European Physical Journal B
First-principles calculations based on density functional theory (DFT) have been performed to study O adsorption in on-surface and subsurface sites. For different coverages, hollow site is found to be the most stable on-surface adsorption site. For the subsurface adsorption at the bare Mo surface, the adsorption energies are found to be higher than those at the on-surface sites, suggesting that these sites are less stable. However, the presence of preadsorbed O overlayer enhances the binding energy of subsurface adsorption, particularly for the adsorption of O at octahedral site. Further, vibrational frequencies, work-function and density of states are presented for O adsorption in on-surface sites.
关键词:
low-temperature adsorption;oxygen-adsorption;ab-initio;plane;mo;pseudopotentials;p(2x2)o/mo(110);electron;elements;phonons
Physical Review B
The fringe contrast observed in a copper film with its Cu[110] parallel to the incident electron beam has been investigated by high-resolution electron microscopy (HREM). According to a geometrical analysis for these fringes, it was assumed that they originated from the Cu-O chains adsorbed on a Cu(110) surface. This assumption was confirmed by a multislice image simulation on the basis of the electron diffraction and imaging theory using an added-row reconstruction model. Our calculation indicates that an added-Cu-O-chain surface reconstruction can generate a regular fringe pattern with sufficient contrast in a thin copper film with a thickness of several nanometers. The present study demonstrates the potential of HREM to investigate surface structures and surface reaction of ultrathin films at the atomic level.
关键词:
electron-microscopy;surface;oxygen;chemisorption
Surface Science
Six surface models for the Fe3O4(110) surface were studied using the density functional theory (DFT), namely the AB-terminated surface (AB model), the AB-terminated with Fe-A vacancy (AB-Fe-A vac model), the AB-terminated with Fe-B vacancy (AB-Fe-B vac model), the B-terminated surface (B model), the B-terminated surface with Fe-B vacancy (B-Fe-B vac model), and the B-terminated surface with O vacancy (B-O vac model). Here, A and B denoted the Fe cations in tetrahedrally (Fe-A) and octahedrally (Fe-B) coordinated interstices. The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other surface models. The half-metallic property remains in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-Fe-A vac, AB-Fe-B vac, B and the B-Fe-B vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property. (c) 2006 Elsevier B.V. All rights reserved.
关键词:
density functional theory;surface;electron density of states;magnetic;properties;1st-principles
Yingjie HUA
,
Xin LIU
,
Changgong MENG
,
Dazhi YANG
材料科学技术（英文）
The discrete-variational method within the framework of density functional theory was used to investigate the process of O2 adsorption occurring on the surface of NiTi alloy. The calculated results showed that O2 exhibits the adsorption state of Odelta2 (0.36O2 only interact with one nearest surface Ti atom, and the Ti atom only adsorbs one oxygen atom of the O2 molecule. Other cluster atoms would not be influenced in the adsorption process. The density of state analysis showed that the interaction between Ti and O atom is mainly contributed to 2p (O) and 4s (Ti) orbitals.
关键词:
NiTi
,
null
,
null
Journal of the American Chemical Society
Au catalysis has been one of the hottest topics in chemistry in the last 10 years or so. How O-2 is supplied and what role water plays in CO oxidation are the two challenging issues in the field at the moment. In this study, using density functional theory we show that these two issues are in fact related to each other. The following observations are revealed: (i) water that can dissociate readily into OH groups can facilitate O-2 adsorption on TiO2; (ii) the effect of OH group on the O-2 adsorption is surprisingly long-ranged; and (iii) O-2 can also diffuse along the channel of Ti (5c) atoms on TiO2(1 10), and this may well be the rate-limiting step for the CO oxidation. We provide direct evidence that O-2 is supplied by O-2 adsorption on TiO2 in the presence of OH and can diffuse to the interface of Au/TiO2 to participate in CO oxidation. Furthermore, the physical origin of the water effects on Au catalysis has been identified by electronic structure analyses: There is a charge transfer from TiO2 in the presence of OH to O-2, and the O-2 adsorption energy depends linearly on the 02 charge. These results are of importance to understand water effects in general in heterogeneous catalysis.
关键词:
catalytically active gold;au nanoparticles;tio2(110) surface;molecular-oxygen;model catalysts;adsorption;clusters;size;dissociation;titania
田鹏飞
,
欧阳李科
,
徐新潮
,
徐晶
,
韩一帆
催化学报
doi:10.1016/S1872-2067(12)60537-3
采用周期性密度泛函理论研究了H2和O2在Pd(111),Pd(100)及Pd(110)表面上直接合成H2O2的反应机理,对反应的主要基元步骤进行了计算和分析.结果表明,Pd(111)表面对H2O2直接合成的催化选择性最好,表面原子密度较低的Pd(100)表面和Pd(110)表面上含有O-O键的表面物种解离严重,不利于H2O2的生成.H2O2的选择性与含有O-O键表面物种的O-O键能和表面物种的结合能有关.含有O-O键的表面物种在表面的结合能越大,越容易发生解离,不利于形成H2O2.
关键词:
钯
,
过氧化氢
,
氢气
,
氧气
,
直接合成
,
密度泛函理论
李淑华
,
沈大为
,
祖媛媛
,
曲长征
,
王富耻
,
冯顺山
稀有金属材料与工程
采用微弧氧化技术,以硅酸盐为主要电解液,在2A06铝合金表面制备出高硬度、高耐磨性的微弧氧化陶瓷膜.用扫描电镜观测膜层的显微结构,用X射线衍射分析其相组成,并对膜层进行耐磨损和抗冲蚀试验.结果表明,氧化时间越长,2A06铝合金表面陶瓷层越厚,陶瓷层粗糙度也越高.陶瓷层由过渡层、致密层和疏松层组成.过渡层与基体和致密层结合紧密.致密层的相组成主要为α-A12O3、γ-Al2O3,疏松层的相组成主要为α-A12O3、γ-A12O3以及Al6Si2O3.致密层中的α-A12O3相的含量远高于疏松层.从试样边缘到试样中心硬度逐渐降低,最高硬度出现在试样表面边缘向内5～20 mm处,平均HV硬度可达20.96 GPa.2A06铝合金的耐磨性比较差,磨轮转速从100 r/min增至400 r/min时,磨损量不断增加且呈线性分布.微弧氧化制备的陶瓷层磨损量在磨损开始时(100 r/min)稍高,磨轮转速到600 r/min时磨损量趋于稳定,磨轮转速到1600 r/min时磨损量仍然呈现较低水平.陶瓷层的冲蚀体积损失率也远低于2A06铝合金基体.
关键词:
2A06铝合金
,
微弧氧化
,
陶瓷层
,
摩擦学特性
