Abstract
Using computational chemistry, we show that the adsorption of ether molecules on Si(001) under ultra-high vacuum conditions can be understood with textbook organic chemistry. The two-step reaction mechanism of (1) dative bond formation between the ether oxygen and a Lewis acidic surface atom and (2) a nucleophilic attack of a nearby Lewis basic surface atom is analysed in detail and found to mirror the acid-catalysed ether cleavage in solution. The O-Si dative bond is found to be the strongest of its kind and reactivity from this state defies the Bell-Evans-Polanyi principle. Electron rearrangement during the C-O bond cleavage is visualized using a newly developed bonding analysis method, which shows that the mechanism of nucleophilic substitutions on semiconductor surfaces is identical to molecular chemistry SN2 reactions. Our findings thus illustrate how the fields of surface science and molecular chemistry can mutually benefit and unexpected insight can be gained.
This work was supported by the Deutsche Forschungsgemeinschaft(DFG) within SFB 1083, GRK 1782 and TO 715/1-1. Computational resources were provided by HRZ Marburg, HLR Stuttgart and CSC-LOEWE Frankfurt. We thank Prof. Ulrich Koert, Prof. Ulrich Höfer (Marburg), Prof. Michael Dürr (Gießen), and Prof. Stacey Bent (Stanford) for discussions.