Interfacial reactions in thin films of Y2O3 on Si(100) have been studied by means of energy dispersive X-ray analysis and high resolution transmission electron microscopy observations. Thin films of yttrium oxide were deposited at 700degreesC by ion beam sputtering and then annealed at 700 and 900degreesC under vacuum and in air, respectively. After an annealing treatment of 2 h at 900degreesC in air a solid-state amorphization is observed at the interface Y2O3/SiOx. After annealing at 700degreesC under vacuum a surprising phenomenon of electron beam irradiation induced epitaxial reconstruction is observed at the Si substrate surface. (C) 2003 Elsevier Science B.V. All rights reserved.