Cu(100)表面CO分子单层膜的原子结构

利用第一性原理研究了覆盖度分别为1.00, 0.50和0.25 ML时CO分子单层膜在Cu(100)表面的吸附系统. 计算表明CO分子对不稳定. 获得了CO分子单层膜在虚拟Cu(100)表面的原子结构, 以及CO分子单层膜在Cu(100)表面吸附系统的原子结构. 当CO分子单层膜在Cu(100)表面的三个吸附位吸附, 覆盖度为1.00 ML时, 顶位和桥位都稳定, 而空心位不稳定; 覆盖度为0.50和0.25 ML时, 三个吸附位都稳定.比较吸附前后CO分子单层膜的原子结构, 可知CO分子和Cu(100)表面的相互作用强于CO分子单层膜之间的相互作用. 关键词： CO分子单层膜 自组装 CASTEP Cu(100)     

On the structure of CO adlayers on Cu(100) and Cu(111)

Alternative models for the high coverage compressed overlayers of CO on copper (100) and (111) are proposed in which the LEED patterns previously attributed to out-of-registry, uniformly compressed structures are re-interpreted in terms of adsorption on linear and bridged sites. The models provide a simpler explanation for the small influence of compression on the frequency of the infrared adsorption bond near 2000 cm^?1 compared with the large change of surface potential.     

Angle-resolved polarization-dependent photoemission from Cu(100) and Cu(111): experiment and theory

Experimental angle-resolved photoemission spectra from Cu(111) and Cu(001) excited by linearly polarized light (21.2 eV) are compared with intensity results calculated by the “one step model” theory. Good overall agreement is obtained both for s- and p-polarized light assuming a classical macroscopic radiation field inside the crystal.     

Chemisorption of CO on Cu(100), Ag(110) and Au(110)

The adsorption of CO on Cu, Ag and Au is studied using core and valence photoemission, X-ray absorption and autoionization of core excited states. The purpose is to investigate the nature of the adsorption bond starting out from the well-established chemisorption system CO/Cu(100)-c(2 × 2), and from the results we suggest that CO forms chemisorbed phases also on Ag(110) and Au(110). The photoemission spectra show strong shake-up satellites both for the valence levels and the core levels. The separation to the satellite appearing closest to the main line is observed to follow the position of the substrate d-band relative to the Fermi level. The CO adsorption strength for the noble metals is deduced to decrease in the order Cu-Au-Ag. This is based on the widths of the XA resonances, which are related to the adsorbate-substrate interaction strength of the core excited states, and the relative shake-up intensities, which are expected to increase with a decreasing adsorption strength in the ground state. The same trends regarding the shake-up intensities are observed both for the valence and core levels.     

洁净和氧吸附的Cu(100)表面重构的理论研究

在密度泛函理论下,计算了清洁和吸附氧原子的Cu(100)表面的驰豫和优势吸附构型。结果表明,氧原子在金属表面采用四重穴位时,具有最大的结合能,顶位吸附时结合能最小,桥位吸附时结合能居间。这一计算结果与实验报道一致。各种密度泛函方法的比较后,发现采用mPW1PW91密度泛函和LanL2dz赝势基组,能够准确给出与实验相符的计算结果。平板模型计算的分态密度图显示,在吸附过程中出现d轨道向Fermi能级移动并越过Fermi能级,而O原子的p轨道能级远离Fermi能级,表明有电子从铜原子的d轨道转移到氧原子的2p轨道,簇模型和平板模型的布居分析显示表面氧带有约0.65～0.7 e的负电荷。研究表明,采用适当的基组和泛函方法,即使采用簇模型来模拟表面,也可以获得与实验比较吻合的计算结果。     

Esdiad from CO on W(100): Evidence for non-vertically adsorbed CO

Mass-discriminating measurements of the angular distributions of electron-stimulated ion desorption (ESDIAD) from CO adsorbed on W(100) and coadsorbed with C and O have been performed. The O⁺ beams indicate normal and off-normal (by 5 to 13°) desorption which is interpreted as due to CO molecules bound in symmetric and in two types of unsymmetric bridges. Preadsorption of C suppresses the vertical state, while oxidation of the surface suppresses the off-normal states.     

Reduced stretch vibration frequency for CO on Na covered Cu(100)

When Na is coadsorbed with CO on Cu(100), EELS show a peak at around 0.17 eV loss energy in addition to the peak at 0.26 eV which is characteristic of CO on Na-free Cu(100). The low energy peak is ascribed to CO molecules adsorbed near Na atoms. The appearance of both the shifted and unshifted loss peaks demonstrates the local nature of the alkali-CO interaction for the present system.     

Cluster modelling of core electron photoabsorption of CO adsorbed on Cu(100)

Quantum chemical calculations of discrete and continuum near-edge X-ray absorption spectra of carbon monoxide adsorbed on Cu(100) are presented and discussed. The surface is modelled by clusters using one-electron effective core potentials for distant atoms, allowing cluster sizes up to 50 atoms to be treated. The employed theoretical approach, the direct, atomic orbital, static exchange technique, implementing the independent-particle approximation close to the basis set limit, is shown to provide good representations of the near edge X-ray absorption spectra both for free and adsorbed CO. The experimental observations of reduction of energy and intensity of the first π1 resonance and a compression of the discrete part of the spectra are reproduced by the calculations. The origin of these effects is discussed.     

Collective vibrational modes in isotopic mixtures of CO adsorbed on Cu (100)

Isotopic mixtures of CO adsorbed on Cu(100) have been studied by infrared spectroscopy. For mixtures of ¹²C¹⁶O/¹²C¹⁸O at a constant coverage of 0.5 it was found that the molecules constitute a collective vibrational system. The C-O stretching vibrations were studied as a function of composition of the overlayer and the data are successfully interpreted by a dipole — dipole coupling theory.     

Metastable (2S) helium atom scattering from NiO(100) and Cu(100) surfaces

The scattering of metastable 2³S He atoms (He*) from cleaved NiO(100) as well as from clean and CO-covered Cu(100) surfaces has been studied. For these varied surfaces, which were characterized in situ by ground state He atom scattering, only broad He* angular distributions without any diffraction peaks were observed. For metastable He atoms scattered from the clean Cu(100) surface a total survival probability of 1×10⁻⁶ was determined. For NiO(100) and the CO-covered Cu(100) surface values of about 1×10⁻⁵ were obtained. Time-of-flight spectra of the surviving He* atoms revealed a substantial energetic broadening which increases with the substrate temperature. This behaviour indicates a large well depth for the He*–surface interaction potential and is discussed in terms of an enhanced multiphonon excitation and/or trapping probability upon the scattering.     

Explosive production of CO2 from (NO + CO)/Pd(100)

Explosive CO₂ production followed by the gradual N₂ production has been observed by TDS as a result of the NO-CO reaction on the Pd(100) surface which does not reconstruct. The location and width of the CO₂ desorption peak have been found to be almost independent of the total coverage. For this autocatalytic reaction, the vacancy requirement model is considered to be valid. Change in the CO₂ production by varying the NO coverage (with the CO coverage fixed) has been also studied, from which information on the island formation is derived.     

The chemisorption of CO on Cu(100) studied with angle resolved photoelectron spectroscopy

Using angle resolved UV photoelectron spectroscopy, coupled with the continuum of polarized light available with synchrotron radiation, we make an interpretation of the photoelectron spectrum of CO adsorbed on Cu(100). We point out that the bonding of CO on Cu as observed by photoemission is considerably different from the bonding of CO on Ni. These differences do not seem to be caused by bonding orientation differences, however, as the CO molecular axis is found to be very close to the surface normal, as was the case for CO on Ni(100). No evidence is found for a second phase of CO on Cu(100).