Cross-sectional view of macroporous Si. Showing (a) an array of microbeakers with depth approximately 8.5 μm and cross-sectional diameter approximately 1.5 μm formed on a 100 Ω-cm wafer, with J = 5 mA/cm2, t = 90 min and HF/DMF ratio = 1:9 and (b) an array of micro test tubes having length approximately 45 μm grown on a 10 Ω-cm wafer with the same parameters as mentioned in (a). The inset shown in (a) is the top-view of the sample showing regular pores thereby revealing that the apparent irregularity of the top surface of the cross-sectional view is introduced during cutting the sample in order to obtain the cross-sectional image. The inset shown in (b) reveals regular nature of the pores running almost parallel to each other with pore size as well as the inter-pore distance typically approximately1 μm.
Ghoshal et al. Nanoscale Research Letters 2011 6:540 doi:10.1186/1556-276X-6-540