Quantitative structure determination using grazing scattering of fast atoms: Oxygen-induced missing-row reconstruction of Mo(112)

Abstract

We present an extensive study on the structure of oxygen adsorbates on Mo(112) by means of grazing scattering of fast hydrogen and helium atoms and low-energy electron diffraction. For projectile energies less than 2 keV, fast atom diffraction provides information on the surface unit cell and on adsorption sites for low coverages. In the classical scattering regime, we employed so-called triangulation techniques where for an azimuthal rotation of the target axial surface channels are identified. From comparison with computer simulation positions of surface atoms can be derived. Aside from the detection scheme of projectile-induced electron emission, we present details for a new variant of triangulation based on the detection of angular distributions of scattered particles. The different sensitivity of the methods to the topmost surface layers allows us to efficiently set up structural models for four adsorbate phases for which contradicting models exist in literature. The c(4×2) phase is revealed to be one step in the formation of a missing-row reconstruction with p(1×2) unit cell. Our studies demonstrate the potential of grazing scattering of fast atoms for quantitative structure analysis.

Reexamination of the interaction of atoms with a LiF(001) surface

“…In Eqs. (6) and (11) of Ref. [19] V + G was approximated by a radial onion potential produced by a series of charged shells.…”

“…In this article we do a quality leap by introducing non-local approximations in terms of ∇n and ∇ 2 n, which allows us to obtain more accurate values, but without losing the simplicity of Eq. (6). For the exchange energy, j = x, we use the well established spin-dependent Becke (B) approximation given by Eq.…”

“…Furthermore, to compare the contribution of this term with the asymptotic limit of V It is also interesting to investigate the following term of the expansion of Eq. (13), which is governed by the coefficient C (6) AO related to vdW forces. The value of C (6) AO can be estimated by using the formula of Slater-Kirkwood [40] as…”

“…Using the onion values given by Eqs. (A1) and (A2), together with the recommended atomic parameters [38,39], listed in Table III, we obtain the C (6) AO values also tabulated in the same table for the different atomonion systems. For He atoms, our C (6) AO coefficients are very close to the ones by Celli et al [42], obtained by fitting experiments of helium atoms bound to a LiF surface.…”

“…The good agreement found for normal energies in the eV-range represents a meaningful evidence of the quality of the present description. In the field of particle-surface interactions, one of the most remarkable experimental advances of the last decade corresponds to the observation of grazing incidence fast atom diffraction (GIFAD or FAD) [1,2], which has emerged as a powerful surface analysis technique [3][4][5][6]. It allows one to inspect the electronic and morphological characteristics of crystal surfaces with an exceptional sensitivity, becoming a useful tool for investigating a wide variety of materials [7][8][9][10].…”