Interfacial chemistry of pentacene on clean and chemically modified silicon (001) surfaces

The interactions between pentacene and the Si(001)-(2 × 1) surface have been investigated using Fourier transform infrared spectroscopy (FTIR), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). The pentacene molecules in the first layer react with the Si surface atoms through the C=C double bonds and via cleavage of C-H bonds. This chemisorption is accompanied by disruption of the conjugated π electron system. The disrupted interfacial layer is stable throughout deposition and evaporation of thicker pentacene films. Pentacene molecules in layers beyond the first layer adsorb molecularly and yield well-defined valence band features that are characteristic of a conjugated π electron system. Functionalization of the Si surface with a monolayer of cyclopentene inhibits dissociation of subsequently deposited pentacene molecules.