Controlled Pore Formation on Mesoporous Single Crystalline Silicon Nanowires: Threshold and Mechanisms

Figure 5

Transmission electron microscopy (TEM) images of highly boron-doped, mesoporous silicon nanowires. (a) Scanning TEM (STEM) micrograph of a 100 nm thick nanowire. Lying on a carbon film the nanowire exhibits a porous surface with a uniform distribution of pores. (b) Selected area electron diffraction (SAED) pattern showing the remaining single crystalline structure of the wire. (c) High resolution TEM of the inner part of silicon nanowire with lattice fringes confirming single-crystalline structure; inset: Fourier transform proving the silicon diffraction pattern and the presence of an amorphous amount resulting from the native SiO₂ layer around the nanowire. (d) TEM image showing the rough and porous surface structure allowing one to estimate a pore diameter distribution from 5 to 15 nm and a depth of about 3 nm.