Silicon, surface attachment

To date, numerous radical-induced hydrosilylations of terminal olefins or acetylenes have been reported for the H-terminated Si(l 11) surfaces. These reactions are mainly performed by using thermal conditions, UV irradiation, or electrochemistry. More recently, a very mild method was developed for the attachment of high-quality organic monolayers on crystalline silicon surfaces. 

Si-C formation technique with hydrogen-terminated silicon substrates can also be used as the covalent attachment of nanomaterials onto silicon surface. The possibility of assembling nanomaterials in order is strongly desired in order to enable efficient utilization of their unique nano-sized properties. Ordered arranging and position controlling of nanomaterials on solid substrates especially on silicon surface have been intensively studied [10]. In this manuscript, the nanoparticle immobilization by thermal Si-C formation will be discussed [11]. 

Linford and coworkers have shown that the attachment of alkenes to H-terminated silicon surfaces can also be initiated by direct mechanical scribing, in a process termed chemomechanical functionalization [145-147]. The reaction of 1-alkenes (as well as 1-alkynes) leads to attachment of the molecule to the surface through two new Si—C bonds. The proposed mechanism is the mechanical cleavage of Si—H and Si—Si bonds, leading to silicon radicals that then react with the reactive liquid. Interestingly, Linford and coworkers have also extended this work to show that chemomechanical functionalization can be carried out not only on H-terminated Si, but also on sihcon covered with oxide, and have shown that the process works with a variety of halides, alcohols, and epoxides in both the liquid and gas phase [146]. 

This is the most important step of microarray technology. Attachment of a single DNA molecule to a silicon surface can be done by either one of the following methods. 

Fig. 12 Illustration outlining MIP film fabrication. The C-terminus nonapeptide epitope is attached through a tether to a glass or oxidized silicon surface by the N-terminal amino acid of the peptide. Monomers are photochemically cross-linked while remaining in contact with the peptide modified surface. Following polymerization, the glass substrate is removed. The protein can now bind to the MIP via its C-terminus nonapeptide epitope. Modified from [114]...

The simplest hydrocarbon molecule is acetylene HC=CH, which in vacuum possesses a triple carbon carbon bond. If this molecule attaches to a clean silicon surface, it has essentially two options it can either adsorb on the tip of a silicon dimer, where the C-C bond in this case is reduced to a double bond or it can attach to two adjacent dimers, if the C-C bond is reduced to a single bond. There was some controversy, a few years ago, about the preferred adsorption site. Different methods seemed to reach a different conclusion concerning the actual adsorption geometry under different thermal conditions (for an outline of the discussion, see [57]). There were essentially two diverging opinions (i) There are only two adsorption... 

Methods for the direct organic functionalization of silicon using wet chemical methods usually begin with H-terminated silicon surfaces. This is because the H-terminated surface is reasonably stable and thus can be handled in various solvents, facilitating the attachment of a variety of molecules via solution phase chemical reactions. While both H-terminated Si(lll) and Si(100) surfaces have been used as starting points for organic... 

Fig. 9. HREELS spectra of functionalized silicon surfaces prepared via photochemical reactions with H/Si(lll). In each case R represents a saturated alkyl chain (9 or 10 carbon atoms long) covalently attached to the Si surface. The methyl and acid terminated surfaces were prepared via reactions with decene and undecylenic acid respectively while the thienyl terminated surface was prepared by reaction of thienyl Li with an ester terminated surface. The dashed line at 1500 cm-1 represents the typical low frequency cut-off for ATR-FTIR measurements on silicon.

As discussed in the introduction, a major motivation for the development of methods to controllably functionalize silicon surfaces is the opportunity to create novel hybrid organic/silicon devices. By integrating organic molecules with silicon substrates it should be possible to expand the functionality of conventional microelectronic devices. Possibilities include high-density molecular memory and logic as well as chemical and biochemical sensors. Realization of these opportunities requires not only the development of the attachment chemistries, as discussed in the previous sections, but also detailed studies of the electronic properties of the resulting surfaces. 

While the discussion in this chapter has focused on molecular layers on single crystal silicon surfaces, the attachment chemistries discussed here could easily be applied to functionalize silicon nanowires or nanoparticles. Silicon nanowires have been shown to exhibit interesting electrical transport characteristics and have been used to fabricate nanoscale pn junctions [95], field effect transistors [96] and biochemical sensors [97-100]. However, all these interesting phenomena have been reported on oxidized silicon nanowires. It is likely that better control over the surface properties, as could be achieved by employing some of the chemistry discussed here, could significantly improve the performance of these nanowire-based devices. From another perspective, silicon nanowires could prove extremely... 

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