Direct observation of fine structure in ion tracks in amorphous Si3N4 by TEM

Thin films of amorphous Si3N4 (thickness 20 nm) were irradiated with 120–720 keV C60+, 2+ ions and observed using transmission electron microscopy (TEM). The ion track produced in an amorphous material was directly observed by TEM. For quantitative analysis, the ion tracks were also observed using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The observed ion track consists of a low density core (radius ∼2.5 nm) and a high density shell (width ∼2.5 nm), which is very similar to the ion tracks in amorphous SiO2 irradiated with high energy heavy ions observed by small angle X-ray scattering (SAXS). Although the observed ion tracks may be affected by surface effects, the present result indicates that TEM and HAADF-STEM have potential to observe directly the fine structures of ion tracks in amorphous materials

In-situ observation of damage evolution in aluminium irradiated with H and He ions

The behavior of bubbles and blisters in aluminum during 10 keV He + ion irradiation at 573 K was investigated. Processes of the evolution of surface damage were clarified using an in-situ electron microscope observation system. The difference among irradiation effects obtained by three kinds of experiments at room temperature was examined using both 15 keV H +2 and 12 keV He+ ions. The obtained results were interpreted by difference in the production rate of vacancies introduced by gas implantation and different mobility of these two ions in aluminum

Quantitative study of Brownian motion of helium bubbles in fcc metals

Dynamical process of helium bubbles in face‐centred cubic (fcc) metals has been studied by in situ irradiation and electron microscopy with a video recording system. Brownian type motion of helium bubbles was demonstrated quantitatively by establishing a proportional relation between the mean square of the bubble migration distance and time. This relation yielded the diffusion coefficient of the bubble. Examples of Brownian motion in the matrix and along general grain boundaries in pure aluminium are shown comparatively. Similar Brownian motion was also observed in an Fe‐16Cr‐17Ni austenitic alloy. It was revealed from scanning transmission electron microscopy–electron energy‐loss spectroscopy that Cr was depleted around the bubble surface, but Ni was enriched. Response of the bubble motion to irradiation with high‐energy self‐ions was examined in pure aluminium and both effects of enhancement and retardation of the bubble mobility were found

Radiation defects in nano-structured materials

We investigated defect formation within nanostructured materials using a transmission electron microscope (TEM) and ion accelerators. Controlling diffusion coefficient of the defects we have first observed changes in pattern of defect clusters, namely, the diffusion-limited reaction of defects in nanocrystals