An in situ field ion microscope study of irradiated platinum-I. Stage I recovery behavior

Direct visual evidence for uncorrelated long-range migration of self-interstitial atoms (SIA's) in substage I_e of irradiated platinum was obtained by a series of in situ field ion microscope (FIM) experiments. High purity [(2-6) · 10(su-5) and (1-3) · 10(su-6) at. fraction impurity level] platinum specimens were irradiated with 20 or 30 ke V Pt⁺ ions under ultra-high vacuum conditions at a specimen temperature of 10 or 11°K. The initial damage pattern at 10°K consisted of depleted zones within ~100 Å of tha irradiated surface and a distribution of immobile SIA's in the bulk of the specimen. Next the specimens were isochronally warmed from 10 or 11°K to 75°K [average linear warming rate = ( 1 3)°K min^-1] at a constant value of the imaging electric field while the specimens' surfaces were photographed at a rate of 1 frame sec^-1. This experiment showed that a flux of SIA's crossed the specimens' surfaces between 13 and 27°K. A detailed series of control experiments were performed to demonstrate that the contrast effects observed were not due to impurity atoms or surface artifacts. Application of our diffusion model (Scanlan et al.) to the isochronal recovery spectrum yielded an enthalpy change of migration of ~0.04eV and a diffusion coefficient of ~(0.08-0.77) exp (-0.04 eV/kT) cm² sec^-1 for the SIA. The FIM specimen was, of course, subjected to a negative hydrostatic pressure during the field ion imaging process which was caused by the required imaging field of 4-4.75 V (A)^-1. Thus, it was possible to combine an existing value for the internal energy change of migration for recovery in substages I_D and I_E with our enthalpy change of migration to yield a range of limiting values for the volume change of migration of a SIA [(2.3-3.2) · 10² at. vol.].