Bimetallic CuZn (brass) nanoparticles are key materials in catalytic applications, yet access to the full compositional range remains challenging using conventional wet chemical synthesis. In this study, we demonstrate the physical synthesis of CuZn nanoparticles across a broad compositional range using spark ablation of alloyed feedstocks (Cu25Zn75, Cu50Zn50, Cu75Zn25). In spark ablation, the nanoparticles are formed directly in the gas phase without the need for post-synthesis treatments and exhibit complete internal mixing, as confirmed by (scanning) transmission electron microscopy ((S)TEM) and energy-dispersive X-ray spectroscopy (EDS). A pronounced evolution over time in nanoparticle composition was observed during continuous generation. To elucidate the underlying mechanisms, a comprehensive set of advanced, time-resolved characterization techniques was employed, including X-ray fluorescence (XRF) of deposited nanoparticles, optical emission spectroscopy (OES) of the spark plasma, in-flight inductively coupled plasma mass spectrometry (ICP-MS), and in-flight X-ray photoelectron spectroscopy (XPS). These complementary characterization methods reveal a gradual compositional evolution linked to changes at the feedstock surface rather than post-formation processes. The results indicate that preferential Zn evaporation governs the temporal evolution of the nanoparticle composition, followed by the establishment of a dynamic steady state during prolonged sparking. Based on the experimental observations, a qualitative mechanism supported by a simple ablation model is proposed to explain the compositional evolution in CuZn spark ablation. Despite the large differences in thermophysical properties between Cu and Zn, a broad Cu-Zn compositional range can be accessed, with stable nanoparticle compositions achieved upon extended operation. This work provides insight into bimetallic nanoparticle formation via spark ablation and how tunable alloy compositions can be achieved via gas-phase synthesis, with direct relevance for catalytic and other composition-sensitive applications.

Pd-Ga alloy nanoparticles with tunable compositions were produced by combining spark ablation with a downstream injection of a metal-organic precursor. This dual-process approach enables control over nanoparticle composition and morphology by adjusting precursor flow rate and sintering temperature. At lower precursor flows, uniform Pd-Ga nanoparticles form, exhibiting stable Pd5Ga2 and Pd2Ga phases. HRTEM and STEM-EDX analyses reveal that as precursor supply increases, Ga incorporation intensifies, leading to structural transitions, phase segregation, and the formation of PdGa dominated phases with amorphous Ga-rich domains, influencing nanoparticle shape and crystallinity. This process unlocks pathways for tailoring alloy compositions inflight with low-melting point materials.

Metal oxide nanoparticles are widely used in catalysis, photovoltaics, and gas sensing, where surface structure and oxidation state strongly influence performance. This work investigates how carrier gas composition, combined with in-flight heating, can be used to control the surface properties of metal oxide nanoparticles generated via the gas-phase method, spark ablation. Sn, Zn, and Al nanoparticles were characterized using in-flight X-ray photoelectron spectroscopy (XPS) at the MAX IV synchrotron radiation facility, enabling near real-time measurement of suspended particles under oxidizing (N2 + O2), inert (N2 and Ar), and potentially reducing (N2 + H2 and Ar + H2) gas environments, without introducing potential changes associated with particle deposition and storage. To support the interpretation of the XPS results, the particle size distributions, spark energy and frequency, and compaction behaviour were studied, providing insight into how material properties and generation conditions affect surface chemistry. The XPS results show that for Sn nanoparticles, surface oxidation state can be tuned from SnO2 to SnO and metallic Sn by selecting appropriate carrier gas and in-flight heating temperature. For Zn, the carrier gas primarily determines the surface composition, while heating has only a minor influence on the balance between ZnO, oxygen-deficient ZnOx, and metallic Zn on the surface. In contrast, the surface oxide of Al nanoparticles remains largely unaffected by both carrier gas and in-flight heating. These findings demonstrate how careful control of carrier gas and in-flight thermal processing can be used to tailor nanoparticle surface properties, providing a pathway for designing materials optimized for specific applications.

A clear understanding of the mechanisms governing the growth of nanowires is crucial to achieving control over their structures and properties. Here, we employ molecular dynamics (MD) simulations to investigate several important phenomena in Au-catalyzed Si nanowires (SiNWs) grown via the vapor-liquid-solid method. MD simulation serves as a complementary tool for uncovering the mechanisms of nanowire growth at temporal and spatial scales that current experimental techniques cannot achieve. After verifying the trend in the phase diagram and the preferred growth direction, we present detailed atomistic insights into the growth mechanisms, including truncation, twinning, nucleation processes, and the dynamics of Au impurities. Our study reveals that nucleation of truncating nanowires occurs at the edge of the main facet where it meets the {111} truncating edge, which tends to have a large truncating area and thus attributes to an asymmetric wetting appearance on the side walls. Observed twinning phenomena confirm the nucleation point as twinning changes the location of {111} truncating edges, subsequently altering the nucleation site. Additionally, we explore the early stage of growth and observe tapering facilitated by changes in the contact angle during the growth, independent of surface diffusion. The "crawling" mechanism is also elucidated through atomistic details. Furthermore, investigations into Au impurity incorporation in SiNWs reveal their predominant presence within the bottom layer of each Si bilayer. Their transient incorporation at the SiNW's top surface at the liquid-solid interface, followed by rapid dissolution into the liquid phase, highlights the dynamic nature of impurity interactions during the growth process. These findings could provide insights into other types of nanowires grown via the vapor-liquid-solid method.

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.

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.

In this study, we used data from LinkedIn networks to gain insight in how different groups network in terms of network size and gender composition among men and women. We have gathered categorical data from 751 LinkedIn networks to quantitatively analyze networking tendencies and network gender compositions in the categories gender, age, sector of work, fi?eld of work, level of education and area of residence. We have also determined networking "savviness" as a quantitative measure of social networking for comparing groups in the categories. The observations made regarding networking behavior among female and male LinkedIn users include that women on average had more female contacts than men in all categories. Female networks working in a non-technical fi?eld were found to have the most gender equal networks of all groups with an average of 42.5% female contacts. The data show further, that men and women in STEM and the private sector were savvier networkers and that users with a PhD had fewer female contacts on average than those without a PhD. Further, Scandinavian networks had signi?cantly more female contacts in their networks than networks from other European countries and North America had.

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.

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.

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 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.

We report on an optical investigation of the pyrolysis and photolysis of trimethylindium (TMIn) as a typical metalorganic precursor for functional nanowire growth, aiming at an in-depth understanding of the governing chemistry and optimization of aerosol-based (aerotaxy) and epitaxial growth processes. A flow reactor with special consideration given to optical access was built to provide the chemical environment for in situ optical measurements on the pyrolysis and photolysis of TMIn. By probing a resonant transition of the indium atom, high-resolution laser absorption and laser-induced fluorescence spectroscopy were applied to obtain the atomic indium concentration at different chosen conditions in a spatially and temporally resolved manner. The results indicate that quantitative measurements of indium atoms under growth conditions are feasible. A 213 nm pulsed laser was employed to induce photolytic dissociation of TMIn vapor under chosen conditions. The photolytic dissociation of TMIn vapor with an ultraviolet laser turns out to be a promising method in generating substantial chemical effects, indicated by the generation of visible clouds of indium particles, and high concentrations of indium atoms far beyond the pyrolytically generated amount.

Surface segregation phenomena dictate core–shell preference of bimetallic nanoparticles and thus play a crucial role in the nanoparticle synthesis and applications. Although it is generally agreed that surface segregation depends on the constituent materials’ physical properties, a comprehensive picture of the phenomena on the nanoscale is not yet complete. Here we use a combination of molecular dynamics (MD) and Monte Carlo (MC) simulations on 45 bimetallic combinations to determine the general trend on the core–shell preference and the effects of size and composition. From the extensive studies over sizes and compositions, we find that the surface segregation and degree of the core–shell tendency of the bimetallic combinations depend on the sufficiency or scarcity of the surface-preferring material. Principal component analysis (PCA) and linear discriminant analysis (LDA) on the molecular dynamics simulations results reveal that cohesive energy and Wigner–Seitz radius are the two primary factors that have an “additive” effect on the segregation level and core–shell preference in the bimetallic nanoparticles studied. When the element with the higher cohesive energy also has the larger Wigner–Seitz radius, its core preference decreases, and thus this combination forms less segregated structures than what one would expect from the cohesive energy difference alone. Highly segregated structures (highly segregated core–shell or Janus-like) are expected to form when both the relative cohesive energy difference is greater than ∼20%, and the relative Wigner–Seitz radius difference is greater than ∼4%. Practical guides for predicting core–shell preference and degree of segregation level are presented.

Boiling heat transfer intensification is of significant relevance to energy conversion and various cooling processes. This study aimed to enhance the saturated pool boiling of FC-72 (a dielectric liquid) by surface modifications and explore mechanisms of the enhancement. Specifically, circular and square micro pin fins were fabricated on silicon surfaces by dry etching and then copper nanoparticles were deposited on the micro-pin-fin surfaces by electrostatic deposition. Experimental results indicated that compared with a smooth surface, the micro pin fins increased the heat transfer coefficient and the critical heat flux by more than 200 and 65-83%, respectively, which were further enhanced by the nanoparticles up to 24% and more than 20%, respectively. Correspondingly, the enhancement mechanism was carefully explored by high-speed bubble visualizations, surface wickability measurements, and model analysis. It was quantitatively found that small bubble departure diameters with high bubble departure frequencies promoted high heat transfer coefficients. The wickability, which characterizes the ability of a liquid to rewet a surface, played an important role in determining the critical heat flux, but further analyses indicated that evaporation beneath bubbles was also essential and competition between the wicking and the evaporation finally triggered the critical heat flux.

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.

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.

Metal oxide shell layers are promising candidates to improve the performance of metal nanoparticles (NPs) in various applications. However, despite a significant amount of experimental work on metal@metal oxide (M@MO) NPs, computational modeling is scarce, particularly on the sintering mechanism, which plays a crucial role in both the synthesis and performance of NPs. Here, we present atomic diffusion and sintering dynamics of M@MO NPs investigated using molecular dynamics based on the ReaxFF potentials. The coalescence process of the metal NPs with amorphous oxide shell is mainly facilitated by the relatively mobile surface atoms and grain-boundary-like diffusion, and thus, it is similar to reported mechanisms for crystalline nanoparticles. Intriguingly, atomic trajectory tracing reveals that surface diffusion is highly localized, contrary to the common understanding of freely moving high-mobility surface atoms. These atomic descriptions provide valuable insights for designing functional NPs with oxide layers and establishing more accurate accounts of the sintering mechanism.

Cost- and resource-efficient growth is necessary for many applications of semiconductor nanowires. We here present the design, operational details and theory behind Aerotaxy, a scalable alternative technology for producing quality crystalline nanowires at a remarkably high growth rate and throughput. Using size-controlled Au seed particles and organometallic precursors, Aerotaxy can produce nanowires with perfect crystallinity and controllable dimensions, and the method is suitable to meet industrial production requirements. In this report, we explain why Aerotaxy is an efficient method for fabricating semiconductor nanowires and explain the technical aspects of our custom-built Aerotaxy system. Investigations using SEM (scanning electron microscope), TEM (transmission electron microscope) and other characterization methods are used to support the claim that Aerotaxy is indeed a scalable method capable of producing nanowires with reproducible properties. We have investigated both binary and ternary III-V semiconductor material systems like GaAs and GaAsP. In addition, common aspects of Aerotaxy nanowires deduced from experimental observations are used to validate the Aerotaxy growth model, based on a computational flow dynamics (CFD) approach. We compare the experimental results with the model behaviour to better understand Aerotaxy growth.

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. (Less)

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. (Less)

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. (Less)