S adsorption on Au(111) and Ag(111): a comparative study of Ion Scattering and Electron Spectroscopies

G. RUANO; E. TOSI; S. BENGIÓ; L. SALAZAR-ALARCÓN; E.A. SÁNCHEZ; M. KHALID; O. GRIZZI; M.L. MARTIARENA; H. ASCOLANI; G. ZAMPIERI

Kioto

Conferencia; ICACS-25 25th International Conference on Atomic Collisions in Solids; 2012

The adsorption of S on Au and Ag surfaces is a subject of interest due to several reasons; among the most important are the poisoning effect in catalysis, the degradation of electronic contacts under S containing atmospheres, and the growth of Self Assembled Monolayers (SAMs) of thiol based molecules. The S/Au system has been studied with different electron and photon spectroscopies, with electron diffraction and by means of electrochemical techniques [1, 2], however a number of controversies still remains unsolved precluding a full understanding of the system behavior. In this work we present an ion scattering study performed in the forward direction in order to detect recoils (DRS)and forward scattered projectiles. Low energy electron diffraction patterns taken at specific exposures were used to identify the S phases. We measured the S and substrate recoiling intensities versus S dose in UHV conditions for both Au(111) and Ag(111), and compared these intensities with Auger (AES) and photoemission (XPS) Au4f and S2psignals. At low incident angles and specific doses we observed strong changes in both spectrum shape and intensity which allow determination of the critical coverages for phase transitions. The difference in the sticking coefficient in Ag and Au is discussed. A detailed study of TOF-DRS versus sample temperature for Au helped us to link previousmeasurements in UHV and in solution.