[en] X-ray crystal truncation rod (CTR) scattering is a powerful tool for studying the atomic structure of buried interfaces nondestructively. The analysis was often limited to the static structures, since the acquisition of CTR profile dataset is lengthy. We have developed a high-speed method which uses a wavelength-dispersive convergent X-rays, aiming for the in operando study of interface phenomena. We demonstrate the capability of the method by showing three examples of live observation of irreversible interface phenomena: photo-induced wettability transition of TiO₂ surface, electrochemical reaction on a Pt(111) electrode surface, and growth process of Bi₂Te₃ topological insulator thin film. (author)