Adsorption of transition metal atoms on the NiO(100) surface and on NiO/Ag(100) thin films

We have studied the adsorption of Au, Pd, and Pt atoms on the NiO(100) surface and on NiO/Ag(100) thin films using plane wave DFT+U calculations. The scope of this work is to compare the adsorption properties of NiO, a reducible transition metal oxide, with those of MgO, a simple binary oxide with the same crystal structure and similar lattice parameter. At the same time, we are interested in the adsorption characteristics of NiO ultra-thin films (three atomic layers) deposited on Ag(100) single crystals. Also in this case the scope is to compare NiO/Ag(100) with the corresponding MgO/Ag(100) films which show unusual properties for the case of Au adsorption. The results show that the transition metal atoms bind in a similar way on NiO(100) and NiO/Ag(100) films, with Pt, Pd, and Au forming bonds of decreasing strength in this order. No charging effects occur for Au adsorbed on NiO/Ag(100) films, at variance with MgO/Ag(100). The reasons are analyzed in terms of work function of the metal/oxide interface. Possible ways to modify this property by growing alternate layers of MgO and NiO are discussed.     

Adsorption and dissociation of NO on stepped Pt (533)

We present an experimental and theoretical investigation of the adsorption, desorption, and dissociation of NO on the stepped Pt (533) surface. By combining temperature programmed desorption and reflection absorption infrared spectroscopy, information about the adsorption sites at different temperatures is obtained. Surprisingly, metastable adsorption structures of NO can be produced through variation of the dosing temperature. We also show that part of the NO molecules adsorbed on the step sites dissociates around 450 K. After dissociation the N atoms can desorb either by combining with an O fragment, or with another N atom, resulting in NO and N(2). The N(2) production can be enhanced by coadsorbing CO on the surface: CO scavenges the oxygen atom, thereby suppressing associative recombinative desorption of N and O atoms. Density functional theory calculations are used to reveal the adsorption energies and vibrational frequencies of adsorbed NO as well as barriers for dissociation of NO and for diffusion of N atoms. The combined experimental results and theoretical calculations reveal that dissociation of NO is the rate limiting step in the formation of N(2).     

NiO(001)表面吸附CO的从头算研究

用量子化学B3LYP方法,以外加点电荷来封闭边界效应的簇为模型,计算了CO在NiO(001)面上不同吸附位置的吸附情况,并计算了振动频率。结果表明:1) CO的最佳吸附方式为C端垂直吸附在Ni位;2)吸附后CO间的振动频率蓝移13 cm-1;3)在O空缺、边和角等位置的吸附不如在完整表面的吸附稳定,这些均与实验结果一致。吸附后CO把主要起反键作用的C2s电子给予簇表面,使得吸附后CO键级加大,导致吸附后振动频率蓝移。并比较了Gaussian98 和Crystal98的计算结果,两者的结果能较好地符合。     

Ab initio study of epitaxial growth on stepped Si(100) surface

Diffusion of a Si adatom over the reconstructed Si(100) surface with a single-height step on it is studied using the pseudopotential total energy method. The S_B rebonded step is shown to act as a good sink for adatoms descending onto the lower ledge. This is due to the presence of deep traps on the lower terrace and to the negative Ehrlich-Schwoebel barrier (the activation barrier for descent from the edge is 0.23 eV lower than for the motion on a flat surface). The diffusion characteristics of the adatom on both terraces are virtually unaffected by the presence of the step. However, the dimer buckling sequence on a lower terrace is strongly dependent on the position of the adatom along the diffusion path. © 1997 John Wiley & Sons, Inc.     

The bonding between NO and the NiO(100) surface

Summary The interaction between NO and different possible adsorption sites of the NiO(100) surface is studied. The Ni²⁺ cation gives a bonding to NO in reasonable agreement with experiment, but only if a crystal potential corresponding to less than completely ionic charges is assumed. The computed angle of 43° is also in good agreement with experiment. O^1– sites in both weak and strong crystal potentials also give a strong interaction with NO, 1.3 and 0.5 eV, respectively. In this case the angle is larger or around 70°. The O^2– anion and Ni¹⁺ sites do not give any significant bonding irrespective of assumed crystal potential and can be excluded as adsorption sites. The computed vibrational frequency for the adsorbed NO show shifts of +50, –85 and –200 cm^–1 for adsorption on Ni²⁺ in the weak potential, and O^1– in strong and weak potential, respectively. Only one, downwards shifted, frequency has been observed in the experiment but the most likely candidate for the experimentally observed adsorption site with a binding of 0.5 eV, is still the Ni²⁺ in a weak potential. Nitrogen core level shifts are also computed and discussed and the fully screened core-hole state is obtained for a cluster model, NiF₄O+NO, of Ni²⁺ in NiO with an ionicity lower than the standard ± 2.This work is dedicated to Prof. Inga Fischer-Hjalmars     

Adsorption and diffusion on a stepped surface: atomic hydrogen on Pt(211)

We present density functional theory calculations for atomic hydrogen interacting with a stepped surface, the Pt(211) surface. The calculations have been performed at the generalized gradient approximation level, using a slab representation of the surface. This is the state-of-the-art method for calculating the interaction of atoms or molecules with metal surfaces, nevertheless only few studies have used it to study atoms or molecules interacting with stepped surfaces, and none, to the best of our knowledge, have considered hydrogen interacting with stepped platinum surfaces. Our goal has been to initiate a systematic study of this topic. We have calculated the full three-dimensional potential energy surface (PES) for the H/Pt(211) system together with the vibrational band structure and vibrational eigenfunctions of H. A deep global minimum of the PES is found for bridge-bonded hydrogen on the step edge, in agreement with experimental results for the similar H/Pt(533) system. All the local vibrational excitations at the global minimum have been identified, and this will serve as a helpful guide to the interpretation of future experiments on this (or similar) system(s). Furthermore, from the calculated PES and vibrational band structure, we identify a number of consequences for the interpretation or modelling of diffusion experiments studying the coverage and directional dependence of atomic hydrogen diffusion on stepped platinum surfaces.     

Adsorption and dissociation of carbon trioxide on Ag(100)

Using density functional theory methods, we have studied carbon trioxide, its adsorption and dissociation on Ag(100). In the gas phase, two isomers are found, D_3h and C_2v, with the latter of 2.0 kcal mol^?1 lower in energy at the PW91PW91/6?31G(d) level. For CO₃ on Ag(100), the calculated adsorption energy is 91.2 and 89.1 kcal mol^?1 for the bi‐coord perpendicular and tri‐coord parallel structures, respectively. Upon the adsorption, 0.50 ～ 0.56 electron is transferred from silver to CO₃, indicative of significant ionic characters of the adsorbate‐surface bonding. In addition, the geometry of CO₃ is largely changed by its strong interaction with silver. For CO_3(ad) → O_(ad) + CO_2(gas), the energy barrier is calculated to be 19.8 kcal mol^?1 through the bi‐coord path. The process is endothermic with an enthalpy change of +17.3 ～ +26.7 kcal mol^?1 and the weakly chemisorbed CO₂ is identified as an intermediate on the potential energy surface. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Adsorption of phenylphosphonic acid on GaAs (100) surfaces

The adsorption of phenylphosphonic acid (PPA) on GaAs (100) surfaces from solutions in acetonitrile/water mixtures was studied using Fourier transform infrared spectroscopy in attenuated total reflection in multiple internal reflections (ATR/MIR), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and atomic force microscopy (AFM). ATR/MIR in situ showed that the accumulation of PPA molecules near the GaAs surface increased with the water concentration in the solution. For water contents lower than 4%, ATR/MIR and XPS results are consistent with the formation of a low-density monolayer. A mechanism is proposed for H2O percentages lower than 4% involving the creation of interfacial bonds through a Br?nsted acid-base reaction, which involves the surface hydroxyl groups most probably bound to Ga. It was found that the morphology of the final layer depended strongly on the water concentration in the adsorbing solution. For water concentrations equal to or higher than 5%, the amount of adsorbed molecules drastically increased and was accompanied by modifications in the infrared spectral region corresponding to P-O and P=O. This sudden change indicates a deprotonation of the acid. XPS studies revealed the presence of extra oxygen atoms as well as gallium species in the layer, leading to the conclusion that phosphonate and hydrogenophosphonate ions are present in the PPA layer intercalated with H3O+ and Ga3+ ions. This mechanism enables the formation of layers approximately 10 times thicker than those obtained with lower H2O percentages. HREELS indicated that the surface is composed of regions covered by PPA layers and uncovered regions, but the uncovered regions disappeared for water contents equal to or higher than 5%. XPS results are interpreted using a model consisting of a monolayer partially covering the surface and a thick layer. This model is consistent with AFM images revealing roughness on the order of 7 nm for the thick layer and 0.2-0.5 nm for the thin layer. Sonication proves to be an effective method for reducing layer thickness.     

Adsorption of trisilylamine on the Si(100) surface

Adsorption of trisilylamine (TSA) on the Si(100) surface has been studied using temperature programmed desorption (TPD) and time‐of‐flight electron stimulated desorption (TOFESD). TPD spectra exhibit the presence of three desorption states denoted by β₁, β₂, and β₃ associated with the presence of a mono‐, di‐, and tri‐hydride state respectively. This behavior is identical with previously observed desorption studies resulting from atomic hydrogen adsorption, indicating that the nitrogen species in the adsorbate has minimal impact on the surface structure of the hydride. Preliminary electron irradiation studies are reported and indicate that the formation of a thin silicon nitride layer is induced as a result of the irradiation. Copyright © 2008 John Wiley & Sons, Ltd.     

洁净和氧吸附的Cu(100)表面重构的理论研究

The interaction of atomic oxygen with the clean Cu(100) surface has been studied by means of cluster and periodic slab models density functional theory in the present paper. The Cu(4,9,4) cluster and a three-layer slab with c(2×2) structure are used to model the perfect Cu(100) surface. Three possible adsorption sites,top, bridge and hollow site, were considered in the calculations. The predicted results show that the hollow site is the prefer site for atomic oxygen adsorbed on Cu(100) surface energetically. This is in good agreement with the experiment. The calculated binding energies are respective 2.014, 3.154 and 3.942 eV for top, bridge and hollow sites at mPW1PW91/LanL2dz level for the cluster model. The geometry of Cu(100) surface has also been optimized theoretically with various density functional methods and the results show that the prediction from the B3PW91/LanL2dz and mPW1PW91/LanL2dz reproduce the experimental observation.The frontier molecular orbitals and partial density of states analysis show that the electron transfer from the d orbital of substrate to the p orbital of the surface oxygen atom.     

NO在氧预吸附Ir(100)表面吸附和解离的第一性原理研究

采用第一性原理密度泛函理论和周期性平板模型研究了NO在O预吸附Ir(100)表面的吸附和解离, 并考察了预吸附的O对可能产物N₂, N₂O和NO₂的选择性的影响. 优化得到反应过程中初态、 过渡态和末态的吸附构型, 并获得反应的势能面信息. 计算结果表明, NO在O预吸附表面最稳定的吸附位是桥位, 其次是顶位. 桥位和顶位的NO在表面存在两条解离通道, 即直接解离通道和由桥位和顶位扩散到平行空位, 继而发生N-O键断裂生成N原子和O原子的解离通道. 此分离机理与洁净表面上NO解离机理相同, 但后一种解离方式优于前一种, 是NO在表面上解离的主要通道. 预吸附的O原子在不同程度上抑制了NO的解离, 导致桥位和顶位NO解离互相竞争. 在O预吸附Ir(100)表面, N₂气是唯一的产物, 不会有副产物N₂O和NO₂的生成, 与实验结果一致. 预吸附的O在N/O低覆盖度下几乎不影响N₂气的生成, 但在较高覆盖度下则促进了N₂气的生成.     

氢在Mg_2Ni(100)面的吸附及扩散

运用第一性原理研究氢在清洁和掺杂Al的Mg2Ni(100)面的吸附及扩散.在清洁Mg2Ni(100)表面,氢原子可稳定地吸附于Mg-Ni桥位和Mg-Mg桥位,吸附能为1.19-1.52eV.在掺杂Al的Mg2Ni(100)表面,氢原子可稳定吸附于Al-Ni、Mg-Ni、Mg-Al桥位,吸附能为0.10-0.29eV.氢在掺杂Al的Mg2Ni(100)表面的吸附能低于其在清洁表面的吸附能,说明掺杂Al后氢原子与表面的相互作用减弱.过渡态计算结果表明,氢原子由清洁的Mg2Ni(100)面及掺杂Al的Mg2Ni(100)面扩散至次表层的势垒分别为0.59及-0.04eV,掺杂Al后氢原子的扩散势垒降低,说明氢原子更易由掺杂Al表面扩散至次表层.Al原子替代Mg2Ni(100)面的Mg原子减弱氢原子与表面的相互作用,降低氢原子由表层扩散至次表层的势垒,这可能是Mg2Ni合金掺杂Al可改善其吸氢动力学性能的主要原因之一.     

N2分子在UO（100）表面的吸附与解离

运用密度泛函理论中广义梯度近似(GGA)的VWN-BP方法结合周期性平板模型,研究N2在UO(100)表面的吸附.研究表明,N2平行吸附在UO(100)表面穴位为最稳定吸附构型,吸附能为79.0 kJ·mol-1.Mulliken布居分析显示,N2获得电子.吸附后,N-N伸缩振动频率发生红移.波数在1770-2143 cm-1之间.态密度分析表明,U原子将df电子转移至N2的2π轨道.计算所得解离反应的能垒为266.9 kJ·mol-1.     

甲醇在FeS2(100)完整表面的吸附和分解

采用基于第一性原理的密度泛函理论结合周期平板模型方法, 研究了甲醇分子在FeS₂(100)完整表面的吸附与解离. 通过比较不同吸附位置的吸附能和构型参数发现: 表面Fe位为有利吸附位, 甲醇分子通过氧原子吸附在表面Fe位, 吸附后甲醇分子中的C―O键和O―H键都有伸长, 振动频率发生红移; 甲醇分子易于解离成甲氧基CH3O和H, 表面Fe位仍然是二者有利吸附位. 通过计算得出甲醇在FeS₂(100)表面解离吸附的可能机理: 甲醇分子首先发生O―H键的断裂, 生成甲氧基中间体, 继而甲氧基C―H键断裂, 得到最后产物HCHO和H₂.     

氮在含氧Mo(100)面上的吸附与反应

 用HREELS, AES, LEED和TDS考察了氮在含氧Mo(100)上的吸附和热脱附. 120 K下氮在含氧Mo(100)上吸附时存在着N—N伸缩振动频率2150和1600 cm-1, 分别对应于线式(γ态)和侧位(α态)两种分子吸附态. 升温引起γ态氮的脱附和α态氮的解离. 其中γ态氮的脱附峰温位于155 K, 遵循一级脱附动力学; 由α态解离生成的N原子占据Mo(100)的四重空位(即β态), 并在高于1?150 K的温度重新化合形成氮而脱附. 120 K时,氮的吸附是无序的; 吸附了氮的表面经1100 K退火后生成了有序的c(2×2)-N表面结构.     

Rh（100表面乙醇吸附与分解的HREELS研究

利用热脱附谱和高分辨能量损失谱技术研究了乙醇在Ｒｈ（１００）表面的吸会和分解过程，结果表明，１３０时Ｒｈ（１００）面暴露乙醇，表面首先形成化学附层，随乙醇暴露增加，表面出现多层凝聚态，表面升温至１５０Ｋ，吸附乙醇从Ｒｈ（１００）表面脱附，同时部分化学吸附乙醇分子发生羟基断裂，生成表面乙氧基，进一步升谩，表面乙氧基脱氢分解，其分解的主要途径是发生甲基脱氧，β－Ｃ与表面发生作用，生成一种含氧的金属有机     

Adsorption of HF and HCl on the beta-AlF3 (100) surface

The current study employs hybrid-exchange density functional theory to investigate the adsorption of HF and HCl to under-coordinated Al ions on the beta-AlF(3) (100) surface. It is shown that the geometries of the adsorbates are strongly dependent on coverage. Furthermore, the adsorption of HCl leads to a number of distinct structures that have very similar energies. It is proposed that this result may explain the high catalytic activity of aluminium fluoride and aluminium chloro-fluoride surfaces towards chlorine-fluorine exchange reactions. The stretching and bending frequencies of the H-F and H-Cl bonds at half and full monolayer coverage are also calculated and the vibrational spectrum is found to be strongly dependent on the adsorption site and the coverage. The vibrational frequency shifts provide, therefore, a mechanism for experimentally characterising these surfaces.     

基于第一性原理研究铱(111)和(100)表面的原子吸附（英文）

本文利用第一性原理密度泛函理论研究了九种不同的吸附原子在铱(Ir)的(111)和(100)表面上的吸附性质.探讨了Ir表面的功能化,因此吸附能、稳定的结构、态密度和磁矩,这将为进一步研究其在催化和其他表面应用中的可能展现的功能提供重要信息.研究表明,三/四重空位点是Ir(111)/(100)表面最有利的吸附位点.通过对大范围的覆盖率(从0.04到1个单层)的研究,表明吸附原子的吸附能具有很强的覆盖率依赖性.吸附能随着覆盖率的增加而增加,这意味着吸附物之间存在排斥相互作用.吸附原子和衬底电子态之间的强杂化会影响吸附性质,同时吸附原子的磁矩被抑制.通过Bader电荷分析,揭示了吸附原子和衬底之间的大量电荷转移.与(111)表面的结合相比,(100)表面吸附原子的结合更强.     

Adsorption of 3-pyrroline on Si(100) from first principles

The chemisorption of 3-pyrroline (C(4)H(7)N) on Si(100) is studied from first principles. Three different structures can be realized for which, depending on the temperature, the chemisorption process is facile (for two of them it is essentially barrierless); among these configurations the most favored one, from a thermodynamical point of view, is a dissociated structure obtained through an exothermic reaction characterized by the formation of a N-Si bond and a H-Si bond in which the H atom is detached from the molecule. Several other chemisorption structures are possible which, however, require overcoming a significant energy barrier and often breaking multiple bonds. A number of reaction paths going from one stable structure to another have been investigated. We have also generated, for the two basic adsorption structures, theoretical scanning tunneling microscopy images which could facilitate the interpretation of experimental measurements, and we propose a possible reaction mechanism for nitrogen incorporation.     

甲醇在清洁和氧预吸咐Pd（100）面上的吸咐与分解

用高分辨电子能量损失谱（ＨＲＥＥＬＳ），热脱咐谱（ＴＤＳ）在１４０Ｋ—７００Ｋ温度范围内研究了清洁和氧改性Ｐｄ（１００）面上ＣＨ_３ＯＨ的吸咐与分解机理。ＨＲＥＥＬＳ结果表明：在１４０Ｋ吸咐甲醇能形成分子吸咐层；当加热甲醇分子层时，甲醇在１８５Ｋ先分解为ＣＨ_３Ｏ_（ａｄ）和Ｈ_（ａｄ），在２００Ｋ以上温度ＣＨ_３Ｏ_（ａｄ）逐步分解为ＣＯ_（ａｄ）和Ｈ_（ａｄ）；预吸咐氧后表面有甲酸物种生成。ＴＤＳ研究表明；除有少量甲醇在１８５Ｋ脱咐外，甲醇分解的主要脱咐产物为Ｈ_２（３２０Ｋ）和ＣＯ（４４０Ｋ）；次要脱附产物为甲烷（２００Ｋ—２１０Ｋ）。综合ＨＲＥＥＬＳ和ＴＤＳ研究指出，在清洁表面甲醇主要通过Ｏ—Ｈ键断裂，经甲氧基中间物种分解为ＣＯ和Ｈ_２，还有部分甲醇通过Ｃ—Ｏ键断裂分解为甲烷，预吸附氧后甲醇的分解除了存在以上两种方式外，氧的存在一方面能够转移ＣＨ_３Ｏ_（ａｄ）中的氢原子在表面形成一定量的甲酸中间物种，另一方面能够稍许提高少量ＣＨ_３Ｏ_（ａｄ）的热稳定性。