ABSTRACT
In the past decades, porous silicon (PSi) has attracted attention as a promising material for optoelectronic applications (Canham et al. 1996; Hirschman et al. 1996; Canhman 1997; Parkhutik 1999; Bisi et al. 2000; Foll et al. 2006; Kochergin and Foell 2006). Microporous Si became famous because of its unexpected optical property of showing strong luminescence from red-orange to blue, depending on its precise structure. However, exploiting this property for devices proved difficult if not impossible until now (Bisi et al. 2000; Kochergin and Foell 2006). Therefore, at present, the interest extends to other applications of PSi including biomedical, micromachining, and sensor applications (Steiner and Lang 1995; Di Francia et al. 1998; Marsh 2002; Angelescu et al. 2003; Zhu et al. 2005). PSi layers are very attractive from a sensor point of view because of a unique combination of crystalline structure: (1) a large internal surface area of up to 200-500 m2/cm2, which ables enhancement of the adsorbate effects, and (2) high activity in surface chemical reactions. Several investigations show that electrical and optical characteristics of PSi may change considerably on adsorption of molecules to their surfaces and by filling the pores (Feng and Tsu 1994; Mares et al. 1995; Canhman 1997; Cullis et al. 1997). This means that surface adsorption and capillary condensation effects in PSi layers can be used for development of effective sensor systems (Anderson et al. 1990; Parkhutik 1999).
