共查询到18条相似文献,搜索用时 103 毫秒
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采用密度泛函理论与周期性平板模型相结合的方法,对CO在Rh(111)表面top、fcc、hcp、bridge四个吸附位和Rh-Pd(111)表面Rh-top、Pd-top、Rh Rh-bridge、Rh Pd-bridge、Pd Pd-bridge、Rh2Pdhcp、Rh Pd2-hcp、Rh2Pd-fcc、Rh Pd2-fcc九个吸附位的13种吸附模型进行了构型优化、能量计算,得到了CO较有利的吸附位;并对最佳吸附位进行总态密度分析.结果表明:CO在Rh(111)和Rh-Pd(111)表面的最稳定吸附位分别为Rh-hcp和Rh-top位,其吸附能的大小顺序为Ph(111)Rh-Pt(111);CO与金属表面成键,属于化学吸附. 相似文献
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采用原子尺度的模拟方法,探讨了在零偏压下扫描隧道显微镜(STM)针尖调制的金属表面岛上原子运动及岛边的层间质量输运. 研究结果显示STM的移动对岛上及岛边的原子扩散有重要的影响. 针尖与吸附原子的交互作用及岛和基体中强的形状变化影响了岛上吸附原子的跳跃扩散及岛边的跳下扩散和交换扩散过程. 研究发现,通过调节针尖与基体的垂直距离及针尖与吸附原子的水平距离,可以降低岛上吸附原子的跳跃扩散能垒及岛边的跳下扩散和交换扩散能垒,从而实现薄膜由三维生长模式向二维生长模式的转变.
关键词:
扫描隧道显微镜
原子运动
质量输运 相似文献
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利用X-射线光电子能谱(XPS)和程序升温脱附谱(TPD)研究了三甲基镓在Pd(111)表面的吸附和解离行为,并考察了表面预吸附H和O的影响。结果表明,在吸附温度为140 K时,三甲基镓在Pd(111)上主要为解离吸附,此时表面物种为Ga(CH3)x (x=1,2,3)和CHx物种。加热将导致Ga的甲基化合物中的Ga-C键发生分步断裂,在不同温度下产生CH4和H2从表面脱附。同时,XPS结果证实了在275~325 K的温度区间内存在Ga甲基化合物的分子脱附。退火至更高温度,表面只观察到积碳和金属Ga物种,这二者随着温度的继续升高逐渐向体相扩散。在Pd(111)表面预吸附O和H对上述吸附和解离行为存在显著的影响。当表面预吸附H时,脱附产物CH4和H2的脱附主要位于315 K,可归属为一甲基镓的解离脱附。当表面预吸附O时,只在258 K观察到CH4和H2的脱附峰,可能来自于Pd-O-Ga(CH3)2吸附结构的解离. 相似文献
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本文使用循环伏安法和电势阶跃法分别研究了添加和不添加Na2SO4的0.1 mol/LH2SO4+0.1 mol/LHCOOH溶液中Pd(111)电极上甲酸氧化反应(FAO)的动力学行为,并与同样条件下0.1 mol/LHClO4中的动力学行为进行比较. 加入0.05 mol/L或者0.1 mol/LNa2O4后,在相同的电位下负向扫描的FAO电流比正向扫描的显著减小. 本文推测在(SO4*ad)m+[(H2O)n-H3O+]或(SO4*ad)m+[Na+(H2O)n-H3O+]吸附层相转变电势以正的电位, 这个吸附层的结构可能随着电位的增加或Na2SO4的加入变得更加致密和稳定. 因此,破坏或者脱附致密的硫酸(氢)根吸附层变得更加困难,使得FAO 动力学在较高电位和随后的负扫电位受到明显的抑制. 相似文献
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P. Weinberger 《哲学杂志》2013,93(12):1747-1764
It is shown that by ‘stacking’ together a semi-infinite sample subsystem with a semi-infinite tip subsystem, difficulties with respect to a common Fermi level for the whole system can approximately be overcome in all those cases when the substrate (serving as lead) and the second lead are different materials. Based on this procedure by means of the spin-polarized (fully) relativistic screened Korringa–Kohn–Rostocker method and an equivalent Kubo equation, theoretical spin-polarized STM spectra for Pt(111)/Co n /Cr15 W22/Cu(111) with respect to an applied external magnetic field are evaluated in terms of difference conductivities as a function of the corresponding free energy. These spectra are interpreted using layer-resolved contributions to the difference conductivities in order to indicate which parts of the sample dominate changes in the tunneling current caused by changing the orientation of the magnetization. Also shown are estimates of the time-scales to switch from perpendicular to in-plane and vice versa. All investigated properties suggest that different situations apply when the number of Co layers on top of Pt(111) is increased from one to three. 相似文献
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《中国物理 B》2021,30(9):96805-096805
The orientation switching of a single azobenzene molecule on Au(111) surface excited by tunneling electrons and/or photons has been demonstrated in recent experiments. Here we investigate the rotation behavior of this molecular rotor by first-principles density functional theory(DFT) calculation. The anchor phenyl ring prefers adsorption on top of the fcc hollow site, simulated by a benzene molecule on close packed atomic surface. The adsorption energy for an azobenzene molecule on Au(111) surface is calculated to be about 1.76 e V. The rotational energy profile has been mapped with one of the phenyl rings pivots around the fcc hollow site, illustrating a potential barrier about 50 me V. The results are consistent with experimental observations and valuable for exploring a broad spectrum of molecules on this noble metal surface. 相似文献
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利用低温超高真空扫描隧道显微镜对单个钴酞菁分子实现了选键化学反应.通过对吸附于Au(111)表面的单个钴酞菁分子外围H原子的"剪裁",并用实验图像和谱学方法,结合第一性原理理论计算研究了逐步去除钴酞菁分子8个外围H原子的过程.理论计算结果再现了实验中所观测到的分子空间构型的变化,并阐明了吸附体系中局域自旋的恢复和变化过程. 相似文献
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A.V. Davydenko Yu.P. Ivanov L.A. Chebotkevich 《Journal of magnetism and magnetic materials》2012,324(6):1248-1252
Giant magnetoresistance of the epitaxial Co/Cu/Co trilayers grown on vicinal Si(111) was determined as a function of Cu spacer coverage in the range from 0 to 7 ML. The first maximum of giant magnetoresistance and antiferromagnetic coupling was detected at 3.0 ML coverage of the Cu spacer. The portion of antiferromagnetic coupling in the first antiferromagnetic maximum was estimated as 17%. 3D growth mode of the Cu spacer leads to the simultaneous occurrence of the ferromagnetically and antiferromagnetically coupled areas between the Co layers. 相似文献
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采用基于广义梯度近似的投影缀加平面波(projector augmented wave) 赝势和具有三维周期性边界条件的超晶胞模型,用第一性原理计算方法,计算并分析了Pd在CeO2(111)面上不同覆盖度时的吸附能,价键结构和局域电子结构. 考虑了单层Pd和1/4单层Pd两种覆盖度吸附的情况. 结果表明:1)在单层吸附时,Pd的最佳吸附位置是O的顶位偏向Ce的桥位;在1/4单层吸附时,Pd最易在O的桥位偏向次层O的顶位吸附.2) 单层覆盖度吸附时,吸附原子Pd之间的作用较强;1/4单层覆盖度吸附时,同层吸附的Pd之间的几乎没有相互作用. 同时在低覆盖度吸附时,Pd和CeO2衬底的相互作用较高覆盖度时强.3) Pd的吸附只对其近邻的衬底原子结构有明显影响.4) Pd在CeO2衬底上吸附后,Pd和CeO2衬底的活性增强,并可能在Pd与CeO2界面处形成活性中心. 以上结果有助于人们对三元催化剂中Pd与CeO2的协同作用机理的理解. 相似文献