In the gas phase, electron beam irradiation of a furoxan molecule results in the production of two NO molecules and concomitant generation of a triple bond. In this study, we examined whether the selective cleavage of furoxan occurs on the surface of silicon wafers. A furoxan-substituted imine layer was prepared by the reaction of aminosilylated silicon wafers with 4-furoxancarbaldehyde. Formation of the imine layer was confirmed by UV-vis spectroscopy, contact angle goniometry, ellipsometry, and XPS. XPS spectroscopic monitoring of the electron beam (400 eV) induced reaction of the modified silicon wafers showed that two of the furoxan ring nitrogen atoms were lost. To determine if a carbon-carbon triple bond had been generated in the surface product of this reaction, FT-IR spectroscopy and NEXAFS (Near Edge X-ray Absorption Fine Structure) were performed. A weak absorption at 2203 cm-1 was observed in the FT-IR spectrum, reflecting the presence of a triple bond. The carbon K-edge NEXAFS spectrum contained a π*(C≡C) peak at 286.5 eV. Based on these results, we conclude that electron beam irradiation of the furoxan, incorporated on a silicon wafer surface, results in the release of nitrogen oxide and the formation of a triple bond containing product.
We have studied ways to control density as well as spacing among functional groups. In particular, we observed that use of aziridine for the surface hyperbranching polymerization yielded extremely high surface density of primary amine that is useful for the immobilization of molecules of biological relevance such as oligo DNA. Also, an employment of dendrons of appropriate molecular architecture provided mesospacing among the reactive functional groups. The spacings was expected to guarantee the freedom of the biological macromolecules so that their properties are close to that in solution in spite of the confinement in the two dimensional world. We demonstrated that this was the case for oligonucleotide microarrays.