The mean radius r (a), height h (b), and separation (wavelength) l (c) of the dots plotted as a function of the ion fluence Φ. The error bars given in the plots represent the widths of the distributions of the respective values. The data are fitted by power-law dependences (dashed lines). (d) The rms-roughnesses of the corresponding AFM images. The ion flux was f = 1.5 × 1014 cm−2 s−1.