Core-shell Configurations Research Articles

Tailoring the Compositions and Nanostructures of Trimetallic Prussian Blue Analog-Derived Carbides for Water Oxidation.

The electrochemical splitting of water for hydrogen production faces a major challenge due to its anodic oxygen evolution reaction (OER), necessitating research on the rational design and facile synthesis of OER catalysts to enhance catalytic activity and stability. This study proposes a ligand-induced MOF-on-MOF approach to fabricate various trimetallic MnFeCo-based Prussian blue analog (PBA) nanostructures. The addition of [Fe(CN)6]3- transforms them from cuboids with protruding corners (MnFeCoPBA-I) to core-shell configurations (MnFeCoPBA-II), and finally to hollow structures (MnFeCoPBA-III). After pyrolysis at 800°C, they are converted into corresponding PBA-derived carbon nanomaterials, featuring uniformly dispersed Mn2Co2C nanoparticles. A comparative analysis demonstrates that the Fe addition enhances catalytic activity, while Mn-doped materials exhibit excellent stability. Specifically, the optimized MnFeCoNC-I-800 demonstrates outstanding OER performance in 1.0mKOH solution, with an overpotential of 318mV at 10mAcm-2, maintaining stability for up to 150h. Theoretical calculations elucidate synergistic interactions between Fe dopants and the Mn2Co2C matrix, reducing barriers for oxygen intermediates and improving intrinsic OER activity. These findings offer valuable insights into the structure-morphology relationships of MOF precursors, advancing the development of highly active and stable MOF-derived OER catalysts for practical applications.

Influence of CoFe2O4 content on the multifunctional properties of BiFeO3–CoFe2O4 core-shell nanocomposites

The utilization of magnetoelectric composites, particularly core-shell configurations, enhances their versatile applications in various sectors such as medicine and data storage. Among these composites, the perovskite-spinel combination is distinguished by its significant potential. A series of (1-x) BiFeO3-(x) CoFe2O4 (where x = 0.0, 0.2, 0.5, and 1.0) nano core-shell structures were synthesized using a sol-gel auto-combustion method to explore their multifunctional capabilities. Structural analyses identified peaks corresponding to both perovskite and spinel phases. Field Emission Scanning Electron Microscopy revealed a reduction in average particle size with an increase in CoFe2O4 content.The particle size in the BFO80-CFO20 sample has been reduced from 243 nm to 34 nm. Additionally, Transmission Electron Microscopy images of the BFO80-CFO20 sample highlighted the evolution of core-shell structures. Our findings indicate that higher CFO concentrations significantly affect the dielectric, ferroelectric, and optical properties. The bandgaps of the nanocomposites BFO80-CFO20 and BFO50-CFO50 were estimated to be 1.43 eV and 1.39 eV, respectively. Magnetic analysis showed increases in both saturation magnetization and remanent magnetization with increased CFO content, while the coercive field followed a different trend. The saturation magnetization values for the samples BFO, BFO80-CFO20, BFO50-CFO50, and CFO were calculated as 0.205, 14.612, 28.374, and 74.105 (emugr), respectively. The measured values for the same samples were 0.08, 5.07, 11.34, and 34.01 (emugr), respectively. Further, the electrochemical properties were thoroughly investigated using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy.

Site-Selective Deposition of Silica Nanoframes and Nanocages onto Faceted Gold Nanostructures Using a Primer-free Tetraethyl Orthosilicate Synthesis.

The Stöber method for forming spherical silica colloids is well-established as one of the pillars of colloidal synthesis. In a modified form, it has been extensively used to deposit both porous and protective shells over metal nanomaterials. Current best-practice techniques require that the vitreophobic surface of metal nanoparticles be primed with a surface ligand to promote silica deposition. Although such techniques have proved highly successful in forming core-shell configurations, the site-selective deposition of silica onto preselected areas of faceted metal nanostructures has proved far more challenging. Herein, a primer-free TEOS-based synthesis is demonstrated that is capable of forming architecturally complex nanoframes and nanocages on the pristine surfaces of faceted gold nanostructures. The devised synthesis overcomes vitreophobicity using elevated TEOS concentrations that trigger silica nucleation along the low-coordination sites where gold facets meet. Continued deposition sees the emergence of a well-connected frame followed by the lateral infilling of the openings formed over gold facets. With growth readily terminated at any point in this sequence, the synthesis distinguishes itself in being able to achieve patterned and tunable silica depositions expressing interfaces that are uncorrupted by primers. The so-formed structures are demonstrated as template materials capable of asserting high-level control over synthesis and assembly processes by using the deposited silica as a mask that deactivates selected areas against these processes while allowing them to proceed elsewhere. The work, hence, extends the capabilities and versatility of TEOS-based syntheses and provides pathways for forming multicomponent nanostructures and nanoassemblies with structurally engineered properties.

An improved preparation method of core-shell Al@Sn-Bi microspheres and its microstructure formation mechanism

This paper presents an improved method for achieving controllable preparation of the composition and size of the monotectic alloy core-shell structure microspheres. This advancement is expected to enhance the commercial application of monotectic alloy core-shell structure microspheres. By installing a heating device at the top of the drop tube in the pulsated orifice ejection method setup, we achieved in-situ heat treatment of falling droplets, resulting in the successful preparation of Al45(Sn42Bi58)55 core-shell structure microspheres. Furthermore, we investigated the formation mechanism of the Al@Sn-Bi core-shell structure. Nine sets of Al-Sn-Bi microspheres with varying in-situ heat treatment temperatures were prepared. Analysis via X-ray diffraction and transmission electron microscopy revealed that the microspheres consisted of Al-rich, Sn-rich, and Bi-rich phases, without any intermetallic compounds. Scanning electron microscopy results indicated that as the in-situ heat treatment temperature increased, the structure of the Al-Sn-Bi microspheres transitioned from irregular to regular core-shell configurations. This suggests that higher heat treatment temperatures prolong liquid phase separation time, leading to increased repetition of Marangoni motion within the droplet, Ostwald ripening of the minor phase droplets, and Soret effect of the matrix phase. However, at temperatures exceeding 700 °C, the solidification rate of alloy droplets decreased, causing the Al-rich phase core to deviate from the center and form a crescent structure due to Stokes motion.

Quantum-informed plasmonics for strong coupling: the role of electron spill-out

The effect of nonlocality on the optical response of metals lies at the forefront of research in nanoscale physics and, in particular, quantum plasmonics. In alkali metals, nonlocality manifests predominantly as electron density spill-out at the metal boundary, and as surface-enabled Landau damping. For an accurate description of plasmonic modes, these effects need be taken into account in the theoretical modeling of the material. The resulting modal frequency shifts and broadening become particularly relevant when dealing with the strong interaction between plasmons and excitons, where hybrid modes emerge and the way they are affected can reflect modifications of the coupling strength. Both nonlocal phenomena can be incorporated in the classical local theory by applying a surface-response formalism embodied by the Feibelman parameters. Here, we implement local surface-response corrections in Mie theory to study the optical response of spherical plasmonic–excitonic composites in core–shell configurations. We investigate sodium, a jellium metal dominated by spill-out, for which it has been anticipated that nonlocal corrections should lead to an observable change in the coupling strength, appearing as a modification of the width of the mode splitting. We show that, contrary to expectations, the influence of nonlocality on the anticrossing is minimal, thus validating the accuracy of the local response approximation in strong-coupling photonics.

Temperature-Controlled Synthesis of Trimodal Hierarchically Porous MOFs with Variable Core–Shell Configurations

Temperature-Controlled Synthesis of Trimodal Hierarchically Porous MOFs with Variable Core–Shell Configurations

Versatile cost-effective fabrication of large-area nanotube arrays with highly ordered periodicity

Nanomaterials typically exhibit physical and chemical properties that differ from those of conventional bulk materials owing to their nanometer-scale structures. Among them, nanotube arrays are characterized by their ability to exhibit remarkably aligned larger surface areas than those of existing arrays. Consequently, they have been used to increase efficiency in various fields such as sensing, energy storage and conversion, and optical communication. Processes such as anodic-aluminum-oxide templating, secondary sputtering, and sputtering are generally used to manufacture nanotube arrays. However, these methods have limitations in creating periodically aligned structures and precisely controlling nanotube characteristics such as diameter, period, and height. Therefore, a method combining direct printing and oblique-angle deposition (OAD) performed by e-beam evaporation is reported in this study for generating nanotubes with a highly ordered periodicity. Using this approach, nanotube arrays of various shapes and specifications can be manufactured by adjusting the type of master stamp used in the direct printing and the OAD parameters. Additionally, this scheme can be leveraged to produce nanotube arrays with metals, inorganic compounds, multilayer structures, and core–shell configurations.

Mechanical characterization of core-shell microcapsules

Core-shell configurations are ubiquitous in nature such as in the form of bacterial and cells. Inspired by this, microcapsules are designed with actives as the cores surrounded by thin shells. They not only play an increasing role as artificial models for understanding dynamic behaviors of biological cells in flows, but are also becoming a fundamental class of artificial vehicles at the heart of drug delivery and release in applications. The mechanical properties of the shells are of great importance in this context. Here, we review recent experimental and theoretical characterizations of microcapsules, focusing on the soft and deformable particles with liquid cores. We begin by exploring the concept and fabrication of artificial microcapsules, followed by a discussion of different methods on the mechanical characterization of the shell.

Effects of size and temperature on the configurations of the Re-Ni clusters

The diffusion and growth dynamic processes of Re adatoms on a Wulff Ni substrate were simulated by combining molecular dynamics and embedded atom method. The configurations of the Re adatoms on Wulff1289 clusters at 100, 200, 300, and 600 K at different growth stages were compared. Results show that the optimal core-shell configurations were achieved at 100 K. The factors of substrate size (201, 586 and 1289 atoms) on cluster growth processes were analyzed. The quality of core-shell clusters obtained at different temperatures and sizes varies. The optimal quality of core-shell structure of Re adatoms growing on wulff586 Ni cluster was obtained at 200 K, while the corresponding temperature for Wulff201 Ni cluster was at 100 K. These findings indicate that optimal core-shell clusters can be obtained within our study’s size range at low temperatures, and the cluster size and temperature should be fully considered when designing the cluster configuration.

A Study on the Dynamics of Compound Materials on Superhydrophobic Surfaces: Effects of Droplet’s Size and Shape

Compound materials have two or more unmixable parts that retain a shared surface with one another for engineering purposes. Such compound materials, like the Janus or core–shell configurations, create opportunities for relevant applications because they offer diverse combinations of complex impinging materials and complex surfaces. However, previous studies have only assumed spherical configurations, or focused on the bouncing dynamics, without considering the effect of the material size. The current work numerically studies the dynamic characteristics of Janus materials with ellipsoidal shapes for various impact speeds and viscosity ratios, to analyze the effect of the size and shape of the material on bouncing and separation behavior. The threshold Weber numbers at which separation starts after the collision are investigated as a function of the droplet size, ellipticity, and viscosity ratio. In addition, a regime map of the separation efficiency of the Janus droplets is established under various viscosity ratios and Weber numbers to investigate the effects of droplet shape on the asymmetric bouncing and separation behavior. It is found that the separation efficiency and mechanism of two prolate spheroids are different from each other at the same ellipticity. This study will provide an efficient strategy to control the bouncing of compound materials in applications, such as drug delivery, liquid purification, and bio- or multi-material printing.

Surface plasmon enhanced fluorescence: self-consistent classical treatment in the quasi-static limit

The problem of enhanced molecular emission in close proximity to dielectric and metallic interfaces is of great importance for many physical and biological applications. Here we present an exact treatment of the problem from the view point of classical electromagnetism. Self-consistent analytical theory of the surface enhanced fluorescence (SEF) is developed for configurations consisting of an emitter in proximity to core–shell metal-dielectric nanoparticles. The dependence of the fluorescence enhancement on the excitation laser and fluorescence frequencies and distance of the emitter to the nanoparticle interface are studied. The developed theory predicts enhanced fluorescence at intermediate distances as well as emission quenching into non-radiative surface plasmon (SP) modes dominating the response for short distances. The conditions for optimal emission enhancement for two core–shell configurations are determined and a comparison to published experimental data is performed showing a good correspondence between theory and experiment. The developed model can be applied toward analyzes and optimizations of various applications related to SP enhance fluorescence spectroscopy.

Structural diagrams and thermodynamics relating to temperature and compositions of Ag561−nCun (n = 0-561) nanoalloys during cooling from atomic simulations

The packing changes of Ag_561-nCu_n (n = 0-561) nanoparticles during cooling were studied by molecular dynamics simulations at atomic scale. Structural diagrams as well as packing images presented liquid, disordered, and some ordered patterns. Pair distribution functions were used to characterize some typical structures. Potential energy and shape factors identified the transition’s temperature regime and the effect of cooling on the shape’s changes of the alloyed particles. The simulation results show composition effect on the transition temperatures and complex structural patterns. For these Cu-Ag nanoalloys, which contain small amount of Cu or Ag atoms, they show alternating FCC and icosahedral packing patterns at low temperatures, and core-shell configurations prefer to occur in the Cu-rich particles, where the Cu occupy the interior of the particles. Compositions and degree of orderliness in packing contribute to the entropy of the alloyed nanoparticles.

Study the influence of shell thickness in bimetallic Ag core&Au shell configurations integrated in bare Si PN junction solar cells

The effect of the gold layer thickness of Ag core&Au shell configurations on the performance of the bare Si n-type layer of a PN junction solar cell was explored. The different forms of Ag core&Au shell configurations were formed via pulsed laser ablation method of Ag and Au plate using second harmonic generation (SHG) of Nd:YAG laser wavelength at 530 nm with 0.61 J/cm2 energy flounce and various pluses repetition rate 350-500. The integrating of Ag core&Au shell configurations in n-type of bare PN Si junction was accomplished via pluses laser illumination of bare PN junction substrate. The photovoltaic results of formed solar cells showed strong dependence on Au shell thickness. Tangible enhancement was observed in the performance of bare Si solar cells after inserting core–shell configuration with specific shell thickness owning to the broadband absorption of plasmonics nanoparticles and the high values of specific surface area.

Epitaxial growth of surface-passivated core-shell ferrierite

Ferrierite (FER) is both a natural and synthetic zeolite that is commonly utilized as a catalyst in commercial processes that take advantage of its two-dimensional network of micropores. The external surfaces of zeolite crystals often impose deleterious effects on catalyst performance, such as external coking or unselective reactions as a result of unconfined acid sites. One technique that can improve the efficiency of zeolite catalysts is surface passivation wherein the aluminosilicate crystal is encapsulated within a shell of its siliceous isostructure. These core–shell configurations eliminate surface acidity, forcing reactions to occur within interior (confined) pores for improved shape-selectivity while simultaneously reducing rates of deactivation, which extends catalyst lifetime. In this study, we examine whether a Si-rich shell can be epitaxially grown on the surface of an aluminosilicate FER crystal in fluoride-free media. Epitaxial growth of an ultra-thin Si-rich shell was confirmed by multiple characterization techniques showing no evidence of pore blockage or misoriented shell growth during core–shell synthesis. The passivation of external acid sites was confirmed using Friedel-Crafts alkylation of mesitylene and benzyl alcohol as a benchmark reaction for probing surface acidity. Overall, these findings confirm that it is possible to synthesize core–shell ferrierite with an aluminosilicate core and a silicon-rich shell via a facile seed-assisted growth procedure.

Thermal behavior of different types of Au–Pt–Pd nanoparticles: Dumbbell-like, three-shell, core-shell, and random-alloy

In recent years, the synthesis of multimetallic nanoparticles with different configurations has been considered due to the special catalytic properties. Since, the catalytic performance of nanoparticles depends on their thermal stability, hence, in this study, the thermal stability of Au–Pt–Pd trimetallic nanoparticles with different configurations, including Au@PtPd core-shell, Au@Pt@Pd three-shell, AuPtPd random alloy, and Au׀Pt׀Pd dumbbell-like was compared using molecular dynamics simulation. Results showed that the Au–Pt–Pd nanoparticles with three-shell, core-shell, and random-alloy configurations are unstable at high temperature and Au atoms with less surface energy segregate to the shell and forms a spherical-like structure of Pd@AuPt with mixed shell. In addition, in the dumbbell-like nanoparticle, the penetration of Au atoms into the Pt and Pd regions leads to a spherical-like structure with a mono-layer shell of PtAu. Furthermore, results showed the following trend for thermal stability of Au–Pt–Pd nanoparticles with different configurations: three-shell ≈ random-alloy ≈ core-shell > dumbbell-like. The three-shell, random-alloy and core-shell nanoparticles with the least strain average show the highest thermal stability and the dumbbell-like nanoparticle with the most strain average shows the lowest thermal stability. Overall, the results of this study illustrate that in addition to factors such as composition, size, and morphology which have been studied in many experimental and theoretical studies, it is possible to synthesis and design of trimetallic nanoparticles with excellent catalytic activity and high thermal stability by adjusting their configuration, including three-shell, core-shell, and random alloy.

Plasmonic Hybrid Nanostructures in Photocatalysis: Structures, Mechanisms, and Applications.

(Sun)Light is an abundantly available sustainable source of energy that has been used in catalyzing chemical reactions for several decades now. In particular, studies related to the interaction of light with plasmonic nanostructures have been receiving increased attention. These structures display the unique property of localized surface plasmon resonance, which converts light of a specific wavelength range into hot charge carriers, along with strong local electromagnetic fields, and/or heat, which may all enhance the reaction efficiency in their own way. These unique properties of plasmonic nanoparticles can be conveniently tuned by varying the metal type, size, shape, and dielectric environment, thus prompting a research focus on rationally designed plasmonic hybrid nanostructures. In this review, the term "hybrid" implies nanomaterials that consist of multiple plasmonic or non-plasmonic materials, forming complex configurations in the geometry and/or at the atomic level. We discuss the synthetic techniques and evolution of such hybrid plasmonic nanostructures giving rise to a wide variety of material and geometric configurations. Bimetallic alloys, which result in a new set of opto-physical parameters, are compared with core-shell configurations. For the latter, the use of metal, semiconductor, and polymer shells is reviewed. Also, more complex structures such as Janus and antenna reactor composites are discussed. This review further summarizes the studies exploiting plasmonic hybrids to elucidate the plasmonic-photocatalytic mechanism. Finally, we review the implementation of these plasmonic hybrids in different photocatalytic application domains such as H2 generation, CO2 reduction, water purification, air purification, and disinfection.

The role of viscosity ratio in Janus drop impact on macro-ridge structure

An interaction of liquid and solid surfaces upon impact has made great progress in understanding the principle behind impinging compound drops, such as single-interface Janus and core–shell configurations, for controlling drop mobility on the surfaces. Despite advancement of recent technologies, fundamentals of how viscosity ratios of Janus drops affect post-impact dynamics on anisotropic surfaces are still unknown. Here, we numerically investigate the asymmetric impact dynamics of Janus drops on a non-wettable ridged surface to demonstrate the feasibility of the separation of the low-viscosity part from the high-viscosity part by reducing the residence time. The separation is investigated for various viscosity ratios, Weber numbers (We), and initial angle, which are discussed in terms of the temporal evolution of the mass and momentum distributions. A regime map for the separation reveals that the low-viscosity parts are more likely to be separated from high-viscosity parts as the viscosity ratio increases. The phenomenon can be related to a retraction time, which is explained by a hydrodynamic model for the low-viscosity part. This study suggests that We thresholds for the separation can be significantly reduced with the help of center-assisted retraction along the ridge. The asymmetric bouncing of Janus drops on a ridged surface can open up possibilities for the efficient control of liquid separation.

Singular behaviour of atomic ordering in Pt–Co nanocubes starting from core–shell configurations

The ordered structure of platinum-cobalt (Pt-Co) alloy nanoparticles has been studied actively because the structure influences their magnetic and catalytic properties. On the Pt-Co alloy's surface, Pt atoms preferentially segregate during annealing to reduce the surface energy. Such surface segregation has been shown to promote the formation of an ordered structure near the surface of Pt-Co thin films. Although this phenomenon seems also useful to control the nanoparticle structure, this has not been observed. Here, we have studied the ordered structure in annealed Pt@Co core-shell nanoparticles using a scanning transmission electron microscope. The nanoparticles were chemically synthesized, and their structural changes after annealing at 600 °C, 700 °C, and 800 °C for 3 h were observed. After being annealed at 600 °C and 800 °C, the particles contained the L12-Pt3Co ordered structure. The structure seems reasonable considering an initial Pt : Co ratio of ∼4 : 1. However, we found that the L10-PtCo structure was formed near the nanoparticle surface after annealing at 700 °C. The L10-PtCo structure was thought to be formed from the surface segregation of Pt atoms and insufficient diffusion of Pt and Co atoms to mix them in the particle overall.

EM Scattering by Core-Shell Gyroelectric-Isotropic and Isotropic-Gyroelectric BoRs Using the EBCM

We employ the extended boundary condition method (EBCM) and construct a solution for the problem of electromagnetic (EM) scattering by anisotropic core-shell bodies of revolution (BoRs). In particular, two different core-shell configurations are examined: the gyroelectric-isotropic and the isotropic-gyroelectric setup. To construct the solution, we employ two groups of integral representations (IRs)—one group for each configuration solved—in conjunction with the discrete eigenfunction (DE) expansion of the fields in terms of spherical vector wave functions (SVWFs) for the gyroelectric regions. We demonstrate the validity and the computational performance of the method by comparisons with the HFSS commercial software for various core-shell setups such as spheroidal, cylindrical, and combined spherical-cylindrical BoRs. We also employ ADDA, a particular version of the discrete dipole approximation (DDA) method, to trace the boundaries of validity of the EBCM. Finally, we present an application of the method to the study of magnetically-tunable spheroidal THz antennas. The method can be used in a variety of potential EM applications including microwaves, functional photonics structures, as well as nanoantenna engineering.

Out-of-equilibrium supported Pt-Co core-shell nanoparticles stabilized by kinetic trapping at room temperature

The chemical stability of supported CoPt nanoparticles in out-of-equilibrium core-shell configurations was investigated mainly by anomalous grazing incidence small angle X-ray scattering (AGISAXS) in association with combined transmission electron microscopy and X-ray absorption spectroscopy. CoPt nanoparticles were prepared at room temperature by ultrahigh vacuum atom beam deposition using two different routes: simultaneous deposition of the two metals (CoPt) or sequential deposition. In this last case, Co deposition on a Pt-core (Pt@Co) and the reverse configuration (Co@Pt) are explored. In the Pt@Co case, our experimental analysis of 2.5 nm particles shows the stability of a Pt rich-core (80% Pt) surrounded by a two-monolayers-thick Co shell. In the reverse case, the core-shell structure is also stabilized, while the codeposited sample leads to an alloyed structure. These results suggest that the growth kinetics can trap the thermodynamically non-favorable core-shell structure even for this system which has a high alloying tendency. Besides the lack of atom mobility at room temperature, this stabilization can also be associated with core strain effects. Post thermal treatment of core-shell samples induces a structural transition from the core-shell configuration to the equilibrium alloyed configuration. This study demonstrates that the element-selective scattering technique, AGISAXS is highly efficient for the extraction of chemical segregation information from multi-component supported nanoparticles, such as core-shell structures, up to ultimate small sizes.