Mechanistic details of the formation and growth of nanoscale voids in Ge under extreme conditions within an ion track

Abstract

The initial steps of Ge nanovoids formation have been studied. Two step energetic ion irradiation processes was used to fabricate novel and distinct embedded nanovoids within bulk Ge. The formation of voids in amorphous-Ge (a-Ge) and their size, and shape evolution under ultra-fast thermal spike within ion track of swift heavy ion, is meticulously expatiated using experimental and theoretical approaches. The 'bow-tie' shape of void formed in single ion track tends to attain spherical shape as the ion tracks overlap at about 1×10 12 ions cm-2 and the void assumes prolate spheroid shape with major axis along the ion trajectory at sufficiently high ion fluences. Small angle X-ray scattering can provide information about primary stage of void formation hence this technique is applied for monitoring simultaneously their formation and growth dynamics. The results are supported by transmission (XTEM) and scanning (XSEM) electron micrographs. The multi-timescale theoretical approach corroborate the experimental findings and relate the bow-tie shape void formation to density variation as a result of melting and resolidification of Ge within thermal spike generated along ion track plus non-isotropic stresses generated towards the end of the thermal spike.

Fundamental Phenomena and Applications of Swift Heavy Ion Irradiations

“…The bow-tie structure results from radially inward re-solidification and expansion of material into the void with a shape well reproduced by simulations (Fig. 23) [106,341]. The produced voids are potential precursors of the formation of a macroscopic sponge-like porosity observed under high fluence irradiations [342].…”