Kinetic and Thermodynamic Control by Chemical Bond Rearrangement on a Si(001) Surface

摘要

The (2 * 1)-reconstructed Si(001) surface, where the surface lattice structure undergoes a reconstruction in which adjacent silicon dimers pair together and form dimers through a bond and a bond, is intriguing in that the chemistry at the surface is frequently analogous to that in organic chemistry owing to its covalent nature. Alkenes, for example, are known to bind to silicon dimers on the Si(001) surface to produce four-member ring analogs in a similar way to [2+2] cycloaddition reactions in organic synthesis. The mechanisms of cycloadditions on the surface have also been argued in terms of orbital symmetry in a similar fashion to organic chemistry. However, it seems likely that adsorbate formation and organic synthesis are different in that it is usually difficult to control the product distributions of surface species on the Si(001) surface, that is, the relative efficiencies of specific reactions to side reactions, by changing reaction temperature. The selectivity of reactions has previously been discussed for the adsorption of 1,3-cyclohexadiene, 2,3-dimethyl-1,3-butadiene, and unsaturated ketones on the Si(001) and Ge(001) surfaces. Those studies have investigated whether the degree of selectivity is determined by thermodynamic or by kinetic factors. However, the conversion from kinetically controlled reactions into thermodynamically controlled ones for the same organic compound by means of heating has not been observed on the Si(001) surface to date. This may be because the binding of organic molecules to the silicon surface is usually strong, which makes reactions irreversible.