Chemisorption of acetonitrile, pyridine and pyrazine on the Si(100)-2x1 surface: theoretical predictions
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The chemisorption of acetonitrile (CH3CN), pyridine (C5H5N) and pyrazine (C4H4N2) on the Si(100)-2 x 1 surface has been investigated by means of first-principles density functional cluster model calculations. For acetonitrile, an N-end-on adsorption state and a side-on adsorption state were found, together with a transition state that connects the two adsorption states. The predicted energetics suggests that the side-on adsorption state can be readily formed at rather low temperature via the end-on precursor state. For both pyridine and pyrazine, an N-end-on adsorption state and two side-on adsorption states were revealed. In the pyridine/Si(100) chemisorption system, the primary adspecies would be the N-end-on adsorbed pyridine as the N-end-on adsorption is the most favorable and barrierless. For the pyrazine case, the N-end-on adsorbed pyrazine would be the primary adspecies at low temperature, while at elevated temperatures the primary adspecies would be the side-on adsorbed pyrazine, which is di-sigma bonded onto the surface dimer through the 2 and 5 carbon atoms. In particular, the finding that the N-end-on adsorption of pyridine on the Si(100)-2 x 1 surface is substantial enlightens us as to the possibility of constructing a pyridine-based, conductive (or semiconductive) polymer film on the Si surface.