SEM micrographs of macropores prepared in the MeOH solutions with different HF concentrations. Cross-sectional views of porous layers anodized in 10–20 Ωcm prepatterned p-type silicon at 14 mAcm−2 for 1 h in HF: H2O:MeOH (a) 22:6:12 (ca. 30 wt.% HF) and (b) 5:6:29 (ca. 8 wt.% HF) in volume. Circles show the positions that have not undergone anodization.