Silicon Monomer Formation and Surface Patterning of Si(001)‑2 × 1 Following Tetraethoxysilane Dissociative Adsorption at Room Temperature He ́ loise Tissot, †,‡,§ Jean-Jacques Gallet,* ,†,‡,§ Fabrice Bournel, †,‡,§ Ahmed Naitabdi, †,‡,§ Debora Pierucci, †,‡,§ Federica Bondino, ∥ Elena Magnano, ∥ Franc ̧ ois Rochet, †,‡,§ and Fabio Finocchi ⊥,○ † Laboratoire de Chimie Physique Matie ̀ re et Rayonnement, Sorbonne Universite ́ s, UPMC Univ Paris 06, UMR 7614, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France ‡ CNRS, UMR 7614, LCPMR, 75005 Paris, France § Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, Gif-sur-Yvette, France ∥ IOM-CNR, TASC Laboratory, s.s. 14 km 163.5, Basovizza, 34149 Trieste, Italy ⊥ Institut des Nano-Sciences de Paris, Sorbonne Universite ́ s, UPMC Univ Paris 06, UMR 7588, 4 place Jussieu, 75252 Paris Cedex 05, France ○ CNRS, UMR 7588, INSP, 75005 Paris, France * S Supporting Information ABSTRACT: The adsorption of tetraethoxysilane (TEOS, Si[OC 2 H 5 ] 4 ) on the Si(001)-2 × 1 surface at 300 K is studied through a joint experimental and theoretical approach, combining scanning tunneling microscopy (STM) and synchrotron radiation X-ray photoelectron spectroscopy (XPS) with first-principles simulations within the density functional theory (DFT). XPS shows that all Si−O bonds within the TEOS molecules are broken upon adsorption, releasing one Si atom per dissociated molecule, while the ethoxy (−OC 2 H 5 ) groups form new Si−O bonds with surface Si dimers. A comparison between experimental STM images and DFT adsorption configurations shows that the four ethoxy groups bind to two second-neighbor silicon dimers within the same row, while the released silicon atom is captured as a monomer on an adjacent silicon dimer row. Additionally, the surface displays alternate ethoxy- and Si adatom-covered rows as TEOS coverage increases. This patterning, which spontaneously forms upon TEOS adsorption, can be used as a template for the nanofabrication of one-dimensional self-organized structures on Si(001)-2 × 1. ■ INTRODUCTION Since the beginning of the silicon surface chemistry studies in the mid-1980s, 1 the grafting of organic monomolecular arrays on silicon surfaces via the direct formation of Si−C bonds (both in ultrahigh vacuum and wet conditions 2,3 ) has stimulated a considerable interest, essentially because of promising applications in molecular electronics. 4,5 Organo- silanes (by definition a silane that contains at least one Si−C bond) are also widely used to form self-assembled monolayers on silicon substrates. 6−8 Within this class of molecules, alkoxysilanes (R n Si(OR) 4−n ) are not attached directly to clean silicon surfaces, but rather to native silicon oxide ones, either through the direct reaction of surface Si−OH with the hydrolyzable (alkoxy) terminations of the molecules or via a more complex process involving the participation of molecular water. Recently, Fan and Lopinski 9 investigated the reaction of an alkoxysilane, in the absence of molecular water, with the surface hydroxyls of the water-reacted surface (H,OH)-Si(001)- 2 × 1. 10 However, the grafting of alkoxysilanes directly on clean Si(001)-2 × 1 is an emerging field of study. Recently, we examined the reaction of n-propyl-triethoxy-silane (PTES, Si[OCH 2 CH 3 ] 3 [CH 2 CH 2 CH 3 ]) on Si(001)-2 × 1 at room temperature and under ultrahigh vacuum conditions. 11 Using X-ray Photoemission Spectroscopy (XPS), we observed that PTES adsorbs dissociatively at room temperature via the scission of Si−O bonds. However, the actual number of broken Si−O bonds in PTES after dissociative adsorption remained elusive due to the presence of nonidentical ligands (one propyl and three ethoxy groups). 11 The latter issue prompted us to examine how a simpler molecule with four identical ligands, tetraethoxysilane (TEOS, Si[OCH 2 CH 3 ] 4 ), reacts with Si(001)-2 × 1. Many unknowns remain about the microscopic processes governing the adsorption of TEOS on Si(001)-2 × 1 at room temperature and under UHV conditions (see, e.g., the review by Rauscher 12 ). In fact most studies focus on the deposition and electrical/structural characterization of SiO 2 films using TEOS Received: July 25, 2013 Revised: December 20, 2013 Published: December 30, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 1887 dx.doi.org/10.1021/jp407411k | J. Phys. Chem. C 2014, 118, 1887−1893