SEM and TEM micrographs from SiNWs on highly boron-doped Si. Cross-sectional SEM and TEM micrographs of long porous SiNWs on p+ Si (resistivity 0.005 Ω·cm) etched for 20 min (a1, b1, and c1) and 60 min (a2, b2, and c2), respectively. Micrographs (a1) and (a2) are SEM images of the nanowires at low magnification and illustrate the existence of a porous Si layer at the interface between the nanowires and the Si substrate. This layer is thicker in the case of the longer etching time, and its structure is porous as it clearly appears in the SEM images (b1) and (b2), obtained at higher magnification. On the other hand this layer is thinner in the case of the 20-min etching time, as illustrated in (b1). Micrographs (c1) and (c2) are dark-field TEM images of the same nanowires etched for 20 min (c1) and 60 min (c2), respectively.