Investigating ripple pattern formation and damage profiles in Si and Ge induced by 100 keV Ar⁺ ion beam: a...

Desired modifications of surfaces at the nanoscale may be achieved using energetic ion beams. In the present work, a complete study of self-assembled ripple pattern fabrication on Si and Ge by 100 keV Ar⁺ ion beam bombardment is discussed. The irradiation was performed in the ion fluence range of ≈3 × 10¹⁷ to 9 × 10¹⁷ ions/cm² and at an incident angle of θ ≈ 60° with respect to the surface normal. The investigation focuses on topographical studies of pattern formation using atomic force microscopy, and induced damage profiles inside Si and Ge by Rutherford backscattering spectrometry and transmission electron microscopy. The ripple wavelength was found to scale with ion fluence, and energetic ions created more defects inside Si as compared to that of Ge. Although earlier reports suggested that Ge is resistant to structural changes upon Ar⁺ ion irradiation, in the present case, a ripple pattern is observed on both Si and Ge. The irradiated Si and Ge targets clearly show visible damage peaks between channel numbers (1000-1100) for Si and (1500-1600) for Ge. The clustering of defects leads to a subsequent increase of the damage peak in irradiated samples (for an ion fluence of ≈9 × 10¹⁷ ions/cm²) compared to that in unirradiated samples.