Figure 6.

Morphology of the porous structure in the direction of pore depth. (a) Cross-sectional SEM image of macroporous silicon after chemical etching in 25 wt.% TMAH for 20 min. (b, c) Tilted images taken at an angle of 45° to the surface of macroporous silicon after chemical etching in 25 wt.% TMAH for (b) 30 and (c) 40 min. The conditions for Au-assisted chemical etching of (111) silicon were the same as those in Figure 5.