Figure 5.

AFM images of Si surfaces after sputtering with 500 eV Ar ions under different angles θ: (a) $\theta ={30}^{\circ }$, $\Phi =5.7\times {10}^{18}$ cm${}^{-2}$, height scale 2 nm; (b) $\theta ={50}^{\circ }$, $\Phi =2\times {10}^{18}$ cm${}^{-2}$, height scale 3 nm; (c) $\theta ={55}^{\circ }$, $\Phi =2\times {10}^{18}$ cm${}^{-2}$, height scale 3 nm; (d) $\theta ={67}^{\circ }$, $\Phi =1.7\times {10}^{18}$ cm${}^{-2}$, height scale 10 nm. The size of the images is $1\times 1$ μm${}^2$; the ion beam was entering from the left.