Density Functional Theory Calculations of the Adsorption of Cytosine on Si(100)

We have performed density functional theory (DFT) calculations to investigate the adsorption structures of cytosine on Si(100). Multiple adsorption configurations that could result from Lewis acid–base reactions or cycloadditions were optimized, and the structural and energetic parameters of the obtained adsorption structures were compared. Row-bridged bidentate configurations with Si-O-C-N-C-N-Si linkages to two silicon atoms in adjacent dimer rows were found to be more stable than other configurations. The Si-N bond was formed by N-H dissociative adsorption, while the Si-O bond was dative. In the monodentate structures, the C-H or N-H dissociative adsorption structures were more energetically favorable than the datively bonded ones. Cycloaddition through the π-electrons of the C=N or C=C bonds of the cytosine ring resulted in relatively unstable adsorption products.