Studies on Fullerenes Using Positron Annihilation Spectroscopy

Abstract

ABSTRACT Results of positron lifetime measurements as a function of temperature and pressure are presented. With the application of pressure, the lifetime in solid C60 is observed to decrease and show signatures of the structural transition from fcc to the simple cubic (sc) phase. Positron lifetime measurements as a function of temperature, carried out in both C60 and C70, indicate an increase in lifetime at elevated temperatures. This is accounted for in terms of thermally activated trapping of positrons from the interstitial regions to the open regions within the cage structure. In addition to studies in the solid state, the annihilation characteristics of the ortho positronium (O-Ps) formed in organic solvents has been monitored with increasing concentration of dissolved fullerenes, C60 and C70. The observed reduction of the ortho positronium lifetime is understood in terms of the formation of O-Ps- Fullerene complex prior to annihilation.