Surface Modificationwith heavy Mon- and Polyatomic Ions

Self-organization of nanopatterns on solid surfaces by ion irradiation is a well-established technique to create regular and ordered structures like ripples or dots. Characteristics of patterns can be controlled selecting different ion species as well as by varying their energy, fluence, incidence angle or the sample temperature during irradiation. To date, mostly monatomic ions with masses between 40 (Ar) and 131 amu (Xe) were used for self-organized nanopatterning or contrary for surface smoothing. A comprehensive review is given.Here, self-organization of periodic patterns by bombardment with polyatomic/cluster ion species with masses of up to ~835 amu is studied – a regime not explored so far. Each impact of a very heavy polyatomic projectile deposits within femtoseconds an extremely high energy density into a local, near-surface volume. The achieved energy density exceeds that of irradiation with monatomic ions of medium mass considerably, it is of the order of femtosecond laser irradiation or swift heavy ion bombardment. Therefore, compared to former ion-induced pattern formation, different pattern based on different mechanisms can be expected.A new quality of pattern on Ge surfaces are obtained by Bi2, Bi3, Bi4 and Au2, Au3 ion irradiation. Polyatomic ions are provided by liquid metal (alloy) ion sources (LM(A)IS) in a mass-separating 30 kV focused ion beam (FIB) system. Results are compared to monatomic Bi and Au ion irradiation using otherwise equivalent irradiation parameters. For this, SEM and AFM were applied to investigate the pattern formation in dependence on ion species, energy per projectile atom, fluence, incidence angle and target temperature. Finally, a consistent, qualitative model for the surface evolution relating on energy density deposition sufficient for localized, transient nano melt pool formation is discussed.