Fig. 3

SEM images of the Si surface etched in solutions with H₂O concentrations of a 46 M, b 48 M, and c 50 M and HF–H₂O₂ molar ratios of (i) 0.7, (ii) 0.75, (iii) 0.8, (iv) 0.85, (v) 0.9, (vi) 0.95, and (vii) 0.99. d–g High-magnification SEM images of the samples in a (i), (ii), (iii), and (vii), respectively. Samples were etched in HF–H₂O₂ for 30 min