Transmission electron microscopy investigations of bubble formation in He-implanted polycrystalline SiC

• We investigated the formation of He bubbles in He-implanted polycrystalline SiC.
• Bubbles at grain boundaries and in grain interiors were investigated by TEM.
• The density and size of bubbles were related to implantation fluence.
• Grain boundaries provide preferential sites for He bubbles nucleation and growth.

The formation of He bubbles observed in the hot-pressed polycrystalline SiC samples implanted with 230 keV He ions with fluences ranging from 5 × 1015/cm2 to 1 × 1017/cm2 at room temperature and subsequently annealed at 1000 °C for 30 min was investigated. The morphology and density of the bubbles in grain interiors (GIs) and at grain boundaries (GBs) are related to the implantation fluence. After a fluence of 5 × 1015/cm2 implantation, the distribution of the bubbles is heterogenous in the damage region. Disk-shaped arrangements of the bubbles associated with dislocation loops and stacking faults are observed in GIs. A high density of triangle-shaped bubbles is observed at GBs. After a fluence of 1 × 1016/cm2 implantation, the distribution of the bubbles is homogenous in the damage region. A high density of circular bubbles associated with dislocation loops is observed in GIs. After fluences of (2.5–10) × 1016/cm2 implantation, the results show a low density but a large mean diameter of the bubbles at GBs as compared to the GIs cases. In GIs, the buried layer of the bubbles broadens as compared to that observed in the sample implanted with a fluence of 1 × 1016/cm2. The distributions of the density and diameter of the bubbles are discussed.