A new assisted molecular cycloaddition on boron doped silicon surfaces: a predictive DFT-D study

Abstract

In the framework of the Density Functional Theory (DFT-D), we investigate the phthalocyanine (H₂Pc) molecule adsorption on SiC(0001)3 × 3 and Si(111)√3 × √3R30°-B (SiB) surfaces, and particularly compare the involved molecular adsorptions. In the H₂Pc–SiC(0001)3 × 3 system, the molecular adsorption can be ascribed to a [10+2] cycloaddition. The H₂Pc–SiB system is considered in three cases: defectless SiB surface (denoted SiB-0D) and SiB surfaces presenting one or two boron defects (denoted SiB-1D and SiB-2D respectively). The SiB-0D surface is passivated by a charge transfer from the Si adatoms to the boron atoms and therefore no chemical bond between the molecule and the substrate is observed. A similar molecular adsorption as already evidenced in the H₂Pc–SiC(0001)3 × 3 system is involved in the SiB-2D case. In the case of the SiB-1D surface, two Si–N bonds (Si1–N1 and Si2–N2) are observed. One of them, Si1–N1, is nearly similar to that found in the H₂Pc–SiB-2D system, but the Si2–N2 bond is unexpected. The Bader charge analysis suggests that, in the presence of the H₂Pc molecule, the boron atoms behave like an electron reservoir whose availability varies following the involved molecular adsorption process. In the SiB-1D case, charges are transferred from the substrate to the molecule, allowing the Si2–N2 bond formation. Such a kind of molecular adsorption, not yet observed, could be designed by “assisted pseudo cycloaddition”.