Pattern formation of Si surfaces by low-energy sputter erosion

The evolution of silicon surfaces has been investigated using atomic force microscopy after low-energy (≤ 50 keV) Xe+ ion irradiation at room temperature with low ion fluences (≤ 1 × 1016 ions/cm2). Different effects have been observed as a function of the incidence angle of the ion beam: mountain-like roughening occurs near normal direction (θ ≤ 45°), whereas ripple formation takes place with the wave-vector parallel (60° ≤ θ ≤ 75°) or perpendicular (θ ≥ 80°) to the ion beam direction for larger angles. Threshold values for the ripple formation have been measured as low as 5 keV for the ion energy and 3 × 1015 ions/cm2 for the ion fluence.