Y. Chimi

Defect Production Induced by Primary Ionization in Ion-Irradiated Oxide Superconductors.

Resistivity as a function of ion-fluence has been measured in situ in thin films of oxide superconductor EuBa 2 Cu 3 O y irradiated with various heavy ions in a wide energy range of 90 MeV–3.84 GeV. From the resistivity measurements, the quantities characterizing the irradiation-induced columnar defects, such as the diameter of the columnar defect and the inside-resistivity (the resistivity inside the columnar defect), have been estimated. It is found that they are not scaled with the electronic stopping power, while they are strongly correlated with the primary ionization rate which is the number of atoms primarily ionized by an incident ion per unit path length. This result suggests that the defect production is triggered by Coulomb repulsion of ionized atoms. Based on the results of thermal annealing of irradiated samples, structure of the columnar defects has also been discussed.

Reaction of Implanted N Isotope with SiO2 Near Si3N4-Film and SiO2-Substrate Interface

We have investigated 100 keV 15N (90% enriched) implantation effects on Si3N4 films on SiO2-glass-substrate. The Si3N4 films were prepared by using reactive RF-magnetron-sputter-deposition method in N2 (natural isotope abundance) gas at room temperature. The composition and film thickness were measured by Rutherford backscattering spectroscopy (RBS) and optical absorption spectroscopy. The RBS and optical absorption spectroscopy show increase in the film thickness with the stoichiometric composition, by 15N ion implantation. These results and depth distribution of the implanted 15N, which is obtained by nuclear reaction analysis (NRA), lead to formation of Si3 15N4 film (embedded isotope rich nitride film). Enrichment of 15N in the grown silicon-nitride film is estimated to be ∼70%.

Terminal Solid Solubility of Hydrogen in Hafnium

The terminal solid solubility (TSS) of hydrogen during hydride dissolution/precipitation is determined by differential scanning calorimetry technique for nonirradiated hafnium (Hf) that is used as control rods of light water reactors. The hydrogen concentration in hydrogenated Hf samples ranged from 27 to 300 wt ppm. The reliability of the TSS data obtained for Hf was confirmed using those for Zircaloy-2 (Zry-2) obtained in this study with the literature data, and best-fit equations for the obtained TSS curves for Hf are derived. The TSS for Hf at 573 K, which corresponds to an operational temperature of control rods in boiling water reactors, is in the range of 10–15 wt ppm, and is found to be 1/5–1/7 of the TSS for Zry-2.