Browsing by Author "Elliman, RG"
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- ItemDiamond structure recovery during ion irradiation at elevated temperatures(Elsevier, 2015-12-15) Deslandes, A; Guenette, MC; Belay, K; Elliman, RG; Karatchevtseva, I; Thomsen, L; Riley, DP; Lumpkin, GRCVD diamond is irradiated by 5 MeV carbon ions, with each sample held at a different temperature (300–873 K) during irradiations. The defect structures resulting from the irradiations are evident as vacancy, interstitial and amorphous carbon signals in Raman spectra. The observed variation of the full width at half maximum (FWHM) and peak position of the diamond peak suggests that disorder in the diamond lattice is reduced for high temperature irradiations. The dumbbell interstitial signal is reduced for irradiations at 873 K, which suggests this defect is unstable at these temperatures and that interstitials have migrated to crystal surfaces. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy results indicate that damage to the diamond structure at the surface has occurred for room temperature irradiations, however, this structure is at least partially recovered for irradiations performed at 473 K and above. The results suggest that, in a high temperature irradiation environment such as a nuclear fusion device, in situ annealing of radiation-created defects can maintain the diamond structure and prolong the lifetime of diamond components. © 2015 Elsevier B.V.
- ItemModification, synthesis and analysis of advanced materials using ion beam techniques(Hindawi Publishing Corporation, 2012-01-01) Balogh, AG; Baba, K; Cohen, DD; Elliman, RG; Ensinger, W; Gyulai, JNot available
- ItemPreferential amorphisation of Ge nanocrystals in a silica matrix(Australian Institute of Physics, 2005-01-31) Ridgway, MC; Azevedo, GDM; Elliman, RG; Wesch, W; Glover, CJ; Miller, R; Llewellyn, DJ; Foran, GJ; Hansen, JL; Nylandsted Larsen, ARelative to bulk crystalline material, Ge nanocrystals in a silica matrix exhibit subtle structural perturbations including a non-Gaussian inter-atomic distance distribution. We now demonstrate such nanocrystals are extremely sensitive to ion irradiation. Using transmission electron microscopy, Raman spectroscopy and extended x-ray absorption fine structure spectroscopy, the crystalline-to-amorphous phase transformation in -8 nm diameter nanocrystals and bulk crystalline material has been compared. Amorphisation of Ge nanocrytals in a silica matrix was achieved at an ion dose -100 times less than that required for bulk crystalline standards. This rapid amorphisation of Ge nanocrystals is attributed to the preferential nucleation of the amorphous phase at the nanocrystal/matrix interface, the pre-irradiation, higher-energy structural state of the nanocrystals themselves and an enhanced nanocrystal vacancy concentration due to the more effective trapping of irradiation-induced interstitials at the nanocrystal/matrix interface and inhibited Frenkel pair recombination when Ge interstitials are recoiled into the matrix. To demonstrate the significance of the latter, we show ion irradiation of -2 nm diameter nanocrystals yields their dissolution when the range of recoiled Ge atoms exceeds the nanocrystal bounds.
- ItemPreferential amorphisation of Ge nanocrystals in a silica matrix(Elsevier, 2004-09-05) Ridgway, MC; Azevedo, GDM; Elliman, RG; Wesch, W; Glover, CJ; Miller, R; Llewellyn, DJ; Foran, GJ; Hansen, JL; Nylandsted Larsen, AExtended X-ray absorption fine structure and Raman spectroscopies have been used to compare the crystalline-to-amorphous phase transformation in nanocrystalline and polycrystalline Ge. We demonstrate Ge nanocrystals are extremely sensitive to ion irradiation and are rendered amorphous at an ion dose ∼40 times less than that required to amorphise bulk, crystalline standards. This rapid amorphisation is attributed to the higher-energy nanocrystalline structural state prior to irradiation, inhibited Frenkel pair recombination when Ge interstitials are recoiled into the matrix and preferential nucleation of the amorphous phase at the nanocrystal/matrix interface. © 2005 Elsevier B.V
- ItemPyrochlore-defect fluorite phase transitions and stability in the Y2Sn2-xZrxO7 system(Committee of Asia-Pacific Societies of Microscopy, 2012-02-07) de los Reyes, M; Whittle, KR; Elliman, RG; Zaluzec, NJ; Ashbrook, SE; Mitchell, MR; Lumpkin, GRThe Y2Sn2-xZrxO7 pyrochlore series undergoes a phase transformation from a cubic pyrochlore structure type (Fd3m) to defect fluorite (Fm3m) actuated by an increase in Zr content, coupled with thermal annealing above 1500 °C. X-ray diffraction analysis reveals the onset of a pyrochlore to defect fluorite transition at Y2Sn0.8Zr1.2O7 with the loss of long range ordering. This is confirmed further by selected area electron diffraction (SAED) illustrating shorter range ordering in the defect fluorite phase incommensurate with unit cell size. This transformation however, occurs at a much higher Zr content than that predicted by classical radius ratio models. The diffuse scattering features observed in electron diffraction patterns of defect fluorite phases indicate some form of shorter range ordering involving compositional-displacive structural modulation. The behaviour of these materials during irradiation will be discussed and linked with the observed structural parameters (diffuse scattering, unit cell size).
- ItemTEM studies of ion-irradiation tolerance in Gd2TiO5(Australian Nanotechnology Network, 2012-02-07) Aughterson, RD; Cairney, JM; Gault, B; Ridgway, MC; Elliman, RG; Lumpkin, GRGd2TiO5 has been identified as a potentially useful material for nuclear based applications such as burnable poison or constituent in waste-forms. A polycrystalline, single phase sample of Gd2TiO5 has been fabricated via the oxide-route reaction. The single phase status and chemical stoichiometry were confirmed using SEM backscattered images, EDS, and laboratory XRD. The structure was confirmed to be orthorhombic, Pnma, space group number 62. The suitability of use for this material in a radioactive environment was tested by in-situ measurement of the materials resistance to transformation from the crystalline to amorphous state via 1MeV Kr2+ ion-irradiation. The in-situ ion-irradiation was carried out using the intermediate voltage electron microscope (IVEM)-Tandem facility at Argonne National Laboratory. The critical dose, Dc, required to render the Gd2TiO5 completely amorphous was determined and the result is compared with other similarly tested materials. Further bulk gold ion-irradiation at various accelerating energies was carried out at the Australian National University using the TANDEM accelerator with damage penetration depth characterised using cross-sectional TEM.