Anomalous KCl(001) surface corrugation from fast He diffraction at very grazing incidence

G. A. BOCAN; H. BREISS; S. SZILASI; A. MOMENI; E. M. STAICU CASAGRANDE; M. S. GRAVIELLE; E. A. SÁNCHEZ; H. KHEMLICHE

Transilvania

Simposio; International Symposium on Ion-Atom Collisions; 2021

Babeș-Bolyai University

The substrate surface corrugation is a key feature in quasiepitaxy, driving the overlayer orientation even for weakly interacting interfaces. In this invited talk we will address the corrugation of the KCl(001)surface by means of grazing incidence fast atom diffraction (GIFAD) [1]. The unexpected ∼ 85% corrugation increase below 100 meV we obtain for 4 He→ <110>KCl(001) suggests that KCl could outperform the usual NaCl or LiF layers often used in organic electronic devices to improve charge injection.Experimental GIFAD patterns were recorded for 4 He→KCl(001) along <110> and <100> channels. In Fig. 1 we show the corrugation ∆Z(E ⊥ ) obtained from the processing of these patterns, together withtwo sets of theoretical corrugations: ∆Z^{PES} , calculated on three high-precision DFT-based He-KCl(001) potential energy surfaces (PESs), two of which included van der Waals (vdW) interactions, and ∆Z^{SIVR}obtained from the processing of simulated GIFAD patterns, built by means of the surface initial value representation (SIVR), a semiquantum approach to the scattering dynamics under a given PES.From the analysis of the potential and the SIVR phase we conclude that: i) For <110>, the increase in ∆Z for decreasing E⊥ is not vdW in origin; ii) The increase of ∆Z^{PES} for <110> is due to the late fading ofthe He-K+ interaction; iii) For both channels, the difference ∆Z^{SIVR} − ∆Z^{PES} is due to dynamical effects, traceable to a shallow attractive region, neither vdW nor polarization in origin; iv) Dynamical effects take hold when E⊥ < 30 meV, yielding the slope sign change for <100> and the sharp increase for <110>. v) GIFAD provides satisfactory structural information for both channels in the E⊥ > 30 meV range.