Raman study of ion irradiated GeSe films

Films of a-Ge20Se80 prepared by vacuum evaporation, are exposed to visible light and irradiated with I MeV Krypton ions. The changes in bonding config urations are studied by Raman spectroscopy. Three bands are observed in the virgin films and are identified as corresponding to the stretching mode of GeSe4/2 corner-sharing tetrahedra (201 cm(-1)) and to the vibrations of Se atoms in four member rings composed of two edge sharing tetrahedra (215 cm (-1)) and Se-Se chains (263 cm(-1)). Upon ion irradiation the band position s remain unchanged and no new band appears. In contrast, light soaking prod uces an additional band at 257 cm(-1). This bond has been identified as ari sing from the stretching vibrations of Se atoms in helical chain-like and r ing-like arrangements. A study of the relative areas under the peaks shows that ion-irradiation causes the Se-Se bridges linked with GeSe4/2 units to convert into Se-Se chains and the number of GeSe4/2 bonds remain unchanged. Upon light soaking, the density of corner-sharing GeSe4/2 bonds increases, no significant variation is observed in the Se bonds. In addition, the wid th of the peak at 201 cm(-1) decreases after ion irradiation but increases upon light soaking. These data show that ion irradiation induces bond chang es in Ge20Se80, which are different from those, created by light soaking. ( C) 2000 Elsevier Science B.V. All rights reserved.