New methods of operating surface reactors, and such reactors, particularly spinning disk reactors, require that a first reactant is fed to a reactor surface (20) and forms a thin radially outward moving film (60) thereon in a reaction passage (42) formed between the reaction surface (20) and a parallel, closely spaced (less than 1 mm) retaining surface (40). The passage thickness is precisely controllable and the surfaces (20, 40) move relative to one another so that strong shear is applied to the material between them. A second reactant is fed to the surface (20) as a second thin film (65) that as it enters the first film (60), preferably perpendicularly, it is immediately merged therewith along a correspondingly very narrow interaction line (66) by the shear at a rate such as to break up molecular clusters in the films, so that their molecules can aggressively and completely interact by forced interdiffusion. In spinning disk (18) apparatus the first film (60) is fed along the spin axis (14), while subsequent films (65, etc.) are fed at respective distances from the axis (14) such that there is adequate shear for the molecular cluster disruption. Preferably each film (65, etc.) after the first (60) is fed into the reaction passage (42) through a respective thin annular nozzle producing a thin circular film (65) that simultaneously merges with the first film (60) along its entire length.