High-resolution electron energy-loss spectroscopy of CO on an Ni(110) surface

High-resolution vibrational electron energy-loss spectra of CO on an Ni(110) surface were studied at 300 K with the in-situ combination of LEED, Auger electron spectroscopy and work-function change measurement. The observed peaks are at 436 cm^?1, 1855 cm^?1 (shifting to 1944 cm^?1 with increasing coverage) and at 1960 cm^?1 (shifting to 2016 cm^?1 with increasing coverage). The experimental results indicate that CO is adsorbed non-dissociatively at all coverages. Three adsorbed states of CO have been found. At fractional CO coverages less than θ ~ 0.9 where the disordered adsorbed structure dominates, CO is adsorbed in two inequivalent sites (short- and long-bridge sites) at random with its axis oriented perpendicular to the surface. At high coverages (θ > 0.9) where the (2 × 1) structure develops, our results indicate that the adsorbed CO molecules may occupy the distorted long-bridge sites forming zig-zag chains which lie essentially in the troughs of the (110) surface.     

Growth and ordering of CuO chains on Ag(110) surface

Growth of CuO chains and their ordering on Ag(110) surface were monitored by scanning tunneling microscopy (STM). When Cu atoms were deposited on a (2 × 1)AgO/Ag(110) surface at room temperature, the AgO chains in the [001] direction diminished and new strings of CuO grew along the [110] direction and yield a (2 × 2) p2mg ordering. When a Ag(110) surface with coexisting AgO and CuO chains was exposed to CO at room temperature, the AgO chains were selectively reduced.     

Adsorption behavior of iron phthalocyanine on a Ag（110） surface

An investigation on the growth behavior of FePc on a Ag(110) surface is carried out by using scanning tunneling microscopy(STM).At an FePc coverage of 3.5 ML,an ordered superstructure(densely packed) with a lateral shift is observed.The densely packed superstructure can be attributed to the substrate commensuration and the intermolecular van der Waals attractive interaction.The in-plane lateral shift in the superphase is specifically along the direction of [10] azimuth.The results provide a new perspective to understanding the intermolecular and the molecule-substrate interactions.     

Bipolaronic excitations of interacting electron(hole) gas in one-dimensional lattice model

By developing a diagonalization scheme we observe that the dynamics of interacting electrons or holes locally coupled to dispersionless phonon mode in one-dimensional lattice can be mapped into that of paired electron or hole states (bipolaronic states), which then gives a physically appealing picture of excitation modes of the interacting electron or hole gas. As a result, the bipolaronic model of the interacting electron or hole gas, obtained from Holstein–Hubbard Hamiltonian in one-dimensional lattice, exhibits normalization of the hopping terms and leads to a reduced effective mass of the bipolaron, which essentially gives support to the bipolaronic theory of high T_c superconductivity.     

The scattering of He from adsorbed layers of gases on Ag(110)

The adsorption of gases on Ag(110) has been studied using inelastic He atom scattering. Vibrational spectra have been obtained for Kr, Xe, C₂H₆, C₂H₄, CH₄, CF₄, CHF₃, CO₂ and H₂O. Spectra have also been obtained for multilayers of Xe (2 layers) and C₂H₆ (3 and 4 layers) where the energy changes move to lower values. The scattering from Kr and Xe can be shown to be dispersionless as has been previously found for these adsorbates on Cu(100) and Cu(110). The energy changes for Kr and Xe are smaller than on Cu surfaces and attempts were made to account for this based on an Einstein model of the adsorbed atoms in the surface holding potential.     

Surface magnetism of Fe(110) from polarized electron scattering

Exchange- and spin—orbit-induced scattering asymmetry spectra of polarized slow electrons from the ferromagnetic Fe(110) surface have been calculated by dynamical theory and found to agree with recent experimental data taken at room temperature. Comparison of exchange asymmetry spectra, obtained for various interaction and layer-dependent magnetization models, with the data implies firstly an enhancement of the surface magnetization by about 30% with respect to the bulk, and secondly the importance of spin-dependent localized inelastic electron—electron scattering processes.     

Structure analysis of an oxidized nickel (110) surface using low energy ion scattering

Low energy (6 keV) argon and neon ion scattering in the low angle mode (θ = 30°) has been used to investigate changes in the surface structure of a Ni(110) surface caused by the adsorption of oxygen at low exposures (10^?6 Torr s). The experimental energy spectra indicate that due to adsorption of oxygen, the interatomic distance in the 〈1̄10〉 direction increases while in the 〈001̄〉 direction this distance seems to decrease. This represents strong evidence that a reconstruction process is taking place during the early stages of oxidation of the Ni(110) face, in which the interatomic distances in the 〈1̄10〉 direction doubles. The oxygen atoms were found to lie in or close to the nickel 〈001̄〉 rows. These results are not in agreement with recently published dynamical LEED calculations.     

Chemisorption and surface reactivity of nitric oxide on clean and sodium-dosed Ag(110)

The chemisorption of NO on clean and Na-dosed Ag(110) has been studied by LEED, Auger spectroscopy, and thermal desorption. On the clean surface, non-dissociative adsorption into the α-state occurs at 300 K with an initial sticking probability of ～0.1, and the surface is saturated at a coverage of about $\text{1}\text{25}$. Desorption occurs without decomposition, and is characterised by an enthalpy of E_d ～104 kJ mol^?1 — comparable with that for NO desorption from transition metals. Surface defects do not seem to play a significant role in the chemistry of NO on clean Ag, and the presence of surface Na inhibits the adsorption of αNO. However, in the presence of both surface and subsurface Na, both the strength and the extent of NO adsorption are markedly increased and a new state (β₁NO) with E_d ～121 kJ mol^?1 appears. Adsorption into this state occurs with destruction of the Ag(110)-(1 × 2)Na ordered phase. Desorption of β₁NO occurs with significant decomposition, N₂ and N₂O are observed as geseous products, and the system's behaviour towards NO resembles that of a transition metal. Incorporation of subsurface oxygen in addition to subsurface Na increases the desorption enthalpy (β₂NO), maximum coverage, and surface reactivity of NO still further: only about half the adsorbed layer desorbs without decomposition. The bonding of NO to Ag is discussed, and comparisons are made with the properties of α and βNO on Pt(110).     

The adsorption of nitrogen dioxide on the Ag(110) surface and formation of a surface nitrate

The adsorption of NO₂ on the Ag(110) surface has been characterized by temperature programmed reaction spectroscopy and high resolution electron energy loss spectroscopy. At 95 K the NO₂ is dimerized to N₂O₄ in a multilayer and a distinct molecular layer, both of which desorb below 200 K. The first adsorption layer contains chemisorbed NO₂ and NO₃, the latter formed by a reaction between NO₂ and its decomposition products. Part of the NO₂ is molecularly chemisorbed via the oxygen atoms with a proposed symmetric bidentate geometry, desorbing at 270 K. Nitrogen dioxide also undergoes partial dissociation to nitrogen and oxygen adatoms. An NO₃ species is formed by the reaction of NO₂ with the oxygen adatoms produced from the partial dissociation of NO₂. The NO₃ is attached to the surface via one oxygen atom and has C_2v symmetry; it decomposes below 500 K. The geometry of both the chemisorbed NO₂ and NO₃ have analogues among inorganic metal complexes.     

Grazing incidence diffraction of keV helium atoms on a Ag(110) surface

Diffraction of fast atoms at grazing incidence has been recently demonstrated on the surface of alkali halides and wide band gap semiconductors, opening applications for the online monitoring of surface processes such as growth of ultrathin layers. This Letter reports energy resolved diffraction of helium on Ag(110) metal surface showing that a band gap is not mandatory to restrict the decoherence due to electron-hole pair excitations by the keV projectile. Measurement of the energy loss, which is in the eV range, sheds light on the scattering process.