Starting from a Fixed Geometry: Real-Time XPS Investigation of a Surface Reaction with Controlled Molecular Configurations

Ether cleavage on the silicon (001) surface was investigated for a well-defined configuration of the ether group with respect to the underlying Si substrate. In order to maintain the reactants in a fixed orientation with respect to each other, cyclooctyne ether was chemoselectively attached on Si(001) via the strained triple bond of cyclooctyne. In this configuration, the ether group of this bifunctional molecule remains intact and its geometry with respect to the substrate is given by the cyclooctyne ring as a linker. The kinetics of the further reaction of the ether group at elevated temperatures was then investigated by means of real-time X-ray photoelectron spectroscopy using synchrotron radiation. A low activation barrier was deduced, which is interpreted in terms of the controlled configurations realized in the experiment in correlation with the underlying reaction mechanism.