The effects of helium, strontium, and silver triple ions implanted into SiC.

The effects of helium (He), silver (Ag) and strontium (Sr) ions triple implanted into polycrystalline silicon carbide (SiC) were investigated. Ag ions of 360 keV were first implanted into polycrystalline SiC to a fluence of 2 × 1016 cm-2 at 600 °C, followed by implantation of Sr ions of 280 keV to a fluence of 2 × 1016 cm-2 also at 600 °C (Ag + Sr-SiC). Some of Ag + Sr-SiC samples were then implanted with 17 keV He ions to a fluence of 1 × 10 17 cm-2 at 350 °C (Ag + Sr + He-SiC). Some of the dual (Ag + Sr-SiC) and triple (Ag + Sr + He-SiC) implanted samples were annealed at 1000 °C for 5 h. Both dual and triple implantation resulted in the accumulation of defects without amorphization of SiC structure. Moreover, triple implantation also resulted in formation of elongated He nano-bubbles and cavities in the damaged SiC accompanied by the appearance of blisters and craters on the surface. Healing of some structural defects was observed after annealing at 1000 °C in both dual and triple implanted samples. Implantation of Sr caused pre-implanted Ag to form precipitates indicating some limited migration while implantation of He caused some migration of both Ag and Sr. The migration of Ag was accompanied by formation of bigger precipitates trapped in He-cavities. Annealing the triple implanted caused the migration of both Ag and Sr governed by trapping of both implanted species by cavities due to some exo-diffusion of He. No migration was observed in the dual implanted samples annealed at 1000 °C. Hence, He bubbles assisted migration of implants and He cavities trap the implanted species.

(Na, Zr) and (Ca, Zr) Phosphate-Molybdates and Phosphate-Tungstates: II-Radiation Test and Hydrolytic Stability.

This paper introduces the results of hydrolytic stability tests and radiation resistance tests of phosphate molybdates and phosphate tungstates Na1-xZr2(PO4)3-x(XO4)x, X = Mo, W (0 ≤ x ≤ 0.5). The ceramics characterized by relatively high density (more than 97.5%) were produced by spark plasma sintering (SPS) of submicron powders obtained by sol-gel synthesis. The study focused on hydrolytic resistance of the ceramics in static mode at room temperature. After 28 days of testing in distilled water, the normalized leaching rate was determined. It was found that the ceramics demonstrated high hydrolytic resistance in static mode: the normalized leaching rates for Mo- and W-containing ceramics were 31·10-6 and 3.36·10-6 g·cm-2·day-1, respectively. The ceramics demonstrated high resistance to irradiation with 167 MeV Xe+26 multiple-charged ions at fluences ranging from 1·1012 to 6·1013 cm-2. The Mo-containing Na0.5Zr2(PO4)2.5(XO4)0.5 ceramics were shown to have higher radiation resistance than phosphate tungstates. Radiation was shown to trigger an increase in leaching rates for W and Mo in the crystal structure of NZP ceramics.

Recrystallization as the governing mechanism of ion track formation.

Response of dielectric crystals: MgO, Al2O3 and Y3Al5O12 (YAG) to irradiation with 167 MeV Xe ions decelerating in the electronic stopping regime is studied. Comprehensive simulations demonstrated that despite similar ion energy losses and the initial excitation kinetics of the electronic systems and lattices, significant differences occur among final structures of ion tracks in these materials, supported by experiments. No ion tracks appeared in MgO, whereas discontinuous distorted crystalline tracks of ~2 nm in diameter were observed in Al2O3 and continuous amorphous tracks were detected in YAG. These track structures in Al2O3 and YAG were confirmed by high resolution TEM data. The simulations enabled us to identify recrystallization as the dominant mechanism governing formation of detected tracks in these oxides. We analyzed effects of the viscosity in molten state, lattice structure and difference in the kinetics of metallic and oxygen sublattices at the crystallization surface on damage recovery in tracks.

The modification of Si nanocrystallites embedded in a dielectric matrix by high energy ion irradiation.

We have followed the effects of heavy ion irradiation on the structural, electrical, and photoluminescence properties of ensembles of silicon nanocrystallites embedded in a dielectric (SiO(2)) matrix. This was done as a function of the irradiation dose and the content of the Si phase. The results obtained can be accounted for self-consistently assuming that a relatively small dose of the irradiation enhances the crystallization while for higher doses the irradiation enhances the amorphization. The corresponding processes suggest that tuning of the above properties can be achieved by swift heavy ion irradiation.

Low-dimensional effects in a three-dimensional system of Si quantum dots modified by high-energy ion irradiation.

Modification of films containing Si nanocrystallites embedded in SiO2 by irradiation with high-energy ions was found to induce peaks in their low-frequency capacitance-voltage characteristics. Considering the nanocrystallite spatial distribution that follows the ion tracks we interpret these peaks as due to the charge transfer along these tracks, similar to the process that was reported previously for two-dimensional arrays of such crystallites. The ion irradiation of the above three-dimensional system appears to be useful then for the fabrication of nanostructures, which have also the properties of low-dimensional arrays.

The impact of morphology upon the radiation hardness of ZnO layers.

It is shown that ZnO nanorods and nanodots grown by MOCVD exhibit enhanced radiation hardness against high energy heavy ion irradiation as compared to bulk layers. The decrease of the luminescence intensity induced by 130 MeV Xe(23+) irradiation at a dose of 1.5 × 10(14) cm(-2) in ZnO nanorods is nearly identical to that induced by a dose of 6 × 10(12) cm(-2) in bulk layers. The damage introduced by irradiation is shown to change the nature of electronic transitions responsible for luminescence. The change of excitonic luminescence to the luminescence related to the tailing of the density of states caused by potential fluctuations occurs at an irradiation dose around 1 × 10(14) cm(-2) and 5 × 10(12) cm(-2) in nanorods and bulk layers, respectively. More than one order of magnitude enhancement of radiation hardness of ZnO nanorods grown by MOCVD as compared to bulk layers is also confirmed by the analysis of the near-bandgap photoluminescence band broadening and the behavior of resonant Raman scattering lines. The resonant Raman scattering analysis demonstrates that ZnO nanostructures are more radiation-hard as compared to nanostructured GaN layers. High energy heavy ion irradiation followed by thermal annealing is shown to be a way for the improvement of the quality of ZnO nanorods grown by electrodeposition and chemical bath deposition.