Structural modification of swift heavy ion irradiated amorphous germanium layers

Swift heavy ion (SHI) irradiation of conventional glasses results in non-saturable plastic flow as a consequence of the ion hammering effect [1]. SHI irradiation of amorphous Si (a-Si) at non-perpendicular incidence also leads to unsaturated plastic flow, which shows a linear dependence on the ion fluence. The positive direction of flow suggests that a liquid phase with density similar to that of the amorphous solid must exist [2]. For room temperature irradiation of a-Si to a very high fluence (~2.5×10 cm), the plastic flow is accompanied by swelling due to the formation of voids. Room temperature SHI irradiation of amorphous Ge performed at the ANU accelerator facility has shown a positive plastic flow as well, demonstrating that liquid polymorphism is common for these two semiconductors [3]. In contrast to amorphous Si, the formation of voids in amorphous germanium begins at a much lower fluence (10 ions/cm). As a consequence of the void formation, a nonlinear plastic flow process is observed. Figure 1 shows an optical micrograph of the surface of the amorphous germanium layer with a thin quadratically shaped gold marker layer. By means of the gold squares on the samples surface the two effects, namely plastic deformation and swelling are clearly visible (see [3, 4] for more information).