L.W. Bruch

Theory of physisorption interactions

Abstract Information on the single-atom holding potential of physical adsorption and the lateral interactions of the adatoms is discussed and summarized. Results on the substrate-mediated dispersion energy and on the interaction of adsorption dipoles are consolidated.

Substrate-mediated dispersion interaction between adsorbed atoms and molecules☆

Abstract The approximation of G. Vidali and M.W. Cole, Surface Sci. 110 (1981) 10, for the polarization potential coefficients is extended to the coefficients in the McLachlan theory of the substratemediated dispersion interaction between physisorbed atoms and molecules. Values for the parameters entering in the approximation are given for several adsorbates and substrates. The values for the strength coefficients obtained with the approximate formulae are in good agreement with values obtained by detailed numerical integrations.

Many-body interactions in physisorption: Nonadditivity of film and substrate contributions to the holding potential

Abstract Calculations are presented of non-pair-additive contributions to the interaction energy of a probe atom with a physisorbed monolayer film and substrate. The Axilrod-Teller-Muto triple dipole energy is summed for triplets composed of probe atom, monolayer atom, and substrate atom. The lateral average, over probe atom positions, of the sum vanishes. A similar result and a nonvanishing term from a higher many-body interaction are derived also from the McLachlan theory of the dispersion interaction of two atoms in the presence of a continuum substrate.

Transitions of gases physisorbed on graphene.

The behavior of gases physically adsorbed on graphene might be expected to be similar to that of ones adsorbed on graphite. Here, three kinds of phase transitions are examined for gases adsorbed on suspended, free-standing graphene. In one case, the quasi-two-dimensional condensation of a van der Waals fluid is evaluated, using perturbation theory. In a second case, changes are discussed for contributions to the ground state energies of monolayer solid and liquid phases of quantum adsorbates (especially He) on graphene. This includes a determination of the leading perturbation terms in the adsorption-mediated (McLachlan) dispersion energy for two adatoms on a graphene sheet. The third problem is the wetting transition of water and other fluids on graphene. In each case, the relevant energies are somewhat different from those for adsorption on graphite.

Continuum approximations to domain walls in uniaxially incommensurate monolayer solids

Abstract Uniaxially incommensurate monolayer solids are modelled using elastic constants for the adatom-adatom energy and amplitudes for the spatially periodic terms of the adatom-substrate potential energy. Rectangular adlayers on bcc(110) substrates and uniaxially incommensurate adlayers derived from triangular commensurate adlayers on triangular substrates are treated. The energy of an isolated domain wall is derived, with a variational approximation, for three structures: a superheavy wall with one-component displacement vector, a heavy wall with two-component displacement vector, and a modified heavy wall which includes both sets of threefold sites of an fcc(111) substrate. The relative stability of the structures as a function of the elastic constants is discussed.

Structures and thermal properties of the N2 monolayer on Pb(1 1 1).

The physisorption of N2 molecules has long been a model system of molecular adsorption. We present a low-energy electron diffraction (LEED) study of the adsorption structures and thermodynamics of monolayer N2 on Pb(1 1 1). The results indicate that the monolayer structure has a triangular incommensurate center-of-mass lattice, and that the N2-substrate interaction is weaker than that observed on other metal surfaces. The N2 monolayer undergoes a phase transition between an orientationally ordered phase (low-temperature) and an orientationally disordered phase at a temperature of 20 K. Potential energy and quasiharmonic calculations indicate that the weak N2-Pb(1 1 1) interaction is the main contributing factor for the difference in orientational order of incommensurate N2 monolayers on Pb(1 1 1) and other similar metal surfaces.

On the orientational alignment of neon adsorbed on basal plane graphite

Abstract The Novaco-McTague theory of orientational alignment is discussed for neon adsorbed on basal plane graphite. A degenerate case of the theory which occurs for a √7 superlattice is evaluated and is shown to lead to a novel registry energy.