F-colour centers and lithium nano-clusters in ion-beam assisted LiF thin films

Various kinds of ionising radiation can be utilised to produce primary F centres (anion vacancies occupied by electrons) and aggregate defects in lithium fluoride (LiF) thin films. The creation of large aggregates of F centres and intrinsic metallic nanometre sized clusters (nano-aggregates) above a critical defect concentration and at irradiation temperatures where the diffusion of single point defects is not negligible has also been reported in LiF crystals. In this work, we present results concerning the stable formation of primary electronic defects (F centres) and lithium nano aggregates in lithium fluoride thin films grown by Xe ionassisted thermal evaporation. The optical properties of the as grown LiF films are reported as a function of the deposition parameters (ion energy, density of the ion-beam current). The mechanism of the simultaneous formation of F colour centres and lithium nano-clusters is tentatively explained in the framework of low energy knock-on collisions and the thermal spike theory.