The crystallographic shear planes of the non-stoichiometric molybdenum oxides as revealed by RHEED: Investigation from the Mo18O52(100) surface

A727 290

Surface

Science 164 (1985) 290-304 North-Holland, Amsterdam

THE INTERACTION OF Cs AND 0, ON THE BASAL PLANE OF MoS, S. KENNOU, S. LADAS and C. PAPAGEORGOPOULOS Physics Department, University of loannina, GR - 453 32 loannina, Greece Received

15 July 1985; accepted

for publication

31 July 1985

The interaction of Cs and 0, on MoS,(OOOl) has been studied both in the alternate adsorption and the codeposition mode by LEED, AES, TDS and WF measurements at 170 and 300 K. Oxygen does not interact with Cs when 8,, ,< 0 04 at 300 K or 0,, G 0.08 at 170 K, where Cs is known to adsorb as strongly ionized, individual adatoms. The interaction at higher &,, where Cs is known to form clusters on MoS,(OOOl), leads to clusters of a Cs/O complex characterized by a Cs(563 eV)/0(512 eV) Auger peak ratio of 1.1-1.3. The minimum WF is 2.1 eV at 300 and 170 K upon alternate adsorption, and 1.7 eV at both T upon codeposition. Upon heating, oxygen and Cs desorb independently, as no oxide desorption is observed. The Cs TDS spectrum is shifted to lower T in the presence of oxygen and a new desorption peak appears at - 880 K. The differences in the Cs/O interaction between MoS,(OOOl) and other semiconductors and metals are attributed to the Cs clustering and the inertness of MoSz(0001) to 0, adsorption.

305

Surface Science 164 (1985) 305-319 North-Holland. Amsterdam

THE CRYSTALLOGRAPHIC SHEAR PLANES OF THE NON-STOICHIOMETRIC MOLYBDENUM OXIDES AS REVEALED BY RHEED: INVESTIGATION FROM THE Mo,,O,,(lOO) SURFACE 0. BERTRAND,

N. FLOQUET

and D. JACQUOT

Laboratoire de recherches sur la RPactivitb des Solides, L.A 23 CNRS, Far&? BP 138, F-21004 Dijon Cedex, France Received

14 May 1985; accepted

for publication

6 August

des Sciences Mirande,

1985

Large Mo,,O,, crystals are obtained by an appropriate crystallization method. The examination of their well developed surfaces by the use of reflection high energy electron diffraction (RHEED) proves that these are (100) surfaces stepped along [OlO] directions. It is concluded that this oxide surface conformation can be connected to the particular Mo,sOs, structure which is built up of MOO, slabs of finite width mutually joined by crystallographic shear planes (CS planes). Transmission electron microscopy (TEM) analysis from Mo,sO,, crystal flakes confirms that these are single crystals without disorder in the periodicity of the CS planes.

320

STUDY OF THE Si(ll1) 7 x 7 SURFACE MEII’AL ADSORPTION Hiroshi DAIMON and Shozo IN0

Surface

Science 164 (1985) 320-326 North-Holland, Amsterdam

STRUCTURE

BY ALKALI-

Department of Physics, Faculty of Science, The University of Tokyo, Hongo, Bunkyo - ku, Tokyo 113, Japan