Adsorption of hydrogen and hydrocarbon molecules on SiC(001)

Adsorption of hydrogen and hydrocarbon molecules on semiconductor surfaces plays a key role in surface science and technology. Most studies have employed silicon (Si) as a substrate because of its paramount technological importance and scientific interest. However, other semiconductor substrates are gaining an increasing interest as well. Silicon carbide (SiC), which is a material with very special properties allowing developments of novel devices and applications, offers particularly fascinating new degrees of freedom for exceptional adsorption behaviour. For example, a very unusual hydrogen-induced metallization of a SiC(001) surface has been reported and hydrogen molecules show very different adsorption behaviour on different SiC(001) reconstructions although the latter exhibit very similar surface dimers. In marked contrast to the Si(001) surface, the adsorption of hydrocarbon molecules on SiC(001) can yield structurally well-defined adlayers in favourable cases which may have large potential for organic functionalization. We review and discuss theoretical ab initio results on conceivable adsorption scenarios of atomic and molecular hydrogen as well as acetylene, ethylene, butadiene, benzene and cyclohexadiene on various reconstructions of the SiC(001) surface. The main emphasize is on a detailed understanding of these adsorption systems and on identifying the physical origin of the particular adsorption behaviour. The results will be discussed in the light of related adsorption events on the Si(001) surface and in comparison with available experimental data.