Grafting and Polymer Formation on Silicon from Unsaturated Grignards:  I− Aromatic Precursors

Abstract

Anodic decomposition of a phenylmagnesium halide at a surface-hydrogenated silicon electrode leads to formation of polymeric layers covalently anchored to the silicon surface. These layers have been characterized using spectroellipsometry, photoluminescence, infrared, and X-ray photoelectron spectroscopies. The phenyl ring appears preserved in the process, and the polymer formed is a polyphenylene. Contamination by aliphatic groups from the solvent may be minimized by using a solvent resistant to hydrogen abstraction by the phenyl radicals. Regioselectivity of the branching may be oriented to the para form by using 4-chlorophenylmagnesium bromide as the precursor.

Electrografting: a powerful method for surface modification

“…Anodic electrografting of Grignard reagents (RMgX) has been investigated on Si, an easily oxidized substrate, but the experiments were performed in extra dry (Grignard reagents are intrinsically dry as they react immediately with traces of water) and oxygen-free conditions to avoid the oxidation of Si to SiO 2 . [101][102][103][104][105][106][107] Photoanodic grafting has been performed to obtain patterned surface by use of a mask. 108 Thermal grafting is also possible with Grignard reagents but the layers are of lower quality.…”

“…It should noted that the solutions are highly resistive, precluding any electrochemical investigation. SiH surfaces have been modified with methyl, 102,111 alkyl, 103,108,111,112 aryl, 106 or vinyl and ethynyl 107,113 Grignard reagents. The modified surfaces have been characterised by IR as Si itself can be used as an ATR (Attenuated Total Reflectance) prism.…”

Regular poly(para-phenylene) films bound to gold surfaces through the electrochemical reduction of diazonium salts followed by electropolymerization in an ionic liquid

“…This method could be applied to different substrates including carbon, platinum, ITO… As it involves an oxidation, the substrate must resist at quite positive potentials. It would be interesting to carry out the strategy on more common and cheaper substrates; experiments are under course to test the approach on substrates such as stainless steel and silicon under ultra dry conditions [60].…”

(Allesandro Volta Award Presentation) Facts and Challenges in the Electrochemistry and Wet Surface Chemistry of Silicon

“…In the context of the development of high-K oxide technology for next-generation MOSFETs, the unique thermal stability of the methylated Si surface has been proposed as a method to avoid formation of an interfacial SiO2 layer during MOCVD deposition of HfO2 on silicon (153). Aromatic or unsaturated groups (vinyl, ethynyl) can also be grafted from Grignard precursors (154,155). However, in that case the aryl, enyl or ynyl radical formed is able to abstract hydrogen from most solvents and to undergo reactions with the already grafted groups.…”

“…Solvent attack may be avoided by exchanging the ether with 1,2-dichlorobenzene, but anyway the reaction is not self-limited to a monolayer. It has been shown that using 4-chlorophenyl magnesium bromide as the precursor orients the attachment of new phenyl groups in the para-position, providing a simple method to form poly-paraphenylene layers anchored to silicon (154).…”