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Study of the desorption mechanism of alkylsiloxane self-assembled monolayers through isotopic labeling and high resolution electron energy-loss spectroscopy experiments

Recently it has been proposed that alkylsiloxane self-assembled monolayers on oxidized Si(100) decompose through C–C bond cleavage [G. J. Kluth, M. M. Sung, and R. Maboudian, Langmuir 13, 3775 (1991)]. To verify this desorption picture, pentadecyltrichlorosilane precursors with four deuterated carbon atoms at the end of the molecule have been synthesized. High-resolution electron energy-loss spectroscopy shows that the monolayers are stable in vacuum up to 750 K. Above 750 K the C–D stretch disappears, while the C–H stretch remains, indicating that the end of the chain desorbs before the entire chain. From these observations it is concluded that the chains decompose primarily through C–C bond cleavage, resulting in the desorption of hydrocarbon fragments and a reduction in chain length.