The transition from dot to ripple formation during erosion sputtering was studied as a function of the angle of incidence of the bombarding ions. For GaSb as target material we found that dot structures are obtained for angles smaller than with respect to the surface normal. We also observed an influence of impurities on the pattern formation. Small amounts of impurities serve as nucleation centers for the formation of differently shaped nanostructures. In addition, larger fragments of GaSb on the surface influence the pattern formation qualitatively; the fragment is sputtered and the sputtered material redeposited in the vicinity assists the generation of ordered dot structures. With the use of low-energy electron diffraction, we looked at the crystallographic surface properties of the dots. Dots produced with a small fluence could be recrystallized by moderate annealing. Higher fluences, however, cause an irreversible amorphization.
The fluence is the ion current in elementary charge per second times the bombarding time in seconds divided by the exposed area in .