Porous orientation dependence

After treating of porous silicon in a solution of HCl a noticeable reconstmction of XANES is observed (Fig. 1). For both types of the substrate orientation the slope of the spectra near absorption edge becomes more sharp. This effect is revealed especially for the sample on <100> oriented substrates as a considerable increase in relative intensity in the range of c-Si edge. It means that there is different kind of chemical activity relative to chemical reagents in the siuface layers of porous silicon depending of the substrate orientation which [2]. 

In an oriented porous medium, the resistance to flow differs depending on the direction. Thus, if there is a pressure gradient between two points and a particular fluid particld is followed, unless the pressure gradient is parallel to oriented flow paths, the fluid particle will not travel from the original point to the point which one would expect. Instead, the particle will drift. 

All the highly crystalline Type I sputtered films are more or less porous, with densities of the order of 3,8 gm cm , compared with a typical value of 4.92 gm cm quoted for fully dense single crystals. Fleischauer et al pointed out that the ease with which the crystals can bend to a basal plane orientation will depend on the crystal size and the density of packing. They also suggested that an increased degree of pre-etching of the substrate would increase the number of reactive sites available for crystal formation, and therefore the density of crystal packing, as well as the... 

As discussed in the previous chapter, the network of the inter-connected membrane pores formed during preparation and fabrication may be tortuous or nearly straight depending on the synthesis and subsequent heat treatment methods and conditions. The microstructure of a membrane, particularly the type with tortuous pores, is too complicated to be described by a single parameter or a simple model. Due to the relatively poor knowledge of flow through porous media, an empirical term called " tortuosity" has been introduced and used by many researchers to reflect the relative random orientation of a pore network and is based on the Kozeny-Carmen equation for the membrane flux, J ... 

Oberlin and coworkers [42, 90] (Fig. 2.7c) used a crumpled sheets of paper model to describe the nanotexture of porous carbons. Figure 2.19 depicts this model and includes an enlarged sketch of pores in sucrose-based carbons [91]. In Fig. 2.19a, each zone of molecular orientation is represented by a shaded area inside of which each individual stack is shown either as a rectangular unit or as two parallel segments depending on whether they are observed in perspective... 

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