Porous silicon specific area

Porous silicon structures have been studied in order to provide combustion and explosion this material. The combustion process has been observed in the porous silicon layers formed by anodization if the specific area is more than 100 mVcm We have also found that the combustion intensity increases with porous silicon specific area and if the latter is larger than 200 mVcm the explosion process occurs. The time response of explosion development is in the microsecond range. 

In addition to dense monolithic ceramics, porous silicon nitrides are gaining more importance in technological applications [24], Some porous silicon nitrides with high specific surface area have already been applied as catalysis supports, hot gas filters and biomaterials [25], There is an emerging tendency to facilitate silicon nitride as biomaterial, because of specific mechanical properties that are important for medical applications [25], Moreover, in a recent study it was shown that silicon nitride is a non-toxic, biocompatible ceramic which has the ability to propagate human bone cells in vitro [25], Bioglass and silicon nitride composites have already been realized to combine... 

Fast oxidation process in a way of combustion and, in some cases, of explosion in porous silicon films has been observed at pore wall thickness less than 10 nm. The increasing of porous specific area results in an enhancement of combustion and explosion intensity. The explosion process has been observed at the specific area more than 200 m /cm. Thus combustion and explosion processes in the porous silicon layers can be attributed to nanoscale phenomena. 

The method discussed shows the availability of platinum coats as catalytic layers for electrodes of micro fuel cells based on porous silicon. The calculated specific surface area confirms the efficiency of the coats obtained. 

Porous silicon (PS) is one of the nanoscale modifications of silicon. There are various approaches to PS producing that are now in use. The technique most generally employed today is known as wet anodization of a crystalline silicon. With this technique, yield parameters of porous material (porosity, pore size and shape, interpore distance) may be readily varied by anodization regimes. However, it is well known the problem of the PS stability influencing the physical properties of the PS layers. P S instability is c onditioned b y very large specific surface area of the porous material. 

Porous silicon films of one particular color have recently shown potential in a number of specific application areas. The so-called black silicon has been etched into a morphology that almost completely suppresses optical reflectivity over a very broad spectral range (Koynov et al. 2006). Its visual appearance however does not directly impact most of the uses currently under development. 

Halimaoui A (1994) Determination of the specific surface area of porous silicon from its etch rate in HF solutions. Surf Sci Lett 306 L550-L554... 

Becker et al. (2010a) have optimized the process to produce thick, high-surface-area por-Si films for applications as an explosive material (see chapter entitled Energetics with Porous Silicon ). Films up to 150 pm thick with specific surface area 700 m g and pore diameters 3 nm were fabricated. 

A variety of processing steps have been utilized to achieve the desired physical forms and surface properties with porous silicon. Judicious choice of their order and overall process route can assist in optimization of properties for a specific use. Further improvements in maximum surface areas and porosities are likely to come from a combination of optimized etching, drying, and passivation steps. Improvements in chemical and mechanical stability are anticipated from optimized passivation and nanocomposite design, respectively. Improvements in control over particle size and shape dispersion are desired, but the feedstocks need to be inexpensive and the processing routes need to be scalable for maximum benefit. Some of the secondary processing techniques developed with other highly porous materials (see, e.g.. Wen et al. 2001, Hollister 2005, Conde et al. 2006, Studart et al. 2006) are likely to be utilized in the future. 

In some applications, porous silicon (PSi) is, however, desired to increase the specific surface area (up to 1000 mVcm ). Several books and reviews have been already published about PSi formation mechanisms, morphologies and optical properties (cf [130-133]). Briefly, PSi is usually prepared from (100) Si wafers by constant-current anodization in an ethanolic solution (mixture of HF with ethanol). The characteristics of the pores are determined by the doping of the substrate, the HF concentration and the cturent density used during the anodization process [134-139]. PSi surfaces present =Si-H, =SiH2> and trihydride (-SiHj) sites. Potential steric hindrances could appear most hkely when micropores formation is obtained. It should be mentioned that PSi received increasing interest in the 1990s because of its luminescence properties in the visible range. 

With a hypothesis of a porous carbon with a porosity of 30%, a diameter of 2pm, and a specific surface area of 300m g Thus the length of silicon in pore reaches 25.58mm per second. 

We carried out comparative studies of the effect of the porous structure of carbon materials on electrochemical electrode characteristics using various carbide carbons (CCs). Main structural characteristics for CCs based on silicon carbide are presented in Table 27.3 and those for titanium carbide are in Table 27.4. Specific surface areas were calculated on the basis of the nitrogen adsorption data with calculation using the DFT technique. This method is used to measure micropores and mesopores, but not macropores. 

A distinctive feature of CCs based on titanium carbide as compared to CCs based on silicon carbide is a higher specific surface area under similar synthesis conditions. Figure 27.18 shows comparison of capacitance-voltage dependences (potentials are measured vs. a porous carbon electrode with high capacitance) for four CCs in a sulfuric acid solution for the range of maximum reversibility, that is, the range of EDL charging. 

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