Paper SS1-MoA8
Role of Substituents in Reactivity of Isocyanates Pre-Adsorbed on Ge(100)-2×1

Monday, October 31, 2011, 4:20 pm, Room 109

Direct attachment of organic molecules to semiconductor surfaces offers the ability precisely control interfacial properties through tailoring of the organic molecule. This study focuses specifically on organic functionalization of germanium, as the ability to control its interfacial properties may enable devices to take advantage of its favorable electronic properties, as compared to silicon. Past studies have shown that a number of isocyanate-containing molecules react with the Ge(100)-2×1 surface in ultra-high vacuum by [2+2] cycloaddition across the C=N bond of the isocyanate. In this study, we use in situ Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy to investigate further reaction following [2+2] cycloaddition. Density functional theory calculations are also used to corroborate and help understand these experimental results. We show that phenyl isocyanate pre-adsorbed on Ge(100)-2×1 is highly sensitive to subsequent exposure to water vapor. Experimental evidence suggests that water reacts with the adsorbed isocyanates to form a diphenyl urea compound, similar to what is expected for the reaction of phenyl isocyanate and water in solution. Extending the analogy with classic organic chemistry in solution, we find that addition of methyl or methoxy substituents to the phenyl ring of phenyl isocyanate can significantly decrease the adsorbed isocyanate’s reactivity towards water. Such ability to easily tune the reactivity of an adsorbate-covered surface using principles from organic chemistry demonstrates the flexibility of organic functionalization and could be of importance when using organic functionalization for various applications.