Formation Of Core-shell Structure Research Articles

Unveiling Core-Shell Structure Formation in a Ni3Fe Nanoparticle with In Situ Multi-Bragg Coherent Diffraction Imaging.

Solid-state reactions play a key role in materials science. The evolution of the structure of a single 350 nm Ni3Fe nanoparticle, i.e., its morphology (facets) as well as its deformation field, has been followed by applying multireflection Bragg coherent diffraction imaging. Through this approach, we unveiled a demixing process that occurs at high temperatures (600 °C) under an Ar atmosphere. This process leads to the gradual emergence of a highly strained core-shell structure, distinguished by two distinct lattice parameters with a difference of 0.4%. Concurrently, this transformation causes the facets to vanish, ultimately yielding a rounded core-shell nanoparticle. This final structure comprises a Ni3Fe core surrounded by a 40 nm Ni-rich outer shell due to preferential iron oxidation. Providing in situ 3D imaging of the lattice parameters at the nanometer scale while varying the temperature, this study─with the support of atomistic simulations─not only showcases the power of in situ multireflection BCDI but also provides valuable insights into the mechanisms at work during a solid-state reaction characterized by a core-shell transition.

Elucidating the intrinsic core-shell structure of carbon nanospheres from glucose hydrothermal carbonization

This study explores the core-shell structure formation mechanisms of primary carbon nanospheres (PCNs) through hydrothermal carbonization (HTC) of glucose at 200 °C, focusing on key phase-change polymerization reactions. Colloidal carbon nanoparticles in the aqueous phase filtrate self-assembled into secondary carbon nanospheres (SCNs) with intrinsic hollow structures during room temperature storage. FTIR results revealed similar functional groups on the surfaces of PCNs and SCNs due to esterification reactions during HTC cooling. XPS and 13 C NMR analyses identified HMF aldol condensation and etherification as dominant reactions for PCNs, while esterification and aldol condensation with levulinic acid were dominant for SCNs. The hypothesis suggests that PCNs initially formed hollow microframeworks but collapsed due to consumption of encapsulated organics, resulting in hydrophobic cores. These cores grew through aggregation (linear) and surface reactions (exponential), internalizing hydrophilic surfaces into hydrophobic cores, forming the final core-shell structure of PCNs.

The growth mechanism of Co atoms on Cu substrates

The growth mechanism of Co atoms on Cu atomic substrates was studied by molecular dynamics simulation with large scale atomic/polar massively parallel simulator (LAMMPS). The embedded atom method (EAM) potential was used to investigate the growth processes of Co atoms on different Cu atom configurations. The growth process of Co on Cu substrate was carefully observed. It was found that Co atoms preferentially grow on the (100) facet on the Wulff configuration. To find out under what conditions the core-shell structure is better formed, the number of Cu atoms adsorbed on the surface and the number of Co atoms entering the interior were calculated as a function of the number of deposited atoms. The Wulff configuration was found to be more favorable for the growth of Co atoms on the Cu substrates. And the effect of the size of the Cu substrate on the growth of the Co atoms was also investigated. The results show that the larger the size of the Cu substrate, the more unfavorable the core-shell structure formation. In addition, the effect of temperature on growth was also analyzed. It was found that the higher the temperature, the more unfavorable the growth.

A novel Cu-Sn-Zr alloy with core-shell structure

In this study, a novel Cu-0.3Sn-0.2Zr (wt.%) alloy was designed to investigate the influence of Zr addition on the microstructure and properties of the Cu-0.3Sn alloys. We have discovered that the addition of Zr could not only greatly refine the grain structures of the Cu-0.3Sn alloy and contribute to forming a large number of nanoscale Zr-rich particles, but also leads to the formation of core-shell structure with a large amount of Sn atoms segregated at the surface of the microscale and nanoscale Zr-rich particles. As a result, all of the tensile strength, electrical conductivity and softening temperature of the Cu-0.3Sn-0.2Zr alloy were improved when compared with the Cu-0.3Sn alloy. After cold drawing at an accumulated strain of 6.8 combined with a two-step aging treatment, a good combination of an ultimate tensile strength of ∼724 MPa, an electrical conductivity of ∼76.8% IACS and a softening temperature of ∼425 °C were achieved in the Cu-0.3Sn-0.2Zr alloy, which was ∼147 MPa, ∼0.7 % IACS and ∼90 °C higher than that of the Cu-0.3Sn alloy after cold drawing at the same accumulated strain of 6.8, respectively. Our research elucidates that the Cu-Sn-Zr alloys represent a category of potential copper alloys with high strength, high conductivity and excellent softening resistance performance.

Kinetics of Spontaneous Formation of Core-Shell Structure in (In,Ga)As Nanowires

Kinetics of Spontaneous Formation of Core-Shell Structure in (In,Ga)As Nanowires

Synthesis of core-shell structured silver-polypyrrole nanocomposite for cost effective photocatalytic degradation of methylene blue under natural sunlight

In this article, we report synthesis of silver-polypyrrole(Ag-PPy) nanocomposites using simple interfacial polymerization method to be applied for photocatalytic degradation of cationic dye Methylene blue (MB) under natural Sunlight. Ag-PPy nanocomposites are synthesized by varying the concentrations (5 mM, 15 mM and 20 mM) of silver nitrate. Field emission scanning electron microscopy (FESEM) show that the particle size of Ag-PPy nanocomposites increases from 200 nm to 450 nm with increasing concentration of silver from 5 mM to 20 mM. Transmission electron microscopy (FETEM) indicates the formation of core shell structure of the nanocomposites with silver at the core. UV–Visible spectra (UV–Vis) show a remarkable broad peak at around 252 nm. The X- ray diffraction spectra (XRD) show characteristic peaks at 2θ = 27.7°,32.1°,46.1°,76.2° for diffraction planes (226),(264),(200) and (311) of FCC structure of silver respectively. FTIR spectra indicates the crosslinking of silver with PPy in the nanocomposite. The photocatalytic activity of the as prepared Ag-PPy nanocatalysts is evaluated by 66 % of degradation of MB dye under natural sunlight irradiation within 3 h.

Design, synthesis and improved sintering behavior of core-shell Mo–Cu composite powders

Molybdenum-copper composites have attracted increasing attention due to their excellent properties in terms of electrical conductivity, thermal conductivity and mechanical property, which are closely related to the density and composition of the sintered material. However, high temperatures are required to obtain high sintering density, resulting in loss of copper in most cases. In this work, a novel core-shell Mo–Cu composite powder was prepared by a ball-milling method followed by hydrogen reduction. The phase compositions and microstructure of prepared powders were studied by XRD, TEM and EDS, and the formation process of core-shell structure of Mo–Cu powders was discussed in detail. It was shown that the significant difference in reduction temperatures between molybdenum and copper oxides contributes to the formation of core-shell structure.

Comprehensive elucidation of experimental results of polytype ZnS‐10H quantum dots produced in single stride

Polytypes of a material exhibit different structures (nanosheets, nanorods, nanospheres etc.), leading to distinct properties pertinent to their respective fields. Theoretical studies using computational methods have elaborated their properties and essence; however, only a few studies were presented experimentally. Ab-initio synthesis of wurtzite ZnS-10 H polytype was carried out and an extensive study was done to unfold the properties to manoeuvre in different fields. Being a potential material for quantum dot sensitized solar cells (QDSSC), ZnS-10 H was synthesized at 70 °C to enhance the properties and in conjunction with the sustainability and durability of the device. Wurtzite crystal structure of polytype ZnS-10 H was confirmed from the studies. Capping agent manifests its role by passivating the material’s surface and the efficacy of the capping agent depends on the binding affinity of ligands and the concentration of the capping agent. Photoluminescence (PL) of uncapped ZnS-10 H shows its luminescence similar to ZnS, and the effect of 2-mercaptoethanol (2-ME) is obtained with 2-ME variations, after a limit (i.e., at 6 mL of capping agent) core-shell structure formation was seen with no emission and no excitation indicating the light capturing ability. Current findings suggest the possible applications of polytype ZnS-10 H in QDSSC, photovoltaic devices and photocatalytic activities.

Synthesis of polyaniline/spinel ferrites core-shell nanocomposites via sucrose auto-combustion and in situ polymerization

Herein, we prepared new nanocomposites from polyaniline (PANI) as a conductive polymer, and ferrites, MFe2O4 (M = Co2+, Cu2+, Mg2+, Ni2+, and Zn2+), as metal-oxide ceramics using sucrose sol–gel auto-combustion and in situ of polymerization. The prepared nanocomposites’ structural, thermal, magnetic, and electrical/dielectric characteristics were investigated. X-ray diffraction (XRD) revealed the formation of the metal-oxide ceramics with weak crystallinity due to their coating in the amorphous structure of the PANI matrix. Transmission electron microscopy (TEM) images exhibited the wrapping of the entire metal-oxide ceramic particles by the PANI matrix, thus confirming the core–shell structure formation. Vibrating sample magnetometer (VSM) results showed drastic reductions in all ferrites’ magnetization by their inclusion in the non-magnetic PANI matrix. The measured coercivity values showed a noticeable lowering in the presence of PANI. Besides, the thermogravimetric analysis (TG) technique indicated apparent increases in the thermal stability of the prepared nanocomposites compared to the pure PANI. Moreover, the electrical conductivity results indicated a change from metallic-like behavior for the pure PANI to the semiconductor by including the ferrites. Furthermore, by comparing the pure PANI, the dielectric properties of nanocomposites increased by the presence of ferrites, suggesting the suitability of the entire nanocomposites to be used in energy storage devices such as capacitors.

Controlling the morphology of polystyrene dumbbell particles

Controlling colloidal particles’ shape is one of the new frontiers in colloidal science. Methods that permit synthesizing polymer particles with a non-spherical shape are increasing and advancing. Of all the non-spherical particles, spheres with protrusions are one of the best investigated, and many recipes have been developed to prepare them. One of the best-developed methods, initially proposed by Park et al. (JACS, 2010), starts with linear polystyrene seed particles, which are swelled and subsequently polymerized with a mixture of styrene and 3-(trimethoxysilyl)propyl methacrylate (MPS). The latter monomer’s hybrid nature creates a hydrophilic and partially crosslinked coating. This prevents the formation of core-shell structure upon further swelling and polymerization with styrene and leads to one or more new lobes. In this work, we investigate many parameters affecting the outcome of this method, including the pH, the duration of the hydrolysis of MPS, its concentration, the presence of crosslinkers in the seed particles, and the use of a different monomer in the last step. The investigation shows the importance of pH control during MPS hydrolysis in the coating step. It also demonstrates that its concentration can effectively be used to control the morphology of the resulting particles, which range from simple one-lobed dumbbells with variable roughness to multilobed particles. Furthermore, a shorter version of the dumbbell synthesis protocol has been obtained.

Diversity of Behavior after Collisions of Sn and Si Nanoparticles Found Using a New Density Functional Tight-Binding Method.

We present a new approach to studying nanoparticle collisions using density functional based tight binding (DFTB). A novel DFTB parametrization has been developed to study the collision process of Sn and Si clusters (NPs) using molecular dynamics (MD). While bulk structures were used as training sets, we show that our model is able to accurately reproduce the cohesive energy of the nanoparticles using density functional theory (DFT) as a reference. A surprising variety of phenomena are revealed for the Si/Sn nanoparticle collisions, depending on the size and velocity of the collision: from core-shell structure formation to bounce-off phenomena.

Phase morphology, rheological behavior and mechanical properties of supertough biobased poly(lactic acid) reactive ternary blends

Poly(lactic acid) (PLA) is one of the most promising bio-based polyester with great potential to replace for the petroleum-based polymers, which can significantly reduce greenhouse gas emissions. However, the inherent brittleness of PLA seriously restricts its broad applications. Herein, PLA/poly(ε-caprolactone) (PCL)/ethylene methyl acrylate-glycidyl methacrylate (EMA-GMA) ternary blends with different phase structures were prepared through reactive blending. The reactions between the epoxy groups of EMA-GMA and the carboxyl and hydroxyl end groups of PLA and PCL and were evidenced from the Fourier transform infrared spectroscopy, dynamic mechanical analysis and rheological results. The atomic force microscopy (AFM) images clearly revealed the formation of stack structure of the PCL and EMA-GMA minor phases in PLA/PCL/EMA-GMA (80/15/5) blend, and core-shell particle structures in PLA/PCL/EMA-GMA (80/10/10) and (80/5/15) blends. In terms of elongation at break and impact toughness, PLA/PCL/EMA-GMA (80/5/15) blend presents the best properties among all the compositions. Moreover, it also behaved excellent stiffness-toughness balance. The toughening mechanism can be ascribed to the formation of core-shell structure and the existence of interfacial adhesion in the ternary blends. This work can provide guide for the preparation and design of PLA-based partially renewable supertough materials that can compete with conventional petro-derived plastics.

Preparation and surface alloying of Al@Dy and Al@Y core-shell particles by magnetron sputtering and pulsed electron beam treatment

The paper is devoted to preparation Al@Dy and Al@Y core-shell structures by magnetron sputtering of Dy and Y on an Al powder. A unique powder holder system is used to obtain continuous powder movement and conglomerates destruction during the treatment. It has been established that powder particles treated using the powder holder system have a uniform coating over the entire surface. The powder coating process regularities were studied depending on the deposition time and the powder charge weight. Simple evaluation criteria for powder coating system efficiency and deposited material content based on the deposition rate were proposed. The complex modification consists of the initial core-shell structure formation and subsequent pulsed low-energy high-current electron beam treatment in the surface layer melting mode was demonstrated. The main goal of the electron beam treatment is to provide better adhesion of the “shell” material to the “core” material. Such treatment led to the deposited shell element alloying into the depth of core particles. Moreover, such electron beam treatment led to the synthesis of intermetallic compounds. In further studies, the prepared structures will be used for the uniform distribution of Dy and Y over the frame elements of self-propagating high-temperature synthesized porous materials.

Evolution of Tb-shell homogeneity in Nd-Fe-B sintered magnets by long-term Tb grain boundary diffusion

Grain boundary diffusion process has been applied to effectively facilitate the coercivity enhancement of Nd-Fe-B magnets by the formation of core-shell structure with less heavy rare earth consumption. However, the excessively thick Tb-rich shells and asymmetric shells formed near the shallow diffused surface, not only have minor contribution to the coercivity enhancement but consume more Tb resources. In this work, the influences of diffusion time on coercivity changes and the evolution of asymmetric to symmetric Tb-rich shell have been investigated for the Tb-diffused Nd-Fe-B magnets. With prolonging the diffusion time at 890 ℃, the coercivity rapidly increases from 17.66 kOe to 24.41 kOe when the diffusion time is less than 18 h and keeps nearly unchanged after a longer diffusion time due to the trade-off effect of Tb-rich shell homogeneity and grain growth. Besides, magnetic domain structure and its dynamic evolution of different core-shell structures in Nd-Fe-B magnet further illustrate the positive effects of homogeneous symmetric Tb-rich shell on coercivity enhancement, which is directly observed by in-situ Lorentz TEM and magneto-optical Kerr microscope, and further proved by micromagnetic simulation. This work thus provides a new insight for tuning the Tb-rich shell distribution in the Nd-Fe-B sintered magnets with high performance by grain boundary diffusion.

Molecular insight into toughening induced by core-shell structure formation in starch-blended bioplastic composites

Binary and ternary blends with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and thermoplastic starch (TPS) were prepared by a melt process to produce biodegradable biomass plastics with both economical and good mechanical properties. The mechanical and structural properties of each blend were evaluated. Molecular dynamics (MD) simulations were also conducted to examine the mechanisms underlying the mechanical and structural properties. PLA/PBS/TPS blends showed improved mechanical properties compared with PLA/TPS blends. The PLA/PBS/TPS blends with a TPS ratio of 25–40 wt% showed higher impact strength than PLA/PBS blends. Morphology observations showed that in the PLA/PBS/TPS blends, a structure similar to that of core-shell particles with TPS as the embedding phase and PBS as the coating phase was formed, and that the trends in morphology and impact strength changes were consistent. The MD simulations suggested that PBS and TPS tightly adhered to each other in a stable structure at a specific intermolecular distance. From these results, it is clear that PLA/PBS/TPS blends are toughened by the formation of a core-shell structure in which the TPS core and the PBS shell adhered well together and stress concentration and energy absorption occurred in the vicinity of the core-shell structure.

Atomically Thin Metal-Dielectric Heterostructures by Atomic Layer Deposition.

Heterostructures increasingly attracted attention over the past several years to enable various optoelectronic and photonic applications. In this work, atomically thin interfaces of Ir/Al2O3 heterostructures compatible with micro-optoelectronic technologies are reported. Their structural and optical properties were determined by spectroscopic and microscopic techniques (XRR, XPS, HRTEM, spectroscopic ellipsometry, and UV/vis/NIR spectrophotometry). The XRR and HRTEM analyses reveal a layer-by-layer growth mechanism of Ir in atomic scale heterostructures, which is different from the typical island-type growth of metals on dielectrics. Alongside, XPS investigations imply the formation of Ir-O-Al bonding at the interfaces for lower Ir concentrations, in contrast to the nanoparticle core-shell structure formation. Precisely tuning the ratio of the constituents ensures the control of the dispersion profile along with a transition from effective dielectric to metallic heterostructures. The Ir coating thickness was varied ranging from a few angstroms to films of about 7 nm in the heterostructures. The transition has been observed in the structures containing individual Ir coating thicknesses of about 2-4 nm. Following this, we show epsilon-near-zero metamaterials with tunable dielectric constants by precisely varying the composition of such heterostructures. Overall, a comprehensive study on structural and optical properties of the metal-dielectric interfaces of Ir/Al2O3 heterostructures was addressed, indicating an extension of the material portfolio available for novel optical functionalities.

Fabrication and characterization of PVA@PLA electrospinning nanofibers embedded with Bletilla striata polysaccharide and Rosmarinic acid to promote wound healing

In this study, a novel nanofiber material with Polylactic acid (PLA), natural plant polysaccharides-Bletilla striata polysaccharide (BSP) and Rosmarinic acid (RA) as the raw materials to facilitate wound healing was well prepared through coaxial electrospinning. The morphology of RA-BSP-PVA@PLA nanofibers was characterized through scanning electron microscopy (SEM), and the successful formation of core-shell structure was verified under confocal laser microscopy (CLSM) and Fourier transform infrared spectroscopy (FTIR). RA-BSP-PVA@PLA exhibited suitable air permeability for wound healing, as indicated by the result of the water vapor permeability (WVTR) study. The results of tension test results indicated the RA-BSP-PVA@PLA nanofiber exhibited excellent flexibility and better accommodates wounds. Moreover, the biocompatibility of RA-BSP-PVA@PLA was examined through MTT assay. Lastly, RA-BSP-PVA@PLA nanofibers can induce wound tissue growth, as verified by the rat dorsal skin wound models and tissue sections. Furthermore, RA-BSP-PVA@PLA can facilitate the proliferation and transformation of early wound macrophages, and down-regulate MPO+ expression of on the wound, thus facilitating wound healing, as confirmed by the result of immunohistochemical. Thus, RA-BSP-PVA@PLA nanofibers show great potential as wound dressings in wound healing.

Small angle neutron scattering studies on RGO incorporated PVB matrix nanocomposites

Given the importance of PVB in laminates, it is imperative that research be carried out on the surface and structural properties of PVB and its composites. In this paper the authors are reporting the preparation and characterization of Reduced Graphene Oxide (RGO) reinforced Polyvinyl Butyral (PVB) Matrix based nanocomposites. Solution casting technique is used to prepare the Nanocomposite films in Teflon Petri dishes at ambient temperature. Small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) were employed to study the surface and structural features of the samples. The scattering data shows power law behavior in the low Q region, suggesting the presence of surface fractal kind of structure. The radius of gyration Rg of pure PVB and RGO incorporated (0.5 wt% and 1.0 wt%) nanocomposites are measured to study the core shell structure formation among the RGO and PVB. The Dynamic light scattering (DLS) and Zeta potential studies are performed to find Hydrodynamic radius and Zeta potentials of individuals and Nanocomposites to know the information about the stability and core shell structure.

Element Distributions in Bimetallic Aerogels

ConspectusMetal aerogels assembled from nanoparticles have captured grand attention because they combine the virtues of metals and aerogels and are regarded as ideal materials to address current environmental and energy issues. Among these aerogels, those composed of two metals not only display combinations (superpositions) of the properties of their individual metal components but also feature novel properties distinctly different from those of their monometallic relatives. Therefore, quite some effort has been invested in refining the synthetic methods, compositions, and structures of such bimetallic aerogels as to boost their performance for the envisaged application(s). One such use would be in the field of electrocatalysis, whereby it is also of utmost interest to unravel the element distributions of the (multi)metallic catalysts to achieve a ratio of their bottom-to-up design. Regarding the element distributions in bimetallic aerogels, advanced characterization techniques have identified alloys, core-shells, and structures in which the two metal particles are segregated (i.e., adjacent but without alloy or core-shell structure formation). While an almost infinite number of metal combinations to form bimetallic aerogels can be envisaged, the knowledge of their formation mechanisms and the corresponding element distributions is still in its infancy. The evolution of the observed musters is all but well understood, not to mention the positional changes of the elements observed in operando or in beginning- vs end-of-life comparisons (e.g., in fuel cell applications).With this motivation, in this Account we summarize the endeavors made in element distribution monitoring in bimetallic aerogels in terms of synthetic methods, expected structures, and their evolution during electrocatalysis. After an introductory chapter, we first describe briefly the two most important characterization techniques used for this, namely, scanning transmission electron microscopy (STEM) combined with element mapping (e.g., energy-dispersive X-ray spectroscopy (EDXS)) and X-ray absorption spectroscopy (XAS). We then explain the universal methods used to prepare bimetallic aerogels with different compositions. Those are divided into one-step methods in which gels formed from mixtures of the respective metal salts are coreduced and two-step approaches in which monometallic nanoparticles are mixed and gelated. Subsequently, we summarize the current state-of-knowledge on the element distributions unraveled using diverse characterization methods. This is extended to investigations of the element distributions being altered during electrochemical cycling or other loads. So far, a theoretical understanding of these processes is sparse, not to mention predictions of element distributions. The Account concludes with a series of remarks on current challenges in the field and an outlook on the gains that the field would earn from a solid understanding of the underlying processes and a predictive theoretical backing.

Nonclassical Crystallization and Core-Shell Structure Formation of Ibuprofen from Binary Solvent Solutions.

Liquid-liquidphase separation (LLPS) or dense liquid intermediates during the crystallization of pharmaceutical molecules is common; however, their role in alternative nucleation mechanisms is less understood. Herein, we report the formation of a dense liquid intermediate followed by a core-shell structure of ibuprofen crystals via nonclassical crystallization. The Raman and SAXS results of the dense phase uncover the molecular structural ordering and its role in nucleation. In addition to the dimer formation of ibuprofen, which is commonly observed in the solution phase, methyl group vibrations in the Raman spectra show intermolecular interactions similar to those in the solid phase. The SAXS data validate the cluster size differences in the supersaturated solution and dense phase. The focused-ion beam cut image shows the attachment of nanoparticles, and we proposed a possible mechanism for the transformation from the dense phase into a core-shell structure. The unstable phase or polycrystalline core and its subsequent dissolution from inside to outside or recrystallization by reversed crystal growth produces the core-shell structure. The LLPS intermediate followed by the core-shell structure and its dissolution enhancement unfold a new perspective of ibuprofen crystallization.