THE KINETICS OF CAF2 METALLIZATION INDUCED BY LOW-ENERGY-ELECTRON IRRADIATION

Results of experimental and theoretical studies on metal colloid growt h after irradiation and subsequent heating of CaF2 are presented. Samp les at a temperature of 200 K were irradiated in UHV for 30 min with 2 .5 keV electrons. After irradiation samples were heated at a rate of a bout 1 K/min and colloid formation was investigated by optical extinct ion spectroscopy. Colloid radii as well as the amount of metal were de termined from a Mie scattering analysis. A steep rise in colloid size was observed between 260 and 270 K, The concentration off centers not aggregated into colloids was below the detection limit for all tempera tures. A microscopic theory of F and H center aggregation taking into account defect creation, interaction, diffusion, and annihilation of d issimilar defects is presented. Theory successfully reproduces the mai n experimental observations of small colloid formation at low temperat ures during irradiation and the onset of colloid growth at a temperatu re where F centers become mobile. (C) 1998 Elsevier Science B.V. All r ights reserved.