Light-induced transformation of C-60 films in the presence and absence of oxygen

The composition and structure of C-60 fullerite films prepared by discrete evaporation in quasi-closed volume, as well as their changes induced by las er irradiation, have been studied by ellipsometry and Rutherford backscatte ring. The starting film has a 150-Angstrom thick stable top layer and a car bon to oxygen ratio of 10:1. Exposure of a film both to vacuum and to air r esults in formation of an insoluble photo-transformed phase, but in the sec ond case the change in the refractive index implies the appearance of compo unds with oxygen. The material does not undergo complete polymerization, al though all structural changes cease at an irradiation dose of 10(4) photons per fullerene molecule. Treatment of the polymerized phase with organic so lvents produces a porous structure, with the voids totaling 48% in the case of exposure in vacuum, and 30% when exposed in air. (C) 1999 American Inst itute of Physics. [S1063-7834(99)03603-5].