Photochemistry of thin amorphous films of Fe(CO)4PPh3 on Si(111) surfaces

The photochemical reactions of Fe(CO)(4)PPh3 and Fe(CO)(3)(PPh3)(2) as amorphous films on silicon surfaces are presented. The mechanism of the reaction of Fe(CO)(4)PPh3 in the films has been studied in some detail. Initial CO loss leads to a thermally unstable intermediate, Fe(CO)(3)PPh3, which decomposes in the film leading to the production of iron. In thick films photoproduced CO remains trapped in the film and may react with Fe(CO)(3)PPh3, regenerating the starting material. Further evidence for this intermediate arises from experiments conducted with PPh3 added to the film. In these films the initial photoproduct is trapped by PPh3 yielding Fe(CO)(3)(PPh3)(2). A quantitative study of the quantum yield efficiency in these films was undertaken. The Fe(CO)(3)(PPh3)(2) films are photosensitive undergoing CO loss to yield Fe(CO)(2)(PPh3)(2), as demonstrated by its trapping, by PPh3, to form Fe(CO)(2)(PPh3)(3). Extended photolysis of Fe(CO)(3)(PPh3)(2) films, including those containing photoproduced Fe(CO)(2)(PPh3)(3), results in the formation of iron. The surface photochemistry of both Fe(CO)(4)PPh3, and Fe(CO)(3)(PPh3)(2) are shown to be compatible with standard lithography. Patterns of 1 x 100 mu m lines of iron oxide were easily produced on a silicon surface. (C) 1998 Elsevier Science S.A.