NiCu双金属纳米粒子的表面偏析、结构特征与扩散  

Surface segregation,structural features,and diffusion of NiCu bimetallic nanoparticles

作　　者：邓永和[1] 张宇文 谭恒博 文大东 高明 吴安如[3] Deng Yong-He;Zhang Yu-Wen;Tan Heng-Bo;Wen Da-Dong;Gao Ming;Wu An-Ru(School of Computational Science and Electronics,Hunan Institute of Engineering,Xiangtan 411104,China;College of Physics,Mechanical and Electrical Engineering,Jishou University,Jishou 416000,China;Hunan Provincial Key Laboratory of Vehicle Power and Transmission Systems,Hunan Institute of Engineering,Xiangtan 411104,China)

机构地区：[1]湖南工程学院计算科学与电子学院,湘潭411100 [2]吉首大学物理与机电工程学院,吉首416000 [3]湖南工程学院,湖南省汽车动力与传动系统重点实验室,湘潭411104

出　　处：《物理学报》2021年第17期238-247,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51701071,51871096);湖南省自然科学基金(批准号:2016JJ5028,2018JJ3100)资助的课题.

摘　　要：NiCu双金属核壳纳米粒子不仅由于其优异的稳定性、选择性以及磁学和催化性能而受到广泛关注,而且可以通过改变其纳米粒子的形貌、表面元素分布和粒径大小而具有可调谐性能.采用分子动力学与蒙特罗方法并结合嵌入原子势对NiCu双金属纳米粒子的表面偏析、结构特征以及Cu吸附原子在Ni基底沉积生长与表面扩散进行了研究,结果表明Cu原子在Ni基底表面具有强的偏析倾向.随着Cu原子浓度的增加,Cu原子优先占据纳米粒子的顶点、边、(100)和(111)面,最终形成完美的Ni核/Cu壳纳米粒子.在生长温度T=400 K时,形成的Ni核/Cu壳结构最稳定.进一步采用肘弹性波方法模拟计算在Ni基表面Cu吸附原子的扩散势垒,结果表明,Cu吸附原子无论是交换还是扩散,都需要克服较大的ES势垒,从而难以在Ni基底表面进行面间扩散.与Ni基底相反,在Cu基底上沉积Ni原子,Ni吸附原子很容易从(111)面迁移至(100)面,且在当前模拟温度下,Ni吸附原子无法在(100)面进行迁移,导致生长构型朝正八面体的形状发展,且其八个顶角几乎被Ni原子所占据.本文经过深入研究,从原子的角度出发,对NiCu纳米催化剂的初步设计提供了一种新的思路和方法.Bimetallic core-shell nanoparticles such as NiCu are of great interest not only due to their excellent stability,selectivity,and magnetic and catalytic properties,but also because they are tunable by changing the morphology,surface element distribution,and particle size of the nanoparticles.The surface segregation and structural features of NiCu bimetallic nanoparticles,the deposition growth and the surface diffusion of Cu adsorbed atoms on the Ni substrate surface are studied by using molecular dynamics and the Montero method combined with embedded atomic potential.The results show that the Cu atom has a strong tendency of surface segregation.With the increase of concentration of Cu atoms,Cu atoms preferentially occupy the vertex,edge,(100),and(111)facet of nanoparticles due to the difference in configuration energy between Cu atoms and surface Ni atoms with different coordination numbers after the exchange,and finally form perfect Ni-core/Cu-shell nanoparticles.When growth temperature T=400 K,the Ni-core/Cu-shell structure formed is the most stable.By observing the NiCu core-shell structure’s growth sequence,it is found that a few Ni atoms are replaced by Cu atoms on the step edge of the Ni substrate.The diffusion energy barrier of Cu atoms adsorbed on a Ni substrate surface is calculated by using the nudged elastic band method.The results show that Cu atoms adsorbed need to overcome a large ES barrier for both exchange and diffusion,making it difficult to diffuse between the facets of Ni substrate surface in a temperature range of 200–800 K.The lowest energy barrier for the diffusion of Cu atoms between facets of Ni substrate surface is 0.43 eV,and the diffusion path is from(111)facet to(100)facet.In contrast to Ni substrate,Ni atoms deposited on Cu substrate can easily migrate from the(111)facet to the(100)facet with a diffusion energy barrier of only about 0.12 eV,and at the present simulated temperature,Ni adsorbed atoms are unable to migrate on the(100)facet,resulting in a growth configuration toward a

关 键 词：NICU 双金属 表面偏析 扩散 沉积生长 NI 核/Cu 壳纳米粒子 

分 类 号：O643.36[理学—物理化学]