Scanning electron microscopy observation of high energy α-bombarded molybdenum surfaces

The surface morphologies of two sets of high energy α-bombarded molybdenum specimens were studied using scanning electron microscopy. The irradiation was performed with 33.5 and 47 MeV α particles to a total dose of about (1-2)x1017 α cm-2. The micrographs of the bombarded surfaces show interesting features. Circular pits of diameter 5-12 μm, small pinhole pits and few elongated blister chains are found. The irregular shape of the pits on the second set of specimens reveal that the reference surface conditions have an important bearing in determining the shape of the pits. The results indicate that, although the lateral stress in the low energy ion implantation plays only a small role in the surface erosion, at high energies the compressive stress created by the lattice defects has an important role as the cascade displacement damage and the thermal spike phenomena are more probable in the near-surface region. These observations also support the idea that the initiation of the fracture plane need not always be around the depth of the peak helium concentration; rather it may develop randomly along the depth distribution of implantation. (orig.)