Anomalous KCl(001) Surface Corrugation from Fast He Diffraction at Very Grazing Incidence.

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

Cluj

Simposio; ISIAC 2021; 2021

Faculty of Physics, Babes,-Bolyai University Cluj-Napoca

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). The unexpected 85% corrugation increase below 100 meV we obtain for 4He!h110iKCl(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 4He-KCl(001) along <110> and <100> channels. In Fig. 1 we show the corrugation DZ(Eperp) obtained from the processing of these patterns, together with two sets of theoretical corrugations: DZ-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 DZ-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 DZ for decreasing Eperp is not vdW in origin; ii) The increase of DZ-PES for <110> is due to the late fading of the He-K+ interaction; iii) For both channels, the difference DZ-SIVR / DZ-PES is due to dynamical effects, traceable to a shallow attractive region, neither vdW nor polarization in origin; iv) Dynamical effects take hold when Eperp < 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 Eperp > 30 meV range.