Pore morphology, porous silicon

Fig. 3 Hysteresis loops of Ni particles (full line), Ni ellipsoides (dotted line), and Ni wires (dashed line) deposited within the pores of porous silicon, whereas the morphology has been the same. The coercivity as well as the remanence decreases with increasing elongation of the metal nanostructures. The magnetic field has been applied perpendicular to the sample surface...

Dvoyashkin et al. (2009) studied surface diffusion of n-heptane in two mesoporous adsorbents with different morphologies of the pore network (Vycor random porous glass and porous silicon with linear pores) using PFG-NMR (Figure 1.238). The obtained diffusivities revealed increasing... 

Fig. 4 SEM images of netiroblastoma cells cultured on a porous silicon porosity gradient. The cells display different morphology dependent upon die pore size, (a) 1,000-3,000 nm pores, (b) 300-1,000 nm. (c) 50-100 nm and (d) 5-20 nm (Khung et al. 2008)...

Thermal analysis and calorimetry offer versatile possibilities to study different physical and chemical changes in materials. Calorimetry gives accurate and valuable information on phase transitions of nanostructured materials and is therefore very usefiil in studies of mesoporous materials. The use of calorimetry in porous silicon research focusing on drug delivery applications and pore morphology determination is reviewed. 

Linsmeier J, Wust K, Schenk H, Hilpert U, Ossau W, Fricke J, Arens-Fischer R (1997) Chemical surface modification of porous silicon with tetraethoxysilane. Thin Solid Films 297 26-30 Mason MD, Sirbuly DJ, Buratto SK (2002) Correlation between bulk morphology and luminescence in porous silicon investigated by pore collapse resulting from drying. Thin Solid Films 406 151-158... 

This kind of pore can be obtained under a variety of conditions and with differing morphologies (see chapter Routes of Formation for Porous Silicon ). In this review, we focus on electrochem-ically etched macropores. The key parameters are the electroljde type (aqueous (aqu), organic (org), oxidant (ox)) the HF concentration, the surfactant, the Si doping type and level (n, n", p, p" ), and in some cases the illumination (backside illumination (bsi) or frontside illumination (fsi)). Detailed reviews regarding their formation are available (F6U et al. 2002 Lehmann 2005 Chazalviel and Ozanam 2005 Lehmann 2002 and handbook chapter Porous Silicon Formation by Anodisation ). 

Table 1 lists t3q)ical values for different t3tpes of porous silicon. The higher the porosity, for similar pore size distributions and skeleton morphology, the lower the Young s modulus. At the highest levels of mesoporosity (with small pore size) studied, it can be reduced to values around 1 GPa, even lower than that of polymers Uke nylon and polyst5n-ene. For primarily macroporous silicon, the reduction in stiffness versus porosity is less dramatic (Wang et al. 2011). 

If a molten active is slowly added to the surface of a porous silicon film attached to its parent wafer, it intrudes into the pore structure at a rate that depends primarily on both the viscosity of the melt and the pore morphology. If the porous silicon is in the form of detached, freestanding flakes, these can... 

Lehmann V, Stengl R, Luigart A (2000) On the morphology and the electrochemical formation mechanism of mesoporous silicon. Mater Sci Eng B 69 11-22 Li MD, Hu M, Liu QL, Ma SY, Sun P (2013) Microstructure characterization and N02-sensing properties of porous silicon with intermediate pore size. Appl Surf Sci 268 188-194 Lysenko V, Vitiello J, Remaki B, Barbier D (2004) Gas permeability of porous silicon nanostructures. Phys Rev E 70(1) 017301... 

The main advantage of most microscopy techniques is that they allow the direct characterization of the morphology at the micron- and nanoscale and thus are not based in indirect results to determine, for instance, the typical nanocrystal or pore size. Also, many of these techniques are nondestructive and can be combined for the study of a given sample. In the following sections, a non-exhaustive review of the most notable uses of different microscopies applied to the study of porous silicon is presented. 

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