Ene-like reaction of cyclopentene on Si(001)-2 × 1: An XPS and NEXAFS study

The control and the understanding of single-molecule covalent coatings on silicon surfaces is increasingly important in designing nanoscale electrical elements, such as organic/inorganic semiconductor hybrid structures. In this respect, ordered arrays of cyclopentene deposited on Si(001)-2 × 1 appear as promising buffer layers for further molecular crystal growth on the substrate. In this work, we examine the adsorption of cyclopentene on Si(001)-2 × 1 at 130 and 280 °C by means of C 1s XPS and NEXAFS. Until now cryogenic and room-temperature adsorption studies tended to prove that cyclopentene adsorption results from a formal cycloaddition ([2 + 2]-like) reaction of the C→C double bond with a silicon dimer. Our XPS/NEXAFS study reveals that an ene-like reaction competes with the [2 + 2]-like reaction channel, leading to the formation of products bearing a C→C bond, already at deposition temperature as low as ∼130 °C. This work helps to determine the optimum conditions leading to optimal chemical order in view of applications of cyclopentene as a buffer layer.