First-Principles Study of Effect of Strain on the Band Structure of ZnO Monolayer

采用基于密度泛函理论的第一性原理计算对单层znO薄膜能带结构的应变调控进行了研究.计算结果表明:沿着之字形方向的压缩应变和扶椅形方向的拉伸应变对薄膜带隙的调控都是线性的,而且带隙调控的范围最大;相反地,在沿着之字形方向的拉伸应变和扶椅形方向的压缩应变的调控下,带隙则呈现出非线性的变化.对于双轴应变的拉伸与压缩,带隙的变化都是非线性的.这种通过不同的应变加载方式来实现对带隙不同程度的调控,对znO薄膜在光学和催化等领域的应用具有重要的指导意义.The effect of strain on the band structure of the ZnO monolayer has been investigated by firstprinciples calculations based on density functional theory.The results reveal that the band structure of the ZnO monolayer presents different dependences on three types of strain.The band gap linearly and steeply varies under uniaxial zigzag compressive strain and armchair tensile strain, while it shows nonlinear dependence on the other types of strain.Therefore, uniaxial zigzag compressive strain and armchair tensile strain should be the most effective to tune the band gap.This work has significant implications for application of strain to tune the optical and catalytic properties of ZnO nanofilms.国家自然科学基金(10702056;11204252); 四川省教育厅(12ZA072)资助项目~

High-index-faceted platinum nanoparticles: insights into structural and thermal stabilities and shape evolution from atomistic simulations

National Natural Science Foundation of China [51271156, 11204252]; Natural Science Foundation of Fujian Province of China [2013J06002]; Specialized Research Fund for the Doctoral Program of Higher Education of China [20130121110012]High-index-faceted Pt nanoparticles exhibit exceptional electrocatalytic activity owing to the high density of low coordinated sites on their surface, and thus have attracted extensive studies over the past few years. In this study, we have employed atomistic simulations to systematically investigate the structural and thermal stabilities and shape evolution of Pt nanoparticles with different high-index facets, that is, tetrahexahedra enclosed by {hk0} facets, trapezohedra by {hkk} ones, and trisoctahedra by {hhk} ones. The results show that {221} faceted trisoctahedral nanoparticles display the best structural and thermal stabilities while {410} faceted tetrahexahedral ones display the worst. The shape stability of these nanoparticles generally decreases in the order from trapezohedron to tetrahexahedron to trisoctahedron. For the same type of polyhedron, the structural, thermal and shape stabilities of the nanoparticles all decrease according to the order of {2kl}, {3kl} and {4kl} facets. Further analyses have discovered that a large proportion of high-coordinated surface atoms are beneficial for enhancing both the thermal and shape stabilities. This work provides an in-depth understanding of surface structures and thermodynamic evolution of high-index-faceted metallic nanoparticles

Single-crystalline and multiple-twinned gold nanoparticles: an atomistic perspective on structural and thermal stabilities

National Natural Science Foundation of China [51271156, 11204252]; Natural Science Foundation of Fujian Province of China [2013J06002]; Fundamental Research Funds for the Central Universities of China [2012121010]Morphologies of gold nanoparticles play an important role in determining their chemical and physical (catalytic, electronic, optical, etc.) properties. Therefore, a fundamental understanding of the morphological stability is of crucial importance to their applications. In this article, we employed atomistic simulations to systematically investigate the structural and thermal stabilities of gold particles with eight representative nanoshapes, including single-crystalline and multiple-twinned structures. Our investigation has revealed that the truncated octahedron and the octahedron possessed the best structural stability, while the tetrahedron and the icosahedron did the worst. Further analyses have discovered different thermal stabilities and diverse melting behaviors in these particles. Especially, an inhomogeneous melting of the icosahedron was disclosed, and the relevant mechanism was elucidated. This study provides significant insight not only into the experimental preparation of gold nanoparticles but also into the design of gold nanostructures with both high catalytic activity and excellent stability

Tetrahexahedral Pt-Pd alloy nanocatalysts with high-index facets: An atomistic perspective on thermodynamic and shape stabilities

Metallic nanoparticles with high-index facets exhibit exceptional electrocatalytic activity owing to the high density of low coordination sites at the surface, thus they have attracted intense interest over the past few years. Alloying could further improve their catalytic activity by the synergy effects of high-index facets and electronic structures of components. Using atomistic simulations, we have investigated thermodynamic and shape stabilities of tetrahexahedral Pt-Pd alloy nanoparticles respectively bound by {210} and {310} facets. Energy minimization through Monte Carlo simulations has indicated that the outermost layer is predominated by Pd atoms while Pt atoms preferentially occupy the sub-outermost layer of nanoparticles. Molecular dynamics simulations of the heating process have shown that the {210} faceted nanoparticles possess better thermodynamic and shape stabilities than the {310} faceted ones. The coordination numbers of surface atoms were used to explore the potential origin of the different stabilities. Furthermore, a high Pt ratio will help enhance their stabilities. For both faceted nanoparticles, the melting has homogeneously developed from the surface into the core, and the tetrahexahedra have finally evolved into sphere-like shape prior to the overall melting. These results are helpful for understanding the composition and thermodynamic properties of high-index faceted nanoparticles, and are also of practical importance to the development of alloy nanocatalysts. ? 2014 The Royal Society of Chemistry

The Resources and Protection of Psammophilous Vegetation on Coasts in Xiamen Guanyinshan, Fujian Province

作者简介:黄雅琴(1984-),女,福建三明人,硕士,研究实习员,从事海洋、海岸带生物与生态研究。E-mail:[email protected] 注：李荣冠为通讯作者。E-mail:[email protected]厦门观音山海岸沙生植被资源丰富,有维管束植物135种,分属于42科113属。但是比较23年前的历史调查数据,鬣刺(Spinifex littoreus)、盐地鼠尾粟(Sporobolus virginicus)等沙滩防风浪固沙护岸先锋植物近乎绝迹。为了改变当地仅存的次生植被现状,应当对残存风水林与灌草丛加强保护,利用海岸沙生植被营造沿海防护林体系,充分发挥其生态效益,达到改善环境条件、有效抗御自然灾害的目的。[英文文摘]There are abundant plant resources of psammophilous vegetation on the coast of Xiamen Guanyinshan, including 135 species of vascular plants belonging to 42 families and 113 genera.Compared with the historical investigation data twenty-three years ago, the pioneer plants like Spinifex littoreus, Sporobolus virginicus and others are nearly extinct. In order to change the secondary vegetation status on the coast, the remnant forest and shrub should be protected strengtheningly. And the coastal protection forest system should be constructed on the basis of coastal psammophilous vegetation, thus to improve the environment condition and effectiveness against natural disasters.海洋公益性行业科研专项(200905008

Melting behavior of Au-Pd eutectic nanoparticle:A molecular dynamics study

采用分子动力学方法结合嵌入原子势,对Au-Pd共晶纳米粒子的热稳定性进行了模拟研究.计算结果表明:Au-Pd纳米粒子的熔点明显高于Au单质纳米粒子而低于Pd纳米粒子.通过计算lIndEMAnn指数发现Au-Pd共晶纳米粒子中的Au原子首先熔化,然后带动Pd原子的熔化;熔化所经历的温度区间明显要宽于单质纳米粒子.In this paper,we present an investigation on thermal stability of Au-Pd eutectic nanoparticle by using molecular dynamics simulation with embedded-atom potential.The results show that the melting point of Au-Pd eutectic nanoparticle is remarkably higher than that of pure Au one but lower than that of Pd one.By the analyses of Lindemann index,it is found that Au atoms first melt,then induce the melting of Pd atoms.The temperature range of melting is broader for Au-Pd eutectic nanoparticle than that for Au and Pd nanoparticles.国家自然科学基金(批准号:10702056);福建省自然科学基金(批准号:2011J05011);四川省教育厅科研基金(批准号:12ZA072)资助的课题---

Molecular dynamics investigation of thermal stability of Pt-Au core-shell nanoparticle

采用分子动力学方法结合嵌入原子势,对PT-Au核-壳纳米粒子的热稳定性进行了研究.计算结果表明:PT-Au纳米粒子的熔点明显高于Au纳米粒子而低于PT纳米粒子.通过计算lIndEMAnn指数发现:壳层中的Au首先熔化,然后逐渐向内部扩展,最终导致核中的PT完全熔化;熔化所经历的温度区间明显宽于单质纳米粒子,而且该熔化过程呈现典型的两阶段熔化特征;在两次熔化之间,存在着固(核)液(壳)共存的结构.In this paper,we have examined the thermal stability of Pt-Au core-shell nanoparticle by using molecular dynamics simulations with embedded-atom potential.The results show that the melting point of Pt-Au core-shell nanoparticle is significantly higher than that of pure Au one but lower than that of Pt one.By the analyses of Lindemann index,it is discovered that the melting first occurs in Au shell,then spreads into interior,finally the overall melting of Pt core appears.The temperature range of melting is much broader for Pt-Au core-shell nanoparticle than for Au and Pt nanoparticles.Moreover,Pt-Au core-shell nanoparticle exhibits a distinct two-stage melting during continuous heating,and the structure of solid(core)-liquid(shell) coexistence has been observed between two meltings.国家自然科学基金(批准号:51271156;11204252); 四川省教育厅(批准号:12ZA072)~

Time-resolved photoluminescence from Si-in-SiNx/Si-in-SiC quantum well-dot structures

Innovation Program of the Chinese Academy of Sciences; National Natural Science Foundation of China [10974227, 51172272, 10904165]; National Basic Research Program of China [2012CB933002]Si-in-SiNx/Si-in-SiC quantum well-dot structures, with Si quantum dots slightly larger than 1.0 nm embedded in both amorphous SiNx and SiC sublayers, were grown at nearly room temperature by using PECVD. Time-resolved photoluminescence for three samples in a period of 100/30 nm, 60/10 nm and 20/10 nm, respectively, has been measured at emission lengths ranging from 430 nm to 490 nm, and fitted with a stretched-exponential function. Typical decay time was at the order of one nanosecond, which could be attributed to the core-state emission. The matrix materials forming the well provide a nonuniform potential background which induces a modulation to the carrier diffusion process, thus resulting in an emission-wavelength dependent decay time. When confinement effect from the well comes into play as in the sample of smaller well width, the decay time can be below 1.0 ns and indifferent to the varied emission wavelength, and the carrier diffusion is dominated by hopping. These quantum well-dot systems of strong and fast decaying light emission in blue-violet colors might find potential utilization in GHz optical connection and other photoelectronic devices. (C) 2013 Elsevier B.V. All rights reserved

Simulation on Localized Surface Plasmon Resonance Behaviors of Nanosized PMMA/Ag Core-Shell Structure

应用米氏理论,对银膜包覆PMMA纳米核壳结构的局域表面等离激元共振行为进行了模拟计算,研究了颗粒尺寸、核壳比等参数对纳米核壳结构局域表面等离激元共振消光光谱的影响;同时将其与实心银纳米球的局域表面等离激元共振光谱行为进行了比较。结果表明,相对于实心银纳米球,银膜包覆PMMA纳米核壳结构的共振峰位更加红移,且共振峰的宽度更窄。这些性能上的提高,是由于纳米PMMA介质核的存在减弱了电子云振荡过程中的滞后效应,利于化学生物传感器方面的应用。Localized surface plasmon resonance(LSPR) spectrum behaviors of PMMA/Ag core-shell nanoparticles are extensively and systematically simulated by a calculation method based on Mie theory.Through the simulation calculation,the dependence of the LSPR behaviors of the core-shell nanoparticle on nanoparticle size,ratio of the radius of PMMA core to the thickness of Ag shell,and some other factors is studied.Furthermore,LSPR behaviors of Ag nanoparticles are simulated as well for comparison.The simulation results show that the nanosized PMMA dielectric core can weaken the retardation effects in the process of free electron resonance in the Ag nanoshell.Thus,compared with the LSPR of Ag nanoparticles,the position of the LSPR peak of the PMMA/Ag core-shell nanoparticles has an even more obvious red shift and the width of the LSPR becomes even narrower.Such simulation results indicate that the core-shell nanoparticles would have more advantages over Ag nanoparticles for potential applications of future chemical and biological nanosensors.国家科技计划国际科技合作与交流专项(2008DFA51230);国家973计划(2007CB936603);国家自然科学基金(11074207;50861007)资助课

Molecular dynamics investigation of thermal stability of Pt-Au core-shell nanoparticle

National Natural Science Foundation of China [51271156, 11204252]; Scientific Research Fund of Sichuan Provincial Education Department, China [12ZA072]In this paper, we have examined the thermal stability of Pt-Au core-shell nanoparticle by using molecular dynamics simulations with embedded-atom potential. The results show that the melting point of Pt-Au core-shell nanoparticle is significantly higher than that of pure Au one but lower than that of Pt one. By the analyses of Lindemann index, it is discovered that the melting first occurs in Au shell, then spreads into interior, finally the overall melting of Pt core appears. The temperature range of melting is much broader for Pt-Au core-shell nanoparticle than for Au and Pt nanoparticles. Moreover, Pt-Au core-shell nanoparticle exhibits a distinct two-stage melting during continuous heating, and the structure of solid (core)-liquid (shell) coexistence has been observed between two meltings