Porous silicon surface derivatization

A second example concerns another common processing step - chemical passivation of porous silicon surfaces, in particles or patterned wafers. There are three dedicated reviews in the handbook that deal with this Oxidation of mesoporous silicon, Silicon-Carbon Bond Formation for Porous Silicon, and Photoluminescent Nanoparticle Derivatization for Porous Silicon. It can be important to perform these passivation treatments after the particle sizing or patterning process otherwise freshly fractured or patterned porous silicon surfaces will not be passivated. Note that for some applications one can also choose to derivatize the pore walls during anodization (Mattei and Valentini 2003) rather than the more common sequence to derivatize after, or even both during and after anodization to get specific surface chemistries and spatially selective functionalization (Valentini et al. 2007). 

Fig. 16.5. Synthetic methods employed for the functionalization of hydride-passivated porous silicon with monolayers bound via Si-C bonds. Derivatization has been accomplished through the cleavage of Si-Si surface bonds as well as by the reaction of Si-H groups.

Harper TF, Sailor MJ (1997) Using porous silicon as a hydrogenating agent derivatization of the surface of luminescent nanocrystalline silicon with benzoquinone. J Am Chem Soc 119 6943-6944... 

Although silicon nanocrystals are now more commonly prepared by a variety of means which are easier to scale up, e.g., pyrolysis of silanes (Xuegeng et al. 2004), thermal treatment of silsesquioxanes (Hessel et al. 2006, 2010), and from reactions of molecular silicon compounds (Wilcoxon et al. 1999 Bley and Kauzlarich 1996), this review will concentrate on routes which proceed via the formation of porous silicon. More general reviews of silicon nanocrystals Irom physics and chemistry perspectives are available (Shirahata 2011 Kang et al. 2011 Heitmann et al. 2005). Derivatization of porous silicon and SiNCs usually relies on the chemistry of the hydrogen-terminated silicon surface, which shares some of the organic reactivity of hydrosilanes (Buriak 2002). Reaction with alcohols results in Si-O-C bonded monolayers (Sweryda-Krawiec et al. 1999), but these are suseeptible to hydrolysis under ambient conditions. Alternately, addition of surface Si-H aeross a C = C double bond produces Si-C bonded monolayers, which are very stable. 

Huck LA, Buriak JM (2012) Toward a mechanistic understanding of exciton-mediated hydrosilylation on nanocrystalline silicon. J Am Chem Soc 134 489 97 Kilian KA, Booking T, Gooding JJ (2009) The importance of surface chemistry in mesoporous materials lessons from porous silicon biosensors. Chem Commun 6 630-640 Kim NY, Laibinis PE (1998) Derivatization of porous silicon by grignard reagents at room temperature. J Am Chem Soc 120 4516 517... 

In most of these applications, silica has the role of a support material. The popularity of silicon-based supports for multiple modification applications is well summarized by Mottola.1 Chemical modification requires seemingly paradoxal support properties (a) supports need to have a surface hydrophilic in nature but also to be insoluble in aqueous solutions and polar solvents (b) supports are required, in many instances, to be porous but retain mechanical stability and (c) they must be chemically stable but easily derivatized. Silica gel meets all of these requirements. 

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