The fabrication of nano porous silicon, nPSi, using alkali etching process has been studied and carried out. The surface chemistry of anisotropic etching of n-type Si-wafer is reviewed and the anisotropic chemical etching of silicon in alkaline solution using wetting agents is discussed. Transformation of crystallographic plane of n-Si (211) to nPSi (100) has occurred on using n-propanol as wetting agent. The rate of pore formation was 0.02478 - 0.02827 μm/min, which was heavily dependent upon the concentration of the etchant containing wetting agents, allowing patterned porous silicon formation through selective doping of the substrate. A particle size of 15 nm for porous nano-silicon was calculated from the XRD data. Porosity of PS layers is about 10%. Pore diameter and porous layer thickness are 0.0614 nm and 16 μm, respectively. The energy gap of the produced porous silicon is 3.3 eV. Furthermore, the combination of PS with Congo Red, which are nanostructured due to their deposition within the porous matrix is discussed. Such nano compounds offer broad avenue of new and interesting properties depending on the involved materials as well as on their morphology. Chemical route was utilized as the host material to achieve pores filling. They were impregnated with Congo Red, which gave good results for the porous silicon as a promising pH sensor.
 Z. Swiatek, E. Betawska, W. Maziarz and F. Krak, “Characterization and Properties of a Modified Si Solar Cell Emitter by a Porous Si Layer,” Material Science and Engineering B, Vol. 101, No. 1-3, 2003, pp. 291-296. doi:10.1016/S0921-5107(02)00718-3
 P. Panek, M. Lipinski and J. Dutkiewicz, “Texturization of Multicrystalline Silicon by Wet Chemical Etching for Silicon Solar Cells,” Journal of Materials Science, Vol. 40, 2005, pp. 1459-1463. doi:10.1007/s10853-005-0583-1
 A. E. H. Kashyout, H. M. A. Soliman, M. Nabil and A. A. Bishara, “Fabrication of Nano-Porous Silicon Using Alkali Etching Process,” Materials Letters, Vol. 100, 2013, pp. 184-187. doi:10.1016/j.matlet.2012.12.107
 P. Rivolo, P. Pirasteh, A. Chaillou, P. Joubert, M. Kloul, J.-F. Bardeau and F. Geobaldo, “Oxidised Porous Silicon Impregnated with Congo Red for Chemical Sensoring Applications,” Sensors and Actuators B, Vol. 100, No. 1-2, 2004, pp. 99-102. doi:10.1016/j.snb.2003.12.029
 P. Pirasteh, J. Charrier, Y. Dumeige, A. Chaillou, M. Guendouz and L. Haji, “Study of Porous Silicon Optical Waveguides Impregnated with Organic Dyes,” Applied Surface Science, Vol. 253, No. 7, 2007, pp. 3440-3443. doi:10.1016/j.apsusc.2006.07.047
 T. E. Belly, P. T. J. Gennissenz, D. DeMunterz and M. Kuhl, “Porous Silicon as a Sacrificial Material,” Journal Micromechanical Microengineering, Vol. 6, No. 4, 1996, pp. 361-369. doi:10.1088/0960-1317/6/4/002
 Z. X. Zhao, R. Q. Cui, F. Y. Meng, B. C. Zhao, H. C. Yu and Z. B. Zhou, “Nanocrystalline Silicon Thin Films Prepared by RF Sputtering at Low Temperature and Heterojunction Solar Cell,” Materials Letters, Vol. 58, No. 30, 2004, pp. 3963-3966. doi:10.1016/j.matlet.2004.09.004