Surface corrugation effects on the adsorption dynamics of xenon on Pt(110)−(1 × 2)

The adsorption probability of xenon on Pt(110)(1 × 2) shows a strong dependence on both the polar (θ_i) and aximuthal angles of incidence. For atoms incident along the (11̄0) direction the adsorption probability increases slowly with increasing angle of incidence, scaling as E_i, cos^0.5θ, whereas along the (100) azimuth it decreases with increasing angle of incidence, exhibiting “negative” energy scaling. The hard cube washboard model does not account quantitatively for these differences with a single consistent set of parameters.     

Ethylene adsorption on Co/Pt(110)(1 × 2) surfaces

Ethylene adsorption has been followed by TDS on Pt(110)(1 × 2) surfaces covered with various amounts of cobalt atoms, including the multilayer range. A peculiar behaviour is found below 2.10 × 10¹⁵ cobalt atoms/cm²: partial desorption of ethylene low temperature replaces decomposition. The behaviour of bulk polycristalline cobalt is found above this coverage.     

How atoms move in the (1 × 1) to (1 × 2) surface reconstruction of fcc (110) planes

The result of a recent study of atomic steps in the (1 × 1) to (1 × 2) surface reconstruction of Pt and Ir (110) planes using ns pulsed-laser heating can only be understood by highly correlated jumps of atoms within a small [110] atom-row. We argue in favor of a simultaneous jump of the entire small [110] row of atoms, possibly stimulated by surface phonon waves propagating in the direction normal to, and also parallel to, the atom-row direction. Surface reconstruction of fcc (110) planes evolves with long-range atomic diffusion, thus the transition occurs relatively slowly. Reconstruction of fcc (001) planes evolves with short-range atomic movements, and the transition occurs very rapidly.     

Lattice dynamics of the si(111) surface: folding effects in the 2×1 structure

We report a bond-charge-model calculation for Si(111):H(1×1). This configuration may be assumed to represent the “ideal” (1×1) surface, as long as the saturation of the dangling bonds by H atoms produces a slight perturbation of the dynamical matrix. We display also the geometric folding of these dispersion curves into the (2×1) configuration and compare our results to recent He scattering data and “ab initio” calculations. Thus we are in the position to discuss which dynamical features of the 2×1 pattern arise from the mere folding of the (1×1) pattern and which are due to the physical changes produced by the specific reconstruction.     

Resonant scattering of He-atoms from missing-row reconstructed Pt(110)1 × 2: comparison of theory and experiment

Close coupled channels calculations concerning the angular dependence of the specular beam were performed on the basis of the He/Pt(110)1 × 2 interaction potential, which we previously derived by analyzing a large number of He-diffraction intensities. The excellent agreement with experimental data obtained for several wavelengths confirms the reliability of the potential form and depth and allows proper assignment of resonant scattering features and thus secure determination of the bound state levels.     

Site-specific core level spectroscopy of CO and NO adsorption on Pt(110)(1×2) and (1×1) surfaces

The adsorption of CO and NO on the (1×2) and (1×1) modifications of the Pt(110) surface was studied by x-ray photoemission spectroscopy, LEED and work-function change measurements. The O(1s) binding energy of adsorbed CO is site-specific and differentiates between on-top and bridge adsorbed species. CO adsorption on Pt(110)(1×2) at 120 K occurred sequentially into on-top and bridge sites yielding an orderedc(8×4) layer at the maximum coverage. At 300 K only on-top bonded CO was present after CO adsorption on the (1×2) surface. CO adsorption on the (1×1) surface at 120 K showed a transient bridge adsorbed CO and on-top CO at saturation, with an ordered (2×1)p1g1 LEED pattern. Heating the (2×1)p1g1 CO layer to 400 K also showed this transient bridge CO species. Work function changes generally correlated with the appearance of different CO species but were complex in detail. The findings for CO adsorption are consistent with the missing row model of the (1×2) surface.Parallel data for NO adsorption on (1×2) and (1×1) surfaces at 120 K were less informative than those for CO because O(1s) spectra showed single broad peaks. Peak contributions due to bridge and on-top bonded NO could be estimated.     

Many-body effects in the Si(111)7×7 reconstructed surface

A two-dimensional Hubbard Hamiltonian is introduced in order to analyse the many-body effects associated with a dangling bond Si(111) 7×7 surface state located at the Fermi energy. Our results indicate that many-body effects can offer an explanation of recently reported experimental data.     

A scanning tunneling microscopy investigation of the 1 × 2 ⇌ 1 × 1 structural transformation of the pt(110) surface

Lifting of the reconstruction of the clean Pt(110) surface under the influence of adsorbed CO proceeds at 300 K through homogeneous nucleation of small holes (with about 10 × 10 Ų size). At 350 K more correlated displacements of [110] strings take place, a characteristic shared with the reverse process, namely the restoration of the 1× 2 phase after desorption.     

Reentrant mechanism for associative desorption: H2/Pt(110)-(1×2)

Calculations of the desorption of hydrogen from Pt(110)-(1×2), a surface used to model nanoparticle edge sites, show the activation energy varying strongly with hydrogen coverage, from 0.8 to 0.3?eV. The predicted temperature programed desorption spectra agree well with experiments, but the formation of the hydrogen molecules occurs only at two types of sites on the surface even though three peaks are observed. The lowest and highest temperature peaks result from desorption from the same strong binding sites at the ridge, while desorption from the weakest binding trough sites is insignificant.     

Adsorption of CO and H2 on Pt(110)(1 × 2) studied by photoemission of adsorbed xenon (PAX)

The adsorption of hydrogen and carbon monoxide on Pt(110)(1 × 2) at 97 K has been studied by photoemission of adsorbed xenon (PAX). For both species, it appears that adsorption takes place first in the valleys between the microfacets of this reconstructed surface. Only when these sites are saturated, does adsorption take place on other sites (microfacets or ridges) of the surface.     

The effect of the sulfur induced reconstruction of the Pt(S)−[6(111) × (100)] surface on CO adsorption

The effect of the sulfur induced reconstruction of the Pt(S)−[6(111) × (100)] surface on CO adsorption was investigated using thermal desorption spectroscopy (TDS). On the unreconstructed surface, desorption states are observed from the (111) terraces and from the high coordinate step edge site. Following the sulfur induced reconstruction of the surface, a new desorption state, ascribed to the upper (100) plane of the two atom high step is observed. Lateral repulsive interactions between S and CO are found to affect the desorption energy on the (111) terrace and the upper face of the (100) step edge. SuIfurCO or COCO interactions do not affect the CO desorption energy from the high coordinate step edge site. Suppression of each CO desorption state appears to be due to sulfur site blocking, as sulfur coverage is increased.     

Low temperature oxidation of Fe2+ surface sites on the (2 × 1) reconstructed surface of α-Fe2O3(011­2)

Temperature programmed desorption (TPD), electron energy loss spectroscopy (ELS) and low energy electron diffraction (LEED) were used to study the interaction of molecular oxygen with the (2 × 1) reconstructed surface of hematite α-Fe₂O₃(011­2) under UHV conditions. The (2 × 1) surface is formed from vacuum annealing of the ‘ideal’ (1 × 1) surface and possesses Fe²⁺ surface sites based on ELS. While O₂ does not stick to the (1 × 1) surface at 120 K, the amount of O₂ that can be reversibly adsorbed at 120 K on the (2 × 1) surface was estimated to be ～ 0.5 ML (where 1 ML is defined as the Fe³⁺ surface coverage on the ideal (1 × 1) surface), with additional O₂ that is irreversibly adsorbed based on subsequent H₂O TPD. Molecularly and dissociatively adsorbed O₂ modifies the surface chemistry of H₂O both in terms of enhanced OH stability (relative to either the (1 × 1) or (2 × 1) surfaces) and in the blocking of H₂O adsorption sites. While O₂ adsorption at 120 to 300 K does not transform the (2 × 1) surface into the (1 × 1) surface, the influence of O₂ on the (2 × 1) surface involves both charge transfer from surface Fe²⁺ sites and formation of an ordered c(2 × 2) structure resulting from O₂ dissociation.     

The growth of Ag films on a TiO2(110)-(1×1) surface

We report here the growth of Ag film and its thermal stability on the TiO₂(1 1 0)-(1×1) surface using combination techniques of low-energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED). At a surface temperature as low as 125 K, a 2D growth of Ag films seems to occur for submonolayer coverages up to ∼0.8 ML. Annealing of low temperature grown Ag films to 500 K for coverage of 1–2.4 ML would result in the formation of metastable Ag layers with rest of Ag forming 3D needle-like islands on top of this Ag film.     

High-resolution study of dipole-active vibrations at the Ag(110) (n × 1)O surface

Atomic chemisorption of oxygen on Ag(110) at room temperature has been studied by high resolution electron energy loss spectroscopy (HREELS). It is well known that upon increasing exposure the LEED pattern sequentially changes as (n × 1), with n = 7, 6, ⋯ 2. We present the first dear evidence that the oxygen vibration frequency changes from (ω⊥ = 38.5 meV (n = 7) to 40.9 meV (n = 2). Simultaneously the surface phonon observed on Ag(110) at 13.2 meV shifts to 17.0 meV (at n = 2) and a second phonon appears at lower energies (8.7 meVatn = 2). We discuss implications of our data for the formation of the (n × 1) added row structure.     

Structural,electronic and magnetic properties of the Mn-Ni(110) c(2×2) surface alloy

<正>Using first-principles total energy method,we study the structural,the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy.Paramagnetic,ferromagnetic,and antiferromagnetic surfaces in the top layer and the second layer are considered.It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases.The buckling of the Mn-Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26 A(1 A=0.1 nm) and the weak rippling is 0.038 A in the third layer,in excellent agreement with experimental results.It is proved that the magnetism of Mn can stabilize this surface alloy.Electronic structures show a large magnetic splitting for the Mn atom,which is slightly higher than that of Mn-Ni(100) c(2×2) surface alloy(3.41 eV) due to the higher magnetic moment.A large magnetic moment for the Mn atom is predicted to be 3.81μB.We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate,which confirms the experimental results.The magnetism of Mn is identified as the driving force of the large buckling and the work-function change.The comparison with the other magnetic surface alloys is also presented and some trends are predicted.