layers serve to shield the nanocrystallites from chemical attack, the organic surfaces themselves are not necessarily inert and can react further; this may be especially useful for the synthesis of functional interfaces that cannot be prepared directly at the silicon surface due to competitive oxidation or other undesired side
reactions. As the chemistry of silicon surfaces continues to advance, it is expected
that additional methods for the preparation of stable monolayers will be discovered, contributing further to the technological development of porous silicon
and to more complete understanding of its fundamental properties and reactivity.
16.4
Chemical Applications Based on Porous Silicon
The native properties of high surface area, luminescence, tunable biostability, and
reactive surface chemistry identify porous silicon as a potentially useful substrate
for a variety of tasks. Presented below are several uses that have been developed by
exploiting the chemical reactivity or changes effected by chemical interactions with
the nanocrystallites. These applications range from use as a material or structural
implant to use as a sensor or analytical support.
16.4.1
Bioactive Porous Silicon
Silicon is an attractive choice as a biomaterial because of its relative abundance,
semiconducting properties, and well-established practices for processing and modification. Bionic sensory and motor implants based on silicon could function as
electronic devices activated by the body’s own neural network [64]. Direct interfacing of silicon to biological systems without destruction of its electronic properties
or induction of cellular death is thus a key step toward the realization of these bionic devices. Flat, unetched bulk silicon is known to be largely bioincompatible
and thus unsuitable for in vivo applications. In contrast, porous silicon was found
to demonstrate bioactivity through the crystallization and growth of hydroxyapatite
films directly upon its surface (Figure 16.7) [65]. Since the publication of this report and subsequent works [66, 67], additional research into this aspect of porous
silicon has investigated the effects of surface terminations on biocompatibility.
It was demonstrated that an alkenyl monolayer interface renders the silicon surface bioinert [30, 68]; neither hydroxyapatite deposition nor dissolution of the
dodecenyl-functionalized porous silicon in simulated body fluid (SBF) was observed. By altering the surface chemistry of nanocrystalline silicon, the bioactivity
of this material can be modestly controlled. Encouraged by these promising findings, other groups are investigating porous silicon for real-world biochemical applications.
Ji et al. have adapted soft lithographic microcontact printing [69, 70] with specific etching procedures to produce patterned porous silicon substrates for the
spatially-controlled deposition of calcium phosphate [71]. Calcification, confirmed
16.4 Chemical Applications Based on Porous Silicon 527
reactions. As the chemistry of silicon surfaces continues to advance, it is expected
that additional methods for the preparation of stable monolayers will be discovered, contributing further to the technological development of porous silicon
and to more complete understanding of its fundamental properties and reactivity.
16.4
Chemical Applications Based on Porous Silicon
The native properties of high surface area, luminescence, tunable biostability, and
reactive surface chemistry identify porous silicon as a potentially useful substrate
for a variety of tasks. Presented below are several uses that have been developed by
exploiting the chemical reactivity or changes effected by chemical interactions with
the nanocrystallites. These applications range from use as a material or structural
implant to use as a sensor or analytical support.
16.4.1
Bioactive Porous Silicon
Silicon is an attractive choice as a biomaterial because of its relative abundance,
semiconducting properties, and well-established practices for processing and modification. Bionic sensory and motor implants based on silicon could function as
electronic devices activated by the body’s own neural network [64]. Direct interfacing of silicon to biological systems without destruction of its electronic properties
or induction of cellular death is thus a key step toward the realization of these bionic devices. Flat, unetched bulk silicon is known to be largely bioincompatible
and thus unsuitable for in vivo applications. In contrast, porous silicon was found
to demonstrate bioactivity through the crystallization and growth of hydroxyapatite
films directly upon its surface (Figure 16.7) [65]. Since the publication of this report and subsequent works [66, 67], additional research into this aspect of porous
silicon has investigated the effects of surface terminations on biocompatibility.
It was demonstrated that an alkenyl monolayer interface renders the silicon surface bioinert [30, 68]; neither hydroxyapatite deposition nor dissolution of the
dodecenyl-functionalized porous silicon in simulated body fluid (SBF) was observed. By altering the surface chemistry of nanocrystalline silicon, the bioactivity
of this material can be modestly controlled. Encouraged by these promising findings, other groups are investigating porous silicon for real-world biochemical applications.
Ji et al. have adapted soft lithographic microcontact printing [69, 70] with specific etching procedures to produce patterned porous silicon substrates for the
spatially-controlled deposition of calcium phosphate [71]. Calcification, confirmed
16.4 Chemical Applications Based on Porous Silicon 527