Nanoparticles have become increasingly interesting for a wide range of applications, because in principle it is possible to tailor their properties by controlling size, shape and composition. One of these applications is heterogeneous catalysis, and a fundamental understanding of the structural details of the nanoparticles is essential for any knowledge-based improvement of reactivity and selectivity. In this work we investigate the atomic structure of brass nanoparticles containing up to 5000 atoms as a typical example for a binary alloy consisting of Cu and Zn. As systems of this size are too large for electronic structure calculations, in our simulations we use a recently parametrized machine learning potential providing close to density functional theory accuracy. This potential is employed for a structural characterization as a function of chemical composition by various types of simulations like Monte Carlo in the Semi-Grand Canonical Ensemble and simulated annealing molecular dynamics. Our analysis reveals that the distribution of both elements in the nanoparticles is inhomogeneous, and zinc accumulates in the outermost layer, while the first subsurface layer shows an enrichment of copper. Only for high zinc concentrations alloying can be found in the interior of the nanoparticles, and regular patterns corresponding to crystalline bulk phases of $α$-brass can then be observed. The surfaces of the investigated clusters exhibit well-ordered single-crystal facets, which can give rise to grain boundaries inside the clusters. The melting temperature of the nanoparticles is found to decrease with increasing zinc-atom fraction, a trend which is well-known also for the bulk phase diagram of brass.
The appraisal of metallic materials requires application of advanced characterisation techniques. In this paper, the use has been made of Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy techniques to characterise morphological, structural and chemical composition of 316-stainless steel and unknown brass sample. The determined lattice parameter of unknown brass sample was 3.6812A and consisted of 63% Cu and 37% Zn by weight. The XRD analysis indicated a faced-centred-cubic crystal structure and the sample concluded…
Dynamic Kinetic Evaluation Favors Compositionally Diverse Multicomponent Alloy Nanoparticles for Hydrogen Evolution
The University of Tokyo（东京大学）；National Institute for Materials Science（物质材料研究机构）；National Institute of Advanced Industrial Science and Technology（产业技术综合研究所）
Bimetallic catalysts can undergo segregation or redistribution of the metals driven by oxidizing and reducing environments. Bragg coherent diffraction imaging (BCDI) was used to relate displacement fields to compositional distributions in crystalline Pt-Rh alloy nanoparticles. 3D images of internal composition showed that the radial distribution of compositions reverses partially between the surface shell and the core when gas flow changes between O2 and H2. Our observation suggests that the elemental segregation of nanoparticle catalysts should be highly active during heterogeneous catalysis …
Pure phase and mixed phase TiO$_2$ nanoparticles have been produced using a pyrolytic method from a non-aqueous carboxylate precursor. The precursor was prepared by a multiphase cation exchange using pentanoic acid (C$_4$H$_9$COOH). The thermal stability, polymorph content, morphology, size distribution and surface region of the produced nanoparticles were studied by TGA/DSC, XRD, FTIR and TEM. High quality monodisperse nanoparticles have been produced in the size range from 7 to 27 nm. The nanoparticles showed room temperature ferromagnetism revealed by VSM within bound polaron model. The car…
The paper presents the results of investigation of the structure of porous condensates of Ag-NaCl and Cu-NaCl composition; chemical and phase compositions and dimensions of nanoparticles, produced from the vapour phase by EBPVD method. Silver and copper nanoparticles in a porous matrix, when removed from vacuum, oxidize in air to lower oxides, and have considerable sorption capacity relative to oxygen and moisture. Heating in air is accompanied by lowering of porous condensate mass, primarily, due to desorption of physically sorbed moisture, as well as afteroxidation to higher oxides due to ph…
At the nanoscale, materials exhibit unique properties that differ greatly from those of the bulk state. In the case of Ag$_x$Pt$_{1-x}$ nanoalloys, we aimed to study the solid-liquid transition of nanoparticles of different sizes and compositions. This system is particularly interesting since Pt has a high melting point (2041 K compare to 1035 K for Ag) which could keep the nanoparticle solid during different catalytic reactions at relatively high temperatures, such as we need in the growth of nanotubes. We performed atomic scale simulations using semi-empirical potential implemented in a Mont…
Active control over the shape, composition and crystalline habit of nanocrystals is a long sought-after goal. Various methods have been shown to enable post-synthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can…
Polymer nanocomposites (PNCs) offer a broad range of thermophysical properties that are linked to their compositions. However, it is challenging to establish a universal composition-property relation of PNCs due to their enormous composition and chemical space. Here, we address this problem and develop a new method to model the composition-microstructure relation of a PNC through an intelligent machine learning pipeline named nanoNET. The nanoNET is a nanoparticles (NPs) distribution predictor, built upon computer vision and image recognition concepts. It integrates unsupervised deep learning …
Bimetallic nanoalloys such as nanoparticles and nanowires are attracting significant attention due to their vast potential applications such as in catalysis and nanoelectronics. Notably, Pd-Pt nanoparticles/nanowires are being widely recognized as catalysts and hydrogen sensors. Compared to unary systems, alloys present more structural complexity with various compositional configurations. Therefore, it is important to understand energetically preferred atomic structures of bimetallic nanoalloys. In this study, we performed a series of simulated annealing Monte Carlo simulations to predict the …
A number of metal-based nanopowders such kinds as Fe, Co, Fe/Co alloy, Fe/C, Fe/organic shell were successfully produced by aerosol synthesis method. The mechanism of nanoparticles formation and the influence of experimental parameters on shape, size distribution, structure, chemical and phase composition of oxide-, carbon-, or organic- coated nanoparticles were evaluated. The sizes of particles can be varied from 6-100 nm with narrow size distribution. The several application fields of synthesized nanoparticles have been studied.
The imaging of active nanoparticles represents a milestone in decoding heterogeneous catalysts dynamics. We report the facet resolved, surface strain state of a single PtRh alloy nanoparticle on SrTiO3 determined by coherent x-ray diffraction imaging under catalytic reaction conditions. Density functional theory calculations allow us to correlate the facet surface strain state to its reaction environment dependent chemical composition. We find that the initially Pt terminated nanoparticle surface gets Rh enriched under CO oxidation reaction conditions. The local composition is facet orientatio…
The atomistic structure of metallic glasses is closely related to properties such as strength and ductility. Here, Ni1-xBx metallic glass nanoparticles of two different sizes are compressed under quasi-hydrostatic high-pressure conditions in order to understand structural changes under stress. The structural changes in the nanoparticles were tracked using in situ high-pressure X-ray diffraction (XRD). The ambient pressure pair-distribution functions generated from XRD showed that the smaller sized nanoparticles had a more compact amorphous structure with lower coordination number. XRD showed t…
In the present work, different synthesis procedures have been demonstrated to fill carbon nanotubes (CNTs) with $\mathrm{Fe}_{1-x}\mathrm{Ni}_x$ alloy nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of magnetic nanoparticles, and provide a protective shield against oxidation as well as prevent nanoparticles agglomeration. By variation of the reaction parameters, the purity of the samples, degree of filling, the composition and size of filling nanoparticles have been tailored and therefore the magnetic properties. The samples were analyzed by scanning electron microsc…
Reinforcement Learning for Chemical Ordering in Alloy Nanoparticles
Department of Energy Conversion and Storage, Technical University of Denmark（丹麦技术大学能源转换与存储系）；CAPeX Pioneer Center for Accelerating P2X Materials Discovery, Technical University of Denmark（丹麦技术大学CAPeX先锋中心）
A Monte-carlo (MC) simulation procedure has been developed where the pair bond energies are allowed to take into account the various coordination numbers of surface atoms and the presence of adsorbates. The pair bond energies are calculated from partial bond energies of atoms which, in turn, are calculated from modified tight binding model in the second moment approximation. The model has been applied to study the role of adsorption of hydrogen, oxygen, carbon monoxide and nitric oxide on the surface composition and surface bond geometry of bimetallic Pd-X (X = Ag, Cu, Ni, Pt) nanoparticles ha…
Ti-O nanoparticles have been synthesized via hollow cathode sputtering in an Ar-O2 atmosphere using high power pulsing. It is shown that the stoichiometry and the size of the nanoparticles can be varied independently, the former through controlling the O2 gas flow and the latter by the independent biasing of two separate anodes in the growth zone. Nanoparticles with diameters in the range of 25 to 75 nm, and with different Ti-O compositions and crystalline phases, have been synthesized.
We report on atom probe tomography analyses of Pd and Pd@Au nanoparticles embedded in a Ni matrix and the effects of local evaporation field variations on the atom probe data. In order to assess the integrity of the reconstructed atom maps, we performed numerical simulations of the field evaporation processes and compared the simulated datasets with experimentally acquired data. The distortions seen in the atom maps for both Pd and Pd@Au nanoparticles could be mostly ascribed to local variations in chemical composition and elemental evaporation fields. The evaporation field values for Pd and N…
We present an experimental investigation of drying suspensions of both hard and soft nanolatex spheres. The crack formation is examined as a function of the proportion of hard and soft deformable particles, leading to tunable elastic properties of the drying film. In our experiments corresponding to a given layer thickness, no crack formation could be observed below an onset value of the proportion in hard spheres around 0.45. During the drying process, the mass of films with various compositions in hard and soft spheres is measured as a function of time. The results suggest that the soft part…
Nanotechnology offers the promise of harnessing quantum properties not available in the bulk phase. These desirable properties are highly dependent on size and composition. Generators that control these variables are therefore essential for progress in the field. The spark discharge generator (SDG) is an outstanding aerosol route for nanoparticle synthesis, which stands out due to its fast kinetics, scalability, high purity, accuracy and reproducibility with the added advantage of allowing the synthesis of nanoparticles of any conducting material. These advantages are a consequence of its vast…
Bimetallic nanoparticles (BNPs) exhibit diverse morphologies such as core-shell, Janus, onion-like, quasi-Janus, and homogeneous structures. Although extensive effort has been directed towards understanding the equilibrium configurations of BNPs, kinetic mechanisms involved in their development have not been explored systematically. Since these systems often contain a miscibility gap, experimental studies have alluded to spinodal decomposition (SD) as a likely mechanism for the formation of such structures. We present a novel phase-field model for confined (embedded)systems to study SD-induced…
Fe$_3$O$_4$ magnetic nanoparticles (MNPs) were synthesized by a co-precipitation method using sodium citrate and oleic acid as modifiers. Phase composition and microstructure analysis indicate that the sodium citrate and oleic acid have been successfully grafted onto the surface of Fe$_3$O$_4$ MNPs. The magnetic behaviors reveal that the modification can decrease the saturation magnetization of Fe$_3$O$_4$ MNPs due to the surface effect. Fe$_3$O$_4$ MNPs modified by sodiumcitrate and oleic acid show excellent dispersion capability, which should be ascribed to the great reduction of high surfac…
Bimetallic nanoparticles are often superior candidates for a wide range of technological and biomedical applications, thanks to their enhanced catalytic, optical, and magnetic properties, which are often better than their monometallic counterparts. Most of their properties strongly depend on their chemical composition, crystallographic structure, and phase distribution. However, little is known of how their crystal structure, on the nanoscale, transforms over time at elevated temperatures, even though this knowledge is highly relevant in case nanoparticles are used in, e.g., high-temperature c…
Chemisorption process and catalytic activity of CO to CO2 conversion on PdXRu1-X (X : 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) extended as a benchmark for further investigation of very complex nanoparticle (NP) structures have been checked into thoroughly by using the synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES). Assessment and diagnostic of core levels and valence bands data highlight valuable information regarding the surface interaction and structure of PdRu bimetallic nanoparticles (BM-NPs). Core level shift observed from the C 1s clearly emphasized that the Pd0.5Ru0.5 NPs whi…
Coupling at the interface of core/shell magnetic nanoparticles is known to be responsible for the exchange bias (EB) and the relative sizes of core and shell components are supposed to influence the associated phenomenology. In this work, we have prepared core/shell structured nanoparticles with the total averaged diameter around $\sim$ 27 nm and a wide range of shell thicknesses through the controlled oxidation of Co nanoparticles well dispersed in an amorphous silica host. Structural characterizations give compelling evidence of the formation of Co$_3$O$_4$ crystallite phase at the shells su…
Nanocomposite NiO:Au thin films, formed by gold nanoparticles embedded in a nickel oxide matrix, have been grown by reactive pulsed laser deposition (R-PLD). Two actively synchronized nanosecond laser sources, a KrF excimer laser (248 nm) and a Nd:YAG laser (355 nm), were used for the simultaneous ablation of nickel and gold targets in oxygen ambient. The morphology, composition, and optical properties of the obtained nanocomposites were investigated and were found to correlate with the concentration of Au nanoparticles. Further, the NiO:Au nanocomposites have been tested as hydrogen sensors. …
A potassium alumina borosilicate glass with the composition 13K2O*13Al2O3*16B2O3*43SiO2*15Fe2O3-x was melted using Fe2O3 as raw material. The melt was dumped from a Pt-crucible with a downpipe in water which resulted in the formation of phase separated droplets with a size of around 100 - 150 nm. In this droplets, magnetite crystals with a size of around 10-20 nm were observed. These magnetite nanoparticles with superparamagnetic behaviour are arranged to larger aggregates. This leads to a higher effective magnetic radius. According to magnetisation measurements the particles show hysteresis. …
Correlations of Spectroscopic and Dielectric Properties of Hafnia-Zirconia Nanoparticles
Frantsevich Institute for Problems in Materials Science of the National Academy of Sciences of Ukraine（乌克兰国家科学院弗拉琴科材料科学问题研究所）；Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Stockholm University（斯德哥尔摩大学）；Ye. O. Paton Institute of Materials Science and Welding, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”（乌克兰国立技术大学“伊戈尔·西科尔斯基基辅理工学院”叶·奥·帕顿材料与焊接研究所）；Oles Honchar Dnipro National University（阿列斯·洪恰尔第聂伯国立大学）；Institute of Physics of the National Academy of Sciences of Ukraine（乌克兰国家科学院物理研究所）
A major motivation for the scientific study of artworks is to understand their states of preservation and ongoing degradation mechanisms. This enables preservation strategies to be developed for irreplaceable works. Intensely-hued cadmium sulphide (CdS) yellow pigments are of particular interest because these are key to the palettes of many important late 19th and early 20th century masters, including Vincent Van Gogh, Pablo Picasso, Henri Matisse, and Edvard Munch. As these paintings age, their cadmium yellow paints are undergoing severe fading, flaking, and discolouration. These effects are …
We report the synthesis of Co2FeGa/SiO2 nanoparticles by sol-gel method and characterization using x-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurements. The Rietveld refinements of XRD data with space group Fm-3m clearly show the formation of A2 disorder single phase and the lattice constant is found to be 5.738 Å. The energy-dispersive x-ray spectroscopy (EDX) confirm the elemental composition close the desired values. The value of coercivity is found to be around 283 Oe and 126 Oe, measured at 10 K and 300 K, respectively. We observed the saturation magne…
Synthesizing unconventional alloys remains challenging owing to seamless interactions between kinetics and thermodynamics. High entropy alloys (HEAs), for example, draw a fundamentally new concept to enable exploring unknown regions in phase diagrams. The exploration, however, is hindered by traditional metallurgies based on liquid-solid transformation. Vapor-solid transformation that is permissible on pressure-temperature phase diagrams, offers the most kinetically efficient pathway to form any desired alloy (e.g., HEA). Here, we report that a technique called "sparking mashups", which involv…
Zn1-xRxO (R = Li, Mg, Cr, Mn, Fe and Cd) were obtained by using co-precipitation synthesis technique with constant weight percent of 3% from R ions. The phase composition, crystal structure, morphology, Density Functional Theory (DFT), and, magnetic properties were examined to comprehend the influence of Zn2+ partial substitution with R ions. X-ray diffraction shows that the ZnO lattice parameters were slightly affected by R doping and the doped sample crystallinity is enhanced. Our results show that introducing Cr, Mn and Fe along with Mg into ZnO induces a clear magnetic moment without any a…
Pt-based bimetallic nanoparticles have attracted significant attention as a promising replacement for expensive Pt nanoparticles. In the systematic design of bimetallic nanoparticles, it is important to understand their preferred atomic structures. However, compared with unary systems, alloy nanoparticles present more structural complexity with various compositional configurations, such as mixed-alloy, core-shell, and multishell structures. In this paper, we developed a unified empirical potential model for various Pt-based binary alloys, such as Pd-Pt, Cu-Pt, Au-Pt, and Ag-Pt. Within this fra…
Embedding silicon nanoparticles in an intermetallic matrix is a promising strategy to produce remarkable bulk anode materials for lithium-ion (Li-ion) batteries with low potential, high electrochemical capacity and good cycling stability. These composite materials can be synthetized at a large scale using mechanical milling. However, for Si-Ni3Sn4 composites, milling also induces a chemical reaction between the two components leading to the formation of free Sn and NiSi2, which is detrimental to the performance of the electrode. To prevent this reaction, a modification of the surface chemistry…
Multicomponent nanoparticles can be synthesized with either homogeneous or phase-segregated architectures depending on the synthesis conditions and elements incorporated. To understand the parameters that determine their structural fate, multicomponent metal-oxide nanoparticles consisting of combinations of Co, Ni, and Cu were synthesized via scanning probe block copolymer lithography and characterized using correlated electron microscopy. These studies revealed that the miscibility, ratio of the metallic components, and the synthesis temperature determine the crystal structure and architectur…
Sought-after ordered structures of mixtures of hard anisotropic nanoparticles can often be thermodynamically unfavorable due to the components' geometric incompatibility to densely pack into regular lattices. A simple compatibilization rule is identified wherein the particle sizes are chosen such that the order-disorder transition pressures of the pure components match (and the entropies of the ordered phases are similar). Using this rule with representative polyhedra from the truncated-cube family that form pure-component plastic-crystals, Monte Carlo simulations show the formation of plastic…
The ceramic pellets of the nominal compositions Bi$_{0.7}$Ba$_{0.3}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.20) were prepared initially by standard solid state reaction technique. The pellets were then ground into micrometer-sized powders and mixed with isopropanol in an ultrasonic bath to prepare nanoparticles. The X-ray diffraction patterns demonstrate the presence of a significant number of impurity phases in bulk powder materials. Interestingly, these secondary phases were completely removed due to the sonication of these bulk powder materials for 60 minutes. The field and temperature dependent …
Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by chemical route. The effect of the size of NPs upon the structure and magnetization compared to its bulk counterpart was investigated. The structure and composition were determined from X-ray diffraction (XRD) and electron microscopy. XRD analysis shows that the samples are having single (A2-type) disordered phase. Magnetization measurements suggest that the samples are soft ferromagnetic in nature with very low coercivity. Enhanced magnetic properties like saturation magnetization, coercive force, retentivity, and Curie-t…
Design of nanoscale structures with desired nanophotonic properties are key tasks for nanooptics and nanophotonics. Here, the correlative relationship between local nanoparticle geometries and their plasmonic responses is established using encoder-decoder neural networks. In the im2spec network, the correlative relationship between local particle geometries and local spectra is established via encoding the observed geometries to a small number of latent variables and subsequently decoding into plasmonic spectra; in the spec2im network, the relationship is reversed. Surprisingly, these reduced …
Nanomaterials based on MoS2 are remarkably versatile; MoS2 nanoparticles are proven catalysts for processes such as hydrodesulphurization and the hydrogen evolution reaction, and transition metal dichalcogenides in general have recently emerged as novel 2D components for nanoscale electronics and optoelectronics. The properties of such materials are intimately related to their structure and dimensionality. For example, only the edges exposed by MoS2 nanoparticles (NPs) are catalytically active, and extended MoS2 systems show different character (direct or indirect gap semiconducting, or metall…
In the present work, multiwalled carbon nanotubes were decorated with rhodium nanoparticles using a colloidal solution in the post-discharge of an RF atmospheric plasma of argon (Ar) or argon/oxygen (Ar:O$_2$). The properties of these hybrid materials towards the room temperature detection of NO$_2$, C$_2$H$_4$, CO, C$_6$H$_6$ and moisture were investigated and discussed in view of compositional and morphological studies. It was found that the presence of oxygen in the plasma treatment is essential to significantly enhance the gas response of Rh-decorated multiwalled carbon nanotubes and to av…
Pd$_{1-x}$Ni$_x$ alloy system is an established ideal transition metal system possessing a composition induced paramagnetic to ferromagnetic quantum phase transition (QPT) at the critical concentration $x_c \sim$ 0.026 in bulk. A low-temperature non-Fermi liquid (NFL) behaviour around $x_c$ usually indicates the presence of quantum criticality (QC) in this system. In this work, we explore the existence of such a QPT in nanoparticles of this alloy system. We synthesized single-phase, polydispersed and 40-50 nm mean diameter crystalline nanoparticles of Pd$_{1-x}$Ni$_x$ alloys, with $x$ near $x_…
In colloid and nanoparticle chemistry, particle size, shape, crystallinity, surface morphology and composition are controlled by employing the mechanisms of burst nucleation, diffusional growth, aggregation, or their combinations. Here we review and survey practical examples of recently developed methods for preparing metal colloids and nanoparticles for industrial applications such as photovoltaics, catalysis, and consumer electronics. We discuss relevant theoretical models, many of which are general, and identify growth mechanisms that play a major role in other systems and applications as w…
The properties and applications of metallic nanoparticles are inseparably connected not only to their detailed morphology and composition, but also to their structural configuration and mutual interactions. As a result, the assemblies often have superior properties as compared to individual nanoparticles. Although it has been reported that nanoparticles can form highly symmetric clusters, if the configuration can be predicted as a function of the synthesis parameters, more targeted and accurate synthesis will be possible. We present here a theoretical model that accurately predicts the structu…
As renewable energy is becoming a critical energy source to meet the global demand, electrochemical energy storage devices become indispensable for the efficient energy storage and reliable supply. The electrode material is the key factor determining the energy storage capacity and the power delivery of the devices. Carbon-based materials are emerging as a viable candidate for electrodes, yet their low energy densities impede the development of advanced energy storage materials. Nanoparticle decoration of the carbon structures is one of the most promising and easy-to-implement a strategy to en…
Nanoparticles (NPs) which combine several magnetic phases offer wide perspectives for cutting edge applications because of the high modularity of their magnetic properties. Besides the addition of the magnetic characteristics intrinsic to each phase, the interface that results from core-shell and, further, from onion structures leads to synergistic properties such as magnetic exchange coupling. Such a phenomenon is of high interest to overcome the superparamagnetic limit of iron oxide NPs which hampers potential applications. In this manuscript, we report on the design of NPs with an onion-lik…
