Fig. 7

TEM images of fabricated SiNWs with a length of ≈20 μm showing the variation of porosity at the middle section with a–c HF–H₂O₂ molar ratio and d, b, c H₂O concentration. a–c HF–H₂O₂ molar ratio of the etchant was 0.92, 0.95, and 0.98, respectively, with [H₂O] = 48 M. d, b, c H₂O concentration of the etchant was 46, 48, and 50 M, respectively, with HF–H₂O₂ molar ratio = 0.95. TEM images of SiNWs with f–h low and i–k high porosity corresponding to those shown in c and e, respectively, but including the f, i top and h, k bottom sections. The scale bar in e and k also applies to the images in a–d and f–j, respectively