| 1. |
- Deppert, Knut, et al.
(författare)
-
Complex Aerosol Nanostructures: Revealing the Phases from Multivariate Analysis on Elemental Maps Obtained by TEM-EDX
- 2020
-
Konferensbidrag (refereegranskat)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.
(författare)
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One-step Gas-phase Synthesis of Core-shell Nanoparticles via Surface Segregation.
- 2019
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Konferensbidrag (refereegranskat)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.
(författare)
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A Continuous One-Step Aerosol Method for Producing Core@Shell Cu@Ag Nanoparticles
- 2019
-
Konferensbidrag (refereegranskat)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.
(författare)
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Core-shell Cu-Ag Nanoparticles Produced by Spark Discharge Generation
- 2019
-
Konferensbidrag (refereegranskat)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.
(författare)
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Direct Observation of Liquid–Solid Two-Phase Seed Particle-Assisted Kinking in GaP Nanowire Growth
- 2023
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Ingår i: Small Structures. - 2688-4062. ; 4:9
-
Tidskriftsartikel (refereegranskat)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.
(författare)
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The effect of electrode composition on bimetallic AgAu nanoparticles produced by spark ablation
- 2024
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 177
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Tidskriftsartikel (refereegranskat)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.
(författare)
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InSb Nanoparticles Produced by Spark Discharge Generation
- 2019
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Konferensbidrag (refereegranskat)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.
(författare)
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InSb Nanoparticles Produced by Spark Discharge Generation
- 2019
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Konferensbidrag (refereegranskat)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.
(författare)
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Combustion of micron-sized Al-Mg alloy wires in hot H2O/O2/N2 flows
- 2024
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Ingår i: Fuel. - 0016-2361. ; 357
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Airborne Gold Nanoparticle Detection Using Photoluminescence Excited with a Continuous Wave Laser
- 2021
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:11, s. 1402-1409
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Seifner, Michael, et al.
(författare)
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Dynamic Processes in Metal-Semiconductor Nanoparticle Heterostructures
- 2021
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Konferensbidrag (refereegranskat)abstract
- Over the last years, there have been huge research efforts in the synthesis of advanced nanoparticle heterostructures to promote their performance in photocatalysis.[1] Especially, the combination of metals with semiconductors has been identified as a potential approach to enhance the photocatalytic activity via efficient charge carrier separation enabled by plasmon- exciton coupling.[2] The physical properties of such heterostructures highly depend on the present crystal facets and heterointerfaces.[3] Consequently, a detailed characterisation of nanoparticle heterostructures to determine the impact of morphological/structural properties on the photocatalytic activity is of high importance in this research field and paves the way towards facet-engineered surface and heterointerface design via advanced synthesis procedures. In this study, we combine Cu3-xP – a p-type semiconductor with a band gap of ~1.5 eV[4] – and Ag to form a metal-semiconductor nanoparticle heterostructure with potential in water splitting and investigate dynamic processes occurring around the synthesis of such structures.For that purpose, Ag-Cu nanoparticle heterostructures synthesised in a spark ablation system[5] were deposited on a heating chip for in situ transmission electron microscopy (TEM) investigations. Subsequently, the heating chip was transferred to an environmental TEM with integrated metalorganic chemical vapour deposition (MOCVD) system. The controlled supply of phosphine (PH3) at moderate temperatures initiated the Cu-Cu3-xP phase transformation in a Ag-Cu nanoparticle heterostructure with a Ag(111)/Cu(111) interface oriented parallel to the electron beam and both phases tilted in their [110] zone axes. We characterized the present phases via high-resolution TEM imaging and energy dispersive X-ray spectroscopy (EDS). The analysis of selected averaged frames of a high-resolution TEM movie capturing the phase transformation reveals the dynamic processes occurring in the nanoparticle heterostructure. The nucleation of the Cu3-xP phase occurred at the triple phase boundary of the Ag-Cu nanoparticle heterostructure and the chemical reaction proceeded perpendicular to the formed growth front. We identified epitaxial relations dominating the arrangement of the phases and observed faceting of the Cu3-xP phase. After the complete transformation of the Cu phase, an additional heterointerface formed and grew at the cost of the heterointerface being initially present in the nanoparticle heterostructure. Several factors promoted the rearrangement of the phases including a well-matched interplanar spacing of planes perpendicular to the new heterointerface. Moreover, we observed an inhomogeneous strain distribution in the Ag phase caused by the presence of two heterointerfaces. As part of the post-synthesis annealing, corner truncation of the faceted Cu3-xP phase to reduce the total surface free energy was observed. The rearrangement process could be accelerated by increasing the temperature resulting in a Ag- Cu3-xP nanoparticle heterostructure with a single interface. The involved planes forming the interface in the observed nanoparticle heterostructure were different to the ones observed in the most common product of the here presented synthesis procedure. Our results show different scenarios occurring during the phase transformation and highlight potential ways to control the synthesis of Ag-Cu3-xP nanoparticle heterostructures with well- defined facets and heterointerfaces via a gas phase approach using Ag-Cu nanoparticle heterostructures as templates. Future experiments will focus on the impact of morphological and structural properties of those nanoparticle heterostructures on their photocatalytic activities.
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| 12. |
- Seifner, Michael S., et al.
(författare)
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Insights into the Synthesis Mechanisms of Ag-Cu3P-GaP Multicomponent Nanoparticles
- 2023
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Ingår i: ACS Nano. - 1936-0851. ; 17:8, s. 7674-7684
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-semiconductor nanoparticle heterostructures are exciting materials for photocatalytic applications. Phase and facet engineering are critical for designing highly efficient catalysts. Therefore, understanding processes occurring during the nanostructure synthesis is crucial to gain control over properties such as the surface and interface facets’ orientations, morphology, and crystal structure. However, the characterization of nanostructures after the synthesis makes clarifying their formation mechanisms nontrivial and sometimes even impossible. In this study, we used an environmental transmission electron microscope with an integrated metal-organic chemical vapor deposition system to enlighten fundamental dynamic processes during the Ag-Cu3P-GaP nanoparticle synthesis using Ag-Cu3P seed particles. Our results reveal that the GaP phase nucleated at the Cu3P surface, and growth proceeded via a topotactic reaction involving counter-diffusion of Cu+ and Ga3+ cations. After the initial GaP growth steps, the Ag and Cu3P phases formed specific interfaces with the GaP growth front. GaP growth proceeded by a similar mechanism observed for the nucleation involving the diffusion of Cu atoms through/along the Ag phase toward other regions, followed by the redeposition of Cu3P at a specific Cu3P crystal facet, not in contact with the GaP phase. The Ag phase was essential for this process by acting as a medium enabling the efficient transport of Cu atoms away from and, simultaneously, Ga atoms toward the GaP-Cu3P interface. This study shows that enlightening fundamental processes is critical for progress in synthesizing phase- and facet-engineered multicomponent nanoparticles with tailored properties for specific applications, including catalysis.
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| 13. |
- Seifner, Michael S., et al.
(författare)
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Interface Dynamics in Ag–Cu3P Nanoparticle Heterostructures
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126.
-
Tidskriftsartikel (refereegranskat)abstract
- Earth-abundant transition metal phosphides are promising materials for energy-related applications. Specifically, copper(I) phosphide is such a material and shows excellent photocatalytic activity. Currently, there are substantial research efforts to synthesize well-defined metal–semiconductor nanoparticle heterostructures to enhance the photocatalytic performance by an efficient separation of charge carriers. The involved crystal facets and heterointerfaces have a major impact on the efficiency of a heterostructured photocatalyst, which points out the importance of synthesizing potential photocatalysts in a controlled manner and characterizing their structural and morphological properties in detail. In this study, we investigated the interface dynamics occurring around the synthesis of Ag–Cu3P nanoparticle heterostructures by a chemical reaction between Ag–Cu nanoparticle heterostructures and phosphine in an environmental transmission electron microscope. The major product of the Cu–Cu3P phase transformation using Ag–Cu nanoparticle heterostructures with a defined interface as a template preserved the initially present Ag{111} facet of the heterointerface. After the complete transformation, corner truncation of the faceted Cu3P phase led to a physical transformation of the nanoparticle heterostructure. In some cases, the structural rearrangement toward an energetically more favorable heterointerface has been observed and analyzed in detail at the atomic level. The herein-reported results will help better understand dynamic processes in Ag–Cu3P nanoparticle heterostructures and enable facet-engineered surface and heterointerface design to tailor their physical properties.
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| 14. |
- Snellman, Markus, et al.
(författare)
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A thermal evaporator for aerosol core-shell nanoparticle synthesis
- 2024
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- Segregated bimetallic nanoparticles like core-shell nanoparticles are of interest in various fields including biomedicine, catalysis, and optoelectronics. Aerosol technology is an optimal platform to control nanoparticle size, structure, and composition, which are some of the most important parameters tuning the material performance for the intended applications. Here, we develop a novel evaporator design to coat core particles on-line with a shell directly in the gas phase. The evaporator employs a local heater that decouples heating the evaporating material from the aerosol particles to limit core-shell alloying. We characterize the system by evaporating Zn onto core particles of Au, Sn, and Bi and demonstrate the core-shell particle formation with controllable shell thickness in each material system. We discuss simple models to explain the observed growth process inside the evaporator and the resulting shell formation.
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| 15. |
- Snellman, Markus
(författare)
-
Aerosol Generated Core-shell Nanoparticles : Synthesis and Characterization
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosol technology is a promising platform to synthesize and study core-shellnanoparticles - a multi-elemental nanoparticle system where the core of one material is covered by a shell of another material. In this thesis, two distinctly separate strategies have been explored to synthesize core-shell nanoparticles by aerosol methods: physical vapor deposition (PVD) by evaporation, and surface segregation via thermal treatment. Using a novel aerosol PVD design with a local heater to decouple shell material heating from the aerosol, Zn condensation on Au core particles was studied and compared to a simple model based on kinetic gas theory and Comsol simulations. Elemental characterization with electron microscopy did, however, reveal an AuZn alloy instead of the intended core-shell morphology. Growth was additionally found to be limited by homogenous nucleation of Zn vapor. In contrast, tube furnace heating of spark discharge generated CuAg agglomerates demonstrated the possibility to obtain both a quasi-Janus and a core-shell nanoparticle morphology, simply by tuning the furnace temperature to control the surface segregation. The chemical composition of core and shell phases determined by machine learning algorithms applied to elemental maps of the particles were in congruence with X-ray Photoelectron Spectroscopy measurements. Further elemental characterization of the spark discharge generated CuAg particles revealed a low inter-particle compositional variance, the reason of which remains to be investigated.
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| 16. |
- Snellman, Markus
(författare)
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Aerosol Synthesis and Characterization of Heterogeneous Bimetallic Nanoparticles
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the proverbial noose tightens around humanity’s resource spending, research is focused on utilizing materials to their fullest potential. Nanotechnology is the ultimate way to economize by splitting objects into smaller parts and dispersing the material properties over greater surface to volume ratios. Emerging quantum effects at the nanoscale present unique tweaking opportunities in applications. This thesis deals with creating and characterizing heterogeneous nanoparticles, including Janus and core-shell nanoparticles: segregated structures where the different parts having different properties allow for multiple functionalities within individual units. Heterogeneous nanoparticles that have already attracted interest in fields ranging from catalysis to biotechnology are typically made by chemical methods. Here, aerosol technology has been used to realize these nanostructures, as such physical synthesis hold advantages in improved purity of the product, and reduced waste from the process.The two main approaches that have been developed in this work to create bimetallic heterogenous nanoparticles, surface segregation and condensational growth, both use spark ablation as the material source. From the optical emission in the electrical discharges, we use machine learning to determine the composition of bimetallic AuAg nanoparticles. Thermally induced surface segregation in CuAg agglomerates forming Janus and core-shell nanoparticles have been studied on- and off-line with aerosol metrology and electron microscopy. Compared to analogue works where the particles sit on a substrate, the aerosol phase is ideal to study surface segregation of “free” nanostructures. A more general route toward arbitrary metal-metal core-shell combinations is explored with condensational growth by thermal evaporation and photolysis. To understand the condensation inside a custom thermal evaporator designed in this work, a novel approach to measure the residence time distribution of aerosol nanoparticles is presented. Condensational growth of aerosol nanoparticles by photolysis of metal-organic precursors is a new route that can be carried out at room temperature. The process therefore allows for formation of core-shell particles of miscible materials and avoids thermophoretic losses of particles experienced in conventional thermal evaporation. Combining on-line compositional monitoring with the unique, precursor-less pathways to create heterogeneous nanoparticles that aerosol technology enables, this thesis is a step toward more sustainable synthesis of tailored bimetallic nanostructures with applications in, for instance, catalysis, sensors, and electronics.
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| 17. |
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| 18. |
- Snellman, Markus, et al.
(författare)
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Continuous gas-phase synthesis of core–shell nanoparticles via surface segregation
- 2021
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Ingår i: Nanoscale Advances. - 2516-0230. ; 3:11, s. 3041-3052
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis methods of highly functional core@shell nanoparticles with high throughput and high purity are in great demand for applications, including catalysis and optoelectronics. Traditionally chemical synthesis has been widely explored, but recently, gas-phase methods have attracted attention since such methods can provide a more flexible choice of materials and altogether avoid solvents. Here, we demonstrate that Cu@Ag core–shell nanoparticles with well-controlled size and compositional variance can be generated via surface segregation using spark ablation with an additional heating step, which is a continuous gas-phase process. The characterization of the nanoparticles reveals that the Cu–Ag agglomerates generated by spark ablation adopt core–shell or quasi-Janus structures depending on the compaction temperature used to transform the agglomerates into spherical particles. Molecular dynamics (MD) simulations verify that the structural evolution is caused by heat-induced surface segregation. With the incorporated heat treatment that acts as an annealing and equilibrium cooling step after the initial nucleation and growth processes in the spark ablation, the presented method is suitable for creating nanoparticles with both uniform size and composition and uniform bimetallic configuration. We confirm the compositional uniformity between particles by analyzing compositional variance of individual particles rather than presenting an ensemble-average of many particles. This gas-phase synthesis method can be employed for generating other bi- or multi-metallic nanoparticles with the predicted configuration of the structure from the surface energy and atomic size of the elements.
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| 19. |
- Snellman, Markus, et al.
(författare)
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On-line compositional measurements of AuAg aerosol nanoparticles generated by spark ablation using optical emission spectroscopy
- 2022
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Spark ablation is an established technique for generating aerosol nanoparticles. Recent demonstrations of compositional tuning of bimetallic aerosols have led to a demand for on-line stoichiometry measurements. In this work, we present a simple, non-intrusive method to determine the composition of a binary AuAg nanoparticle aerosol on-line using the optical emission from the electrical discharges. Machine learning models based on the least absolute shrinkage and selection operator (LASSO) were trained on optical spectra datasets collected during aerosol generation and labelled with X-ray fluorescence spectroscopy (XRF) compositional measurements. Models trained for varying discharge energies demonstrated good predictability of nanoparticle stoichiometry with mean absolute errors <10 at. %. While the models utilized the emission spectra at different wavelengths in the predictions, a combined model using spectra from all discharge energies made accurate predictions of the AuAg nanoparticle composition, showing the method's robustness under variable synthesis conditions.
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| 20. |
- Snellman, Markus, et al.
(författare)
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On-line compositional measurements of AuAg aerosol nanoparticles using optical emission from spark ablation
- 2022
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Konferensbidrag (refereegranskat)abstract
- Spark ablation is an established method for generating aerosol nanoparticles. By changing the electrodes, synthesis of monometallic, multimetallic and semiconducting nanoparticles has been demonstrated. Apart from using electrodes of specific composition, compositional tuning of bimetallic nanoparticles during synthesis has recently been demonstrated (Kohut, et al., 2021). In many applications, it is desirable to have a specific stoichiometry and monitoring the composition on-line provides important feedback during the process and for the samples generated. Common methods to determine aerosol composition involves lengthy sampling and off-line characterization. Most on-line tools are complex and expensive to operate. In both cases, the characterization is destructive. There is a need for fast and low-cost methods that can give rapid compositional feedback during synthesis. Optical diagnostics is a promising approach for aerosol monitoring due to the on-line and non-destructive capabilities (Samuelsson, et al., 2021). Analysing the optical emission during the spark discharges can provide valuable information related to the nanoparticle properties, including their composition. In this work, we demonstrate a simple setup to monitor the composition of AuAg aerosol nanoparticles generated by spark ablation using optical emission from the discharges on-line. The optical setup cost was low by using an untriggered spectrometer with long integration time. The complex optical spectra were related to the AuAg nanoparticle composition, measured by an aerosol X-ray fluorescence (XRF) setup, by calibration models using the least absolute shrinkage and selection operator (LASSO).Models trained for varying discharge energies demonstrated good predictability of nanoparticle stoichiometry with mean absolute errors < 10 at. % and root mean square errors comparable to other machine learning techniques. While the models utilized different wavelengths in the predictions, a combined model using spectra from all discharge energies made accurate predictions of the AuAg nanoparticle composition, showing the method’s robustness under variable synthesis conditions. We suggest future improvements to the methodology with respect to hardware and pre-processing to improve the signal-to-background and calibration models.Kohut, A., Villy, L. P., Kéri, A., Bélteki, Á., Megyeri, D., Hopp, B., . . . Geretovszky, Z. (2021). Full range tuning of the composition of Au/Ag binary nanoparticles by spark discharge generation. Scientific reports, 11, 1–10. Samuelsson, P., Snellman, M., Magnusson, M. H., Deppert, K., Aldén, M., & Li, Z. (2021). Airborne Gold Nanoparticle Detection Using Photoluminescence Excited with a Continuous Wave Laser. Applied Spectroscopy, 75, 1402–1409.
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| 21. |
- Snellman, Markus, et al.
(författare)
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Synthesis and characterization of Au@Zn core@shell aerosol nanoparticles generated by spark ablation and on-line PVD
- 2021
-
Konferensbidrag (refereegranskat)abstract
- An interesting subset of nanoparticles is core-shell nanoparticles: encapsulating a core particle of one material with a shell of another material can be utilized to combine and even extend the properties of the respective material. Strategies to synthesize core-shell nanoparticles in the aerosol phase remain relatively unexplored, despite the benefit of the continuous, ambient pressure nature of the process. Arguably, the most straightforward way to accomplish the core-shell morphology is to condense the shell material onto pre- formed core particles via physical vapor deposition (PVD). Previous works have utilized a second tube furnace in the aerosol circuit to evaporate the shell material and condense it onto the core particles (Karlsson, et al. 2004, Harra, et al. 2015). However, heating the entire aerosol may lead to unintended alloying of core and shell materials (Karlsson, et al. 2004). In this work we revisit the thermal evaporation approach using a coating chamber in which the evaporating material is only locally heated. As a test system, we coat Au nanoparticles generated by spark ablation with Zn due to the high evaporation rates achievable even at low heating temperatures.The coating setup, shown schematically in Fig. 1, uses a tandem DMA setup to size select the aerosol prior to, and after condensational growth in the growthchamber. The first DMA and tube furnace allows us to introduce a monodisperse, spherical Au aerosol into the growth chamber, after which the Zn growth is readily measured by scanning mobility diameter shift using the second DMA and an electrometer at different heater temperatures (Fig. 2). Further, the second DMA enables size selection of the core-shell particles corresponding to a desired shell thickness. The inset in Fig. 2 demonstrates a clear condensational growth up to heater temperatures of 400 °C, after which growth decreases, presumably due to homogenous nucleation of Zn. We will further discuss the characterization of the aerosol using electron microscopy and elemental characterization, as well as process limitations and opportunities.
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