Reversible quasicrystallization in GeSe2glass

Abstract

Absorption of photons at low power levels below the band edge reversibly alters the molecular structure of Ge${\mathrm{Se}}_2$ glass. These structural changes have been analyzed by continuously monitoring the Raman scattering spectrum as a function of time and laser power level. At sufficiently high power levels irreversible crystallization can take place. In the reversible regime four distinct stages of ordering, including a new phenomenon called quasicrystallization, have been observed. Each stage of ordering has been interpreted in terms of rearrangement or joining of molecular clusters which are embedded in the glassy matrix. The relationship between photon-induced cluster reconstruction and photo-darkening is discussed. The new phenomena described here demonstrate the inadequacy of chemically ordered continuous-random-network models of chalcogenide glasses and confirm the structural validity of the partially polymerized cluster model.