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 framework, we performed a series of Monte Carlo (MC) simulations that quantify the energetically favorable atomic arrangements of Pt-based alloy nanoparticles: an intermetallic compound structure for the Pd-Pt alloy, an onion-like multi-shell structure for the Cu-Pt alloy, and core-shell structures (Au@Pt and Ag@Pt) for the Au-Pt and Ag-Pt alloys. The equilibrium nanoparticle structures for the four alloy types were compared with each other, and the structural features can be interpreted by the interplay of their material properties, such as the surface energy and heat of formation.
Bimetallic plasmonic nanoparticles enable tuning of the optical response and chemical stability by variation of the composition. The present numerical simulation study compares Ag-Au alloy, Ag@Au core-shell, and Au@Ag core-shell bimetallic plasmonic nanoparticles of both spherical and anisotropic (nanotriangle and nanorods) shapes. By studying both spherical and anisotropic (with LSPR in the near-infrared region) shapes, cases with and without interband transitions of Au can be decoupled. Explicit comparisons are facilitated by numerical models supported by careful validation and examination o…
At the nanometric scale, the synthesis of a random alloy (i.e. without phase segregation, whatever the composition) by chemical synthesis remains a not easy task, even for simple binary type systems. In this context, a unique approach based on the colloidal route is proposed enabling the synthesis of face-centred cubic and monodisperse bimetallic, trimetallic, tetrametallic and pentametallic nanoparticles with diameters around 5 nm as solid solutions. The Fe-Co-Ni-Pt-Ru alloy and its subsets are considered which is a challenging task as each element has fairly different physico-chemical proper…
To understand the vibrational and configurational entropy effects for the stability of core-shell and solid-solution bimetallic nanoparticles, we theoretically investigated the excess energy of PdPt nanoparticles, adopting the (PdPt)201 model of ca. 2 nm by using the density functional method. The vibrational energy and entropy terms contributed to the total energy of both core-shell and solid-solution nanoparticles. The configurational entropy term was defined only for the solid-solution nanoparticles. Although the absolute values of vibrational energy and entropy terms were much larger than …
An embedded-domain phase-field formalism is used for studying phase transformation pathways in bimetallic nanoparticles (BNPs). Competition of bulk and surface-directed spinodal decomposition processes and their interplay with capillarity are identified as the main determinants of BNP morphology. The former is characterized by an effective bulk driving force $Δ\tilde{f}$ which increases with decreasing temperature, while the latter manifests itself through a balance of interfacial energies captured by the contact angle $θ$. The simulated morphologies, namely, core-shell, Janus and inverse core…
Tracking atomic-scale interdiffusion in immiscible bimetallic nanoparticles via four-dimensional electron tomography
Beijing National Laboratory for Molecular Sciences, Center for Integrated Spectroscopy, College of Chemistry and Molecular Engineering, Peking University（北京大学化学与分子工程学院集成光谱中心北京分子科学国家实验室）
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…
Kiel University（基尔大学）；University of Duisburg-Essen（杜伊斯堡-埃森大学）
Accurately measuring the size, morphology, and structure of nanoparticles is very important, because they are strongly dependent on their properties for many applications. In this paper, we present a deep-learning based method for nanoparticle measurement and classification trained from a small data set of scanning transmission electron microscopy images. Our approach is comprised of two stages: localization, i.e., detection of nanoparticles, and classification, i.e., categorization of their ultrastructure. For each stage, we optimize the segmentation and classification by analysis of the diff…
Structures of iron and cobalt bimetallic clusters for optimized chemical vapor deposition growth of single-walled carbon nanotubes
The University of Tokyo（东京大学）；Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS)（基础科学研究院多维碳材料中心）；Dalian University of Technology（大连理工大学）；University of Antwerp（安特卫普大学）
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…
Structure-Dependent Chemical Order Modification in Strained Alloy Nanoparticles
Guangdong Technion – Israel Institute of Technology（广东以色列理工学院）；Universidad de Castilla-La Mancha（卡斯蒂利亚-拉曼恰大学）；Aristotle University of Thessaloniki（塞萨洛尼基亚里士多德大学）
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）
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…
Within first-principles density functional theory (DFT) frameworks, accurate but fast prediction of electronic structures of nanoparticles (NPs) remains challenging. Herein, we propose a machine-learning architecture to rapidly but reasonably predict electronic density of states (DOS) patterns of metallic NPs via a combination of principal component analysis (PCA) and the crystal graph convolutional neural network (CGCNN). By applying PCA, one can convert a mathematically high-dimensional DOS image to a low-dimensional vector. The CGCNN plays a key role in reflecting the effects of local atomi…
Monte Carlo simulations of ${\rm Ni Fe_2O_4}$ Nanoparticles
我们使用蒙特卡罗模拟来研究${\rm Ni Fe_2O_4}$纳米颗粒。有限的尺寸和表面效应使它们与散装对应物区分开来。连续版本的Wang-Landau算法被用来有效地计算联合态密度$g(M_z, E)$。从$g(M_z, E)$出发，我们得到了粒子的Bragg-Williams自由能，以及其它物理量。当纳米颗粒同时具有表面无序性和表面各向异性时，观察到滞后。我们发现，有限的双折射率是表面无序和表面各向异性相互作用的结果。如果没有表面无序或表面各向异性相对较弱，则纳米颗粒通常表现出超顺磁性。
Towards an understanding of the chemisorption and catalytic activity of Pd$_{X}$Ru$_{1-X}$ nanoparticles using photoelectron spectroscopy
利用同步辐射硬X射线光电子能谱学（HAXPES）研究了PdXRu 1-X（X：0，0.1，0.3，0.5，0.7，0.9和1）催化剂的化学吸附过程和CO转化为CO2的催化活性。核心水平和价带数据的评估和诊断突出了有价值的信息，表面相互作用和结构的PdRu纳米粒子（BM-NPs）。从C1观察到的芯能级位移清楚地强调了提供最高催化效率（CO氧化）的Pd0.5Ru0.5 NP表现出CO分子在顶部位点的优先吸附。否则，我们的结果还显示，其余的NP表现出两个组件分配到桥和空心CO网站。结合Pd 3d 5/2和Ru 3 p 3/2核能级的结果指出，随着Ru的摩尔比的增加，从合金结构向核-壳构型的转变。价带最大值（VBM）表明了一个位置依赖于Ru的摩尔组成。此外，通过深入挖掘每个NP的电子结构（形状和宽度），我们清楚地强调了组成，原子排列，d带和双金属PdRu的催化性能之间的有价值的关系。根据HAXPES的结果，强有力的和明确的证据，提高CO到CO2的转化能力的Pd 0.5Ru 0.5-NP可以归因于存在一个最有利的空间d-带扩展和核壳和合金结构之间的最佳平衡。电子和化学数据和解释是一致的PdRu催化性能。这一展望为更好地了解二元、三元和多金属纳米粒子与反应物的催化表面相互作用迈出了新的一步。
We present molecular dynamics (MD) simulations of radiation damage in pure Fe nanoparticles (NP) and bimetallic FeCu core-shell nanoparticles (CSNP). The CSNP includes a perfect body centered cubic (bcc) Fe core coated with a face-centered cubic (fcc) Cu shell. Irradiation with Fe Primary Knock-on Atoms (PKA) with energies between 1 and 7 keV leads to point defects, without clustering beyond divacancies and very few slightly larger vacancy clusters, and without interstitial clusters, unlike what happens in bulk at the same PKA energies. The Fe-Cu interface and shell can act as a defect sink, a…
Magnetic hyperthermia properties of nanoparticles inside lysosomes using kinetic Monte-Carlo simulations : influence of key parameters, of dipolar interactions and spatial variation of heating power
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）
Nonmagnetic impurities and roughness effects on the finite temperature magnetic properties of core-shell spherical nanoparticles
受最近研究[V. Dimitriadis et al. Phys. Rev. B \textbf{92}，064420（2015）]的启发，我们研究了具有核-壳结构的球形纳米颗粒的有限温度磁性，包括淬灭的（i）表面和（ii）界面杂质（静态孔）以及（iii）粗糙化界面效应。粒子核由铁磁自旋组成，并且它被铁磁壳包围。通过基于改进的Metropolis算法的蒙特卡罗模拟，我们实现了经典的海森堡哈密顿纳米粒子。特别注意也被致力于阐明这些系统的热和磁相变功能上的颗粒尺寸的影响。对于表面层不完整的纳米颗粒，发现较大的颗粒具有较低的补偿点，该补偿点随着空位量的增加而逐渐减小，并在某一临界值处消失。考虑到纳米粒子的稀释界面，我们的蒙特卡罗模拟结果表明，在无序谱中存在一个区域，补偿温度随稀释参数的减小而线性降低。对于具有粗糙界面的纳米颗粒，观察到粗糙度对补偿点和临界温度的变化都不起任何显著作用。然而，低温饱和磁化的核和壳界面区域敏感地依赖于粗糙度参数。
Driving force of atomic ordering in Fe$_{1-x}$Pt$_{x}$, investigated by density functional theory and machine-learning interatomic potentials Monte Carlo simulations
Finite-Size and surface effects in maghemite nanoparticles: Monte Carlo simulations
用蒙特卡罗模拟模拟了$γ$ O $_3$（磁赤铁矿）单颗粒模型，研究了细颗粒体系中的晶粒尺寸效应和表面效应.周期性边界条件已被用来模拟的整体性质和结果相比，一个球形粒子与自由边界的证据所发挥的作用，表面上的异常磁性显示这些系统在低温下。该模型的几个结果与实验结果定性一致。随着颗粒尺寸的减小，磁有序温度、自发磁化强度和矫顽场均降低。此外，磁滞回线变得拉长与高值的微分磁化率，类似于那些从挫折或无序系统。这些事实是形成具有比核心更高程度的磁无序的表面层的结果，对于小尺寸，核心主导颗粒的磁化过程。然而，与一些作者的假设相矛盾的是，我们的模型并没有预测表面层冻结成类似自旋玻璃的状态。结果表明，磁无序在表面简单地促进热退磁的颗粒在零场，而磁化强度增加，在中等领域，因为表面无序减少亚铁磁相关的颗粒内。磁滞回线的形状与颗粒尺寸的变化表明，反转模式的强烈影响，减少原子的协调和无序的表面。
Magnetic properties of dense nanoparticle arrays with core/shell morphology
我们计算了有序阵列的复合磁性纳米粒子的铁磁（FM）的核心和反铁磁（AFM）壳，位于三角形晶格和耦合通过静磁力的磁滞。每个纳米颗粒由一对交换耦合（J）的各向异性自旋（Meiklejohn-Bean模型）描述。使用Metropolis Monte Carlo算法获得磁化磁滞回线。对于硬磁纳米颗粒，我们发现随着偶极耦合强度的增加，矫顽磁力减小，而交换偏置场则表现出非单调行为，这是由于随机各向异性和颗粒间偶极相互作用之间的竞争造成的。讨论了通过增加堆积密度来提高交换偏置场的可能性。
