Quantum threshold reflection of He-atom beams from rough surfaces

6 pags., 5 figs., 1 tab.Quantum reflection of thermal He atoms from various surfaces (glass slide, GaAs wafer, flat, and structured Cr) at grazing conditions is studied within the elastic close-coupling formalism. Comparison with the experimental results of Zhao et al. [Phys. Rev. Lett. 105, 133203 (2010)PRLTAO0031-900710.1103/PhysRevLett.105.133203] is quite reasonable but the conclusions of the present theoretical analysis are different from those discussed in the experimental work. The universal linear behavior observed in the dependence of the reflection probability on the incident wave-vector component perpendicular to the surface is only valid at small values of the component whereas, at larger values, deviation from the linearity is evident, approaching a quadratic dependence at higher values. The surface roughness seems to play no important role in this scattering. Moreover, the claim that one observes a transition from quantum to classical reflection seems to be imprecise.This work is supported by the Programa Nacional de Ciencias Básicas de Cuba under Grant No. P223LH001-108 (G.R.L. and J.R.S.); by the Ministerio de Ciencia, Innovación y Universidad (Spain) under Grant No. FIS2017-83473-C2-1-P (S.M.A.); and by grants from the Israeli Science Foundation and the Minerva Foundation, Munich (E.P.)