We report new and exciting experimental results on ion-induced nanopatterning of a-Si and a-Ge surfaces. The crystalline Si (100) and Ge (100) wafers were amorphized and an a/c interface was developed by pre-irradiation with a 50 keV Ar beam at normal incidence with an ion fluence of 5.0 10 ions cm. These amorphized surfaces were post-irradiated with Ar and Kr beams at an angle of 60°. The post irradiation was done with ion fluences of 1.0 10 ions cm. For each beam, two energies (50 and 200 keV for Ar, 100 and 250 keV for Kr) were chosen to ensure ion stopping in both sides of the a/c interface. Regular nanopatterning (in the form of ripples) is observed on the Ge surface only with the post irradiation of the Kr beam. The Si surface showed regular nanopatterning with the irradiation of both beams with two energies. For the ion beams crossing the a/c interface, ripples of higher amplitude and longer wavelength were formed. Further, the irradiation with a heavy beam yielded surface ripples of relatively larger amplitudes. The Raman measurements confirm amorphization of the pre-irradiated surfaces. Surprisingly, the post-irradiated Si surface with the 100 keV Kr beam showed evidence of recrystallization. In the paper we discuss the physics at the interface and explain the experimental findings.
Keywords: on-induced nanopatterning; a-Si and a-Ge surfaces; crystalline Si (100) and Ge (100) wafers;
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