首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 62 毫秒
1.
冯卫  赵爱迪 《物理学报》2012,61(17):173601-173601
利用扫描隧道显微镜和扫描隧道谱(STM/STS)及单原子操纵,系统研究了单个钴原子(Co) 及其团簇在Rh (111)和Pd (111)两种表面的吸附和自旋电子输运性质. 发现单个Co原子在Rh (111)上有两种不同的稳定吸附位,分别对应于hcp和fcc空位, 他们的高度明显不同,在针尖的操纵下单个Co原子可以在两种吸附位之间相互转化. 在这两种吸附位的单个Co原子的STS谱的费米面附近都存在很显著的峰形结构, 经分析认为Rh (111)表面单个Co原子处于混价区,因此这一峰结构是d轨道共振 和近藤共振共同作用的结果.对于Rh (111)表面上的Co原子二聚体和三聚体, 其费米面附近没有观测到显著的峰,这可能是由于原子间磁交换相互作用 和原子间轨道杂化引起的体系态密度改变所共同导致.与Rh (111)表面不同, 在Pd (111)表面吸附的单个Co原子则表现出均一的高度.并且对于Pd (111)表面所有 单个Co原子及其二聚体和三聚体,在其STS谱的费米面附近均未探测到显著的电子结构, 表明Co原子吸附于Pd (111)表面具有与Rh (111)表面上不同的原子-衬底相互作用与自旋电子输运性质.  相似文献   

2.
We performed detailed molecular statics calculations of energy barriers for various adatom movements in the vicinity of small island on (111) surfaces of Pt and Rh using Rosato-Guillope-Legrand interatomic potential. We found that for both systems the exchange processes are energetically favorable in comparison with direct jumps of an adatom. We observed that Ehrlich-Schwoebel barriers for exchange decrease significantly on small islands in comparison to single step on the surface. A comparison of both materials is presented. Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999. Financial support for this work was provided by the COST project P3.80.  相似文献   

3.
In the growth process of ultrathin films of vanadium oxides on Pd(111), a sequence of novel oxide phases with layer-dependent structures and oscillating oxidation states has been detected experimentally and understood theoretically. These phases are interface mediated and metastable with respect to further oxide growth. Transformation into the stable oxide configuration occurs beyond a critical thickness, where energetics combined with kinetic limitations determine the oxide multilayer structure.  相似文献   

4.
S-decorated Cu trimers are a likely agent of S-enhanced Cu transport between islands on Cu(111). According to ab initio calculations, excellent S bonding to trimer-Cu dangling valence results in an ad- Cu(3)S(3) formation energy of only approximately 0.28 eV, compared to 0.79 eV for a self-adsorbed Cu atom, and a diffusion barrier < or =0. 35 eV.  相似文献   

5.
Adsorption of NO and O2 on Rh(111) has been studied by TPD and XPS. Both gases adsorb molecularly at 120 K. At low coverages (θNO < 0.3) NO dissociates completely upon heating to form N2 and O2 which have peak desorption temperatures at 710 and 1310 K., respectively. At higher NO coverages NO desorbs at 455 K and a new N2 state obeying first order kinetics appears at 470 K. At saturation, 55% of the adsorbed NO decomposes. Preadsorbed oxygen inhibits NO decomposition and produces new N2 and NO desorption states, both at 400 K. The saturation coverage of NO on Rh(111) is approximately 0.67 of the surface atom density. Oxygen on Rh(111) has two strongly bound states with peak temperatures of 840 and 1125 K with a saturation coverage ratio of 1:2. Desorption parameters for the 1125 peak vary strongly with coverage and, assuming second-order kinetics, yield an activation energy of 85 ± 5 kcalmol and a pre-exponential factor of 2.0 cm2 s?1 in the limit of zero coverage. A molecular state desorbing at 150 K and the 840 K state fill concurrently. The saturation coverage of atomic oxygen on Rh(111) is approximately 0.83 times the surface atom density. The behavior of NO on Rh and Pt low index planes is compared.  相似文献   

6.
We studied the atomic arrangements and the phase diagram of two-dimensional (2D) Bi–Sn binary films on Rh(111) with low-energy electron diffraction and scanning tunneling microscopy (STM). The 2D binary films exhibited (“2” × √3)-(Bi,Sn), (√7 × √7)R19°-(Bi,Sn), and (7 × 3√3)-(Bi,Sn) structures, depending on the compositional ratio of Bi and Sn. Atomically resolved STM images revealed that the binary films formed a BiSn3 ordered alloy for the (√7 × √7)R19°-(Bi,Sn) structure and a solid solution alloy for the (“2” × √3)-(Bi,Sn) structure. The atomic configuration for the (7 × 3√3)-(Bi,Sn) structure was closely related to that of (√7 × √7) R19°-(Bi,Sn).  相似文献   

7.
Self-limited growth of a thin oxide layer on Rh(111)   总被引:1,自引:0,他引:1  
The oxidation of the Rh(111) surface at oxygen pressures from 10(-10) mbar to 0.5 bar and temperatures between 300 and 900 K has been studied on the atomic scale using a multimethod approach of experimental and theoretical techniques. Oxidation starts at the steps, resulting in a trilayer O-Rh-O surface oxide which, although not thermodynamically stable, prevents further oxidation at intermediate pressures. A thick corundum like Rh2O3 bulk oxide is formed only at significantly higher pressures and temperatures.  相似文献   

8.
The reaction of NO with CO on Rh(111) has been studied with temperature programmed reaction (TPR). Comparisons are made with the reaction of O2 with CO and the reaction of NO with H2. The rate-determining step for both CO oxidation reactions is CO(a) + O(a) → CO2(g). Repulsive interactions between adsorbed CO and adsorbed nitrogen atoms lead to desorption of CO in a peak at 415 K which is in the temperature range where the reaction between CO(a) and O(a) produces CO2(g). Thus the extent of reaction of CO(a) with NO(a) is less than that between CO(a) and O(a) due to the lower coverage of CO caused by adsorbed N atoms and NO. A similar repulsive interaction between NO(a) and H(a) suppresses the NO + H2 reaction. CO + NO reaction behavior on Rh(111) is compared to that observed on Pt(111).  相似文献   

9.
《Applied Surface Science》1987,29(1):143-146
ESD energy analysis is used to study the reaction products produced during coadsorption of CO-O2 and CH4-O2 on Rh(111). Residence of CO2 on the surface is confirmed by detection of a CO2+ ionic component with energy of 1.8 eV. Adsorption and dissociation of CH4 on oxygen- covered Rh(111) is inferred as a result of a low energy component present in the energy spectra of desorbed O+.  相似文献   

10.
The adsorption of CO on Rh(111) has been studied by thermal desorption mass spectrometry and low-energy electron diffraction (LEED). At temperatures below 180 K, CO adsorbs via a mobile precursor mechanism with sticking coefficient near unity. The activation energy for first-order CO desorption is 31.6 kcal/mole (νd = 1013.6s?1) in the limit of zero coverage.As CO coverage increases, a (√3 ×√3)R30u overlayer is produced and then destroyed with subsequent formation of an overlayer yielding a (2 × 2) LEED pattern in the full coverage limit. These LEED observations allow the absolute assignment of the full CO coverage as 0.75 CO molecules per surface Rh atom. The limiting LEED behavior suggests that at full CO coverage two CO binding states are present together.  相似文献   

11.
Carbon monoxide induced ordering of an organic molecule, benzene, has been studied on the Pt(111) and Rh(111) crystal surfaces using low-energy electron diffraction, high-resolution electron energy loss spectroscopy, and thermal desorption spectroscopy. We propose detailed geometries for all the ordered structures of coadsorbed CO and benzene. Ordering in the adsorbed overlayer is proposed to result from the interactions between adsorbed CO molecules in the presence of benzene.  相似文献   

12.
The diffusion of two-dimensional adatom-islands (up to 100 atoms) on Cu(111) has been studied, using the self-learning kinetic Monte Carlo method (Trushin et?al 2005 Phys. Rev. B 72 115401). A variety of multiple-?and single-atom processes are revealed in the simulations, and the size dependences of the diffusion coefficients and effective diffusion barriers are calculated for each. From the tabulated frequencies of events found in the simulation, we show a crossover from diffusion due to the collective motion of the island to a regime in which the island diffuses through periphery-dominated mass transport. This crossover occurs for island sizes between 13 and 19 atoms. For islands containing 19-100 atoms the scaling exponent is 1.5, which is in good agreement with previous work. The diffusion of islands containing 2-13 atoms can be explained primarily on the basis of a linear increase of the barrier for the collective motion with the size of the island.  相似文献   

13.
The co-adsorption of oxygen and hydrogen on Rh(111) at temperatures below 140 K has been studied by thermal desorption mass spectrometry, Auger electron spectroscopy, and lowenergy electron diffraction. The co-adsorption phenomena observed were dependent upon the sequence of adsorption in preparing the co-adsorbed overlayer. It has been found that oxygen extensively blocks sites for subsequent hydrogen adsorption and that the interaction splits the hydrogen thermal desorption into two states. The capacity of the oxygenated Rh(111) surface for hydrogen adsorption is very sensitive to the structure of the oxygen overlayer, with a disordered oxygen layer exhibiting the lowest capacity for hydrogen chemisorption. Studies with hydrogen pre-adsorption indicate that a hydrogen layer suppresses completely the formation of ordered oxygen superstructures as well as O2 desorption above 800 K. This occurs with only a 20% reduction in total oxygen coverage as measured by Auger spectroscopy.  相似文献   

14.
The oxidation of Pd(111) leads to an incommensurate surface oxide, which was studied by the use of scanning tunneling microscopy, surface x-ray diffraction, high resolution core level spectroscopy, and density functional calculations. A combination of these methods reveals a two-dimensional structure having no resemblance to bulk oxides of Pd. Our study also demonstrates how the atomic arrangement of a nontrivial incommensurate surface can be solved by molecular dynamics in a case where experimental techniques alone give no solution.  相似文献   

15.
本文针对在多种催化反应的重要中间体乙烯,使用(meta)-GGA等级的包含PBE,BEEF-vdW,SCAN以及SCAN+rVV10在内的多种交换关联泛函,系统研究了在过渡金属表面(Ag,Rh和Ir)上乙烯吸附势能面对泛函的依赖关系. 研究发现,对于乙烯在贵金属Ag(111)上的吸附,除了PBE外,BEEF-vdW,SCAN以及SCAN+rVV10均能预测出物理吸附态的存在. 对于乙烯在Rh(111)面的吸附,SCAN和SCAN+rVV10预测在化学吸附位之前存在有物理吸附前驱态,而基于PBE和BEEF-vdW的势能面并没有发现前驱态的存在. 而对于乙烯在Ir(111)上的吸附,BEEF-vdW也能微弱地预测出化学吸附前驱态的存在. 研究结果表明,无论在哪一种金属表面上,四种泛函中SCAN+rVV10给出的吸附能最强,其次是SCAN,最后是PBE或者BEEF-vdW.  相似文献   

16.
《Surface science》1986,172(1):L515-L522
The molecular structure of benzene coadsorbed with CO on Rh(111) has been investigated by angle resolved UV photoemission (ARUPS), LEED and thermal desorption spectroscopy. The symmetry of the benzene adsorption complex in a mixed benzene-CO (3×3) LEED structure has been determined to C6v by ARUPS. This indicates that the benzene molecules remain essentially undistorted in the CO coadsorbate layer, as it has been found for the pure benzene layer on Rh(111).  相似文献   

17.
First-principles calculations imply that neither H2O bilayers nor half-dissociated, H2O+OH+H monolayers are thermodynamically stable on clean Rh(111). Thus, the experimental observation that Rh(111) supports a periodic 2D water adlayer needs an explanation. Chemistry involving common surface impurities, notably C atoms, may be the answer. Calculations show they provide favorable binding sites for H atoms detached from H2O. The resulting OH fragments can anchor a 2D water layer to the surface.  相似文献   

18.
19.
20.
The diffusion properties of small clusters Agn, Cun, and Aun on the Cu(111) and Au(111) surfaces were studied using the molecular statics (MS) in order to understand the atomistic processes underlying the motion. In this work, the atomic interaction potential is modeled by a semi-empirical Embedded Atom Method (EAM), while the drag method is used to determine the static activation energy for each diffusion path. The presented results indicate that the dimer can diffuse on the (111) surface via the zig-zag and concerted motion mechanisms. The trimer diffuses according to the concerted motion mechanism. For the tetramer diffusion, the mechanism that consumes the least amount of energy is the zig-zag motion, in which only two atoms are needed for the diffusion process at one time. This allows finding a static activation energy smaller compared to the trimer diffusion.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号