摘要：
We performed Monte Carlo simulations to determine the roles of energetic factors and nanoscale effects in the surface segregation and chemical ordering patterns of Ag–Pd nanoalloy particles. Ag atoms significantly segregate onto the surface and preferentially occupy the low-coordinated sites, which significantly reduces the surface and strain energies of the nanoalloys. The segregation isotherms reveal that surface Ag composition is enhanced with increasing particle size or Ag concentration to circumvent the finite matter effects. Chemical ordering favored by attractive heterobonds can coexist and compete with surface segregation. Accordingly, small and Pd-rich nanoalloys display a continuous transition from Pd-core/mixing-shell to mixing-core/Ag-shell, where an ordered core is absent as a result of surface segregation and limited Ag supply. By contrast, large nanoalloys with equimolar or Ag-rich concentration exhibit the strong core ordering characteristics of bulk alloys. Particularly, surface patterns with partially alloyed facets and Ag-blocked vertices and edges are formed. This study also discussed the effects of isolating and blocking surface Pd active sites by Ag on the hydrogen evolution reaction and selective hydrogenation of acetylene.
关键词：
Structure of nanoparticle;Metals and alloys;Growth from solid phases;Molecular dynamics
摘要：
The growth of Al atoms on an Fe rhombohedral nanoparticle with 1,105 atoms in the temperature range of 100–1,200 K is studied by molecular dynamics and embedded atom method. Several thermodynamics parameters, including potential energy, radial distribution function, and Lindemann index are used for the growth process analysis. This study reports an increasing energy per Fe atom and a decreasing energy per Al atom with increasing temperature. Alloying between Fe and Al atoms accelerates at higher temperatures, because of the incorporation of more Al atoms into the Fe core. Three different growth configurations are found for the simulations at different temperatures. At temperatures below 800 K, the core–shell configuration with Fe and Al as core and shell, respectively, is the most favorable. At approximately 800 K, a nanoparticle with surface alloying order is formed. Finally, surface melting occurs at growth temperatures higher than 900 K.
关键词：
Crystal growth;Diffusion in nanoscale solids;Metals and alloys;Structure of nanoparticles
摘要：
Ni - Al bimetallic nanoparticle structures are studied from a kinetic point of view. The diffusion and growth of Ni (or Al) atoms on Al (or Ni) cores with the Wulff structure are simulated by molecular dynamics and nudged elastic band methods. An analytic embedded atom model is applied to the two metals. The energy barriers of several typical diffusion processes of the adatoms on the nanoparticle surface are calculated. Results show that the incorporation of the Ni atoms into the Al core easily occurs, and the reverse process does not readily proceed. The growth simulations reveal that a better core-shell nanoparticle is obtained when the Al atoms are deposited on the Ni core at lower temperatures, and the deposition of the Ni atoms on the Al core leads to an amorphous surface. (C) 2013 Elsevier B.V. All rights reserved.
关键词：
Structure of nanocrystals and nanoparticles;Vacuum deposition;Impact phenomena;Molecular dynamics;Nanoparticle growth mechanism;Modeling and simulation
摘要：
The use of energetic particles can change the growth mode and provide control of nanoalloy morphology and properties. The impact deposition of Ni (or Al) on the truncated octahedral nanoparticle of Al (or Ni) is studied. The embedded atom method is used for the description of the interatomic interactions in combination with molecular dynamics method for the growth simulation. Three configurations of Ni–Al nanoparticle are obtained depending on incident energy and deposition sequence. A perfect core–shell nanoparticle with Ni-core/Al-shell is obtained as Al atoms are deposited over Ni nanoparticle. For the deposition of Ni atoms on Al nanoparticle, an onion-like nanoparticle at smaller incident energy, and a configuration with Al-shell and alloyed Ni–Al core at larger incident energy are observed, respectively. The formation energies show that the latter is energetically favorable.
作者：
Wang, Yong;Tang, Jianfeng;Ouyang, Xicheng;Liu, Buqiong*;Lin, Rong Han
期刊：
Materials Research Bulletin,2013年48(6):2123-2127 ISSN：0025-5408
通讯作者：
Liu, Buqiong
作者机构：
[Ouyang, Xicheng; Tang, Jianfeng; Wang, Yong] Hunan Agr Univ, Dept Appl Phys, Changsha 410128, Hunan, Peoples R China.;[Liu, Buqiong] Hunan Agr Univ, Dept Grad Studies, Changsha 410128, Hunan, Peoples R China.;[Lin, Rong Han] Northwestern Univ, Dept Chem, Evanston, IL 60208 USA.
通讯机构：
[Liu, Buqiong] H;Hunan Agr Univ, Dept Grad Studies, Changsha 410128, Hunan, Peoples R China.
关键词：
A. Optical materials;D. Luminescence;D. Optical properties
摘要：
The AlN-doped BaMgAl10O17:Eu2+ phosphors were synthesized by conventional solid-state reaction. Powder X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum (PL) were used for characterization. The growth mechanism was carried out by computer simulation with CASTEP application, and revealed that an ideal hexagonal shape, particle size in 5 μm and 2.5–3 μm in thickness, could be obtained by AlN doping. Additionally, due to the low electronegativity of N3−, the AlN-doped sample showed 35% increase in PL intensity and improvement of thermal stability. These fine particle size and better photoluminescence properties are expected to be applicable to industrial production of BaMgAl10O17:Eu2+ phosphors.
作者：
Jianfeng Tang;Lei Deng;Huiqiu Deng;Shifang Xiao;Wangyu Hu
作者机构：
[Jianfeng Tang; Huiqiu Deng; Shifang Xiao; Wangyu Hu] Department of Applied Physics,Hunan University,Changsha 410082,China;[Jianfeng Tang; Lei Deng] Department of Applied Physics,Hunan Agricultural University,Changsha 410128,China
会议名称：
China-Europe International Workshop on Alloy Nanoparticles(中欧双金属纳米簇国际研讨会)
会议时间：
2013-11-18
会议地点：
北京
会议主办单位：
北京化工大学
会议论文集名称：
China-Europe International Workshop on Alloy Nanoparticles(中欧双金属纳米簇国际研讨会)论文集
期刊：
JOURNAL OF PHYSICS-CONDENSED MATTER,2011年23(39):395004 ISSN：0953-8984
通讯作者：
Yang, Jianyu
作者机构：
[Yang, Jianyu] Hunan Inst Engn, Dept Math & Phys, Xiangtan 411104, Peoples R China.;[Hu, Wangyu] Hunan Univ, Dept Appl Phys, Changsha 410082, Hunan, Peoples R China.;[Tang, Jianfeng] Hunan Agr Univ, Dept Appl Phys, Changsha 410028, Hunan, Peoples R China.
通讯机构：
[Yang, Jianyu] H;Hunan Inst Engn, Dept Math & Phys, Xiangtan 411104, Peoples R China.
摘要：
The diffusion of single tungsten adatoms on the surfaces of rhombohedral clusters is studied by means of molecular dynamics and the embedded atom method. The energy barriers for the adatom diffusing across and along the step edge between a {110} facet and a neighboring {110} facet are calculated using the nudged elastic band method. We notice that the tungsten adatom diffusion across the step edge has a much higher barrier than that for face-centered cubic metal clusters. The result shows that diffusion from the {110} facet to a neighboring {110} facet could not take place at low temperatures. In addition, the calculated energy barrier for an adatom diffusing along the step edge is lower than that for an adatom on the flat (110) surface. The results show that the adatom could diffuse easily along the step edge, and could be trapped by the facet corner. Taking all of this evidence together, we infer that the {110} facet starts to grow from the facet corner, and then along the step edge, and finally toward the {110} facet center. So the tungsten rhombohedron can grow epitaxially along the {110} facet one facet at a time and the rhombohedron should be the stable structure for both large and small tungsten clusters.
摘要：
The surface diffusion of Pt dimers on Wulff polyhedral clusters with 586-12934 atoms was studied by the embedded atom method. The minimum energy diffusion path and the corresponding energy barrier for dimer diffusion on cluster surfaces were determined through a combination of the quenched Molecular Dynamics and the Nudged Elastic Band method. It was found that the diffusion of a dimer across the step-edge by dissociation and consecutive single-atom exchange with the edge atoms, rather than diffusion over the edge as a unit. Therefore, the step can enhance the dissociation of the dimer. For small Wulff polyhedral clusters containing up to 2000 atoms, the energy barrier for dimer diffusion from the {111} to the {100} facet is almost equal to that for the single adatom diffusion on the flat {111} surface. From the calculated cluster size dependence of the energy barrier, we conclude that the Wulff polyhedral cluster is stable, as the cluster has more than about 2000 atoms.
摘要：
Taking the WKB approximation to solve the Dirac field equation in a Schwarzschild black hole spacetime, we can get the classical momenta. Employing the classical momenta and state density equation corrected by a modified dispersion relation, we will obtain the number of quantum states with energy less than ω. Then, it is used to calculate the statistical-mechanical entropy of the Dirac field. Solving the integral for r exactly, we obtain the leading term of entropy that is proportional to the event horizon area, and correction terms take the form of A−1, but the logarithmic correction term by this approach is not given.
