Adsorption Of Rare-gas Atoms Research Articles

English

Adsorption of rare-gas atoms on a three layer model of Cu(111) surface was studied at the DFT level with two different functionals. The binding energy values increase from He to Ar, then decreases somewhat to Kr. For He, atop atom site seems most favourable, for others it is the bridge site. Bond distances change little from He to Kr, and for binding sites. Various other molecular parameters such as dipole moment, HOMO and LUMO energies, charges on various moieties, electronegativity and electrophilicity values are shown as function of adsorbate-metal distance. Density of states (DOS) plots also show effect of rare-gas atoms.

Van der Waals corrected DFT simulation of adsorption processes on transition-metal surfaces: Xe and graphene on Ni(111)

The DFT/vdW-WF2s1 method, recently developed to include the van der Waals interactions in the density functional theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe and graphene with a transition-metal surface, namely, Ni(111). In general, the adsorption of rare-gas atoms on metal surfaces is important because it is prototypical for physisorption processes. Moreover, the interaction of graphene with Ni(111) is of great interest for practical applications, for instance concerning the efficient and large-scale production of high-quality graphene; from a theoretical point of view, it is particularly challenging, since it can be described by a delicate interplay between chemisorption and physisorption processes. The first-principles simulation of transition metals requires particular care also because they can be viewed as intermediate systems between simple metals and insulating crystals. Even in these cases the method performs well as demonstrated by comparing our results with available experimental data and other theoretical investigations. We confirm that the rare-gas Xe atom is preferentially adsorbed on the top-site configuration on the Ni(111) surface too. Our approach, based on the use of the maximally localized Wannier functions, also allow us to well characterize the bonds between graphene and Ni(111).

Rare Gas Adsorption to Silver-Exchanged Zeolites

The adsorption of rare gas atoms to silver aluminosilicate has been investigated using density functional theory (DFT) with the local density approximation, generalized gradient approximation, and dispersion correction. The adsorption energies of rare gas atoms to the honeycomb lattice of silver aluminosilicate were calculated, and the results are discussed. The relationship between the electric charge density distribution and the adsorption energy is discussed. It indicates that the xenon atom has the most electrons to affect the van der Waals dispersion, so it has the highest minimum charge density, strongest polarization, most spacious spherical scope, and most favorable adsorption on silver zeolites.

Local electric fields above individual surface atoms in the presence of field-adsorbed rare gas atoms: an additional field enhancement

Absolute field ion appearance energy measurements for He + and Ne + ions were carried out at steps of Rh(012) plane. Data of local electric fields close to the surface atoms, F hkl loc, are derived from appearance energies and compared with external field strengths, F hkl 0, determined by electron energy spectroscopy and i–V (Fowler-Nordheim) measurements. In both cases the step-site surface atoms were covered with field-adsorbed gas atoms, He and Ne, respectively. A field ionization flicker experiment with a Ne/Ar gas mixture probing Rh(111) was carried out using mass-to-charge separation of ions in the magnetic field. If Ne was ionized above the field-adsorbed Ar atoms, the appearance energy of Ne + ions increased, providing the direct evidence for additional local field enhancements above the adsorbed rare gas atoms. The experimental results are discussed in terms of additional local field enhancement above the field-adsorbed image gas atoms and in view of recent self-consistent calculations of the spatial local field distribution in the proximity of protruding surface atoms. It is shown that the presence of a certain field enhancement is necessary to achieve the field adsorption of rare gas atoms under usual FIM conditions.

Cluster modeling of solid state defects and adsorbates: Beyond the hartree-fock level

The use of finite clusters of atoms to represent the physically interesting portion of a condensed matter system has been an accepted technique for the past two decades. Physical systems have been studied in this way using both density functional and Hartree–Fock methodologies, as well as a variety of empirical or semiempirical techniques. In this article, the author concentrates on the Hartree–Fock based methods. The attempt here is to construct a theoretical basis for the inclusion of correlation corrections in such an approach, as well as a strategy by which the limits of a finite cluster may be transcended in such a study. The initial appeal will be to a modeling approach, but methods to convert the model to a self-contained theory will be described. It will be seen for the case of diffusion of large ions in solids that such an approach is quite useful. A further study of the case of adsorption of rare gas atoms on simple metals will demonstrate the value of inclusion of electron correlation.

The adsorption of rare-gas atoms on microsurfaces of large aromatic molecules

The adsorption of rare-gas atoms on microsurfaces of large aromatic molecules

Anisotropy of the work function change in physical adsorption

Smoluchowski's concept of the surface double layer of bare metals is extended for physical adsorption of rare gas atoms on metal surfaces. With the use of the polarization approach it is possible to show that the work function decrease on physical adsorption of rare gases is anisotropic. A simple rule is suggested according to which the work function change produced by physical adsorption of the given rare gas on different crystal faces of the same metal [-Δφ( hkl)] decreases with increasing work function of the bare face [φ 0( hkl)] and/or with increasing packing density of the bare face. The former correlation is quantitative, whereas the latter correlation is only qualitative. The above predictions are compared with the first data available in the literature.

Point defects in the adsorption of rare gas atoms on a xenon crystal

The adsorption of rare gas atoms at vacancy or chemical impurity sites in the (100) face of a Xe crystal has been studied. The total energy of the system has been minimized by confining the quantum treatment to the motion of the adsorbed atom and by considering local relaxation of the crystal atoms. It is shown that the local relaxation induced by the adsorbed atom is almost negligible. It is found that introducing a Kr impurity atom produces only a slight increase in the energy of the adsorbed atom. Differences are much greater at the surface vacancy, essentially due to the change in the “coordination number” for the adsorbed atom.

The significance of many-body interactions in physical adsorption

The significance of many-body interactions in the physical adsorption of rare gas atoms on solid surfaces has been investigated. A simple model of the system was considered in which the atoms of the solid and the adsorbed atom were represented by interacting isotropic point dipoles. The fullN-body interaction energy between the adsorbed atom and the solid was calculated exactly to lowest order in the expansion parameter [αα0ηπ(ω0/ω)2]/4d 3 (ω, α and ω0, α0 are the solid atom's and adsorbed atom's characteristic frequency and polarizability,d is the distance from the surface of the adsorbed atom, and η is the number of atoms per unit volume in the solid). The interaction was then evaluated for the adsorption of various rare gas atoms on rare gas solids. It was found that the fullN-body interaction deviated at most by only2 1/2% from the interaction obtained by considering only two-body interactions. In addition, it was found that a finite expansion in two-, three-, ... body expressions may lead to erroneous results for the interaction energy since extensive cancellations occur between successive terms of the series.

Adsorption of Rare Gas Atoms on Xenon

The problem of adsorption of rare gas atoms on solids is treated for the case of submonolayer films. An energy spectrum calculation method which is suitable for band structure or heat capacity calculations is discussed. It is particularly useful for adsorbate-substrate systems in the region intermediate between ``tight binding'' and ``plane wave'' behavior. The method employs a technique introduced by Kohn and Luttinger of using the eigenfunctions corresponding to a particular point in the Brillouin zone as a basis set. The cases of He and Ne adsorbed on Xe are discussed.