Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions

Polycrystalline tungsten (W) and molybdenum (Mo) materials both non-annealed and annealed at temperatures of 800-1750 ^o C have been irradiated with low-energy (220 eV), high-flux (∼10²¹ ions/m² ·s) He + at an irradiation temperature of 600 ^o C and at a dose of 1.0×10 25 ions/m² . This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials. A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He + dose of 1.0×10 ²⁵ ions/m² . Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W. Compared to W, Mo suffered much less surface damage after being irradiated at various He ⁺ doses.