X-ray absorption studies of aluminum and niobium interface reactions and of krypton-implanted in solid materials.

摘要

X-ray absorption experiments using synchrotron radiation have been carried out to study ion-beam induced aluminum and niobium interface reactions and to study the formation of krypton precipitates in solid materials. The interface structure of bilayered Al and Nb prepared by sputtering onto a float glass substrate is studied using glancing angle EXAFS (extended x-ray absorption fine structure) and x-ray reflectivity. For the as-sputtered sample, the reflectivity data suggest a sharp Al surface and Al/Nb interface on a local scale, with a roughness corresponding to only a few atomic steps. The Nb K-edge EXAFS results indicate that the Nb atoms in the interface region are in the same body-centered-cubic structure as the bulk metal. However, a small number of Nb-Al bonds are identified. Ion-beam irradiation with 1 {dollar}times{dollar} 10{dollar}sp{lcub}16{rcub}{dollar} Al/cm{dollar}sp2{dollar} resulted in the formation, between the Al and Nb layers, of an amorphous layer in which the Nb-Al pairs exhibit greater disorder than the Nb-Nb pairs. Irradiation with 1.5 {dollar}times{dollar} 10{dollar}sp{lcub}17{rcub}{dollar} Al/cm{dollar}sp2{dollar} led to a less well defined interface. The high sensitivity of glancing angle EXAFS in probing the interface structure is demonstrated. The krypton local environment in niobium, aluminum, graphite and Grafoil hosts is investigated by measuring the Kr K-edge absorption spectrum. The near-edge data (XANES) demonstrate that krypton atoms form precipitates in samples implanted to high dosages ({dollar}ge{dollar}5 {dollar}times{dollar} 10{dollar}sp{lcub}16{rcub}{dollar} Kr/cm{dollar}sp2{dollar}). The precipitates appear to be in the solid phase in the Nb hosts even at 300 K, but exist in both solid and non-solid forms in Al, graphite and Grafoil hosts. The lattice parameter values estimated from XANES data suggest a high pressure in the range of 2-10 GPa within the solid precipitates. In addition, the structural modification of iron, nickel and copper metals by Kr implantation is studied by EXAFS measurements at the metal K edges using total electron yield detection.