| 141. |
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| 142. |
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| 143. |
- Sedrpooshan, Mehran, et al.
(författare)
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Single-step generation of 1D FeCo nanostructures
- 2024
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Ingår i: Nano Express. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic one-dimensional structures are attractive nanomaterials due to the variety of potential applications they can provide. The fabrication of bimetallic 1D structures further expands the capabilities of such structures by tailoring the magnetic properties. Here, a single-step template-free method is presented for the fabrication of 1D FeCo alloy nanochains. In this approach, charged single-crystalline FeCo nanoparticles are first generated by the co-ablation of pure Fe and Co electrodes under a carrier gas at ambient pressures and attracted to a substrate using an electric field. When reaching the surface, the particles are self-assembled into parallel nanochains along the direction of an applied magnetic field. The approach allows for monitoring the self-assembly particle by particle as they are arranged into linear 1D chains with an average length controlled by the deposited particle concentration. Magnetometry measurements revealed that arranging nanoparticles into nanochains results in a 100% increase in the remanent magnetization, indicating significant shape anisotropy. Furthermore, by combining x-ray microscopy and micromagnetic simulations, we have studied the local magnetization configuration along the nanochains. Our findings show that variations in magnetocrystalline anisotropy along the structure play a crucial role in the formation of magnetic domains.
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| 144. |
- Sedrpooshan, Mehran, et al.
(författare)
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Template-free generation and integration of functional 1D magnetic nanostructures
- 2023
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3372 .- 2040-3364.
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Tidskriftsartikel (refereegranskat)abstract
- The direct integration of 1D magnetic nanostructures into electronic circuits is crucial for realizing their great potential as components in magnetic storage, logical devices, and spintronic applications. Here, we present a novel template-free technique for producing magnetic nanochains and nanowires using directed self-assembly of gas-phase-generated metallic nanoparticles. The 1D nanostructures can be self-assembled along most substrate surfaces and can be freely suspended over micrometer distances, allowing for direct incorporation into different device architectures. The latter is demonstrated by a one-step integration of nanochains onto a pre-patterned Si chip and the fabrication of devices exhibiting magnetoresistance. Moreover, fusing the nanochains into nanowires by post-annealing significantly enhances the magnetic properties, with a 35% increase in the coercivity. Using magnetometry, X-ray microscopy, and micromagnetic simulations, we demonstrate how variations in the orientation of the magnetocrystalline anisotropy and the presence of larger multi-domain particles along the nanochains play a key role in the domain formation and magnetization reversal. Furthermore, it is shown that the increased coercivity in the nanowires can be attributed to the formation of a uniform magnetocrystalline anisotropy along the wires and the onset of exchange interactions.
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| 145. |
- 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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| 146. |
- 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
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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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| 147. |
- 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.
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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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| 148. |
- Shamun, Sam, et al.
(författare)
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Detailed characterization of particulate matter in alcohol exhaust emissions
- 2017
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Ingår i: COMODIA 2017 - 9th International Conference on Modeling and Diagnostics for Advanced Engine Systems. - 2424-2918.
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Konferensbidrag (refereegranskat)abstract
- A way to reduce net CO2 emission and circumvent the high particle emissions from compression ignition (CI) engines, while retaining high efficiency, is by utilizing lighter alcohols in the partially premixed combustion (PPC) process. Methanol and ethanol have a very short carbon chain, and form less soot/particulate matter (PM) during combustion compared to diesel fuel. This study analyzes and compares the characteristics of PM emissions from methanol, ethanol and diesel in terms of soot mass concentration, number concentration and particle size distribution in one cylinder of a six cylinder Scania D13 heavy duty (HD) engine under two operating loads; 6 bar and 10 bar gross mean indicated effective pressure (IMEPG). An electrostatic precipitator (ESP) was used to sample PM on copper grids for transmission electron microscopy (TEM) and energy dispersive X-ray analysis. Also, new and used lubrication oil together with methanol and diesel were analyzed for their sulphur and metal content. Nucleation mode and the majority of accumulation mode particles from methanol and ethanol combustion, showed mainly Ca, S, P and Zn in the energy dispersive X-ray spectrometry (EDX) analysis and were hypothesized to be emitted mainly from the lubrication oil rather than the combustion of the fuel itself. From diesel combustion, the accumulation mode particles were more abundant in comparison with the alcohols and PM/soot emissions measured with the photo-acoustic technique were 3 to 10 times higher than for the alcohols. There were also fewer nucleation mode particles present; although they consisted of the same four abovementioned elements. Utilizing alcohols in CI engines have a great advantage regarding PM, particle number emissions and efficiency. However, the resulting nucleation mode particles need to be reduced to avoid future health concerns.
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| 149. |
- Shi, Juanzi, et al.
(författare)
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Photoluminescence Polarization of MAPbBr3 Perovskite Nanostructures. Can the Dielectric Contrast Effect Explain It?
- 2022
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:12, s. 3888-3898
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric contrast effect is usually evoked to explain anisotropy of optical properties of elongated nanoobjects, for example, semiconductor nanowires. We applied two-dimensional polarization imaging microscopy to measure the polarization of photoluminescence (PL) excitation and PL intensity of nanoaggregates of in-situ formed MAPbBr3perovskite nanoparticles in a stretched polymeric matrix. Scanning electron microscopy images of these objects were also acquired to characterize their sizes and shapes. We find that individual perovskite aggregates with sizes of 100-300 nm often possess a PL excitation polarization degree as high as 0.5-0.9, which is up to three times higher than the polarization degree of absorption predicted by the dielectric contrast effect. Small aggregates of nanoparticles possess an emission polarization degree substantially higher than that of excitation. Computer simulations of many possible scenarios show that the dielectric contrast alone cannot quantitatively explain the polarization properties of the studied objects. We propose energy transfer to localized emitting sites and the dependence of PL yield on excitation power density as possible factors strongly influencing the polarization properties of PL emission and PL excitation, respectively.
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| 150. |
- 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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