Diffraction of He atoms from A Xe overlayer adsorbed on graphite (0001)

Diffraction of He atoms from Xe monolayer adsorbed on the graphite (0 0 0 1) revisited: the importance of multiple scattering processes

“…1 and 2, of Ref. 3, and of the ones obtained from the present calculation is given in Table 1. Note here that in order to obtain the amplitudes given in the first row of this Table we have corrected two errors appearing in the HCW shape function ζ 0 (R) quoted in Eq.…”

“…The authors discussed a specific model of phonons in the Xe monolayer and used it in a scattering calculation based on the hard-wall model and the eikonal approximation with the aim to reproduce and interpret the experimental He atom diffraction intensities reported by Bracco et al 3 . However, as we shall show, neither their description of phonons in the Xe overlayer, nor the results of calculations for the scattering intensities are consistent with the previous experimental and theoretical studies of the system Xe/Gr(0001) and the results of revisited calculations described below.…”

“…The measurements of diffraction intensities from He beams incident normal to a ( √ 3× √ 3)R30 0 monolayer lattice of Xe atoms on Gr(0001) carried out by Bracco et al 3 indicated large corrugation amplitudes as probed by HAS. These authors have attempted to interpret the measured diffraction spectra by using the hard corrugated wall (HCW) to model surface corrugation amplitudes obtained from pairwise summation of atomic He-Xe potentials 4 , and the eikonal approximation 5 to calculate the diffraction intensities pertinent to the thus constructed HCW.…”

“…However, the applicability of this approach suffers from two fundamental restrictions 14 which were already noted and discussed in Ref. 3. First, the eikonal approximation is known to neglect the multiple scattering processes and therefore cannot be used in the cases of large surface corrugations and low projectile incident energies in which multiple scattering becomes important.…”

“…The well depth D of the He-Xe/graphite potential is known with high precision from the studies reported in Refs. 17 and 18 and amounts to D = 7.4 meV, and hence the He atoms scattered into the (50) and (60) To remedy the shortcomings of the HCW model in applications to the He→Xe/Gr(0001) system, KKK have assumed 1,2 the magnitudes of corrugation parameters of the HCW shape function ζ(R) for modelling the Xe/Gr(0001) surface that are somewhat different from the best fit parameters suggested by Bracco et al 3 and, moreover, are inconsistent with the corrugation of the isopotential surface at 64 meV that can be constructed from the best available He-Xe gas phase binary potentials (c.f Fig. 1).…”