Adsorption Height Research Articles

Structure of N2O monolayer on Ag surface

The first-principle technique has been employed to determine the atomic structure of nitrous oxide (N2O) monolayer and the N2O/Ag system in different coverage. The potential structures of N2O monolayer on the virtual and real Ag(100), Ag(110) and Ag(111) surfaces have been proposed. The stable structure is N2O monolayer adsorbed on Ag(110) through the terminal N atom in the top site with the coverage is 0.50 ML, which is not agree with experimental work done with NEXAFS of N2O on Ag(110). The structural parameters are as follow: the adsorption height is 2.37 Å, the angle between the N–N bond of the molecule and the substrate is 37°, the bond angle of absorbed N2O is 177°. The interaction between the monolayer and the Ag surface is weak, and the chemisorption energy and the adsorption height confirm the conclusion.

Adsorption geometry determination of single molecules by atomic force microscopy.

We measured the adsorption geometry of single molecules with intramolecular resolution using noncontact atomic force microscopy with functionalized tips. The lateral adsorption position was determined with atomic resolution, adsorption height differences with a precision of 3pm, and tilts of the molecular plane within 0.2°. The method was applied to five π-conjugated molecules, including three molecules from the olympicene family, adsorbed on Cu(111). For the olympicenes, we found that the substitution of a single atom leads to strong variations of the adsorption height, as predicted by state-of-the-art density-functional theory, including van der Waals interactions with collective substrate response effects.

Tuning and probing interfacial bonding channels for a functionalized organic molecule by surface modification

The potassium-induced missing row reconstruction of Ag(110) is used to selectively modify the local chemical interaction between the functional anhydride groups of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and Ag(110). We find a significant upward shift of the anhydride groups, while the adsorption height of the perylene core is essentially preserved. This demonstrates an attractive perylene/substrate interaction for PTCDA/K:Ag(110), elucidating also the bonding situation for the potassium-free system.

Adsorption of alkali, alkaline-earth, and 3dtransition metal atoms on silicene

The adsorption characteristics of alkali, alkaline earth and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon, are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, workfunction and dipole moment of the metal adsorbed silicene sheets. Alkali metals, Li, Na and K, adsorb to hollow site without any lattice distortion. As a consequence of the significant charge transfer from alkalis to silicene metalization of silicene takes place. Trends directly related to atomic size, adsorption height, workfunction and dipole moment of the silicene/alkali adatom system are also revealed. We found that the adsorption of alkaline earth metals on silicene are entirely different from their adsorption on graphene. The adsorption of Be, Mg and Ca turns silicene into a narrow gap semiconductor. Adsorption characteristics of eight transition metals Ti, V, Cr, Mn, Fe, Co, Mo and W are also investigated. As a result of their partially occupied d orbital, transition metals show diverse structural, electronic and magnetic properties. Upon the adsorption of transition metals, depending on the adatom type and atomic radius, the system can exhibit metal, half-metal and semiconducting behavior. For all metal adsorbates the direction of the charge transfer is from adsorbate to silicene, because of its high surface reactivity. Our results indicate that the reactive crystal structure of silicene provides a rich playground for functionalization at nanoscale.

Effect of van der Waals Interactions on the Adsorption of Olympicene Radical on Cu(111): Characteristics of Weak Physisorption versus Strong Chemisorption

We report the results of Olympicene radical (C19H11) adsorption characteristics on Cu(111) obtained within the density functional framework with and without the inclusion of self-consistent van der Waals (vdW) interactions to evaluate their effects. Our calculations suggest that the vdW interactions enhance the adsorption energies, and the degree of enhancement strongly depends on the implementation. Among the considered configurations, the highest adsorption energy calculated using PBE is found to be 0.24 eV, while those obtained with the inclusion of vdW interactions are 1.32 eV (rPW86), 1.91 eV (optPBE), 2.29 eV (optB88), and 2.65 eV (optB86b). The high energetic contribution obtained using the vdW interactions correlates with the changes in the adsorption heights (from 3.4 A (PBE and rPW86) to 2.24 A (optB86b)), the change in the structural integrity of Olympicene radical upon adsorption, and the changes in the surface electronic structure. Furthermore, our calculations reveal a net charge transfer of...

Adsorption height determination of nonequivalent C and O species of PTCDA on Ag(110) using x-ray standing waves

The normal incidence x-ray standing wave (NIXSW) technique is used to determine the adsorption geometry of submonolayer 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) adsorbed on the Ag(110) surface. An accurate analysis of both C1$s$ and O1$s$ photoemission (PE) spectra allows the respective adsorption heights of carbon and oxygen atoms in different chemical environments within PTCDA to be distinguished. Due to the intricacy of the PE fitting models, a systematic error analysis of NIXSW structural parameters was developed and employed. Based on the adsorption geometry of PTCDA on Ag(110) a bonding mechanism is discussed.

Methane adsorption on graphite(0001) films: A first-principles study

Using first-principles methods, we have systematically investigated the electronic density of states, work function, and adsorption energy of the methane molecule adsorbed on graphite(0001) films. The surface energy and the interlayer relaxation of the clean graphite(0001) as a function of the thickness of the film were also studied. The results show that the interlayer relaxation is small due to the weak interaction between the neighboring layers. The one-fold top site is found most favourable on substrate for methane with the adsorption energy of −133 meV. For the adsorption with different adsorption heights above the graphite film with four layers, the methane is found to prefer to appear at about 3.21 Å above the graphite. We also noted that the adsorption energy does not dependent much on the thickness of the graphite films. The work function is enhanced slightly by adsorption of methane due to the slight charge transfer from the graphite surface to the methane molecule.

First Principles Calculation on Adsorption of S on Fe(100) with Different Pressure

Using periodic density functional theory within the generalized-gradient approximation to electron exchange and correlation, we have studied S adsorption four-fold hollow site on Fe(100) in different hydrostatic pressure. We find that the adsorption height decreases with hydrostatic pressure increasing is non-monotonic. The adsorption energy decreases with an increase with pressure is monotonic and we have obtained density of states is almost unchanged, the adsorption energy change is mainly caused by lattice deformation in the hydrostatic pressure, and the adsorption energies increase linearly with pressure.

Comparative study of friction properties for hydrogen- and fluorine-modified diamond surfaces: A first-principles investigation

The van der Waals corrected first-principles approach within density functional theory has been performed to calculate the interaction energies and friction coefficients for hydrogen- and fluorine-terminated diamond film systems. Comparative studies show that the fluorine-terminated diamond film is more stable and chemically inert than that of hydrogen termination. The repulsive interactions between two fluorine-terminated diamond films are stronger than that of hydrogen termination system, and the former system has a larger equilibrium adsorption heights than that of the latter. Quantitative calculations show that the hydrogen-terminated diamond film system has larger potential barriers and hence larger friction coefficients of about 0.15 under the loads of 0.5–3nN, which are almost twice larger than that of fluorine-terminated system (about 0.08). The results are in good agreement with experiments and other theoretical predictions.

Structure and stability of weakly chemisorbed ethene adsorbed on low-index Cu surfaces: performance of density functionals with van der Waals interactions

We have investigated the performance of popular density functionals that include van der Waals interactions for the experimentally well-characterized problem of ethene (C2H4) adsorbed on the low-index surfaces of copper. This set of functionals does not only include three van der Waals density functionals—vdwDF-PBE, vdwDF-revPBE and optB86b-vdwDF—and two dispersion-corrected functionals—Grimme and TS–but also local and semi-local functionals such as LDA and PBE. The adsorption system of ethene on copper was chosen because it is a weakly chemisorbed system for which the vdW interactions are expected to give a significant contribution to the adsorption energy. Overall the density functionals that include vdW interactions increased substantially the adsorption energies compared to the PBE density functional but predicted the same adsorption sites and very similar C–C bonding distances except for two of the van der Waals functionals. The top adsorption site was predicted almost exclusively for all functionals on the (110), (100) and (111) surfaces, which is in agreement with experiment for the (110) surface but not for the (100) surface. On the (100) surface, all functionals except two van der Waals density functionals singled out the observed cross-hollow site from the calculated C–C bonding distances and adsorption heights. On the top sites on the (110) surface and the cross-hollow site on the Cu(100) surface, the ethene molecule was found to form a weak chemisorption bond. On the (111) surface, all functionals gave a C–C bonding distance and an adsorption height more typical for physisorption, in agreement with experiments.

Modulating Morphology of Thiol-Based Monolayers in Honeycomb Hydrogen-Bonded Nanoporous Templates on the Au(111) Surface: Simulations with the Modified Force Field

The difference in monolayer morphology caused by different functional thiols (ASH, BP3SH, and C12SH) within the surface-supported porous network of naphthalene tetracarboxylic di-imide (NDI) and melamine (MEL) molecules has been investigated by molecular dynamics simulations with the modified force field. The hydrogen-bonded bimolecular network is taken as the template when different thiols are deposited on the Au(111) surface. Force field parameters of intermolecular (NDI–NDI, MEL–MEL, NDI–MEL, and thiol–thiol) and interfacial (Au···S) interactions are modified to reproduce MP2 potential energy curves and the adsorption height. Interfacial interactions between the network and the Au(111) surface support the NDI–MEL bimolecular template, lying flat in an ordered hexagonal pattern on the substrate. The packing morphology of the triple hydrogen-bonded network obtained from molecular dynamics simulations and quantum chemical calculations matches the image from the scanning tunneling microscope. The backbone ...

Geometrical surface structure of ultra thin Al film on the W(110) surface

Using low energy electron diffraction (LEED) and low energy ion scattering spectroscopy (ISS) we investigated the structure of the surface of 1.0 monolayer (ML) Al/W(110) prepared by annealing at 900 K. A p(1 × 1) LEED image was acquired for the 1.0 ML Al/W(110) surface while the substrate temperature was maintained at 900 K during Al deposition. We found that, 1.0 ML Al atoms cover the W(110) surface uniformly, and do not form three-dimensional islands. We also measured the Al adsorption site at the 1.0 ML Al/W(110) surface using ISS. The ISS results show that the 1.0 ML Al/W(110) surface prepared by annealing at 900 K has two domains with a p(1 × 1) structure. The experiments reveal that the Al atoms were adsorbed at the centers of the hollow sites and are located ± 0.55 Å to the [1 1 ¯ 0] side, and the adsorption height was 2.13 Å above the W surface.

Surface reconstruction of W2C(0001)

A single crystal surface of ditungsten carbide,W2C(0001) was investigated using low-energy (LEED) and high-energy electron diffraction, Augerelectron spectroscopy, x-ray photoelectron spectroscopy (XPS), and high-resolution electronenergy loss spectroscopy (HREELS). A new reconstruction, , was found as a clean surface structure after annealing theW2C at > 1900 K.The surface carbon content is shown as larger than that in the bulk. Our preliminary results showedthat the same structure is realized also on WC(0001). The same surface periodicity is described foran Mo2C(0001) LEED pattern in the literature. This reconstruction phase is presumablycommon on the (0001) surface of hexagonal group-6 transition-metalcarbides. In the off-specular HREELS, an atomic vibration of 44.8 meV (361 cm − 1) appeared within the gap energy region of the bulk phonon bands, which was assigned to asurface carbon vibration perpendicular to the surface. One possible explanation of the lowvibrational frequency is very low adsorption height of the surface carbon atoms.

Normal-incidence x-ray standing-wave study of copper phthalocyanine submonolayers on Cu(111) and Au(111)

Understanding the adsorption and growth mechanisms of large $\ensuremath{\pi}$-conjugated molecules on noble metal surfaces is a crucial aspect for designing and optimizing electronic devices based on organic materials. The investigation of adsorption heights for these molecules on different surfaces can be a direct measure for the strength of the adsorbate-substrate interaction, and gives insight into the fundamental bonding mechanisms. However, the adsorption strength is often also influenced by intermolecular (lateral) interactions which cause, e.g., island formation in the submonolayer regime and influence the adsorption geometry of individual molecules. The lateral structure can then dominate the vertical structure formation and influence the adsorbate-substrate interaction. In this context, the adsorption of copper-phthalocyanines on noble metal surfaces [Au(111), Ag(111), and Cu(111)] represents an ideal model system since the lateral structure formation, as well as the molecular adsorption geometries, strongly depend on coverage and temperature, and hence can be tuned easily. We demonstrate that for CuPc/Au(111), a system dominated by physisorption, the adsorption height of the molecules is independent from the lateral adsorption geometry. In contrast, a strong chemisorption of CuPc on Cu(111) shows a clear gradient in the interaction strength: Individual molecules in diluted phases are significantly stronger bonded than molecules in dense phases. This finding quantifies the increase of the exchange correlation in the binding process, which goes along with the tendency to a more site-specific adsorption geometry at small coverages.

Methane adsorption on graphene from first principles including dispersion interaction

The methane–graphene interaction is studied using density functional theory complemented with a semiempirical dispersion correction scheme (DFT-D), an ab initio van der Waals density functional (vdW-DF) ansatz as well as using Møller Plesset perturbation theory (MP2). The adsorption energy of 0.17 eV and the molecular distance of 3.28 Å obtained from the MP2 calculations are close to the experimental data, while the vdW-DF scheme results either in a realistic adsorption energy or a realistic adsorption geometry, depending on the underlying exchange-correlation functional. The present implementation of DFT-D overbinds about as much as bare DFT calculations underbind, but yields a meaningful adsorption height.

Effective elastic properties of a van der Waals molecular monolayer at a metal surface

Received 25 October 2010; published 23 November 2010; publisher error corrected 23 November 2010 Adsorbing anthracene on a Cu111 surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young’s modulus of 1.5 GPa and a Poisson ratio 0.1. These values suggest interpretation of the molecular monolayer as a porous material—in marked congruence with our microscopic observations.

Adsorption ofn-butane on Cu(100), Cu(111), Au(111), and Pt(111): Van der Waals density-functional study

The adsorption of $n$-butane on Cu(100), Cu(111), Au(111), and Pt(111) is studied as a prototypical physisorption system of organic molecule-metal interface by using a fully nonlocal Van der Waals density functional (vdW-DF) [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] and a second version of it (vdW-DF2). Adsorption energies and heights are compared with experiments and conventional local (local-density approximation) and semilocal (generalized gradient approximation) functionals. The adsorption energies and heights predicted by vdW-DF2 agree most favorably with known estimates. Lateral intermolecular interactions at a full coverage are calculated to be about 25% of total adsorption energy. A summation up to the second-nearest-neighbor pairs, i.e., six contacting neighbors, is enough to make the pairwise sum converged.

Comparison of hydrogen and deuterium adsorption on Pd(100)

Low energy ion recoil spectroscopy is a powerful technique for the determination of adsorbate position on metal surfaces. In this study, this technique is employed to compare the adsorption sites of hydrogen and deuterium on Pd(100) by detection of either H or D recoil ions produced by Ne(+) bombardment. Comparisons of experimental and Kalypso simulated azimuthal yield distributions show that, at room temperature, both hydrogen isotopes are adsorbed in the fourfold hollow site of Pd(100), however, at different heights above the surface (H-0.20 A and D-0.25 A). The adsorbates remain in the hollow site at all temperatures up to 383 K even though they move up to 0.40-0.45 A above the surface. Density functional theory calculations show a similar coverage dependent adsorption height for both H and D and confirm a real difference between the H and D adsorption heights based on zero point energies.

THE ROLE OF SUBSTRATE IN PACKING STRUCTURES OF SEXITHIOPHENES ON AG (111) SURFACE: MOLECULAR DYNAMICS SIMULATIONS AND QUANTUM CHEMICAL CALCULATIONS

Packing structures and orientation of sexithiophene (6T) molecules on Ag (111) surface are investigated by molecular dynamics (MD) simulations and quantum chemical calculations. Both the cluster and the slab models are employed. The density functional theory and molecular mechanism calculations demonstrate a weak physisorption and little site-preference in thiophene/ Ag (111) system. The MD simulations show that in the first layer close to the surface, the nearly coplanar 6T strips lie parallel with long axes deviating from [Formula: see text] direction about 20° – 30° and 75° – 90°. The average adsorption height of the monolayer is about 3.2 Å with most of the sulfur atoms in thienyl rings sitting on the bridge site of Ag (111) surface. The 6T molecules tend to take tilted orientations when they are far away from the surface. The packing structures of 6T layers deposited on the surface resulted from the competition between the molecule–substrate and intermolecular interactions.

Simple connections in alkali adsorption

Stimulated by recent two-photon photoemission spectroscopy and density-functional theory studies by Petek and co-workers, a retrospective look at some fundamentals in the theory of ionic alkali adsorption on metal surfaces is presented that provides a simple correlation between free-atom ionization potentials, ionic size, adsorption heights, and spectroscopically observed alkali valence-electron binding energies.