Fast ion diffraction of protons on NaCl, the discovery of GIFAD

Grazing incidence fast atom diffraction (GIFAD or FAD) has become a technique to track the surface topology of crystal surface at the atomic scale. The paper retraces the events that led to the discovery of unexpected quantum behavior of keV atoms during the thesis of Patrick Rousseau in Orsay and Andreas Schueller in Berlin. In Orsay, it started by diffraction spots whereas in Berlin supernumerary rainbows were first identified at keV. Though the discovery was not anticipated, it did not take place by accident, everything was in place several years before, waiting only for an interest in neutral projectiles with a touch of curiosity.
Comment: 9 pages, 9 figures, and 152 references, Submitted to NIM-B special issue dedicated to the IISC-24 conference held in Charleston SC 10-15 Sept. 2023