A combined STM, HREELS and ab initio study of the adsorption of uracil on Si(001)-2x1

Adsorption of the nucleic acid base uracil on Si(100)-2 x 1 has been studied using scanning tunnelling microscopy (STM), high-resolution electron energy-loss spectroscopy (HREELS) and ab initio calculations. The STM images show that uracil is able to form ordered structures on the surface on which the molecules adsorb preferentially along dimer rows. The HREEL spectra show a stronger intensity of the in-plane modes compared with the out-of-plane vibrations. This indicates that the orientation of the molecular plane is more upright. The observation of a distinctive Si-H band in the vibrational spectra of Si(100)-2 x 1 exposed to uracil indicates that adsorption of the molecule occurs through cleavage of an O-H/N-H bond. The vibrational spectra show that only the enol tautomer interacts with the surface, mainly through cleavage of the OH bond and the formation of an Si-O linkage. Copyright (C) 2002 John Wiley Sons, Ltd.