Selective functionalization of the Si(100) surface by a bifunctional alkynylamine molecule: density functional study of the switching adsorption linkage. 2.

The reaction of the bifunctional organic molecule 1-(dimethylamino)-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations employing a two-dimer cluster model. We found that, once in the physisorbed dative bonded well (-20.0 kcal mol(-1)), DMAP can proceed via a number of pathways, involving the formation of Si-C sigma bonds, which lead to thermodynamically more stable configurations. We first considered the cycloaddition of the CC triple bond, leading to a Si-C di-sigma bonded product (-58.7 kcal mol(-1)), for which we computed an energy barrier of only 12.5 kcal mol(-1), consistently with the observed switching of DMAP adsorption linkage at 300 K. We also explored the dissociative pathway involving the methylene C-H bond cleavage on the dative bonded DMAP, leading to three adsorption products with one (-57.3 kcal mol(-1)) and three Si-C sigma bonds (-58.7 and -60.6 kcal mol(-1)). The energy barrier for this pathway is computed 24.7 kcal mol(-1) and may therefore compete at temperature above 300 K with the reaction pathway involving the addition of the alkyne unit.