Stability of organic thin films on inorganic substrates : prototype studies using metal phthalocyanines

Abstract

Thin films of metal phthalocyanines (PbPc and RuPc) on inorganic substrates (Ag, Pt, Cu, Au, Al203 and Agl) In the submonolayer and monolayer range were investigated. Their chemical compositions and electronic and dynamic structures were characterized by means of photoemission and vibrational spectroscopy, with particular emphasis on the influence of the film/substrate and film/gas phase interfaces. The results indicate that RuPc surfaces are always unstable in air because of an energetically favourable oxide formation involving the central (Ru) atom. Lead phthalocyanina is more stable. Lead oxides are formed only after exposing thin films prepared under ultra-hlgh vacuum to pure oxygen. Even for PbPc, decomposition was observed at certain substrate/film interfaces: organic fragments were found in the submonolayer range on platinum substrates, an exchange of the central atom on copper substrates and catalytic decomposition of organic films on gold substrates after storage in air. Chemically perfect films without decomposition were found on Al203, Agl and Ag substrates. The results are discussed by taking into account the energetic structure of interfacial electronic states.