Yoneda peak

Yoneda peak (also Yoneda–Vineyard peak) is an enhancement in scattering intensity from scattered radiation propagating as an evanescent wave underneath a surface or another material interface. It appears under an exit angle α_f that is close to the critical angle for total external reflection α_c. For x-rays and neutrons, critical angles are small. The Yoneda peak is typically observed in off-specular reflectometry and in grazing-incidence small-angle scattering (GISAS), where it is also used for calibration. The phenomenon was described by Yasuharu Yoneda in 1963^[1] and later given a rigorous theoretical foundation by George H. Vineyard [de].^[2]