Microstructure of photodeposited Fe in porous Vycor glass

The products derived from the UV photolysis of Fe(CO)₅ physisorbed onto porous Vycor glass have been examined by x-ray microprobe analysis, Mossbauer spectroscopy, and extended x-ray absorption fine structure spectroscopy (EXAFS). Although the photolysis and subsequent heatings are carried out in air, spectroscopic data reveal two surprisingly different forms of iron. Isomer shift, pre-edge, and EXAFS data indicate that one product is similar to α-Fe₂O₃ and consists of an Fe ³⁺ ion octahedrally surrounded by six oxygen atoms at a distance of 1.8 Å. Isomer shift, EXAFS, and pre-edge feature analysis show that the second compound, which comprises ∼50% of the reaction product, is mainly elemental iron, in which a central Fe atom is surrounded by approximately eight other Fe atoms at a distance of 2 Å. X-ray microprobe analysis shows that aggregation occurs during photolysis due to the diffusion of Fe(CO)₅ from the interior into exterior photodepleted volumes of glass. Heating has little effect on product ratio or distribution, but consolidating the glass at 1200°C leads to further aggregation and formation of magnetically ordered particles that exhibit magnetic hyperfine fields of 370 and 425 kG.