Cooperative molecular dynamics in surface reactions.

The controlled imprinting of surfaces with specified patterns is important in the development of nanoscale devices. Previously, such patterns were created using self-assembled physisorbed adsorbate molecules that can be stabilized on the surface by subsequent chemical bonding. Here we show a first step towards use of the bonding within a surface to propagate reactions for patterning, namely the cooperative reaction of adjacent silicon atoms. We exploit the double-bonded silicon dimer pairs present on the surface of Si(100)-2×1 and show that the halogenation of one silicon atom (induced by electrons or heat) results in cooperative halogenation of the neighbouring silicon atom with unit efficiency. The reactants used were two 1-halopentane molecules physisorbed over a pair of silicon atoms. This cooperative pair of halogenation reactions was shown by ab initio calculation to be sequential on a timescale of femtoseconds.