Stability of small chemical groups on hexagonal-SiC(0001) surfaces: A theoretical study
Résumé
Density functional theory (DFT) calculations are used to investigate the stability on SiC(0001) surfaces of different chemical groups -NH2, -NO2, -CH3, -OH, -SH and -CN. The adsorption stability decreases in the order -NO2 > -OH > -NH2 > -SH > -CN > -CH3. The stability of the single molecule-substrate bond is strongly influenced by the polarizability, which in turn depends on different parameters such as the electronegativity, atomic size and chemical environment. In a further step, methyl (-ACH(3)) and phenyl (-AC(6)H(5)) substituted groups are also considered and similar behaviour is observed. The inductive effect of the -CH3 or -C6H5 groups modifies the polarization of the Si adatom-molecule bond and the steric hindrance due to their size influences the molecular orientation. These two parameters affect the calculated adsorption energy, and are more important for -C6H5 substituent. This study provides clear tendencies that can be applied to more complex systems. Comparison of the adsorption of two large molecules, H2Pc (metal-free phthalocyanine) and PTCDI (perylene tetracarboxylic diimide) on the SiC(0001) surface is presented as an example. (C) 2012 Elsevier B.V. All rights reserved.