RADIATION-ENHANCED DIFFUSION IN MGO

Radiation enhanced diffusion and ion beam mixing of O-18, Ca, and Zn b uried tracer layers in MgO, grown by molecular beam epitaxy, have been measured following irradiation with 2.0 MeV Kr+ and 1.0 MeV Ne+, He+, and H+ from 30 to 1500 degrees C. The ion beam mixing parameter varie d between 1.0 and 5.0 Angstrom(5) eV(-1) for the, different tracers at 30 degrees C and increased slowly with increasing temperature. These results are consistent with ballistic mixing. In the highest temperatu re range investigated, 1350-1500 degrees C, the radiation enhanced dif fusion coefficient for O-18 was proportional to the square root of the irradiation flux and displayed an apparent activation enthalpy of 1.2 eV. These dependencies on flux and temperature are indicative of reco mbination-limited kinetics, with the measured activation enthalpy repr esenting one-half the migration enthalpy of anion vacancies. From 1150 to 1350 degrees C an activation enthalpy of 4.1 eV was obtained. The unexpectedly high value is attributed to the dissociation energy of sm all vacancy clusters. Measurements on the cation sublattice were limit ed to temperatures below 900 degrees C owing to the excessive thermal diffusion associated with extrinsic vacancies, which are present for t rivalent impurity charge compensation. (C) 1998 American Institute of Physics.