MICROSTRUCTURE OF PHOTODEPOSITED FE IN POROUS VYCOR GLASS

The products derived from the UV photolysis of Fe(CO)5 physisorbed ont o porous Vycor glass have been examined by x-ray microprobe analysis, Mossbauer spectroscopy, and extended x-ray absorption fine structure s pectroscopy (EXAFS). Although the photolysis and subsequent heatings a re carried out in air, spectroscopic data reveal two surprisingly diff erent forms of iron. Isomer shift, pre-edge, and EXAFS data indicate t hat one product is similar to alpha-Fe2O3 and consists of an Fe3+ ion octahedrally surrounded by six oxygen atoms at a distance of 1.8 angst rom. Isomer shift, EXAFS, and pre-edge feature analysis show that the second compound, which comprises approximately 50% of the reaction pro duct, is mainly elemental iron, in which a central Fe atom is surround ed by approximately eight other Fe atoms at a distance of 2 angstrom. X-ray microprobe analysis shows that aggregation occurs during photoly sis due to the diffusion of Fe(CO)5 from the interior into exterior ph otodepleted volumes of glass. Heating has little effect on product rat io or distribution, but consolidating the glass at 1200-degrees-C lead s to further aggregation and formation of magnetically ordered particl es that exhibit magnetic hyperfine fields of 370 and 425 kG.