Short Bridge Site Research Articles

Single-Molecule Vibrational Spectroscopy and Inelastic-Tunneling-Electron-Induced Diffusion of Formate Adsorbed on Ni(110)

We have investigated the inelastic-tunneling-electron-induced vibrational excitation of single formate (HCOO− and DCOO−) molecules adsorbed on Ni(110) using a low-temperature scanning tunneling microscope (STM). Formate molecules adsorbed on the long-bridge site can be moved laterally along [11̅0] by the injection of tunneling electrons from the STM tip. Using an isotope-labeled molecule, the diffusion probability and distance were found to be enhanced significantly when the applied voltage reaches the energies of specific vibrational modes, that is, C−H bending and C−H stretching modes. Inelastic electron tunneling spectroscopy based on STM (STM-IETS) and scanning tunneling spectroscopy was used to identify the vibrational and electronic state of a single formate molecule adsorbed at different sites. The STM-IETS spectrum of formate adsorbed at the short-bridge site exhibited a broad peak at 80 mV and a sharp resonance peak at 360 mV. The former peak is assigned to the electronic states generated by the metal−molecule hybridization; the latter peak is assigned to the C−H stretching mode. The STM-IETS spectrum of formate adsorbed at the long-bridge site showed features similar to those of formate adsorbed at the short-bridge site, but the intensity of the broad peak appearing at near the Fermi level was markedly suppressed, indicating a weak metal−molecule interaction.

Cluster and periodic DFT calculations of adsorption of hydroxyl on the Au( h k l) surfaces

Adsorption of hydroxyl on the Au(1 1 0), Au(1 0 0), and Au(1 1 1) surfaces has been investigated by means of density functional based methods and cluster models and periodic slabs. According to the cluster models, the optimized results indicate that the use of different functional has an indistinct effect on the equilibrium geometry, but adsorption energies computed by different exchange–correlation functionals may differ up to 0.8 eV. At the B3LYP level, the final structures of adsorbed OH are upright and the preferred modes for its adsorption onto the Au(1 1 0), Au(1 0 0), and Au(1 1 1) surfaces are the short-bridge site with an adsorption energy of −1.96 eV, the bridge site (−1.79 eV), and the hollow hcp site (−1.25 eV), respectively. According to the periodic calculations, the final (OH) ads structures are in a few cases more tilted as compared to the cluster model data, as well as giving a different preferred adsorption site for the Au(1 1 1) surface ( i.e.: the bridge site). Furthermore, the stability order of adsorption gathered on the three surfaces, i.e.: Au(1 1 0) > Au(1 0 0) > Au(1 1 1), is in accord with experimental reports and in concordance with the decreasing of the coordination number of the gold atoms in each surface. Finally, periodic calculations carried out for the stepped Au(3 2 1) surface reveal that adsorption of OH is more favorable on the bridge between the Au(1 1 1) and Au(1 0 0) microfacets, and its adsorption energy is higher than on the low-index surfaces.

Adsorption and Organization of the Organic Radical 3-Carboxyproxyl on a Cu(110) Surface: A Combined STM, RAIRS, and DFT Study

We report on a combined experimental and theoretical study of the adsorption of the paramagnetic organic radical 2,2,5,5-tetramethyl-3-carboxypyrrolidine nitroxide (3-carboxyproxyl, 3CP) on a Cu(110) surface. Information from scanning tunneling microscopy (STM), reflection absorption infrared spectroscopy, and periodic density functional theory (DFT) calculations reveals important insights into the nature of the molecule−metal interface. We find that the molecule is robustly anchored to the surface via the formation of two Cu−O bonds between the carboxylate functionality and specific short-bridge adsorption sites on the Cu(110) surface. The adsorbed organic radicals appear in STM as discrete entities on the surface and can be imaged with submolecular resolution. We observe a tendency for local 2D ordering. Importantly, 3CP molecules adopt a preferred site, dictated by the strong interaction of the carboxylate groups and the steric repulsion of the methyl groups with the surface which orient the molecular ...

First-principles studies of the oxygen adsorption on unreconstructed and reconstructed Ni(1 1 0) surfaces

First-principles calculations have been performed to investigate the adsorption of oxygen on unreconstructed and reconstructed Ni(1 1 0) surfaces. The energetics, structural, electronic and magnetic properties are given in detail. For oxygen adsorption on unreconstructed surface, ( n × 1 ) ( n = 2 , 3 ) substrate with oxygen atom on short-bridge site is found to be the most stable adsorption configuration. Whereas energetically most favorable adsorption phase of reconstructed surface is p ( n × 1 ) substrate with oxygen atom located at long-bridge site. Our calculations suggest that the surface reconstruction is induced by the oxygen adsorption. We also find there are redistributions of electronic structure and electron transfer from the substrate to adsorbate. Our calculations also indicate surface magnetic moment is enhanced on clean surfaces and oxygen atoms are magnetized weakly after oxygen adsorption. Interestingly, adsorption on unreconstructed surface does not change surface magnetic moment. However, adsorbate leads to reduction of surface magnetic moment in reconstructed system remarkably.

Remarkably long-ranged repulsive interaction between adsorbed CO molecules on Pt modified Ge(001)

We have studied the adsorption of CO molecules on a Pt modified Ge(001) surface at 77 K. The CO molecules preferentially adsorb on the self-organized Pt chains rather than on the terraces. We have identified two different adsorption sites at 77 K: one either on the short-bridge site or on top of one of the atoms of a buckled Pt dimer, and the other one on the long-bridge site in between two Pt dimers. The CO molecules are mobile at room temperature but immobile at 77 K. A statistical analysis of the nearest-neighbor spacing of the CO molecules reveals that adsorbed CO molecules interact repulsively along the Pt-dimer chains. This repulsive interaction, composed of electrostatic terms and a strain-mediated term, gradually fades away over, for simple molecules, a remarkably long distance of 3--4 nm.

Ab-initio pseudopotential study of electronic structure and chemisorption of oxygen on aluminium surface

Chemisorption of oxygen atom on aluminium (1 1 1), (1 1 0) and (1 0 0) surfaces is studied using ab- initio plane wave pseudopotential method based on density functional theory (DFT). Oxygen atom chemisorbed on three different high symmetry sites; top, short-bridge and hollow sites on the aluminium surfaces are examined. It has been found that the O-adatom adsorbed at the hollow site on aluminium (1 1 1), (1 1 0) and (1 0 0) plane yield energetically most stable structure. Calculation of chemisorption energies of O-adatom on aluminium surfaces shows that oxygen is most strongly bound to aluminium atoms on Al(1 1 1) plane and the calculated value of the chemisorption energy of O-adatom at the hollow site on Al(1 1 1) surface is 4.8 eV. In this work, the chemisorption energies calculated for O-adatom on Al(1 1 0) and Al(1 0 0) surfaces are reported for the first time. The electronic structures and the electronic charge density distributions of the oxygen chemisorbed aluminium surfaces are also investigated. Calculations show that for aluminium, p orbitals also contribute significantly along with the s orbitals during the bond formation with oxygen atom. Therefore, the possibilities of hybridizations lead to the strong bonding configurations.

DFT and RAIRS Investigations of Methanol on Cu(110) and on Oxygen-Modified Cu(110)

The adsorption and subsequent reaction of methanol on Cu(110) and on the oxygen stripe phase on Cu(110) was investigated using reflection absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD) and density functional theory (DFT) calculations. It was shown that during high methanol exposures water can coadsorb and it is incorporated into the methanol rows formed in the chemisorbed layer. The RAIR spectra of adsorbed methanol are very similar with and without coadsorbed oxygen. This is due to the fact that the ν(CO) vibration is at the same frequency for both methanol and methoxy adsorbed in the more stable short-bridge site. However, methoxy adsorbed in the long-bridge site shows the ν(CO) vibration at lower wavenumbers and is found with increasing surface temperature. With coadsorbed oxygen the reaction products are formaldehyde, H2, and CO2. DFT and RAIRS results suggest that the intermediate leading to CO2 is an η2-formaldehyde and OH species on the surface, rather than formate.

Atomic adsorption on the (020) surface ofα−Pu: A density functional study

Adsorption of atomic carbon, nitrogen, and oxygen on the (020) surface of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$ has been investigated using the full-potential linearized augmented-plane-wave plus local basis method. The Perdew-Burke-Ernzerhof exchange-correlation functional is used and the surface is modeled by a four-layer periodic slab consisting of a total of $32\phantom{\rule{0.3em}{0ex}}\mathrm{Pu}$ atoms. Adsorption energies have been optimized with respect to the distance of the adatom from the Pu surface for four adsorption sites, namely, the onefold top, onefold hollow, twofold short-bridge, and the twofold long-bridge sites. To investigate the effects of spin-orbit coupling on the adsorption process, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling (NSOC) and one at the fully relativistic level with spin-orbit coupling (SOC). The short-bridge site was the most stable adsorption site for C, with chemisorption energies of 5.880 and $6.038\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at the NSOC and SOC levels of theory, respectively. The long-bridge site was the most stable adsorption site for N and O, with chemisorption energies at the NSOC and SOC levels of theory, respectively, being 5.806 and $6.067\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for N and 7.155 and $7.362\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for O. The respective distances of the C, N, and O adatoms from the surface for the most stable adsorption sites were found to be 1.32, 1.26, and $1.35\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Our results show that SOC adsorption energies are more stable than NSOC adsorption energies in the $0.14--0.32\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range. The work function and net spin magnetic moments, respectively, increased and decreased in all cases upon chemisorption compared to the bare surface. The local density of states and difference charge densities have been used to analyze the interaction between the adatoms and the substrate.

Combinedab initioand LEEDI∕Vstudy of submonolayer adsorption of In on W(110)

The atomic structure of various indium adlayers at submonolayer coverages on W(110) is investigated by a density functional theory (DFT) approach as well as by analysis of low-energy electron diffraction intensities (LEED $I∕V$). Single-atom adsorption is studied by DFT, with the result that adsorption at the pseudo-fourfold coordinated sites of the W(110) is most preferable, followed by bonding to the pseudo-threefold and twofold short-bridge sites. Both theory and experiment reveal that for the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure, which corresponds to a coverage of 0.33 monolayer (ML), indium atoms occupy exclusively pseudo-fourfold coordinated sites, while for the $(1\ifmmode\times\else\texttimes\fi{}4)$ phase (0.75 ML coverage) and $(1\ifmmode\times\else\texttimes\fi{}5)$ phase (0.80 ML coverage), pseudo-threefold and twofold short-bridge sites are also occupied. According to DFT, the $(1\ifmmode\times\else\texttimes\fi{}4)$ structure is the most stable one, closely followed by the $(1\ifmmode\times\else\texttimes\fi{}5)$ structure. Analysis of DFT studies on free monolayers of In reveals the significant influence of In-In bonding on the formation of these adlayer structures. The low-coverage $(3\ifmmode\times\else\texttimes\fi{}1)$ structure is energetically the least favorable one, in agreement with the experimental finding that the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure is only metastable and transforms with increasing time or upon annealing into islands of $(1\ifmmode\times\else\texttimes\fi{}4)$ patterns. In order to investigate whether the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure might be stabilized by contaminants, DFT calculations were also performed for coadsorbing hydrogen and oxygen with indium on W(110). However, the $(3\ifmmode\times\else\texttimes\fi{}1)$ structure always remains metastable. Furthermore, we find that phase separated regions of oxygen patches and $(1\ifmmode\times\else\texttimes\fi{}4)$ In islands are stabilized by about $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$/atom relative to mixed $(3\ifmmode\times\else\texttimes\fi{}1)$ $\mathrm{In}+\mathrm{O}$ configurations. This is in very good agreement with the experimental observation that the $(3\ifmmode\times\else\texttimes\fi{}1)\ensuremath{\rightarrow}(1\ifmmode\times\else\texttimes\fi{}4)$ transition can be triggered by additional oxygen.

Interaction of carbon dioxide with Ni(110): A combined experimental and theoretical study

We present a combined experimental and theoretical study of the CO2 interaction with the Ni(110) surface. Photoelectron spectroscopy, temperature-programmed desorption, and high-resolution electron energy loss spectroscopy measurements are performed at different coverages and for increasing surface temperature after adsorption at 90 K with the aim to study the competing processes of CO2 dissociation and desorption. Simulations are performed within the framework of density functional theory using ab initio pseudopotentials, focusing on selected chemisorption geometries, determining the energetics and the structural and vibrational properties. Both experimental and theoretical vibrational frequencies yield consistent indications about two inequivalent adsorption sites that can be simultaneously populated at low temperature: short-bridge site with the molecular plane perpendicular to the surface and hollow site with the molecular plane inclined with respect to the surface. In both sites, the molecule has pure carbon or mixed oxygen-carbon coordination with the metal and is negatively charged and bent. Predicted energy barriers for adsorption and diffusion on the surface suggest a preferential adsorption path through the short-bridge site to the hollow site, which is compatible with the experimental findings. Theoretical results qualitatively support literature data concerning the increase of the work function upon chemisorption.

Hopping Motion and Reaction of a Single Water Molecule on Cu(110)

The authors studied the isolated water molecules and hydroxyl species on Cu(110) using a low-temperature scanning tunneling microscope (STM). A water molecule adsorbs on top of Cu atom and thermally hops along the atomic row at 6 K. The migration is also induced by STM via the excitation of molecule-substrate vibration. An isolated hydroxyl species, produced by dissociating a water molecule with the STM, adsorbs at the short-bridge site with its axis inclined along [001]. The orientation was found to be dynamically flipped, wherein substantial isotope effect was observed in the rate.

Ab initiostructural and electronic analysis ofCH3SHself-assembled on a Cu(110) substrate

Ab initio Density Functional Theory calculations are here reported to characterize the adsorption of methanethiol at the Cu110 surface. Theoretical results suggest that the binding of the adsorbate to the substrate is rather weak and the molecular geometry is correspondingly almost unaffected by the adsorption. Otherwise, when CH3SH deprotonates producing methanethiolate, a stronger chemical bond is realized between the sulfur atom of CH3S radical and Cu surface atoms. A detailed study of structural and electronic properties of methanethiolate on Cu110 for a p2 2 and a c2 2 overlayer structure has been carried out. We find that, in the most stable configuration, the molecule adsorbs in the shortbridge site. The chemical bond arises due to a strong hybridization among p orbitals of sulfur and d states from the substrate, as it is deduced by an analysis of partial densities of states and charge densities.

A theoretical study of hydrogen adsorption and diffusion on a W(1 1 0) surface

We have used density functional theory to investigate hydrogen adsorption and diffusion on a W(1 1 0) surface. Hydrogen adsorption structures were examined from low coverage to one monolayer, and a threefold hollow site was found to be the most stable site at all coverages. In contrast to previous assertions, the work function decrease is not due to electron transfer from the hydrogen atoms to the W surface, but due to electron depletion at the vacuum region above the hydrogen atoms. Hydrogen atoms can diffuse via short-bridge sites and long-bridge sites at a coverage of θ = 1.0. Although the calculated activation energy for hydrogen diffusion via a short-bridge site is as small as 0.05 eV, field emission microscope experiments have shown that the activation energy for hydrogen diffusion is about 0.20 eV, which agrees fairly well with our calculated value of the activation energy via a long-bridge site. This discrepancy can be related to hydrogen delocalization on the W(1 1 0) surface, which has been suggested by electron energy loss spectroscopy experiments.

The Effect of Coadsorbed Oxygen on the Adsorption and Diffusion of Potassium on Rh(110): A First-Principles Study

The adsorption and diffusion of potassium and oxygen on Rh(110), as well as the co-adsorption of K and O and its effect on K diffusion, has been studied using periodic density functional theory (DFT) calculations (PW91-GGA). On both the non-reconstructed (1x1) and the missing-row (MR) reconstructed surfaces, O prefers the short bridge site at low coverage, with a binding energy of ca. -5.2 eV at 1/4 ML. At theta_O>1/2 ML O atoms occupy alternating threefold sites along the ridge and forms a zigzag pattern. Interaction with the ridge sites is enhanced by the MR reconstruction. K prefers to be in the trough, with a binding energy of -2.3 eV on the (1x1) surface and -2.9 eV on the MR surface at 1/8 ML. Thus the adsorption of both O and K at low to medium coverage promotes the MR reconstruction. The co-adsorption of K and O enhances the binding energy of K to a maximum of -3.6 eV at the highest oxygen coverage studied, 1-3/8 ML. Oxygen adsorption is also stabilized by K, though to a smaller extent on a per-O atom basis. On both surfaces, K prefers to diffuse in the [110] direction with a barrier of ca. 0.05more » eV. O diffusion also prefers the [110] direction on the MR surface but is not clearly anisotropic on the (1x1) surface. The barrier to O diffusion ranges from 0.6~0.8 eV depending on the coverage and reconstruction. In the presence of co-adsorbed O, the diffusion barrier of K tops out at ca. 0.12 eV, much lower than earlier estimates based on mean-field models. Possible reasons for this apparent contradiction are discussed.« less

Quantum states of a hydrogen atom adsorbed onCu(100)and (110) surfaces

Quantum states of a hydrogen atom adsorbed on $\mathrm{Cu}(100)$ and $\mathrm{Cu}(110)$ are studied theoretically. In calculating eigenenergies and wave functions of hydrogen atom motion, three-dimensional adiabatic potential energy surfaces (PESs) are constructed within density functional theory and the Schr\odinger equation for hydrogen atom motion on the PESs is solved by the variation method. The wave function on $\mathrm{Cu}(100)$ indicates a localized mode on the hollow (HL) site at the ground state. Wave functions of the first few excited states indicate vibrational modes on the HL site and suggest migration from an HL site to a neighboring HL site over the bridge (BR) site. In the case of $\mathrm{Cu}(110)$, the ground state wave function is spread from the short bridge (SB) site and to the pseudothreefold (PT) site. The first few excited states are vibrational modes centered at the SB and long bridge (LB) sites. The excited state wave function of the hydrogen atom motion on $\mathrm{Cu}(110)$ show isotope effects as follows. The fourth excited state wave function for the H atom motion shows a localized character on the LB site, and those for D and T atom motion show vibrational modes parallel to the surface. On the other hand, the fifth excited state wave functions for D and T atom motion show localized characters on the LB site and that for H atom motion shows a vibrational mode parallel to the surface. Our calculated eigenenergies of the hydrogen atom motion in excited states on $\mathrm{Cu}(100)$ and $\mathrm{Cu}(110)$ are fairly in agreement with their corresponding experimental findings.

Electronic and structural investigation of tetracene adsorbed on Ru(1010) surface

The electronic states of tetracene adsorbed on Ru (1010) surface as well as their adsorption sites and directions has been studied by using ultraviolet photoelectron spectroscopy (UPS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and scanning tunneling microscopy (STM). The UPS measurements show that the six peaks from the tetracene are 2.1, 3.5, 4.8, 6.0, 7.1 and 9.2 eV below the Fermi level. The ARUPS measurements suggest that the plane of tetracene molecule is parallel to the Ru(1010) surface. The STM image shows that the tetracene molecule is adsorbed on Ru (1010) surface with its longer axis lying in the direction of either ［0001］ or ［1210］. The adsorption structure was confirmed with an ab initio calculation based on density functional theory (DFT). The short-bridge site and the hollow site are the most favorable sites when the molecule has its longer axis oriewted along ［0001］ and ［1210］, respectively.

Quantum states of hydrogen (H, D, T) atoms on Cu(1 0 0) and (1 1 0) surfaces

We investigate the quantum mechanical behavior of adsorbed hydrogen (H, D, T) on Cu(1 0 0) and (1 1 0) surfaces. We construct potential energy surfaces (PESs) for the motion of the hydrogen H atom on Cu(1 0 0) and (1 1 0) surfaces within the framework of density functional theory. The potential energy takes a minimum value on the hollow site of Cu(1 0 0) and on the short bridge site of Cu(1 1 0). Moreover, we calculate the quantum states of hydrogen atom motion on these calculated PESs. The ground state wave function of the hydrogen atom motion is strongly localized around the hollow site on the Cu(1 0 0) surface. On the other hand, the ground state wave function of the hydrogen atom motion on Cu(1 1 0) is distributed from the short bridge site to two neighboring pseudo-threefold sites. We finally show isotope effects on the quantum states of the motion of hydrogen on both surfaces.

A theoretical investigation on Pt 3Sn(1 0 2) surface alloy and CO–Pt 3Sn(1 0 2) system

The adsorption properties of CO on experimentally verified stepped Pt 3Sn(1 0 2) surface were investigated using quantum mechanical calculations. The two possible terminations of Pt 3Sn(1 0 2) were generated and on these terminations all types of possible adsorption sites were determined. The adsorption energies and geometries of the CO molecule for all those sites were calculated. The most favorable sites for adsorption were determined as the short bridge site on the terrace of pure-Pt row of the mixed-atom-ending termination, atop site at the step-edge of the pure row of pure-Pt-ending termination and atop site at the step-edge of the pure-Pt row of the mixed-atom-ending termination. The results were compared with those for similar sites on the flat Pt 3Sn(1 1 0) surface considering the fact that Pt 3Sn(1 0 2) has terraces with (1 1 0) orientation. The LDOS analysis of bare sites clearly shows that there are significant differences between the electronic properties of Pt atoms at stepped Pt 3Sn(1 0 2) surface and the electronic properties of Pt atoms at flat (1 1 0) surface, which leads to changes in the CO bonding energies of these Pt atoms. Adsorption on Pt 3Sn(1 0 2) surface is in general stronger compared to that on Pt 3Sn(1 1 0) surface. The difference in adsorption strength of similar sites on these two surface terminations is a result of stepped structure of Pt 3Sn(1 0 2). The local density of states (LDOS) of the adsorbent Pt and C of adsorbed CO was utilized. The LDOS of the surface metal atoms with CO-adsorbed atop and of their bare state were compared to see the effect of CO chemisorption on the electron density distribution of the corresponding Pt atom. The downward shift in energy peak in the LDOS curves as well as changes in the electron densities of the corresponding energy levels indicate the orbital mixing between CO molecular orbitals and metal d-states. The present study showed that the adsorption strength of the sites has a direct relation with their LDOS profiles.

First principles study of H 2S adsorption and dissociation on Fe(1 1 0)

We report first principles density functional theory (DFT) results of H 2S and HS adsorption and dissociation on the Fe(1 1 0) surface. We investigate the site preference of H 2S, HS, and S on Fe(1 1 0). H 2S is found to weakly adsorb on either the short bridge (SB) or long bridge (LB) site of Fe(1 1 0), with a binding energy of no more than 0.50 eV. The diffusion barrier from the LB site to the SB site is found to be small (∼0.10 eV). By contrast to H 2S, HS is predicted to be strongly chemisorbed on Fe(1 1 0), with the S atom in the LB site and the HS bond oriented perpendicular to the surface. Isolated S atoms also are predicted to bind strongly to the LB sites of Fe(1 1 0), where the SB is found to be a transition state for S surface hopping between neighboring LB sites. The minimum energy paths for H 2S and HS dehydrogenation involve rotating an H atom towards a nearby surface Fe atom, with the S–H bonds breaking on the top of one Fe atom. The barrier to break the first S–H bond in H 2S is low at 0.10 eV, and breaking the second S–H bond is barrierless, suggesting deposition of S on Fe(1 1 0) via H 2S is kinetically and thermodynamically facile.

Adsorption geometry of C2H4 and C2H on Ni(110) surface

The favorite adsorption sites of ethylene (C2H4) and acetylide (CCH) on the Ni(110) surface are investigated by the theoretical calculation of the pseudo-potential plane-wave method. At low coverage the ethylene molecule occupies approximately the midway between the short-bridge and atop sites. The C-C axes of molecules are almost parallel to the ridges of the Ni atoms. The tilt angle of C-C axis relative to the Ni surface is about 12°. The C—C bond length is 0.147nm. At high coverage(0.5ML), ethylene molecules form a c(2×4) phase. The local adsorption sites of two ethylene molecules in a surface unit mesh are found to be quite similar to that at low coverage, but the C—C bond lengths are shorter than that in the case of the low coverage. The adsorption site of cetylide, decomposed from ethylene, is similar to that of the ethylene molecule on the surface, but there is a small displacement towards the atop site, the C—C bond length is 0.131nm, and the hydrogen atom bonds with the carbon a an atop site, the tilt angle of C-H axis relative to the Ni surface is about 45°.