MO(CO)6 ON SI(111)2 X-1 - A SYNCHROTRON RADIATION-EXCITED PHOTOEMISSION-STUDY

A synchrotron radiation-excited photoemission study of the adsorption behaviour of Mo(CO)6 on Si(111)2 × 1 is reported. The compound has been investigated in the temperature range 50 K-room temperature (RT), and in the exposure range 0.1-200 L (1 Langmuir = 10-6 Torr s-1). Both core (Mo 3d, C 1s, Si 2p, O 1s) and valence levels were investigated. At T ≦ 100 K and exposures ≧0.5 L, the adsorption of Mo(CO)6 on cleaved Si is molecular, as clearly indicated by a 1: 1 correspondence of the features in the valence band (VB) spectrum with those already reported for free Mo(CO)6, at the same photon energy. At T ≦ 100 K and very low exposures (0.1 L) we found evidence of a decomposition process taking place. At T ≧ 150 K, the adsorption is dissociative at exposures ≮ 120 L and molecular at higher exposures. As the temperature increases up to 200 K, only dissociative processes are detected, also at high exposures. At RT, no adsorption at all was detected. Reacted surfaces were exposed to zero-order light to promote metal deposition on Si. A metal layer on top of Si was obtained after short exposures. CO adsorbs on this layer and is partially dissociated. Molecular CO is removed by further exposure to zero-order light. The presence of atomic C and O from CO partial dissociation and of carbide species was detected. © 1990 IOP Publishing Ltd.