Charged-Particle Radiation Damage Observed as Dimpling of Thin Silicon Targets

When thin uniform silicon targets are bombarded with energetic ions, macroscopic deformation of the target occurs in the irradiated region. This deformation, which is euphemistically termed a ``dimple'', may be interpreted as a radiation-induced lattice expansion. Measurement of the amount of deformation allows lattice expansion to be determined with a sensitivity comparable to or better than the most sensitive existing methods. Measurements on silicon irradiated at room temperature by 1.8-MeV He ions show that the lattice expansion at low flux increases essentially linearly with fluence below about 5×1016 He ion/cm−2, whereupon it increases more rapidly until saturation starts to occur at an order-of-magnitude higher fluence. Isochronal annealing results are discussed.