UV-laser photodeposition of iron films from Fe(CO)5: role of gas-phase and surface dissociation processes

The laser-induced chemical vapor deposition (LCVD) of thin iron films from Fe(CO)5 has been studied under high-vacuum conditions (base pressure < 2 × 10-7 Torr), and the content and chemical state of the carbon and oxygen in the film examined by profiling AES and XPS analysis. Greater than 70% of the carbon and oxygen are found in the carbidic and oxide form, respectively, with the rest present as adsorbed CO. C/Fe and O/Fe ratios are found to be equal in the bulk film, and dependent on the product of laser fluence and gas-phase absorption cross-section, as well as on the properties of the substrate. We have developed a deposition model which includes deposition of both primary [Fe(CO)x] and secondary (bare Fe) photoproducts, thermally and photo-induced decarbonylation at the growing film surface, and thermally and photo-induced dissociation of CO in the film. The latter process is discussed in terms of weakening of the C-O bond at the surface and a statistical redistribution of resonantly absorbed UV photon energy. An absorption cross-section for the Fe(CO)x photofragment was estimated from the model, with a value of (2 ± 1) × 10-16 cm2, approximately equal to that for the initial resonant absorption step in the parent carbonyl. These results suggest an approach to depositing nearly pure iron films by LCVD of Fe(CO)5.