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.     

Mixed pseudo-potential approach to the on-top chemisorption of atomic hydrogen on the (100) silver surface

A mixed pseudo-potential approach in which the Ag atoms interacting directly with the adsorbate are treated by dealing explicitly with their 11 valence electrons whereas the remaining atoms are treated as one-electron atoms proves to be satisfactory with respect to the case in which all atoms are treated as 11-electron atoms. This approach permits, on the one hand, an easier interpretation of the results obtained and, on the other hand, the possibility of extending the model without being forced to carry out expensive calculations.The results for the Ag₅H and Ag₉H systems show that the same interactions are present in the two models, leading to nearly identical values for the adsorbate-surface distance, the vibrational frequency of the adsorbate perpendicular to the surface, and the net charge on the adatom.     

Surface enhanced infrared absorption observed with attenuated total reflection (ATR-SEIRA): modeling the optical response

The gain in sensitivity due to Surface Enhanced Infrared Absorption (SEIRA) when analyzing an adsorbate on a metal island film was calculated for the ATR configuration under full consideration of the anisotropy of the film. Modeling the islands as spheroids coated with the dielectric adsorbate leads to such extraordinarily high refractive indices and low absorption indices as experimentally observed and to an enhancement of the absorption bands of the coating. Simulation of the ATR reflectance indicated further enhancement as a result of the optical properties of the island film. The predicted total level of enhancement was about one order of magnitude superior to what commonly is found in experiments. This was attributed to percolation of the metal islands which almost inevitably occurred in practice: the resulting lateral conductivity was found to have a strongly decreasing effect on the enhancement.     

Surface enhanced infrared absorption observed with attenuated total reflection (ATR-SEIRA): modeling the optical response

The gain in sensitivity due to Surface Enhanced Infrared Absorption (SEIRA) when analyzing an adsorbate on a metal island film was calculated for the ATR configuration under full consideration of the anisotropy of the film. Modeling the islands as spheroids coated with the dielectric adsorbate leads to such extraordinarily high refractive indices and low absorption indices as experimentally observed and to an enhancement of the absorption bands of the coating. Simulation of the ATR reflectance indicated further enhancement as a result of the optical properties of the island film. The predicted total level of enhancement was about one order of magnitude superior to what commonly is found in experiments. This was attributed to percolation of the metal islands which almost inevitably occurred in practice: the resulting lateral conductivity was found to have a strongly decreasing effect on the enhancement. Received: 23 December 1997 / Revised: 9 March 1998 / Accepted: 15 March 1998     

Selected properties of Pt(111) modified surfaces: A DFT study

Density functional theory calculations were employed to investigate the electronic properties of a Pt(111) surface modified with foreign atoms. The effects of alloying platinum with molybdenum, palladium, and tin changed the interaction between adsorbate orbital and metal d band. This letter discusses the interaction between metal atoms and adsorbate and its influence on electronic structure rearrangement of the species—changes that must be taken into account to explain the behavior of catalytic systems and sensors. Mo/Pt(111) and Sn/Pt(111) exhibited lower susceptibility to poisoning by CO, compared with pure platinum. Both Pt-based materials are expected to find utility in electrodes for alcohol and hydrogen oxidation.     

Adsorption of small molecules on helical gold nanorods: A relativistic density functional study

We study the adsorption of a variety of small molecules on helical gold nanorods using relativistic density functional theory. We focus on Au₄₀ which consists of a central linear strand of five gold atoms with seven helical strands of five gold atoms on a coaxial tube. All molecules preferentially adsorb at a single low‐coordinated gold atom on the coaxial tube at an end of Au₄₀. In most cases, there is significant charge transfer (CT) between Au₄₀ and the adsorbate, for CO and NO₂, there is CT from the Au₄₀ to adsorbate while for all other molecules there is CT from the adsorbate to Au₄₀. Thus, Au₄₀‐adsorbate can be described as a donor–accepter complex and we use charge decomposition analysis to better understand the adsorption process. We determine the adsorption energy order to be C₅H₅N >NO₂ > CO > NH₃ > CH₂?CH₂ > CH₂?CH? CHO > NO > HC?CH > H₂S > SO₂ > HCN > CH₃OH > H₂C?O > O₂ > H₂O > CH₄ > N₂. We find that the Au? C, Au? N, Au? S, and Au? O bonds are surprisingly strong, with clear implications for reactivity enhancement of the adsorbate. The Au? H bond is relatively weak but, for interactions via an H atom that is bonded to a carbon atom (e.g., CH₄), we find that there is large charge polarization of the Au? H? C moiety and partial activation of the inert C? H bond. Although the Au? S and Au? O bonds are generally weaker than the Au? C and Au? N bonds, we find that adsorption of H₂S or H₂O causes greater distortion of Au₄₀ in the binding region. However, the degree of distortion is small and the helical structure is retained, demonstrating the stability of the helical Au₄₀ nanorod under perturbations. © 2014 Wiley Periodicals, Inc.     

Effects of adsorbate molecules on the quadrupolar interaction of framework aluminum atoms in dehydrated zeolite H,Na-Y

The effect of adsorbate molecules on the quadrupolar interaction of framework aluminum atoms with the electric field gradient in dehydrated zeolite H,Na-Y has been studied by (27)Al MAS NMR and (27)Al MQMAS NMR spectroscopy at magnetic fields of 9.4 and 17.6 T. Upon adsorption of molecules interacting with bridging OH groups by hydrogen bonds (acetonitrile and acetone), the quadrupole coupling constant of framework aluminum atoms was found to decrease from 16.0 MHz (unloaded zeolite) to 9.4 MHz. Adsorption of molecules, which cause a proton transfer from the zeolite framework to the adsorbates (ammonia and pyridine), reduces the quadrupole coupling constant to 3.8 MHz for coverages of 0.5-2 molecules per bridging OH group. The experiments indicate that the quadrupole coupling constant of framework aluminum atoms in dehydrated zeolite H,Na-Y reflects the chemical state of adsorbate complexes formed at bridging OH groups. In agreement with earlier investigations it was found that a proton affinity of the adsorbate molecules of PA = 812-854 kJ/mol is necessary to induce a proton transfer from the zeolite framework to the adsorbed compounds. This proton transfer is accompanied by a strong improvement of the tetrahedral symmetry of zeolitic framework AlO(4) tetrahedra and a decrease of the electric field gradient.     

Surface modification of III–V semiconductors: chemical processes and electronic properties

The possibilities of controlling the surface electronic properties of III–V semiconductors by varying the adsorption chemistry are analyzed. Variations of the adsorption process parameters and the adsorbate reactivity are able to affect the surface atomic and electronic structure of the semiconductor. The adsorbate reactivity is considered within the framework of the density functional theory using the reactivity indices. The easiest way to affect the reactivity of a particular adsorbate is to create a solvation shell around it, as is possible in both liquid solutions and the gas phase (microsolvation). Solvation of ions before their adsorption by different solvents affects considerably the relative nucleophility of the central atom in the ion, which results in a different charge transfer mechanism from the surface states on adsorption, and thus, in a different modification of the surface electronic structure of the semiconductor. The effect of halogen, sulfur and metal atoms reactivity on the electronic structure of the resulting adsorbate-covered surface of III–V semiconductor is discussed.     

Atomic-Scale Insights into Electrode Surface Dynamics by High-Speed Scanning Probe Microscopy

Atomic-scale processes at electrode surfaces in liquid electrolytes are central elemental steps of electrochemical reactions. Detailed insights into the structure of these interfaces can be obtained with in situ scanning tunnelling and atomic force microscopy. By increasing the time resolution of these methods into the millisecond range, highly dynamic processes at electrode surfaces become directly observable. This review gives an overview of in situ studies with video-rate scanning probe microscopy techniques. Firstly, quantitative investigations into the dynamic behaviour of individual adsorbed atoms and molecules are described. These reveal a complex dependence of adsorbate surface diffusion on potential and co-adsorbed species and provide data on adsorbate–adsorbate and adsorbate–substrate interactions in a liquid environment. Secondly, results on collective dynamic phenomena are discussed, such as molecular self-assembly, the dynamics of nanoscale structures, nucleation and growth, and surface restructuring due to phase-formation processes.     

O2 dissociative adsorption on the Cu‐, Ag‐, and W‐doped Al(111) surfaces from DFT computation

The O₂ adsorption and dissociation on M‐doped (M = Cu, Ag, W) Al(111) surface were studied by density functional theory. The adsorption energy of adsorbate, the average binding energy and surface energy of Al surface, and the doping energy of doping atom were calculated. All the doped atoms can be stably combined with Al atoms, while being slightly embedded in the surface to a certain depth. The TOP‐type surfaces are the most stable doped surfaces for O₂ adsorption, which is related to the orbital hybridization between the adsorbate and the surface atoms, the electronegativity, and the orbital energy level of the doping atoms. Moreover, the O atoms and doping atoms contribute significantly to the density of states (DOS), especially the O‐p orbital electrons and the d orbital electrons of doping atoms. The degree of O₂ dissociation is related to the doping atoms on Al surfaces, and the doping atoms actually resist the dissociation of O₂. W atoms have the best resistance effect on the O₂ dissociation as compared with Cu and Ag atoms, especially W‐1NN surface, which has both large barrier energy and reaction energy.     

Condensed phase photoelectron asymmetry

Large directional asymmetries were observed in photoelectron distributions from core and valence levels in metals and adsorbate atoms. Intensities varied by factors up to 25 as the angle between A and p was varied. The energy dependence of asymmetry showed atomic behavior similar to that expected for free atoms, modified for the tendency p∥A.     

On the role of d electrons in chemisorption and catalysis on transition metal surfaces

A new model is proposed for the role of the d electrons in chemisorption and catalysis on transition metal surfaces. In this model, the d electrons remain localized on the atoms and do not participate in forming dsp hybrid bonds with the adsorbate. However, electrons in doubly-occupied d orbitals can be promoted to anti-bonding or non-bonding valence orbitals. These additional electronic configurations help increase the binding energy of the adsorbate and help stabilize reaction intermediates. This effect is enhanced by spatial rotation of the singly-occupied d orbitals which become perpendicular to the adsorbate. The singly-occupied d orbitals are also able to recouple their spins during the reaction, allowing the reaction to proceed on otherwise forbidden reaction paths.     

On the structure of bilayer condensed phases confined between crystalline walls of triangular symmetry

Grand canonical ensemble Monte Carlo simulation method is used to study the structure of Lennard-Jones fluids confined between the parallel walls, formed by the (111) planes of the face centered cubic crystal. Thin slit pores with a width allowing for the formation of only two atomic layers are considered. It is shown that the structure of confined solidlike phases is very sensitive to the pore width, the misfit between the size of adsorbate atoms and the size of surface lattice, as well as the corrugation of the surface potential. In particular, when the misfit between the adsorbate atoms and the surface lattice is very small, even a weakly corrugated surface potential highly stabilizes solidlike phases of triangular symmetry. On the other hand, in the case of large misfit the packing effects become a dominating factor and lead to the appearance of solidlike phases of different structures and symmetries.     

Effects of nonideal adsorption on the surface of a liquid stationary phase in gas chromatography. The degree of freedom restriction

Based on the concept that the properties of the surface of liquids applied onto solid supports in gas-liquid chromatography differ from those of an ideal flat adsorbent, the effects of the fine structure of the surface of a nonpolar liquid (microscopic protrusions formed by the end atoms) on the freedom of motion and the steric factor of the adsorbate molecule were considered.     

Second-harmonic generation and effect of adsorbates for free-electron metal and semiconductor surfaces

We discuss aspects of a developing microscopic theory of SHG from simple metal and semiconductor surfaces. For semiconductors calculations of the dynamical nonlinear susceptibility on the basis of realistic tight-binding parametrizations of the electronic Hamiltonian provide a practical scheme. In the resulting spectra the effect of the dangling bonds on SHG is clearly seen together with a strong decrease upon saturation with H atoms. In the metal case the adsorbate induced changes of the static nonlinear electron density can be calculated self-consistently by applying density functional theory to the jellium model. The second-order dipole moment determines the effect of adsorbates on the SHG intensity in the adiabatic limit. Quite general a correlation with the nature of the adsorbate expressed by its electronegativity and the characteristic charge transfer, adsorption dipole and polarizabilities in first and second order is found.     

Analysis of the linear tension of two-dimensional droplets on heterogeneous adsorbents

A procedure for analyzing the formation processes of two-dimensional droplets of an adsorbate on a rigid adsorbent support is considered. The molecular theory is based on data on the potential functions between adsorbent atoms and adsorbate molecules. Interactions between nearest neighbors are considered in the quasi-chemical approximation. The internal motions of adsorbent atoms and adsorbate molecules are ignored. Problems of describing the formation of droplets on heterogeneous adsorbents are associated with calculations for binodals (illustrated with the simplest example of two different homogeneous crystal faces) due to the choice of methods for calculating linear tension and the structural model of the region of the liquid–vapor transition. The dependence of the characteristics of droplets in the layered structural model on the method for determining the reference lines of the tension is shown for their metastable and equilibrium states. It is found that for a number of structural parameters, the thermodynamic determination of the line of tensions of metastable droplets can result in nonmonotonic dependences of the linear tension on their radii. The characteristics of two-dimensional liquid–vapor interfaces are compared for two structural models: coordination sphere and layered. It is found that the coordination sphere model allows the exclusion of the structural parameter of the layered model, but both models need refinement at small radii.     

Experimental and theoretical surface enhanced Raman scattering study of 2-amino-4-methylbenzothiazole adsorbed on colloidal silver particles

The adsorption of 2-amino-4-methylbenzothiazole (2-AMBT) on colloidal silver particles has been investigated by a surface enhanced Raman scattering (SERS) study. The SERS spectra of the 2-AMBT molecule at varied adsorbate concentrations recorded in different time domains are compared with its Fourier transform infrared (FTIR) spectrum and normal Raman spectrum (NRS) in the bulk and in solution. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using ab initio restricted Hatree-Fock (RHF) and density functional theory (DFT) calculations. The most favorable adsorptive sites of the 2-AMBT molecule have been estimated by natural population analysis (NPA) using the above-mentioned high level of theories. The enhancement of the in-plane modes together with the appearance of Ag-N stretching frequency at 215 cm(-1) indicates that the 2-AMBT molecule is adsorbed on the silver surface through the lone pair electrons of both nitrogen atoms with the molecular plane nearly vertical to the surface.     

The chemisorption of carbon monoxide on Ni(110) studied by electron energy loss spectroscopy

The vibrational spectrum of carbon monoxide chemisorbed on Ni(110) at 300K has been recorded as a function of surface coverage. At low and intermediate coverage the adsorbate is bonded either to single nickel atoms (linear site) or to two nickel atoms in contact (B₂ site). As the coverage approaches unity the spectrum changes rapidly until at saturation virtually all adsorbed molecules are of B₂ type.     

Comparison of the periodic slab approach with the finite cluster description of metal–organic interfaces at the example of PTCDA on Ag(110)

We present a comparative study of metal–organic interface properties obtained from dispersion corrected density functional theory calculations based on two different approaches: the periodic slab‐supercell technique and cluster models with 32–290 Ag atoms. Fermi smearing and fixing of cluster borders are required to make the cluster calculation feasible and realistic. The considered adsorption structure and energy of a PTCDA molecule on the Ag(110) surface is not well reproduced with clusters containing only two metallic layers. However, all clusters with four layers of silver atoms and sufficient lateral extension reproduce the adsorbate structure within 0.04 Å with respect to the slab‐supercell structure and provide adsorption energies of ( 0.08 eV) consistent with the slab result of −4.47 eV. Thus, metal–organic adsorbate systems can be realistically represented by properly defined cluster models. © 2018 Wiley Periodicals, Inc.     

2-氯噻吩在 Rh(111) 表面吸附的密度泛函理论研究

 采用密度泛函理论探讨了 2-氯噻吩分子在 Rh(111) 表面上吸附行为. 结果表明, 平行的 hol 位及 bridge 位上的吸附最稳定. 吸附后, 2-氯噻吩键长发生明显变化, 分子平面被扭曲, 分子中 C–H(Cl, S) 相对于金属表面倾斜上翘. 垂直吸附模式不如平行吸附模式稳定, 但吸附后噻吩环未发生变形. hol 及 bridge 吸附模式下 2-氯噻吩的芳香性已遭破坏, 噻吩环上的碳原子呈现准 sp3 杂化. 在平行的 hol 位吸附后, 2-氯噻吩环累计得到 0.77 个电子, 而 Rh(111) 表面累计失去 1.19 个电子.