and as seed-particles for nanowire growth. Owing to the simple, zero-waste and continuous production method, SDG is an ideal platform for such nanoparticle generation and investigation.
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| 5. |
- Hu, Tianyi, et al.
(author)
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Direct Observation of Liquid–Solid Two-Phase Seed Particle-Assisted Kinking in GaP Nanowire Growth
- 2023
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In: Small Structures. - 2688-4062. ; 4:9
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Journal article (peer-reviewed)abstract
- In the last decades, the metal-assisted growth approach of semiconductor nanowires (NWs) has shown its potential in controlling crystal properties, such as crystal structure, composition, and morphology. Recently, literature reports have shown successful semiconductor NW growth with multiphase seed particles under growth conditions. Exploring alternative metal seeds and the mechanisms for growing semiconductor NWs is an exciting research field aiming to improve the control over the crystal growth process. Herein, the gallium phosphide (GaP) NW growth using Cu as seed particles inside an environmental transmission electron microscope is studied. In particular, the transformations of the Cu-rich seed particles during the nucleation and growth of GaP NWs are observed. The supply of a relatively high amount of Ga atoms by the precursor mixture led to a solid Cu-rich seed particle core covered by a liquid phase. Different growth dynamics within the two-phase seed particle resulted in local competition in NW growth. As a result, the GaP NW kinked into another growth direction by forming a new interface at the NW growth front. The generated results enable insights into fundamental processes occurring in the seed particle during growth, creating leverage points for controlling the NW morphology.
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| 6. |
- Jönsson, Linnéa, et al.
(author)
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The effect of electrode composition on bimetallic AgAu nanoparticles produced by spark ablation
- 2024
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In: Journal of Aerosol Science. - 0021-8502. ; 177
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Journal article (peer-reviewed)abstract
- A flexible way to generate bimetallic nanoparticles with high control of their composition is to use spark ablation of alloyed electrodes. It has been generally accepted and stated that particles produced using spark ablation of alloyed electrodes obtain the same chemical composition as the electrodes. However, we identify a lack of studies fully supporting the connection between electrode and particle composition, presented in a small literature survey. The aim of the study is, hence, to explore the validity of the statement by analysing the relation between alloyed electrodes and their resulting particle composition using three sets of AgAu electrodes containing Au and 25, 50, and 75 atomic % Ag, respectively. The resulting composition is thoroughly investigated using both single particle (scanning- and transmission electron microscopy) and ensemble particle techniques (inductive coupled plasma-mass spectroscopy, x-ray photoelectron spectroscopy, x-ray fluorescence, and optical measurements of surface plasmon resonance. We also investigate how sample size (e.g., the number of particles analysed) affects the reliability of the resulting sample mean. For single-particle measurements of a sample with a compositional standard deviation of a few atomic percentage points, a sample size of 20 particles is a good benchmark for obtaining reliable results of the sample mean. Furthermore, this article aims to challenge the practice in which the composition of nanoparticles is measured, presented, and interpreted, to improve and facilitate future research related to this topic. From the results of this study, it could be concluded that for the investigated Ag–Au material system, the particles obtained a composition very similar to the alloyed AgAu electrodes.
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| 7. |
- Ludvigsson, Linus, et al.
(author)
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InSb Nanoparticles Produced by Spark Discharge Generation
- 2019
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Conference paper (peer-reviewed)abstract
- We present the synthesis of monodisperse aerosol InSb nanoparticles of high crystalline quality using the spark discharge generation (SDG) method. Apart from successfully using metallic In and Sb electrodes, we demonstrate the feasibility of using pure semiconducting InSb wafers as electrode material. We investigated the influence of carrier gas on the quality of the size selected particles. We show that addition of 5% hydrogen in the carrier gas (nitrogen or argon) reduced particle oxidation and drastically lowered the compaction temperatures. Further we found an influence of the compaction temperature on the stoichiometry and crystallinity. While uncompacted particles contained excess Sb, the InSb particles reached 1:1 molar ratio after full compaction. The spark discharge method shows promise for generating large quantities of high-quality InSb nanoparticles with applications in e.g. optoelectronics and plasmonics, and the method may be extended to generate nanoparticles of other semiconductor materials.
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| 8. |
- Ludvigsson, Linus, et al.
(author)
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InSb Nanoparticles Produced by Spark Discharge Generation
- 2019
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Conference paper (peer-reviewed)abstract
- We present the synthesis of monodisperse aerosol InSb nanoparticles of high crystalline quality using the spark discharge generation (SDG) method. Apart from successfully using metallic In and Sb electrodes, we demonstrate the feasibility of using pure semiconducting InSb wafers as electrode material. We investigated the influence of carrier gas on the quality of the size selected particles. We show that addition of 5% hydrogen in the carrier gas (nitrogen or argon) reduced particle oxidation and drastically lowered the compaction temperatures. Further we found an influence of the compaction temperature on the stoichiometry and crystallinity. While uncompacted particles contained excess Sb, the InSb particles reached 1:1 molar ratio after full compaction. The spark discharge method shows promise for generating large quantities of high-quality InSb nanoparticles with applications in e.g. optoelectronics and plasmonics, and the method may be extended to generate nanoparticles of other semiconductor materials.
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| 9. |
- Ruan, Can, et al.
(author)
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Combustion of micron-sized Al-Mg alloy wires in hot H2O/O2/N2 flows
- 2024
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In: Fuel. - 0016-2361. ; 357
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Journal article (peer-reviewed)abstract
- The use of aluminum-magnesium (Al-Mg) alloy particle as energetic additive in solid propellants was previously shown to have many advantages over pure Al particle, such as relatively low ignition temperature, high reaction rate and low particle agglomeration rate. In this paper, the combustion of Al-Mg alloy in hot H2O/O2/N2 flows was experimentally studied using wires with a diameter of 200 µm. The employment of wires instead of particles provided a unique opportunity to obtain fundamental insights into the combustion process due to the spatial stabilization and large size of the sample. High-speed imaging showed that the combustion of Al-Mg alloy wire could be divided into three stages, namely pre-heating, ignition, and combustion. Spectral measurements suggested that the chemiluminescence emissions from Mg, MgO and MgOH dominated the collected spectra, in spite of only 3% Mg (by weight) existed in the alloy. Additionally, it was observed that moderate gaseous reactions could occur well before the breakup of the passive oxide coating, generating obvious fine oxide smokes. Moreover, consumption rates of the wire in different hot oxidizers were obtained and compared. It was shown that O2 featured more significant promotion of the reaction than H2O. Nevertheless, without O2, much less metal-oxide particles were generated. Temperature measurements indicated that the ignition temperature lied within 2160 ∼ 2220 K, which was lower than the melting points of Al2O3 (2350 K) and MgO (3125 K). Large single burning Al-Mg alloy droplets (∼200 µm diameter) were generated after the micro-explosion inside the wire. It was found that the combustion of Al-Mg alloy in both H2O/O2/N2 and H2O/N2 atmospheres were diffusion-controlled with a stand-off distance around 150 µm (stand-off ratios at ∼ 1.3). Finally, SEM and EDS measurements revealed that Al, Mg and O elements coexisted on the surface of the burnt wires. Nevertheless, it was observed that the oxidization of Mg started before Al, and the reaction of alloy was more intense when O2 existed. This led to the generation of much thicker oxide layers and larger number of nanoparticles.
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| 10. |
- Samuelsson, Per, et al.
(author)
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Airborne Gold Nanoparticle Detection Using Photoluminescence Excited with a Continuous Wave Laser
- 2021
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In: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:11, s. 1402-1409
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Journal article (peer-reviewed)abstract
- We report the observation of photoluminescence emission from airborne gold, silver, and copper nanoparticles. A continuous wave 532 nm laser was employed for excitation. Photoluminescence from gold nanoparticles carried in a nitrogen gas flow was both spectrally resolved and directly imaged in situ using an intensified charge-coupled device camera. The simultaneously detected Raman signal from the nitrogen molecules enables quantitative estimation of the photoluminescence quantum yield of the gold nanoparticles. Photoluminescence from metal nanoparticles carried in a gas flow provides a potential tool for operando imaging of plasmonic metal nanoparticles in aerosol reactions.
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