S. Furuno

Tracks of high energy heavy ions in solids

Abstract The observation of tracks of high energy heavy ions produced in some materials was made with electron microscope in order to clarify the governing factors and mechanisms for track formation. Irradiation experiments were performed with specified and well collimated ion beams of 100 MeV class obtained from the tandem accelerator. Target specimens were evaporated thin films of germanium, silicon and titanium, and crystals of MoO3 and MoS2. The present experiments showed that there were threshold values in the energy deposition of ion to specimens for the track formations and that the size of the tracks depended on the energies deposited into the specimens. The correlations between the sizes of the tracks and the energy depositions of incident ions were examined for the tracks produced in the evaporated films of germanium, and the results were interpreted in terms of a time dependent line source model of thermal spike. Even in such a high energy region, tracks produced through nuclear collision process were observed under some conditions.

Radiation damage in yttria-stabilized zirconia under Xe ion irradiation

Abstract Single crystals of yttria-stabilized zirconia were irradiated with 60 keV Xe ions in an electron microscope at several temperatures in the range 300–1473 K and the process of damage evolution was studied. Amorphization did not occur in the zirconia irradiated with 60 keV Xe ions up to the fluence of 1.8×1016 Xe/cm2 at all irradiation temperatures. In the specimen irradiated with Xe ions below 1073 K, defect clusters are formed first and then bubbles are formed. On the contrary, in the specimen irradiated above 1073 K bubbles are formed first and then defect clusters are formed. From the observation of bubble sizes and densities, temperature and dose dependence of bubble swelling were estimated. With increase in fluence or irradiation temperature the average size of the bubble increased resulting in greater values of swelling.

In-situ observation system of the dynamic process of structual changes during ion irradiation and its application to SiC and TiC crystals

Abstract A newly designed system of in-situ observation during ion irradiation and implantation was constructed by combining an electron microscope with an ion beam. The mass analyzed ion beam is introduced into the electron microscope in the horizontal direction and deflected by a large angle of 72° inside the specimen chamber so as to be incident nearly normally to the specimen surface maintained at temperatures up to 1350°C. The ion flux at the specimen position is so high, 6 × 10 18 ions m −2 s −1 , that the whole process from the initial stage to heavy irradiation of the fluence of 10 22 ions/m 2 can be recorded in an hour. The ion energy is 10 keV so that it is adequate for the study of dynamic reaction processes of ions implanted in thin films of about 100 nm in thickness. The results of applications of this system to SiC and TiC crystals are presented.

In situ EELS and TEM observation of silicon carbide irradiated with helium ions at low temperature and successively annealed

Abstract Structural and compositional changes in SiC crystal due to helium ion irradiation were examined by an electron microscope equipped with a thermal field-emission gun and electron energy-loss spectroscope. Amorphization was confirmed both by the shift of the plasmon loss peaks and the change of the carbon core loss peaks in EELS as well as by the change of electron diffraction patterns in SiC irradiated with 12 keV helium ions to a fluence above 6 × 10 19 ions/m 2 at 22 K. He 1s–2p transition peak (21.8–23.8 eV) was observed for SiC irradiated to a fluence above 1.8 × 10 21 ions/m 2 at 22 K. Recrystallization was found to occur during annealing above 1173 K after the irradiation.

Microstructural study of irradiated isotopically tailored F82H steel

Abstract The synergistic effect of displacement damage and hydrogen or helium atoms on microstructures in F82H steel irradiated at 250–400 °C to 2.8–51 dpa in HFIR has been examined using isotopes of 54 Fe or 10 B . Hydrogen atoms increased slightly the formation of dislocation loops and changed the Burgers vector for some parts of dislocation loops, and they also affected on the formation of cavity at 250 °C to 2.8 dpa. Helium atoms also influenced them at around 300 °C, and the effect of helium atoms was enhanced at 400 °C. Furthermore, the relations between microstructures and radiation-hardening or ductile to brittle transition temperature (DBTT) shift in F82H steel were discussed. The cause of the shift increase of DBTT is thought to be due to the hardening of dislocation loops and the formation of α′-precipitates on dislocation loops.

EELS ANALYSIS OF SIC CRYSTALS UNDER HYDROGEN AND HELIUM DUAL-ION BEAM IRRADIATION

Abstract Electron microscopy and Electron energy loss spectroscopy (EELS) measurement were performed in SiC irradiated with three kinds of irradiation mode, namely, H2+ ions, He+ ions, and a dual beam of He+ and H2+ ions. Amorphization occurred in SiC at a damage density from 0.2 to 0.4 displacement per atom (dpa) irrespective of ion species. High resolution EELS revealed that a large amount of implanted hydrogen is contained in the form of hydrogen molecules and C–H compound in bubbles. It is inferred that some of hydrogen atoms implanted in SiC are trapped in both Si- and C-sites. Most of the helium atoms implanted are considered to exist in bubbles.

Ion irradiation and annealing effects in Al2O3 and MgAl2O4

Abstract In situ observation of structural changes of Al2O3 and MgAl2O4 induced by Xe and He ion irradiations and successive annealing were performed in an electron microscope equipped with ion accelerator. By Xe ion irradiation amorphization occurred in both the materials and bubbles were formed in MgAl2O4. By He ion irradiation bubbles were formed in both the materials, but amorphization was not observed to a fluence of 1.8 × 1021/m2 (11 dpa). By annealing after the irradiation, bubbles began to grow large by coalescence at 1000°C in Al2O3, and at 900°C in MgAl2O4, respectively. Amorphization began to recover in both materials at these temperatures. In the case of MgAl2O4 amorphous region recovers completely to polycrystalline state at 1000°C, and in the case of Al2O3 to original single crystal, respectively. Pit formation and exfoliation also occur in both materials at about 1100°C.

Irradiation effects on yttria-stabilized zirconia irradiated with neon ions

Abstract In situ TEM observation was performed on yttria-stabilized zirconia during 30 keV Ne + ion irradiation at room temperature, 923 and 1473 K, respectively, and annealing was performed after irradiation. The observed results revealed clear difference in morphology of damage evolution depending on irradiation temperature. In the irradiation at room temperature defect clusters and bubbles were formed homogeneously at random, and defect clusters were formed earlier than bubbles. In the irradiation at 923 K bubbles and dislocation loops are formed heterogeneously almost at the same time. Moreover, bubbles existed almost only on the loop planes but were almost invisible outside of loop planes in the early stage of irradiation. In the irradiation at 1473 K only bubbles were formed and they grew remarkably with the increasing ion fluence. In annealing remarkable growth of bubbles were observed when temperature was raised from 1373 to 1473 K.

Dynamic behavior of bubbles and blisters in aluminum during helium ion irradiation in an electron microscope

Dynamic behavior of bubbles and blisters in aluminum during helium ion irradiation was examined with the in-situ observation equipment. Violent growth of bubbles by coalescence and bursting or decomposition of the largely grown bubbles were observed repeatedly under irradiation at 300 °C with high flux of ions of about 6 × 1018ions/m2s. In situ observation during annealing after irradiation revealed the remarkable annihilation mode of small bubbles formed by irradiation at 200 ° C: They are for the most part stable during annealing up to 400 ° C, and then many of them disappeared suddenly after they had grown up largely by mutual coalescence at temperatures of 460 to 540 ° C, leaving cavity free areas of circular shape in the places which had been occupied by the largely grown bubbles.

Effect of hydrogen on the formation of interstitial loops in hydrogen-irradiated aluminum

Abstract The role of hydrogen atoms in the formation of interstitial type dislocation loops in aluminum irradiated with 15 keV hydrogen ions was investigated by electron microscopy. It was found that the loop density satisfied and Arrhenius relation with the pre-irradiation temperature, yielding an apparent activation energy of about 0.3 eV. Experimental results are interpreted in terms of the mechanism that small hydrogen-vacancy complexes formed by the pre-irradiation of hydrogen ions act as nucleation sites of dislocation loops in the subsequent electron irradiation. A basically identical mechanism seems to be acting in the irradiation with hydrogen ions at room temperature.