Adsorption of Organic Molecules on Silicon Surfaces: Dynamics, Kinetics, and Control

The adsorption of organic molecules on silicon proceeds in most cases via a nonactivated reaction channel including a noncovalently bound intermediate state. This intermediate state, which typically exhibits a binding energy in the range of several tenths of an electronvolt, controls both the dynamics and the kinetics of the adsorption process. In the entrance channel of the potential energy surface, reaction into the intermediate state is largely decoupled from the further reaction into the final state, and the gas–surface dynamics are thus mainly determined by the intermediate state. The reaction barrier from the intermediate to the final state and the interplay between adsorption and desorption, the latter being determined by the binding energy, then controls the kinetics of the adsorption into the final state. Chemoselectivity of bifunctional molecules on silicon can be achieved taking this situation into account: if a functional group exhibits a direct reaction channel, adsorption via this functionality will be always preferred compared to the vast majority of functional groups which react via the described intermediate state. The strained triple bond of cyclooctyne reacts on silicon via such a direct reaction channel, thus leading to chemoselective adsorption of functionalized cyclooctynes.