CO adsorption on alkali-metal covered Ni(100)

The effect of preadsorbed alkali metal atoms Na, K and Cs on CO adsorption on Ni(100) has been studied using Auger spectroscopy and thermal desorption. It was found that the presence of alkali metals causes an appearance of several more tightly bound states in the CO thermal desorption spectra. The observed difference in carbon and oxygen Auger peak line shape on a bare and alkali modified Ni(100) is indicative that the presence of alkali adatoms induces CO decomposition on the Ni(100) surface. The fraction of dissociated CO increases with the amount of alkali adatoms present. At the same overlayer coverage the dissociation probability increases in the sequence Na, K, Cs. A comparison of the strength of the promoting effect on CO dissociation with the changes in the surface electron density in the presence of alkali adatoms has shown that at low overlayer coverages the electronic factor plays a major role in explaining the action of the surface modificators.     

CO adsorbed on a Xe covered Cu(100) surface studied by infrared spectroscopy

When a Cu(100) surface covered by a full Xe monolayer is exposed to CO at 60 K no infrared absorption associated with the CO vibration is observed. If the temperature is increased to 90 K, when the Xe atoms are desorbed, the ordinary CO spectrum develops. This observation can be explained, if the CO molecules on the Xe covered surface are oriented on the average with their molecular axes parallel to the surface.     

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)     

Infrared intensity enhancement of the CN stretch of HCN by coadsorbed CO on the Cu(100) surface

Reflection absorption infrared spectra reveal a strong enhancement in the intensity of the CN stretch in a mixed ordered overlayer of HCN and CO on the Cu(100) surface. Various combinations of HCN and CO isotopomers show that the intensity enhancement decreases with increasing frequency difference between nu(CN) and nu(CO). The intensity of the 2092 cm(-1) band of H12C14N is enhanced by a factor of 155+/-20 through coupling to the 2077 cm(-1) band of 12C16O. A simple two-state coupling model explains the isotopomer dependence of the degree of enhancement.     

Unusually low stretching frequency for CO adsorbed on Fe(100)

For CO adsorption on Fe(100) different adsorption species are detected with high resolution EELS (electron energy loss spectroscopy) which sequentially fill in with increasing coverage. Up to ～ 350 K and low CO exposure (≦1 L), a predominant molecular species with an unusually low stretching frequency, 1180–1245 cm^?1, is detected. This unusual CO bond weakening is consistent with a “lying down” binding configuration of CO. For higher CO coverages at 110 K, further CO adsorption states with vibrational frequencies of 1900–2055 cm^?1 are populated which are due to CO bound with the molecular axis perpendicular to the surface.     

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.     

Theoretical investigation of image states of hydrogen covered Cu(100)

A model for atomic hydrogen covered Cu(100) is presented and the calculated energy spectrum of localized electronic states in the X gap of Cu(100) is discussed. These states form a series of unoccupied adsorption states (for n = 2,3,…) lying below the vacuum level V₀ and having energies E_n which satisfy the formula E_n = V₀−10/n²eV. The lowest state (n = 1) is expected to lie about 5.5 eV below the Fermi level.     

XPS and XAES study for oxidation of V/Cu(100) and V,Na/Cu(100) surfaces

Oxidation states of vanadium overlayers ( 0.1 to 2.0 ML) on a Cu(100) surface with and without sodium on the surface were investigated by XPS and XAES. The vanadium overlayers gave a V₂O₃-like surface oxide after exposure up to 600 L O₂, showing a chemical shift of the V2p_3/2 peak by 3.5 eV without coverage dependence. The surface vanadium oxide was easily oxidized further to V⁵⁺ to give a chemical shift of 5.5 eV after addition of sodium atoms on the oxide and heating at 530 K for 5 min. The high oxidation state was interpreted by a mixing of vanadium oxide and oxidized sodium. This mixing is affirmed by spectral changes showing a separation of sodium ions from the oxide during the formation of sodium acetate by adsorption of acetic acid.     

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.     

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.     

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.     

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).     

Radio frequency magnetron sputtered epitaxial Cu2ZnSnS4 thin film on ZnS(100)

Heteroepitaxial growth of kesterite Cu₂ZnSnS₄ (CZTS) thin film on cubic ZnS(100) single crystal substrate was achieved by radio frequency magnetron sputtering from a single CZTS target. An optimal substrate temperature in the range of 470–500 °C is found suitable for this epitaxial growth. The growth of CZTS was confirmed to be along a‐axis. The sputtered CZTS thin film is homogeneous throughout the whole film. The band gap of the film is found to be approximately 1.51 eV, i.e., promising for high efficiency thin film solar cells.

     

Dissociation of CO on Mo(100)

LEED and Auger spectroscopy have been used to obtain the superficial carbon density on a carburized Mo(100) surface. Using this calibration procedure, comparison is made between the carburization and the adsorption of CO. The results are consistent with the dissociation of the (β-CO phases; using this assumption the adsorption kinetics of CO on Mo(100) is reinterpreted.     

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.