Figure 2: Predictions and comparison with experiment.

Comparison between predicted and measured wavelength for Si irradiated by Ar⁺ at 250 eV. Coefficients S_X(θ) and S_Y(θ) in the linearized evolution equation (4) were calculated with a flux of f=3.5×10¹⁵ ions cm⁻² s⁻¹ for comparison with experimental conditions²³. (a, b) Coefficients of ∂²h/∂x² and ∂²h/∂y² in the linearized evolution equation using the experimental flux. These coefficients are dominated by redistributive effects. (c) Comparison of predicted ripple wavelengths with average experimentally observed wavelengths (see ref. 23). Circles/squares indicate experimental patterns with wavevector parallel/perpendicular to the beam (parallel mode and perpendicular mode, respectively), and the vertical dashed black lines indicate experimental phase boundaries. Error bars indicate the full-width at half-maximum measure of the peaks in the power spectral density associated with atomic force microscopy images of experimental samples. On top of this, the solid black line indicates our predicted wavelengths (which are all parallel mode), and the dashed blue line indicates the wavelengths predicted if erosion were neglected entirely.