The adsorption of maleic anhydride on the Si(001) surface was investigated using the first-principles pseudopotential formalism. Our results indicate that C2H2-C2O3 adsorbs through a [2+2] cycloaddition of the C-C bond to the dangling bonds of Si-Si dimers, as observed for other small hydrocarbons. According to our calculations, the adsorption of a second maleic anhydride molecule will preferentially occur on first-neighbours Si-Si dimer sites in either the dimer chain our dimer row, i.e. considering a (4×2) reconstruction, C2H2-C2O3 can either form a linear chain or a zig-zag chain, depending on the growth conditions. Although both structures are found to be stable from the energetic point of view, only our STM theoretical images for the linear chain are comparable to available experimental data.
