Chemisorption and decomposition of thiophene and furan on the Si(100)-2 x 1 surface: A quantum chemical study

The chemisorption and decomposition of thiophene (C4H4S) and furan (C4H4O) on the reconstructed Si(100)-2 x I surface has been investigated by means o f the hybrid density functional (B3LYP) method in combination with a cluste r model approach. Two chemisorption mechanisms, i.e., [4 + 2] and [2 + 2] c ycloadditions of C4H4X (X = S,O) onto a surface dimer site, have been consi dered comparatively. The calculations revealed that the former process is b arrierless and favorable over the latter, which requires a small activation energy (2.6 kcal/mol for thiophene and 1.2 kcal/mol for furan). The di-sig ma bonded surface species formed by [4 + 2] cycloaddition-type chemisorptio n can either undergo further [2 + 2] cycloaddition with a neighboring Si=Si dimer site, giving rise to a tetra-sigma bonded surface species, or underg o deoxygenation (desulfurization) by transferring the heteroatom to a neigh boring Si=Si dimer site, leading to a six-member ring metallocyclic C4H4Si2 surface species. The latter process was found to be slightly more favorabl e than the former, especially in the case of thiophene.