Radiation-induced formation of cavities in amorphous germanium

Prethinned polycrystalline Ge TEM samples were irradiated with 1.5 MeV Kr+ ions at room temperature while structural and morphological changes were observed in situ in the Argonne High Voltage Electron Microscope-Tandem Facility. After a Kr+ dose of 1.2×1014 ions/cm2, the irradiated Ge was completely amorphized. A high density of small void-like cavities was observed after a Kr+ dose of 7×1014 ions/cm2. With increasing Kr+ ion dose, these cavities grew into large holes transforming the irradiated Ge into a sponge-like porous material after 8.5×1015 ions/cm2. The radiation-induced nucleation of void-like cavities in amorphous material is astonishing, and the final structure of the irradiated Ge with enormous surface area may have potential applications.