Angle-dependent sputtering and pattern formation by polyatomic ion irradiation

The very high erosion rates of heavy projectiles, in particular Bi dimer and trimer ions on different substrates were investigated in relation to the ion incidence angle. In the case of high angle irradiation attended by a ripple structure formation the erosion rate is decreased due to the wide variety of surface angles faced to the beam. On the eroded surfaces very regular, high-amplitude dot and ripple patterns on Ge and Si are formed under the heavy polyatomic ion impacts, which differs significantly from surface mor-phologies formed by monatomic ion irradiation [1]. Dot and ripple heights equal to their wavelengths can be achieved. The Bi2+ and Bi3+ ions are extracted from a liquid metal ion source [2], are mass separated, focused and scanned using a focused ion beam sys-tem. Studies are performed for fluences of 1e14 to 1e17 ions/cm2 in the ion impact angle range from normal to 85°. In Ge hexagonally ordered dot patterns with ~30 nm diameter and nearly the same height are found in the incidence angle range from 0° to 30° for Bi3++ ions [3] followed by a smoothening region up to 60°. Incidence angles from 60° to 80° cause a pronounced ripple structure on the Ge surface. For nearly grazing incidence, shingles perpendicular to the beam direction are found. FIB cross section imaging shows that the slope of the shingles is parallel to the ion incidence direction. The angle-dependent behaviour of pattern formation is summarized in a phase diagram.
[1] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, Journal of Vacuum Science and Technology B 30 (2012) 06FF12.
[2] L. Bischoff, W. Pilz, P. Mazarov and A.D. Wieck, Applied Physics A99 (2010) 145.
[3] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz, Nucl. Instr. and Meth. B 272 (2012) 198.