Helium-surface interaction potential of Sb(111) from scattering experiments and close-coupling calculations

Abstract

Helium atom scattering (HAS) was used to study the antimony Sb(111) surface beyond the hard-wall model. HAS angular distributions and drift spectra show a number of selective adsorption resonance features, which correspond to five bound-state energies for He atoms trapped in the surface-averaged He-Sb(111) potential. As their best representation, a 9-3 potential with a depth of 4.4 ± 0.1 meV was determined. Furthermore, the charge density corrugation of the surface was analyzed using close-coupling calculations. By using a hybrid potential, consisting of a corrugated Morse potential (short range) and a 9-3 potential (long range), a peak-to-peak corrugation of 17% was obtained. The kinematic focusing effects that occurred were in good agreement with surface phonon dispersion curves from already published density functional perturbation theory calculations.

A comparative study of the He–Sb(111) interaction potential from close-coupling calculations and helium atom scattering experiments

“…As already observed in earlier CC-studies, the plain Morse potential (red circles) fails in describing the first-order ΓK as well as the second order ΓM peaks [9]. This fact seems to be to some degree dependent on the incorrect exponential shape of the attractive part of the interaction, since all the other potentials at least expect some intensity at those positions.…”

“…Within the last few years, SARs have been used to determine the bound state energies of the He-Bi(111) [7] as well as the He-Sb(111) [3] surfaceaveraged interaction potential. In a previous work, angular HAS measurements have been used to determine the lowest five bound state energies (BSE) of the He-Sb(111) surface-averaged interaction potential [9]. A more careful analysis of recent angular scans and time-offlight (TOF) measurements consistently revealed additional features which led to the finding of two additional BSEs.…”

“…Extending our considerations onto a wider variety of interaction potentials, which are listed in Section 4, allows a more detailed view on the applicability for each interaction potential. Table 1 lists the fitted bound state energy values for each considered potential as well as the measured BSEs already known [9] complemented with the two newly found values. The last line in Table 1 denotes the quality of the fitted energy values in comparison to the measured ones and is defined by…”

“…Due to the additional information, the fitted potential parameters given in previous work [9] have been revised. The considered interaction potentials did not seem to be able to describe the energetic separations in between the bound states satisfactorily.…”

“…However, a Morse potential does not describe the correct long-range interaction behavior since it assumes the attractive part to be of an exponential shape, while theory suggests that it should be proportional to 1/z 3 , with z being the distance to the surface normal. This basic discrepancy leads to the repeatedly observed inability of the corrugated Morse potential to describe second order ΓM or first order ΓK scattering on hexagonal surfaces [9,10]. To describe the complete interaction correctly, a broader scope on the overall potential shape must be given.…”