Density Functional Study on the Interaction of a Polycyclic Aromatic Molecule and the Silicon (001) Surface

Surface functionalization with nonalternant aromatic compounds: a computational study of azulene and naphthalene on Si(001)

Nonalternant aromatic π-electron systems show promises for surface functionalization due to their unusual electronic structure. Based on our previous experiences for metal surfaces, we investigate the adsorption structures, adsorption dynamics and bonding characteristics of azulene and its alternant aromatic isomer naphthalene on the Si(001) surface. Using a combination of density functional theory,ab initiomolecular dynamics, reaction path sampling and bonding analysis with the energy decomposition analysis for extended systems, we show that azulene shows direct adsorption paths into several, strongly bonded chemisorbed final structures with up to four covalent carbon-silicon bonds which can be described in a donor-acceptor and a shared-electron bonding picture nearly equivalently. Naphthalene also shows these tetra-σ-type bonding structures in accordance with an earlier study. But the adsorption path is pseudo-direct here with a precursor intermediate bonded via one aromatic ring and strong indications for a narrow adsorption funnel. The four surface-adsorbate bonds formed lead for both adsorbates to a strong corrugation and a loss of aromaticity.

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.